Study On Flame Retardant Modification Of Low-Rate Foamed Syndiotactic Polypropylene

Syndiotactic polypropylene(sPP)has unique mechanical properties including high modulus,toughness and elasticity,however,there are no researches on its application,especially,research about extrusion foaming.Simliar as isotactic polypropylene(iPP),sPP also has the disadvantages of low melt strength and difficulty in foaming,therefore,it needs to be modified by blending or cross-linking.In addition,the sPP is both easy to burn,which futher restricts their application.Therefore,it is important to suppress its burning by flame retardant modification.This work discussed the foaming conditions of sPP including blending and cross-linking foaming,and explored the fire retardancy of foamed sPP.The specific content is as follows:1.The sPP and LDPE composite was formed by blending,the tensile properties was explored.Compared with iPP and LDPE blends.It was found that the tensile strength of sPP and LDPE blends was lower than that of iPP and LDPE blends,but the elongation at break was higher when blending in 3:2.In addition,LDPE could promote the crystallization of sPP while the crystallization of iPP and LDPE blends was suppressed to a certain extent.The two blend systems were foamed,it can be found that the foaming ratio of about 2.1 times.However,the sPP/LDPE blended foam had better cell morphology,therefore,it presentedhigher elongation at break.2.The dicumyl peroxide(DCP)and a variety of cross-linking agents were introduced into sPP to crosslink.It was found that the melt index of sPP decreased and the melt strength increased after cross-linking.For extrusion foaming of cross-linked sPP,it was found that the foaming ratio can reach about 2 times.Compared with the cross-linked iPP foam prepared by similar process,it is found that the cross-linked sPP had better cell morphology,the elongation at break and tensile strength were higher than those of the cross-linked iPP foam.3.The ammonium polyphosphate(APP),triazine char-forming agent(CFA),montmorillonite(MMT)and red phosphorus were added to cross-linked sPP to improve its fire retardancy.it was found that the system could reach the UL-94 V-1 rate,and the limiting oxygen index could reach 28.7%whenthe amount of flame retardant was 25wt%and APP/CFA/MMT/red phosphorus system mass ratio was 13:5:1:1.However,for cross-linked foam,it can be found that the amount of 35wt%of APP/CFA/MMT(mass ratio 14:5:1)can achieve the V-0 rate.Based on,the red phosphorus is introduced into above flame retarded foam,it can be found that total addition amount of APP/CFA/MMT/red phosphorus(mass ratio 13:5:5:1)is reduced to 30wt%,the foam can reach the V0 rate.Besides,the introduction of red phosphorus had better cell morphology,therefore,it had higher elongation at break.