Modification of Interfacial Interaction with Trialkoxyfunctional Silane Compounds in Polypropylene-CaCO3 Composites [antikvár]

INTRODUCTION Beside polyethylene and PVC, the third commodity polymer produced and applied in large quantities is polypropylene (PP). The wide range of application of this polymer can be explained by its advantageous properties such as good toughness, relative high stiffness and high melting temperature (160 °C). However, the ever increasing requirements of the market cannot be always met by the neat polymer, thus its modification is unavoidable. Originally cheap fillers were applied to reduce the price of the composite compared to that of the unmodified polymer. As a result of modification, however, in many cases the composite has shown better properties than the neat polymer itself. Fillers increase the stiffness and dimensional stability of the composites reducing its shrinkage and improving surface properties at the same time. Talc, CaCOa, mica, wollastonite, glass-beads, wood fiber and wood male all are used as fillers in significant quantities. Glass fiber modified PP competes with engineering thermoplastics like polyamide, polybutylene-therephtalate, polyoxymethylene in many fields. However, glass fibers are used in much smaller quantities, than talc and CaCOa and its application will not reach the level of these fillers in the future either. The application of CaC03 shows the highest growth rate at the moment, thus considerable attention is focused on the development of its PP composites. CaCOs is considered to be an inactive filler due to its nearly spherical shape and to the lack of active -OH sites on its surface. The reactivity of PP is also low since its carbon chain is apolar, it does not contain reactive groups. When CaCOs is introduced into a PP matrix, the tensile properties of the composite usually become poorer than to those of the neat PP. Mechanical properties cannot be improved by the surface treatment of the filler, because of the inactivity of the two components. Nevertheless, a great number of compounds such as silanes, titanates, non-ionic tensides together with elastomers, stearic acid, ethyleneoxyde oligomers etc. have been experimented as coupling agents, but an enhancement of strength has been seldom achieved. In the few cases when an improvement was observed the published data could be hardly interpreted and the mechanism of increased component interaction was not known. The primary goal of our work was the invesfigation of the effect of trialkoxy functional silane coupling agents on the overall mechanical properties of PP/CaC03 composites. This thesis can be divided into three major parts. The first describes the synthesis of new silane compounds, the chapters in the second part focus on the mechanical properties of the composites including tensile and fracture characteristics, while the third section attempts to throw light on the mechanism of interaction between the components of the system studied.