Synthesis Of Cardanol Grafted Onto Liquid Polyisoprene Rubber And Its Application In Natural Rubber Composites

The strain-induced crystallization of natural rubber（NR）endows it with excellent mechanical strength and fatigue crack propagation resistance,so it is widely used in dynamic products,such as tires,seals,dampers and conveyor belts.However,the high viscosity of natural rubber makes it difficult to be processed and energy dissipate.Secondly,unreinforced vulcanized natural rubber is difficult to meet the requirements of most practical applications.The dispersion of fillers and the interaction between fillers and rubber are the key factors determining the dynamic and static mechanical properties of rubber composites.In this paper,cardanol grafted onto liquid isoprene rubber（CA-g-LIR）was synthesized by solvent-free method.The grafting reaction conditions were optimized,and the performance and interfacial effect of CA-g-LIR were discussed.The plasticizing effect of CA-g-LIR on natural rubber and its compatibilizing effect on silica（Si O₂）reinforced natural rubber were studied.The main research contents and results are as follows:1.CA-g-LIR was synthesized by solvent-free method.Its interfacial force with Si O₂was investigated.The test results of UV-visible absorption spectrometer,Fourier transform infrared spectrometer and ¹H NMR spectroscopy showed that cardanol monomer was successfully grafted on the molecular chain of LIR.CA-g-LIR with a grafting rate of 6.01%was obtained by adding 7 phr of cardanol monomer and 0.2wt%of 2,2-Azobisisobutyronitrile（AIBN）initiator per 100 phr of LIR and reacting for 12 h at 70°C.CA-g-LIR shows obvious plasticizing effect,as is certified by its far high elongation at break（increase by 800%）,decreased viscosity（reduction by 62%）and declined glasstransition temperature（T_g,decline by 5.0℃）compared with LIR.Moreover,CA-g-LIR shows good interfacial performance.The dispersion of Si O₂ particles in CA-g-LIR is better than that in LIR.2.A series of NR/CA-g-LIR blends with different ratios were prepared by the traditional open-mixing method.The effect of CA-g-LIR concentration on the properties of natural rubber was discussed.CA-g-LIR is a good plasticizer and anti-aging agent for NR.Compared with NR,the tensile strength of NR/CA-g-LIR blends increased by 61.09%,the elongation at break increased by 92%,the Mooney viscosity decreased by 33.39%,the scorch time was prolonged by 18.82%,the T_g was decreased by 2.3℃,and the aging coefficient was increased by 277.05%,When the contents of CA-g-LIR is 15 phr.Most importantly,the chemical bonds between CA-g-LIR and natural rubber prevent the migration of of CA-g-LIR,which is the drawback of petroleum-based plasticizer.CA-g-LIR is a nontoxic green plasticizer and is expected to become a new multifunctional plasticizer in rubber industry.3.A series of NR/CA-g-LIR/SiO₂ and NR/LIR/SiO₂ composites filled with different contents of Si O₂ were prepared by the traditional open-mixing method.The compatibilization effect of CA-g-LIR on natural rubber and Si O₂ was studied.The results of Mooney Viscometer（MV）,scanning electron microscope（SEM）,and rubber process analyzer（RPA）demonstrated that CA-g-LIR plasticizing effect is better than LIR.CA-g-LIR improved the dispersion of Si O₂ in NR and decreased the Payne effect of Si O₂ in NR.The tensile strength of NR/CA-g-LIR/Si O₂ composites was 26.67%,13.25%and 18.42%higher than that of NR/LIR/Si O₂ composites when the Si O₂ content was 30,40,and 50 phr,respectively.CA-g-LIR shows good interfacial behaviour between NR and Si O₂,and the wear resistance of NR/CA-g-LIR/Si O₂ composites is also improved.CA-g-LIR synthesized by solvent-free method without post-treatment is a green and versatile to realize industrialization.It has obvious plasticizing effect,compatibilizing effect and anti-aging performance on natural rubber.CA-g-LIR as a natural plasticizer overcomes the migration of traditional plasticizer in the matrix.This study will provide experimental and theoretical basis for the research and production of new multifunctional rubber agents.