Preparation And Performance Of Epoxidized Natural Rubber Composites With Exchangeable Interfacial Crosslinking

Nano-filled rubber composites have numerous applications due to its high flexibility and good mechanical properties.However,those nano-filled rubber composites are generally cross-linked by a sulfur-based curing package or by peroxides,which cannot be reprocessed or reshaped due to the irreversibility of the permanent network.Hence,waste rubbers have given rise to great waste of resources and environmental pollution,which impedes the development and application of crosslinked rubbers.To circumvent the aforementioned problem,in this dissertation,by implementing exchangeable interfacial linkages between rubber and fillers,the elastomers with mechanical robustness and reprocessability are achieved.(1)Carboxyl groups were covalently anchored on carbon black(CB)based on diazonium chemistry.The modified CB(g-CB)was used to crosslink the epoxidized natural rubber(ENR).The results confirm the formation of interfacial β-hydroxyl ester linkages between g-CB and ENR matrix.g-CB serves as both reinforcement and cross-linker,endowing the vitrimer composites with mechanical robustness.The elastomeric vitrimer composites are able to rearrange network topology and relax stress via transesterification reactions in the ENR-CB interphase at elevated temperatures,endowing them with malleability and reprocessability.At relatively low temperature,the composites exhibit good elastic-recovery behavior due to the rearrangement of network topology is frozen.Furthermore,all recycled samples exhibit remarkable recovery of their initial mechanical properties.For example,the recycled CB-20 sample shows up to 83% recovery of tensile strength and complete recovery of ultimate elongation.(2)Carboxyl groups were covalently anchored onto multi-walled carbon nanotubes(MWCNTs)based on diazonium chemistry.The modified MWCNTs(g-MWCNTs)were incorporated into epoxided natural rubber(ENR).The interfacial crosslinks based on β-hydroxy ester bonds were concurrently resulted,which improve the dispersion of MWCNTs and increase the mechanical properties of the vitrimeric composites.For example,upon addition of 20 phr g-MWCNTs,the tensile modulus of EC20 reaches a high value of 11.4 MPa,which is ~50% higher than that of control sample(the tensile modulus of ECB20 is 7.1 MPa).The elastomeric vitrimer composites can rearrange network topology and relax stress via catalyzed exchange reactions at high temperature,endowing them with malleability and reprocessability.Compared with the counterpart(ECB20 shows up to 60%,36% and 56% recovery of tensile strength,tensile modulus and elongation,respectively),the excellent mechanical recovery of EC20(90%,96% and 77% recovery of tensile strength,tensile modulus,and elongation,respectively)indicates that the formation of interfacial β-hydroxy-ester bridges have promoted effect on the reprocessibility of EC20 sample.During multiple reprocessing,the network rearrangement upon compression molding may homogenize the overall dispersion state of carbon nanotubes in rubber matrix,which results in the advanced reprocessibility in mechanical properties for multi-recycled samples.