Doctor of Philosophy (PhD)


Renewable Natural Resources

Document Type



The effect of inorganic fillers including precipitated calcium carbonate (PCC), glass fiber (GF), and nano-clay on properties of structured WPCs was investigated. In PCC-bamboo-polymer hybrid composites, tensile and flexural moduli were improved with increasing PCC content. After silane treatment of bamboo, RBF-filled hybrid composites showed better mechanical properties compared to those of GBP-filled hybrid composites. The hybrid composites showed 3-4 times higher modulus than those of PCC-filled composites at high PCC levels. Various property differences were observed between weak- and strong-core coextruded systems with shell composition changes. While the weak-core systems showed improved flexural strengths compared to their core-only control, the strong-core systems had lowered flexural strengths. In both systems, impact strengths increased at low shell filling levels but decreased at high shell filling levels. Impact fracture types varied with core quality and shell filling composition. Coextruded composites with treated PCC-filled shell showed better water absorption (WA) property compared to core-only controls and coextruded composites with high WF-filled shell. Plastic-only shell increased overall coefficient of thermal expansion (CTE) of coextruded composites, but filled shells led to the CTE decreases of coextruded composites. GF in shell behaved as an effective reinforcement for coextruded composites. The comparisons of flexural property among different core systems show that GF reinforcements were optimized at high GF loadings in a shell layer and GF alignments in the shell layer also played an important role. In coextruded composites with different shell thicknesses, the flexural property enhanced with the increase of shell bending modulus and strength at a given shell thickness. When the flexural property of shell was less than that of core, the increase of shell thickness led to reduced flexural property. On the other hand, when the flexural property of shell was higher than that of core, the opposite was true. In sound transmission loss (TL) testing, the stiffness and surface density were major factors influencing the sound insulation property of materials. The experimental TL results showed that the addition of clay or PCC and/or wood fiber (WF) fillers led to the increases of general resonance frequencies and TL in filled composites. However, at high filling levels, composite stiffness decreases led to TL reduction. The experimental TL curves of filled HDPE and WPCs were well approximated with the combined TL predictions from their corresponding stiffness-1 and stiffness-2 TL for S-region and mass law TL for M-region.



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Committee Chair

Wu, Qinglin