Study On Thermoreversible Crosslinking Of Polar Rubber And Co-crosslinked With PVC

Polyvinyl chloride(PVC),as the world's second-largest general resin,has the advantages of flame resistance,chemical resistance,and low cost.It has a wide range of applications in industrial production and daily life.Due to its own structural characteristics,PVC has problems such as poor thermal stability,easy to become brittleness and rigidity,poor toughness,and poor cold resistance.In order to improve the performance of PVC materials,crosslinking modification of PVC is an effective method.The traditional chemical crosslinking modification is irreversible,which improves the performance of PVC while losing thermoplasticity.Introducing dicyclopentadiene diformate crosslinking agent into the formulation of PVC resin can constructs thermoreversible crosslinking bridges through esterification reaction,endow cross linked PVC thermoplasticity.However,PVC resin has fewer active chlorine sites,the esterification crosslink density is lower,and the improvement of performance is not obvious.Therefore,this subject intends to introduce polar unsaturated rubber neoprene(CR)and nitrile rubber(NBR)into PVC resin by adding dicyclopentadiene dicarboxylic acid(DCPDCA)and dicyclopentadiene sodium dicarboxylate(DCPD(COONa)2),The mixture is used as a composite crosslinking agent to build a thermoreversible co-crosslinking network based on the reversible Diels-Alder(DA)reaction between PVC and unsaturated rubber molecular chains,enhancing the thermoreversible crosslinking density of PVC.The main research contents are as follows:(1)The feasibility of NBR and CR polar unsaturated rubber esterification crosslinking with DCPDCA was studied.The results show that NBR is more suitable for the esterification reaction with DCPDCA;the crosslinking agent DCPDCA is processed to prepare PEG4000-DCPDCA composition successfully,it was found that DCPDCA can be partially dissolved in PEG4000,thereby improving dispersion and dissolution of the crosslinking agent in the polymer.The DSC curves show that DCPDCA dissolved in PEG4000 has characteristic of reverse D-A reaction at high temperature,and the D-A reaction reoccurs when the temperature is lowered.(2)Determine suitable formulation for NBR esterification crosslinking:NBR 100phr,catalyst(TSA)6.4phr,PEG4000-DCPDCA composition 8.6phr(mass ratio of 5:7),antioxidant 2246 2phr,carbon black N330 45phr.By comparing the changes of swelling degree and gel content of crosslinked NBR under different compress conditions,the suitable reaction conditions were determined as follows:compress at 190? for 120min.(3)The performance of the crosslinked NBR obtained under the above suitable formulation and compress conditions was investigated.The equilibrium torque measurement of the crosslinked NBR samples at different temperatures verified that the crosslinked NBR samples can undergo reverse D-A reaction at high temperature to de-crosslinking;compared with the NBR after compress without the addition of crosslinking agent,the elastic modulus and tensile strength of crosslinked NBR had been significantly improved;after the second thermoplastic processing,the crosslinked NBR still has a high tensile performance.(4)NBR and PVC blend is prepared,using DCPDCA-DCPD(COONa)2 mixture as a composite crosslinking agent,to achieve crosslinking between PVC and NBR.The crosslinked insoluble gels were analyzed by FTIR and DSC to confirm the formation of co-crosslinked network.SEM images show that the tensile cross-section of co-crosslinked PVC is brushed and illustrate ductile fracture.