Extrudable melamine resin for wood plastic composites

Lee-Wen Chen

Wood plastic composites (WPCs) are usually comprised of wood particulates and thermoplastic resins, i.e. high density polyethylene (HDPE), polyvinylchloride (PVC), or polypropylene (PP). In this research project, a novel melamine resin was used as a matrix for extruding WPCs. This modified melamine adhesive (Hipe®esin) exhibits thermoplastic behavior at temperatures between 100 to130 ℃, and crosslinks at temperatures above 150℃ making it possible to utilize in an extrusion system. Mechanical properties, thermal, and creep resistance of a polymer could be increased by crosslinking reaction. In order to prevent curing inside the extrusion system, understanding the crosslinking behavior of the melamine resin is crucial to improve processing and mechanical performance. Our research examined the crosslinking behavior and the thermal properties of the melamine resin. We also evaluated the processing and the mechanical performance of the wood-melamine-resin composites. Utilizing differential scanning calorimetry (DSC) techniques, kinetics of the crosslinking reaction were found and the activation energy was also determined. In addition, the torque rheometry results indicated a low processing temperature between 70 to 100 ℃. The effect of wood content was also found to dramatically influence the crosslinking kinetics and the processing of the wood-filled melamine resins. A higher wood content caused a quicker curing and a lower curing temperature. This study also evaluated the extrusion parameters including: barrel/die temperature profile and post-extrusion curing. Reducing the processing temperature from 120 to 70℃ increased the strength and modulus of composites. Additionally, 6 hours of post-extrusion curing was found to raise the bending strength of composites. On the other hand, there was a negligible affect on the flexural modulus. Water uptake of the composites was slow because of the high resistance to water attack of melamine resins. Composites that post-cured in the condition room at the room temperature presented better moisture resistance and lowest diffusion coefficients. However, samples after 6 hours post-cured at 175℃ showed the best dimensional stability.

Extrudable melamine resin for wood plastic composites

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