Mechanical Properties of the Bio‐Composites: Effect of Kraft Lignin and Flax Fabric to Camphoric Acid Based Unsaturated Polyester Resin's Reinforcement

ABSTRACT The development of the technology for bio‐based resin and related composites production has nowadays become a key focus in materials research. In line with that, in this study, the effect of the structure of camphoric acid (C _f A) based unsaturated polyester resin (C _f ‐UPR) on the mechano‐chemical properties of related C _f ‐UPR/K _f L composites, produced at 5–20 wt.% of Kraft lignin (K _f L) addition, was examined. Camphoric acid, along with bio‐based maleic anhydride (MA) and propylene glycol (PG), was used in the synthesis of the C _f ‐UPR designed to enhance the wetting power of K _f L providing improvement in mechanical properties and thermal stability of the composites. The structure of C _f ‐UPR was proved using FTIR and NMR techniques. The morphological and mechanical properties of C _f ‐UPR/K _f L composites were studied using FE‐SEM, TEM, TGA, DTA, micro indentation, and tensile test measurements. The tensile strength and toughness increase, compared to pure C _f ‐UPR, for 23.9% and 93.4% at 5 wt.% K _f L addition in C _f ‐UPR, respectively, while at higher K _f L addition the values gradually decrease. The maximum increase in microhardness, 33.1%, was recorded with the addition of the 5 wt.% K _f L. Furthermore, the tensile strength of the flax fabric‐reinforced laminated composite (C _f ‐UPR/Ff) increased by an impressive 481%, which corroborates the idea about future consideration of sustainable production of high‐performance bio‐based composites. By using renewable resources and minimizing environmental impact, this method not only improves the material's performance but also complies with green chemistry principles. These composites are suitable for use in construction materials, automobile parts, and other sectors looking for environmentally friendly substitutes.