Study On Reversible Cross-linking Agent Of Polyethylene

In this paper, allyl cyclopentadienyl (A-CPD) was synthesized separately through sodium method and phase transfer catalysis. Besides, both of the synthetic methods were compared. Effect of reaction time, reaction temperature, NaOH concentration, molar ratio of reactants and other conditions on the yield of A-CPD synthesiszed through phase transfer was explored. By solution grafting method, dicumyl peroxide (DCP) as initiator, the A-CPD was grafted onto the polyethylene chain, and the graft product was analysised by IR spectroscopy. By mixing method, benzoyl peroxide (BPO) as initiator, the A-CPD and linear low density polyethylene (LLDPE) was mixed in the mixer to prepare the A-CPD/LLDPE cross-linked polymer. The gel content of cross-linking LLDPE was studied by changing the dosage of A-CPD and BPO. The thermal properties and structure of cross-linking product were also characterized.By reactive extrusion technology, dicumyl peroxide (DCP) as initiator, A-CPD and LLDPE was melt extrused in the extruder. And the melt flow rate and mechanical properties of cross-linked product were tested. Besides, the thermally reversible behavior of the cross-linking product was studied.The result showed, the yield of A-CPD synthesized through sodium method was higher, was 60% to 65%. The optimum reaction condition of synthesizing A-CPD by phase transfer catalysis was:reaction temperature is 0℃, reaction time is 2h, the NaOH concentration is 40%, the molar ratio of Cyclopentadiene and bromine propylene is 1.3:1. And the yield of A-CPD is about 55%.A-CPD grafted polyethylene by the solution method was characterized through IR spectroscopy. The result showed, compared with pure polyethylene, C=C double bond absorption peak appeared in infrared spectrum, indicating that A -CPD had been grafted onto the polyethylene chain. The mixing reaction condition of A-CPD cross-linking LLDPE is that the quality ratio of LLDPE, BPO and A-CPD is 100:2:1, the temperature is set to 180℃, the mixing time is about 3min. The gel content of cross-linked products of is up to 85%.The infrared spectra of cross-linking product showed he characteristic absorption peak of DCPD appeared, which indicated A-CPD connected to the LLDPE molecular chains; groups of CPD had been polymerized and achieved crosslinking of LLDPE. The DSC showed the endothermic peak at 170℃of cross-linking samples was same as the depolymerization temperature of DCPD, indicating the existence of the thermally reversible behavior of cross-linking LLDPE.With the increase of crosslinking degree, the melt flow rate of the cross-linking product decreased slightly, indicating that the increase of crosslinker will increase the viscosity crosslinked of product. The ensile strength of cross-linking product has significantly rised, but the elongation at break downwarded.