In the recent decade, there has been an increase in global warming, environmental changes, and other issues. Environmentally friendly products, such as natural composite materials, are being developed by researchers and academics to protect life on the planet. The purpose of this research is to see if cellulose and cellulignin fibres obtained from sugarcane bagasse (SCB) waste may be used as reinforcing filler in a thermoplastic polymer matrix. The injection method was used to create the low density polyethylene (LDPE) and sugarcane bagasse (SCB) composites. Fiber loading was set to be varied from 10 to 30 wt%. To improve interfacial bonding, the fibres were chemically modified using an alkali treatment, and the effects on the fiber/matrix interaction were evaluated using scanning electron micrographs (SEM). Tensile, impact, and hardness were used to determine the mechanical properties and corrosion tests. The findings revealed that sugarcane bagasse fibers, like other natural fibers, strengthen polyethylene. It has been found that the tensile strength and tensile modulus of the treated SCB fibers have been improved significantly by about 13% and 196%, respectively, compared to neat LDPE. This was due to the observed enhancement in the interfacial adhesion between the fiber and matrix. The impact resistance and hardness of the composite enhanced by 55.28% and 26%, respectively, over neat LDPE. According to SEM analysis, the alkali treatment affected the morphology of fibers.