Continuous microcellular foaming of polyvinyl chloride and compatibilization of polyvinyl chloride and polylactide composites

This dissertation focuses on overcoming existing limitations of WPCs which prevent them from realizing their full market potential. These limitations include: (i) lack of a continuous extrusion process for microcellular foaming of polyvinyl chloride (PVC) and its composites using supercritical fluids to reduce the high density of the WPCs, (ii) need for an efficient coupling agent for WPCs to overcome the poor compatibility between wood and plastic, and (iii) unproven use of wood as a filler for the biopolymer polylactide (PLA) to make "green" composites. These limitations were addressed through experimentation to develop a continuous extrusion process for microcellular foaming, and through surface modification of wood flour using natural coupling agents.; The effects of wood flour, acrylic modifier and plasticizer content on the rheological properties of PVC based WPCs were studied using an extrusion capillary rheometer and a two-level factorial design. Wood flour content and acrylic modifier content were the major factors affecting the die swell ratio. Addition of plasticizer decreased the true viscosity of unfilled and filled PVC, irrespective of the acrylic modifier content. However, the addition of acrylic modifier significantly increased the viscosity of unfilled PVC but decreased the composite viscosity.; Results of the rheological study were used to set baseline conditions for the continuous extrusion foaming of PVC WPCs using supercritical CO 2. Effects of material composition and processing conditions on the morphology of foamed samples were investigated. Foamed samples were produced using various material compositions and processing conditions, but steady-state conditions could not be obtained for PVC. Thus the relationships could not be determined.; Incompatibility between wood flour and PVC was the focus of another study. The natural polymers chitin and chitosan were used as novel coupling agents to improve interfacial adhesion between the polymer matrix and wood fiber. Results indicated that addition of chitin and chitosan significantly increased the flexural properties and storage modulus of PVC WPCs, compared to composites without coupling agent. Significant improvements were attained with 0.5 wt. % chitosan and with 6.67 wt. % chitin.; Based on the efficiency of chitosan as a coupling agent for PVC based WPCs, a biodegradable composite using polylactide (PLA) and chitosan was developed. Wood flour (0--40 wt. %) was evaluated as a filler for PLA composites and its effect on mechanical, thermal and chemical properties was studied with and without chitosan (0--10 wt. %). Addition of wood flour significantly increased the flexural and storage moduli of PLA-wood flour composites, but had no effect on glass transition temperature (Tg). Chitosan had no significant effect on any of the properties of the composites studied.; Development of an efficient and effective coupling agent for PVC wood composite is a significant development which will increase performance while reducing cost. Wood filled PLA composites can further expand WPCs into applications such as packaging and automotive. Results from these studies have broadened the current knowledge base for WPC products and will be useful in the continued expansion of wood composites technology into a variety of industries.