A recent study published in Polymer Composites evaluated the effectiveness of maleic anhydride-grafted poly(lactic acid) (MAH-g-PLA) as a compatibilizer in bio-sourced poly(lactic acid)/poly(butylene succinate) (PLA/PBS) biocomposites reinforced with hemp fiber (HF).
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Background
With increasing concerns over plastic pollution, biopolymers like PLA and PBS have gained significant attention as sustainable alternatives. PLA offers biodegradability and a reduced carbon footprint but suffers from brittleness and low thermal resistance.
PBS, a ductile semi-crystalline polyester, enhances PLA’s flexibility and crystallization rate when blended. However, further improvements in mechanical and thermal properties are necessary for advanced applications.
Incorporating natural fibers (NFs) into polymer blends is a promising strategy to enhance their performance. HF is one of the oldest and most commonly used fibers in polymer composites, second only to sisal. However, its hydrophilic nature poses challenges in biocomposites. Using MAH-g polymers can help improve interfacial interactions between NFs and polymer matrices.
Methods
Before processing, all raw materials were dried at 80 °C for 12 hours to remove moisture. The polymer blends were compounded using a twin-screw co-rotating extruder at 180 °C. A mini-injection molding machine was then used to shape the composites, transferring the melt from the extruder die into the mold under 8 bar pressure at room temperature.
A control PLA/PBS blend was prepared at an 80/20 ratio, based on literature data. Then, HF-reinforced polymer composites (NFRPCs) were produced by adding 5, 10, 20, and 30 wt% HF to the matrix. Based on the characterization results, NFRPCs with compatibilizers were synthesized by incorporating 1, 3, and 5 wt% MAH-g-PLA into the selected 20 wt% HF-containing composites.
Characterization techniques included Fourier-transform infrared (FTIR) spectroscopy for chemical analysis, field emission scanning electron microscopy (FESEM) for morphology examination, and differential scanning calorimetry (DSC) for thermal property assessment.
Thermal stability was analyzed using a thermogravimetric analyzer in a nitrogen environment from 25 to 600 °C. A dynamic mechanical analyzer (DMA) measured thermomechanical properties, while tensile tests evaluated tensile strength, Young’s modulus, and elongation.
Results and Discussion
FTIR analysis showed no major functional differences between uncompatibilized and compatibilized PLA/PBS/HF biocomposites. However, slight peak variations in the compatibilized composites suggested interactions between the –OH groups of HF and the epoxy groups of MAH-g-PLA.
Morphological analysis revealed weak adhesion between HF and the polymer matrix, leading to fiber pull-out, holes, and grooves. This poor interfacial bonding contributed to lower tensile strength and flexibility due to restricted polymer chain movement. Despite this, MAH-g-PLA significantly improved the tensile modulus.
DMA results indicated that HF enhanced the stiffness and energy storage capacity of PLA/PBS blends. Additionally, MAH-g-PLA increased the elastic modulus, though excessive compatibilizer led to a decline in modulus. Both HF and MAH-g-PLA improved thermal stability, slowing down thermal degradation. However, MAH-g-PLA was not an effective compatibilizer for PLA/PBS/HF biocomposites due to the absence of functional groups in HF and the polymer matrix, along with unsuitable reaction conditions.
Despite this, PLA/PBS/HF biocomposites offer potential as sustainable materials for automotive components like door handles. Future research should explore alternative compatibilization methods, such as incorporating epoxy-functionalized Joncryl, surface treatments for HF, or grafting alternative functional groups onto MAH-g-PLA to enhance material performance for practical applications.
Journal Reference
Ucpinar, B., Sivrikaya, T., Aytac, A. (2025). Sustainable hemp fiber reinforced polylactic acid/poly(butylene succinate) biocomposites: Assessing the effectiveness of MAH‐g‐PLA as a compatibilizer. Polymer Composites. DOI: 10.1002/pc.29569, https://4spepublications.onlinelibrary.wiley.com/doi/10.1002/pc.29569
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