Recyclability Assessment of Lignocellulosic Fiber Composites: Reprocessing of Giant Reed/HDPE Composites by Compression Molding

Abstract

This study verified the possibility of recycling polyethylene-based composites with up to 40% of lignocellulosic reinforcement after 5 cycles of compression molding, milling and extrusion. Two forms of filler from the same plant species, Arundo donax L., were studied, namely, fibers and shredded aerial parts of the plant. The properties of composites were assessed at each processing step, finding that the reprocessing affects to more extend the particulate filler than the fibrous one; the lower particle size resulted in lowered tensile properties. However, despite the fiber size reduction, as aspect ratio is not drastically diminished, the better dispersion of the fibers in the matrix counteracts the negative effects of their shorter size. Impact properties are improved with the recycling, possibly due to the increased homogeneity of the samples, which is also translated into a higher density (and lower porosity). The thermomechanical stability of the fiber composites is higher than for the shredded ones. The reduction in size of the fillers is reflected in the lowered viscosity obtained after the reprocessing. The fibers continue stiffening the matrix after the 5 reprocessing cycles, where the milled material acts more as a filler, reducing tensile properties, although showing a good flexural behavior.