Rheograms of cellulosic polymers from the melt flow index

Data on the variation of melt viscosity over a wide range of shear rates and temperatures are necessary in the processing of cellulosic polymers. An effective method has been proposed to estimate the viscosity vs. shear rate flow curves of a cellulosic resin at temperatures relevant to the processing conditions, from its melt flow index and glass transition temperature. The method involves the use of a master curve obtained by coalescing the rheograms of various grades in terms of a modified viscosity, η˙MFI, and a modified shear rate, γ˙/MFI. Master curves have been reported for cellulose esters and ethers.     

高熔体流动速率PP产品质量控制

生产高熔体流动速率(MFR)聚丙烯的过程中,丙烯质量、MFR、等规指数、灰分及造粒工艺条件是影响产品质量的主要因素.根据生产经验,提出了丙烯及精制合格丙烯的质量指标,分析了影响产品MFR、等规指数和灰分的控制措施:主要通过控制H2和引发剂加入量调节MFR;当n(A1)/n(Si)和n(Si)/n(Ti)分别控制在5.0和5.5左右时,产品等规指数可较好地满足质量要求;结合设备状况和工艺参数的控制,提出了保证造粒机切粒效果的方法.     

基于动态过程划分的熔融指数软测量建模

牌号切换过程是聚合反应过程节能降耗的关键环节,已有的模型往往因为质量样本较少而弱化甚至避开这一过程。因此,在之前专门针对牌号切换过程提出的三阶段分解方法的基础上,进一步面向整个生产过程,针对聚丙烯反应过程存在的同一牌号的稳定生产过程以及不同牌号间的切换过程具有不同动态过程的特性,按照不同的生产模式和生产牌号划分不同动态过程的样本,采用多模型的方法在各自的样本集上建立子模型,有针对性地把握相应的动态变化规律。为了实现多个子模型之间的切换,进一步基于反应条件和反应结果估计值构建了综合判断模型。最后,通过实际数据验证,三阶段多模型相对Kim多模型、单一模型来说,具有更好的预测结果。     

Effect of the melt flow index and melt flow rate on the thermal degradation kinetics of commercial polyolefins

In this study, several polyolefins, including different grades of polypropylene (PP), high‐density polyethylene, linear low‐density polyethylene, and low‐density polyethylene, were tested by thermogravimetric analysis (TGA), and the relationships of their melt flow index (MFI) and melt flow ratio (MFR) values to the thermogravimetry (TG) curves, differential thermogravimetry (DTG) curves, and activation energy of thermal degradation were investigated. Kinetic evaluations were performed by Friedman and Kissinger analysis methods, and the apparent activation energy values for the overall degradation of different grades of polyethylenes (PEs) and PPs were determined. We found that for the samples with lower MFIs, the thermograms shifted to higher temperatures. Meanwhile, a higher activation energy was needed for their thermal degradation. Also, for samples with higher values of MFR, as a means of molecular weight distribution, a lower activation energy was needed for their thermal degradation, and their TGA thermograms shifted to lower temperatures. The breadth of the DTG curves depended on the MFR in the PEs, although MFR had little effect on the DTG curves in the studied PP grades. Among all of the samples studied, the injection‐molding grades with medium MFIs and low MFRs degraded at higher temperatures and showed better thermal stability. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012     

基于操作域划分的聚丙烯熔融指数软测量

讨论了如何建立聚丙烯熔融指数软测量模型及模型更新问题.首先根据聚丙烯反应器中的氢气浓度划分操作域,对于每个操作域,用一种新的非线性部分最小二乘方法建立熔融指数软测量子模型,然后将各个子模型进行组合,建立全局模型.为了使模型适应过程的变化,提出一种递推非线性部分最小二乘算法,利用新获得的数据对原模型进行更新.同时基于滑动窗方法,提出模型在线估计和更新策略.实际应用结果表明,模型取得了很好的估计性能,计算精度满足工业生产的实际要求.     

