Graduate Thesis Or Dissertation
 

Improved interfacial adhesion in wood-plastic composites : Development of new compatibilizers

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  • In wood-plastic composites (WPCs) a compatibilizer is often used to improve the interfacial adhesion between the hydrophilic wood filler and the hydrophobic plastic matrix. At present, while the basic concepts of compatibilization are understood, the optimized chemical structures of an effective compatibilizer, including the ideal structures of the wood-binding domain and the plastic-binding domain, are poorly understood. Poly(N-acryloyl dopamine) (PAD), a mimicking polymer of marine adhesive protein, was synthesized. The bonding between PAD and maple veneers was strong and highly water-resistant. The addition of polyethylenimine further increased the adhesive strengths. PAD should be able to serve as an effective wood-binding domain for a wood-plastic compatibilizer. Terminally functionalized polyethylenes (PE), PE-MDI (methylene diphenyl diisocyanate) and PE-PMDI (polymeric methylene diphenyl diisocyanate), were prepared through the reactions between polyethylene monoalcohol (PEA) and MDI and between PEA and PMDI, respectively. The performance of PEA, PE-MDI and PE-PMDI as compatibilizers for wood-PE composites was investigated. These compatibilizers had well-defined structures with a linear PE chain as a PE-binding domain and a bydroxyl group or an isocyanate group as a wood-binding domain. All these compatibilizers increased the strength of the wood-PE composites. Composites with PE-MDI or PE-PMDI had a higher modulus of rupture (MOR) than those with PEA. The addition of PE-MDI and PE-PMDJ decreased the water uptake rate of the composites while PEA increased this rate. The superior compatibilization effects of PE-MDI and PE-PMDI were attributed to the formation of covalent bonding between isocyanate and wood. This covalent bonding was demonstrated by the FTIR spectra of the wood residues after a p-xylene extraction. Both PMDI and N-vinylformamide grafted polypropylene (VFPP) were effective compatibilizers for increasing both the strength and stiffness of the resulting wood-PP (polypropylene) composites. The combination of PMDI and VFPP further increased the MOR and the modulus of elasticity (MOE) of the resulting wood-PP composites. This new PMDI-VFPP compatibilizer system was comparable to maleic anhydride-grafted polypropylene (MAPP) in terms of enhancing the strength and stiffness of the wood-PP composites. This PMDI-VFPP compatibilizer system also greatly reduced the water sorption of the resulting wood-PP composites.
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file details ZhangCheng2005.pdf 2017-08-14 Pubblico Scaricare