Flat-pressed wood plastic composites from sawdust and recycled polyethylene terephthalate (PET): physical and mechanical properties
© Rahman et al.; licensee Springer. 2013
Received: 9 October 2013
Accepted: 20 November 2013
Published: 23 November 2013
This study deals with the fabrication of composite matrix from saw dust (SD) and recycled polyethylene terephthalate (PET) at different ratio (w/w) by flat-pressed method. The wood plastic composites (WPCs) were made with a thickness of 6 mm after mixing the saw dust and PET in a rotary type blender followed by flat press process. Physical i.e., density, moisture content (MC), water absorption (WA) and thickness swelling (TS), and mechanical properties i.e., Modulus of Elasticity (MOE) and Modulus of Rupture (MOR) were assessed as a function of mixing ratios according to the ASTM D-1037 standard. WA and TS were measured after 24 hours of immersion in water at 25, 50 and 75°C temperature. It was found that density decreased 18.3% when SD content increased from 40% to 70% into the matix. WA and TS increased when the PET content decreased in the matrix and the testing water temperature increased. MOE and MOR were reached to maximum for the fabricated composites (2008.34 and 27.08 N/mm2, respectively) when the SD content were only 40%. The results indicated that the fabrication of WPCs from sawdust and PET would technically feasible; however, the use of additives like coupling agents could further enhance the properties of WPCs.
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 2004). 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. 2006; Najafi et al. 2007; Lee et al. 2010; Ayrilmis et al. 2011; Ayrilmis and Jarusombuti 2011; Jarusombuti and Ayrilmis 2011) which typically ranges between 50 to 80% of SD or fibre either as filler or reinforcements (Clemons 2002). 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. 2014; Clemons 2008).
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. 2007). Recycled plastics can also consider for manufacturing of WPCs depending on their melting temperature (Stark et al. 2010). 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. 2008). 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 2011). 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. 2010) 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 2011). 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 2011; Jarusombuti and Ayrilmis 2011) and increase the moisture resistance properties compared to the conventional wood based composites (Jarusombuti and Ayrilmis 2011). 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
Formulations of sawdust-PET composites
WPC composition based on % weight
Sawdust content (%)
PET content (%)
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 1999), 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. (2011).
Where, mc is the moisture content, mint is mass with moisture (g) and mod is mass after drying.
Where, A1 is the thickness before soaking, and A2 is the thickness after soaking.
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 1999).
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
Effect of sawdust content on the properties of SD-PET composites
WPC panel type
Modulus of elasticity (MOE)
Modulus of rupture (MOR)
Effects of PET content on the properties of composites
Effects of PET content on composite properties
Regression coefficient (R2)
Density (Kg/m 3 )
y = 6.321x +662.1
y = −0.40x + 3.367
WA (%) at 25°C
y = −0.518x + 43.67
WA (%) at 50°C
y = −0.488x +49.81
WA (%) at 75°C
y = −0.547x + 56.53
TS (%) at 25°C
y = −0.129x + 13.81
TS (%) at 50°C
y = −0.141x + 15.24
TS (%) at 75°C
y = −0.161x + 16.98
MOE (N/mm 2 )
y = 18.86x + 917.4
MOR (N/mm 2 )
y = 0.545x - 5.469
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.
PET contents decreased moisture content, water absorption and thickness swelling of composite. It has also relative effects on density and bending strength.
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.
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