【作者】 刘海英；

【导师】 顾继友；

【作者基本信息】 东北林业大学 ， 木材科学与技术， 2008， 博士

【摘要】 本文在综述有关乳液聚合技术、聚醋酸乙烯乳液及聚醋酸乙烯乳液耐水性研究的基础上,采用与羧基功能性单体共聚的方法,从羧酸单体的种类、浓度、加入方式和中和度等角度出发,系统研究了羧酸在水溶性较大的醋酸乙烯共聚体系中对乳液稳定性能、粒径及粘度和耐水性能的影响,合成了耐水性提高的单组分醋酸乙烯/Veova10共聚乳液。利用Zeta电位仪、电导滴定法、激光粒度仪、DMA、DSC、SEM、流变仪等手段从Zeta电位、表面羧基密度、羧基和乳液组分中的相互作用、羧酸改性后胶膜的力学性能、水的存在状态、粒径分布、流变性能和微观形貌方面探索了羧基提高乳液耐水性的机理。研究结果表明:羧基改性乳液的乳胶粒表面带有负电荷,加入羧基单体,羧基部分分布于乳胶粒子表面,乳液Zeta电位绝对值升高,乳液稳定性增强。SEM结果表明羧酸改性后的乳液微观分散状态良好,适度的表面羧基密度和适量的离子化羧基对提高乳液的湿强度是有效的。从DMA、DSC和流变测试结果可知:羧酸加入后乳液胶膜的模量提高,在一定的条件下乳液在-42.6℃～-50.1℃出现可冻结结合水的冻结峰,与PVAc和VAc/Veova10未改性乳液相比,融化峰的Onset值降低,耐水性较好的乳液在低剪切速率下乳液出现最大粘度时的剪切速率较小。适宜的粒径以及粒径分布较窄的乳液耐水性能较好。综合上述分析结果,初步得出羧基提高乳液耐水机理为:当少量羧基功能性单体参加共聚后,一定数量的羧基和离子化的羧基分布于乳胶粒子表面,羧基和聚乙烯醇羟基由于氢键作用相互作用增强,改变自由水的存在状态,出现可冻结结合水和聚乙烯醇结合,可以“保护”聚乙烯醇的羟基,提高乳液的耐水性。羧基和聚乙烯醇上的羟基之间的相互作用,使乳液外相缠结结构发牛改变,增强乳液的流动性,提高乳液的耐水性。羧基和乳液中羟基之间是假交联现象,提高胶膜本身的模量,增加胶膜的致密程度,提高乳液耐水性。由于羧基起到成核的作用,改变乳液的粒径和分布,适宜的乳液粒径及窄分布的粒径,可提高对基材的渗透能力,乳液的利用率增大,使乳液耐水性提高。采用原位聚合法,添加无机纳米粒子SiO₂合成耐水性提高的无机/有机复合乳液,利用SEM、DMA、DSC、激光粒度仪、流变仪等测试手段,从微观形貌、体系中水的状态、流变性能、胶膜的力学性能等方面表征乳液的性能。结果表明:经超声处理的SiO₂粒子加入乳液中,乳胶粒分散状态良好,提高了乳液的耐水性。加入SiO₂后,胶膜的模量提高,玻璃化温度升高,耐水性较好的乳液在低剪切速率下乳液出现最大粘度时对应的剪切速率较小,乳液未出现可冻结结合水的冻结峰,自由水的融化峰起始位置发生改变,推测加入SiO₂改变了体系中自由水的存在状态,在这方面不同于羧酸改性的乳液。在乳化剂改性方面,合成了一种含用羧基的高分子乳化剂P（VAc/AA）并应用于醋酸乙烯乳液,与传统乳化体系OP-10和SDS复合乳化剂相比,胶膜的吸水率降低。系统研究了SVS、HAPS、HPMAS、DNS-86四种反应性乳化剂以及复合型乳化剂DNS-628在聚醋酸乙烯乳液聚合中的应用,结果表明:分别以DNS-86为乳化剂采用预乳化工艺、以DNS-628为乳化剂采用半连续种子乳液聚合工艺均可合成稳定的乳液,为聚醋酸乙烯乳液的合成开辟新的途径。更多还原

