Utility, deterioration and preservation of marine timbers in India

Title

Utility, deterioration and preservation of marine timbers in India

Published Date/ Author 
2005 - B Tarakanadha, M V Rao, M Balaji, P K Aggarwal, K S Rao

Timber is extensively used in India in the marine environment for various purposes due to its several advantages over modern materials. Infact, its use is increasing in recent years, finding wider and wider applications and this scenario is not going to change in the near future. Though, the bio-deterioration problem is found very severe in tropical waters, still indigenous methods are widely employed for the protection of fishing craft and the present level of chemical treatment is well below 5% of total timber used. This is due to socio economic problems of the potential timber user groups, unavailability of treatment plants in the coastal areas, lack of awareness in user groups, etc. In this paper, types of fishing craft used in the country, timber uses in the marine environment, bio-deterioration losses, research conducted on bio-deterioration aspects at various places and methods applied for the protection of wooden structures are presented.

Keywords: Fishing craft, marine borers, fouling organisms, timber species, protection methods, wood preservatives, bio-deterioration losses

Conference: 05-04-24/28 Bangalore, India 

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The identification and preservative tolerance of species aggregates of Trichoderma isolated from freshly felled timber

Title

The identification and preservative tolerance of species aggregates of Trichoderma isolated from freshly felled timber

Published Date / Author 
1992 - R J Wallace, R A Eaton, M A Carter, G R Williams

The surface disfigurement of antisapstain treated timber by preservative-tolerant fungi remains a major problem in stored timber. Identification of a range of isolates of Trichoderma based on microscopic morphological characteristics was found to be imprecise due to the variable nature of this organism. In addition, studies to compare visual (morphological) characteristics of these isolates with their tolerance to the antisapstain compound methylene-bis-thiocyanate (MBT) using minimum inhibition concentration (MIC) tests showed no clear correlations. Isoenzyme electrophoresis was used to investigate the taxonomic relationships between species aggregates of Trichoderma isolated from antisapstain field trials and to identify physiological differences between 30 isolates of Trichoderma which show tolerance to MBT at concentrations ranging from less than 4 ppm to 34 ppm. Results indicate that there is considerable variability in the preservative tolerance of different Trichoderma isolates from particular locality. This highlights the need for field testing of an antisapstain compound in the same locality and under the same conditions in which it will be used in practice.

Keywords: ANTI-SAPSTAIN TREATMENTS; GEL ELECTROPHORESIS; TAXONOMY; IDENTIFICATION; ISOLATES; BIOCIDE TOLERANCE; TRICHODERMA

Conference: 92-05-10/15 Harrogate, England, UK 

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Field performance of wood preservative systems in secondary timber species

Title

Field performance of wood preservative systems in secondary timber species

Published Date / Author 
1997 - P E Laks, K W Gutting, R C De Groot

The objective of this ongoing study is to evaluate the performance of new, potential, and standard wood preservative systems in secondary North American timber species. Eleven preservative systems were evaluated in this study - ACQ Type B, Copper Citrate 2: l, CDDC, chlorothalonil/chlorpyrifos, copper-8-quinolinolate, tebuconazole/chlorpyrifos, RH287, propiconazole/chlorpyrifos, copper naphthenate, CCA. and creosote. Field evaluations are being performed with ground contact field stakes and termite-specific testing in Hawaii, along with laboratory soil bed tests. The major wood species used with all the systems and evaluation methodologies are loblolly pine, northern red oak, tulip poplar, and cottonwood. More limited evaluations (field stakes only) are being conducted with eastern hemlock, red maple, and sweetgum. Information is presented from laboratory soil bed, field termite, and field stake evaluations. There is good correspondence between soil bed and field stake results. The more highly developed preservative systems and those in an AWPA P9 Type A oil carrier tend to perform better, and there can be a strong affect on performance from the wood species.

Keywords: WOOD PRESERVATIVE; HARDWOOD;SOFTWOOD; FIELD STAKES; SOIL BE

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Improved analysis of field test data related to service life prediction of tropical wood species

Title
Improved analysis of field test data related to service life prediction of tropical wood species

Published Date/ Author 

2010 - J Van den Bulcke, A Wong, Ling Wang Choon, Yoon Soo Kim, J Van Acker

Long field trials of wood in ground contact give valuable data on the natural durability of the material. The European Standard EN 350 gives guidance on how to perform these durability classification, but is limited to the use of averages of in-service life of a set of specimens compared to a reference set. Starting from a database of visual assessment of field stake testing, it is possible to obtain a durability classification based on Weibull distributions and accompanying percentiles. For this study a set of 39 Malaysian timber species, exposed for over 30 years, is used. The in-ground durability of the stakes was tested and decay was rated according to ASTM D1758. Weibull statistics and the approach as applied in EN 350 standardization are compared. By taking into account the use of reference specimens, these classifications could be transferable to other climatic regions in order to harmonise durability and with the ultimate goal to get general applicable statistical data on durability, going beyond classification, and related strength with regard to the biological nature of wood.

Keywords: natural durability, Weibull statistics, EN 350, Malayasian timber species 


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Pseudallescheria angusta, A LIGNINOLYTIC MICROORGANISM FOR WOOD FIBRES BIOMODIFICATION

Title
Pseudallescheria angusta, A LIGNINOLYTIC MICROORGANISM FOR WOOD FIBRES BIOMODIFICATION


Author 
Gema Guisado,, Maria J. Lopez,, M. Carmen Vargas-García,, Francisca Suárez-Estrella,, Joaquin Moreno


Abstract

Nowadays, the discovery of lignocellulolytic microorganisms that are better adapted to operational conditions while exhibiting the strong degrading activities is highly desired for successful lignocellulose biotransformation processes. In this study, microorganisms were isolated from lignocellulose-rich composting materials by selective methods. A screening of isolates known to have lignocellulolytic abilities was performed using several tests. Seven microorganisms showed ligninolytic potential and were subjected for further analysis according to their degrading activity. The fungus Pseudallescheriaangusta MF4 demonstrated high decolorization rates for three aromatic dyes: Poly R-478, Poly S-119, and Remazol Brilliant Blue R. In addition, the fungus showed a high production rate of ligninolytic enzymes in the presence of inducers. This fungus achieved the highest values of growth after 21 days of incubation on sawdust without any additional nutrients. Owing to its proven ligninolytic activity and capability of growing on a lignocellulosic substrate, the application of this isolate could be of interest in different biotechnological applications, particularly in biological treatment of wood fibres in order to improve the production of wood-based composites.


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Chapitre 4 Physical and mechanical properties of particleboard made from extracted black spruce and trembling aspen bark

4.1 Résumé

L’écorce essentiellement utilisée pour la production d’énergie pourrait être davantage valorisée dans la fabrication de panneaux de particules à base d’écorce. L’écorce est riche en extractibles utilisables dans plusieurs domaines comme la cosmétologie, la pharmacologie ou la production des adhésifs. Cette étude vise à analyser les effets de l’extraction à l’eau chaude des particules d’écorce sur les propriétés mécaniques et physiques des panneaux de particules comme le module d’élasticité (MOE), le module de rupture (MOR), la cohésion interne (CI), la dureté Janka (DJ), le gonflement en épaisseur (GE) et la dilatation linéaire (DL). En outre, ces propriétés sont comparées à la fois à celles des panneaux témoins (100% particules de bois) et à celles de leurs homologues faits d’écorce non extraites. Les résultats ont montré que les propriétés mécaniques des panneaux de particules à base d’écorce extraite d’épinette noire et de peuplier faux-tremble diminuent avec l’augmentation de la proportion d’écorce. Parallèlement et dans les mêmes conditions, la DL augmente. En règle générale, des valeurs élevées de CI et basses de GE avec des panneaux constitués de fines particules ont été obtenues. L’extraction à l’eau chaude appliquée aux particules d’écorce a détériorée toutes les propriétés physiques et mécaniques des panneaux de particules fabriqués à l’exception de la dureté. Cependant, le MOE et le MOR des panneaux ayant 50% d’écorce extraite d’épinette noire et de peuplier faux-tremble ont respecté les exigences de la norme ANSI A208.1-1999 pour les panneaux de particules à moyenne densité à usage commercial (M-1) et de sous-plancher (PBU). En revanche, aucun des panneaux fabriqués n’a respecté les exigences de la norme en matière de stabilité dimensionnelle (GE et DL).

4.2 Abstract

Bark residues are mostly used for thermal energy production. However, a better utilization of that resource could be as raw material for particleboard manufacturing. Bark is also a source of numerous extractives used for several applications including pharmacology and adhesive production. This study aims at analyzing the effect of hot water extracted bark particle content and size on the mechanical and physical properties of bark particleboards including the modulus of elasticity (MOE), modulus of rupture (MOR), internal bond (IB), Janka hardness (HJ), thickness swelling (TS) and linear expansion (LE). Moreover, these properties were compared both to a control (100% wood particles) and to particleboard made from unextracted bark. The results showed that, while the mechanical properties of the particleboard made from extracted black spruce and trembling aspen bark decreased with increasing bark content, LE increased. Particleboard made of fine particles often showed higher IB and lower TS values. Hot water extraction of the bark had a detrimental effect on all the physical and mechanical properties of the particleboards produced except for the Janka hardness where no significant decrease was found. The MOE and MOR of the particleboards made from 50% black spruce and trembling aspen bark met the requirements of the ANSI standard for commercial (M-1) and underlayment (PBU) grades. In contrast, the dimensional properties (TS and LE) of all the boards did not fulfill the minimum requirements of the ANSI standard.

4.3 Introduction

Large quantities of bark are produced by the forest industry and are mostly used for thermal energy production. In the Province of Quebec, Canada, more than 3.5 million tons of anhydrous bark was produced in 2005 (Anonymous 2007). Research projects are carried out in order to foster the use of bark for higher value added products such as alternative raw material for particleboard manufacturing (Blanchet 1999, Blanchet et al. 2000, Villeneuve 2004, and Ngueho Yemele et al. 2007).

