Preparation Of Functionalized Emulsions With Core-Shell Structure And Their Performance In Wood Processing

Because of the mature manufacturing process,excellent performance,and environmental friendliness,polymer-based emulsion as a water-dispersed polymer material has been widely used in traditional wood processing and industrial fields.Along of the process of industrial development and technological progress,higher requirements and usage standards are put forward to the manufacture and research of polymer-based emulsion products,including higher quality,zero pollution,and universal applicability.Core-shell structured polymer emulsion with multi-phase separation structure endows the colloidal multi-component composite characteristics due to its special multi-level layered structure,which can realize the matching and superposition of multiple properties,having very broad research value and use-value.The core-shell structure enables the different polymer phases gathered inside the latex particles to be arranged in an orderly manner according to a specific spatial structure,resulting in significant promotion in processing performance and use performance of the polymer emulsion product without increasing the cost.Moreover,the core-shell structured latex particles can load additional components with specific functions due to the special three-dimensional stratification effect,thereby realizing functionalization of the core-shell emulsion and giving the core-shell emulsion product novel functions.The purpose of this research is to explore the preparation,functional modification,and film-forming properties of different types of coreshell emulsions,and to lay the foundation for the formulation of high-performance emulsions and the development of new functional applications.The research in this thesis focused on the preparation of multi-system polymer-based emulsions with core-shell structure based on the method of "particle design" and the semicontinuous seed emulsion polymerization,and the evaluation of related performance,making full use of characteristics of the core-shell structural platform in the preparation of multicomponent polymer emulsions in a micro-nanoscale.First of all,based on the structural compounding characteristic between various components of the latex particle given by the core-shell structure,different types of functionalized polyvinyl acetate(PVAc)-based core-shell emulsions were prepared.The effect of functional modification outside the surface of shell layer or inside the core layer on the morphology and structure of core-shell latex particles and emulsion performance was systematically studied.Secondly,the frame of core-shell structure can give polymer latex particles unique phase separation characteristics and control the morphology of latex particles,maintaining relative independence of the core polymer and the shell polymer in physicochemical properties and thermodynamic properties,while giving the emulsion a good film-forming ability,which lays the foundation for the reversible bonding performance of the latex film formed by the PVAc-based core-shell emulsion with shape memory function.The study systematically investigated the shape memory effect of the film formed by PVAc-based core-shell emulsion,and the reversible bonding performance of the latex film based on the shape memory function.Furthermore,given the poor coating performance and low film-forming efficiency of polymer-based emulsions after film-formation,comprehensive research strategies relating to the preparation of polybutyl acrylate-based coreshell emulsion with functional modification of particle surface and the film formation based on the UV curing were developed,in which the advantages of core-shell structure in latex particle composition control and latex particle functional modification,as well as UV light curing technology that exhibited the characteristics of high efficiency,rapidity,and low energy consumption in the film-forming process,were all taken into account together.The preparation of functional modification of latex particles,the film-forming process,and the film properties,have been systematically studied.Finally,due to the designability of the latex particle components and particle morphology of the core-shell structured emulsion,it can not only improve the performance of the emulsion product itself but its unique functions in the composite material can also be exerted.Therefore,based on the all-round control in the composition,morphology,and size of core-shell latex particle,the core-shell latex particle/cellulose nanocrystal(CNC)composite membrane was prepared,and the effect of the addition of core-shell latex particles on the film-forming properties of latex particles/CNC composite film and the influence of color control were systematically investigated.The specific research content is as follows:(1)Taking PVAc-based core-shell latex particles as the research object,polyvinyl acetate/polystyrene(PVAc/PS)core-shell emulsions with the targeted introduction of functional components into the core polymer or shell polymer were prepared,where vinyl trimethoxysilane(VTMS)and hydroxyethyl acrylate(HEA)were used as the functional modification components of the shell,and ethylene glycol dimethacrylate(EGDMA)were used as a core internal modification monomer.The research results have shown that when VTMA was introduced to modify the surface shell of PVAc-based core-shell particles,the freeze-thaw stability of the emulsion could be significantly ameliorated,and the water-resistance of bonding species also could be improved.Functional modification via HEA on the surface of PVAc/PS core-shell latex particles can increase the bonding performance of the emulsion.At the same time,the introduction of hydroxyl groups could promote the penetration of water molecules and increase the wettability of the film.PVAc/PS core-shell particles could be internally cross-linked by the EGDMA.By increasing the cohesive strength of that particle themselves,the adhesive dry/wet strength was significantly improved,and at the same time,the water absorption degree of the latex film could be reduced,and the boiling-water resistance time can be significantly extended.(2)On the basis of particle functionalization,tri-functional reactive monomer trimethylolpropane triacrylate(TMPTA)was firstly introduced into PVAc/PS core-shell latex particles,and PVAc/PS core-shell particles with intra-core network cross-linking structure were successfully prepared.The results of the research have shown that the TMPTA core-crosslinked PVAc/PS core-shell latex film exhibits an efficient triple shape memory effect during the thermomechanical functionalization.The study found that the PVAc/PS core-shell latex particles with cross-linked core had the potential of independent triple shape memory on the micro-nano scale.The macroscopic changes of the latex film and the microscopic particles were simultaneously produced in the shape memory process,which further revealed the triple shape memory formation mechanism of core-shell latex film.The research further explored the construction of the water molecule switch in the shape memory system of the PVAc/PS coreshell latex film,and then developed the latex film prepared by PVAc-based core-shell emulsion system with quad shape memory effect.Based on the exploration of the shape memory effect,the study found that in the high-temperature compression-recovery shape memory cycle,there was simultaneous adhered-unblocked reversible bonding between the latex film and the surface of the wooden substrate,and this reversible bonding strength did not decrease with the number of bonding.(3)Pointing at the problems of poor performance and low film-forming efficiency in the application process of acrylic emulsion products for wood coating.the styrene-acrylic functional emulsions with a core-shell structure were prepared based on the semi-continuous seeded emulsion polymerization and the functional modification of core-shell latex particles,in which butyl acrylate(BA),styrene(St),and methyl methacrylate(MMA)were used as the main components.The UV cross-linking and curing film formation of styrene-acrylic coreshell emulsion based on the physical-chemical synergistic cross-linking system and the chemical cross-linking network system was put forward.The results have shown that when acrylic acid(AA)or hydroxyethyl acrylate(HEA)containing polar functional groups was introduced into the surface of styrene-acrylic core-shell latex particles for functional modification,and an additional functional monomer N-methylolacrylamide(NMA)was also introduced into the emulsion curing system,the emulsion system could be cured under UV irradiation,and the inside of the latex film could form network-like cross-linking structure.With the increase of the NMA content and the degree of functionalization of the particle surface,the hardness and tensile properties of the styrene-acrylic latex film can be significantly improved,while maintaining the good film-forming performance and high transparency of the latex film.The research revealed the film-forming mechanism based on the physical-chemical synergy effect under UV radiation.In addition,the study further explored the UV curing filmforming system of the styrene-acrylic core-shell emulsion functionalized with reactive monomer surface.The research results have shown that the chemical crosslink can be formed between the reactive groups on the surface of the latex particles and the water-soluble polymer of the system once the styrene-acrylic latex particle was modified by reactive monomer on the surface of particles,thereby realizing the chemical cross-linking curing of the film-forming system.(4)Through the semi-continuous seed emulsion polymerization method and the"starvation" feeding method,four emulsions with different particle sizes were prepared,namely,PS emulsion,PVAc/PS core-shell emulsion,and P(VAc-co-BA)/PS core-shell emulsion with different core composition.The average particle diameters of the prepared emulsions were 100 nm,200 nm,230 nm,and 280 nm,respectively.The effect of colloidal particle size in the colloidal particle/cellulose nanocrystalline composite film on the structure color of the composite film was systematically studied.The study has found that the addition of core-shell structure latex particles can enhance the film-forming performance of CNC and improve the flexibility of latex/CNC composite film.The reflectivity of the composite film prepared by mixing PVAc/PS core-shell emulsion and CNC suspension was as high as 70%.As the colloidal particle size increases from 100 nm to 280 nm,the reflected light wavelength ?max of the composite film was 478 nm,532 nm,562 nm,and 646 nm,respectively.Studies have demonstrated that latex particles can control the spiral pitch of the CNC chiral nematic layer,and as the particle size increases,the spacing between the nematic layers was increased,resulting in an increase in the wavelength of reflected light and a red shift in the color of the composite film,and finally realizing the colloid/CNC composite film color control.