Study On Morphology Control,stabilization Mechanism And Adhesive Properties Of PVAc/PS Core-shell Emulsion

The core-shell structured emulsion can make the emulsion have more excellent properties due to its special multi-phase structure,so it was widely used in wood bonding fields.In this research,the conventional chemical raw material such as poly(vinyl acetate)(PVAc),polystyrene(PS)was used as the main raw material,PVAc/PS inverted core-shell emulsion with stable structure was prepared by constructing acrylonitrile(AN)graft structure,and the semi-continuous heterogeneous seed emulsion polymerization was used.The AN graft structure can effectively inhibit the reverse conversion of the cores and shells.The effects of the construction method of inverted core-shell structure,the degree of shell polymerization and the kinetics factors of thermodynamic non-equilibrium on the morphology,structure and properties of core-shell structured latex particles were systematically investigated.In addition,the regularity of morphological evolution of latex particles and the mechanism of kinetic regulation were analyzed and elaborated.The practical properties of the core-shell structured emulsion such as wood adhesive and water-resistance were studied through emulsion performance test.The detailed research contents are as follows:(1)The inverted core-shell structured emulsion with PVAc as cores and PS as shells was fabricated by constructing AN graft active point on the PVAc core surface.The effects of different degree of shell polymerization on the morphology,structure and properties of core-shell structured emulsion were investigated.The results illustrated that latex particles with special morphology can be obtained at different degree of shell polymerization,and the morphological evolvement of latex particles was a continuous dynamic process with the degree of shell polymerization increased.The special morphological changes of the latex particles can have significant effects on the particle size,phase structure and thermal mechanical properties of the core-shell latex.The bongding properites of the inverted core-shell structured emulsion to the wood blocks were also explored.The results showed that the shear strength was increased,and the boiling water separation time of glued wood blocks was greatly extended.The water-resistance of latex was also evaluated by the water absorption of latex films,and the results illustrated that the water absorption of the latex film was significantly reduced.The experimental results provided a reasonable support for the controlled growth of St monomer,that is,the self-nucleation of St monomer can be transformed to in-situ coating growth on the PVAc core surface depending on the AN-active grafting points,and the kinetic regulation of the morphology and structure of latex particles was realized.(2)PVAc/PS inverted core-shell structured emulsion with different grafting-transition layer structure was synthetised with AN as grafting monomer and butyl acrylate(BA)as transition layer monomer.The morphological evolvement of latex particles with different graft-transition layers and different degree of shell polymerization and the formation of secondary particles in the system were studied.The experimental results considered that the grafting-transition layer structure can regulated and inhibited the formation of the secondary particle,and the morphology of the latex particle was a continuous evolution process with the degree of shell polymerization increased.The grafting-transition layer structure can adjust the particle size and enhance the ability of the latex film to resist thermal-induced viscoelastic deformation,and thus its thermal mechanical properties was improved.The performance test of the core-shell structured emulsion showed that the grafting-transition layer structure can significantly improve the bonding and water-resistance of the core-shell emulsion.The maxmum values of adhesive dry strength and wet strength of the prepared core-shell structured emulsion were 13.19 MPa and 5.72 MPa,respectively.The minimum water absorption of latex film was 2.84%,and the maximum boiling water time of adhesive bonded sample was 134 min.(3)The PVAc-based inverted core-shell structured emulsion with different core and shell glass transition temperatures(Tg)was constructed by using AN as grafting monomer,and the effects of core and shell Tgs on the morphology,structure and properties of latex particles were investigated systematically.The grafting structure synthesized by AN monomer between the cores and shells can induce and initiate shell monomer polymerization on the core surface,and weakened the chain segment migration between the cores and shells.By adjusting the Tg of the core polymer,the morphology of the latex particles gradually evolved from strawberry structure to spherical structure,and the protuberance volumn of the shell polymer on the core surface gradually decreased.When the Tg of the shell polymer was gradually increased,there was no significant changes in the morphology of the latex particles and the protuberance volumn of the shell polymer on the core surface.The effect of free radical distribution on the morphological evolvement was explored.The effect of the morphological structure on the particle size and phase structure of the obtained latex were also discussed.More importantly,the experimental results provided a reasonable support for the morphology of latex particles which could be precisely controlled by the free radical distribution and the controllable design and kinetic control mechanism.The results of latex properties test showed that the different Tg of core and shell polymer and special latex particle morphology have different effects on the bonding and water-resistance of the latex.