engleski

The role of interface in nanoparticulate filled polymer systems

Nanofiller particles with diameter under 100 nm might have, due to their large specific surface area, a great influence to polymer matrix in composites and particulate filled blends. Interphase is in that case the three-dimensional area that has strong influence on the properties of the material as a whole. The conditions of the effective adhesion at the interface between nanofiller and polymer matrix might be predicted by measuring the surface energy of particular components of the selected nanoparticulate filled polymer systems. In composites it is the minimal interfacial energy with good wetting and high work of adhesion. In blends with two polymer matrices in the case of effective adhesion it seems that nanofillers should be thermodynamically forced to stay at the interface. Filler surface functionalization by various surface pre-treatments in order to improve compatibility might cause increased interactions between polymer matrix and filler. In both cases of key importance is preparation of nanosystems in which nanofillers are equally dispersed, in order to obtain homogeneous morphology without usual agglomerates. Otherwise we are dealing with classical micro-composites. In this work the influence of various nanofillers on the structure and properties of segmented polyurethanes (PU) were investigated. In order to improve interactions at the filler-matrix interface, fillers with different particle size and filler modified with silane coupling agent were used. The effective coupling agents should lower the filler surface energy, improve the wetting and increase the interactions with polymer matrix. The surface free energy of fillers and polymer matrix using contact angle measurements with different testing liquids were determined, and parameters of adhesion at the interface were calculated. Distribution of the filler in the polymer matrix was analyzed using scanning electron microscopy (SEM), and changes in morphology using optical polarization microscopy. The influence of filler addition on mechanical properties was determined using tensile measurement. Thermal and structural changes in PU composites were determined by using differential scanning calorimetry (DSC). The comparison with conditions of effective adhesion in PU composites and blends ware made. Results show that the addition of filler influences on spherulite morphology of the PU polymer matrix, and decreases crystallinity depending on the filler aggregation. The results proved that the higher work of adhesion, lower interfacial free energy and positive coefficient of wetting and homogeneous morphology of evenly distributed nanoparticles is of key importance for the significant improvements and/or new properties.

polyurethan composites; filler surface modification

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