Semester

Fall

Date of Graduation

2008

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 goal of this study was to recycle acrylonitrile-butadiene-styrene (ABS) into wood plastic composites (WPCs). One major concern in this application is flammability. Thus, halogenated and non-halogenated flame retardants (FRs) were investigated. FRs were mixed with ABS using an internal mixer or an extruder, and samples were molded using a hot press or an injection molding machine. Mechanical properties were assessed by flexural tests, and flammability was measured by UL-94 type tests and limiting oxygen index. Thermogravimetric analysis (TGA) and FTIR were also performed in order to understand the decomposition behavior of ABS-based WPCs.;Mechanical results showed that adding wood flour and FRs to ABS increased its flexural modulus; however, the addition of FRs into ABS-based WPCs reduced the flexural strength. All FRs could help to reach V-0 rating on the UL-94 test, but use of ammonium polyphosphate (AP423) required the least amount (20wt%) of FR when the wood content was fixed at 30wt%. Also, synergism existed between halogenated and non-halogenated FRs.;From TGA curves, the shift of the first peak of Rmax (maximum weight change rate) of ABS-based WPCs to a lower temperature with addition of non-halogenated FRs indicated that a dehydration reaction took place between wood and FRs. This was further verified by FTIR study. Common fillers, such as talc or calcium carbonate, likely to be present in recycled ABS were found to negatively affect the fire retardancy of ABS-based WPCs. However, one could add a coupling agent to recover the fire performance.;It was found that the coupling agent, after decomposition, formed a cross-linked network with non-halogenated FRs. Polybutadiene (PB) could further improve the fire resistance of ABS-based WPCs; however, high loading levels led to a poor dispersion, resulting in negative effects. Further, the use of triphenyl phosphate (TPP) shows synergism with AP423 in fire retardancy, and it also enhances the color of ABS-based WPCs. Another way to get improved color is to use gentler extrusion processing. By comparing ABS-based WPCs to polyolefin-based WPCs at the same level of fire performance, it was found that ABS-based WPCs had better performance in mechanical properties, indicating that ABS-based WPCs could have wider applications than ever polyolefin-based WPCs.;By minimizing the amount of added wood, one can flame retard ABS. Here, a halogen-free flame retardant system was developed for ABS using cellulose as a charring material and APP as a catalyst. The use of these additives permits compounding and injection molding of ABS at low temperatures. The resulting materials have an attractive balance of mechanical properties and can achieve a V-0 or V-1 rating on UL-94 type tests.

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