Preparation And Properties Of Green Crosslinked Diene Rubber

Rubber is widely used in social life because of its unique high elasticity.An important prerequisite for achieving high elasticity is the crosslinking among rubber chains.However,the existing traditional crosslinking methods in rubber industry suffer from some significant deficiencies,such as the utilization of toxic additives and“black pollution”brought out by waste rubber.What’s more,traditional rubber crosslinking process produces toxic and unpleasant smell.To tackle the above issues,green crosslinked and easily recyclable diene rubbers were prepared through functionalization of commercialized rubber.The main research contents of this subject are as followed:（1）TGDDM was selected as a crosslinker with four epoxy terminated units and tertiary amine structure,and the carboxyl groups onto the XNBR chains serve as crosslinking points.TGDDM could crosslink XNBR efficiently and rapidly.The crosslinking reaction presented self-catalytic property,and a self-catalytic mechanism was brought out through kinetics research.Furthermore,ethanol was innovatively used to replace toxic THF as the green reaction solvent.The recycling of XNBR through a closed-loop method could be achieved by bond-breaking of ester groups.Recycled XNBR showed excellent mechanical properties after reprocessing.Therefore,the above method provided an efficient,self-catalytic and green crosslinking method for carboxyl functionalized rubber,and an efficient green recycling idea for crosslinked rubber with ester linkages.（2）The epoxy-functionalized SSBR（ESSBR）with various epoxidation degrees were obtained by an in-situ epoxidation reaction.The ESSBR was crosslinked by itaconic acid（IA）producing exchangeableβ-hydroxyl ester bonds.Silica and carbon black（CB）were used as reinforcing agent respectively.During processing,the interfacial chemical interaction between silanol groups and ESSBR consumed most of the epoxy groups.ESSBR/IA/Silica rubber composite could not be crosslinked effectively.ESSBR/IA/CB rubber composite exhibits excellent mechanical properties and low rolling resistance due to good dispersion of CB and effective crosslinking of IA.In the presence of a catalyst,the resulting covalent crosslinking networks can undergo network rearrangements via transesterification reactions at high temperatures.ESSBR/IA/CB rubber composite possesses good reprocessing performance,and tensile strength could be restored up to 74%.The"black pollution"brought out by end-of-life tires is expected to be tackled through above method.（3）The amidoxime NBR（AO-NBR）with various contents of amidoxime degrees was obtained by addition reaction of hydroxylamine hydrochloride and raw NBR.It was found that strong hydrogen bonding can be formed and self-condensation reaction can occur between amidoxime bonds.Multi-cross-linking network structure could be prepared without addition of crosslinking agents and reinforcing fillers.Network structure consists of“covalent”crosslinking network formed by AO-NBR self-crosslinking,“hydrogen bond”cross-linking network between AO-NBR and“metal-ligand coordination bond”crosslinking network formed by AO-NBR and Zn²⁺.Hydrogen bonds and metal-ligand coordination bonds were developed as sacrificial motifs,which break prior to covalent crosslinking with large energy dissipation under external force.Specifically,tensile strength of AO-NBR with“covalent”,“hydrogen bond”and“metal-ligand coordination bond”triple crosslinking networks could reach up to 28.3 MPa.Thus,the above method provides a self-crosslinking and self-reinforcing green crosslinking approach for NBR.