| Natural rubber(NR)has excellent comprehensive properties and plays an irreplaceable role in the field of national defense and people’s livelihood.In addition,NR has the characteristic of "strain-induced crystallization",which gives it high tensile strength and tear resistance.However,NR also has some disadvantages,such as poor compatibility with polar materials,poor wet skid resistance,low oil resistance,low air tightness,and that like.Moreover,rubber must be crosslinked to obtain high elasticity,but the traditional covalent crosslinking system contains a large amount of toxic additives,which will not only trigger the emission of "vulcanization smoke",but also cause great difficulty in recycling and serious "black pollution".In order to solve the above problems,this thesis prepared epoxidised natural rubber(ENR)with different epoxy degrees by modifying NR with epoxy functional groups as crosslinking sites,and replaced sulfur with a series of different structural carboxylic acids as green crosslinking agents to build a non-catalytic green crosslinking system.On the other hand,the effects of epoxidation modification and different cross-linking systems on their strain-induced crystallization properties were studied.Finally,the industrial preparation technology of ENR was explored,a pilot production line was established and detailed performance tests were carried out for its application in the tire industry.This thesis includes the following contents:(1)A series of new carboxylic acid crosslinkers with different chain lengths and functionalities were prepared based on the catalyst-free alcoholysis of maleic anhydride.A dynamic covalent crosslinking network exchangeable β-hydroxy ester bonds was constructed by the reaction between carboxylic acid and epoxy groups.The results show that the increase in chain length and functionalities of the carboxylic acid crosslinkers can effectively increase the crosslinking rate and enable the crosslinking of ENR under non-catalytic conditions with excellent mechanical properties.The tensile strength,300% modulus and elongation at break of the ENR/CB composites were 26.4 MPa,13.9 MPa and 454% respectively,which were 1.5,2.9 and 1.5 times higher than those of the maleic acid cross-linked system and close to the performance of the sulfur system.Due to the presence of exchangeable β-hydroxy ester bonds,the topological rearrangement can be achieved under the action of high temperature and ester exchange catalyst,and the recovery of tensile strength and elongation at break of the composites can reach up to 75.4% and 104.5% after three repetitions of processing,which has good prospects for industrial applications.In addition,due to the high thermal stability of the ester bonds,the composites also possess excellent thermal and oxygen aging properties.(2)The strain-induced crystallization properties of a range of ENR vulcanizates with different levels of epoxidation(5,10,20,33 and 45 mol% epoxy content)were investigated by WAXD,and the effects of the cross-linked systems of sulfur,peroxide and itaconic acid on the strain-induced crystallization of ENR-10 were further compared using a combination of WAXD,AFM and P-IR techniques.The results show that lower levels of epoxidation modification(≤20 mol%)promote strain-induced crystallization due to the ability of the epoxy groups to be incorporated into the lattice as "defects" on the one hand,and the ability of the rigid epoxy groups to promote the orientation of the molecular chains on the other,whereas higher levels of epoxide modification(≥33 mol%)have a hindering effect on crystallisation due to the high Tg and the fact that a large number of epoxy groups cannot all be discharged into the lattice.In addition,the sulfur system exhibited the best mechanical and crystallization properties with a maximum crystallinity of 14.2%;for the peroxide and itaconic acid sulfide systems,the maximum crystallinity was 3.8% and 5.2%,respectively.This is because the sulfur crosslinked system has a large degree of microscopic inhomogeneity,which makes it have a lower crystallization onset strain,and the broken rearrangement of polysulfide bonds can disperse the stress and promote the orientation of molecular chains,and finally the microcrystals generated by SIC can share the stress with the high cross-linked density network domains,which renders it better mechanical properties.In contrast,the cross-linked bonds of the peroxide and itaconic acid system are more rigid,the microstructure is more homogeneous,and the crystallization onset strain is larger.The microcrystals generated in the SIC process are not sufficient to bear the stresses under large strains,leading to the fracture of the sample before the crystallinity grows further.(3)We investigated the effect of ENR reaction conditions on the epoxy degree and side reactions,the effect of flocculation process on the performance of ENR,and the effect of epoxy degree on the comprehensive performance of ENR,and designed and built the only ENR pilot production line in China,and investigated the comprehensive performance of ENR applied to highperformance load tires and green car tires.The results show that ENR preparation requires mild reaction conditions,and high temperature or long reaction time will aggravate the epoxy group ring opening side reaction.Steam flocculation can effectively solve the problem of difficult and costly latex flocculation,and the steam flocculated ENR also has excellent mechanical properties.The mechanical properties of NR with low epoxy are better,while the mechanical properties of ENR with high epoxy are reduced,but the wet slip resistance is improved.Thanks to the good affinity between ENR and silica,the addition of ENR can reduce the use of coupling agent,and the application of ENR in load or car tires can significantly improve the performance of anti-slip,airtightness and wear resistance,which proves that ENR has great potential and application value in the field of new green load tires and car tires. |
