【作者】 王海花；

【导师】 沈一丁；

【作者基本信息】 陕西科技大学 ， 材料学， 2008， 博士

【摘要】 环境保护的压力迫使传统的溶剂聚氨酯逐渐淡出市场,而代之以水性聚氨酯产品。但在水性聚氨酯现有合成方法中,或多或少地使用了一定量的有机溶剂,以解决合成阶段的溶解性问题以及在分散阶段调整黏度。尽管低沸点有机溶剂可以提高乳液的干燥速率,高沸点溶剂可改善乳液的成膜性能,但综合来看,既增加了成本又污染了环境。所以,完全杜绝有机溶剂,将水性聚氨酯变成真正意义上的环境友好材料显得越来越重要。此外,有关该体系的系统应用工作就很多,关于该体系的的结构、流变特性和涂层在使用性能之间的相关性的系统设计与研究很少。其在一定意义上制约了水性聚氨酯应用的研究与开发。本研究通过引进不同的交联组分,改变分散体颗粒的大小等方式来研究颗粒间的相互作用对体系相行为形态、流变形为、热性能和机械性能的控制,为改善聚合物成膜性能和使用性能提供基础,并为该类材料的合成、成型和建模提供指导。本研究亦从材料的环境友好性出发,采用原位聚合法制得系列无溶剂聚氨酯微乳液复合体系,彻底摒弃了传统水性聚氨酯中所添加的助溶剂,解决环境污染问题。本课题采用种子乳液聚合法和原位聚合法两种方法成功制得系列聚氨酯/聚丙烯酸酯复合乳液,分别为PUA₁和PUA₂系列。并于体系中引入自交联单体三羟甲基丙烷（TMP）、功能性单体丙烯酸羟乙酯（HEA）、羟甲基丙烯酰胺（HAM）和环氧交联单体（E-44）。考察了聚氨酯大分子稳定剂作用下,聚合温度、丙烯酸酯单体总浓度及引发剂对共聚合动力学的影响,建立了转化率-时间关系曲线的模型函数——Boltzmann函数,并以其拟合了转化率-时间关系曲线,获得了聚合过程的重要特征参数。同时通过曲线非线性拟合,得到了总动力学模型即Rp^∝[M]^2.38[I]^0.883。并结合实验数据,对所建立动力学模型进行了最小二乘方线性回归,结果表明该模型对共聚合具有较好的预测能力。研究了PUA₂原位聚合体系稳定性的影响因素。结果表明,电解质类单体或引发剂的加入会引起PU乳胶粒聚沉,而非电解质亲水单体（HEA、HAM和AM）和非电解质引发剂ZAM可大幅改善乳液的稳定性。与单独的MMA和BA相比,MMA和BA的混合物作为预聚体连续相时,所制乳液稳定性可与以NMP等有机溶剂为连续相制得的乳液稳定性相媲美。为无溶剂聚氨酯/丙烯酸酯复合乳液的制备提供了确凿的依据。且其含量控制在10-30%之间,异氰酸根指数（R值）介于1.2-1.4,反应温度介于55-70℃,HAM含量介于10%-20%,环氧含量低于20%时,乳液稳定性较佳。系统分析了交联单体对各体系乳液形貌、粒径及其分布的影响。结果表明,纯聚氨酯颗粒间相互黏附,形成了类似虫状胶束的形状,粒径较小,呈单峰分布;PUA₁未能形成真正的核壳结构,而是形成一种嵌入式结构的复合粒子,且PUA₁乳液中有单独的PU和PA粒子存在,部分PA嵌入到PU中形成新的粒子。核磁共振分析亦表明PUA₁体系中苯乙烯和丙烯酸丁酯与PU发生了接枝反应。乳胶粒粒径为90.9nm,呈双峰分布,分布系数为0.074。随着TMP用量的增加,乳液粒径增加至103.9nm。而随着HEA用量的增加,乳液粒径可减小至72.3nm。PUA₂乳胶粒间相对分散,呈现夹心型近球状形态,疏水性聚丙烯酸酯与聚氨酯形成互穿网络。当HAM用量较大时,乳胶粒间亦发生团聚,乳液稳定性下降。而经环氧改性后,EPUA乳液颗粒间高度分散,呈现球状形态,乳液呈现一定的核壳结构,但核壳界限相对于PUA₂模糊一些。PUA₂乳液粒径为48.0nm,较PUA₁变小,呈双峰分布,分布系数为0.111。而环氧和丙烯酸酯共同改性制得的EPUA₂乳液粒径高于EPU,与PUA₂接近,平均粒径为53.4nm,且呈双峰分布,但分布较PUA₂变窄。乙烯基单体的后期引发聚合反应使乳液的粒径有所增加,由44.1增加至48.0nm,增幅不大;但粒径分布大幅增加,由0.035增加至0.111。随着MMA和BA的增加,乳液粒径由48.0增加至67.9nm;而当HAM用量由10%提高至15%时,体系粒径由70.2降至48.0nm,分布系数由0.127降至0.111。稳态流变行为研究表明聚氨酯体系在相反转前,黏度约为10²Pa·s且几乎不随剪切应变的变化而变化,呈现牛顿流体行为。在相反转点,体系黏度高达10⁵Pa·S,比相反转前增加了3个数量级。体系在相反转后变为O/W体系,黏度下降,但由于水基微粒间的相互作用,低剪切率下的黏度有所增加,并呈现剪切变稀行为。纯PU乳液为近牛顿流体,黏度基本不受剪切率的影响;纯PUA₁乳液亦呈现牛顿流体行为,无触变行为,零剪切黏度为0.016Pa.s。PUA₁乳液黏度随TMP用量的增加而下降,随HEA用量的增加而增加。TMP的加入可使体系呈现一定的剪切变稀行为和触变性,而HEA无此作用。若同时加入TMP和HEA,在一定TMP用量下,乳液的黏度亦随着HEA用量的增加而增加,且当HEA用量为0.8时,由于核壳交联结构的引入,乳液呈现复杂的触变行为。对PUA₂体系,以BA为预聚体连续相时,所制PUA₂B乳液黏度较高,达10²Pa.s以上,表现强烈的假塑行为;以MMA为连续相时,所制PUA₂M乳液黏度下降了2个数量级,乳液的假塑行为较弱;而分别以MMA和BA的混合物、NMP为连续相时,所制PUA₂MB、PUA₂N乳液流变曲线基本吻合,黏度为0.1 Pa.s,呈现牛顿流体行为。PUA₂体系黏度均高于PUA₁体系。且该体系均具有一定的触变性能。乳液零剪切黏度随着CAPA分子量、HAM用量的增加而增加;随着TMP用量的增加而下降。经环氧改性后,乳液呈现非牛顿流动,并存在屈服应力σ_y,具有塑性体的可塑性质,乳液在低剪切率范围内黏度较高,有利于乳液流平性的改善。随着剪切率的进一步增加,体系呈现明显的假塑性流动行为,可使材料易于涂刷使用。动态流变行为研究表明,对PUA₁体系,随着TMP和HEA用量的增加,乳液的储能模量上升,内耗tanδ减低。说明PUA₁体系由粘性行为向弹性行为转变,颗粒间相互作用增强。纯PUA₁乳液的储能模量G′随着时间的延长基本保持不变。而经TMP和HEA改性后,G′随着时间的延长呈一定的上升趋势,且上升幅度随着TMP和HEA用量的增加而增加,乳液内部发生交联反应。对PUA₂体系,体系不存在明显的松弛行为。PUA₂M乳液的内耗tanδ在0.65左右,G′在低频区表现出平台区,且G′与G″在0.35Hz处相交,乳液弹性较高,颗粒易发生聚集或团聚,稳定性较差;PUA₂MB和PUA₂B具有较强的频率依赖性,且PUA₂B体系无序性较强,PUA₂MB的tanδ为1.1左右,PUA₂B的tanδ为1.3左右,稳定性相对较佳。对PUA₂MB体系,随着TMP用量的增加,乳液黏度下降,触变性减弱,体系结构相对无序,流动性较佳,乳液的内耗tanδ由1.1增加至1.5,储能模量下降,乳液由黏弹行为向纯粘性行为转变,体系趋于不稳定。当环氧量为8%,体系储能模量的频率依赖性较强,体系流动性较好;而当环氧量为20%时,G′在2.5Hz处出现转折点,tanδ～ω曲线上出现明显的转折点,说明体系存在一定的相分离和松弛行为。同时,对体系的热稳定性、力学性能、耐介质性和热降解动力学进行了研究。结果表明,CAPA分子量的提高,适量TMP、HEA、HAM和环氧的加入可在一定程度上提高体系的热稳定性、力学性能和耐介质性。热降解动力学研究亦表明,Kissinger法、Flynn-Wall-Ozawa法拟合的相关系数均高达0.97以上,适用于PUA₁体系。Flynn-Wall-Ozawa法和Friedman法对PUA₂体系拟合的相关系数亦高达0.97以上,适用于该体系。某阶段降解活化能的增加表明体系热稳定性增强。环氧树脂的加入可使胶膜的初始热分解温度由236.31℃提高至271.36℃,拉伸强度由12.7MPa增加至20.8MPa,T-剥离强度由2.1 N.mm^-1升高至8.1 N.mm^-1,断裂伸长率由456%降至191%;吸水率由12.7%降至2.14%,吸甲苯率由112%降至70%,接触角由90.00°增加至106.49°;但过多的交联剂用量会消弱体系的综合性能。最后,综合研究了体系的相容性及相行为。结果表明,聚氨酯与环氧共混乳胶膜（PU/ER）的内耗峰为双峰,峰值分别为-56.2℃和130℃,且两峰之间的阻尼因子较小,两峰相对独立,体系两组分之间的相分离程度较高;PUA₂体系亦具有两个内耗峰,峰值分别为-29.6℃和50.5℃,与共混物相比,相容性得到一定提高;而EPUA₂体系只具备一个内耗峰,峰值为26.6℃,介于上述两个玻璃化温度之间。表明环氧共聚交联单体的引入,使得体系具有较高的相容性。更多还原

