Wood fiber reinforced bacterial biocomposites: Effects of interfacial modifers and processing on mechanical and physical properties

Scott Powell Anderson

Derived from renewable resources, polyhydroxybutyrate (PHB) exhibits good mechanical properties relative to its polyolefin based counterparts. Reinforcing PHB with wood fiber (WF) results in a biodegradable composite with costs significantly decreased. In this study, PHB/WF composites are produced with percentages of wood fiber comparable to current commercial wood plastic composites (WPCs). In order to improve mechanical and physical properties, interfacial modifiers were added to the PHB/WF composites and processed through injection molding at levels of 1, 2, and 4% on total. Tensile, impact, density, and water absorption properties were investigated for composites modified with maleic anhydride-grafted PHB (MA-PHB), D.E.R., Uralac, and poly(methylene diphenyl diisocyanate) (pMDI). All interfacial modifiers demonstrated improvements in mechanical and physical properties, however composites modified with pMDI displayed properties far superior from the rest. Fracture morphology has been investigated through scanning electron microscopy (SEM) and indicates enhanced fiber adhesion. Morphological studies utilizing dynamic scanning calorimetry (DSC), and dynamic mechanical analysis (DMA), suggest that pMDI is serving to increase mechanical properties not by crosslinking of the PHB matrix, but rather through interactions at the fiber-PHB interface. Parallel formulations were also produced through 35-mm extrusion to investigate composite differences due to processing. The mechanical and physical properties of unmodified and modified (at levels of 4% on total) were contrasted for both injection molded and extruded composites through tensile, impact, density, and water absorption testing. Results indicated similar trends in tensile properties for all modified composites through both processing methods. Because of a pre-compounding step through a twin-screw extruder, the injection molded samples indicated higher stiffness and strength due to better dispersion. Differences in density were detected and found to have a significant impact on stiffness and strength. Water absorption tests showed similar trends across modifying agents from injection molding to extrusion. However, variation in fiber orientation within injection molded samples resulted in surface cracking and increased water uptake of specimens.

Wood fiber reinforced bacterial biocomposites: Effects of interfacial modifers and processing on mechanical and physical properties

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