Properties of High-Density Polyethylene-Polypropylene Wood Composites

Abstract

We investigated the effects of polymer blend variation on the physical, mechanical, and thermal properties of wood-polymer composites (WPC). We used high-density polyethylene (HDPE) and polypropylene (PP) and a combination of 80% PP, 20% HDPE, and 80% HDPE, 20% PP as polymer blends for WPC formulations to simulate recycled plastics. We used black spruce (Picea mariana Mill.) hammer milled fibers (75–250 μm) at 35 wt% as a filler for all the formulations. A two-step process was used for WPC manufacturing; pellet extrusion followed by test samples injection. Tensile and three bending tests characterized the WPC mechanical properties. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) characterized the WPCs’ thermal properties. Water absorption and contact angle measurements assessed the composite dimensional stability. Infrared spectroscopy (FTIR) and electron scanning microscopy (SEM) investigated the WPCs’ surface chemistry and microstructure. Mechanical properties and dimensional stability varied according to polymer composition, with better performance for WPC containing higher PP proportions. Thermal properties varied with the polymer composition in the WPC, with better thermal stability for the formulation containing higher HDPE proportions. Surface chemistry analysis did not reveal any chemical changes on the WPCs surface. Scanning electron microscopy analysis revealed distinct phases in all WPCs without evidence of interfacial adhesion.

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“…PET is the most common semi-crystalline thermoplastic polymer of the polyester family, known for valuable features such as easy processing capacity, low cost, lack of toxicity, high stiffness, excellent mechanical strength and chemical resistance [ 4 ]. Part of the polyethylene family, HDPE occupies second place in the most commonly used plastics list due to its good chemical resistance ability, along with high flexibility, weatherproof properties, good low temperature toughness and low cost [ 5 ]. PP, a partially crystalline and non-polar polymer that belongs to the polyolefins group, is located at the fifth place as one of the most durable types of plastic [ 6 , 7 ].…”