Mechanical performance and long-term indoor stability of polyhydroxyalkanoate (PHA)-based wood plastic composites (WPCs) modified by non-reactive additives

Abstract

This study aims to understand the material properties and long-term indoor stability of a biocomposite based on pine wood flour and poly(3-hydroxybutyrate-co-3hydroxyvalerate) (PHBV) modified by a nucleating agent, boron nitride (BN), and an inorganic filler, talc, and to develop knowledge of the linkage between the microscalestructure and mechanical properties. Both BN, at a loading of 1 wt% and talc, at 5 wt%, had a nucleating effect on polymer crystallisation, with BN being more effective as evidenced by Avrami kinetic analysis. The addition of 5 and 10 wt% of talc enhanced the tensile strength of the PHBV/wood flour (50/50 wt%) composite from 22.3 ± 1.3 2 MPa (mean ± 95% confidence interval) to 24.3 ± 0.6 MPa and 24.7 ± 0.9 MPa respectively. The tensile modulus was also improved from 5.6 ± 0.6 GPa to 6.9 ± 0.4 GPa and 8.1 ± 0.7 GPa respectively. The micron-sized talc may fill voids within the composite matrix and/or act as an alternate filler, altering the deformation mechanism.However, the level of improvement in modulus was reduced after 1 year of conditioned ageing under a controlled environment (20 o C, 50% humidity). It is proposed that the combined effects of the swelling of wood through moisture uptake, the shrinkage of PHBV through secondary crystallisation, and the localised stress around talc particles led to weakened talc-PHBV interfaces. KeywordsPolyhydroxyalkanoate (PHA); Wood flour; Wood polymer composites; Talc; Mechanical properties; Indoor stability 1. Highlights  BN and talc increases the rate of crystallisation of the wood-PHBV composites.  Wood-PHA composites are mechanical stable at ambient temperature for at least 1 year.  Talc offers complementary space-filling morphology and improves composite stiffness. The level of stiffness improvement from talc is reduced after 1-year of ageing. A mechanism for the weakened talc-PHBV interface upon ageing is proposed.

Wood-PHA Composites: Mapping Opportunities

“…During extrusion processing with wood fibres, a higher MFI can lead to a better impregnation of the fibres (wetting) and reduce the amount of mixing and shear intensity required for a homogenous fibre distribution. Initial developments on Wood-PHA composites [20,21,22,23] indicate that properties similar to commercially available PP and PE based WPCs are readily achievable. Table 1 summarises the mechanical properties of Wood-PHA composites in early development, compared to commercially available PE- and PP-based WPC products, showing that the tensile strength and tensile moduli were similar.…”

Mechanical and physical stability of polyhydroxyalkanoate (PHA)-based wood plastic composites (WPCs) under natural weathering

“…The pre-mixed formulations were then fed to a co-rotating twin screw extruder (Eurolab 16 (ThermoScientific), diameter: 16 mm, L/D ratio: 40:1). The optimised extrusion parameters were determined based on a preliminary study [19]…”

The effects of UV degradation on the physical, thermal, and morphological properties of industrial nylon 66 conveyor belt fabrics

“…When sensitive thermoplastic polymers, such as polypropylene, polyethylene, and poly (methyl methacrylate) and aramid fibers, absorb UV radiation, chains degradation, and loss of strength occur at the critical points of the chain structure. Some researchers have evaluated the change in the chemical and mechanical properties of the polymers by UV degradation [9][10][11][12][13][14].…”