Tailoring Thermoplastic Olefin Elastomers for Automotive Applications through Intensive Mixing

Use of thermoplastic olefin elastomers (TPO) is expected to enjoy a 12% annual growth worldwide through 1996. The majority of growth is in au tomotive applications such as bumper fascia, claddings, exterior panels, airbag covers and instrument panels, etc. This healthy forecast is fueled by the overall cost/performance, the wide range of properties available, the ease of processing and the recyclability of this class of material. The current TPO business is dominated by compounded grades which offer: freedom in formulation to meet specific customer needs, good balance of physical properties, minimal dimen sional change during processing, and flexibility to incorporate colors and other additives for tailored applications. In compounding, the dispersion and distribution of polymer phases as well as fillers and additives can be controlled through mixing. This article discusses the methodology involved in studying the effect of mixing on the performance of TPO formulations with different filler levels in a laboratory scale intensive batch mixer. Variables studied are mix time and batch size. Properties ana lyzed include heat elongation, tear strength, mold shrinkage, melt flow rate, density and cold temperature impact. The behavior of these compounds is graphically illustrated using a statistical software package. The results, in gen eral, suggest an optimal mix time of around three minutes for most of the