【Abstract】 The technology of emulsion polymerization and the development of polyvinyl acetate emulsion included the water resistance of the emulsion were summarized in this paper.The copolymer emulsions of vinyl acetate（VAc）/vinyl ester of versatic acid（Veova） with elevated water resistance were synthesized by the semi-continuous seeding emulsion polymerization in the presence of methacrylic acid（MAA）.The stability,the viscosity and the latex particle diameter of the emulsion,and the water resistance of the emulsions were greatly dependent on the types of carboxylic acid,the content of MAA,the method of introduction of MAA and the degree of neutralization of MAA.Zeta potential,density of surface carboxyl groups,the interaction between carboxyl groups and component in copolymerization emulsion,mechanical properties of films,state of water,particle diameter and distribution of particle diameter and theological behavior of emulsion were investigated by Zeta meter,the conductometric titration, particle size apparatus,dynamic mechanics analysis（DMA）,differential scanning calorimmetry（DSC）,scanning electron microscope（SEM）,rheological apparatus,respectively, to study the mechanism on the water resistance of modified PVAc emulsion.After modification of vinyl acetate and vinyl ester of versatic acid copolymerized with MAA,partial carboxylic groups exist on the surface of latex particles with negative electric charge,and the stability of modified emulsion was increased with the increase of the Zeta potential.The morphology of dispersive emulsion particle was observed by SEM.The results showed that the moderate amount of surface carboxyl groups and ionization carboxyl were available to the improvement of water resistance of latexes.The storage modulus of modified emulsion film with the addition of MAA was increased and the shear rate of the emulsion with maximum viscosity was lower than that of the emulsion with poor water resistance.The peak of freezing bound water was observed between -42.6℃and -50.1℃and the value of onset for the thawing peak of the emulsion was decreased than that of the PVAc and the VAc/Veova emulsion.The moderate particle size and its distribution can improve the water resistance of the emulsion film.The mechanism of improved water resistance of modified PVAc emulsion with MAA was summarized as follows:some carboxyl groups and ionization carboxyl were located on the surface of the latex particles.Freezing bound water was observed in modified emulsion with MAA by hydrogen bond between carboxyl and hydroxyl of polyvinyl alcohol（PVA） and H₂O,and the state of free water was different with pure water.The moderate amount of freezing bound water could protect the hydroxyl to improve water resistance.Carboxyl could influence the congregate structure of PVA and the emulsifiers,affecting rheology of emulsion, water resistance were intensified.The storage modulus of modified film were increased compared with the film of PVAc and VAc/Veova to make the film compact to enhance water resistance.Carboxyl had greatly effect on the formation of particles in the aqueous phase.The moderate particle size and narrow distribution particles could rise the amount of the emulsion in porous wood,so water resistance were improved.The nano-silica/polyvinyl acetate organic-inorganic composite latex was synthesized by in-situ emulsion polymerization of vinyl acetate in the presence of silica nano-particles.The mechanics properties,the state of water,the dispersibility of the silica nano-particles and latex particles and the rheological behavior of the emulsion were studied by the analysis of DMA, DSC,SEM and rheology apparatus.The results indicated that the process of the nano particles by ultrasonic can make a good dispersibility of the silica nano particles and the latex particles in emulsion,which induced better water resistance than the PVAc emulsion.The modified organic-inorganic composite latex had low shear rate of emulsion under the maximum viscosity and the storage modulus of the film increased.The value of the peak for thawing onset of the emulsion was decreased to that of PVAc emulsion,but the peak of freezing bound water was not observed in the composite latex.The observed results are different compare with modified emulsion with MAA.The polymeric emulsifier,reactive emulsifier DNS-86 and composite emulsifier DNS-628 were used in the synthesis of the PVAc emulsion.The poly（vinyl acetate-co-acrylic acid） P（VAc/AA）emulsion was synthesized with acrylic acid and vinyl acetate.The water absorption of film with the polymeric emulsifier was less than original OP-10/SDS emulsifiers.At the same time,the polyvinyl acetate emulsions were prepared by batch polymerization with HAPS, HPMAS,SVS,DNS-86 and DNS-628 as emulsifier.The results showed that the PVAc emulsion with DNS-86 and DNS-628 were better than that with HAPS,HPMAS and SVS in polymerization stability.The stable PVAc emulsion was synthesized with DNS-628 by semicontinuous emulsion polymerization.However,the pre-emulsified process were used to prepare stable PVAc emulsion with DNS-86.更多还原