Wood–plastic composites have emerged and represent an alternative to conventional composites reinforced with synthetic carbon fiber or glass fiber–polymer. A wide variety of wood fibers are used in WPCs including birch fiber. Birch is a common hardwood tree that grows in cool areas such as the province of Quebec, Canada. The effect of the filler proportion on the mechanical properties, wettability, and thermal degradation of high-density polyethylene/birch fiber composite was studied. High-density polyethylene, birch fiber and maleic anhydride polyethylene as coupling agent were mixed and pressed to obtain test specimens. Tensile and flexural tests, scanning electron microscopy, dynamic mechanical analysis, differential scanning calorimetry, thermogravimetry analysis and surface energy measurement were carried out. The tensile elastic modulus increased by 210% as the fiber content reached 50% by weight while the flexural modulus increased by 236%. The water droplet contact angle always exceeded 90°, meaning that the material remained hydrophobic. The thermal decomposition mass loss increased proportional with the percentage of fiber, which degraded at a lower temperature than the HDPE did. Both the storage modulus and the loss modulus increased with the proportion of fiber. Based on differential scanning calorimetry, neither the fiber proportion nor the coupling agent proportion affected the material melting temperature.
A maximum of 20% (w/w) lignin was used as a filler in low-density polyethylene (LDPE), together with 3-6% maleic anhydride-grafted LDPE as compatibilizer and 3-10% copper(II) sulphate pentahydrate (CuSO 4 Á5H 2 O) as lignin's dispersing agent. The resulting composites were investigated for both their mechanical properties and their melting point following the ASTM standards as well as their behaviour was compared with neat LDPE. The results reveal that addition of compatibilizer significantly improved the mechanical properties of lignin, yielding closer values to those of neat LDPE. In fact, the addition of 3% maleated polyethylene induced a 37% increase of the Young's modulus, whilst 3% CuSO 4 Á5H 2 O provides a good lignin dispersion. The above observations are further supported by the scanning electron micrographs of the blend specimens. Finally, the differential scanning calorimetry analysis revealed that the melting temperature and the crystallinity of LDPE slightly increase with the addition of 3% CuSO 4 Á5H 2 O.
This study reports the effects of wood fibers and 3 wt% maleic anhydride-grafted polypropylene used as coupling agent on the tensile properties of polypropylene/wood composites. Compounding was done in a roller-based internal batch mixer followed by compression molding. Our findings show that both birch and aspen wood fibers improve the elastic modulus and the tensile strength of composites, and the chemical treatment improves the fiber-matrix interface. A comparison of experimental results' elastic modulus with micromechanics theoretical models shows that the Lavengood-Goettler model is closer to experimental data. Also the results showed that the polypropylene/ wood composites' elastic modulus exceeds high-performance thermoplastics commonly used in gears manufacturing. Thus, the price of polypropylene/wood fibers makes it a viable alternative for similar application.
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