Effect of Reactive PLA on the Mechanical Properties of Hand Layup 3D Printed Hybrid Hemp Composites

This study investigated the mechanical and thermal properties of polylactic acid (PLA) composites produced using a hand layup 3D printing process, highlighting advancements in the manufacturing of hybrid hemp fibre PLA composites. Alkali-treated and corn starch-coated hemp fibres were used as reinforcing materials. Polyethylene glycol (PEG200) provided the necessary flexibility, whereas benzoyl peroxide (BPO) initiated the grafting of maleic anhydride (MA) to PLA. Fourier transform infrared (FTIR) spectroscopy revealed increased intensities of the C=C peak and a reduction in O–H peaks, indicating successful interactions among BPO, MA, hemp and PEG200. Thermogravimetric analysis (TGA) showed that PLA/hemp grafted with MA and modified with PEG200 (mPLA-g-MA/hemp) is thermally stable up to 287°C, exhibiting a 235% increase in the degree of crystallization, as observed on differential scanning calorimetry (DSC). Tensile tests indicate that the short hemp composite achieved the highest improvement in elastic modulus, with an increase of approximately 11%. However, this was accompanied by notable reductions in tensile strength and impact strength, by about 24% and 21%, respectively. In contrast, the mPLA-g-MA/hemp composite demonstrates a balanced enhancement of both toughness and stiffness, showing improvements of about 15% and 4%, respectively, when compared with neat PLA. Additionally, the PLA hybrid composites exhibit a 38% increase in tensile strength, outperforming the 11% enhancement observed in the PLA/hemp composites. These findings highlight the potential applications of hybrid composite materials in the automotive sector for interior components, though they may not be suitable for direct use in load-bearing parts.