In this study, thermoplastic composites reinforced with cupula fiber were determined their mechanical, physical and thermal properties. The polyethylene composites made with various percentages (30, 40, and 50 wt.%) of cupula fibers were produced. The polyethylene graft maleic anyhydride as a couple agent with loading (3%) of composite was used. However, alkali treatment was applied to the cupula fibers as 5% by weight sodium hydroxide (NaOH) during 24 hours in order to improve technological properties of the composites. Based on the finding results, the composites with alkali treatment of the cupula fibers was provided better mechanical properties compared to untreated fiber reinforced composites. The values of the water absorption and thickness swelling of the composites reinforced with alkali treated the cupula fibers, especially in the composite with alkali treated at 50% cupula fiber, were increased compared to untreated fiber reinforced composites.
