长支链型高熔体强度聚丙烯流变性能的研究——剪切流变

通过辐照法制备了长支链型高熔体强度聚丙烯（LCB-HMSPP），采用高级流变扩展系统（ARES）表征了其熔体黏弹性，采用毛细管流变仪研究了其在高剪切速率下的流变行为。讨论了敏化剂用量、超高相对分子质量聚乙烯（PE-UHMW）对PP熔体黏弹性、流动曲线和黏流活化能的影响。动态剪切流变数据表明，辐照改性制备的LCBHMSPP具有较好的熔体黏弹性，并且其熔体弹性随敏化剂用量的增加而增强，表现在低频端剪切储能模量明显提高，内耗正切变小，零切黏度增大，特征松弛时间变长；辐照过程中添加极少量PE-UHMW也可提高PP的熔体黏弹性。静态毛细管剪切流变测试表明，线形PP和长支链PP的流动曲线较相似，LCB-HMSPP的黏流活化能较线形PP有显著提高，其剪切黏度具有较高的温度敏感性。     

梳状聚合物二醇的结构与流变性能关系

制备了一系列支链结构不同的梳状聚合物二元醇(CPD),并用FTIR对其结构进行了表征。着重研究了CPD梳状支链结构和温度对其流变性能的影响,并测定了CPD的流动活化能ΔE_η0。研究发现,梳状支链的长度增加和极性增大,CPD的黏度增加,出现剪切变稀行为的剪切速率降低。CPD的η-γ曲线出现两次剪切变稀行为,在两次行为之间存在一平台,这一平台随温度增加向高剪切速率方向移动,并逐渐变短,最后在50℃时消失。随梳状支链长度增加和极性增大,CPD的流动活化能ΔE_η0增加。     

短支链PP对长支链PP加工流变行为的影响及机理

研究了线型等规聚丙烯(iPP)和短支链聚丙烯(SCBPP)的引入对长支链聚丙烯(LCBPP)加工流变行为的影响。结果表明:将线型iPP引入LCBPP相当于降低了长支链分子在共混体系中的含量;而当SCBPP引入LCBPP时,由于短支链的隔离作用会使LCBPP分子链间距增大,并且阻碍了LCBPP长支链分子间的缠结,而未缠结的长支链则起到类似增塑剂的作用。因此,线型iPP和SCBPP的引入均会使LCBPP的剪切黏度降低,其中在用量相同的条件下,SCBPP对LCBPP剪切黏度的降低效果明显优于线型iPP。     

氮氧稳定自由基聚合与原子转移自由基聚合结合制备梳形支化聚苯乙烯的反应行为

为了实现对梳形支化聚苯乙烯结构的精确控制,采用核磁共振(1H-NMR)、多角度激光散射联用凝胶渗透色谱(GPC-MALLS)和气相色谱(GC)表征聚合物结构和观察反应动力学,研究了苯乙烯(St)与对氯甲基苯乙烯(p-CMS)氮氧稳定自由基共聚合(NMP)制备P(St-co-CMS)的反应行为以及以P(St-co-CMS)为大分子引发剂引发苯乙烯原子转移自由基聚合(ATRP)制备梳形支化聚苯乙烯的反应行为。结果表明,在反应温度为130℃,苯甲醚为溶剂,BPO/HTEMPO为引发体系引发St与p-CMS的氮氧稳定自由基共聚合过程中,St和p-CMS的转化速率接近,p-CMS按其在单体混合物中的比例均匀进入共聚物分子链,共聚物分子量随转化率增加线性增大,P(St-co-CMS)的组成和分子量可控。在反应温度为100℃,苯甲醚为溶剂,CuCl/PMDETA为催化体系,P(St-co-CMS)为引发剂引发St的ATRP反应体系中,氯甲基全部用于引发St聚合,形成梳形支链;低转化率阶段,聚合物分子量随转化率增加呈线性增长,分子量分布较窄;在较高转化率下,聚合体系发生交联,形成凝胶;P(St-co-CMS)中p-CMS含量越高,凝胶越早发生。通过选择不同p-CMS含量的P(St-co-CMS)为大分子引发剂以及将苯乙烯转化率控制在一定范围,制得了主链分子量在25000~30000、支链数目在6.3~42.6、支链分子量在6000~17000的一系列梳形支化PS。     