Bark is also an important source of extractives used in several fields including pharmacology and adhesive production. Experimental studies support the significant role of the polyphenols as anti-inflammatory, anti-allergic, and antiviral agents (Middleton 1998) as well as their effect in cancer prevention (Savouret and Quesne 2002) and cardiovascular diseases (Frankel et al. 1993). Recent developments in tannin-based adhesives were presented by Pizzi (2006).

Two major approaches to manufacture bark particleboards can be identified in the literature. The first one is based on bark plasticization and extractives polymerization for the self bonding of the bark particles (Burrows 1960, Chow and Pickles 1971, Wellons and Krahmer 1973, Chow 1975, Troughton and Gaston 1997). The second one focuses more on bark particles for their physical properties rather than their chemical properties. Synthetic adhesives including urea-formaldehyde, phenol-formaldehyde, isocyanates and extractives based adhesives were used to bond bark particles (Dost 1971, Deppe and Hoffman 1972, Maloney 1973, Lehmann and Geimer 1974, Anderson et al. 1974ab, Place and Maloney 1977, Wisherd and Wilson 1979, Muszynski and McNatt 1984, Suzuki et al. 1994, Blanchet et al. 2000, Villeneuve 2004, Nemli et al. 2004b, Nemli and Colakoglu 2005, Ngueho Yemele et al.2007). 

The presence of extractives in the raw material impacts the particleboard in both negative and positive ways. Moslemi (1974) reported that extractives can have adverse effects on the setting of adhesives, thereby lowering the particle-particle bond strength. Extractives may cause blows and severely reduce the internal bond strength. In the other hand, phenolic extractives can react with formaldehyde and limit water absorption as well as improve thickness swelling resistance of the board (Moslemi 1974, Anderson et al. 1974abc, Plackett and Troughton 1997, Nemli et al. 2004ab and 2006, Nemli and Colakoglu 2005). For instance, Nemli et al. (2004a, 2006) found a significant improvement of thickness swelling, decay resistance and formaldehyde emission of particleboard made from wood particles impregnated with bark extractives. However, the mechanical properties of these boards were lower than for those made from unimpregnated particles. Similar results were reported by Nemli et al. (2004b) and Nemli and Colakoglu (2005) with addition of black locust and mimosa bark particles to the furnish. Anderson et al. (1974a, c) found that paraformaldehyde added to wood sprayed with concentrated ponderosa pine and white fir bark extract reacted with phenolic compounds present in the extract and formed a waterproof bonding agent which improved the board water absorption resistance and thickness swelling. Therefore, extracted bark particles may lead to high moisture absorption and thickness swelling. The high content of condensed polyphenol present in bark and able to react with formaldehyde was pointed out as the main raison of the aforementioned improvement (Nemli et al. 2004b).

Nevertheless, the use of bark in wood particleboard manufacturing is currently viewed negatively due to the fact that excessive bark content in the raw material produces significant adverse effects on strength and dimensional properties. Several examples given in the literature demonstrate a decrease of the modulus of elasticity (MOE), modulus of rupture (MOR) and internal bond (IB) with addition of bark while the linear expansion (LE) increased (Dost 1971, Lehmann and Geimer 1974, Wisherd and Wilson 1979, Muszynski and McNatt 1984, Blanchet et al. 2000, Ngueho Yemele et al.2007). Muszynski and McNatt (1984) indicated that particleboards suitable for furniture manufacturing could be made from up to 30% spruce bark content. Suzuki et al. (1994) found 35% as the tolerable limit of bark substitution for particleboards. Xing et al. (2006) included up to 40% bark fibers in medium density fiberboard and found its effect on the mechanical and physical properties more detrimental for the MOE, MOR, IB, and LE than for thickness swelling (TS) and water absorption.

Particle geometry is a prime parameter affecting both board properties and its manufacturing process (Moslemi 1974). Suchsland and Woodson (1990) pointed out the high significance of particle geometry in the development of board properties. It has a definite relationship with the compression ratio, and thus it will influence the density of the composite (Brumbaugh 1960, Bhagwat 1971, Hoglund et al. 1976, Kelley 1977).

The type of particle, its geometry and the combination of particles of different type and geometry have significant impacts on board quality (Maloney 1993). The variation of particle geometry results in different fiber surface areas which have a direct impact on the adhesive content per unit fiber surface area (kg/m²) (Moslemi 1974). Generally, the specific surface area (m²/kg) of longer fibers is lower than that of shorter fibers of the same species and thickness due to the higher surface of the fiber cross sections. Thus, the adhesive content per unit fiber surface area is higher for long fibers than for short fibers at a given adhesive content per unit oven-dry mass of particles.

Only few studies examined the effect of bark particle geometry on the properties of particleboard. Gertjejansen and Haygreen (1973) compared properties of wafer and flake- type particles and found that the IB, the LE and the TS were higher on waferboard made from 13 mm wide (1/2 inch) flakes than those made from 38 mm wide (1-1/2 inch) wafers. Blanchet (1999) found that the substitution of wood particles by wood fibers in the surface layer improved the MOE and the MOR of particleboards made from black spruce bark. Ngueho Yemele et al.(2007) found that the MOE, MOR, and IB of particleboard made from black spruce and trembling aspen unextracted bark decreased with increasing bark content. They also found that the IB of the boards often decreased with increasing bark particle size. 

The objectives of this study were 1) to determine the effect of extracted bark particle content and size on the physical and mechanical properties of particleboard made from black spruce and trembling aspen bark; 2) to compare the physical and mechanical properties of particleboard made from extracted bark to those of unextracted bark.

4.4 Material and methods

4.4.1 Bark extraction and particle production

Fresh black spruce (Picea mariana (Mill.)) and trembling aspen (Populus tremuloides (Michx.)) bark was collected respectively from Arbec Forest Products Inc. softwood sawmill located in L’Ascension, Québec, Canada and from the Louisiana Pacific Canada, oriented strandboard mill located in Chambord, Québec, Canada. The raw bark was taken directly from the debarking units in each mill. Bark anhydrous density, wood content of bark residues, and the effective bark content ratio (ebacr) of the panels were determined according to the procedure described in Ngueho Yemele et al. (2007).

Hot water extraction was performed at a large scale in order to produce extracted particles for particleboard manufacturing. Bark was soaked in warm water at the initial temperature of 55°C water. The mean concentration was 35 and 28 g of dried weight per litre of hot water for black spruce and trembling aspen, respectively. The system was heated with water vapor and the average temperature maintained at 100°C for 3 hours. The weight loss ratio was determined gravimetrically and the results were reported as a percentage of the dry raw material weight. Weight loss comprises the extracts and undesirable materials like sand, stone, etc. A weight loss after extraction and air-drying of 16.6 and 10.8% was obtained for black spruce and trembling aspen, respectively.

The air-dried extracted bark was crushed in a hammer mill and sieved in four groups: one for the surface layer and three for the core layer. Wood particles were added to the bark particles to produce mixed wood and bark particleboards. The particle size distribution of each raw material type (extracted bark and wood) was determined with a CE Tyler testing sieve shaker.

4.4.2 Bark organic and inorganic extractive content

The bark was sampled and prepared according to Tappi T 257 cm-02. Total extractive contents, for both unextracted and extracted bark, were determined by successive extraction of bark flour with organic solvents (first with hexane and after with denatured ethanol) and then with hot water, according to Tappi T 204 cm-07 and T 207 cm-99 standards. The ash content was determined according to Tappi T 211 om-07. Two replicates were used for each sample. 

4.4.3 Raw material pH value and buffering capacity measurement

Knowledge of pH and buffering capacity of the raw material (bark and wood) is important for the understanding of the adhesive curing process. For each particle size, the aqueous extract was prepared by refluxing 25 g of dry powdered bark in 250 ml of distilled water for 20 min. Two replicates for each sample were prepared. After refluxing, the mixture was filtered through a filter paper using a vacuum. The aqueous extract was cooled to room temperature in a 25 ml pipette and diluted to 50 ml before titration. After recording the initial pH, 50 ml of extract solution was titrated potentiometrically to a pH of 3 (for alkaline buffering capacity) and 7 (for acid buffering capacity) with nominal 0.025 N H₂SO₄ and 0.025 N NaOH solution respectively. 

4.4.4 Particleboard production

Particleboards measuring 560 x 460 x 8 mm with a target density of 800 kg/m³ were manufactured using a 1000 x 1000 mm Dieffenbacher hot press equipped with a PressMAN control system manufactured by Alberta Research Council. A liquid phenol-formaldehyde adhesive from Dynea Company Ltd was used. The adhesive content shown in Table 27 was determined by the procedure described by Ngueho Yemele et al.(2007) in order to maintain the adhesive per unit specific surface (kg. m^-2) constant. Panels were pressed at a platen temperature of 200 ± 0.1°C for a press closing time of 20 seconds, curing time of 200 seconds and an opening time of 60 seconds which resulted in a total press cycle of 280 seconds. One and 0.5% of wax were added respectively to the surface and core layer particles in the blender. 

4.4.5 Determination of mechanical and physical properties

The panels were conditioned at 20 ± 3°C and 65 ± 1% for one week. Mechanical and physical properties were determined according to the American National Standards Institute (ANSI) standard A.208.1-1999. The properties determined were the modulus of elasticity (MOE) and modulus of rupture (MOR) in static bending, internal bond (IB), Janka hardness (HJ), thickness swelling (TS), and linear expansion (LE). However, in order to consider the impact of the sample density on the mechanical and physical properties of particleboards, the obtained values were adjusted (Garcia et al. 2005, Xing et al. 2007). Thus, other dependent variables such as the specific modulus of elasticity (MOE_spec = MOE/sample density), the specific modulus of rupture (MOR_spec = MOR/sample density), the specific internal bond (IB_spec = IB/sample density), the specific hardness (HJ_spec= HJ/sample density), the specific thickness swelling (TS_spec = TS/sample density), and the specific linear expansion (LE_spec = LE/sample density) were used to perform statistical analyses.

