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。     

用熔体流动指数仪研究三元乙丙橡胶熔体的流变性能

用熔体流动指数仪研究了三元乙丙橡胶(EPDM)熔体的流变性能,建立了实验条件下EPDM的熔体流动指数(MFI)与流变参数、门尼黏度之间的关系。结果表明,EPDM 70的非牛顿指数和活化能比EPDM 80的大,2种橡胶熔体的剪切速率与MFI成线性关系,剪切黏度与MFI成乘幂关系。     

不同复合助剂对聚丙烯薄壁注塑料性能的影响

为提高聚丙烯薄壁注塑料的加工性能,对不同复合助剂在聚丙烯薄壁注塑料中的应用进行了实验.分别采用DSC3500型差示扫描量热仪、CM-5型测色计、GT-7200-MIA型熔体流动速率测定仪等设备对不同复合助剂应用配方的结晶温度、结晶度、黄变指数、熔体流动速率、力学性能、雾度等指标进行表征.结果表明:含抗氧剂626和水滑石...     

“不好的”熔体流动速率测试结果告诉我们什么?答案很多

树脂的熔体流动速率(MFR),也被称为熔体流动指数(MFI),是一种塑料行业常见的材料性能测试。测试用来测定树脂在特定剪切应力及温度下的熔体流动性能(单位:g/10min)(与施加载荷有关)。该测试由挤压塑度计进行,人们常称其为"熔体流动速率测试仪"(旧称"熔融指数测试仪")。它用于测试天然的、     

熔体流动速率仪的发展与应用

介绍了我国熔体流动速率仪的发展现状,阐述了熔体流动速率仪在热塑性塑料质量流动速率和体积流动速率试验、熔体密度测量、流动比测量、流变曲线测绘中的应用。     

两种医用聚乳酸的流变性能研究

系统研究了两种聚乳酸（PLLA和PDLLA）在不同温度和不同剪切速率下的毛细管流变性能,结果表明：聚乳酸熔体呈现剪切变稀型现象,具有非牛顿流体的流动特征;随着温度升高,两种聚乳酸熔体的非牛顿指数增大,牛顿性略有增加;在温度和剪切速率相同的情况下,PDLLA的非牛顿指数略大于PuA;两种聚乳酸的结构粘度指数△η介于0．9～1．4,随熔体温度的增高,△η减小,纺丝加工性能得到改善。     

线性双峰聚乙烯／低密度聚乙烯共混物的流变行为与力学性能

研究了线性双峰聚乙烯（LBPE）与低密度聚乙烯（LDPE）共混物溶体的流变行为，讨论了共混物的组成，剪切应力和剪切速率以及温度对熔体流变行为，熔体粘度的影响，测定了不同配比熔体的非牛顿指数（n)，熔体流动速率（MFR）及力学性能，为双峰聚乙烯的加工和使用提供了理论依据。     

聚丙稀(PP)/纳米SiO2复合材料的流变行为、力学性能和相态学研究

以毛细管流变仪研究了PP/纳米SiO2复合材料熔体的流变行为,讨论了复合材料的组成、剪切应力和剪切速率对熔体流变行为、熔体粘度的影响,测定了熔体的非牛顿指数、熔体流动速率和膨胀比。结果表明:PP/纳米SiO2复合材料属假塑性流体,其熔体粘度随纳米SiO2含量的增加而增大,非牛顿指数和熔体流动速率均随纳米SiO2含量的增加而减小;在恒定剪切应力下,膨胀比随纳米SiO2含量的增加而减小。对复合材料的力学性能测试结果表明:纳米SiO2对PP的力学性能有显著改善作用。以扫描电镜和偏光显微镜研究了复合材料的相态学,其结果进一步证明了纳米SiO2对PP具有增强增韧作用。     

体积法熔流仪的检定及影响因素分析

介绍体积法熔体流动速率仪的检定方案。采用熔体流动速率仪与密度天平相结合,使用经中国计量科学研究院认证的聚乙烯标准物质进行测量,将熔体体积流动速率(MVR)向熔体质量流动速率(MFR)换算,以满足JJG 878-1994《熔体流动速率仪检定规程》的技术要求,并从熔体流动速率仪及密度天平两方面对测试过程中加料量、切样间隔、样品形状、测试过程四个影响因素进行简要分析。     

LDPE／LLDPE共混物熔体挤出流动性的研究

考察了毛细管挤出过程中LDPE/LLDPE共混物熔体的流动行为及其影响因素。发现熔体的末端压力损失△P_(end)随LDPE的质量分数Φ_(LD)的增加而增大,并与表现剪切速率γ成指数律关系;熔体的剪切流动大体上服从指数律;熔体粘度对剪切速率的敏感性随着Φ_(LD)的增加而增强,而对温度的依赖关系可由形如Arrhenius方程的表达式描述。     