【Abstract】 Driven by environmental regulation, waterborne polyurethane （WPU） has attracted more and more attention. However, in the preparation process of WPU, certain amount of organic solvent was added to adjust the viscosity of PU prepolymer. Although drying rate of the emulsion can be enhanced by adding low boiling point solvent, and film-forming properties can be improved by adding high boiling point solvent, organic solvent addtion not only brings pollution to the environment but also leads to high product cost. Therefore, completely replacement of organic solvent by water is of growing importance, which can make WPU a real sense of environmental friendly material. In addition, much emphasis has been placed on the application of this system. There are relatively little systematic reports on fundamental insights into the relationships among structure, rheological properties and application properties, which would restrict the deep research and exploitation of WPU to a certain extent. In this research, different crosslinkers were introduced to change the size and distribution of particles, thereby to study how controlled changes in particle interaction alter the phase behavior, micromorphology, rheology behavior, thermal properties and mechanical properties, which could provide fundamental information for film-forming performance and performance that the systems are likely to encounter during use. Simultaneously, the study can guide the synthesis, processing and modeling of these materials. Furthermore, in-situ polymerization was used to synthesize polyurethane micro-emulsion without any organic solvent. In this research, two series of polyurethane/polyacrylate composite emulsions were succesfuly prepared by seed emulsion polymerization and in-situ emulsion polymerization, named PUA₁ and PUA₂, respectively. At the same time, self-crosslinking monomer （trimethylolpropane, TMP）, functional monomer （2-hydroxyethyl acrylate, HEA）, （n-methylolacrylamide, HAM） and epoxy monomer （E-44） was introduced into the system.With the action of polyurethane stabilizer, effect of polymerization temperature, monomer concentration and initiator concentration on copolymerization kinetics were investigated. Model function of cumulative conversion versus reaction time--Boltzmann Fnction was built up, and was employed to fit the samples of cumulative conversion versus reaction time. The maximum polymerization rate（MV）, average polymerization rate（AV） in the steady stage, average nucleation rate（NV） and the corresponding cumulative conversion at moment of nucleation stage ceasing and at the steady stage completing were estimated by calculating extremums and inflexions of its fitted Boltzmann Function. Whereafter, the polymerization rate versus