Mechanical properties of recycled polyester carpet composites for structural applications

A substantial number of plastic products, especially single-use products such as polyethylene terephthalate (PET) or high-density polyethylene (HDPE) bottles and durable goods like carpets, are predominantly discarded into landfills, resulting in massive volumes of municipal solid waste. While the recycling of PET and HDPE from packaging has been extensively studied, the resulting recycled products are often more expensive and of comparatively lower quality than virgin materials, limiting their industrial and consumer adoption. Carpet recycling primarily involves recovering fibers through shredding and backing separation, which is expensive and results in minimal incentive to recycle. This work explores alternative applications for recycled materials by fabricating composites using compression molding with intact post-consumer PET carpets (cPET) with recycled PET (rPET) and recycled HDPE (rHDPE) resin. Process optimization was conducted for rPET/cPET composites, while preliminary studies examined rHDPE/cPET systems. The work evaluated the mechanical and functional properties of the developed composites to identify potential for structural applications. The rPET/cPET composites resulted in superior mechanical properties, including flexural strength and modulus, creep, impact resistance, and interlaminar shear strength, surpassing structural application requirements and cPET-alone performance. The addition of compatibilizer improved toughness and interlaminar shear strength, showing improved interfacial adhesion. An improvement in interfacial adhesion was confirmed through SEM fractography. Flammability and weathering tests validated their durability under adverse conditions. Acoustic testing showed their potential use as noise barriers. To summarize, rPET/cPET composites offer a potential solution to divert post-consumer PET carpets from landfills. Conversely, rHDPE/cPET composites require further process optimization to achieve comparable performance. However, additional research is required to improve the manufacturing process of rHDPE/cPET composites. Future studies should focus on advanced manufacturing techniques for composite systems and perform life cycle analysis and cost estimation to assess their feasibility for commercial applications.