拉伸工艺对聚偏氟乙烯薄膜结晶特性的影响

采用挤出法制备了PVDF片材;利用单轴拉伸工艺制备了β相含量相对较高的聚偏氟乙烯(PVDF)薄膜;采用偏光显微镜、差示扫描测试仪、X射线衍射仪等仪器,分析了拉伸过程中PVDF薄膜的形貌、结晶度以及结构变化,讨论了不同拉伸温度、不同拉伸比以及不同拉伸速率对薄膜微观结构及β相相对含量的影响。结果表明:PVDF薄膜拉伸过程中α相受外力作用转变成β相。PVDF挤出片材在拉伸温度80℃、拉伸比5倍,拉伸速率50mm/min条件下进行拉伸时,薄膜中β相的相对含量可高达57%。     

表面引发接枝聚合制备MWCNTs-g-PMMA及对PVDF微孔膜性能的影响EI北大核心CSCD

以表面引发接枝聚合制备多壁碳纳米管接枝聚甲基丙烯酸甲酯(MWCNTs-g-PMMA)。通过非溶剂致相分离(NIPS)法制备聚偏氟乙烯(PVDF)/MWCNTs-g-PMMA复合微孔膜。通过差示扫描量热和衰减全反射红外光谱测试考察了微孔膜的热性能和结晶性能,通过水接触角和水通量测试分析了膜的亲水性能,通过场发射扫描电子显微镜和力学性能测试分析了膜的微观形貌和力学性能。随着MWCNTs-g-PMMA接枝率和含量的增大,PVDF复合微孔膜的结构和性能明显改善。当MWCNTs-g-PMMA接枝率和含量分别为28. 6%和1%时,PVDF复合微孔膜的亲水性能、结晶度、β相和力学性能相对纯PVDF膜提升最为明显。     

表面引发接枝聚合制备MWCNTs-g-PMMA及对PVDF微孔膜性能的影响

以表面引发接枝聚合制备多壁碳纳米管接枝聚甲基丙烯酸甲酯(MWCNTs-g-PMMA)。通过非溶剂致相分离(NIPS)法制备聚偏氟乙烯(PVDF)/MWCNTs-g-PMMA复合微孔膜。通过差示扫描量热和衰减全反射红外光谱测试考察了微孔膜的热性能和结晶性能,通过水接触角和水通量测试分析了膜的亲水性能,通过场发射扫描电子显微镜和力学性能测试分析了膜的微观形貌和力学性能。随着MWCNTs-g-PMMA接枝率和含量的增大,PVDF复合微孔膜的结构和性能明显改善。当MWCNTs-g-PMMA接枝率和含量分别为28. 6%和1%时,PVDF复合微孔膜的亲水性能、结晶度、β相和力学性能相对纯PVDF膜提升最为明显。     

高温拉伸制备交联聚乙烯微孔膜的探索研究

采用热拉伸-高温退火-冷拉的拉伸工艺制备了交联聚乙烯微孔膜,考察了交联聚乙烯的交联度、拉伸温度、退火温度和冷拉等工艺条件对交联聚乙烯微孔膜成孔性能的影响,并对成孔过程和机理进行了探讨.交联聚乙烯的交联度显著影响成孔性能,随着交联度的增加,成孔性增加.拉伸温度在90～120℃时,膜片基本由纤维状晶构成.拉伸温度升至130℃,并在此温度进行高温退火处理,膜片开始出现细缝状微孔.施加冷拉可以调控细缝状微孔形态演变,进一步被拉伸成圆形或椭圆洞状微孔.本文所用拉伸工艺为制备高性能聚乙烯微孔膜提供了一种新的思路,有助于开发自主知识产权的聚乙烯微孔膜技术,突破锂离子电池隔膜等高端聚乙烯微孔膜的国外技术垄断.     

退火温度对PVDF薄膜结构的影响及其性能研究

通过拉伸工艺,在不同的退火温度下,制备了PVDF薄膜,用XRD分析了退火温度对拉伸PVDF薄膜β相含量的影响.实验结果表明,退火温度为120℃时,β相的含量达到最大值,薄膜呈现明显的铁电性,矫顽场接近1.0mV/cm,电位移D为5μC/cm2.在25℃时,薄膜的热释电系数p为0.3×10-8C/cm2·K.     

