Semester

Summer

Date of Graduation

2007

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Chemical and Biomedical Engineering

Committee Chair

Rakesh K Gupta

Abstract

The increase in modulus of polypropylene (PP) upon addition of montmorillonite (MMT) makes PP-based polymer nanocomposites (PNCs) ideal matrix materials for wood/plastic composites (WPCs) for decking, railing, roofing and siding applications, among others. In this work, the influence of maleated PP (that is used both as a coupling agent for WPCs and as a compatibilizer for the PNC) on increasing the modulus of extruded and injection molded PP-based WPCs is investigated. Also examined are the effects of the sequence of compounding steps and the use of different processing conditions. The improvement in mechanical properties is examined by varying the amount of wood flour (WF), montmorillonite (MMT) and maleated PP in the WPCs and is explained with the help of available composite modeling theories. It is also related to the composite morphology with the help of scanning and transmission electron micrographs. The results indicate that by proper compounding, adding 2wt% to 4wt% of nanoclay in the matrix of the WPCs could significantly increase the modulus of WPCs without sacrificing the strength of WPCs. This increase in modulus can be explained with the help of a modified rule of mixtures.;The rate of water absorption of PP-based wood plastic composites was measured to determine if the rate of water absorption of WPCs is affected by the processing variables such as screw speed, residence time and screw geometry. The results indicate that a longer residence time and high screw speed both help reduce the rate of water absorption of WPCs by 10 to 40% without affecting in mechanical properties. The lower rate of water absorption seems to correlate with smaller particle sizes and a reduction in WPC density.;When wood was first compounded with the polymer and clay was added in the second step, it was found that WPC modulus was increased without significant reduction in strength. Furthermore, even in the presence of clay, the rate of water absorption could be kept at the same level as in the absence of clay when proper compounding procedures were used.

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