Irradiation Oxidation Of Polypropylene And Its Foaming With Supercritical CO₂

When polypropylene?PP?is used as a medical device material,it is prone to oxidative degradation during the radiation sterilization,which will affect the product performance.Therefore,it is significant to study the degree of oxidative degradation and specific change in the performance of PP irradiated in air.The use of PP foam is limited due to its narrow foaming window temperature and poor foaming performance caused by its poor melt strength and low viscosity.Radiation crosslinking of PP can improve the melt strength effectively and provide more nucleation sites for the scCO₂ foaming,so as to improve its foaming performance.The changes of the structure and properties of PP powder and PPR sheet irradiated by gamma-ray or electron beam were studied.PPR was micro-crosslinked by adding crosslinking agent in the process of irradiation,which improved its foaming performance.The research content and result are as follows:?1?Polypropylene?PP?and PP with 2%crosslinking agent triallyl isocyanurate?TAIC??J-PP?powders were irradiated by gamma-ray or electron beam in air at room temperature.The changes of the free-radical concentration,chemical structure,thermal stability,and oxidation scission induced by gamma-ray or electron beam irradiation were studied,and the effects of the crosslinking agent,absorbed dose and dose rate on the properties of PP were also discussed.The results showed that peroxy radicals and oxidative products were formed upon irradiation for both PP and J-PP powders,the free radical concentration of J-PP was lower than PP powder.and the addition of the crosslinking agent TAIC could not prevent the degradation of polypropylene.The average molecular weight of the irradiated PP and J-PP powders declined with the increasing absorbed doses.?2?PPR and PPR/TAIC sheets were irradiated by gamma-ray in air at room temperature.The variation of free radical species and concentration,the degree of oxidative scission and thermal stability of PPR containing crosslinking agent or not was studied after irradiation.The results showed that when the absorbed dose was less than 25kGy,the free radicals were mostly oxidized into peroxide radicals;when exceeding25kGy,more alkyl radicals would be generated in the sample and not easy to be oxidized.The degree of oxidative scission increased with the increasing absorbed dose,the crosslinking agent could induce PPR radiation crosslinking moderately and improve its thermal stability.?3?The PPR,PPR/TAIC?1%?and PPR/TAIC?2%?sheets were irradiated by?-rays and then foamed by supercritical carbon dioxide?scCO₂?.The effects of TAIC and absorbed dose on the PPR structure and the foaming ability were investigated.It was found that PPR was crosslinked by TAIC in the process of melt blending and the crosslinking degree of PPR/TAIC?2%?was higher than PPR/TAIC?1%?.After irradiation,the degree of crosslinking in PPR/TAIC?2%?increased,the degree of oxidative degradation increased simultaneously with the absorbed dose.There are?and?crystals in PPR and more?crystals was found after crosslinking.The?crystals were helpful to induce more nucleation sites and form better foams.The suitable foaming window temperature was expanded to 10?.