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Effects of water immersion‐freeze‐thaw cycling on the properties of wood‐polypropylene composites containing pigments

Svetlana Butylina (Mechanical Engineering, Lappeenranta University of Technology, Lappeenranta, Finland)
Ossi Martikka (Mechanical Engineering, Lappeenranta University of Technology, Lappeenranta, Finland)
Timo Kärki (Mechanical Engineering, Lappeenranta University of Technology, Lappeenranta, Finland)

Pigment & Resin Technology

ISSN: 0369-9420

Article publication date: 8 November 2011

Abstract

Purpose

The purpose of this paper is to study the effects of water immersion‐freeze‐thaw treatment on the physical properties, flexural strength (FS) and morphology of wood‐polypropylene composites containing pigments.

Design/methodology/approach

Wood‐polypropylene composites containing brown, green and grey pigments were compounded in a conical twin‐screw extruder. A composite manufactured without any pigment addition was used as a reference. The amount of pelletized wood, polypropylene and coupling agent (MAPP) was kept constant. The moisture content, thickness swelling (TS), FS and surface colour of the composites were measured before and after water immersion‐freeze‐thaw cycling. Scanning electron microscopy (SEM) was used to study the morphology of the composites.

Findings

FS and dimensional stability were reduced after exposure to water immersion‐freeze‐thaw cycling for all composites. The surface properties (colour and roughness) of the composites also changed after exposure to water immersion‐freeze‐thaw cycling. The degree of change depended on the presence of pigment and the type of polypropylene (neat or recycled), however.

Research limitations/implications

This study is a part of an ongoing study on weathering of wood‐polymer composites (WPC) containing different additives. The results of this study were obtained from accelerated laboratory experiments.

Practical implications

Inorganic pigments are widely used as additives in plastics, because they have an excellent UV absorption, good IR‐reflective properties and heat stability. The research revealed that metal‐containing pigments had an effect on degradation in quality of wood‐polypropylene composites exposed to water immersion‐freeze‐thaw cyclic treatment. The addition of metal‐containing pigments to composite formulation resulted in a higher susceptibility of wood‐polypropylene composites to water absorption, and as a consequence to a higher drop of FS compared to composites made without pigment. The polymer matrix plays an important role in the protection of WPC against weathering.

Originality/value

This paper will help in understanding possible problems in the durability of wood‐polypropylene composites compounded with metal‐based pigments when they are exposed to water immersion‐freeze‐thaw cyclic treatment.

Keywords

Citation

Butylina, S., Martikka, O. and Kärki, T. (2011), "Effects of water immersion‐freeze‐thaw cycling on the properties of wood‐polypropylene composites containing pigments", Pigment & Resin Technology, Vol. 40 No. 6, pp. 386-392. https://doi.org/10.1108/03699421111180536

Publisher

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Emerald Group Publishing Limited

Copyright © 2011, Emerald Group Publishing Limited