对聚醋酸乙烯乳液木材胶粘剂压缩剪切强度指标的认识和正确判定

正确认识聚醋酸乙烯乳液木材胶粘剂的类型,检测压缩剪切强度:干强度、湿强度指标的重要性,及对执行企业标准产品的正确判定。     

无机胶粘剂的套接压缩剪切强度

研究了调胶比、固化温度及固化时间、粘接表面粗糙度和配合间隙等因素对氧化铜-磷酸铝无机胶粘剂套接压缩剪切强度的影响。试验结果表明:调胶比在4~4.5g/mL,轴孔配合间隙在0.2~0.4mm,固化温度120℃左右,固化时间为3h时既能获得良好粘接性能,又能获得充裕的粘接操作时间;同时粘接表面越粗糙,套接压缩剪切强度越高。     

静电纺丝参数对聚乙酸乙烯酯纤维形貌的影响

以N,N-二甲基甲酰胺(DMF)为溶剂,采用静电纺丝法制备了聚乙酸乙烯酯(PVAc)纤维.用场发射扫描电镜观察了PVAc纤维的形貌,研究了PVAc溶液质量分数、纺丝电压、收集距离等对纤维形貌及平均直径的影响.研究结果表明,PVAc溶液质量分数和纺丝电压对纤维的形貌有显著影响,随着PVAc溶液质量分数和纺丝电压的增大,纤维的平均直径增大;收集距离对纤维形貌的影响较小.尝试采用静电纺丝法制备了炭黑和PVAc的复合纤维,以增强纤维的导电性,成为导电碳纤维,但炭黑会显著降低PVAc的成纤性,因为它会吸附溶剂DMF,使溶剂在电纺过程中不易挥发,射流不能固化成纤维.     

淀粉与乙酸乙烯酯-丙烯酸乙酯的合成与应用研究

以玉米淀粉为接枝骨架,过硫酸铵为引发剂,丙烯酸乙酯(EA)和乙酸乙烯酯(VAc)为接枝单体,进行接枝共聚,制备淀粉基木材胶粘剂.研究了反应时间、反应温度、引发剂用量以及两单体配比对淀粉与丙烯酸乙酯-乙酸乙烯酯接枝共聚反应的影响.结果表明,当引发荆浓度9.7×10-3mol/L、反应温度65℃、反应时间3h、VAc和EA体积比为6:4时,可得到较高的接枝效率和接枝率.     

聚(丙烯腈-乙酸乙烯酯)/黄粘土纳米复合材料研究

采用乳液原位插层聚合方法首先创制了聚(丙烯腈-乙酸乙烯酯)/黄粘土纳米复合材料.通过红外光谱(IR),X射线荧光(XRF),X射线衍射(XRD),能谱,扫描电镜(SEM),差热分析(DSC)等方法对该纳米复合材料分析表征,研究结果表明采用单体原位插层聚合法制备纳米复合材料的乳液聚合方法成功制备了直径在纳米级的聚(丙烯腈-乙酸乙烯酯)/黄粘土纳米颗粒.     

高含氢聚甲基硅氧烷改性聚丙烯酸酯乳液的研究--(Ⅱ)原料配比对乳液稳定性的影响

用单体乳液滴加法合成了聚甲基硅氧烷／聚丙烯酸酯复合乳液,通过对乳液的界面张力、表现粘度、乳胶的结构形态分析,探讨了高含氢聚硅氧烷用量、丙烯酸用量、乳化荆用量影响乳液稳定性的规律．结果表明,由于乳胶粒子的核壳(或草莓型)结构在一定程度上抑制了复合乳液的相分离,有利于乳液的稳定．当PHMS为单体质量的16％、AA用量为单体质量的3％、乳化剂用量为单体质量的5％时,乳液的稳定性最好．     

