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Monday 24 July 2017

Wood-plastic composites as promising green-composites for automotive industries!

Published Date
 2008 Jul;99(11):4661-7. Epub 2007 Dec 18.

Author

Author information

1
Department of Chemical Industries, Iranian Research Organization for Science and Technology, PO Box 15815-3538, Tehran, Iran. ashori@irost.ir

Abstract

Wood-plastic composite (WPC) is a very promising and sustainable green material to achieve durability without using toxic chemicals. The term WPCs refers to any composites that contain plant fiber and thermosets or thermoplastics. In comparison to other fibrous materials, plant fibers are in general suitable to reinforce plastics due to relative high strength and stiffness, low cost, low density, low CO2 emission, biodegradability and annually renewable. Plant fibers as fillers and reinforcements for polymers are currently the fastest-growing type of polymer additives. Since automakers are aiming to make every part either recyclable or biodegradable, there still seems to be some scope for green-composites based on biodegradable polymers and plant fibers. From a technical point of view, these bio-based composites will enhance mechanical strength and acoustic performance, reduce material weight and fuel consumption, lower production cost, improve passenger safety and shatterproof performance under extreme temperature changes, and improve biodegradability for the auto interior parts.
PMID:
 
18068352
 
DOI:
 
10.1016/j.biortech.2007.09.043

For further details log on website :
https://www.ncbi.nlm.nih.gov/pubmed/18068352

Effect of adding rubber powder to poplar particles on composite properties.

Published Date
 2012 Aug;118:56-60. doi: 10.1016/j.biortech.2012.02.041. Epub 2012 Feb 28.

Author
Xu M1Li J.

Author information

1
Northeast Forestry University, 26 Hexing Road, Harbin 150040, PR China.

Abstract

The effect of adding rubber powder derived from waste tires to poplar wood particles on mechanical and water-resistant properties of particleboards was examined. Sixty panels were made with rubber contents of 0-40% at hot-pressing temperatures of 140-180 °C, methylene diphenyl diisocyanate resin contents of 2-6% and panel densities of 0.6 to 1 g cm(-3). Although the modulus of rupture (MOR), modulus of elasticity (MOE), internal bond (IB) strength were reduced by adding rubber powder, the thickness swelling (TS) was reduced by 7.3-61% when 10-40% rubber powder was added. Four regression equations (rubber content, pressing temperature, resin content and target panel density as functions of MOR, MOE, IB and TS) were developed and a nonlinear programing model was derived with operation research theory to obtain the most desirable panel properties under some production constraints.
PMID:
 
22705506
 
DOI:
 
10.1016/j.biortech.2012.02.041

For further details log on website :
https://www.ncbi.nlm.nih.gov/pubmed/22705506

Wood plastic composites based on microfibrillar blends of high density polyethylene/poly(ethylene terephthalate).

Published Date
 2010 May;101(10):3665-71. doi: 10.1016/j.biortech.2009.12.069. Epub 2010 Jan 25.

Author
Lei Y1Wu Q.

Author information

1
School of Renewable Natural Resources, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, United States. yonglei168@hotmail.com

Abstract

High-melting-temperature poly(ethylene terephthalate) (PET) was successfully introduced into wood plastic composites through a two-step reactive extrusion technology. Wood flour was added into pre-prepared PET/high density polyethylene (HDPE) microfibrillar blends (MFBs) in the second extrusion at the temperature for processing HDPE. Addition of 25% in situ formed PET microfibers obviously increased the mechanical properties of HDPE, and more significant enhancement by the in situ formed recycled PET microfibers was observed for the recycled HDPE. Adding 2% E-GMA improved the compatibility between matrix and microfibers in MFBs, resulting further enhanced mechanical properties. The subsequent addition of 40% wood flour did not influence the size and morphology of PET microfibers, and improved the comprehensive mechanical properties of MFBs. The wood flour increased the crystallinity level of HDPE in the compatibilized MFB in which PET phase did not crystallize. The storage modulus of MFB was greatly improved by wood flour.
PMID:
 
20100654
 
DOI:
 
10.1016/j.biortech.2009.12.069

For further details log on website :
https://www.ncbi.nlm.nih.gov/pubmed/20100654

Use of recycled plastics in wood plastic composites - a review.

