Multi-functional Polar Polypropylene Prepared Via Solid State Grafting With Assistance Of SC CO₂

Polypropylene(PP)is one of the most widely used plastics,due to its excellent physical and chemical properties along with low cost.However,PP has its inherent disadvantages such as low surface energy,lack of chemical functionality and poor compatibility with synthetic polar polymers,which restrict its further applications.This can be resolved through grafting copolymerization,a well established method for modification of polyolefins properties.Free radical grafting copolymerization of butyl acrylate(BA)onto PP matrix was investigated using supercritical CO2 as a novel soaking solvent and carrier.Effects of different experimental conditions such as soaking time and temperature,supercritical CO2 pressure;monomer and initiator concentration;PP particle diameter;solid phase grafting reaction time and temperature on grafting reactions were studied.FTIR and SEM results of grafted products indicate that the monomers were indeed grafted onto PP chains.TGA results show that grafted products have a higher onset thermal degradation temperature and a lower weight loss at a particular temperature than pure PP.DSC results show that the melting points(Tm)and apparent crystallinity(Xc)decrease with the grafting rate increas.The MFR and mechanical analysis results show that grafting products remain its versatile physical properties.This is prominent when it is compared with melt grafting products and normal solid grafting products.Besides,grafting soft-hard monomer onto PP particles using solid phase grafting was investigated.Styrene(St)is selected as a comonomer because of its property of electron donator in improving grafting percentage of maleic anhydride(MAH),as MAH is an electron acceptor and hard monomer.They can form Charge Transfer Complex(CTC)to help shape long-chain branching.Butyl methylacrylate(BMA)as a soft monomer is used as the third monomer to tune polarity and flexibility of grafted polymer.Results show that this can get a higher grafting percentage.More important,the properties of grafting products are favorable.The grafting percentage can be controlled easily by changing grafting conditions.The structures and thermal properties of grafted polymers were characterized through FTIR,TGA and MFR etc.