高MFR的LDPE在聚烯烃色母粒中的应用

将熔体流动速率(MFR)分别为20,40,80,200g/10 min的低密度聚乙烯(LDPE)分别与MFR为7g/10 min的LDPE以质量比为1:1共混,制备颜料质量分数为30%的蓝色母粒。采用毛细管流变仪研究该系列色母粒的加工流变性能、着色性能及制品的力学性能,并与经典的聚乙烯蜡色母粒配方对比。结果表明:将高MFR的LDPE应用于聚烯烃色母粒体系,在不使用聚乙烯蜡的情况下,可制备出综合性能优良的新型色母粒。     

Gel permeation chromatography on branched polymers

In gel permeation chromatography on long-chain branched polymers, calibration with linear samples leads to incorrect results. There are, however, several ways in which the data can be treated correctly. All of them call for the use of extra experimental information, such as viscosity or light scattering data of the whole polymer or the GPC eluent. The Drott—Mendelson method, using [η] of the whole polymer and GPC data, has been employed for analysing three low density polyethylene samples. The potentialities of viscometry and light-scattering measurements in the GPC effluent have also been examined. From [η], M_w and GPC data the long-chain branching index g′ can be derived in three ways, although it should be stated that the average g′-values so found for polydisperse samples are different.     

氮气保护在PP熔体流动速率测试中的作用

通过比较在有、无氮气保护的情况下聚丙烯(PP)熔体质量流动速率和熔体体积流动速率测试值的不同,探讨了PP熔体流动速率测试过程中氮气保护的作用。无氮气情况下PP在高温发生热氧化降解,分子链断裂,熔体变稀,致使测得的熔体流动速率值偏大;使用氮气吹扫可有效保护试样,更准确地测定熔体流动速率。     

高熔体流动速率抗冲共聚聚丙烯M30RH的开发

在环管聚丙烯(PP)装置上利用非对称外给电子体技术和直接聚合法生产了高熔体流动速率抗冲共聚PP M30RH。通过工艺改造、优化操作参数、筛选后期活性更高的DQC602型催化剂、采用使PP刚韧平衡性更好的成核剂VP-101B,实现了M30RH的大批量稳定生产。与用降解法生产的国内同类PP相比,M30RH无异味、不发黄,刚韧平衡性好,在洗衣机和汽车零部件专用改性树脂等领域得到广泛应用。     

Copolymer melt rheograms from melt flow index

Available literature data on the variation of melt viscosity with shear rate are shown to coalesce together to give unique curves for each copolymer type, independent of temperature and copolymer grade, based on a normalising technique using the Melt Flow Index. The unified curves obtained are useful for estimating the flow curves of the copolymers at the temperature of interest if the Melt Flow Index of the copolymer at the specific temperature is known. Coalesced curves are presented for a number of commonly known copolymers such as acrylonitrile-butadiene-styrene, styrene-butadiene-styrene. vinyl chloride-vinyl acetate, ethylene-vinyl-acetate, polyester elastomer and an olefinic-tyype thermoplastic elastomer.     

Prediction of melt viscosity flow curves at various temperatures for some olefin polymers and copolymers

A knowledge of the variation of melt viscosity of thermoplastic polymers with both shear rate and temperature is of considerable importance to plastics engineers as well as to polymer rheologists. The actual measurement of melt viscosity at a large number of temperatures and shear rates is frequently a tedious and time-consuming task. A technique has been developed, based upon the applicability of shear rate-temperature superposition, for predicting the flow curves of a number of olefin polymers and copolymers at various temperatures from experimental data obtained at one temperature for the material in question. The experimental validity for superimposing log shear stress—log shear rate curves at different temperatures along the log shear rate axis has been established for both high and low density polyethylenes, polypropylene, polybutene-1, and poly (ethylene vinyl acetate) copolymers. The temperature dependence of the resultant shift factors has been determined for each system, and the method of utilizing this information to predict viscosities as a function of temperature and shear rate is discussed.     

高流动抗冲击共聚聚丙烯K9928的工业生产

通过分析高流动抗冲击共聚聚丙烯(PP)专用树脂的应用要求,确定PP K9928的乙烯质量分数需达到9.5%～11.5%,其橡胶相的乙烯质量分数需达到52.2%～56.3%。采用红外分析、升温淋洗分级、差示扫描量热法、凝胶渗透色谱法等分析了K9928的橡胶相含量、化学组成、熔融和结晶、长链立构规整性、相对分子质量及其分布等。结果表明:K9928的乙烯质量分数较高,达10.4%;丙烯高立构规整长序列含量较高,乙烯序列分布较为均匀;产品兼具良好的刚性和韧性。     

21．6kg负荷熔体流动速率的测定及其影响因素

采用德国Zwick/ROell熔体流动速率仪,进行熔体流动速率(MFR)的测定,考察了影响结果精密度的一些因素,如温度、切样间隔、切样位置、料筒内的加料量.指出规范操作可以获得高精密度的测试结果.     

