Influence of free volume on the mechanical properties of epoxy based composites: A correlation study

Abstract

AbstractEpoxy resins need toughening for enhancement of their usage in various applications. The commonly used rubber for toughening epoxies is silicones. In the present study, the effect of Amine containing silicones (ACS) as modifiers and hollow micro sphere such as cenospheres as fillers on DGEBA epoxy resin is studied. To understand the microstructure and its influence on the mechanical properties, free volume measurements have been carried out using Positron Annihilation Lifetime spectroscopy (PALS). The positron results indicate that the mechanical properties like tensile strength and modulus have a significant dependence on free volume. Attempts to correlate the available free volume with chain mobility and mechanical properties have led to the the general belief that any process, which reduces free volume, increases tensile strength and similar change in tensile modulus. From positron data it was observed that both free volume hole size, Vf and fractional free volume, Fv decreases as the cenospheres wt% increased up to 30 wt% and a slight increase thereafter in the siliconized epoxy composite. The tensile strength of cenospheres filled composite shows moderate increase of about 17.5% while an opposite trend is observed in fractional free volume which is on the expected lines. However tensile modulus exhibits behaviour different from tensile strength. This may be possibly due to low density of the fillers and the also the characteristics of epoxies as far as mechanical properties are concerned. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)