Abstract
Talc is a popular filler for the fabrication of plastic composites. The presence of talc helps improve mechanical, thermal, and flame resistance properties of the composite. In this work, we report the influence of a talc-filled plastic shell layer on thermal stability and fire flammability of the core-shell structured wood high-density polyethylene (HDPE) composites manufactured through coextrusion. The result showed that morphological analysis of the char layer after combustion confirmed the formation of a continuous surface char layer with talc addition in the composites, helping block fire penetration and enhance overall fire resistance of the composites. The shell thickness averaged at 1.0±0.2 mm, which represents a fair thick shell over a 10 mm thick WPC core layer. The surface of regular wood-filled HDPE showed large cracks, allowing more rapid fire penetration and reducing its fire resistance. At 800°C, average residual weight for all composite was 21.5±13.8%, most of which was attributed to the inorganic nonvolatile talc components. With the increase of talc level, THR values of coextruded WPC decreased from 302.47 MJ/m2 (5 wt% of talc) to 262.96 kW/m2 (50 wt% of talc). When talc content in the shell layer was less than 25 wt%, the flame resistance properties were slightly enhanced compared with the composites containing unmodified HDPE shells. When talc content in the shell exceeded 25 wt%, the composite’s total heat release and its rate substantially decreased.
Highlights
Coextruded core-shell structured wood-plastic composites (WPCs) as an emerging type of green structural materials have been developed to enhance performance of wood/natural fiber-reinforced polymer composites [1,2,3]
A shell layer composed of properly filled plastics can help reduce flammability and thermal degradation properties of the composite compared with coextruded WPC with unfilled shell and/or regular WPC without a core-shell structure
Studies have been conducted on the development of a stable shell layer over the coextruded WPCs by blending high-density polyethylene (HDPE) with additives using combination of various minerals with wood [8] and precipitated calcium carbonate (PCC) [9] in the shell layer
Summary
Coextruded core-shell structured wood-plastic composites (WPCs) as an emerging type of green structural materials have been developed to enhance performance of wood/natural fiber-reinforced polymer composites [1,2,3]. The combined use of wood fiber and plastic through core-shell structure design can help reduce overall composite costs and improve stiffness and biological resistance. They are advantageous in terms of melt processing and weather resistance. The presence of a plastic shell (with large thermal expansion and low modulus) over a WPC core in the coextruded WPCs can, negatively affect overall fire flammability and thermal stability of the composite [4]. Studies have been conducted on the development of a stable shell layer over the coextruded WPCs by blending high-density polyethylene (HDPE) with additives (such as compatibilizers, photostabilizers, and nanosized TiO2) using combination of various minerals with wood [8] and precipitated calcium carbonate (PCC) [9] in the shell layer. More cost-effective materials and design are still needed as shell layers for the coextruded WPC
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