Bioplastic Development, Characterisation, and Optimization of Fused Filament Fabrication Parameters

Abstract

Additive manufacturing, commonly known as 3D printing, is a rapidly expanding technology that has the potential to support a circular and sustainable economy. This technology supports a wide variety of raw materials and offers design flexibility, expanding its use in prototype and custom part production. One of the most common additive manufacturing technologies is Fused Filament Fabrication (FFF), which utilizes thermoplastic polymers as the raw material. Thermoplastic polymers commonly used in FFF include polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), polyamide (PA), polycarbonate (PC), and Nylon 12. Despite its popularity, high-density polyethylene has not been thoroughly studied in fused filament fabrication due to problems with warping and significant thermal shrinkage of printed parts after solidifying. It has been suggested that adding organic fillers will lessen these difficulties. The use of organic fillers in polymers results in biocomposites that have improved thermal properties and potential for biodegradation. However, printability, low-layer agglomeration, and reduced mechanical properties are some of the challenges that have to be overcome during FFF. Determining the best combination of printing parameters can significantly improve the printability of these biocomposites. In this study, rice husk waste was used as an organic filler in recycled high-density polyethylene to develop a biofilament for FFF. High-density polyethylene was chosen as the polymer since, though it is highly recyclable, it has not qualified as a potential raw material in FFF. This is due to challenges such as high thermal shrinkage that causes it to warp during printing. Organic fillers in polymers have been recommended as a means of reducing warpage of HDPE and enhancing printing directionality. Through the design of an experiment, various filler-to-polymer combinations were tested with the addition of a compatibilizer to enhance the filler’s miscibility in the polymer matrix. Using the ball mill, the rice husks were ground into powder with particles smaller than 75 μm. The biofilament's highest composition included 35 wt.% rice husk filler, 35 wt.% recycled high-density polyethylene, and 30 wt.% compatibilizer, indicating an improvement in rice husk filler content compared to earlier research. Digimat 2024.1 was used as the platform for material modeling and printing simulation to identify printing issues, such as warpage and residual stresses. Through a coupled simulation, a finite element model was analyzed to predict part performance. The model was validated experimentally using the standard tensile test specimen. The Taguchi Grey Relational Analysis (TGRA) was used to optimize the printing process due to its efficiency and robustness for multi-response experiments. Printability was successful up to the biofilament whose composition comprised 30 wt.% rice husk filler, 40 wt.% recycled high-density polyethylene, and 30 wt.% compatibilizer. This biofilament's mechanical properties included a tensile strength of 8.53 MPa with a standard deviation of 1.32 MPa, a tensile modulus of 128.56 MPa with a standard deviation of 13 MPa, and a maximum tensile strain of 6.6% with a standard deviation of 0.03%. Experimental validation of warpage yielded a maximum error margin of 5.43%, while validation of residual stresses resulted in a maximum error margin of 5.56%. The incorporation of rice husk filler, a natural reinforcement, into recycled high-density polyethylene improved the crystallinity of the biofilaments, which helped reduce shrinkage and warpage in printed parts. Biodegradability was also enhanced up to 10 % in a period of 24 weeks. The outcome of this study will provide valuable information for the manufacture of functional parts, such as biomedical devices, including microfluidic substrates, from biocomposite materials using FFF.