Recycled filtered contaminants from liquid-fed pyrolysis as novel building composite material

Liquid-fed pyrolysis allows the conversion of contaminated postconsumer plastic waste into valuable resources, removing contaminants through wax dissolution and filtration. One of the main challenges is currently represented by the management of its main byproduct, the contaminant-rich retentate from the filtration process. New circular economy strategies are needed to use this waste plastic-based composite as secondary raw materials. Despite the increasing trend in using plastic and plastic-waste composites for the building sector, there are currently limited applications of industrial recycling waste as engineering construction materials, e.g., from pyrolysis. This study evaluates the suitability of contaminant-rich retentate from liquid-fed pyrolysis of postconsumer multilayer packaging waste as novel composite materials for the building sector, taking advantage of its intrinsic composite nature. Thermogravimetric analysis was conducted to assess the composition of the retentate from filtration, a mixture of wax, polyethylene, polyethylene terephthalate, and aluminum. The compressive mechanical properties and densities were then evaluated on samples obtained through hot compression molding, using two batches to assess possible anisotropic behavior from the manufacturing process or the aluminum part orientation. The results indicate the suitability of the waste composite material for the building sector, reaching compression strengths (10–12 MPa) superior to construction bricks and brickworks (7 MPa), as well as 57 % lower density, 0.77 g/cm 3 . The ductile fracture behavior indicates its potential use for applications requiring failure prediction and safety constraints. This high strength-to-weight ratio composite represents a valuable alternative to virgin materials, showing potential for structural and aesthetic applications, including lightweight bricks, interior textured panels, decorative facades, and customized pavement tiles and slabs. Hot compression molding of pyrolysis waste composite paves the way for the real use of plastic-based composites from mixed and contaminated industrial waste in the building sector, contrasting resource depletion. • Byproducts from liquid-fed pyrolysis can be used as a new building composite material. • The compressive strength exceeds those of common building elements (∼10–12 MPa). • The ductile fracture behavior improves failure predictability in construction parts. • The composite is 57.3 % and 12.5 % lighter than clay bricks and lightweight bricks. • This high strength-to-weight ratio composite reduces the need for virgin materials.