PVDF/PS共混微孔膜的制备

将聚偏氟乙烯和聚砜共混,通过溶胶一凝胶相转化法研制高孔隙率微孔膜．考察了聚合物浓度、PVDF／PS配比、溶剂种类和组成、添加剂浓度、凝胶浴温度和组成、溶剂挥发时间和热处理温度对膜孔径和孔隙率的影响．实验发现：使用DMF／DMAc混合溶剂可提高膜孔径和孔隙率;随LiCl含量的增加,膜孔径和孔隙率逐步增加;凝胶浴温度对膜的水通量没有太大的影响,但凝胶浴组成对膜性能有很大的影响;延长溶刺挥发时间,导致平均孔径减小．选择适当的膜液组成,可制得孔径为0.2～1.0μm,孔隙率达到90％以上的PVDF／PS共混微孔膜,而且共混膜的孔隙率比单组分PVDF膜有大幅度的提高．说明共混化是一种改善PVDF膜性能的有效方法,具有极好的实用开发价值,     

光引发点击化学接枝聚合制备多壁碳纳米管接枝聚(N-异丙基丙烯酰胺)及对聚偏氟乙烯超滤膜性能的影响

以紫外光引发的巯基-炔基绿色点击化学反应接枝聚合制备多壁碳纳米管接枝聚(N-异丙基丙烯酰胺)(MWCNTs-g-PNIPAM),通过改变接枝时间得到了不同接枝率的MWCNTs-g-PNIPAM,并通过非溶剂致相分离法(NIPS)制备了聚偏氟乙烯(PVDF)/MWCNTs-g-PNIPAM复合超滤膜。通过差示扫描量热分析和红外光谱、水接触角和水通量、场发射电子显微镜和机械拉伸试验研究了MWCNTs对PVDF超滤膜的结晶度和β相结晶含量、亲水性能、表面和断面形貌、拉伸强度和断裂伸长率的影响。结果表明,无金属催化剂的光引发点击化学在接枝时间为3 h时,PNIPAM的最大接枝率为9.76%,改善了碳纳米管与PVDF的界面结合力,使碳纳米管能够满足亲水性的同时还能在PVDF基体中良好分散。其中,β相结晶含量由纯PVDF膜的68.64%提升至95.32%,结晶度由46.30%提升至57.95%,拉伸强度与断裂伸长率分别由5.37 MPa和53.2%提升至7.85 MPa和54.32%,水接触角由95°降至69.75°,水通量由3.18 LMH提升至21.68 LMH。     

PVDF/HCEC共混微孔膜研究

采用S/L相转化法制备了PVDF/HCEC共混微孔膜。讨论了共混比、固含量、添加剂对膜性能的影响。结果表明,固含量为15%,w(PVDF)∶w(HCEC)=8∶2的无水LiCl为成孔剂时共混膜在0.1MPa下的纯水通量为157.88L.m-2.h-1,对卵清蛋白的截留率为91.38%。对共混膜的化学稳定性和抗蛋白质污染性与纯PVDF膜进行了对比测试,共混膜的耐酸、耐氧化性较纯PVDF膜好,耐碱性能较差。     

天然纤维粉体对聚偏氟乙烯多孔膜结构与性能的影响

采用溶液相转化法制备了羽绒粉体/聚偏氟乙烯（PVDF）和苎麻粉体/PVDF复合微孔膜,对膜结构和性能进行了分析和测试。结果显示苎麻粉体/PVDF复合膜、羽绒粉体/PVDF复合膜、纯PVDF膜的形态一致,均为致密皮层和多孔亚层,孔隙率和水通量依次降低,结晶度依次增加;但膜的吸水率按照羽绒粉体/PVDF复合膜、苎麻粉体/PVDF复合膜、纯PVDF膜依次下降;这说明复合膜水通量主要受孔隙率的影响,而膜吸水率主要受纤维粉体吸水性大小的影响。膜力学性能测试显示加入粉体之后,PVDF膜的强度增加,断裂伸长率有所下降。     

MMA-co-AA两亲性共聚物对聚偏氟乙烯膜性能及微观结构的影响

以甲基丙烯酸甲酯(MMA)和丙烯酸(AA)为单体,偶氮二异丁腈(AIBN)为引发剂,采用自由基共聚合成了两亲性无规共聚物MMA-co-AA,并将其与聚偏二氟乙烯(PVDF)共混,通过浸没沉淀相转换法制备了PVDF共混膜。利用X射线衍射(XRD)、差示扫描量热法(DSC)、扫描电子显微镜(SEM)以及水接触角等对共混膜的性能与微观结构进行了研究。结果表明,N,N-二甲基甲酰胺(DMF)溶剂以及两亲性共聚物MMA-co-AA有利于提高PVDF的结晶度,能促进β-PVDF晶型的形成。同时,MMA-co-AA能引发PVDF共混膜表面出现微孔,随着两亲性共聚物含量的不断增加,共混膜的接触角逐渐减小,表面亲水性得到改善。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。