Dynamic mechanical properties of oil palm fibre (OPF)-linear low density polyethylene (LLDPE) biocomposites and study of fibre–matrix interactions

The dynamic mechanical properties of oil palm fibre (OPF) linear low density polyethylene (LLDPE) composites in terms of storage modulus (E′), loss modulus (E″) and damping parameter (tan δ) in a temperature range of −150 °C to 100 °C is presented in this paper. The effect of fibre content, fibre size and fibre surface treatment on the dynamic mechanical properties was studied. The storage modulus and damping parameters were predicted using different equations. The storage modulus and loss modulus increased with increase in fibre content and also upon alkali treatment on fibres. The glass transition temperature of pure LLDPE was −145 °C, which increased to −128 °C for composites with 40% fibre content. Fibre loading in composite and alkali treatment on fibre increased the loss modulus peak. Single tan δ peaks were observed for all the composite samples tested. The tan δ peak values decreased upon fibre addition whereas alkali treatment increased the tan δ peak at all frequencies indicating better impact properties after alkali treatment. The interfacial strength indicator values (B) decreased upon alkali treatment and higher B values were observed for composites containing fibre size range 75–177 μ followed by 425–840 μ and 177–425 μ indicating decreased order of bond strength. Activation energy was found to be high for composites with 425–840 μ size fraction (80.7 kJ mol−1) followed by 177–425 μ size fraction (72.6 kJ mol−1) and 75–177 μ size fraction (68.1 kJ mol−1). Storage modulus (E′) and damping parameters predicted using different equations were in agreement with experimental values.

► Alkali treatment of fibre and fibre loading of polyethylene composites studied.
► Alkali increased storage and loss modulus; loading increased storage modulus.
► Fibre loading and alkali treatment increased the loss modulus peak.
► Fibre addition decreased the tan δ peak, but values increased upon alkali treatment.
► Alkali decreased interfacial strength, and fibre always increased activation energy.