each single polymerization parameter was analyzed with non-linear fitting and the related equation was obtained, that is, Rp∝[M]^2.38[I]^0.883. Finally, least squares linear regression was performed on the model, the result show that this model own excellent forecasting ability to this copolymerization.The factors influencing the stability of PUA₂ emulsion were studied. It was found that aggregate took place among particles with the addition of electrolyte , while the stability of PUA₂ emulsion can be improved by the addition of HEA, HAM, acrylamide （AM） and waterborne initiator （ZAM）. The system prepared with the mixture of MMA and BA as the continuous phase of prepolymer has comparative stability with the system using organic solvent （such as N-methyl pyrrolidone, NMP）, and superior to the system using methyl methacrylate （MMA） or butyl acrylate （BA）, providing accurate basis for the preparation of polyurethane/polyacrylate composite emulsion without any organic solvent. The stability of PUA₂ system reach optimum under the following conditions: the dosage of MMA and BA ranges from 10% to 30%, R value ranges from 1.2 to 1.4, copolymerization temperature ranges from 55℃to 70℃, HAM dosage ranges from 10% to 20%, and epoxy monomer dosage is lower than 20%.Effects of crosslinker on the micromorphology, particle size and distribution of emulsion were systematically investigated. It was found that particles of pure polyurethane adhere to each other, similar to wormlike micelle. The particle size of pure polyurethane was very small, showing unimodal distribution. It was also found that core-shell structure didn’t form in PUA₁ system prepared by seed emulsion polymerization, and an embedded structure was detected instead. Moreover, individual PU and PA particle was detected in this system, and part PA was grafted into PU, which can also be demonstrated by nuclear magnetic resonance （NMR）. As the increase of TMP dosage, the particle size increases from 90.9nm to 103.9nm, with bimodal distribution. And the particle size decreases from 90.9nm to 72.3nm with the increase of HAM dosage. However, the PUA₂ emulsion displays sandwich morphology with relative dispersed particles, and hydrophobic polyacrylate/polyurethane interpenetrating network was formed. Aggregation tends to take place among particles as the increase of HAM dosage, resulting in the decrease of emulsion stability. But particles in the emulsion modified with epoxy monomer are highly dispersed with core/shell spherical morphology, and it is difficult to discern the boundary between core and shell. The particle size of PUA₂ emulsion was 48.0nm, smaller than that of PUA₁ emulsion, exhibiting bimodal distribution with distribution coefficient of 0.111. The particle size of EPUA₂ emulsion modified with epoxy and acrylate is about 53.4nm with bimodal distribution which is higher than EPU and similar to PUA₂. But the PUA₂ system shows broader distribution. In addition, the particle size increases from 44.1nm to 48.0nm, and distribution coefficient increased greatly from 0.035 to 0.111 through post polymerization of vinyl monomer. The particle size increases from 48.0nm to 67.9nm as the dosage of MMA and BA