Published Date
 2013 Sep;33(9):1898-905. doi: 10.1016/j.wasman.2013.05.017. Epub 2013 Jun 15.

Author

Author information

1
Department of Wood and Paper Science and Technology, Natural Resources Faculty, Tarbiat Modares University, Iran. skazemi@modares.ac.ir

Abstract

The use of recycled and waste thermoplastics has been recently considered for producing wood plastic composites (WPCs). They have great potential for WPCs manufacturing according to results of some limited researches. This paper presents a detailed review about some essential properties of waste and recycled plastics, important for WPCs production, and of research published on the effect of recycled plastics on the physical and mechanical properties of WPCs.

KEYWORDS:

Degradation; Physical and mechanical properties; Waste and recycled plastics; Wood plastic composites
PMID:
 
23777666
 
DOI:
 
10.1016/j.wasman.2013.05.017

For further details log on website :
https://www.ncbi.nlm.nih.gov/pubmed/23777666

Technical assessment of three layered cement-bonded boards produced from wastepaper and sawdust.

Published Date
 2007;27(11):1611-6. Epub 2006 Nov 1

Author

Author information

1
Department of Forestry and Wood Tech, Federal University of Technology, PMB 704 Akure, Nigeria

Abstract

The technical properties of three layered cement-bonded boards (CBBs) made from wastepaper and sawdust were investigated. The CBBs were produced at three density levels of 1000, 1200 and 1300 kg/m3 and at four cement/particle ratios of 2.0:1, 2.5:1, 3.0:1 and 3.5:1 on a weight to weight basis. The technical properties evaluated were modulus of rupture (MOR), modulus of elasticity (MOE), water absorption (WA) and thickness swelling (TS). The MOR values ranged from 4.85 to 11.69 MPa and MOE values ranged from 2.80 to 5.57 GPa. The mean values of WA and TS after 24 h of water soaking of the CBBs ranged from 18.18% to 40.49% and 3.55% to 12.13%, respectively. MOR and MOE of the CBBs increased with increase in board density, but MOR decreased with the increase in cement/particle ratio. On the other hand, WA and TS decreased with increase in board density and cement/particle ratio. CBBs produced from wastepaper and sawdust at cement/particle ratios of 3.0:1 and 3.5:1 are suitable for building construction such as paneling, ceiling and partitioning.
PMID:
 
17098411
 
DOI:
 
10.1016/j.wasman.2006.09.005

For further details log on website :
https://www.ncbi.nlm.nih.gov/pubmed/17098411

Flat-pressed wood plastic composites from sawdust and recycled polyethylene terephthalate (PET): physical and mechanical properties

Published Date
. 2013; 2: 629.
Published online 2013 Nov 23. doi:  10.1186/2193-1801-2-629

Author
Khandkar- Siddikur Rahman, Md Nazrul Islam,corresponding author Md Mushfiqur Rahman, Md Obaidullah Hannan, Rudi Dungani, andHPS Abdul Khalil

