Christopher, Shahrul Izwani, et al. “Study on Optimization of Extrusion Process for Polypropylene Ultra High Molecular Weight Polyethylene As Fused Filament Fabrication (FFF) 3D Printer Material”. Progress in Engineering Application and Technology, vol. 7, no. 1, May 2026, pp. 490-7, https://publisher.uthm.edu.my/periodicals/index.php/peat/article/view/22880.