Thermal Expansion Behavior of Nonoriented Polypropylene/Clay Composites

Linear thermal expansion coefficient (LTEC) was measured for compression molding samples of polypropylene (PP)/clay composites with clay loading of 0 to 7 wt%. Composites were prepared by internal batch mixer and specimens were prepared by compression molding. These processing methods are not anticipated to have a preference for orientation; therefore effect of anisotropy was minimal. The LTEC was measured along three different faces of the compression molding sheets, parallel to compression direction S1 and perpendicular to compression directions S2 and S3. The LTEC for neat PP measured by current research,  mm/mm/°C, was not found to be altered by direction of the measurements. Similar behavior was observed with composites having very moderate clay content, that is, 5 wt%. An interesting finding by current study was that incorporating clay particles into the PP matrix led to better shrinkage or contraction behavior of the samples prepared by compression molding.