支化结构对树枝状聚合物溶液剪切前后流变性能的影响

采用吴茵混调器模拟聚合物在其配制、输送、注入中的机械剪切作用,研究了不同支化程度对剪切前后的驱油用树枝状聚合物溶液的流变性能的影响。首先制备了3种不同支化程度的树枝状聚合物,研究了剪切前后的树枝状聚合物的分子链粒径分布和分子量大小,然后研究了不同因素对树枝状聚合物流变性能的影响并考察了树枝状聚合物溶液的黏弹性能,最后结合环境扫描电镜分析支化结构对剪切前后树枝状聚合物溶液的流变性能的影响。结果表明：支化程度高的树枝状聚合物具有更大的流体力学半径和分子量,受环境影响较小;树枝状聚合物溶液呈现假塑性流体特征,支化程度越高,剪切前后的聚合物溶液幂律指数n越小、稠度系数K越大;支化程度高的树枝状聚合物溶液支链间越容易发生缠结,形成致密、多层的空间网状结构,致使剪切前后的聚合物溶液的流变性能越好。     

PET长支链的表征及其对流变和结晶性能的影响

本工作利用多检测器凝胶渗透色谱仪表征了长链支化聚对苯二甲酸乙二酯(PET),确定了PET的长链支化结构和支化参数(BRs).通过旋转流变仪和差示扫描量热仪分析含有少量长支链的PET,发现当重均分子量相同时,BRs为0.94的长链支化PET熔体的零剪切黏度提高约60％,且长链支化PET具有更高的储能模量和更明显的剪切变稀...     

氢氧化镁阻燃EVAC的流变性能研究

采用熔融共混法制备了Mg(OH)2阻燃乙烯-乙酸乙烯酯塑料(EVAC),并采用毛细管流变仪对其流变性能进行了研究。讨论了温度、剪切速率和剪切应力对熔体表观黏度的影响;研究了黏流活化能与剪切速率的变化规律。结果表明,熔体的表观黏度随温度的升高而降低,随剪切速率和剪切应力的增大而减小;黏流活化能随剪切速率的增大而降低。其非牛顿指数小于1,说明Mg(OH)2阻燃EVAC为假塑性流体。当剪切应力无限小时,由Spencer-Dillon公式外推得到阻燃EVAC的零切黏度。     

1,2-聚丁二烯接枝丁苯共聚物的流变性能

用双筒毛细管流变仪研究了丁苯共聚物支链含量不同的3种接枝1,2-聚丁二烯的流变性能,并与线型1,2-聚丁二烯进行了比较。结果表明,丁苯共聚物的接枝使得1,2-聚丁二烯的数均分子量减小,重均分子量增大,分子量分布变宽;接枝前后1,2-聚丁二烯的1,2-结构摩尔分数均大于80%,都属于高乙烯基聚丁二烯。在80～120℃内,接枝前后1,2-聚丁二烯的表观黏度均随温度的升高而降低,接枝后的黏流活化能明显增大;随丁苯共聚物接枝量的增加,接枝橡胶的黏流活化能逐渐减小,黏温敏感性减弱。丁苯共聚物的接枝对1,2-聚丁二烯黏度剪切敏感性的影响比较复杂,在150～3 000 s-1的剪切速率内,接枝前后1,2-聚丁二烯的表观黏度均随剪切速率的增加而降低;线型及接枝质量分数为5%的1,2-聚丁二烯的非牛顿指数明显降低,接枝质量分数为1%的非牛顿指数增大,更接近牛顿流体行为,而接枝质量分数为7%的非牛顿指数基本不变。在温度为80℃和100℃时,于相同的剪切速率下,随着丁苯共聚物接枝量的增加,3种接枝橡胶的表观黏度有先降低后升高的趋势,其中接枝质量分数为7%的1,2-聚丁二烯的表观黏度最大。     

