I am grafting folic acid on PHB in DMF. I used 50 mg PHB, 0.6 mmol NHS and 0.6 mmol EDAC.HCL. PHB is soluble in DMF and the Folate grafted PHB is precipitated out at alkaline pH. But the product is very low. The recovered product is only 15 mg. I use 14000 rpm for centrifugation. What strategy should be used to increase the product? I have attached the picture of precipitated product.