Synthesis,Structure And Properties Of The PVAc-Based Inverse Core/shell Composite Emulsion Via Grafting-polymerization

Based on the pratical problems of the poly(vinyl acetate)emulsion in application,i.e.the poor water-and heat-resistance and the poor low temperature resistant and so on,a novel design idea was proposed in this paper for fabricating one-component and high-performance poly(vinyl acetate)-based core/shell emulsions to promote the water-resistance of poly(vinyl acetate)emulsion,i,e.without changing the basic emulsion polymerization process and the cost of emulsion preparation,the theory of particle design was used as the basis to fabricate the core/shell structural composite emulsion with vinyl acetate polymer as core,the polymer of hydrophobic monomer as shell.In this dissertation,the poly(vinyl acetate)-based core-shell composite emulsions with various morphologies were synthesized via the technique of "starved feeding" and semi-continuous seeded emulsion polymerization.The effect of react conditions on morphologies and structures of the products was thoroughly investigated with the structural and morphological test means,including FTIR?DSC?DLS and micro morphology characterizations(SEM,TEM).Based upon the experimental results,the possible formation mechanisms and morphological evolution mechanism of the prepared latex particles were discussed.In addition,the adhesive bonding properties and water resistance of the prepared composite emulsion were further investigated through mechanical properties,boiling water resistance and water absorption test.The main points of this paper were summarized as follows.Using maleic anhydride as grafting monomer,the PVAc-MA/PS inverse core-shell composite emulsion was successfully prepared with poly vinyl acetate as core and polystyrene as shell.The particle size of PVAc-MA/PS inverse core-shell latex particles was about 330nm and had relatively uniform particle size distribution.The latex particles with various morphologies were prepared by adjusting the core/shell ratio and maleic anhydride content,and the growth mechanism of latex particles was further illustrated.The maximum values of adhesive dry strength and wet strength of the prepared composite emulsion were 9.SMPa and 2.1 MPa,respectively.Moreover,the water absorption ratio of latex film was gradually reduced with the increasing of maleic anhydride and styrene content.The maximum boiling water time of adhesive bonded sample was more than 180 minutes.The PVAc-AN/PS inverse core/shell composite emulsion was successfully prepared by acrylonitrile grafting.The particle size of prepared core/shell emulsion was about 280nm and had uniform distribution.The expetimental rasults showed that the morphology of latex pariticle had obviously regular evolution with the changing of core/shell ratio and acrylonitrile content,and the secondary nucleation can be controlled by the acrylonitrile content.Combined with TEM and SEM results,the morphological evolution mechanism of PVAc-AN/PS inverse core/shell latex particles was further discussed.The maximum values of adhesive dry strength and wet strength of the prepared composite emulsion were 10.4MPa and 2.7MPa,respectively.Furthermore,the water absorption ratio of latex film was gradually reduced with the increasing of acrylonitrile and styrene content.The maximum boiling water time of adhesive bonded sample was more than 180 minutes.Using acrylonitrile as grafting monomer,the core/shell eomposite emulsion that utilized vinyl acetate/butyl acrylate copolymer as core and polystyrene or styrene/butyl acrylate copolymer as shell was successfully prepared via the technique of "starved feeding" and semi-continuous seeded emulsion polymerization.The particle size of composite core/shell latex particles was about 250nm and had a relatively uniform particle size distribution.The thermodynamic experiment and morphological analysis results showed that the glass transition temperature of prepared composite emulsion was regularly reduced with the increasing of butyl acrylate,and the latex morphology was mainly controlled by the butyl acrylate content in the shell layer.Meanwhile,the formation mechanism of P(VAc-BA)-AN/P(St-BA)composite latex particles was preliminarily discussed.The maximum values of adhesive dry strength and wet strength of the prepared composite emulsion were 14.OMPa and 1.5MPa,respectively.The boiling water resistance and the water absorption of the composite emulsion were decreased with the increasing of the butyl acrylate content in the core layer.With the increasing of the butyl acrylate content in the shell layer,the water absorption rate was decreased,and the boiling water resistance was increased slightly.In this thesis,through introducing the grafting monomer to fabricate core/shell latex particles,the core-shell inverse reversal due to the difference of hydrophilicity between the different components had been controlled successfully.The latex particles with different morphology were prepared via adjusting core/shell ratio and content of grafting monomer,and the secondary nucleation formation from styrene self-polymerization can be effectively restrained.Moreover,the glass transition temperature and the particle size of the prepared composite emulsion can be adjusted by introducing the butyl acrylate comonomer.In brief,the final prepared poly(vinyl acetate)-based core/shell composite emulsion by controlling and adjusting the each component had a good water-resistance and bonding property.