Preparation,Structure And Properties Of Tetrafluoroethvlene-Propylene Copolymer Rubbers

Tetrafluoroethylene-propylene (TFE-P) copolymer is a type of fluoropolymer with alternating structure and low glass transition temperature, and can be further chemical crosslinked to prepare fluororubber with excellent heat, oil and chemical resistance. Due to the lack of studies on synthesis, structure and properties of crude and crosslinked TFE-P copolymer rubber, TFE-P emulsion copolymerizations were carried out to synthesize TFE-P copolymers with high molecular weight and Mooney viscosity. Besides, effects of molecular weight of TFE-P copolymers and processing aids on the structure and properties of crosslinked fluororubber were investigated in this thesis. To solve the problem of low crosslinking reactivity of TFE-P copolymer, heat treatment of TFE-P copolymers to form unsaturated bonds and synthesis of TFE-P copolymers containing a cure-site monomer were studied, and the relationship between structure and properties of modified TFE-P copolymer and modified crosslinked fluororubber were investigated.Firstly, TFE-P copolymers were prepared by emulsion polymerizations at low temperature using water-soluble initiator A or water-soluble initiator B, a reducer, promoter C and D. The variations of copolymerization rate and average molecular weight of the TFE-P copolymers with the composition and addition policy of the redox system, polymerization temperature, et al, were investigated. The results showed that the copolymerization rate could keep stable and be high in case of adding the initiator and the promoter at the beginning of copolymerization, and adding the reducer continuously during the copolymerization. The copolymerization rate was increased as the feeding rate of the reducer increased. When the polymerization temperature was 30℃ and 35℃, the initial copolymerization rate was very high, and the copolymerization rate decreased significantly at late stage of polymerization due to the high consumption rate of initiator. The addition of buffer system containing NaOH/Na2HPO4 helped to increase the copolymerization rate when water-soluble initiator A was used as the initiator. However, copolymerization rate decreased with the addition of buffer system when water-soluble initiator B was used, and the average molecular weight and Mooney viscosity of the prepared copolymers were lower than that of copolymers prepared by using water-soluble initiator A. Through controlling the temperature and the feeding rate of reducer, the copolymer with high average molecular weight and high alternating structure can be obtained.Secondly, effects of molecular weight of TFE-P copolymers, usages of crosslinking agent, type and usages of crosslinking coagents, type and usages of filler on structure and properties of crosslinked fluororubber were investigated. It was found that the gel fraction, crosslinking density, tensile strength and Shore A hardness of crosslinked rubbers were increased with the average molecular weight of TFE-P copolymer and the usages of dicumyl peroxide (DCP) crosslinking agent increased. The maximum crosslinking degree and the maximum tensile strength were achieved when the triallyl isocyanurate (TAIC) usages were 4 phr. Using OVPOSS as the crosslinking coagent could obviously improve the crosslinking degree, tensile strength and thermal properties. Carbon black N550 could be dispersed well in the rubber matrix and had the best reinforced effect to fluororubber. The selected silica with homogeneous porosity could also be dispersed well in the fluororubber matrix, and the properties of crosslinked fluororubber reinforced by nanometer silica were closed to that of crosslinked fluororubber reinforced by N550 carbon black. The optimized processing formulation was obtained as follows:crude rubber/reinforced filler/DCP/TAIC/sodium stearate= 100/20-25/1/4/1.Thirdly, to solve the problem of low crosslinking reactivity of TFE-P biopolymer, the introduction of unsaturated bond through heat-treatment of TFE-P copolymer was studied. It was found that heat-treated TFE-P bipolymer with peroxide A or peroxide A/MgO compound could not only reduce the temperature and time of heat treatment, but also reduce the emission of HF. When TFE-P copolymer blended with 2 phr peroxide A and 1 phr MgO was heated at 200℃ for 20min, the crosslinked fluororubber based on the above modified crude rubber exhibited the tensile strength and thermal stability closed to that of crosslinked fluororubber based on commercial TFE-P copolymer with trade name of AFLAS 100S.Finally, TFE-P-cure-site monomer emulsion copolymerizations were carried to improve the crosslinking ability of crude rubber, and the structure and properties of terpolymer rubbers were studied. The addition of VDF and VMA had some effect on the kinetics. The crosslinking degree of modified TFE-P copolymers was greater than that of TFE-P copolymer at the same crosslinking conditions, especially for TFE-P-VCA and TFE-P-VMA copolymers. The modified crosslinked fluororubber exhibited better mechanical properties and thermal stability than that of crosslinked fluororubber based on TFE-P copolymer.The above results played good guidance role to prepare, process and modify TFE-P copolymer rubbers.