4.4.6 Experimental design and data analyses

The factorial design used in this work is presented in Table 27. The factors chosen were species (black spruce and trembling aspen), extracted bark content (50 and 100%), and bark particle size of the core layer (fine, medium and coarse). For mixed extracted bark and wood particleboards, a bark and wood content of 50% was used in both surface and core layers. The mixture of extracted bark and wood particles was made in a cylindrical rotary blender in order to obtain a homogeneous mixed furnish material. This led to 12 combinations with 3 replicates resulting in a total of 36 panels (Table 27). Moreover, 3 control panels were manufactured in the same laboratory conditions with wood particles obtained from a particleboard mill.

The Statistical Analysis System (SAS) software 9.1 was used for statistical analyses. The analysis of variance (ANOVA) was performed at 13 levels (12 levels of treatments and 1 level of control). Contrasts were performed to determine interactions between the factors studied. Comparisons between treatments and control were performed in order to identify the best treatments following the method of Scott and Knott (1974). Finally, properties of particleboard made from extracted bark were compared to those made from unextracted bark from a previous study (Ngueho Yemele et al.2007).

Table 27 Factorial experimental design used for each species and adhesive content of core layer

4.5 Results and discussion

4.5.1 Raw material characteristics and properties

Relevant characteristics and properties of raw material are summarized in Figure 1 and Tables 28, 29 and 30. Figure 29 shows the size distribution of extracted bark and wood particles used in the surface layer. The size classes and distributions of extracted black spruce and trembling aspen bark particles as well as the industrial wood particles used in the core layer are presented in Table 28. They indicate that the sizes of more than 77% of the industrial wood particles used in the core layer are below 2.60 mm. Therefore, only the bark particles of size 1.5-2.6 mm fit that optimum size range used in wood particleboard manufacture.

Bark organic and inorganic extractive contents presented in Table 29 show significant differences between the denatured ethanol solubility of unextracted and extracted bark of both species. There was also a significant difference between the hot water solubility of unextracted and extracted trembling aspen bark. In contrast, the hexane solubility indicated that there was no significant effect of the hot water extraction on the lipophilic extractives of the two species (Table 29). Nevertheless, both extracted and unextracted trembling aspen bark exhibited higher amount of lipophilic substances than the black spruce bark.

Results on the pH value and buffering capacity of raw materials are presented in Table 30. Because of their important role for the understanding of the adhesive curing process, discussion is carried out on this topic in the last section.

Figure 29 Size distribution of extracted bark and wood particles used in surface layer (BSB= extracted black spruce bark; TAB= extracted trembling aspen bark; W SL= industrial wood particles of surface layer). 

Table 28 Extracted bark particle size classes for the core layer and distributions

Table 29 Bark organic and inorganic extractive content

4.5.2 Mechanical and physical properties of particleboards

The ANOVA results are summarized in Table 5. Detailed analyses of the effect of extracted bark content and particle size on each mechanical and physical property as well as comparison with results obtained for unextracted bark particles of the same species (Ngueho Yemele et al. 2007) are discussed in the following sections.

Table 30 pH and buffering capacity of raw materials

Table 31 Results of the analysis of variance (F values) for mechanical and physical properties of particleboard made from extracted bark of black spruce and trembling aspen

4.5.1 Bending properties

ANOVA results presented in Table 31 show a significant effect of extracted bark content on the static bending properties (MOE_spec and MOR_spec) at the 0.01 probability level and a significant effect of species and bark particle size on the MOE_spec at the 0.01 and 0.05 probability level respectively. Figures 30 and 31 show that for both species, the MOE_spec and the MOR_spec obviously decreased with increasing extracted bark content. Likewise for particleboards with 100% bark content, Figure 30 shows an increase of MOE_spec with increasing particle size. All the boards produced with 50% extracted bark content exhibited higher values of MOE and MOR than that obtained with 100% bark content. Moreover, there was no significant difference of MOE and MOR among the particleboards made from 50% extracted bark content of both species. In fact, Ngueho Yemele et al. (2007) reported a lower cellulose content of black spruce and trembling aspen bark compared to wood particles. Because of its degree of polymerization and linear orientation, cellulose is responsible for strength in the wood fibers (Winandy and Rowell 1984). This involves lower bending properties of particleboard made from 100% bark content than that of those made from 50% bark content. In addition, Blanchet et al. (2000) also found that the tack of the bark particle furnish and the rate of heat transfer through bark particles furnish were lower than for a wood particles furnish. This may result in an incomplete adhesive cure and could explain the decrease noticed for MOE and MOR with increasing bark content. Table 31 also shows a significant effect of the interaction between extracted bark content and bark particle size on the MOE_spec at the 0.01 probability level and a significant effect of the interaction between species and extracted bark content on both MOE_spec and MOR_spec at the 0.01 probability level. This may suggest that the effect of extracted bark content on the MOE_spec and MOR_spec depends on bark particle size and species. The MOE and MOR values of the boards made from 50% extracted bark content of black spruce and trembling aspen were 33 and 50% lower than the control.Nevertheless, those values of MOE and MOR still exceeded the minimum requirements for the commercial (M-1) and the underlayment (PBU) grades (Figures 30 and 31). In contrast, no boards made from 100% bark content of both species met these requirements.

Figure 30 Effect of extracted bark content and particle size on the specific modulus of elasticity (BSB= black spruce bark; TAB= trembling aspen bark. M-1, PBU: ANSI standard particleboard grades).

Figure 31 Effect of extracted bark content and particle size on the specific modulus of rupture (BSB= black spruce bark; TAB= trembling aspen bark. M-1, PBU: ANSI standard particleboard grades).

4.5.2 Internal bond

Table 31 indicates a significant effect of species, extracted bark content and bark particle size on the specific internal bond (IB_spec) at the 0.01 probability level. Figure 32 shows that IB_spec of the particleboard made from extracted black spruce bark obviously decreased with increasing extracted bark content. For those panels made from extracted trembling aspen bark, the decrease is observed merely on fine and medium particle size classes. For coarse particles of trembling aspen bark, no significant difference of IB was noticed between 50 and 100% bark content. The highest value of IB was found on the particleboard made from 50% extracted fine bark particle of both species (Figure 32). In fact, those particles showed a low slenderness (length-thickness) ratio. Table 31 also shows a significant effect of all the interactions of the factors species, extracted bark content and bark particle size on the specific internal bond (IB_spec) at the 0.01 probability level. However, the F value of the factors extracted bark content and species were respectively twenty and six times higher than that of bark particle size (Table 31). Thus, the variation observed on the IB_spec could be explained more by the difference of extracted bark content and species than on bark particle size. This may be due to a decrease of pH or/and a decrease of reactive materials like polyphenols, particularly bark tannin which can positively react with the adhesive and could have been extracted by hot water treatment. Although, the IB of the 50% bark boards of fine particles was 65% lower than the control, they met the requirement for M-1 and PBU grades of the ANSI standard as shown in Figure 32.

Figure 32 Effect of extracted bark content and particle size on the specific internal bond (BSB= black spruce bark; TAB= trembling aspen bark. M-1, PBU: ANSI standard particleboard grades).

4.5.3 Hardness (Janka)

Table 31 shows a significant effect of the extracted bark content on specific Janka hardness (HJ_spec) at the 0.01 probability level. Figure 33 obviously shows that HJ_spec decreased with increasing bark content. There is also a significant effect of the triple interaction among species, extracted bark content and bark particle size on specific Janka hardness (HJ_spec) at the 0.05 probability level. Moreover, the factor extracted bark content exhibited the highest F value (Table 31). Particleboard made from 100% extracted black spruce bark showed higher HJ than the particleboard made from 100% extracted trembling aspen bark. In contrast, all the boards made from 50% extracted trembling aspen bark showed higher HJ than the 50% extracted black spruce bark except those of medium size particles which was found to be not significantly different to those made from 50% trembling aspen bark (Figure 33).The HJ of those boards were 9% higher than the control. All the particleboards produced met the requirements of the ANSI A208.1-1999 standard except for those made from 100% extracted fine particles of trembling aspen bark (Figure 33).

Figure 33 Effect of extracted bark content and particle size on the specific Janka hardness (BSB= black spruce bark; TAB= trembling aspen bark. M-1, PBU: ANSI standard particleboard grades).

4.5.4 Thickness swelling

Table 31 indicates a significant effect of species, extracted bark content and bark particle size on specific thickness swelling (TS_spec) at the 0.01 probability level. Figure 33 obviously shows that TS_spec of particleboard made from trembling aspen bark is lower than for particleboard made from black spruce bark. In fact, trembling aspen bark contains much more lipophilic extractives (Table 31) than black spruce bark which can increase thickness swelling resistance. A similar trend was reported for unextracted bark particles (Ngueho Yemele et al. 2007). The TS_spec value of particleboard of medium bark particle size was often higher than the two other size classes. Table 31 also indicates significant interactions between species and bark particle size as well as species and extracted bark content on specific thickness swelling (TS_spec) at the 0.01 probability level. This means that the effect of species on TS depends on the extracted bark content and bark particle size. Boards made from 100% fine and coarse extracted trembling aspen bark particles exhibited the lowest TS value which was 29% higher than the control and also exceeded the maximum value required by the ANSI standard for manufactured home decking (D-2 and D-3) grades as shown in Figure 34.