微胶囊Mg (OH)2的合成及其对乙烯-乙酸乙烯酯共聚物的阻燃作用

用原位聚合方法合成了以微米Mg（OH）₂粒子为芯材、交联聚脲为壁材的微胶囊Mg（OH）₂（M-Mg（OH）₂）阻燃剂,并把M-Mg（OH）₂加入到乙烯-乙酸乙烯酯共聚物（EVA）中,研究了M-Mg（OH）₂对EVA的阻燃作用。采用FTIR、SEM、热分析和酸滴定方法研究了M-Mg（OH）₂的性质,用极限氧指数（LOI）和垂直燃烧方法（UL-94）研究了M-Mg（OH）₂/EVA复合材料的阻燃性能以及酸腐蚀对M-Mg（OH）₂/EVA复合材料阻燃性能的影响。结果表明,采用原位聚合方法能够成功地在Mg（OH）₂粒子表面包覆交联聚脲壁材,得到M-Mg（OH）₂。与纯Mg（OH）₂相比,M-Mg（OH）₂的颗粒尺寸增大,热稳定性增加,在水中溶解度显著降低,在EVA基体中分散更加均匀。阻燃剂用量相同时,M-Mg（OH）₂/EVA复合材料的LOI总是比Mg（OH）₂/EVA复合材料的数值稍大。阻燃剂与EVA质量比小于135∶100时,两种复合材料的垂直燃烧级别均为V-2级,阻燃剂与EVA质量比在135∶100~150∶100之间时,前者的燃烧级别为V-0级,而后者只能达到V-2级,阻燃剂与EVA质量比超过150∶100时,两种复合材料都能达到V-0级。M-Mg（OH）₂/EVA复合材料的耐酸性比Mg（OH）₂/EVA大幅度提高,可以在酸性环境中使用。     

叔碳酸乙烯酯(VeoVaTM10)的研究进展与应用情况

叙述了叔碳酸乙烯酯(VeoVaTM10)以及共聚物涂层的优良特性,综合分析了各种叔碳酸乙烯酯合成技术的特点和进展,介绍了叔碳酸乙烯酯的应用情况,指明了行业方展中应注意的问题。     

电场极化与振荡剪切对聚偏氟乙烯β相形成的影响

通过电场极化、振荡剪切及以上两种外场同时作用于聚偏氟乙烯(PVDF)熔体,借助红外光谱仪对PVDF在外场作用下结晶形成β相的行为进行了研究。结果表明,电场极化作用能促进PVDF极性β相的形成,随着电场强度提高,β相含量逐渐增加。振荡剪切对β相的形成也有一定促进作用,β相含量随振荡频率的提高略有增加;但两种外场的同时作用,却并不表现出协同效果。     

固相剪切碾磨对聚偏氟乙烯结构和介电性能的影响

利用固相剪切碾磨技术(S~3M)制备了高β晶含量的聚偏氟乙烯(PVDF)微米级粉体,研究了PVDF粉体的结构形态、粒径及粒径分布,碾磨遍数对粉体结晶结构和介电性能的影响。结果表明,固相力化学反应器强大的挤压和剪切作用可使PVDF中α晶转变为晶,从而有效提高PVDF粉体中β晶相对含量;随碾磨遍数增加,PVDF粉体β晶含量逐渐提高,未碾磨PVDF中的β晶相对含量为37%,碾磨15遍后β晶相对含量达90%以上;同时,介电常数则由1.20增加至10.77,提高约1个数量级。固相剪切碾磨技术为高介电性能材料的制备提供了新途径。     

聚醋酸乙烯酯纳米乳液的稳定性

采用扩散过程控制的乳液聚合方法,合成聚醋酸乙烯酯纳米乳液,研究乳化剂的种类和配比及缓冲溶液、助乳化剂、聚合物等对聚醋酸乙烯酯纳米乳液稳定性的影响.研究结果表明,使用十二烷基硫酸钠(SDS)/辛基苯基聚氧乙烯基醚(OP-10)复合乳化剂体系、碳酸氢钠缓冲溶液、十六烷等助乳化剂和聚苯乙烯等能有效提高醋酸乙烯酯纳米乳液的贮存...     

单分散微米级聚醋酸乙烯酯微球的合成与表征

研究了醋酸乙烯酯在醇/水介质中以过硫酸钾-亚硫酸氢钠为氧化-还原引发剂的分散聚合.考察了分散介质的醇水比、聚合温度及搅拌速率等因素对聚合体系的稳定性、微球粒径及其分布的影响,用扫描电镜对聚合物粒子形态进行表征.研究结果表明,在异丙醇/水介质中,聚醋酸乙烯酯微球的粒径随着醇水比、聚合温度和搅拌速率的提高而增大,粒径分布变宽.在标准配方条件下,制得了单分散,粒径分别为2.0 μm、4.0 μm和5.0 μm的聚醋酸乙烯酯微球.     

分散剂对聚醋酸乙烯酯共混乳液的影响

对聚醋酸乙烯酯乳液改性进行了研究,通过与丙烯酸丁酯共聚来提高粘接强度,加入分散剂来调节乳液的黏度,改善雾化效果。具体讨论了分散剂的作用以及分散剂的用量对粘接强度和乳液性能的影响,通过透射电镜照片,比较了分散剂加入前后乳液的分散情况。结果表明,当加入适量的丙烯酸丁酯后,分散剂用量为0.05%时,具有较好的粘接效果,乳液的分散效果较好,稀释稳定性也比较好。     

Properties of Hot-Melt Extruded Theophylline Tablets Containing Poly(Vinyl Acetate)