Thermal degradation of polypropylene in a capillary rheometer

Melt viscosity of a polypropylene (PP) resin was measured in a capillary rheometer between 220 and 260°C. The melt viscosity showed a power law behavior with strong shear rate dependence. The effects of temperature and shear rate on the degradation were studied in the rheometer by heating at 260 and 280°C, and extruding at shear rates up to 10000 sec ?1 . Melt flow index (MFI) of samples after shearing and heating treatment was measured to characterize the molecular weight change. An increase in MFI was found for PP sheared at high temperature. Heating for longer time also increased MFI. Increase of shear rate had a small effect on increasing MFI at 260°C but produced a larger effect at 280°C. A constant increment in MFI was observed in PP subjected to high temperature processing and was attributed to degradation due to oxygenated products.     

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.     

高效催化剂对聚丙烯树脂分子量、分子量分布及纺丝性能的影响

燕山石化公司化纤地毯厂在采用高效催化剂前、后生产的新、老3702聚丙烯树脂(熔体流动指数MFI均为12—15)纺丝时,纺丝温度和纤维性能发生了显著变化。研究结果表明,这种差别主要是由于它们的分子量分布不同所引起的。新3702由于分子量分布较窄,与老3702聚丙烯树脂相比,即使在相同的MFI条件下,粘均分子量和零切变粘度也是较低的,因而纺丝温度也低。在工业生产中表明,除测定MFI外还应测定聚丙烯熔体在230℃下的零切变速率粘度,这对指导生产,能提供可靠依据。采用高效催化剂生产MFI为7—11的新3602牌号聚丙烯在燕山石化公司化纤地毯厂试纺中,废丝率下降了7%以上,成丝质量得到了提高。     

Polyethylene dispersions in bitumen: The effects of the polymer structural parameters

Polymer‐modified bitumens are very important to the transportation sector. Polyethylene is one of the most used polymers in bitumen modification. The effects of the structural parameters of polyethylene on its dispersion in bitumen and the performance of the resulting polymer‐modified bitumens were studied. With the addition of different polyethylenes to bitumen, the performance of bitumen at high temperatures increased as the polymer melt‐flow index (MFI) decreased. At low temperatures, the performance of bitumen decreased as the polyethylene MFI decreased. Furthermore, a decrease in the polyethylene MFI intensified its dispersion instability. At very low MFIs, the dispersions were unstable, even under the very high shear forces applied by a double mixer. Moreover, changes in the polyethylene MFI did not improve the dispersion stability at an elevated temperature (165°C). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3183–3190, 2003     

凝胶丁腈共聚弹性体增韧聚甲醛的加工流变行为及力学性能

研究了聚甲醛(POM)/凝胶丁腈共聚弹性体(GNBE)共混物的熔体流动指数(MFI)、高压毛细管流变行为和力学性能。结果表明,共混物MFI随GNBE用量的增加下降较大。聚酰胺(PA)对POM/GNBE共混体系的MFI影响较小,而热塑性酚醛树脂(PFR)的影响显著。当PFR的质量份为4时,POM共混物的MFI达最小值(0.053g/min),约为未加增容剂POM共混物MFI的1/6。随着剪切速率的提高,共混物剪切黏度迅速与POM接近。这种黏度变化行为说明共混物比GNBE对剪切速率更敏感,共混物的黏度受POM的影响较大。随着剪切速率的提高,POM与GNBE的黏度比迅速减小,并接近1,说明POM和GNBE在高剪切速率下共混时,GNBE的液滴能够在POM连续相中分散达到最小。含20份GNBE的POM共混物在高剪切速率下的熔体表观黏度与POM相当;在PFR质量份为6时,POM共混物的缺口冲击强度达到21.6kJ/m2,超过了GNBE质量份为40的POM共混物。当PFR质量份为4时,共混物的缺口冲击强度为对应的不加增容剂共混物的冲击强度的2倍多,扯断伸长率提高了55.4%。     

The hierarchy structure and orientation of high density polyethylene obtained via dynamic packing injection molding