4.5.5 Linear expansion

Table 31 shows a significant effect of extracted bark content on the specific linear expansion (LE_spec) at the 0.01 probability level. Figure 35 indicates that the LE_spec increased with increasing bark content for both species. There are also a significant effect of the interactions between extracted bark content and bark particle size on the one hand, and between species and bark particle size on the other hand on the specific linear expansion (LE_spec) at the 0.01 and 0.05 probability level, respectively. Thus, the LE_spec of the particleboard made from 50% extracted bark content, increased with increasing bark particle size. The trend seems to be opposite for boards made from 100% extracted trembling aspen bark content (Figure 35). In contrast, no significant difference was found between the LE of the particleboards made from 100% black spruce and the LE of particleboards made from other extracted bark contents and species. Low LE value was obtained for the boards made from 50% of fine and medium extracted black spruce bark particle, which was 52% higher than the control. Some of the boards produced fulfilled the LE requirements of the ANSI A208.1 standard but not all of them as shown in Figure 35.

Figure 34 Effect of extracted bark content and particle size on the specific thickness swelling (BSB= black spruce bark; TAB= trembling aspen bark. M-1, PBU: ANSI standard particleboard grades).

Figure 35 Effect of extracted bark content and particle size on the specific linear expansion (BSB= black spruce bark; TAB= trembling aspen bark. M-1, PBU: ANSI standard particleboard grades).

4.5.6 Effect of extracted versus unextrated bark particles on the properties of particleboards

Physical and mechanical properties of particleboard made from extracted bark were compared to those obtained by Ngueho Yemele et al. (2007) for particleboards made from unextracted bark. Table 32 shows that the hot water extraction applied in this study had a detrimental effect on the physical and mechanical properties of particleboard made from black spruce and trembling aspen bark. However, the effect of the extraction was light on the bending properties (MOE and MOR) of boards made from 50% trembling aspen bark. The IB of the boards made from extracted bark was significantly reduced (from 16 to 67%) except for particleboard made from 50% of coarse particles of black spruce bark probably due to its low effective bark content ratio. The TS of boards made from extracted bark was higher than that of those made from unextracted bark except for those made from 100% trembling aspen bark as shown in Table 32. In fact, for those boards, the high lipophillic content of both extracted and unextracted trembling aspen bark acts as a barrier to reduce water absorption and thickness swelling. No significant difference was found between the LE of furnish made from extracted and unextracted bark of both species except for those made from coarse black spruce raw material which showed an increase of 30%. No significant decrease of the extraction process implemented was found on the HJ of the boards (Table 32). Furthermore, an improvement of 22% was observed on the HJ value of the particleboard made from 50% extracted trembling aspen bark.

He and Riedl (2004) reported that pH and buffering capacity are important factors influencing PF adhesive curing. A decrease of the PF/particle system pH led to a decrease of the adhesive functional group reactivity. Therefore, both the quality of the interactions (PF adhesive/particles) and the mechanical properties of the boards decrease. Significant differences were found between the average pH values of extracted and unextracted bark of both species presented in Table 29. In addition, the values of acid and alkaline buffering capacity increased and doubled. This suggests a positive correlation between the alkaline buffering capacity and the mechanical properties (MOE, MOR and IB) of the particleboards. In fact, the higher the alkaline buffering capacity, the longer the delay for PF acidification. A decrease of the pH observed on extracted bark particles of the two species led to the alteration of the adhesive reticulation conditions and its interaction with bark particles.

The decrease of the mechanical properties of particleboard made from extracted (or hydrothermally treated) bark could also be explained by the kind of interactions between particles and PF adhesive. Previous studies have shown that the interactions between PF adhesive and wood are of secondary nature and mainly based on hydrogen bonds (He and Riedl 2004, Laborie and Frazier 2006). Hot water extractives are essentially polyphenols including tannins that can react with formaldehyde, free sugars and ash. Extracted bark particles after hot water treatment exhibit less secondary interactions than unextracted bark due to a decrease of the functional groups (hydroxyl, carbonyl, carboxylic). These groups involved in the hydrogen bonds were removed together with the hydrophilic compounds during the hot water extraction process. Therefore, the mechanical properties (MOE, MOR and IB) of the boards made from extracted bark particles should be lower than that of those made from unextracted bark. This is confirmed by the results obtained in the current study as presented in Table 32.

Table 32 Comparison of particleboards made from extracted bark versus those of unextracted bark

Table 32 also shows an increase of TS value of particleboard made from extracted bark particles as compared to that made from unextracted bark. In fact, during the extraction process, extractives soluble in alcohol and water are released from the rhytidome cells (Srivastava 1964, Martin and Crist 1970). Thus, the porosity of extracted bark particles and the whole furnish might increase and they became less resistant to water absorption and thickness swelling.

The significant impact of bark acidity on the curing of PF adhesive suggests that the properties of particleboard made from bark could be further improved by using an appropriate adhesive formulation as well as more specific manufacturing parameters for each kind of raw material. 

4.6 Conclusions

In this study, the physical and mechanical properties of particleboard made from extracted black spruce and trembling aspen bark were investigated. The effect of the hot water extraction on these properties was evaluated. The following conclusions can be drawn:

1. The mechanical properties including modulus of elasticity (MOE), modulus of rupture (MOR), internal bond (IB) and Janka hardness (HJ) decreased with increasing extracted bark content. In contrast, an increase in extracted bark content resulted in an increase in linear expansion (LE) and a slight effect on thickness swelling (TS).
2. The effect of particle size was observed mostly on IB and TS. Particleboard made from fine particles often showed higher IB and lower TS values. 
3. The hot water extraction applied on black spruce and trembling aspen bark had detrimental effect on all the physical and mechanical properties of the particleboards produced except for the Janka hardness.
4. Bark extracts are highly desired in pharmacology and for adhesive production. Therefore, it becomes necessary to carry out studies in order to manufacture value added products with the residues remaining after the extraction process. Although, boards made from extracted bark showed lower physical and mechanical properties than unextracted ones, the high hardness exhibited by extracted bark boards suggests that some of them could be suitable for flooring products where hardness is the main property required.

For further details log on website :

http://archimede.bibl.ulaval.ca/archimede/fichiers/25190/ch05.html

Development of Natural Fibre Composites in India

Soumitra Biswas, G Srikanth & Sangeeta Nangia Abstract

India, endowed with an abundant availability of natural fibres such as jute, coir, sisal, pineapple, ramie, bamboo, banana etc., has focussed on the development of natural fibre composites primarily to explore value-added application avenues. Such natural fibre composites are well suited as wood substitutes in the housing & construction sector.

The development of natural fibre composites in India is based on a two-pronged strategy of preventing depletion of forest resources as well as ensuring good economic returns for the cultivation of natural fibres. 

Jute & coir based composites have been developed as substitutes for plywood & medium density fibre boards. Panel & flush doors have also been developed out of these composite boards especially for low-cost housing needs. Other product development activities include usage of sisal fibre based composites as panel & roofing sheets. Incorporation of glass with jute brings about large increases in mechanical properties of composites. 

The natural fibre composites can be very cost-effective material especially for building & construction industry (panels, false ceilings, partition boards etc.), packaging, automobile & railway coach interiors and storage devices.

Due to an occurrence of a wide variety of natural fibres in the country, Indian researchers have directed efforts for quite some time in developing innovative natural fibre composites for various applications.While the national research agencies in India have excellent scientific achievements to their credit for development of natural fibre composites, efforts on their commercialization have been limited so far.

In order to improve upon the laboratory-industry linkages towards application development & commercialization including the natural fibre composites, the Advanced Composites Mission programme was launched by the Department of Science & Technology, Government of India. The Mission mode activities are being implemented by Technology Information, Forecasting and Assessment Council (TIFAC), an autonomous organization under DST.

Introduction

The developments in composite material after meeting the challenges of aerospace sector have cascaded down for catering to domestic and industrial applications. Composites, the wonder material with light-weight, high strength-to-weight ratio and stiffness properties have come a long way in replacing the conventional materials like metals, woods etc.

The material scientists all over the world focused their attention on natural composites reinforced with jute, sisal, coir (coconut fibre), pineapple etc. primarily to cut down the cost of raw materials.

Eastern India has been bestowed with abundant cultivation of jute. The production of processed jute fibre in India has touched 1.64 million tonnes in 1999-2000. Jute as a natural fibre has been traditionally used for making twines, ropes, cords, as packaging material in sacks & gunny bags, as carpet-backing and more recently, as a geo-textile material. But, lately the major share of its market has been eroded by the advent of synthetic materials, especially polypropylene. 

In order to save the crop from extinction and to ensure a reasonable return to the farmers, non-traditional outlets have to be explored for the fibre. One such avenue is in the area of fibre-reinforced composites. Such composites can be used as a substitute for timber as well as in a number of less demanding applications. Jute fibre due to its adequate tensile strength and good specific modulus enjoys the right potential for usage in composites.

Jute composites can thus ensure a very effective and value-added application avenue for the natural fibre. Interest in using natural fibres as reinforcement in polymer matrices and also in certain applications as partial replacement of glass fibres has grown significantly in recent years for making low cost composite building materials. Thus, new alternative materials have emerged that could partially meet the demands of conventional materials especially wood in buildings. 

Natural Fibres

Jute, sisal, banana and coir (coconut fibre), the major source of natural fibres, are grown in many parts of India. Some of them have aspect ratios (ratio of length to diameter) > 1000 and can be woven easily. Sisal and banana fibres are cellulose-rich (> 65%) and show tensile strength, modulus and failure strain comparable with other cellulose-rich fibres like jute and flax whereas the lignin-rich (> 40%) coir fibre is relatively weak and possess high failure strain.

These fibres are extensively used for cordage, sacks, fishnets, matting and rope, and as filling for mattresses and cushions (e.g. rubberized coir). Cellulosic fibres are obtained from different parts of plants, e.g. jute and ramie are obtained from the stem; sisal, banana and pineapple from the leaf; cotton from the seed; coir from the fruit, and so on.

Recent reports indicate that plant-based natural fibres can very well be used as reinforcement in polymer composites, replacing to some extent more expensive and non-renewable synthetic fibres such as glass. The maximum tensile, impact and flexural strengths for natural fibre reinforced plastic (NFRP) composites reported so far are 104.0 MN/m2 (jute-epoxy), 22.0 kJ/ m2 (jute-polyester) and 64.0 MN/m2 (banana-polyester), respectively. The properties of some of the natural fibres are compared in Table 1.0.

