The influence of glass transition temperature and interphase on the dynamic properties of unidirectional fibrous composites

Abstract

Dynamic mechanical analysis (DMA) is a useful method which completes the results obtained from several traditional thermal analysis techniques such as Differential Scanning Calorimetry (DSC), thermogravimetric analysis (TGA), and thermal elastic analysis (TMA).  Dynamic constants such as storage and loss modulus depend on temperature and supply valuable information about interfacial bonding between filler and polymeric matrix of a fibrous composite material. In the meanwhile, the glass transition temperature is defined as the point at which the specific volume versus temperature curve changes abruptly slope, marking the region between rubbery polymer and glassy polymer nature. Thus, the behavior of unidirectional fibrous composites was investigated at this region. Further, an examination of the glass transition temperature, which evidently constitutes an upper limit for the structurally important glassy region through the loss factor, was performed by its consideration as a combination of glass transition temperature of matrix and interphase. In the current article, the authors focus on epoxy unidirectional fibrous composites reinforced with long fibers and examine the above mentioned   properties at the glass transition region. In this context, a concentric three – phase cylindrical model was taken into account. In particular, the overall material was assumed to consist of three distinct phases with the intermediate phase developed between matrix and fibers, named interphase, to have variable properties depending on those of main phases and the mode of preparation of the composite. The theoretical results of the present work constitute an extension of a previous work by the authors, on the dynamic properties of unidirectional short fiber composites and indeed may be considered as basic ones.