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Abstract
The purpose of this research was to investigate the use of cellulose nanofibers (CNF) compounded into an impact modified polypropylene (IMPP) matrix. A IMPP was used because it shrinks less than a PP homopolymer during FLM processing. An assessment of material properties from fused layer modeling (FLM), an additive manufacturing (AM) method, and injection molding (IM) was conducted. Results showed that material property measurements in neat PP were statistically similar between IM and FLM for density, strain at yield and flexural stiffness. Additionally, PP plus the coupling agent maleic anhydride (MA) showed statistically similar results in comparison of IM and FLM for density and strain at yield. Nano-composite sample groups for FLM processing underperformed in all mechanical properties when compared to IM processing. The groups with CNF content of 15% wt.% and coupling agent performed 8% better that the neat PP for tensile strength, 33% better tensile stiffness, 9% improved flexural strength and 20% higher flexural stiffness for IM processing. In IM and FLM, the neat and PP+MA groups exhibited the highest Izod impact strength values at 125 and 106 J/m, respectively. Scanning electron microscopy (SEM) imaging shows dispersion of CNF particles, composite porosity (micro and macro), voids produced by FLM filament processing and the deposition inaccuracy observed in FLM test coupon processing. The samples containing CNF fibers exhibited over/under filling defects (necking), dimensional accuracy errors attributed to polymer shrinkage, coupled with the dimensional inaccuracy observed in FLM samples. The use of PP in FLM processing shows potential with the neat PP results obtained from this study.