Effects Of Toughening Agent And β-nucleating Agents On The Structure And Properties Of Isotactic Polypropylene

On the one hand, a novel impact i PP-based graft copolymer(IPGC) was obtained via irradiation graft method with a purpose to modify i PP. The mechanical properties, crystallization behaviors and rheological properties of i PP/IPGC blends were studied in order to clarify the phase structure of IPGC and the mechanism of IPGC. On the other hand, two kinds of β-nucleating agents were employed to modify i PP and the crystallization behaviors upon different thermal treatments as well as the thermal stability of β-crystals were systematically investigated with an aim to find out the β-nucleation mechanism of β-nucleating agents on i PP.It was found that IPGC had an excellent toughening effect on i PP and the best impact strength occurred at an irradiation dose of 50 k Gy. The ambient and low temperature impact strength of i PP was improve from 5.93 k J/m2 and 2.58 k J/m2 to 13.59 k J/m2 and 2.34 k J/m2, improved by 129.17 % and 68.22 % while the tensile strength decreased by only 12.57 %. Compare with common toughening agent POE, IPGC had a better low temperature toughening effect with the same adding concentration.Due to the difference of crystallization temperature between LLDPE and i PP, IPGC can form a so-called “core-shell” structure with the core of LLDPE and the shell of ethylene-octane copolymer(POE), the graft copolymer formed during irradiation process acts as compatibilizer throughout the LLDPE core and ipp matrix.β-I had better toughening effect than β-II at the concentration of 0.05 wt%, the impact strength of i PP was improved from 5.93 k J/m2 to 12.12 k J/m2, improved by 104.38 %. The relative percentage of β-phase induced by β-II was 83.64 % which was the highest among all the β-nucleating agents including compound β-nucleating agents, but the β-crystals induced by β-I had a better thermal stability.The crystallization behavior of β-i PPs was greatly influenced by thermal treatments, at a higher fusion temperature(Tf), the relative percentage of β-phase in β-i PP remained very high, while crystallization temperature became higher and the relative content of β-phase decreased and even cannot be observed at lower Tfs, at the same Tf the crystallization curves of β-i PPs stayed constant with the changes of holding time.The nucleating effect of β-nucleating agents can be divided into two cases: at higher Tfs, under the influence of β-nucleating agents, molecular chains of i PP are gradually ranged from random coil state into locally ordered structure, which have high β-nucleation efficiency, then the ordered structures form β-embryos and the finally the occurrence of β-crystals; at relatively low Tfs, most of the i PP molecular chains are already ordered structures and the β-nucleation effect is restrained, as a result, the β-crystals are largely decreased until none β-crystal melting peak is observed.