Table 1.0: Properties of Select Natural Fibres

Property	Jute	Banana	Sisal	Pineapple	Coir (Coconut fibre)
Width or Diameter (mm )	-	80-250	50-200	20-80	100-450
Density (gms./cc)	1.3	1.35	1.45	1.44	1.15
Volume Resistivity at 100 volts (W cm x 105)	-	6.5-7	0.4-0.5	0.7-0.8	9-14
Micro-Fibrillar Angle (degree)	8.1	11	10-22	14-18	30-49
Cellulose/Lignin Content (%)	61 /12	65 /5	67 /12	81 /12	43 /45
Elastic Modulus (GN/m2)	-	8-20	9-16	34-82	4-6
Tenacity (MN/m2)	440-533	529-754	568-640	413-1627	131-175
Elongation (%)	1-1.2	1.0-3.5	3-7	0.8-1.6	15-40

There are many examples of the use of cellulosic fibres in their native condition like sisal, coir, jute, banana, palm, flax, cotton, and paper for reinforcement of different thermoplastic and thermosetting materials like phenol formaldehyde, unsaturated polyester, epoxy, polyethylene, cement, natural rubber etc.

Different geometries of these fibres, both singly and in combination with glass, have been employed for fabrication of uni-axial, bi-axial and randomly oriented composites. Amongst these ligno-cellulosic fibres, jute contains a fairly high proportion of stiff natural cellulose. 

Rated fibres of jute have three principal chemical constituents, namely, a -cellulose, hemicellulose and lignin. In addition, they contain minor constituents such as fats and waxes, inorganic (mineral) matter, nitrogenous matter and traces of pigments like b -carotene and xanthophyll. 

As in synthetic fibre composites, the mechanical properties of the final product depend on the individual properties of the matrix, fibre and the nature of the interface between the two. Where the fibre is an agricultural one, it is possible to tailor the end properties of the composite by selection of fibres with a given chemical or morphological composition.

Several studies of fibre composition and morphology have found that cellulose content and microfibril angle tend to control the mechanical properties of cellulosic fibres. Higher cellulose content and lower microfibril angle result in higher work of fracture in impact testing.

Sisal and banana fibres show better reinforcing efficiency than coir and the specific strength properties of the composites are comparable to those of glass fibre reinforced plastics (GRP). On the other hand, coir fibre, despite having low strength and modulus, improves the impact resistance of polyester due to its large strain energy absorption. 

Jute and Glass Fibres

Although the tensile strength and Young’s modulus of jute are lower than those of glass fibres, the specific modulus of jute fibre is superior to that of glass and when compared on modulus per cost basis, jute is far superior. The specific strength per unit cost of jute, too, approaches that of glass.

Therefore, where high strength is not a priority, jute may be used to fully or partially replace glass fibre. The need for using jute fibres in place of the traditional glass fibre partly or fully as reinforcing agents in composites stems from its lower specific gravity (1.29) and higher specific modulus (40 GPa) of jute compared with those of glass (2.5 & 30 GPa respectively).

Apart from much lower cost and renewable nature of jute, much lower energy requirement for the production of jute (only 2% of that for glass) makes it attractive as a reinforcing fibre in composites. The comparison of mechanical properties for jute & glass fibres is given in Table 2.0.

Table 2.0 : Mechanical Properties of Glass and Jute Fibres

Property	E-glass	Jute
Specific Gravity	2.5	1.3
Tensile Strength (MN/m2 )	3400	442
Young’s Modulus (MN/m2 )	72	55.5
Specific Strength (MN/m2 )	1360	340
Specific Modulus (GN/m2 )	28.8	42.7

The natural fibre imparts lower durability and lower strength compared to glass fibres. However, low specific gravity results in a higher specific strength and stiffness than glass. This is a benefit especially in parts designed for bending stiffness. In addition, the natural fibres offer good thermal and acoustic insulation properties along with ease in processing technique without wearing of tool. 

The jute composites may be used in everyday applications such as lampshades, suitcases, paperweights, helmets, shower and bath units. They are also used for covers of electrical appliances, pipes, post-boxes, roof tiles, grain storage silos, panels for partition & false ceilings, bio-gas containers, and in the construction of low cost, mobile or pre-fabricated buildings which can be used in times of natural calamities.

Effect of Moisture on Natural Fibres

There is, however, a major drawback associated with the application of natural fibres for reinforcement of resin matrices. Due to presence of hydroxy and other polar groups in various constituents of natural fibre, the moisture uptake is high (approx. 12.5% at 65% relative humidity & 20oC) by dry fibre. All this leads to :

• poor wettability with resin and
• weak interfacial bonding between the fibre and relatively more hydrophobic matrices.

Environmental performance of such composites is generally poor due to delamination under humid conditions. With increase in relative humidity up to 70%, the tenacity and Young’s modulus of jute increases but beyond 70%, a decrease is observed. Thus, it is essential to pre-treat the fibre so that its moisture absorption is reduced and the wettability by the resin is improved.

Modification of Natural Fibre 

In order to develop composites with better mechanical properties and environmental performance, it is necessary to impart hydrophobicity to the natural fibres by chemical reaction with suitable coupling agents or by coating with appropriate resins.

Such surface modification of fibre does not only decrease moisture adsorption, but also concomitantly increases wettability of fibres with resin and improve the interfacial bond strength, which are critical factors for obtaining better mechanical properties of composites.

Modification of jute and other natural cellulosic fibres can be done by following means :

• Chemical means
• Coating with polymeric solutions and
• Graft co-polymerization. 

Natural fibre is chemically treated with isopropyl triisostearoyl titanate (abbreviated as titanate), g -aminopropyl trimethoxy silane (abbreviated as silane), sebacoyl chloride (SC), and toluene di-isocynate (TDI). All these reagents are expected to block the hydroxy groups of jute thus making the fibres more hydrophobic. These surface modifiers penetrate and deposit into lumens of cell wall of fibre, minimizing the possible extent of moisture ingress.

Polymeric coating of natural fibre with phenol-formaldehyde or resorcinol formaldehyde resins by different approaches are highly effective in enhancing the reinforcing character, giving as high as 20-40% improvement in flexural strength and 40-60% improvement in flexural modulus. These modifications improve the fibre-resin wettability and lead to enhanced bonding. 

Natural fibre such as jute can be graft co-polymerized with vinyl monomers such as methyl methacrylate, ethyl acrylate, styrene, vinyl acetate, acrylonitrile & acrylamide in presence of different redox initiator systems such as vanadium-cyclohexanol, vanadium-cyclohexanone etc. 

Grafting of poly-acrylonitrile (10-25%) imparts 10-30% improvement in flexural strength and flexural modulus of the composites. Grafting of polymethylmethacrylate is also effective in this respect, though to a lower degree. 

Jute-Polyester Composite

Polyester resin forms an intimate bond with jute fibres upto a maximum fibre : resin ratio (volume/volume) of 60:40. At this volume fraction, the Young’s modulus of the composite is approximately 35 GN/m2. For higher volume fraction of fibre, the quantity of resin is insufficient to wet fibres completely. 

In order to overcome the poor adhesion between resin matrix and jute fibres, a multifunctional resin like polyesteramide polyol has reportedly been used as an interfacial agent. Significant improvement in mechanical properties of jute fibre composites was observed by incorporation of polyesteramide polyol. Also, hybrid composites of glass at surface and treated jute fibre at inner core can be a good alternative. Apart from imparting improved strength to the product, such hybrids result in cost & weight savings.

There are several types of unsaturated polyester resins - general purpose, flexible, resilient, low-shrinkage (low profile), weather resistant, chemical resistant and fire retardant varieties.

These polyester resins are prepared from a blend of phthalic anhydride and maleic anhydride esterified with propylene glycol to form linear polyester chains having molecular weights in the range  1000-3000. For curing such unsaturated polyester resins with fibre, azo type initiators (R-N=N-R) and organic peroxides (R-O-O-R) are generally used. 

Fabrication of Composites

Hybrid composite of glass and jute fibre can be fabricated initially by the hand lay-up technique for making the sheet-moulding compound and subsequently by using a compression-moulding machine.

10-ply hybrid laminates containing 8 inner plies of untreated/silane/ titanate/TDI treated jute fibre sandwiched between two outer plies of glass fibre (weight content of jute : 25-27%) can be made by the aforesaid process. Curing is done at 800C under a pressure of approx. 2 X 105 N/m2 for 90 min.

Jute composites are at present being used commercially in India for applications like automobile interiors. There are also some temporary outdoor applications like low cost housing for defence etc. However, as use of jute alone as reinforcing fibre is not suitable for high strength applications, jute-glass fibre combination can be well suited for such applications. Incorporation of glass with jute brings about large increase in mechanical properties of composites. 

Phenolic resins is one of the first synthetic resin exploited commercially for fabrication of jute-composite products mainly because of its high heat resistance, low smoke emissions, excellent fire retardance properties and compatibility with jute fibres. Phenol-formaldehyde based jute composites products have been used for quite sometimes as wood & ceramic substitutes. 

Today, where costs & performance have a high impact on economics, phenolic resins have been accepted in many high performance applications for composites. Compression moulding of composites based on jute-phenolic system has been commonly practised since a few decades.

In this process, jute is impregnated with the phenolic resin by spraying process followed by drying under hot air dryer. These pre-impregnated jute layers are arranged together for desired thickness and compression moulded at high pressure of 700-800 kg/m2 and at temperature of around 120-140oC

A report from the National Institute of Research on Jute and Allied Fibre Technology (NIRJAFT), Kolkata reveals that, usually for moulded jute composites with polyester resin, the resin intake can be maximum up to 40%. Both hot press moulding and hand lay-up technique can be used for its fabrication.