The evaluation of microstructure and crystal morphology in injected-molded bar becomes much complicated because of the existence of a shear gradient and a temperature gradient from the skin to the core of the samples. To understand the relationship between shear rate-molecular weight and oriented structure of injection molded bar, in this work, the hierarchy structure and the effect of molecular weight on the formation of shish-kebab structure were investigated by examining the lamellar structure of injection molded samples of high density polyethylene (HDPE) with different melt flow index (MFI), layer by layer, along the sample thickness. To enhance the shear effect, so-called dynamic packing injection molding (DPIM), in which the melt is firstly injected into the mold and then forced to move repeatedly in a chamber by two pistons that move reversibly with the same frequency as the solidification progressively occurs from the mold wall to the molding core part, was used to obtain the molded bar. Furthermore, a small amount of ultra-high molecular weight polyethylene (UHMWPE) was added into HDPE to explore the effect of UHMWPE on the crystal morphology and orientation. Our results indicated (1) that the overall orientation in the molded bar increased with decreased MFI, and a small amount of UHMWPE could enhance substantially HDPE orientation; (2) at the skin, there existed intertwined lamellae constituting an interlocked lamellar assembly, a typical shish-kebab structure gradually developed from the subskin-layer to the core, with increased shish content toward the center, but in the core was a spherulite-like superstructure with randomly distributed lamellae; (3) UHMWPE played an important role not only in the formation of shish, but also in the transformation from spherulite to shish-kebab oriented structure for HDPE with a low molecular weight (high MFI).     

Effect of nanosize CaSO4 and Ca3(PO4)2 particles on the rheological behavior of polypropylene and its simulation with a mathematical model

Nanosize CaSO₄ and Ca₃(PO₄)₂ fillers were synthesized with an in situ deposition technique, and their sizes were confirmed by X‐ray diffraction. CaSO₄ was prepared in 12‐ and 22‐nm sizes, and Ca₃(PO₄)₂ was prepared in 13‐ and 24‐nm sizes. Experimental variables, such as torque, shear viscosity, shear stress, and shear rate, of the nanofilled polypropylene (PP) composites were measured with torque rheometry and melt flow index (MFI) measurements. Torque versus time, shear viscosity versus weight percentage, and MFI versus weight percentage were plotted to investigate the rheological behavior of the nanofilled composites. The Cross–Williamson (CW) model was simulated with the MATLAB simulation package to study the thinning behavior of the PP composites. The experimental results show a decrease in the shear viscosity with increasing weight percentage of filler. Shear thinning in the molten PP composites was comparatively greater with decreasing nanosize of CaSO₄ and Ca₃(PO₄)₂. This kind of behavior was confirmed by the N parameter as determined from the CW model. The simulation of experimental data also showed similar trends as the theoretical data. At a certain stage, a violation of theoretical data was observed. This was because of practical limitations of the equation, as the equation does not include consideration of the physical situation of chain entanglements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4190–4196, 2006     

Atomistic simulations for adsorption and separation of flue gas in MFI zeolite and MFI/MCM-41 micro/mesoporous composite

Adsorption of pure CO₂ and N₂ and separation of CO₂/N₂ mixture in MFI zeolite and MFI/MCM-41 micro/mesoporous composite have been studied by using atomistic simulations. Fully atomistic models of MFI and MFI/MCM-41 are constructed and characterized. A bimodal pore size distribution is observed in MFI/MCM-41 from simulated small- and broad-angle X-ray diffraction patterns. The density of MFI/MCM-41 is lower than MFI, while its free volume and specific surface area are greater than MFI due to the presence of mesopores. CO₂ is preferentially adsorbed than N₂, and thus, the loading and isosteric heat of CO₂ are greater than N₂ in both MFI and MFI/MCM-41. CO₂ isotherm in MFI/MCM-41 is similar to that in MFI at low pressures, but resembles that in MCM-41 at high pressures. N₂ shows similar amount of loading in MFI, MCM-41 and MFI/MCM-41. The selectivity of CO₂ over N₂ in the three adsorbents decreases in the order of MFI>MFI/MCM-41>MCM-41. With increasing pressure, the selectivity increases in MFI and MFI/MCM-41, but decreases in MCM-41. The self-diffusivity of CO₂ and N₂ in MFI decreases as loading increases, while in MFI/MCM-41, it first increases and then drops.     

Studies on rheology and morphology of POE/PP thermoplastic elastomer dynamically crosslinked by peroxide

An ethylene‐octene copolymer (POE)/polypropylene (PP) thermoplastic elastomer was prepared through dynamically crosslinking by 2,5‐dimethyl‐2,5‐dilbuty (Peroxy) hexane (DHBP). The effects of DHBP concentration, POE/PP ratio, melt flow index (MFI) of PP, and mixer rotation on rheology and morphology of the thermoplastic elastomer were studied. The results showed that with increasing DHBP concentration or POE content, the size of crosslinked particles as well as the melt viscosity increased. Furthermore, agglomerates or a network structure formed as the size of crosslinked particles increased. The melt viscosity also increased as MFI of PP decreased, while the size of crosslinked particles decreased under the same condition. Research on the morphology of dynamically crosslinked POE/PP thermoplastic elastomer flowing through a capillary rheometer at different shear rates show that the reprocessing had little effect on the morphology of dynamically crosslinked elastomer. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers.