共聚-接枝连续聚合构建PVAc基高性能核壳乳液及其胶接构效特性研究

In order to meet with low-cost and high-performance demands of wood adhesives in manufacturing glued laminated timber, e.g. decorative veneer, a novel design idea based on copolymerizing-grafting successive polymerization is proposed for fabricating one-component and high-performance poly(vinyl acetate)-based core/shell emulsions, i.e. without changing the basic emulsion polymerization process, successive polymerization of two kinds of transition-layer monomers is utilized to transform the self-polymerization of monomers featuring distinguished properties in the emulsion polymerization to a process that shell monomer is largely polymerized and coated onto PVAc seed particles periphery, forming one-component, ambient-cured, and boiling water-resistance PVAc-based core/shell emulsions. The effect of synthetic technologies and the compositions of core/shell copolymer on the morphology and structure of latex particles will be investigated to elucidate the design discipline and synthetic mechanism of novel PVAc-based core/shell structured emulsions. The effect of transition-layer microstructure on the morphology and structure of latex particles will be explored to reveal the structure-property relationships between latex particle morphology and film-forming properties, bonding strength, water- and heat-resistance properties, and curing mechanism, by which lay the theoretical foundation and technical support for the development and application of novel high-performance emulsion adhesives for glued laminated timber.

为满足饰面用薄木、单板等胶接木制品生产制造过程中对于低成本、高性能胶黏剂的实际需求，本项目提出了一种基于共聚-接枝连续聚合构建单组份高性能PVAc基核壳乳液的设计思想，即在基本不改变传统乳液聚合工艺的基础上，通过两种过渡层单体的连续聚合，使不同性质聚合物单体在乳液聚合过程中的自聚反应转化成为壳层单体在PVAc种子乳液外层的包覆生长过程，进而合成单组份室温固化、可耐沸水胶接的PVAc基核壳结构乳液。研究合成工艺与核壳聚合物组成对乳胶粒形态与结构的影响，阐明新型PVAc基核壳结构乳液的设计原则与合成原理；考察过渡层结构对乳胶粒形态与结构的影响，研究乳胶粒形态结构与成膜性能、胶接强度、耐水热性能及固化反应之间的胶接构效关系，为木材胶接用新型高性能乳液胶黏剂的开发与应用奠定理论基础和技术支撑。

基于高附加值饰面薄木、单板用低成本高性能乳液的需求，本项目针对聚合物差异性大、常规聚合方法难以实现的乳液体系，提出新的乳胶粒核壳结构设计思想，即在不改变传统乳液合成工艺基础上，通过核壳乳液粒子设计实现了PVAc复合乳液胶黏剂的低成本化、单组份化和高性能化。项目系统研究了核壳乳液构建方式、反应条件以及壳聚合程度等因素对乳胶粒形貌与结构的影响规律，阐明了PVAc/PS反向核壳乳胶粒的合成原理，提出PS壳层在PVAc核乳胶粒表面为原位包覆生长聚合，由于接枝活性点改变了壳层单体的聚合场所，使其由游离在体系中的自聚转变为在乳胶粒核表面的自聚包覆过程；同时研究了动力学因素对核壳乳胶粒形貌与结构的影响规律，揭示了乳胶粒形貌衍化与结构调控机制，提出在热力学非平衡体系中，当乳胶粒中分子链段迁移被自身玻璃态及接枝结构抑制时，通过调控自由基分布可实现对乳胶粒形貌与结构的精确调控。项目采用丙烯酸丁酯核层共聚与丙烯腈接枝在乳胶粒结构中的连续聚合，彻底解决了反向核壳乳液的结构翻转问题，显著抑制了乳液聚合过程中的二次成核现象，为实现不同聚合物在同一乳胶粒结构中的功能性复合与乳胶粒子的高性能化开辟了一条新的途径。项目进一步考察了核壳乳胶粒形貌与结构对乳液性能的影响，揭示了乳胶粒结构与胶接特性之间的内在联系。研究表明：所构建的PVAc/PS核壳乳液不仅具有优异的胶接强度、耐水性能以及成膜性能等，还可赋予乳液优异的耐水热胶接特性，胶接试件可耐沸水煮达2小时以上，不仅满足了饰面薄木、单板加工等对高性能乳液的需求，还为实现水热条件下乳液胶黏剂对木材的耐久胶接、拓展PVAc基乳液在木材加工行业领域的应用奠定了坚实的基础。