In the latter process, the resin take up may go up to 300-400 % of jute fibre used, which is not economical. Also, it is seen that some pre-processing of jute/treatment of fibre is required so that the interface problem could be solved. Generally, when unsaturated polyester resin is used with glass fibre, the ratio maintained is 2.5:1.

Whereas, for resin with jute, the ratio maintained is 3.5-4:1. However, an increase in temperature increases the productivity. Even with unsaturated polyester resin, hot condition impregnation is usually done for higher productivity.

Pultrusion is another unique process that converts primary raw materials directly into finished products, continuously and automatically, utilising most of thermoset/thermoplastic resins. Jute, available in continuous forms such as mat, roving, tapes, yarn etc., is impregnated with resin & passed through hot die to cure the product.

The speed of pultrusion ranges from 0.4-1.0 m/min depending on the complexity of the products. The loading of jute is anywhere between 50-70%. Pultruded jute composites have good electrical insulation, corrosion & high fire retardance properties. They find applications in roofing sheets, cable trays, doors & window frames, panelling, sections for wardrobe, partitions, etc. 

Resin Transfer Moulding (RTM) is a quick and cost effective process for the production of quality volume composites. Jute based reinforcement using combinations of woven fabric and non-woven needle punched felt forms have been used successfully in the moulding various complex shapes. 

The characteristics of natural fibre composite boards are as follows :

• Attractive natural look
• Can be painted, polished or laminated
• Water proof with minimum surface absorption
• Economical
• Strong and rigid
• Environment-friendly as wood substitute
• Can be nailed, screwed and cut sharply

A composite has three entities that are susceptible to failure - the reinforcement, the matrix and the interface. The failure of one can initiate failure of the others, and the actual process that takes place in any particular case is determined by the stress required to activate each individual mechanism. The mechanism activated by the lowest stress will normally govern composite failure.

Thus, in order to increase the potential application area of natural fibres as reinforcement in composites, it is necessary to concentrate more on three major aspects :

• fibre modification 

• resin compatibility 

• coupling agents. 

Properties of Composites

The mechanical properties of a natural fibre composite depend on many parameters such as fibre strength, modulus, fibre length and orientation, in addition to the fibre-matrix interfacial bond strength. Fibre-matrix interface plays an important role in the composite properties.

A good interfacial bond is required for effective stress transfer from the matrix to the fibre whereby maximum utilization of the fibre strength in the composite is achieved. In addition, it improves resistance to moisture induced degradation of the interface and the composite properties. 

For effective reinforcement, the elastic modulus of the fibre should be higher than that of matrix. The mechanical properties of unidirectionally aligned continuous fibre composite with polyester matrix along with that of randomly oriented short fibre composites are given in Table 3.0.

Fibres such as sisal show very high impact performance with specific impact strength comparable to that of FRP and show the most balanced mechanical properties in different modes. Coir performs as good as high strength fibres like jute and banana with respect to impact strength of composites.

Table 3.0 : Mechanical Properties of Unidirectionally Aligned Continuous Fibre with Polyester Matrix Vs. Randomly Oriented Short Fibre Composites

Fibre (wt%)	Tensile Strength MPa	Young Modulus GPa	Flexural Strength MPa	Flexural Modulus GPa	Impact Strength KJm-2
Unidirectional
Sisal (40)	129	8.5	192	7.5	98*
Banana (30)	121	8.0	-	-	52*
Coir (30)	45	4	56	4	44*
Chopped random
Sisal (25)	34.5	1.9	86.4	-	30
Banana (25)	43.5	2.3	92	-	10
Coir (25)	14.0	1.4	31.2	-	11
Fabric
Banana-cotton	27.9-35.9**	3.3	50.6-64*	-	3.1-7.5**

* Impact Strength (Charpy) for 0.5Vf
** Depending on type of fibre in the test direction.

Among thermoset composites, phenol formaldehyde matrix composites show higher strength and modulus than epoxy composites followed by polyester composites, since fibre-matrix interfacial bond strength increases for the matrices in the order PF > epoxy > polyester.

Lignin-rich fibre (e.g. coir) composites show better resistance to weathering when compared to cellulose-rich fibre (e.g. sisal and banana) composites. Lignin, which has lower affinity towards moisture, appears to act as a protective barrier for cellulose microfibrils from moisture absorption.

Cashew Nut Shell Liquid as Natural Resin

A whole lot of R&D activities have been directed towards developing a cheaper resin alternative from natural and renewable resources. The cashew nut shell containing a dark reddish brown liquid, the pericarp fluid of the nuts, is an excellent source for such natural resin.

Cashew nut shell liquid (CNSL) consists chiefly of two naturally occurring unsaturated phenolic compounds, anacardic acid (90%) and cardol (10%) with minor amounts of 2-methyl cardol. Positioned as a versatile industrial raw material, CNSL finds a wide array of applications such as friction linings, paints & varnishes, laminating resins, rubber compounding resins, cashew cements, polyurethane based polymers, surfactants, foundry chemicals and intermediates for chemical industry. The specifications of untreated CNSL as per IS:840-1964 are given in Table 4.0. 

Table 4.0 : BIS Specifications for Untreated Cashew Nut Shell Liquid (IS:840-1964)

Sl. No.	Properties	Specified Values
1.	Specific gravity, 30/30	0.950 - 0.970
2.	Viscosity at 300C, centipoise	550
3.	Moisture content (% by weight)	1.0
4.	Matter insoluble in toluene (% by weight)	1.0
5.	Loss in weight on heating (% by weight)	2.0
6.	Ash content (% by weight)	1.0
7.	Iodine value Wij’s method Catalytic method	250 375
8.	Polymerization Time in minutes Viscosity at 300C, centipoise Viscosity after acid wash at 300C, centipoise	4 30 200

Unlike resins derive from petrochemicals, CNSL can be polymerized by various routes thus offering unique application advantages. The following are the possible routes for polymerization of cashew nut shell liquid :

Addition polymerization through side chain double bonds

Condensation polymerization at the ortho & para positions of the phenolic ring with various chemicals

Polymerization after chemical modification

Oxidative polymerization

Polymerization by physical means : heat, pressure, radiation, electrical discharge

Various combinations of above methods

The cashew nut shell liquid based polymers offer the following advantages :

Internal plasticization

Solubility in organic solvents with improved processability

Low fade characteristics on friction & resistance to cold wear

Good heat & electrical resistance with better water repellancy

Compatibility with other polymers

Improved acid & alkali resistance

Termite & insect resistance

CNSL finds good application as a friction lining material in brake lining & clutch facings. The linings made of cashew nut shell liquid are softer in nature and quite efficient for cold wear up to 2050C which is the maximum temperature likely to be generated in low speed automobiles.

Paints & varnishes developed from CNSL are superior to conventional oils or synthetic resin. CNSL can also be used for producing laquers and various coatings suitable for insulation, protection and decoration. Fire resistant paints have been developed from CNSL by pigmenting chlorinated CNSL with sodium silicate, red mud, titanium dioxide, antimony oxide, mica powder, asbestos etc.

The anti-corrosive primer developed from CNSL finds excellent applications on ships’ bottom. Such speciality coatings are also applied to the wooden surface of fishing boats. Polyurethane adhesives, foams & coatings based on CNSL offer excellent characteristics and the technology is now available in India.

CNSL is also used extensively as resin binder for various natural fibre composites and reconstituted wood. CNSL impregnated coir sponge provides excellent acoustic insulation and is used as noise barrier on highways. Such sponge can also be used for cold insulation on AC ducts & pipelines. 

Natural Fibre Composites : Initiatives in Product Development

The natural fibre composites can be very cost-effective material especially for building & construction industry (panels, false ceilings, partition boards etc.), packaging, automobile & railway coach interiors and storage devices. 

Due to an occurrence of a wide variety of natural fibres in the country, Indian researchers have directed efforts for quite some time in developing innovative natural fibre composites for various applications. Development of diversified composite materials as wood substitutes is being considered an attractive solution with a view to conserve forest resources.

The commonly used wood substitutes such as particle/fibre board and other materials cannot meet the demanding quality requirements. The national institutions such as National Institute of Research on Jute & Allied Fibre Technology (NIRJAFT)-Kolkata, Indian Jute Industries’ Research Association (IJIRA)-Kolkata, Central Glass & Ceramic Research Institute (CGCRI)-Kolkata, Department of Textile Technology-IIT Delhi, Regional Research Laboratory (RRL)-Bhopal, Institute of Jute Technology-University of Calcutta, Central Building Research Institute (CBRI), Roorkee specially merit the mention for their long standing research activities. 

IJIRA has carried out extensive work on pre-treatment of jute fibres with acrylonitrile for improving their compatibility with thermoset plastics. IJIRA has fabricated jute-thermoset composites using RTM process. The comparative properties of jute-polyester and glass-polyester composites fabricated by RTM are given in Table 5.0.

Table 5.0 : Comparative Properties of Jute-Polyester and Glass-Polyester Composites Fabricated by RTM 

Properties	Jute-Polyester	Glass-Polyester
Density, gms./c.c.	1.25	1.45
Water Absorption % After 2 hrs. soaking After 24 hrs. soaking After 2 hrs. boiling	0.24 0.84 1.11	0.09 0.17 0.39
Thickness Swelling % After 2 hrs. soaking After 24 hrs. soaking After 2 hrs. boiling	0.07 0.17 0.90	Nil 0.12 0.53
Flexural Strength, MPa	60.12	138.2
Flexural Modulus, Gpa	2.97	4.02
Tensile Strength, MPa	44.25	117.4
Tensile Modulus, Gpa	2.88	6.08

The products fabricated using jute-polyester composites are chair shell, door and partition, instrument panel, home furnishings, car body panel etc. 

Different types of polyolefins and other thermoplastics, properly coupled with natural fibre, provide techno-economic solution for a wide range of products. The jute-polypropylene composites have been used for potential product range viz. automotive interiors, shipping pellets, bobbins & spools, flower pots, toys, plastic decking & fencing, furniture, handles etc.

