Sorption Isotherm of Southern Yellow Pine-High Density Polyethylene Composites.

Feihong Liu,Qinglin Wu,Guangping Han,Wanli Cheng

doi:10.3390/ma8010368

Feihong Liu, Qinglin Wu + Show 2 more

Open Access

https://doi.org/10.3390/ma8010368

Copy DOI

Abstract

Temperature and relative humidity (RH) are two major external factors, which affect equilibrium moisture content (EMC) of wood-plastic composites (WPCs). In this study, the effect of different durability treatments on sorption and desorption isotherms of southern yellow pine (SYP)-high density polyethylene (HDPE) composites was investigated. All samples were equilibriumed at 20 °C and various RHs including 16%, 33%, 45%, 66%, 75%, 85%, 93%, and100%. EMCs obtained from desorption and absorption for different WPC samples were compared with Nelson’s sorption isotherm model predictions using the same temperature and humidity conditions. The results indicated that the amount of moisture absorbed increased with the increases in RH at 20 °C. All samples showed sorption hysteresis at a fixed RH. Small difference between EMC data of WPC samples containing different amount of ultraviolet (UV) stabilizers were observed. Similar results were observed among the samples containing different amount of zinc borate (ZB). The experimental data of EMCs at various RHs fit to the Nelson’s sorption isotherm model well. The Nelson’s model can be used to predicate EMCs of WPCs under different RH environmental conditions.

Highlights

Wood-plastic composites (WPCs) are extensively used for decking, railing, and fencing [1]
Data achieved through the absorption process were lower than those obtained from desorption at the same relative humidity (RH), indicating sorption hysteresis. This result was similar to the previous studies on wood-based materials including oriented straw board (OSB), middle density fiberboard (MDF), and solid wood [18]
The routes of water molecules diffusion into WPCs are the gaps and the interfaces between wood fibers and plastic matrix resulted from poor interface compatibility and the micro-cracks formed in the process of compounding first

Summary

Introduction

Wood-plastic composites (WPCs) are extensively used for decking, railing, and fencing [1]. After exposure of WPCs to varying environmental conditions, especially UV radiation from sunlight, the composites will undergo photo-degradation leading to undesirable effects, including a loss in mechanical properties and surface quality, i.e., surface micro-cracking and color change [2,3,4]. The adverse effects of UV radiation on WPCs can be delayed or minimized with the use of UV stabilizers such as UV absorbers (UVA) and hindered amine light stabilizers (HALS) (free-radical scavengers). Other studies showed that addition of HALS or UVA or both photo-stabilizers delayed and minimized the impacts of natural weathering on HDPE-wood fiber (WF) composites [8]. The stabilized HDPE-WF composite with UVA showed the best protection in the loss of flexural modulus among the test samples [8]

Objectives

Results

Conclusion