Structural Properties of PE-Based Wood–Plastic Composites Depending on the Share of Lignocellulosic Particles

Wood–plastic composites (WPCs) are an excellent example of materials that, thanks to the possibility of using recycled raw materials, directly fit into the circular economy. The properties and quality of composites depend largely on the appropriate selection and proportions of components. These studies included composites produced on the basis of an HDPE-recycled matrix filled with sawdust or bark particles in the amounts of 40%, 50%, and 60%. Their structural features were analyzed for the produced composites. It was shown that a smaller share of filler ensures its more even distribution in the matrix. In turn, the type of filler affects the crystallinity and thermal transformations of the composite. The use of bark as a filler provides more favorable structural parameters of WPCs.