Investigation of in-situ chemical cross-linking during fused filament fabrication process on parts shrinkage reduction and interlayer adhesion

The fast shrinkage nature and volume reduction after printing are the main problems whereby semi-crystalline polymers like polypropylene (PP) are not commonly used as a fused filament fabrication material. Finding a solution to shrinkage reduction, therefore, is of great importance. This work has formulated peroxide-coagent modified PP filament to suit the fused filament fabrication (FFF) process to reduce shrinkage through in-situ cross-linking. The peroxide-coagent composition was optimized through the melt-mixing study by evaluating the processing temperature and peroxide-coagent concentration. Experimental results were confirmed the in-situ bond formation during printing and the impact on printed samples' shrinkage and mechanical performance. Several printing parameters (printing temperature, infill ratio, layer height) were evaluated to obtain a 3D printed sample with less shrinkage. The sample printed at 245 °C with 0.2 mm layer height and 100% infill was found to have a higher gel content and improved welding between the adjacent layers, enhancing the mechanical property and reducing shrinkage on the printed part. The elevated bed and printing temperature helped keep the layer in a partially liquefied stage during printing, making pressure relaxation and progress in inter-layer adhesion. Generally, this work expands PP utilization in the FFF 3D printing process and provides insight into the cross-linking during 3D printing.