increases. The particle size decreases from 70.2nm to 48.0nm when the HAM dosage increases from 10% to 15%, with distribution coefficient decreasing from 0.127 to 0.111.Steady rheology study shows that the viscosity of polyurethane is about 10²Pa·s and kept invariable with shear rate, exhibiting Newtonian liquid behavior before the phase inversion. While reaching the phase inversion point, the viscosity increased to 10⁵Pa·s, accompanied by the decrease of viscosity after phase inversion. Moreover, an oil-in-water system was built instead of water-in-oil system; and the viscosity at lower shear rate increases owing to the interaction between waterborne particles, exhibiting shear thinning behavior.A Newtonian response is obtained for PU emulsion, as well as PUA₁ emulsion. And no thixotropy behavior was detected in this system. The zero shear viscosity of PUA₁ emulsion was 0.016Pa.s, decreasing with the TMP dosage. While an increase in HEA dosage caused the increase of PUA₁ viscosity. Furthermore, shear thinning behavior and thixotropy behavior can be observed in this sytem with TMP addition, which can’t be obtained by HEA addition. If TMP and HEA were simultaneously added into the system, its viscosity increased with HEA dosage, and complex thixotropy behavior was observed due to the crosslinking structure between core and shell.For the PUA₂ system, the viscosity of the PUA₂B emulsion prepared with BA as the continuous phase of prepolymer reaches 10²Pa.s, presenting strong pseudoplastic behavior. The viscosity of PUA₂M emulsion prepared with MMA as the continuous phase was reduced by two orders of magnitude, showing weaker pseudoplastic behavior. While steady rheologival cure of PUA₂MB emulsions prepared with mixture of MMA and BA as continuous phase is similar to that of PUA₂N emulsion prepared with NMP as the continuous phase, their viscosity were about 0.1 Pa.s, presenting Newtonain flow behavior. In a word, the viscosity of PUA₂ was higher than that of PUA₁, and PUA₂ system was endowed with certain thixotropy. The zero shear viscosity increased with the increase of the CAPA molecular weight and HAM dosage, and decreased with the increase of TMP dosage. Furthermore, yielding stressσ_y and plasticity existed in the PUA₂MB emulsion modified by epoxy resin, presenting non-Newtonian flow behavior. Moreover, the viscosity at low shear rate was relative higher, beneficial to the improvement of leveling. And pseudoplastic flow was observed with the increase of shear rate, which was good for brushing.Dynamic rheological investigation was also performed on the system. As to pure PUA₁ system, it was found that storage modulus（G’） kept invariable with time, while the storage modulus increased with TMP and HEA addition, but internal friction tanδwas opposite, indicating a transformation from pure viscous behavior to viscoelastic behavior, and enhanced interaction between particles. It was also found that the rising amplitude increased as TMP and HEA increased, which can be ascribed to the occurrence of crosslinking reaction in the emulsion.For the PUA₂ system, an obvious relaxation behavior was detected. tanδof PUA₂M was about 0.65, and a platform area was observed in the low