Abstract
Environmentally sound composites reinforced with natural fibers or particles interest many researchers and engineers due to their great potential to substitute the traditional composites reinforced with glass fibers. However, the sensitivity of natural fiber-reinforced composites to water has limited their applications. In this paper, wood powder-reinforced polypropylene composites (WPCs) with various wood content were prepared and subjected to water absorption tests to study the water absorption procedure and the effect of water absorbed in the specimens on the mechanical properties. Water soaking tests were carried out by immersion of composite specimens in a container of distilled water maintained at three different temperatures, 23, 60 and 80 °C. The results showed that the moisture absorption content was related to wood powder percentage and they had a positive relationship. The transfer process of water molecules in the sample was found to follow the Fickian model and the diffusion constant increased with elevated water temperature. In addition, tensile and bending tests of both dry and wet composite samples were conducted and the results indicated that water absorbed in composite specimens degraded their mechanical properties. The tensile strength and modulus of the composites reinforced with 15, 30, 45 wt % wood powder decreased by 5.79%, 17.2%, 32.06% and 25.31%, 33.6%, 47.3% respectively, compared with their corresponding dry specimens. The flexural strength and modulus of the composite samples exhibited a similar result. Furthermore, dynamic mechanical analysis (DMA) also confirmed that the detrimental effect of water molecules on the composite specimens.
Highlights
Bio-sourced materials, the most abundant resources on the planet, are emerging as reinforcing materials for composites, which have attracted much scientific and industrial attention owing to their attractive advantages such as renewability, biodegradability, sustainability, low density, low cost and better mechanical properties [1,2,3,4,5]
It shows that wood powder plays a profound effect on the water absorption behavior of samples, that is, the moisture content increases with the increase of wood powder content, which is consistent with the studies of other researchers [7,15,17,30]
As a kind of lignocellulose materials, can absorb more moisture compared with pure polypropylene due to the existence of the polar group-hydroxyl, the composites filled with wood powder exhibit better water uptake than pure polypropylene, and the water content increases with wood powder content increasing because the increase of wood powder content means that the existence of a great number of hydroxyl groups
Summary
Bio-sourced materials, the most abundant resources on the planet, are emerging as reinforcing materials for composites, which have attracted much scientific and industrial attention owing to their attractive advantages such as renewability, biodegradability, sustainability, low density, low cost and better mechanical properties [1,2,3,4,5]. The secondary utilization of wood resources can be realized, and environmental problems can be avoided Another important component, polypropylene (PP), as a kind of common engineering thermoplastic, can be recycled after service time, for example, PP fibers used in textile or other industries can be recycled into granulation and reused in polymer matrix composite materials. The PP-based composites filled with wood powder can be recycled after service time, which is superior to traditional high-performance or glass fiber composite materials in this respect Whether it is wood powder or polypropylene, they absorb moisture when in a humid environment or when immersed in water [7]. Study how the water molecules degraded the mechanical properties of the composites
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