Soumitra Biswas, G Srikanth & Sangeeta Nangia Abstract
Conclusion
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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.
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.
** 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 :
|
|
|
|
|
|
The cashew nut shell liquid based polymers offer the following advantages :
|
|
|
|
|
|
|
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.
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For further details log on website :
http://www.tifac.org.in/index.php?option=com_content&id=541:development-of-natural-fibre-composites-in-india&catid=85:publications&Itemid=952
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