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

Abstract

Isotactic polypropylene (iPP) is a versatile polymer. It accounts for the second-largest polymer consumption worldwide. However, iPP is difficult to 3D print via extrusion-based processing. This is attributable to its rapid crystallization rate. In this study, spray-dried cellulose nanofibrils (SDCNF) and maleic anhydride polypropylene (MAPP) were investigated to reveal their effects on the nonisothermal crystallization kinetics and thermal expansion of iPP. SDCNF at 3 wt % and 30 wt % accelerated the crystallization rate of iPP, while SDCNF at 10 wt % retarded the crystallization rate by restricting crystal growth and moderately increasing the nucleation density of iPP. Additionally, adding MAPP into iPP/SDCNF composites accelerated the crystallization rate of iPP. The effective activation energy of iPP increased when more than 10 wt % SDCNF was added. Scanning electron microscopy and polarized light microscopy results indicated that high SDCNF content led to a reduced gap size among SDCNF, which hindered the iPP crystal growth. The coefficient of thermal expansion of iPP/SDCNF10% was 11.7% lower than the neat iPP. In summary, SDCNF, at 10 wt %, can be used to reduce the warping of iPP during extrusion-based additive manufacturing.

Interference of Biodegradable Plastics in the Polypropylene Recycling Process

“…In general, the presence of biodegradable polymers in the PP matrix caused a decrease of the crystallinity, as the enthalpy values of crystallization and melting decreased. The decrease of crystallinity may be due to the fact that biodegradable polymers in the blend make difficult the pack of PP chains, since the presence of biodegradable polymers acts as impurities, and thus, they would reduce the free volume of PP [ 48 , 49 ].…”

Material extrusion‐based additive manufacturing of polypropylene: A review on how to improve dimensional inaccuracy and warpage

“…Simultaneously, the coefficient of expansion was decreased by 11.7%, which in turn reduced the shrinkage tendency. Although the real warpage of 3D‐printed specimens was not analyzed by the authors and it is influenced by far more factors than discussed by Wang et al ., a trend toward a reduced part warpage due to the decreased crystallization rate and coefficient of expansion can be expected.…”

“…Wang et al . did a prestudy on the warpage behavior of PP compounds, in which the complex crystallization behavior of PP was assumed to be responsible for the warpage susceptibility.…”

“…For semicrystalline thermoplastics, filaments with a low degree of crystallinity and a slow crystallization rate are preferred, as the material's tendency to shrink and warp is therefore extensively reduced . Simultaneously, the thermal expansion is diminished, resulting in a dimensionally more accurate 3D‐printed part …”

Polypropylene Filled With Glass Spheres in Extrusion‐Based Additive Manufacturing: Effect of Filler Size and Printing Chamber Temperature

“…Polypropylene (PP), for example, is a promising material for FFF due to its high impact strength, chemical resistance, moisture stability, and low cost . However, little research has been conducted on the main drawback connected with the 3D printing of PP, which is the fact that PP parts are prone to dimensional inaccuracies, in particular to warpage . These are facilitated by the introduction of orientations during printing and the material's high crystallinity .…”