Introduction

Wood plastic composites (WPCs) are relatively new generation of composite materials and also the most promising sector in the field of both composite and plastic industries. In 1970s, the modern concept of WPC was developed in Italy and gradually got popularity in the other part of the world (Pritchard ). Wood in the form of flour/particles/fibers are combined with the thermoplastic materials under specific heat and pressure for producing WPCS where additives are added for improving the quality. Many researchers have been worked on WPCs by flat-pressed method at various wood-plastic ratio (Chen et al. ; Najafi et al. ; Lee et al. ; Ayrilmis et al. ; Ayrilmis and Jarusombuti ; Jarusombuti and Ayrilmis ) which typically ranges between 50 to 80% of SD or fibre either as filler or reinforcements (Clemons ). The higher strength and aspect ratio of natural fibres offers good reinforcing potential in composite matrix compared to the artificial fibres (Abdul Khalil et al. ; Clemons ).
Virgin plastics include high and low density polyethylene (HDPE and LDPE respectively), polypropylene (PP), polystyrene (PS) and poly vinyl chloride (PVC) which are commonly used for the production of WPCs (Najafi et al. ). Recycled plastics can also consider for manufacturing of WPCs depending on their melting temperature (Stark et al. ). Additives can also be added to improve the quality of the composites by eliminating the off-putting properties. However, the utilization of recycled plastic in WPC manufacturing is still limited, and a major portion of global municipal solid waste includes post consumer plastic materials like HDPE, LDPE, PVC, and PET which have the potentiality for being used in the WPCs (Chaharmahali et al. ). These post consumer plastics also pose a serious threat to the environment unless they are recycled.
Polyethylene terephthalate commonly known as PET and is formed from terephthalic acid (TPA) and ethylene glycol (EG). It is a long-chain polymer (C10H8O4)n belongs to the polyesters family. It shows both amorphous (transparent) and semi-crystalline nature (Ozalp ). PET is intensively used by the packaging industries for bottles and containers of food and other consumer products. Later, PET has started to use in injection molded and extruded articles, primarily for reinforcement with glass fibre (Sinha et al. ) which do not degrade in the outdoor environment. Thus, increasing interest has recently been focused on the recycling of plastic wastes, especially PET for these various purposes which could prevent the environmental pollution. Saw dust, a waste from wood processing industries, also creates environmental hazard unless reprocessed for different applications like particleboard, pulp. The recycled PET and saw dust can be used to produce wood plastics by flat-press method which might a good value added products from waste and would help to minimize the waste. Flat press method is newly introduced method in the WPC sector and is similar to the industrial particleboard manufacturing process. Though extrusion and injection molding are the predominant technologies to produce WPCs, but flat press process is technically more advantageous (Jarusombuti and Ayrilmis ). This technology possesses some advantages like higher productivity with relatively lower pressure requirement and as a consequence naturally given wood structure lefts undestroyed. Thus, the density of WPCs reduces considerably (Ayrilmis and Jarusombuti ; Jarusombuti and Ayrilmis ) and increase the moisture resistance properties compared to the conventional wood based composites (Jarusombuti and Ayrilmis ). However, there is very limited/no work so far on the fabrication and properties of flat-pressed WPCs from sawdust and recycled PET at various mixing ratios. Thus, the purpose of this study was to investigate the feasibility of wood plastic composites fabrication from sawdust and PET. Determining the physical and mechanical properties of WPCs as a function of mixing ratio was also an objective of this study.

Materials and methods

Preparation of raw materials

Sawdust was obtained from the local saw mills in Khulna, Bangladesh. Sawdust was screened to remove the impurities. It was then dried in an oven at 103 ± 2°C for 24 hours for a moisture content of 2%. Clean consumer drinking water bottles were collected locally and grind in a grinder for getting the recycled PET powder. The PET powder was sieved by 60 mesh size sieve to remove the oversized particles. The PET powder was then dried in an oven at 103 ± 2°C for 24 hours for a moisture content of 3% or less. Density, melt flow index and melting point of recycled PET was 1370 (Kg/m3), 18.4 g/10 min and 260°C, respectively.

Flat-pressed sawdust-PET composite manufacturing

The ensuing sawdust and PET powder were mixed for 6 minutes in a rotary drum type blender according to the ratio of Table 1 for producing a homogenous composite. WPC panels were manufactured by flat press process using a dry blending method which was similar to an industrial production process. The mixture was placed in an aluminium caul plate using a forming box to form uniform mat. The press cycle consisted of three phases (Chen et al. ), i.e., first phase involved the manual pressing to reduce the mat height, second phase involved in shifting it to the electrically heated improvised hot press for hot pressing, and finally for cold pressing to facilitate the setting of thermoplastic resin. The maximum pressing temperature, pressure, time and cold pressing or pressure holding time were 190°C, 5 N/mm2, 25 minutes and 6 minutes, respectively. Lower temperature (190°C) compared to melting temperature (260°C) of the PET was set to avoid the degradation of the wood components. After cold pressing, the WPCs were removed from the press for further cooling. At least six replications of each type of WPC panels having 30 × 25 × 0.6 cm dimension were fabricated. The WPC panels were then trimmed and put into a conditioning room before testing for 48 hours.
Table 1
Formulations of sawdust-PET composites

