Enhancing the characteristics of natural coir fiber yarns using biopolymer for textile reinforced cementitious composites

Abstract

Textile reinforced mortar (TRM) composites typically comprise of high strength textiles (such as carbon, glass, and other synthetics fiber based textiles) embedded into cementitious matrix to improve the strength and stiffness of the resulting composites. However, with increasing global emphasis on sustainability and environmental consciousness has spurred the emergence of utilizing sustainable reinforcing materials such as natural plant fibers (in particular coir textile) in construction sectors. Nevertheless, natural coir fibers come with inherent drawbacks, including their hydrophilic nature and lower tensile strength/ stiffness. In addressing these challenges, coir yarns were fabricated by coating (one, two, and three layers) them in PLA (polylactic acid) suspension to obtain biocomposites. The average tensile strength of raw coir yarns (without polymer coating) is 42 MPa, which increased by 38% with one layer PLA-coating, 98% with two layers, and 107% with three layers, respectively. Additionally, the initial tangent modulus of raw coir yarns coated with three layers of PLA suspension improved by 121%. The changes in the mechanical characteristics is predominantly due to the improved material crystallinity after PLA-coating over the coir yarns. Further, the fractography analysis revealed the formation of tensile cracks on the surface of coir yarns exhibiting significant alterations corresponding to the number of PLA-layers applied. Finally, the optimally treated coir yarns were used as reinforcement in cement mortar along with pretensioning. The pretensioned PLA-coated coir yarns reinforced TRM composites enhanced the tensile strength by 133% and initial tangent modulus by 139% as compared to the reference specimens, while distributing the tensile stress uniformly (based on image analysis using DIC) along the length of the TRM composites.