碱溶性羟乙基纤维素在复合溶剂体系中的流变性能

使用平行板流变仪,以氢氧化钠/硫脲/尿素/水溶液作为碱溶性羟乙基纤维素(HEC)的复合溶剂,研究了HEC在该溶剂体系中的流变性能,并考察了剪切速率、温度及溶液浓度对溶液的非牛顿指数、结构黏度指数及黏流活化能的影响。结果表明:溶液属于切力变稀型假塑性流体,随溶液温度下降及浓度增加,溶液的表观黏度和结构黏度指数增大,非牛顿性增强;该溶液的黏流活化能随着剪切速率的增加而下降。     

热塑性淀粉/生物降解共聚酯共混物流变性能的研究

研究了热塑性淀粉(TPS)以及TPS/生物降解共聚酯共混物的流变行为,讨论了增翅剂用量、共聚酯用量和熔体温度对流变行为的影响.研究表明,TPS和TPS/生物降解共聚酯共混物熔体呈明显的非牛顿特征;增塑剂的使用可以大幅度改善淀粉的塑化行为,通过调节增塑剂用量,可以在一定范围内控制TPS的流变行为.对于共聚酯和TPS的共混体系而言,在共聚酯用量较低时,流动过程中TPS分子链受到较强剪切力作用而发生断链,共混物熔体表观黏度降低.在共聚酯用量较高时,共混物熔体黏度则表现出对温度有较大的敏感性.TPS的黏流活化能较小,TPS/生物降解共聚酯共混物的黏流活化能随共聚酯用量的增加迅速增大,且随剪切速率的增加迅速降低.     

管道支管连接补强及计算

管道设计中,支管连接方式的确定为管道设计重要内容。主要探讨在不能选用标准管件、需要通过焊接支管连接时,焊接支管补强形式的确定及补强面积计算。同时综合ASME、GB、SH标准对管道补强的相关规定,对焊接支管连接及补强计算中需要考虑的其他因素做了阐述。     

Influence of the short‐chain branch length on the calibration of temperature rising elution fractionation systems

The effects of short‐chain branch (SCB) length on the calibration of temperature rising elution fractionation (TREF) were examined. Samples of ethylene–hexene, ethylene–octene, and a novel polyolefin produced using Eastman Chemical Company's Gavilan catalyst technology were used to prepare TREF calibration curves. Preparative TREF was used to collect fractions of the materials based on their crystallizability, and the branching frequencies of the fractions were determined by NMR. Calibration curves were generated by plotting the branching frequency as a function of the TREF elution temperature. The results indicate that the calibration curves shift to lower TREF elution temperatures as the length of the SCB increases from methyl to butyl to hexyl. Other factors that may contribute to this shift include chain microstructural differences from variations in catalyst structure and process conditions. The shift can be decreased by plotting the data in “number of branches per 1000 backbone carbons” versus TREF elution temperature instead of the more traditional “number of branches per 1000 total carbons.” These data indicate that the branch type must be known a priori to calculate SCB averages and SCB distributions and that unique calibration curves exist for copolymers made using different α‐olefin comonomers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 722–728, 2003     

Proton exchange membrane bearing entangled structure: Sulfonated poly(ether ether ketone)/bismaleimide hyperbranch

