BACKGROUND
The purpose of this study was to reduce the delivered fiber cost to wood-plastic composite (WPC) manufacturers. The low density and higher volume of the wood flour make longer distance transportation disadvantageous in terms of cost. While the production cost of wood pellets is slightly higher than wood flour, a higher weight of pellets can be transported via truck trailer due to a bulk density roughly three and half times higher than wood flour. This study explored the utilization of a compacted wood flour, i.e., wood pellets to manufacture WPCs and compare performance characteristics against WPCs manufactured using conventional wood flour. Then, the physical and mechanical properties of the resulting composite products were determined.
MATERIAL PREPARATION
Northern White Cedar (Thuja occidentalis), Eastern White Pine (Pinus strobus), Eastern Spruce-Balsam Fir (Picea rubens-Abies balsamea) and Red Maple (Acer rubrum) mill residues (planar shavings, sawdust, and small chips) were obtained from local sawmills in Maine. A Bliss Eliminator Hammermill with 0.5 mm screens was used to reduce the mill residues, then classified using a Gilson screen shaker at 20, 40, 60, 80, and 100 mesh sizes. The wood flour for each species collected at the 40-mesh screening (425-850 micron) was used as the feedstock for both wood pellet and control WPC sample production.
PRODUCTION
Pellet Manufacture
A Lawson Mills plate-type Pellet Mill (LM72A) was used for the production of wood pellets. For each species, pellets were manufactured using the 40-mesh size fraction, with the moisture content of the wood flour maintained between 10 and 15% to allow for optimal pellet formation.
WPC Manufacture
For each wood species, 40-mesh wood flour and wood pellets manufactured from the same flour were oven dried and used as the fiber source. The wood pellets were ground back to a powder using a Brabender knife grinder. Four formulations (Figure 1) for each wood species were manufactured using polypropylene (PP) sourced from ExxonMobil. In Formulations #3 and #4, maleic anhydride polypropylene (MAPP) from SI Group, Inc. was used as a compatibilizer. Each of the 16 formulations were compounded using a 20 mm Brabender twin-screw extruder. The compounded filaments were cooled, knife milled, then injection molded into standardized testing coupons using a Mini-Jector Model #55E injection molder
