Dynamic mechanical analysis of randomly oriented intimately mixed short banana/sisal hybrid fibre reinforced polyester composites

The dynamic and static mechanical properties of randomly oriented intimately mixed short banana/sisal hybrid fibre reinforced polyester composites were determined. Dynamic properties such as the storage modulus (E'), damping behaviour (tan delta) and static mechanical properties such as tensile, flexural and impact properties were investigated as a function of total fibre volume fraction and the relative volume fraction of the two fibres. Keeping the relative volume fraction of banana and sisal (1:1), the volume fraction of the fibre was optimised. The storage modulus was found to increase with fibre volume fraction above glass transition temperature (T-g) of the matrix and maximum value was obtained at a volume fraction (V-f) of 0.40. The tan delta peak height was minimum and peak width was maximum at 0.40 V-f. Tensile modulus and flexural strength were found to be the highest at 0.40 volume fraction, which indicates effective stress transfer between the fibre and matrix. A positive shift in T-g of polyester matrix at 0.40 V-f also indicates better fibre/matrix interaction. Keeping the total fibre volume fraction, 0.40 V-f, hybrid composites having different volume ratios of the fibres and unhybridised composites were prepared and analysed. Sisal/polyester composite showed maximum damping behaviour and highest impact strength as compared to banana/polyester as well as hybrid composites. However, maximum stress transfer between the fibre and matrix was obtained in composites having volume ratio of banana and sisal as 3:1,which has lowest tan delta value and highest E' value at T-g. The tensile strength and flexural modulus were also the maximum and impact strength was the minimum at this volume ratio. Fractographic evaluations carried out under scanning electron microscope (SEM) confirm the quantitative characterisation obtained from static and dynamic mechanical analysis. The Arrhenius relationship has been used to calculate the activation energy of the glass transition of the polyester. The highest activation energy was found in hybrid composite with volume ratio of banana and sisal as 3:1. A master curve was constructed based on time-temperature superposition principle. Finally, the experimental results were compared with theoretical predictions. (c) 2004 Elsevier Ltd. All rights reserved.