Study On Grafting Modification Of Polypropylene Via SC CO₂

The polypropylene (PP) was modified via SC CO₂ grafting copolymerization with pentaerythritol triacrylate (PETA) and styrene (St). The hydroperoxidant polypropylene (HPP) was obtained oxidating PP by dibenzoyl peroxide (BPO) in purgation air; this followed by monomers mixture of styrene and pentaerythritol triacrylate were swelled into HPP particles simultaneously using supercritical carbon dioxide (SC CO₂) as a solvent and swelling agent. Then monomers were grafted onto the PP backbone preparing PP with functional and long branches in distilled water by thermal cleavage.The effects of various factors on the grafting percentage and efficiency were investigated. Those factors included the reaction time, temperature, monomers and oxidant concentrations, swelling pressure, time, temperature, hydroperoxidant temperature, time, press, and size of the PP particles et al. The content of hydroperoxidant was measured by iodometric titration in vary conditions. And find out the main factors of affecting grafting percentage and grafting efficiency, select the optimal synthesis condition last.FTIR spectra confirmed that PETA and St had been grafted onto PP. High grafting percentage and efficiency product was obtained in the case of little hydroperoxidant. Maximum grafting efficiency was observed to be greater than 90%, grafting percentage was observed about 28%, in the condition that hydroperoxidant temperature is 80℃, time is 2h; Swelling temperature is 43℃, the pressure is 8.6MPa, time is 3h; Reacting temperature is 80℃, time is 8h. Reacting temperature and oxidant concentrations are the main factors of grafting percentage and grafting efficiency.We grafted PP using methods with one and two steps, studied the capability of product by melting PP into slice; We found that the grafting efficiency relatively low, capability of product is not good when the monomers concentrations increased; Monomers'variety, grafting percentage, oxidant concentrations are the main factors of affecting capability of product. Soft and hard monomers were used at the same time are better.