Structural analysis of polyamide-6,6 reinforced with glass fibre by the use of Fourier transform infra-red spectroscopy with photoacoustic detection and differential scanning calorimetry

Abstract

The effect of fibre reinforcement, industrial processing and subsequent annealing on the structure of polyamide-6,6 was analysed in this paper from the correlation between photoacoustic Fourier transform infra-red (PA FTi.r.) spectroscopic and differential scanning calorimetry (d.s.c.) thermal measurements. Using the band situated at 1650 cm −1 as an internal reference band, no spectral change was detected in the bands at 936 and 1146 cm −1. Furthermore, the bands centred at 1335 and 1224 cm −1, which are related to chain-folding, appear in the unannealed composite, whereas in the matrix these were only detected at the highest annealing temperatures. It seems that the manufacturing process used for the composite determines its microstructure and the subsequent annealing does not produce further conformational changes. On the other hand, the composite satisfies a two-phase conformational model, different from that of the matrix, which can be related to the strong interactions between the polymer and the glass fibres with surface treatment. In the thermal analysis, in contrast to the spectroscopic results, substantial changes in the endothermic melting peaks and in the degree of crystallinity can be noted. Up to an annealing temperature of ∼ 120–150°C, the composite crystallinity is constant and lower than the matrix crystallinity, but above this temperature the value rises and tends towards the values of the matrix. Furthermore, there was a more homogeneous crystalline distribution detected in the unannealed matrix, along with a greater size and perfection of the crystals than that seen in those of the unannealed composite. We suggest that the d.s.c. variation in the crystallinity can be attributed to an improvement in the fibre-matrix interface, in which the crystals of the interfacial phase change to more perfect ones as a result of the annealing treatment.