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Viscoelastic and thermal behaviour of flax preforms reinforced epoxy composites

This study investigates the thermal and viscoelastic properties of flax preform reinforced epoxy composites. Plain woven flax fabric and 1 × 1 weft rib knitted structures were used as reinforcements and flax preforms reinforced epoxy composites were produced using hand lay-up method. Thermogravimetric analysis (TGA) indicates a decrease in thermal stability of the matrix polymer with the incorporation of flax woven and knitted preforms. The dynamic mechanical analysis revealed a higher storage modulus for woven preform reinforced composite compared to knitted preform reinforced composites. The storage modulus was found to decrease with temperature in all cases. Loss modulus showed shifts in the (Tg) compared to virgin epoxy, with the addition of flax preforms as reinforcing phase, which indicate that preforms plays an important role with respect to Tg. Single tan δ peaks were observed for all the composite samples tested. The tan δ peak height was maximum for virgin epoxy matrix, indicating that there is a large degree of mobility, thus good damping behaviours. However, lower peaks were observed for both woven and knitted preform reinforced composites. With respect to the viscoelastic properties the rigidity and endurance of the fibres are highly affected by thermal treatment at temperatures above 70℃ and up to 100℃.