The influence of accelerated weathering on the mechanical and physical properties of wood-plastic composites

H Kallakas,T Poltimäe,T-M Süld,A Krumme,J Kers

doi:10.3176/proc.2015.1s.05

Abstract

This research concentrates on the effect of moisture absorption and UV radiation on the mechanical and physical properties of wood-plastic composites (WPC). The goal is also to evaluate the importance of wood flour fraction size on the mechanical properties of WPC and their influence on the accelerated weathering results. Wood flour reinforced composites with three different fractions of wood flour made from birch (Betula) chips were prepared. Additionally, Bleached-Chemi-Thermo- Mechanical aspen (Populus tremula) pulp (Aspen BCTMP) was used. Thermoplastics (LLDPE-g-MAH, PP) were used to prepare composites. Wood flour and BCTMP surface were treated with two different coupling agents: 3-aminopropyltriethoxysilane (APTES) and polyvinyalcohol (PVA). The WPC specimens were prepared by injection molding. Accelerated weathering tests were carried out to evaluate the influence of weathering on the mechanical and physical properties of composites. Three-point bending test and Charpy impact test were used to test mechanical properties. The test results showed that using wood flour as a filler material in composites made the WPC material more rigid and brittle. Due to the water absorption and swelling of WPC, the flexural modulus (MOE) and strength decreased and impact strength increased by making the material weaker with increasing the deflection of the WPC. The UV radiation decreased the composites flexural strength and MOE, while impact strength was increased. After the accelerated weathering cycles, cracks and voids were found on the surface of the WPC materials. After the UV radiation treatment, also the WPC colour was lightened.

Highlights

This research concentrates on the effect of moisture absorption and UV radiation on the mechanical and physical properties of wood-plastic composites (WPC)
Due to the degradation of this thin surface layer, water absorption into the composites can occur through gaps and flaws at the interfaces between wood fibres and thermoplastic matrix resulting in the reduction of the mechanical properties of WPCs [4]
Increasing the wood flour fraction size decreased the flexural strength of WPCs slightly up to 8%

Summary

Introduction

This research concentrates on the effect of moisture absorption and UV radiation on the mechanical and physical properties of wood-plastic composites (WPC). H. Kallakas et al.: Accelerated weathering of wood-plastic composites strong bonding between wood fibers and thermoplastic polymers in order to avoid unwanted effects on the WPCs dimensional stability and mechanical properties [4]. Polyvinyl alcohol (PVA) has been used for wood fibre surface treatment due to the strong bonding with wood [7,8] This improves the adhesion and wetting between the polymer matrix and wood filler in the composites. Due to the degradation of this thin surface layer, water absorption into the composites can occur through gaps and flaws at the interfaces between wood fibres and thermoplastic matrix resulting in the reduction of the mechanical properties of WPCs [4]

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