Thermal stability and ageing properties of PP–PE film modulated by nano-silica particles: comparison between dry and moist particles

In this work, we studied the effects of water on the nano-silica surface upon cast films. The cast films were fabricated using a copolymer (polypropylene–polyethylene). Three different nano-silica particles were incorporated within the copolymer: an uncoated particle and two particles coated with different coupling agents (γ-methacryloxypropyl-trimethoxy silane and dimethoxydiphenil silane). The water effect was elucidated using two processes: (a) the nanomaterial was incorporated into the copolymer as it was received and (b) drying the nanoparticles previously of the incorporation into the copolymer. After the melt mixing, the films were fabricated with the same process conditions. The morphological, thermal, photo-oxidative, and mechanical properties of the cast film were investigated. It was shown that water has two main effects on the copolymer properties; the water restrains the incorporation of the nano-silica in the matrix of the copolymer and inhibits the performance of the coupling agent as a result the nanocomposites with moist particles increased the crystallization temperature in 6 °C. However, the water on the nano-silica´s surface delayed thermal oxidation in 49 °C. Also, the mechanical properties did not reduce significantly with the presence of the water on the surface of nano-silica. The difference of strain rupture was 12.2% which was into the range of the standard deviation.