2.1. Materials

The waste polyethylene (WPE) from the dumptank in the reactor (HIP Petrohemija A.D., Pančevo, Serbia) with a processing temperature of 195 °C to 220 °C, a density of 0.936–0.949 g/cm³, and a melt flow index of 0.27–0.32 g/10 min was used as a polymer. The used WPE is a copolymer of ethylene and hexene, intended for the production of blown films. The exceptional workability and tenacity of the melt enable the extraction of thin films. Mechanically ground wood, i.e., paper pulp (Metso Paper Oy, Gothenburg, Sweden), was used as wood fiber reinforcement in the WPE matrix. The wood reinforcement was dried in an oven for 24 h at 90 °C to a constant mass in order to eliminate the initial moisture content. The cross-linking bonding agent—Fusabond^® W PC-576D, DuPont, Mississauga, ON, Canada, designated as FB—is an anhydride-modified ethylene co-polymer capable of increasing density and flexural modulus of elasticity in WPCs [56,69]. As the metal layer, a steel metal wire grid (Mesh 12, wire diameter of 0.2 mm) was used.

The mechanism of the chemical reactions is presented in Figure 1. Polyethylene, one of the most consumed thermoplastic polymers worldwide, is grafted with maleic anhydride [70]. Also, maleic anhydride is joined with cellulose from wood flour [71]. In this way, the used FB compatibilizer affects the creation of strong bonds between the polymer matrix and the filler, which results in excellent physical and mechanical properties of the WPC. Detailed steps of the mechanism of chemical reactions are reported elsewhere [72].

Chemical coupling mechanisms in maleated wood–plastic composites.