Evaluation of composite properties

For both physical and mechanical properties, room temperature and relative humidity was 23 ± 2°C and 65 ± 2%, respectively. According to the ASTM standard D-1037 (ASTM ), all specimens were carefully prepared and tested to evaluate the physical and mechanical properties of each type of WPCs. At least 24 specimens from 6 replications were used for each type of WPC panel for the evaluation of physical and mechanical properties. The results were compared with the wood based panels as there was no WPC panel standard for comparison as were reported by Ayrilmis et al. ().

Physical properties

Density was measured according to the standard for composites. Moisture content of WPC panels was measured by oven dry method by using the equation 1:
equation image
1
Where, mc is the moisture content, mint is mass with moisture (g) and mod is mass after drying.
After soaking the samples in water for 24 hours at 25, 50 and 75°C, water absorptions and thickness swelling were measured according to Najafi et al. (). The water absorption (A) and thickness swelling (G) of the specimens were calculated as percentage. The water absorption (A) and thickness swelling (G) was calculated according to the Equation 2 and 3, respectively:
equation image
2
Where m2 is the weight (g) of the specimen after soaking and m1 is the weight (g) of the specimen before soaking.
equation image
3
Where, A1 is the thickness before soaking, and A2 is the thickness after soaking.

Mechanical properties

WPC panels were cut into rectangular sections for determining MOE and MOR. The dimension of the specimen was 240 mm × 50 mm × 6 mm. MOE and MOR were measured by following the three point bending test using universal testing machine IMAL-IB600 according to the ASTM D 1037–93 standard (ASTM ).

Statistical analysis of data

Statistical analysis was done by using SAS system software (version 6.12) at 95% confidence level. The significance of different treatments was determined by least significant difference (LSD) test.

Results and discussion

Physical properties

Density

The most important indicator of composite’s performance is density, which basically affects all the properties of composites. Density of the SD-PET composites decreased with the increase of SD percentage in the thermoplastic matrices. The lowest density (856.73 Kg/m3) was found in composites made with a mixing ratio of 70:30 (SD:PET), whereas the highest density (1048.55 Kg/m3) was found when the ratio was 40:60 (SD:PET) (Figure 1). The lower density of sawdust compared to PET might be the cause of this density reduction. Statistical analysis illustrated significant differences (α = 0.05) for density among the SD-PET composites for different mixing ratio (Table 2). According to ANSI () standard, the density of high density particleboard is above 800 Kg/m3. Hence, the density of SD-PET composites was above that required standard for high density particleboard. Chen et al. () reported that the smaller wood particles like sawdust would make a thinner mat and the compaction ratio would be higher resulting high density composite materials. That might be another reason for this higher density of WPCs found in this study.
Figure 1
Density of SD-PET composites at varying ratio.
Table 2
Effect of sawdust content on the properties of SD-PET composites

Moisture content

The moisture content of the SD-PET composites increased along with the increase of SD percentage from 40 to 70% (Figure 2). Adding SD into the thermoplastic matrix increased the moisture content due to the hydrophilic nature of wood. Additionally, the gaps and flaws at the interfaces, and the micro-cracks in the matrix formed during the manufacturing process boosted up the moisture content as reported by Adhikary et al. (). From the variance analysis and LSD (Table 2), it was observed that there was significant difference (α = 0.05) in moisture content among composites. According to the ANSI () standard, the mean moisture content of the board shall not exceed 10% (based on the oven dry weight of the board). The moisture content of SD-PET composites was substantially lower than that of the required standard. The same increasing pattern of MC was also reported by Chen et al. () for the thermoplastic composites made from HDPE and recycled wood particles.
Figure 2
Moisture content of SD-PET composites at varying ratio.

