Weight reduction: Wood versus mineral fillers in polypropylene

This paper compares various wood fillers to commercially available mineral and glass fillers in injection-molding-grade polypropylene. Although the data presented is previously reported, this paper places an emphasis the weight reduction afforded by wood fillers for packaging and transportation applications. Data for both homopolymer and high impact block copolymer is presented. Comparisons were made at both equal weight and approximately equal volume filler loadings. This distinction is important because the specific gravity of most minerals is around 2.7 to 2.8, and fiberglass is 2.5. Wood, when compressed to its maximum density by the melt pressures incurred during compounding and injection molding, has a specific gravity of approximately 1.3 to 1.4. Therefore, wood displaces roughly twice the volume of polymer as minerals at the same weight loadings. The same processing and test equipment was used throughout the study.