Water absorption measurements on WPCs: Assessment of size and direction dependencies in order to design fast and accurate quality control tests. (August 2019)

• Record Type: Journal Article
• Authors: Faure, Florent; Perrot, Arnaud; Pimbert, Sylvie; Lecompte, Thibaut
• Is Part Of: Polymer testing. Volume 77(2019)
• Publication Date: 2019-08
• Subjects: Water aging methodology -- Wood flour -- Polyethylene -- Wood-plastic composites -- Water absorption -- Sample sizes -- Absorption kinetics -- Pseudo-fickian behavior; Polymers -- Testing -- Periodicals; Polymères -- Tests -- Périodiques; 620.1920287
• DOI: 10.1016/j.polymertesting.2019.105899
• Languages: English
• ISSNs: 0142-9418

Abstract

Abstract: Wood-plastic composites (WPCs) are water-sensitive materials. Standards describe water absorption protocols on composites to obtain results after a long period of aging. From an industrial point of view, it is necessary to obtain the same information (i.e. equilibrium water content and absorption kinetics) over a short time. In this paper, we propose a new immersion aging protocol based on cubes taken from a reference WPC. This new methodology was validated by varying several test parameters (temperature, sample size, etc.) and applying it to other WPCs. Cubic samples were found to diverge from a Fickian behavior after a certain time of aging because of swelling and cracking that creates another characteristic pore scale and an increase of diffusion coefficient. Compared to the same formulation of cubic samples, the plate samples usually used for water absorption didn't crack. Fick's law approximation was used to determine the diffusion coefficient on plate materials. The coefficients measured in the three directions of WPC decks and a 3D model enabled us to recalculate the apparent coefficient of cubic samples for short-term absorption. Comparison of diffusion coefficients for short and long-term absorption showed the water concentration dependence of composites. Long-term diffusion coefficients and swelling stress coefficients were used in the pseudo-Fickian model to predict the water absorption behavior for composites undergoing water concentration dependence. Highlights: Development of a new protocol that can provide accurate values of water absorption. Influence of several test parameters on water absorption on WPCs. Recommending a water absorption protocol for WPCs. The assessment of diffusion theories, adapted to the protocol. The evidence of water concentration dependence and cracking phenomena on water diffusion.