Water absorption

Figure 3 illustrates the water absorption of the SD-PET composites based on various SD content and different temperatures (25, 50 and 75°C) after 24 hours of immersion in water. WA of the composites increased with the increase of SD content. The highest WAs were 29.52, 36.10 and 40.33% for 25, 50 and 75°C temperature, respectively with 70% SD content. These results mainly attributed due to the hydrophilic nature of wood. Wood is a hydrophilic porous composite which consists of cellulose, lignin and hemicellulose polymers that are rich in functional groups such as hydroxyls, which readily interact with water molecules by hydrogen bonding (Clemons ) and due to this reason, the WPCs have the potentiality to uptake water under humid condition (Adhikary et al. ). Similar results for increasing pattern of WA were also reported by Chen et al. () for the WPCs made from HDPE and recycled wood particles. On the other hand, higher water resistance of composites with the increasing PET content can be attributed to the hydrophobic character of PET, though it is semi-crystalline in nature. Figure 3 also illustrated the water uptake as a function of temperature. Immersion temperature had also significant influence on the WA of the composites. In composites with higher SD contents, WA increased more rapidly when the temperature increased from 25°C to 75°C. The trend was reverse for composites having lower SD content. Statistical analysis showed that there was significant difference (α = 0.05) in WA after 24 hours at three different temperatures (25, 50 and 75°C) among the SD-PET composites (Table 2). Najafi et al. () reported that besides the percentage of wood flour/particle, there were several factors including plastic type, virginity of the plastic and surrounding temperature also influenced the water absorption of WPCs.
Figure 3
Water absorption of SD-PET composites at varying ratio.

Thickness swelling

The tendency of TS was similar to the WA (Figure 4). From the statistical analysis (Table 2), it was observed that the TS were significantly different (α = 0.05) for WPCs at three different temperatures (25, 50 and 75°C). It also illustrated that the SD-PET composites having lower percentage of PET were more susceptible to the thickness swelling than those of panels having higher PET content. This might be due to the increasing SD content in the WPC formulation. Ayrilmis et al. () reported that for thickness swelling and water absorption of WPCs, wood fibers were mainly responsible. The TS at room temperature (25°C) ranged between 5.7 and 10.0% for composites made from 40-70% SD content. The lowest thickness swelling was found for SD-40 composites which might be because of the higher compatibility between SD and PET when compared to the other formulations. This increasing pattern of TS was similar to the results of TS stated by Chen et al. () for the thermoplastic composites made from HDPE and recycled wood particles. Wood has a critical surface energy in the range of 40–60 mJ/m2 (Gupta et al. ) which is higher than that of PET. The large difference in surface energy between PET and wood might make the PET to be water repellent or hydrophobic.
Figure 4
Thickness swelling of SD-PET composites at varying ratio.

Mechanical properties

Modulus of elasticity (MOE)

The MOE of composites decreased along with higher SD loading from 40 to 70% in the formulation (Figure 5). This variation might be due to the poor interfacial interaction between the sawdust and PET. The melting temperature of PET was 260°C, however, the pressing temperature was 190°C as a result the thermoplastic (PET) might not flow well within the composites. Shibata et al. () reported that the lower MOE of the composites could be mainly attributed to the poor interfacial interaction between the polymeric matrix and wood particle, not allowing efficient stress transfer between the two phases of the material though the modulus of the natural fibers are higher than the polymeric materials. Some other researches with various thermoplastic materials either virgin or recycled indicated that the MOE of the WPCs would increase with the increase of wood content up to 60% and deceased after 60% of wood content. This was because of more than 60% wood particle used to manufacture WPCs, the plastic material could not totally cover fine wood particles (Chen et al.  and Sanadi et al. ). Moreover, Maloney () reported that the relatively large surface area of the fine materials might be another cause of strength loss of the composites. The MOE of WPC panels were statistically different according to the ANOVA and LSD (α = 0.05). MOE of the SD-PET composites could not fulfill the required standard of ANSI () for the high density particle board (2400 N/mm2) but all the composites except the 70:30 (SD:PET) fulfilled the required standard (1725 N/mm2) for medium density particleboard.
Figure 5
MOE of SD-PET composites at varying ratio.

