Development of Polylactic Acid Films with Alkali- and Acetylation-Treated Flax and Hemp Fillers via Solution Casting Technique

Polymers (Basel). 2024 Apr 5;16(7):996. doi: 10.3390/polym16070996.


This study aims to enhance value addition to agricultural byproducts to produce composites by the solution casting technique. It is well known that PLA is moisture-sensitive and deforms at high temperatures, which limits its use in some applications. When blending with plant-based fibers, the weak point is the poor filler-matrix interface. For this reason, surface modification was carried out on hemp and flax fibers via acetylation and alkaline treatments. The fibers were milled to obtain two particle sizes of <75 μm and 149-210 μm and were blended with poly (lactic) acid at different loadings (0, 2.5%, 5%, 10%, 20%, and 30%) to form a composite film The films were characterized for their spectroscopy, physical, and mechanical properties. All the film specimens showed C-O/O-H groups and the π-π interaction in untreated flax fillers showed lignin phenolic rings in the films. It was noticed that the maximum degradation temperature occurred at 362.5 °C. The highest WVPs for untreated, alkali-treated, and acetylation-treated composites were 20 × 10-7 g·m/m2 Pa·s (PLA/hemp30), 7.0 × 10-7 g·m/m2 Pa·s (PLA/hemp30), and 22 × 10-7 g·m/m2 Pa·s (PLA/hemp30), respectively. Increasing the filler content caused an increase in the color difference of the composite film compared with that of the neat PLA. Alkali-treated PLA/flax composites showed significant improvement in their tensile strength, elongation at break, and Young's modulus at a 2.5 or 5% filler loading. An increase in the filler loadings caused a significant increase in the moisture absorbed, whereas the water contact angle decreased with an increasing filler concentration. Flax- and hemp-induced PLA-based composite films with 5 wt.% loadings showed a more stable compromise in all the examined properties and are expected to provide unique industrial applications with satisfactory performance.

Keywords: acetylation; composite; flax fiber; hemp fiber; poly (lactic) acid.