Polyester Composite Bending Strength Optimization Strengthened with Coastal Cottonwood Tree Bark Fiber and Fly Ash Filler

Composite material is a combination of more than one type of material and is designed to get the best combination of characteristics from each constituent component. Composite materials have many advantages, including lighter weight, higher strength and durability, corrosion resistance and wear resistance. This study aims to determine the optimum conditions of polyester composites bending strength reinforced with Coastal Cottonwood bark fibers and fly ash fillers. The method used was alkalizing the fiber of coastal cottonwood tree bark by immersing 5% NaOH solution for 2 hours. The specimen was made by the Hand Lay-Up method, the fiber volume fraction was 35.8; 40; 50; 60 and 64.14% with filler 2,93; 5; 10; 15 and 17.071%. Bending testing used the ASTM D790 standard and data analysis used the response surface method with Central Composite Design. The optimization results showed the best conditions were in the fiber volume fraction of 52.79% and filler volume fraction of 9.73% with a bending strength of 101.05 N/mm2. The mathematical model obtained from the experiment is: y = 100.296 + 5.009 x1 – 2.710 x2 – 10.285 x12 - 3,006 x22 - 1,415 x1*x2. Surface response method is an efficient method used to determine the levels of free change that can optimize response.