Preparation Of High Flow Polypropylene And Polyethylene Grafted By Maleic Anhydride

Isotactic polypropylene (IPP) with super high melt flow rate (MFR≥800g/10 min, 2.16kg/190℃) was prepared by chemical degradation in solidstate reactor under stirring at 80～120℃, and effects of reaction condition onMFR and molecular weight of polypropylene were investgated. The structureand performance of products obtained were characterized by IR,DSC,viscosity measurement and capillary rheometer. It was shown that thecarbonyl group and unsaturation bond appeared in main chain of PPdegraded, and increased as the degrading time increased, meanwhile, MFRwas increased with time, and can be reach to above 800g/10min (2.16kg/190℃) in two hours, whereas the molecular weight descend from 140 000g/molto 46 000g/mol; the formulation between MFR and molecular weight wasdeduced: M_η=160 448MFR^-0.2173, which can be used for the calculated forviscosity molecular weight; the The results of DSC showed that the meltingtemperature (T_m) descent from 163.7℃to 157.1℃. Rheological propertieshave shown that in the same shear rate, the apparent viscosity of pp meltdecreased about 250 Pa.s per 1℃as the temperature increased, and the meltexhibited as Newtonian fluid at 210℃.Another subject in this paper is solid phase grafting Maleic anhydride(MA) onto Linear low density polyethylene(LLDPE), the relationshipbetween the degree of grafting (DG) and monomer, initiator and time wereinvestigated, and the structure and performance have been charaterized. Thedegree of grafting increased with the time, and reached to be 2.3% in 4hours, then remained constantly, the degree of cross-linking (DC) firstlyincreased slowly, and then raised sharply after 200 minutes; The resultsshowed that the degree of grafting raised with the amount of MA and thetemperature, the maximum (DG=2.7%) was obtained when MA was 13% in105℃; with the addition of Triphenyl phosphate, the degree of crosslinking and grafting both decreased. The temperature of melt and crystalling ofLLDPE also decrased with the increase of the degree of grafting. Thestructure of the crystalline is unchanged, but the degree of the crystallity has aslightly increase, it is deduced that the grafting mainly occurs in amorphouszone.LLDPE/LLDPE-g-MA blends were preapred by melt extrusion,followed by injection molding. The results indicated that the degree ofcrystallity decrease slightly, but the structure remainedαcrystalline. PureLLDPE is easily to form big spherulites, but with the addition ofLLDPE-g-MA, the big spherulites disappeared, The blends prior to formsmall lamellar crystallines, melt temperature and crystallization temper -atureindicated that the crystalline was easily to form heterogeneous nucleation.Pure LLDPE fracture exhibited typical brittle fracture due to spherulitesstructure, but the blends obtained exhabited a large amount of orientatedmicrofibers morphology, and thefracture changed as ductile rupture. With 10percents addition of LLDPE-g-MA (DG=1.26%), the impact strength ofblends raised from 13.6kJ/m² to 22.1 kJ/m², but the tensile and flexuralstrength have slightly decrease; meanwhile,the effects of LLDPE-g-MA usedas the compatilizer for LLDPE/TiO₂ was investigated, with 10 percentsaddition of LLDPE-g-MA (DG=3.06%), the impact strength increased from8.8kJ/m² to 14.4 kJ/m², nearly raised 63.7%.