Preparation And Modification Of High Acrylonitrile Content Copolymer Emulsion

Polyacrylonitrile has a regular molecular structure,high crystallinity and high cohesion energy,which make it hard and with excellent mechanical properties,and it is widely used in polyacrylonitrile-based carbon fibers,ultrafiltration membranes and acrylics.At present,under the conditions of this research system,the preparation of polyacrylonitrile is mostly done by solution polymerization and suspension polymerization,and less research has been done on the preparation of polyacrylonitrile by emulsion polymerization,mostly using acrylonitrile as a modified monomer to participate in polymerization.Emulsion polymerization has the advantages of fast polymerization rate,high molecular weight of products,and direct use of emulsion.Moreover,under the international environment and national policy requiring green and resource-saving,aqueous emulsions are widely used.Based on the above research background,this thesis systematically investigates the emulsion polymerization of acrylonitrile and the modification and application of polyacrylonitrile emulsions,the main contents are as follows:（1）The main factors affecting the emulsion polymerization of acrylonitrile（AN）were discussed,namely the dosing method,mass fraction of acrylonitrile monomer,emulsification system,mass fraction of emulsifier,and copolymerization monomer.The results showed that,the single acrylonitrile emulsion polymerization had poor stability,large particle size,low conversion rate and easy to break the emulsion.Butyl acrylate（BA）was added as co-monomer,stable copolymerized emulsions with up to 70wt%acrylonitrile content were successfully produced by conventional emulsion polymerization.The preparation process conditions such as dosing method,AN mass fraction,emulsifier composition and concentration have a great influence on the performance of copolymer emulsions.Compared with the monomer pre-emulsion droplet addition,the particle size distribution of the emulsion prepared by the one-time feeding method is narrow,and the average particle size is small;with the increase of the mass fraction of acrylonitrile,the particle size distribution became wider and the average particle size became larger（from 63 nm to 140 nm）;the emulsion is prepared by the one-time feeding method,and the maximum content of acrylonitrile of the stable emulsion is 70 wt%AN,the emulsion performance is the best;OP-10/SDS complex emulsifier compared to Span 80/SDS and PGPR/SDS for better emulsification;the average particle size of the emulsion prepared under 7.5 wt%OP-10/SDS compound emulsifier was106.6 nm,and the core-shell structure of the prepared AN-BA copolymer emulsion particles could be observed by SEM and TEM test results.（2）Vinyl silane coupling agent（MPS）,nano-SiO₂particles,and homemade silicone emulsion were selected to modify the high acrylonitrile content copolymer emulsion.The results showed that the maximum addition of MPS in the system was 7 wt%,and the particle size of the emulsion widened with the increase of MPS amount,and the average particle size became larger to 144.3 nm;with the increase of hard monomer acrylonitrile monomer at the same stirring speed,the apparent viscosity of the emulsion would decrease accordingly;the introduction of MPS made the polymer form a cross-linked mesh structure,and the glass transition temperature increased to 73℃,and the thermal decomposition temperature was also increased compared with that of the unmodified polymer.The physical modification of SiO₂nanoparticles,the right amount of nanoparticles has little effect on the emulsion particle size and does not affect the emulsion stability;in the characterization of thermal properties,the oxidation process of thermal decomposition will be different because of the presence of small molecular groups on the surface of its particles.The physical blending of high content acrylonitrile copolymer emulsions was modified using homemade silicone emulsions,and different compounding ratios and film-forming temperatures were discussed.The different molecular configuration of silicone emulsions can effectively improve the film-forming state of copolymer emulsions because of the flexibility of their silicone chains,and the compound volume ratio is 5:3 is optimal,and better polymer films can be obtained under natural drying conditions.