Effect of functional additives and natural fibers on the thermal and mechanical properties of compression-molded PLA biocomposites

Polylactic acid (PLA) is a biodegradable polymer with growing industrial appeal, but its inherent brittleness, limited thermal stability, and poor impact resistance hinder its use in demanding applications. This study explores the development of PLA-based biocomposites incorporating a range of functional additives and reinforcements — including polyethene glycol (PEG), polyamide 11 (PA11), lauryl peroxide, Dellite 67G nanoclay, hemp chips, and basalt short fibres — to enhance thermal and mechanical performance. The formulations were prepared through melt blending using a twin-screw extruder and subsequently processed via compression molding into test specimens. Thermal analysis revealed that Dellite nanoclay significantly enhanced crystallinity (up to 75%), while PA11 and hemp disrupted the crystalline structure, reducing thermal stability. Mechanical testing showed that 5 wt.% Basalt fibers increased tensile and flexural modulus by over 36%, and lauryl peroxide promoted remarkable ductility, increasing elongation at break by 381%. Conversely, PA11 caused severe embrittlement, reducing tensile strength by 67%. Impact tests highlighted the effectiveness of peroxide modification, which more than doubled the absorbed impact energy, while moderate basalt fiber content offered a balanced improvement in stiffness and toughness. These findings confirm that targeted combinations of fillers and additives, along with careful processing, can tailor PLA performance for advanced applications, although compatibility and filler dispersion remain critical factors.