Cellulose nanofibril‐reinforced polypropylene composites for material extrusion: Rheological properties

Abstract

Polypropylene (PP) is not typically utilized in 3D printing material extrusion because PP shrinks and warps during the printing process. Cellulose nanofibrils (CNF) have the potential to make PP 3D printer processable and also enhance mechanical properties of PP printed parts. The rheological behavior of CNF-PP composites during material extrusion requires study because it is different from injection molding and compression molding processes. This study revealed the effects of CNF contents (3 and 10 wt%) and maleic anhydride polypropylene (MAPP) coupling agent on the rheological properties of CNF-PP composites. Morphological analysis showed that CNF agglomerated during spray drying and a spherical structure was formed. Rheological tests showed that the elastic modulus, complex viscosity, viscosity, and transient flow shear stress of PP were increased by the addition of 10 wt% CNF, while the creep strain of PP was reduced. The damping factor and stress relaxation time remained the same when 10 wt% CNF was added to the PP. Incorporation of MAPP into the CNF-PP composites impacted the rheological properties of the CNF-PP composites. Flexural strength and modulus of PP were improved by 5.9% and 26.8% by adding 10 wt% CNF compared to the control. POLYM. ENG. SCI., 58:793-801, 2018.

Spray-Dried Cellulose Nanofibril-Reinforced Polypropylene Composites for Extrusion-Based Additive Manufacturing: Nonisothermal Crystallization Kinetics and Thermal Expansion

“…A coarse fiber is a better heterogeneous nucleation agent. Based on a previous study, SDCNF is mostly a spherical particle with a smooth surface [14,15]. This explains the weak nucleation ability of SDCNF for iPP and makes the SDCNF a suitable additive for iPP targeting EAM processing.…”

“…More masterbatch manufacturing details are available elsewhere [15]. Raw materials were oven-dried for 2 h at 105 • C. SDCNF and iPP were hand-mixed using a fiber content of 30 wt % and metered into a co-rotating twin-screw extruder (C. W. Brabender Instruments, South Hackensack, NJ, USA) for compounding.…”

“…However, the dispersion of individual CNF was not achieved because the shear forces during compounding did not break down the SDCNF agglomerates [15]. The space among SDCNF in iPP/SDCNF3% is large.…”

“…After drying, the SDCNF exhibits a circle-equivalent diameter of approximately 10 µm. Moreover, the majority of SDCNF particles exhibit a spherical structure with a small aspect ratio and smooth surface [14,15]. Those morphological properties can diminish the nucleation ability of CNF.…”

“…So far, how SDCNF affects the nonisothermal crystallization kinetics and thermal expansion of iPP has not been studied. This experiment was primarily designed to analyze the effect of SDCNF content and MAPP on the nonisothermal crystallization kinetics of iPP at four cooling rates (5,10,15,20 • C/min). The cooling rates were chosen based on the previous analysis of the crystallization temperature during 3D printing as shown in Figure 1.…”