Highly Filled, Durable, and Sustainable Wood-Plastic Composites from Recycled Thermoplastics

Abstract

The increasing concern for environmental sustainability and the accumulation of solid waste (e.g. single-use plastics) has led to an increased interest in the utilization of renewable feedstocks and recycling of plastics to produce sustainable products, such as wood plastic composites (WPCs). As such, the first two stages of this thesis investigated reprocessing polypropylene (PP) as well as maleated PP (MAPP) to simulate recycling as a potential matrix for highly filled WPCs (70 wt.% wood). The extent of PP and MAPP recycling was analyzed using high temperature gel permeation chromatography (H-GPC), light scattering, nuclear magnetic resonance (NMR), rheology, microscopy, and other physical/mechanical properties. Successive thermo-mechanical reprocessing caused noticeable chain scission, shown by the melt viscosity and the slight reduction in the average molecular weight. Furthermore, other properties like tensile strength and modulus did not change significantly with respect to recycling. The repeated reprocessing allowed to incorporate high loading of wood fiber to produce highly filled WPC. This indicates that the recycling of PP could be of great importance to reduce waste accumulation and produce highly filled WPCs. As well, the recycling of MAPP could be an important and effective strategy to reduce virgin and petroleum-based MAPP manufacturing while revitalized mechanical properties for WPCs. The last stage of this project involved the chemical modification of WF with dodecenylsuccinic anhydride (DDSA), in order to enhance the hydrophobicity of the wood, as well as the recycling and maleation of poly(lactic) acid (PLA). The successful modification of the WF was evaluated using X-ray photoelectron (XPS) and Fourier transform infrared (FTIR) spectroscopy as well as solvent dispersibility analysis. Recycling of PLA had a profound effect on PLA’s crystallinity and modulus as other properties were not affected. The recycling of PLA had a considerable effect on PLA’s crystallinity and modulus even though other properties were not affected. The addition of WF more significantly affected PLA’s crystallinity; all the while, also increasing the storage and loss modulus of the fabricated biocomposites. Moreover, the modified wood flour (mWF) WPCs had greatly enhanced water repellent capabilities. Lastly, the maleation of the recycled PLA allowed better interaction with the WF, which further aided in controlling the dimensional stability of the WPCs even as tensile properties were not affected. Overall, this study aimed to develop highly-filled, more durable, and recycled WPC for both the construction and packaging industries and the success of this project has many benefits to the emerging circular economy and closed loop recycling.