Utilization of Recycled Material Sources for Wood-Polypropylene Composites: Effect on Internal Composite Structure, Particle Characteristics and Physico-Mechanical Properties

Abstract

In this study, various wood material sources were used for the manufacture of wood-polymer composites (WPC). The materials were categorised as virgin wood particles (VWP), reprocessed WPC particles (RWP) and recycled thermoset composite particles (RCP) and derived from two virgin wood sources, three-layer particleboards, medium-density fibreboards (MDF) boards, or two different wood/polypropylene composites. All produced wood-polypropylene compounds contained 60% wood material and were manufactured using a co-rotating extruder. Malleated polypropylene was used as a coupling agent. Specimens were injection moulded and subsequently tested for their physico-mechanical properties. To characterize particles before and after processing, dynamic image analysis (DIA) measurement were performed. Additionally, X-ray micro-computed tomography (XµCT) was used to characterize the internal structure of the composites and to verify the obtained particle’s characteristics. It was found that length and aspect ratio of particles were remarkably different before and after processing (loss in length of 15–70% and aspect ratio of 10–40%). Moreover, there were notably differences between the particle sources (RCP retained the highest length and aspect ratio values, followed by VWP and RWP). The results suggest that increased aspect ratios can indeed significantly improve mechanical properties (up to 300% increase in impact bending strength and 75% increase in tensile strength, comparing WPC based either on virgin spruce or MDF material). This phenomenon is suggested to be partially superimposed by improved dispersion of particles, which is expected due to lower variance and increased mechanical properties of RWP composites. However, no notable alterations were observed for composite density. Reprocessed WPC and, particularly, RCP material have proved to be an appealing raw material substitute for the manufacturing of wood–polymer composites.

Surface Activation of Polylactic Acid-Based Wood-Plastic Composite by Atmospheric Pressure Plasma Treatment

“…Studies by Bütün et al and Krause et al showed that recovered fibers from fiberboards are a suitable material source for the WPC production. Utilizing fibers from medium-density fiberboards revealed beneficial effects on the produced WPC’s physicomechanical properties [ 4 , 5 ]. However, the change of the physicomechanical properties of a particle or fiber-containing polymer is not only affected by its source, but also significantly depending on the particle size and filling level [ 6 ].…”

The Effect of Recycling on Wood-Fiber Thermoplastic Composites

“…Wood-polymer composites (WPCs) are a group of materials mainly consisting of a thermoplastic polymer as a matrix, wood as reinforcement, and a minor amount of additives such as lubricants and coupling agent [ 5 ]. Due to the increase in consumer ecological awareness, the WPCs have gained more attention as an alternative to traditional polymeric materials [ 6 , 7 ]. Recycled plastics have been used for the production of WPCs since the 1990s with an expressed increase in the last few years [ 8 ].…”

“…Recycled plastics have been used for the production of WPCs since the 1990s with an expressed increase in the last few years [ 8 ]. However, nationwide WPCs recycling systems are still missing [ 7 ]. By understanding the properties of the recycled WPCs, the re-processing of WPCs can be adjusted and the relationship between physical and mechanical properties can be used to establish a new circular-economy approach for sustainability.…”

Properties of polypropylene composites filled with microsilica waste

“…In case of polypropylene, which is one of the most commonly used thermoplastic polymers in the industry, the most popular fillers are chalk and talc. There are also known examples of using other fillers which constitute industry waste, such as phosphogyp sum [19], eggshells [20], wood flour [21,22] or nutshells [23]. By introducing various types of powder fillers into a polypropylene matrix, the stiffness and hardness can be significantly increased.…”