The Effect of Atmospheric Plasma Treatment on the Environmental Durability of Flax Fiber-Reinforced Polyurethane Composites

This study investigates the effect of Diffuse Coplanar Surface Barrier Discharge (DCSBD) plasma treatment of flax fabric on the aging resistance of flax fabric/polyurethane composites. Plain-weave flax fabric was DCSBD plasma-treated and processed into slab-shaped laminates by vacuum-assisted hot pressing. Flexural stress at 5 and 10 mm mid-span deflection, tensile strength, and dynamic puncture response were evaluated before and after accelerated environmental aging. Three aging protocols were applied: water immersion at 40°C for 14 days, 20 freeze–thaw cycles, and combined cyclic moisture–thermal–UV and freeze–thaw aging. Post-aging analysis revealed superior property retention in DCSBD plasma-treated specimens. Untreated laminates exhibited substantial flexural stress losses, ranging from approximately 29% to 73%, depending on the aging protocol. In contrast, DCSBD plasma-treated specimens exhibited flexural stress losses limited to 20–54%, demonstrating enhanced resistance to environmentally induced degradation. DCSBD plasma-treated laminates also showed a 10–17% increase in absorbed puncture energy after aging. Overall, the findings indicate that DCSBD plasma treatment improves the retention of flexural performance and alters the post-aging puncture response of flax/PU laminates, supporting its potential for enhancing the durability of flax/PU composites used under environmentally exposed conditions.