Processing and characterization of waterborne polyurethane-coated flax nonwovens for automotive applications

Flax fiber is a renewable, biodegradable material with favorable mechanical properties and a low environmental footprint, making it a promising reinforcement for sustainable composite. In this study, waste flax fibers were processed into eco-friendly needle-punched nonwovens for automotive interior applications. The nonwovens were subsequently impregnated with waterborne polyurethane (WPU) at 10, 20, and 30 wt.%, dried at 120°C, and calendared under a pressure of 5 kN. The resulting materials were characterized in terms of their physical, morphological, mechanical and thermal properties. The results showed that flax nonwovens containing 20 wt.% or more WPU exhibited improved maximum tensile force compared with the untreated nonwoven. FTIR and SEM analyses confirmed WPU deposition on the flax fibers and indicated enhanced fiber-polymer interactions. Moreover, abrasion testing revealed a substantial improvement in wear resistance with increasing WPU content. While the untreated flax nonwoven failed before 10 000 Martindale cycles, the sample coated with 30 wt% WPU withstood 50,000 cycles with a mass loss of 12.67%, indicating its suitability for demanding automotive interior applications. In addition, WPU treatment reduced the water absorption of the flax nonwoven from 35% to 14.75% and increased the water contact angle from 53° for the untreated material to 122°, 127°, and 129.3° for the WPU-coated samples, demonstrating enhanced surface hydrophobicity. The WPU coating also enhanced the thermal stability and fire resistance of the flax nonwovens. Overall, the developed WPU-coated flax nonwovens exhibited improved durability, hydrophobicity, thermal performance, and flame resistance, highlighting their potential as sustainable materials for automotive interior applications.