Polyolefins are used in the automotive industry in various components from fairly simple console bins to complex instrument panels. Since scrap is unavoidable in manufacturing process, the use of regrind is important to maximize resin usage and to avoid landfill. In addition to evaluating the physical property changes at different levels of regrind, the application specific requirements are important. The effect of different levels of regrind on weld strength is one of the important factors that need to be considered in some automotive applications. This study evaluated the weld strength of polyolefins using a two-factor (meltdown and pressure), two-level design of experiments. Unfilled polypropylene copolymer samples at 0%, 25%, 50%, 75% and 100% regrind levels were welded to a TPO in a T-Joint geometry to simulate production situations. The highest weld strength was seen in TPO welded to itself and was used as the baseline strength. With the TPO to polypropylene welds, there was a 13% decrease in weld strength with the 0% regrind whereas at the 100% regrind level, the decrease in weld strength was only 5.6%. It was determined that the weld strength of the polypropylene material to itself was 36-44% lower than that of the baseline strength. Aside from the 75% regrind samples, the highest joint strengths were derived from the 1 mm meltdown and 1 MPa pressure settings. Thermal analysis of the propylene samples indicates that the material at the weld is more amorphous than that of the bulk.
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