Physical cross-linking of sulfonated poly(ether ether ketones) sPEEKs with hyper-branched bismaleimide oligomer (modified bismaleimide, mBMI) leads to densely packed polymer. Different curing conditions on the two sPEEK samples containing Bismaleimide (BMI) monomer and modified Bismaleimide oligomers (mBMI) mole ratios of 70:30 (mBMI(30)) and 2:98 (mBMI(98)) are present. As the amount of BMI monomer increases, the branched structure and their degree of entanglement with sPEEK polymer matrix also increase. More rigid and more compact membrane is found in the case of mBMI(30). In contrast, relatively loose entangled network is found for mBMI(98) sample where the mBMI unit remains far apart and mostly un-connected, until high concentration of mBMI(98) is present. The branched structure and their degree of entanglement with sPEEK polymer matrix increases with longer curing time. The results shows physical cross-linking with highly branched mBMI is effective in reducing water uptake, lower methanol permabiity with reduced sPEEK membrane swelling. Except for heavily entangled sample (sPEEK/mBMI(30)) annealed for 20 h, all membranes displayed fair proton conductivity above 10⁻² S/cm at room temperature. Methanol permeability is also substantially reduced to 1.39 × 10⁻⁷ cm²/s for sPEEK/15% mBMI(98). The DMFC single cell assembled by the sPEEK/20% mBMI(98) membrane (59 μm thickness) displayed the highest OCV of 839 mV with a power density reaching 30 mW/cm² at 60 °C. This value is higher than that using sPEEK membrane alone.     

Controlling melt reactions during preparing long chain branched polypropylene using copper N,N-dimethyldithiocarbamate

Effect of copper N,N-dimethyldithiocarbamate (CDD) on melt reactions during preparing long chain branched polypropylenes (LCB-PP) via free radical grafting was studied. The structure and rheological properties of the modified PPs were characterized. The results showed that CDD could efficiently control two side reactions, i.e. degradation of PP backbone and homopolymerization of multifunctional monomer (trimethylol propane triacrylate (TMPTA)) in the presence of peroxide. Meanwhile the addition of CDD also increased the efficiency of forming LCB structure. The reaction between CDD and active free radicals (carbon centered and alkoxy species) led to forming in situ dithiocarbamate radicals, which cannot attack PP backbone and are weaker initiator for TMPTA. The resultant dithiocarbamate radicals could react with the PP macroradicals and the acrylic radicals reversibly, which prolong the life time of PP macroradical and increase the reaction probability between macroradicals. The obtained LCB-PP showed high melt strength.     

Characterization of structure of comblike polymer by pyrolysis gas chromatography and Fourier transform infrared spectroscopy

The characterization of branching in comblike polymers using high‐resolution pyrolysis gas chromatography (HRPGC) and Fourier transform infrared spectroscopy (FTIR) is investigated. The branching type can be identified from characteristic peaks of monomer and a group of dimers in pyrograms derived from α‐ and β‐scission of branched atoms. By resolving the overlapping bands between 2800–3000 cm^?1, the relative absorbance of CH₂ can be used to calculate the average branch length L. This method is helpful in evaluating the property of drag‐reduction agents. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 359–363, 2001     

塑料三通管挤胀成型过程的运动学研究

通过对三通管挤胀成型过程中的不同变形部位进行分区建立坐标系，确定了不同区域内材料塑料性流动的速度场分布。     

隔热型材滚压复合的力学探讨及应用

分析了常见的穿条隔热型材滚压复合过程中的隔热条以及铝合金型材的受力情况,对隔热槽口而言,采用闭环公差,优化开齿质量等是生产优质隔热型材的必要条件。     

管件三通塑性极限载荷估算式研究进展

三通几何结构和受载较复杂,是管系中的薄弱环节,准确预测三通的塑性极限载荷,成为管道完整性评估的关键技术。综述了国内外三通塑性极限载荷的研究现状,对今后三通塑性极限载荷的研究和安全评定标准的制定具有一定的指导意义。     

外弯矩作用下焊接支管应力增大系数

通过大量的有限元计算,得出了关于焊接支管之平面内、外应力增大系数,弥补了在d/D>0.75时,ASMEB31.3规范应力值偏小问题,为管道应力分析结果的真实、可靠提供少许帮助。     

关于压力管道支管补强计算的探讨

比较了GB 50316-2000(2008年版)、GB/T 20801和ASME B31.3-2008中关于压力管道支管补强计算的相关规定,论述了等面积补强法的理论依据,说明GB/T 20801和ASME B31.3中认为等面积补强法是支管连接的最低要求,对其适用条件的规定是必要的.基于"当主管直径/厚度比Dh/Th≥...