frequency region for G’. Moreover, the intersection of G’ and G" was found at 0.35Hz, implying higher emulsive elastic. Under such circumstances, it is easy for particles to aggregate or accumulate, resulting in the decrease of emulsion stability. At the same time, strong frequency dependence was found in both PUA₂MB and PUA₂B system, and PUA₂B system own higher randomness. Furthermore, compared with PUA₂M, PUA₂MB and PUA₂B were endowed with better emulsion stability, tanδof PUA₂MB was about 1.1, tanδof PUA₂B was about 1.3.With respect to PUA₂MB system, the viscosity decreases with the increase of TMP dosage, and the thixotropy was weakened. The fluidity of this system was improved with relatively disordered structure. Furthermore, tanδof the emulsion increases from 1.1 to 1.5, while the storage modulus showed contrary tendency, and a transition from viscoelastic behavior to pure viscous behavior took place in this system, leading to the decrease of emulsion stability. When the epoxy resin（E-44） dosage was 8%, a strong frequency dependence and good fluidity were observed in the emulsion; but when E-44 dosage increase to 20%, a turning point was detected in both G’～ωand tanδ～ωcurves, which indicated that phase separation and relaxation behavior occur in the emulsion.Simultaneously, thermal stability, mechanical properties and solvent resistance of the system were studied. The results showed that thermal stability, mechanical properties and solvent resistance of the system can be enhanced to a extent with proper amount of TMP、HEA、HAM and epoxy resin, as well as CAPA with higher molecular weight. At the same time, thermal degradation kinetics was investigated. It was found that the correlation coefficients fitted by Kissinger and Flynn-Wall-Ozawa method all exceed 0.97, indicating that these two methods were suitable for PUA₁ system. It was also found that the correlation coefficients fitted by Flynn-Wall-Ozawa and Friedman method for PUA₂ system were also over 0.97. The increase of the degradation activation energy in some stage manifests the enhancement of thermal stability.In addition, the initial decomposition temperature increased from 236.31℃to 271.36℃by the introduction of E-44, the tensile strength increased from 12.7MPa to 20.8MPa, T-peel strength increased from 2.1N.mm^-1 to 8.1 N.mm^-1, while elongation at break decreased from 456% to 191%; water absorption decreased from 12.7% to 2.14%, toluene absorption reduced from 112% to 70%, the contact angle increased from 90.00°to 106.49°. However, the comprehensive properties of the system will be weakened with excess crosslinking agent.Finally, compatibility and phase behavior of the system were investigated by Dynamic Mechanical Analysis. Two peaks were observed in the the tanδ～T curve of film prepared from blend of polyurethane and epoxy resin （PU/ER） .They were -56.2℃and 130℃, respectively, indicating higher degree of phase separation. Two internal friction peaks were also found in the PUA₂ system, -29.6℃and 50.5℃, respectively. But the compatibility was improved to an extent. However the compatibility can be improved greatly with E-44 addition, and only one internal friction peak was observed at 26.6℃.更多还原