Abstract
Wood fiber reinforcement of plastics is almost limited to polypropylene, polyethylene, polyvinyl chloride and polystyrene. Wood fiber reinforcement of thermoplastic polyurethanes (TPU) is a new research field and paltry studied scientifically. Wood fiber reinforcement can carry out synergistic effects between sustainability, material or product price reduction, improved mechanical properties at high elongation, and brilliant appearance and haptics. In order to evaluate to what extent the improvement of mechanical properties depend on material-specific parameters (fiber type, fiber content) and on process-specific parameters (holding pressure, temperature control and injection speed), differently filled compounds were injection molded according to a partial factorial test plan and subjected to characterizing test procedures (tensile test, Shore hardness and notched impact test). Tensile strength showed significant dependence on barrel temperature, fiber type and interaction between holding pressure and barrel temperature in the region of interest. Young’s modulus can be influenced by fiber content but not by fiber type. Notched impact strength showed a significant influence of cylinder temperature, fiber content, fiber type and the interaction between cylinder temperature and fiber content in the region of interest. Shore hardness is related to fiber content and the interaction between mold temperature and injection flow rate. Our results show not only that wood-filled TPU can be processed very well by injection molding, but also that the mechanical properties depend significantly on temperature control in the injection-molding process. Moreover, considering the significant reinforcing effect of the wood fibers, a good fiber-matrix adhesion can be assumed.
Highlights
Parameters (Table 1), the fiber type and the fiber content in terms of tensile strength matrix exists of fiber the fiber length
Our studies reveal any influence of fiber length sition the contents wood fibers released volatile organic components (VOC)
The achievable tensile strength decreases significantly. This can be explained by the incipient decomposition of the wood fibers and subsequently released volatile organic components (VOC) of the wood fibers, which interact with the matrix material, resulting in vacuoles and hydrolytic matrix degradation due to water reposition in the cells of the wood fiber
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Polar means a charge shift is existing in the molecular chain and a dipole is formed, whereas nonpolar materials do not form a dipole in the molecular chain This physicochemical discrepancy results in poor fiber/matrix adhesion and low mechanical properties. For cavities with large geometric freedom, flow front breaks up so that the cavity is filled irregularly and not under headstream It has been shown by Soxhlet extraction that segregation between the fibers and the matrix occurs at long flow paths [22,23]. Diestel & Krause conducted studies on the water absorption of wood-filled TPU compounded in a compression molding process utilizing a heating-cooling mixer [27]. An increase in tensile strength was observed for TPU filled with microcrystalline cellulose, whereas, for other compounds, a decrease in tensile strength was observed above a fiber content of 30-wt-%. We investigate the processability of wood-filled thermoplastic polyurethanes by injection molding, in order to define a suitable parameterization and to record the mechanical properties of wood-filled TPU
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