NIRJAFT has developed a whole set of novel jute & other natural fibre composite products based on hot press moulding and hand lay-up techniques. A whole lot of efforts has gone into the studies on resin/fibre ratio, physical & chemical characterization of jute composites, water absorption properties etc. apart from developing products such as panels, boards, packaging material etc.

The grading of raw material and its implementation for the benefit of both cultivators & industry has been a major contribution of NIRJAFT. They have developed a commercially viable technology for the manufacture of particleboards from jute stick, which is an agro-waste. IIT-Delhi has been quite active in developing jute-based geo-textiles for applications in prevention of soil erosion, leaching etc. CGCRI-Kolkata has worked on jute-glass hybrid components for cost reduction without sacrificing the mechanical properties. 

An excellent example for commercial exploitation of jute composites has been the fabrication of automobile interiors (door panels) by Birla Jute Industries Ltd., Kolkata. 

A systematic study has been carried out at CBRI on sisal & jute fibre composites for their application in construction sector. Various coupling agents (silane, titanate, N-substituted methacrylamide) have been used to improve the wettability of these fibres. Process know-how for fabricating these natural fibre composites has been established by CBRI.

Sandwich composite panels have been manufactured by hand lay-up using natural fibre based laminate as face material and corrugated sheet as core material. These panels are lightweight and have excellent bending stiffness besides good thermal & sound insulation. For semi-structural applications, hybrid composites have been developed with glass fibre, sisal fibre & polyester resin. The tensile strength of hybrid composites is 56 MPa with an elastic modulus of approx. 2 GPa. 

Further, CBRI has carried out developmental efforts using sisal fibre and wollastonite as synergistic reinforcement alternative to glass fibres in dough & bulk moulding compounds to widen their usage in the housing sector. The physico-mechanical properties such as thickeners, monomer type, sisal/wollastonite/glass fibre content of the moulding are studied as a function of various constituents.

Addition of sisal fibres in wollastonite/polyester mix reduces the brittleness and acoustic-damping coefficient. Sisal based dough moulding compound can be used for developing building materials such as checker floor plate, roof tile, sanitary-ware etc. 

An attempt has also been made by CBRI to fabricate jute pultruded doorframes using woven jute cloth and phenolic resin. The pultruded doorframe (2140 mm X 920 mm) can accommodate 35 mm thick door. The density of these profiles fabricated has been 873 ± 10 Kgs./m3.

CBRI has also evaluated the mechanical properties of these pultruded doorframes. It was observed that the variation in tensile & flexural strength of profiles at low humidity condition has been marginal while a progressive deterioration is observed at high humidity levels.

The pultruded doorframe was performance tested for 2-3 years. There was no sign of warping, bulging, discoloration etc. The moisture content of profiles has been nearly 2-3 times lesser than the wooden doorframe thus indicating good dimensional stability against external agents. Pultruded jute composites have good electrical insulation and corrosion resistance properties. The comparative properties of wooden and pultruded jute composite doorframe are furnished in Table – 6.0. 

Table – 6.0 : Comparative Properties of Wooden and Pultruded Jute Composite Door Frame

Property	Wooden door frame Specified Value (IS:4021-83)	Pultruded JRP Door Frame-Experiment
Moisture content (%)	8-15	4.40
Seasoning/treatment	Preventing from warping and mould growth	Not required
Dimensions/size (cm)	H-199-209, W 79-99	H-214, W-92
Hold fasts	3	3
Gluing of joints	BWR adhesive	Reinforced adhesive
Installation	Solid	Inside frame is filled by concrete/foam
Finish	Priming followed by varnish/ paint	PU paint/varnish/melamine
Weathering	A1 priming required	Resin rich layer
Dimensional stability	No warping/twisting	Exposure 2-5 years, no defects

(Source : CBRI, Roorkee)

CBRI has developed another technology for production of coir (coconut fibre)-cement roofing sheet having a thickness of 6-8 mm. The manufacturing process involves soaking of coir fibre in mineralised water and then mixing with dry cement in the ratio of 1:5 by weight. A sheet is made with this wet mix of cement coated fibres and is held under pressure for 4-8 hrs. The long-term performance under actual conditions has been ascertained. The properties of coir-cement roofing sheet are given in the Table – 7.0.

Table – 7.0 : Properties of Coir-Cement Roofing Sheet

Property	Natural Fibre Sheet	Asbestos Sheet
Density (gms/cm3)	1.02	2.0
Water Absorption 24 Hrs. (%)	3 - 5	25
Thickness (mm)	3.31	6
Pitch Length (mm)	75	146
Pitch Depth (mm)	19.25	48
Weight (Kgs./m2)	3 – 4	13.50
Bending Strength (MPa)	45 – 58	25 – 30
Deflection (mm)	30 – 40	-
Thermal Conductivity (K Cal/m2/Hr./0C)	0.12 – 0.15	0.24

(Source : CBRI, Roorkee)

CBRI has developed medium density composite doors containing coir fibre, cashew nut shell liquid (CNSL) as natural resin and paraformaldehyde as major constituents. Coir fibre contributes mechanical strength to the composite while the CNSL with paraformaldehyde act as a binder. Coir is impregnated with CNSL and is compression moulded under high temperature. The pressure require

These boards can be used as wood substitute for paneling, cladding, surfacing and partitioning and other interior applications. The boards have density between 0.5 – 0.9 gms/cm3 and can be cut, sawed, nailed & screwed. The boards have very low water absorption and negligible swelling.

The natural fibre reinforced thermoplastic composite granules made of waste fibres can also be a good wood substitute. DMSRDE, Kanpur has been working towards development of this material. The basic raw materials used are industrial (Polypropylene & Polyethylene waste) & agro-wastes (jute/saw/rice mill waste).

The granules are moulded/extruded by a cost-effective production process for the products viz. crates, pallets, trays, boxes, bobbin, spool, suitcase shell etc. and other applications in railways, automobile, electrical & electronics and chemical industries. The mechanical characterization, compounding formulations and standardization & certification of products etc. need to be investigated in future for commercial acceptance. 

While the national research agencies in India have excellent scientific achievements to their credit for development of natural fibre composites, efforts on their commercialization have been limited so far. In order to improve upon the laboratory-industry linkages towards application development & commercialization, The Advanced Composites Missionwas launched by the Department of Science & Technology, Government of India.

The Mission mode activities are being implemented by Technology Information, Forecasting & Assessment Council (TIFAC), an autonomous organization under DST. Among a wide array of composite product development activities, the Mission has taken up a few projects focussing on natural fibre composites.

The project on Jute-based Composites - An Alternative to Wood Products deals with the production of coir-ply boards with oriented jute as face veneer and coir plus waste rubber wood inside. A very thin layer of jute fibres impregnated with phenolic resin is used as the face veneer for improved aesthetics and to give a wood like finish.

The orientation & uniformity of jute fibre improve with carding and this also helps in better penetration of resin into the fibre. As colour of jute is important for appearance, a mixture of brown & white jute gives better appearance like natural wood than completely white fibre. The thin jute face veneer is supported by a sheet of craft paper and this also serves as an impervious layer helping in reduced consumption of paints while finishing the board. 

Process

Jute Face Veneer - The jute slivers (dried earlier in a chamber by circulating hot air) are passed through a bar with a number of pins to obtain a layer of combed and aligned jute. A craft paper support is given by continuously feeding the paper along with the jute layer running at almost the same speed. The jute layer is then sprayed with phenolic resin followed by drying with hot air (at around 120oC) to form the veneer. 

Inner Coir & Rubber Wood Waste Layer - In the needle felt plant, the coir is passed through the feeding system consisting of openers, air feeding device, distributors and conveyers. The web of coir is needle punched to give a continuous felt. A specially formulated coir compatible phenol-formaldehyde resin with reasonably fast curing properties is sprayed on coir felt. The resin impregnated coir felt is then dried in the hot air dryer. The pieces of rubber wood waste are manually impregnated with phenolic resin. 

Composite Board Assembly - After making oriented jute face layers & inner coir layers, the assembling is done manually at the press plant. The assembling is carried out by placing oriented jute layer with paper back-up at two outer faces with semi-cured coir felt sheets inside. For the boards containing rubber wood waste, the resin impregnated wood pieces are arranged as intermediate layers during assembly. The number of intermediate coir and rubber wood layers depends on the board thickness. 

The moisture contents of both inner & face layers are checked before assembly. Curing is done in multi-plated hydraulic press with continuous monitoring of temperature, pressure & time. All the cured boards are removed from the press and are cooled in a cooling press with cold water circulation. After trimming, the boards are inspected for dimension, surface finish, delamination etc. Sample specimens are tested for mechanical properties at the laboratory. The schematic process flow-chart is given in Fig. 1.0.

In this project, 80% of the material used in the composite are renewable natural fibres such as jute and coir. The coir fibre contains 45.84% lignin as against 39% in teakwood. Therefore, it is more resistant than teakwood against rotting under wet and dry conditions and has better tensile strength. Similarly low cellulose content in coir (43%) as against 63% cellulose in wood makes it more durable than teakwood. 

Two major categories of composite boards namely, coir-ply boards(jute + rubber wood + coir) as plywood substitute and natural fibre reinforced boards (jute + coir) as medium density fibre (MDF) board substitute have been developed under the project.

These natural fibre composite boards can be used in place of wood or MDF boards for partitioning, false ceiling, surface panelling, roofing, furniture, cupboards, cabinets, wardrobes etc. Panel & flush doors made of jute-coir composite boards have also been developed and tested as per IS-4020. The detailed properties of jute-coir boards tested as per IS-12406 against the specified values of MDF boards are given in Table 8.0.

