This paper reports on the effect of additives on the properties of injection moulded composites based on polypropylene (PP) and high density polyethylene (HOPE) filled with wood and cellulose flour. Three types of additives were studied: dispersion aids, elastomeric additives, and adhesion promoting agents. Some of the dispersion aids were found to improve the filler dispersion and the impact strength. The modulus remained relatively undected while the strength was lowered. The high molecular weight elastomeric additives increased the impact strength and ductility, while the stiffness was reduced. An adhesion promotor based on a maleic anhydride modified polypropylene was found to behave as a true coupling agent, i.e. the strength and ductility increased, the melt strength was improved, and also the hot water resistance was raised. The experimentally determined composite moduli are found to agree relatively well with theoretical predictions. The effect of processing on the shape and size of the filler particles is evaluated using automatic image analysis.
synopsisPronounced maxima in resistivity-temperature curves have been found at or above T, for a number of amorphous polymers (PS, PMMA, PVC) containing a small percentage of carbon black. The maxima appeared only after a certain period of storage at T < To or at heating rates substantially higher than those used in coding the samples prior to the measurement. For this reason, no maxima were observed during cooling. In crystalline polymers (PE, PP), maxima at T, appeared both on heating and cooling. Marked relaxaticn effects (time-dependent resistivity) were recorded in the To and T, regions. Good agreement was found between resistivity and thermal noise data.
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