The measurement of melt flow and melt stability

The melt flow of a plastic as measured by the standard method (ASTM D-1238) is at a high enough stress so that the flow is non-Newtonian. If the die in the plastometer is replaced by a nonstandard, tapered die of large orifice, a lower stress can be used and the flows are shown to be comparable to Newtonian viscosities measured in a cone and plate rheometer. Under these conditions the plastometer can be used as a sensitive measure of the melt stability of a plastic.     

Synthesis and characterization of well-defined comb-like branched polymers

Well-defined comb-like branched polymers having one branch in each repeating unit have been successfully synthesized by the coupling reaction of living polystyrene (PS) and polyisoprene (PI) anions with 1, 1-diphenylethenyl (DPE) groups along PS backbone prepared via atom transfer radical polymerization (ATRP) of 4-vinylbenzyloxy benzophenone (Sc) followed by Wittig reaction. The resulting comb-like branched polymers were characterized by IR, ¹H-NMR, gel permeation chromatography (GPC) and static light scattering (SLS) in detail. The effect of living chains and DPE group molar ratio on grafting efficiency was discussed. The results show the coupling reaction of living chains and DPE groups was highly effective, and the coupling efficiency can be controlled via the feed molar ratios of living chains and DPE groups. Moreover, the effect of molecular weights of backbone (PSe) and PSLi or PILi on grafting efficiency was also discussed. The results show that when excess living polymers were used, the almost quantitative grafting efficiency could be achieved. __________ Translated from Acta Polymerica Sinica (China), 2007, (3): 203–208 [译自: 高分子学报]     

Synthesis and characterization of well-defined comb-like branched polymers

Well-defined comb-like branched polymers having one branch in each repeating unit have been successfully synthesized by the coupling reaction of living polystyrene (PS) and polyisoprene (PI) anions with 1, 1-diphenylethenyl (DPE) groups along PS backbone prepared via atom transfer radical polymerization (ATRP) of 4-vinylbenzyloxy benzophenone (Sc) followed by Wittig reaction. The resulting comb-like branched polymers were characterized by IR, ¹H-NMR, gel permeation chromatography (GPC) and static light scattering (SLS) in detail. The effect of living chains and DPE group molar ratio on grafting efficiency was discussed. The results show the coupling reaction of living chains and DPE groups was highly effective, and the coupling efficiency can be controlled via the feed molar ratios of living chains and DPE groups. Moreover, the effect of molecular weights of backbone (PSe) and PSLi or PILi on grafting efficiency was also discussed. The results show that when excess living polymers were used, the almost quantitative grafting efficiency could be achieved.     

Modeling of melt electrospinning for semi-crystalline polymers

A comprehensive model for the stable jet region in electrospinning of crystallizing polymer melts has been presented. First, the conventional flow-induced crystallization (FIC) model by Ziabicki was coupled with the non-isothermal melt electrospinning model. The modeled initial jet profiles were compared to digitized experimental images of the stable Nylon-6 melt jet near the spinneret. The final jet diameters were also compared to the average thickness of collected fibers. The results were in good agreement with the flow visualization experiments for various melt temperatures and flow rates. The modeled crystallinity predictions were also in agreement with experimental data from collected fiber mats. Then, a new FIC model that can provide microstructure information, such as crystallite number density and average size, has been proposed and validated under isothermal and non-isothermal conditions in the bulk as well as in the confined geometry of the polymer melt jet in electrospinning. Nylon-6,6 was used as the model polymer in this crystallization study, and the results are in good agreement with the widely-used Ziabicki FIC model.     

聚合物熔融接枝技术研究进展

综述了聚合物熔融接枝改性影响因素的研究新进展,包括接枝单体类型、第3单体、引发剂、反应温度和时间、设备及工艺等,分析了各因素对接枝反应的接枝率、接枝效率及副反应的影响,指出了聚合物熔融接枝未来的发展之路。