The objectives of this study were to investigate the properties of poly(vinyl acetate) (PVAc) as a retardant polymer and to study the drug release mechanism of theophylline from matrix tablets prepared by hot-melt extrusion. A physical mixture of drug, polymer, and drug release modifiers was fed into the equipment and heated inside the barrel of the extruder. The cylindrical extrudates were either cut into tablets or ground into granules and compressed with other excipients into tablets. Due to the low glass transition temperature of the PVAc, the melt extrusion process was conducted at approximately 70°C. Theophylline was used as the model drug in this study. Theophylline was present in the extrudate in its crystalline form and was released from the tablets by diffusion. The Higuchi diffusion model and percolation theories were applied to the dissolution data to explain the drug release properties of the matrix systems. The release rate was shown to be dependent on the granule size, drug particle size, and drug loading in the tablets. Water-soluble polymers were demonstrated to be efficient release rate modifiers for this system.     

水基胶中乙酸乙烯酯测定的不确定度评定

为了评价顶空-气相色谱法测定水基胶中乙酸乙烯酯结果的准确性,建立相关数学模型,计算影响测量的各个不确定度分量,建立不确定度的评定方法。结果表明:1由标准工作溶液制备、标准工作曲线拟合、回收率实验等引入的不确定度分量所占权重较大,而试样制备、重复性所引入的不确定度占权重较小;2当水基胶样品中残留量为54.08mg/kg时,其合成标准不确定度为1.36mg/kg,扩展不确定度为2.72mg/kg(p=95%,k=2)。可以通过改变标准溶液浓度范围,使其与样品浓度值相匹配,以减小曲线拟合和回收率引入的不确定度,提高测量结果的可靠性和准确性。     

Dynamic Compressibility of Poly (Vinyl Acetate) and Its Relation to Free Volume

The complex bulk compliance (dynamic compressibility) of a commercial sample of poly (vinyl acetate), AYAT, was measured at frequencies from 50 to 1,000 cycles per second, temperatures from 0 to 100 °C, and static hydrostatic stresses from 0 to 981 bars (gage pressure) using an alternating hydrostatic stress generated and detected by piezoelectric transducers mounted in an essentially noncompliant cavity with dimensions small in comparison to a wavelength. The above temperature range was more than sufficient to cover the dispersion region in which an inflection in the storage compliance and a maximum in the loss compliance were observed. The data were reduced to functions of reduced variables using the WLF Equations extended to include static pressure with the “universal” WLF Constants and dT/dP = 0.020 °C/bar. The difference in limiting compliances at zero and infinite frequencies was larger than that predicted from the dT/dP shift using the free volume concept. A discussion is presented on possible processes that might contribute to an excessive value between limiting compliances.     

The Temperature and Frequency Dependence of the Bulk Compliance of Poly(Vinyl Acetate). A Re-Examination

Measurements are described and analyzed for the determination of thedynamic bulk compliance for Poly(vinyl acetate) [PVAc] as a function offrequency and temperature at atmospheric pressure to generate a mastercompliance curve over a total frequency range of about 12 decades.Measurements are based on the compressibility of a specimen confined to anoil-filled cavity resulting from pressurization by a piezoelectricdriver and response of a like receiver. Experimental problems addressinglimitations in resolution capability are discussed. The results arecompared with the classical measurements obtained by McKinney andBelcher over thirty years ago. Further comparison of the bulk with shearcompliance data shows that the extent of the transition ranges for thetwo material functions are comparable, but the two transitions belong todifferent time scales, that of the bulk response falling mostly into theglassy domain of the shear behavior. One concludes thus that forlinearly viscoelastic response the molecular mechanisms contributing toshear and bulk deformations have different conformational sources.     

乙酸乙烯醋密度温度校正系数的测定及其应用

通过比重瓶法和密度计法相结合的方案,测定了外售乙酸乙烯酯的密度,并根据最小二乘法的原理,运用线性回归法,求得乙酸乙烯酯密度的温度校正系数,并在外售乙酸乙烯酯的液体重量计量工作中得到应用。     

PU/P(VC-VAc)复合材料的合成及性能

在聚氨酯预聚体制备中加入氯乙烯-醋酸乙烯共聚物,通过液相熔融共混,在预聚体的固化反应中形成PU/P(VC-VA c)半互穿网络结构。探讨了氯乙烯-醋酸乙烯共聚物的质量含量、混熔温度、共混时间等因素对复合材料性能的影响,确定了最佳制备工艺条件,并用红外光谱、X射线衍射等方法对产物组成及聚集态结构进行了表征,该复合材料表面电阻系数可达1015Ω以上,体积电阻系数达1014Ω.cm以上,极大地提高了聚氨酯的介电强度。