The fiber loading capacity and poor adhesion between fibers and matrix remains an area of concern in fiber polymer composites. The fiber loading capacity and aspect ratio of mercerized Urena Lobata fiber on mechanical properties (tensile strength, tensile modulus, tensile toughness, elongation, flexural and impact strength) of Urena Lobata fiber polyester composites was investigated. Urena Lobata fiber was extracted using water retting approach. The extracted fiber was mercerized at optimum treatment condition of 3.504wt%/NaOH and 50.322mins soaking time. The polyester composite samples were prepared using hand layup method for general unsaturated polyester resin, 1% methyl ethyl ketone peroxide (MEKP) catalyst and 1% Cobalt naphthenate accelerators and commingled with treated and untreated fibers respectively at optimum treatment conditions. The fiber loading of 10-50 wt% and aspect ratio of 42.68-213.38mm/mm were used. The mechanical properties of mercerized Urena Lobata fiber polyester composites were determined and optimized using  RSM of MATLAB statistical tool box. The tensile strength, tensile modulus, toughness elongation, flexural strength and impact strength for unreinforced polyester resin was 29.60MPa, 3.1541GPa, 0.32649MPa, 1.875%, 80.0MPa and s360KJ/m², respectively. At optimum aspect ratio and fiber loading, the mercerized Urena Lobata fiber increased the tensile strength, tensile modulus, toughness, elongation, flexural strength and impact strength of the unreinforced polyester resin by 43.0, 63.6, 73, 28, 64 and 106%, respectively. Thus mercerized Urena Lobata fiber enhanced the mechanical properties of polyester composites.

Urena Lobata fiber, polyester resin, mercerization, mechanical properties.