ZnO Treatment on Mechanical Behavior of Polyethylene/Yellow Birch Fiber Composites When Exposed to Fungal Wood Rot.

Wood plastic composite (WPC) usage and demand have increased because of its interesting chemical and mechanical properties compared to other plastic materials. However, there is a possibility of structural and mechanical changes to the material when exposed to the external environment; most research on wood plastic is performed on the material with elevated fiber content (40-70%). Therefore, more research needs to be performed regarding these issues, especially when the fiber content of the WPC is low. In this study, composite materials composed of high-density polyethylene (HDPE) reinforced with yellow birch fibers (20 and 30%) were made by injection molding. The fibers were treated with dissolved zinc oxide (ZnO) powder in sodium oxide (NaOH) solution, and the fabricated material was exposed to fungal rot. ZnO treatment in this case is different from most studies because ZnO nanoparticles are usually employed. The main reason was to obtain better fixation of ZnO on the fibers. The mechanical properties of the composites were assessed by the tensile and Izod impact tests. The impact energies of the samples fabricated with ZnO-treated fibers and exposed to Gloephyllum trabeum and Trametes versicolor decreased, when compared to samples fabricated with ZnO-nontreated fibers. The mechanical properties of the samples composed of ZnO-treated fibers and exposed to rot decreased, which were reported by a decreased Young's modulus and impact energies. The usage of ZnO treatment prevented mycelium proliferation, which was nonexistent on the samples. It has been noted that the decrease in mechanical properties of the treated samples was because of the action of NaOH used to dissolve the ZnO powder.

Mechanical Properties, Wettability and Thermal Degradation of HDPE/Birch Fiber Composite.

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.

Damage Characterization of Bio and Green Polyethylene-Birch Composites under Creep and Cyclic Testing with Multivariable Acoustic Emissions.

Despite the knowledge gained in recent years regarding the use of acoustic emissions (AEs) in ecologically friendly, natural fiber-reinforced composites (including certain composites with bio-sourced matrices), there is still a knowledge gap in the understanding of the difference in damage behavior between green and biocomposites. Thus, this article investigates the behavior of two comparable green and biocomposites with tests that better reflect real-life applications, i.e., load-unloading and creep testing, to determine the evolution of the damage process. Comparing the mechanical results with the AE, it can be concluded that the addition of a coupling agent (CA) markedly reduced the ratio of AE damage to mechanical damage. CA had an extremely beneficial effect on green composites because the Kaiser effect was dominant during cyclic testing. During the creep tests, the use of a CA also avoided the transition to new damaging phases in both composites. The long-term applications of PE green material must be chosen carefully because bio and green composites with similar properties exhibited different damage processes in tests such as cycling and creep that could not be previously understood using only monotonic testing.