Fibres from different structural parts of the coconut palm tree (Cocos nucifera, linn.) have been examined for properties such as size, density, electrical resistivity, ultimate fracture mode, microfibrillar angle as well as cellulose and lignin contents of these fibres have been determined. The observed properties have been related to the internal structure and chemical composition of the fibres. Some potential uses of these fibres have been I isted .tensile strength, initial modulus and percentage elongation. The stress-strain diagrams, --

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Thermally aged Nomex fibres manifest several residual effects viz. reduction in X-ray crystallinity, weight loss and deterioration in tensile characteristics. Surface damages in the form of longitudinal openings, holes, material deposits etc have also been observed. Based on the data from thermally exposed fibres, the time needed for states of zero tensile strength and modulus have been predicted.

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The structural changes which accompany decomposition of Kevlar 49 fibres at T = 500°C and 550°C, respectively, have been elucidated. At both these temperatures, cumulative thermal exposures of specific durations, teem(T), are required to result in decomposition. The conspicuous features which characterize isothermal decomposition of the fibres are: (i) progressive reduction and an eventual total loss in fibre crystallinity, (ii) progressive loss in weight, (iii) introduction of surface damages, (iv) introduction of hollowness, and (v) deterioration in tensile proptrties.

The residual effects of thermal aging on Twaron fibers have been studied using X-ray diffraction, weight analysis, scanning electron microscopy and tensile testing. X-ray data from isothermally aged fibers indicate the introduction of changes at the level of the crystal lattice, which include reduction in crystallinity, variations in 20 values, half width and azimuthal spread of reflections. Isothermal aging also introduces weight loss. Examination of the surface of fibers has shown that damages in the form of holes, materials deposits, etc., are introduced by isothermal aging. These data on Twaron further show that the thermally induced effects are controlled by two parameters: temperature T and cumulative exposure time to T, i.e. tcum(T). Among the tensile properties, the tensile strength is found to be more sensitive to thermal aging than modulus. In addition to the structural studies on the thermal aging behavior of Twaron, a one-to-one comparison has also been attempted between the tensile behavior of Twaron and Kevlar 49 fibers, which are also made up of the same polymer.

The residual effects of thermal aging of Kevlar 49 fibers in the temperature range 150-450′C have been analyzed. Thermal aging introduces crystallographic as well as macro-structural changes. Weight losses and deterioration in tensile properties were also observed. The order in which the deterioration in crystallinity, weight and tensile strength occur has been identified. Master curves for predicting the time needed for 50% deterioration at various temperatures and the corresponding activation energy have been estimated. The role of the parameter, tcum( T), the cumulative exposure to any temperature T, on thermally induced effects has been unambiguously established. In particular, the influence of the T- tcum( T) effect on crystallographic parameters has been observed for the first time.

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