Preparation Of Polypropylene Foams With High Expansion Ratio And High Cell Density Based On Adding Nucleating Agents

Polypropylene(PP)foam has many good advantages,such as excellent mechanical properties,good thermal properties,natural degradation and wonderful chemical resistence.It was considered as a more competitive thermoplastic resin for producing polymer foams than others,such as polyethylene(PE)and polystyrene(PS).Propylene-ethylene blockcopolymer(PPB)has attached more attention due to its foamability.However,the bubbles formed in homogeneious nucleation which make it hard to form a lot of bubbles and get good foams with high expansion ratio and high cell density.In order to resolve this problem,molecular sieve,graphene and nucleating agent were added to accerate the formation of bubbles,improve the crystallization behavior and mechanical properties,prepare good PPB foams with high expansion ratio and high cell density.Firstly,the crystallization behavior,mechanical properties and foaming properties of PPB were investigated.The results showed that 13X molecular sieves(13X)can lead PPB to form?-crystal.When the content of 13X is 0.5 wt%,the content of ?-crystal(kp value)was increased from 0.17 for neat PPB to 0.64 for PPB/13X-0.5%.The impact strength was increased from 838.9 J/m to 952.9 J/m.The crystallization peak temperature was increased from 122.2 ? to 130 ?.The foaming temperature and foaming pressure were studied through single factor analysis.The PPB foams with high expansion ratio of 41.2 times was prepared at optimum conditions in this research.Secondly,the effect of industrial grade multilayered graphene(GN)on the crystallization behavior,rheological behavior and foaming properties of PPB were investigated.The results showed that PPB can form a-crystal.When the content of GN was 3 wt%,the crystallization peak temperature of PPB can be increased by 5.5 ?.The rheological results showed that optimum concentration of GN was 0.5 wt%?1 wt%.Further study showed GN can significantly decrease the average cell diameter from 141.4 ?m for PPB to 83.6 ?m for PPB/GN-1%,and the cell density was increased from 6.43�106 cell/cm3 for pure PPB to 1.02�107 cell/cm3 for PPB/GN-1%.Finally,the effect of an efficient ?-crystal nucleating agent 1,3:2,4-bis(p-methylbenzylidene)sorbitol(S20)on the crystallization behavior,mechanical properties and foaming properties were investigated.The results showed that the crystallization peak temperature of PPB was increased by 18.4 ? and the flexural modulus was increased by about 10%at the content of S20 was 0.4 wt%.The non isothermal crystallization kinetics certified that S20 had good nucleation effect in PPB.The foaming temperature and foaming pressure was systematically investigated using batch foaming process.The expansion ratio was increased from 35.3 times for neat PPB to 57.6 times for PPB/S20-0.4%,cell density was increased from 6.43�106 cell/cm3 to 1.02�108 cell/cm3.