Table-8.0: Properties of Jute-Coir Boards Tested as per IS-12406

Sl. No.	Tests	Observed Values (Average)			Specified Values
		Board Thickness
		8 mm	6 mm	4 mm
1.	Cross Breaking Strength (Kgs./cm2) - Perpendicular to Grain Direction
a)	Before Boiling	318	391	373	275 (min.)
b)	After 8 Hrs. Boiling	266	270	240	150 (min.)
2.	Bulk Density (Kgs./cm3)	700	739	760	500-900

Sl. No.	Tests	Observed Values (Avg.)			Specified Values
		Board Thickness
		8 mm	6 mm	4 mm	Exterior Grade	Interior Grade
1. (a)	Moisture Content (%)	5.73	5.90	5.92	5-15	5-15
(b)	Variation from mean moisture content (%)	-2.1	+0.9	+1.2	+3.0	+3.0
2.	Max. water absorption (%)
(a)	After 2 Hrs. soaking	4.5	5.1	2.9	6	9
(b)	After 24 Hrs. soaking	9.1	9.2	6.8	12	18
3.	Max. linear expansion (% swelling in water)
(a)	Due to general absorption after 24 Hrs. soaking
i.	Thickness	Average value : 1.0			4	7
ii.	Length	Average value : 0.13			0.3	0.4
iii.	Width	Average value : 0.21			0.3	0.4

Jute-coir composite boards enjoy excellent applications in railway coaches for sleeper berth backing, for building interiors, doors & windows and also in the transportation sector as backings for seat & backrest in buses. Conventional MDF boards do not prove well on the grounds of moisture absorption & screw holding strength. Cabinet made of jute-coir composite boards is shown in Fig. 2.0.

The Advanced Composites Mission has launched another project for manufacturing cost-effective Jute-glass composite components’ for glass shutter assembly and louver shutter assembly for railway coaches. The products made of jute-glass composites can be used as a replacement of high-cost sheet moulding compound & low-strength dough moulding compound based glass-fibre composites.

The technology for the fabrication of hybrid composites incorporating jute felt and glass fibre using polyester resin as a matrix has been developed successfully by CGCRI, Kolkata. Jute fibre is not as efficient as glass fibre in its resin distribution properties.

It has greater flow resistance and it tends to be less buoyant in dry state and compressed more readily thereby entrapping small air bubbles in the laminates. Some of these deficiencies can be overcome be pressure moulding and by using jute-glass hybrid composites. 

In these composites, jute can play a role as filler fibre in the applications where strength and modulus requirements are not demanding. Moisture absorption can be reduced from 25% to 6% by weight using glass fibre layer on either side of the jute fibre layer.

Replacement of glass fibre reinforcement by 80% by weight of jute and replacement of filler (calcium carbonate) by 25% by weight of jute in DMC formulation increase the mechanical properties of the composite at a greater level. Such judicious selection of jute fibre for making hybrid composite with glass fibre brings down the cost of the laminate by almost 28%. A comparative study has been done on DMC & Jute-glass hybrid composite as given in Table - 9.0.

Table-9.0 : Comparative properties of Dough Moulding Compound (DMC) and Jute-Glass Fibre Hybrid Composite (JGHC)

Type of Composite & Resin	Tensile strength (Mpa)	Tensile Modulus (Gpa)	Flexural Strength (Mpa)	Flexural Modulus (Gpa)
Dough Moulding Compound (DMC)	60-80	8-14	70-100	5-8
Jute-Glass Fibre Hybrid Composite	110-150	10-16	110-180	10-14
Polyester resin	35-60	3-4	50-70	3-4

The Advanced Composites Mission has launched another a project on Jute Based Composite Components for Footwear. The end products to be developed under the project are toe puff, counter stiffener, insoles and cut & skived components for ready to use as per customer requirement.

Toe puff is used in toe (front) portion and counter stiffener is used in backside of footwear. Both are inserted between the leather & lining material for the purpose of stiffness, shape retention etc. 

The main target of the project is to replace the existing materials as produced from leather board, man made synthetic non-woven, woven cotton fabrics etc. with jute. Jute woven & raised fabrics are impregnated with the emulsion made of Polystyrene- SBR, Latex, PVA etc. for the purpose of obtaining desired stiffness.

The impregnated fabric is hot melt adhesive (EVA-polyester, polyamide) coated for bonding with leather components. Since jute has good strength & compatibility with rubber, thermoplastic hot melt adhesives, this new technology could lead to better shape retention, strength, mouldability, flexibility etc. of the footwear component apart from considerable cost reduction.

The usage of jute with thermoplastic resin for shoe components is an innovative approach and this promises a new application avenue for jute in footwear industry.

The technology for rice-husk particle boards with bamboo mat as face veneer has been developed successfully and the product is being manufactured in India. The product is eco-friendly & manufactured out of agro-waste products such as rice-husk & cashew nut shell liquid.

The cleaned rice-husk is blended with phenolic resin & cashew nut shell oil to have a thin coat of resin on the surface. Predetermined quantity of coated rice-husk is spread with two bamboo mat face veneers, coated with phenol formaldehyde, and pressed to predetermined pressure and cured at elevated temperature. 

The boards have been successfully field tested by constructing such temporary shelters for dormitories, go-downs, kiosks etc. The rice-husk particle boards are manufactured in various densities, thickness, types and grades to suit a wide range of applications. Temporary shelter made of such particle board is shown in Fig. 3.0.

Some of the applications of bamboo mat veneered rice husk particle boards are given in Table – 10.0. The rice-husk boards were tested as per IS-3087-1985 & IS-2380-1977 against the specified values. The properties of rice husk boards are given in the Table –11.0.

Table – 10.0 : Applications of Bamboo Mat Veneered Rice Husk Particle Boards 

Wall Panelling	Medium density rice-husk particle boards, both plain and overlaid with decorative laminates can be used as wall panels
Doors, furniture, windows, table tops	Plain and overlaid decorative medium density boards can be used instead of wood-based boards. These boards when used as the core for flush doors and window shutters ensure freedom from insect attack.
False ceilings	Tiles made of low-density boards make attractive false ceilings. Thermal insulation and sound absorption are added advantages
Roofing panels	Medium & high density boards make excellent pre-fabricated, light-weight roof panels for low cost housing, roof terrace houses, geodesic domes, garden houses, beach booths etc., because of their resistance to decay and fire retardance
Insulation	Low density boards can be used as thermal insulation material in air-conditioning, refrigeration
Partitions and stage settings	The low cost & fire resistance of these boards makes them suitable for partition and stage settings
Industrial and domestic flooring	High abrasion resistance make these boards ideally suited for floorings

able – 11.0 : Properties of Bamboo Mat Veneered Rice Husk Particle Boards

Sl. No.	Tests	Observed Value	Specified Value
1.	Density (Kg/m3)	640-870	500-900
2.	Average moisture content (%)	8.0	5-15
3.	Water absorption by weight (%)
	i) 2 hrs. soaking	4-13	25
	ii) 24 hrs. soaking	12-35	50
4.	Swelling (%) – 2 hrs. soaking
	i) thickness	4-6	10
	ii) length	0.2-0.3	0.5
	iii) width	0.2-0.3	0.5
5.	Modulus of rupture min. upto 20 mm thick (N/mm2)	20.90-23.50	15.00
6.	Tensile strength perpendicular to surface min. upto 20 mm thick (N/mm2)	3.40-3.62	0.45
7.	Tensile strength perpendicular to surface (N/mm2)
	i) after cyclic test	0.30-0.33	0.20
	ii) after accelerated water resistance test	2.86-2.93	0.15
8.	Screw withdrawal strength (N)
	i) face	1616-1646	1250
	ii) edge	1285-1312	850

Conclusion

Natural fibre can be a potential candidate in making of composites, especially for partial replacement of high-cost glass fibres for low load bearing applications. As such, commercial exploitation of jute composites for non-structural applications promises excellent potential. Jute fibre (density, 1.3 g/cc) being lighter than glass fibre (density, 2.5 g/cc) offers additional advantages.

From the point of view of wood substitution, natural fibre composite boards could offer an excellent eco-friendly solution as wood substitutes. With ever-depleting forest reserves and corresponding premium on wood, a composite based on renewable resources such as jute, coir, sisal etc. is poised to penetrate the market.

Any value-added application avenues for these fibres would directly contribute to the economic benefits of their growers. Indigenous wood supply for plywood industry in India having been stopped virtually and with increasing landed cost of imported plywood veneers, the jute composite boards provide very good value for the users without any compromise in product quality. 

With increasing emphasis on fuel efficiency, natural fibre such as jute based composites would enjoy wider applications in automobiles and railway coaches. In fact, the market segments such as railway coaches & buses for public transport system in India have vast potential, which is yet to be tapped to a good extent. 

As large varieties of bamboo grow abundantly in many parts of India, there exists an excellent opportunity in fabricating bamboo based composites towards a wide array of applications in building & construction such as boards & blocks as reconstituted wood, flooring tiles etc.

Value-added novel applications of natural fibre & bamboo based composites would not only go a long way in improving the quality of life of people engaged in jute & bamboo cultivation, but would also ensure international market for cheaper substitution.

Abbreviations

BIS – Bureau of Indian Standards

CBRI – Central Building Research Institute

CGCRI – Central Glass & Ceramic Research Institute

CNSL – Cashew Nut Shell Liquid

DMC – Dough Moulding Compound

DMSRDE – Defence Materials & Stores Research & Development Establishment

DST – Department of Science & Technology

FRP – Fibre Reinforced Plastic

GPa – Giga Pascals

GRP - Glass Reinforced Plastic

IIT – Indian Institute of Technology

IJIRA – Indian Jute Industries’ Research Association

IS – Indian Standards

KJ – Kilo Joules

MDF – Medium Density Fibre

MPa – Mega Pascals

NFRP – Natural Fibre Reinforced Plastic

NIRJAFT – National Institute of Research on Jute & Allied Fibre Technology

PVA – Poly Vinyl Acetate

RRL – Regional Research Laboratory

RTM – Resin Transfer Moulding

TIFAC – Technology Information, Forecasting & Assessment Council

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