Modulus of rupture (MOR)

Figure 6 illustrates the effects of SD content on the MOR of the WPCs. The tendency of the MOR was similar to the MOE. It was observed that the MOR of the composites decreased with the increase of SD content and ranged between 11.69 and 27.08 N/mm2. It appeared that the binding capacity of the utilized PET gradually decreased. The mechanical behavior of WPCs was greatly influenced by the uniformity of lignocellulosic materials dispersed in the polymeric matrix (Chen et al.  and Raj et al. ). The ratio of 40:60 (SD:PET) had the highest MOR value compared to the other formulations. Based on the statistical analysis, significant difference (α = 0.05) was found for the MOR properties of the WPC panels (Table 2). Moreover, only MOR of the SD-40 and SD-50 composites fulfilled the required standard of ANSI () for the high density particleboard (16.5 N/mm2). However, all the formulation of composites fulfilled the required standard (11 N/mm2) for medium density particleboard. Ayrilmis and Jarusombuti () reported that MOR would increase up to 40–50% for wood fiber content and would start to decrease after 50–60% wood fiber content for flat-pressed PP bonded WPCs.
Figure 6
MOR of SD-PET composites at varying ratio.

Effects of PET content on the properties of composites

Effects of PET content on SD-PET composites are presented in Table 3. Table 3 illustrates that the higher content of PET in the WPC formulation increases the density and bending strength of composites. In the mean time, the increasing PET content in the formulation decreases the moisture content, WA and TS at temperatures of 25, 50 and 75°C. Similar results were also reported by Najafi et al. (). It seems that the effect of PET content on moisture content, WA and TS of WPC is positive. Among all the properties of SD-PET composites, PET content showed the most relative effect on WA at 25°C (R2 = 0.926), while PET content showed least effect on WA at 75°C for WPCs (R2 = 0.693).
Table 3
Effects of PET content on composite properties

Conclusion

This study investigated the technical evaluation of flat-pressed wood plastic composites fabricated from different mixing ratios of sawdust and PET. On the basis of physical and mechanical properties, it appears that fabrication of SD-PET composites with dry blending method followed by flat press process is technically feasible for various structural purposes. Therefore, from the above presented results and discussion the following specific conclusions can be drawn:
  1. The physical and mechanical property differences among the WPCs are due to the raw material characteristics and the mixing ratios used in the formulations. Therefore, the property of SD-PET composites depends on raw material and mixing ratio.
  2. PET contents decreased moisture content, water absorption and thickness swelling of composite. It has also relative effects on density and bending strength.
  3. Immersion temperature has significant effect on the water absorption and thickness swelling of WPCs. With the increasing immersion temperature, water absorption and thickness swelling increases.
Though the flat-pressed WPC fabrication from the sawdust and PET is technically feasible, it would be better to mix additives like coupling agents to enhance interaction between sawdust and PET by reducing the melting temperature of PET, and thus, could ensure the adequate physical and mechanical properties of composites.

Footnotes

Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
KS Rahman and MM Rahman carried out the field study. R Dungani drafted the manuscript. MN Islam, MO Hannan and HPS Abdul Khalil edited the manuscript. I also declare that all authors read and approved the final manuscript.

Contributor Information

Khandkar- Siddikur Rahman, moc.oohay@rsk_anar.
Md Nazrul Islam, moc.oohay@71lurzan.
Md Mushfiqur Rahman, moc.liamg@89461sqifhsum.
Md Obaidullah Hannan, moc.liamg@nannahhalludiabom.
Rudi Dungani, di.ca.bti.htis@idur.
HPS Abdul Khalil, moc.liamg@sphlilahka.

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