Influence of inorganic filler on properties of polymeric composites of HEMA–TEOS system

Abstract

The influence of the composition of 2-hydroxyethyl methacrylate (НEMA) – tetraethoxysilane (TEOS) system on the thermal properties and structural organization of hybrid organic-inorganic composites obtained by the sol-gel method was studied. Formation of composites occurred in the process of concurrent compatible polymerization of mixtures of liquid organic and inorganic components. During the proceeding of sol-gel transformations in organic polymer medium, the inorganic structure is formed in situ in polymer matrix. Complex thermogravimetric and differential thermal analysis of the obtained composites was carried out. The thermograms of the thermal destruction of the samples were obtained, according to which the temperature intervals, the mass loss of the samples and the thermal effects of each stage were determined. The temperature-conversion parameters of thermal destruction of composites were calculated. Based on direct experimental data, taking into account the features of the destruction process, the value of the reduced temperature of composite destruction for the evaluation of their thermal stability was calculated. The dependence of the thermal stability of the material on the amount of inorganic filler in the polymer matrix has been shown. It was found that there is an optimal ratio of HEMA: TEOS, equal to 95:5 % vol., at which the composite is characterized by high thermal resistance. Such character of the inorganic phase influence on the properties of composites of the HEMA–TEOS system can be explained by the so-called “effect of small additions”. That is, with the introduction of minor amounts of the filler, its particles are distributed in a polymer matrix in micro regions with lower density – defective and weakly cross-linked zones. This leads to a decrease in the defectiveness of the polymer matrix due to the “additional ordering” of the defective zones, their compaction and, as a result, to the improving of the thermal properties of the composite. Further increase of the concentration of the inorganic phase in the system leads to a microheterogenization of the structure of the composites and deterioration of their properties. Keywords: organo-inorganic composite, sol-gel system, thermogravimetry, differential thermal analysis, thermal stability.