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.     

Rheological characterization of HDPE/sisal fiber composites

The present paper summarizes an experimental study on the molten viscoelastic behavior of HDPE/sisal composites under steady and dynamic mode. Variations of the melt viscosity and die swell of the composites with an increase in shear rate, fiber loading, and coupling agent concentration have been investigated using capillary rheometer. The shear rate γ at the wall was calculated using Rabinowitsch correction applied to the apparent shear rate values. It was observed that the melt viscosity of the composites increased with the addition of fibers and maleic anhydride-grafted PE (MAPE). Die swell of HDPE also decreased with the addition of sisal fibers and MAPE. Further, the dynamic viscoelastic behavior of the composites was measured employing parallel plate rheometer. Time–temperature superposition was applied to generate various viscoelastic master curves. Temperature sweeps were also carried out to study the flow activation energy determined from Arrhenius equation. The fiber–matrix morphology of the extrudates was also examined using scanning electron microscopy. POLYM. ENG. SCI., 47:1634–1642, 2007. © 2007 Society of Plastics Engineers     

PET熔体流变特性的研究与应用

作者用毛细管流变仪和Ｂｒａｂｅｎｄｅｒ流变仪测试了ＰＥＴ熔体的流变特性，发现熔体的粘度对温度非常敏感，熔体剪切变稀的现象很明显，并就粘度特性对物料加工温崐度等参数的影响及热流道的温度控制进行了讨论。     

高黏度聚酯流变行为的研究

采用毛细管流变仪研究了高黏度聚酯(PET)的表观黏度及黏流活化能随温度(280～300℃)及剪切速率(20～104s-1)的变化。结果表明:高黏度PET熔体随着剪切速率的增加出现切力变稀现象,随着熔体温度升高,剪切速率对熔体的表观黏度的影响降低;高黏度PET的黏流活化能随着剪切速率的提高而降低;在温度为300℃,剪切速率为3 000 s-1时,高黏度PET熔体具有较好的流动性。     

Degradation of polycarbonate during recycling in a capillary rheometer

Polycarbonate was recycled in a capillary rheometer at high constant shear stresses (0.15–0.95 MPa) and at temperatures between 275 and 320°C. Changes in melt viscosity and molecular weight were evaluated. Significant polymer degradation was observed on repetitive extrusion. An activation energy of 113 kJ/mol was determined for the initial stages of the process. The degradation kinetics were in agreement with a non-random chain scission. It was concluded that bonds were more susceptible to scission the closer they were to the middle of the polymer molecule and that the extent of degradation increased with an increase in molecular weight.     

Melt flow behavior of blends from poly(vinyl chloride) and epoxidized natural rubber

Blends from poly(vinyl chloride) (PVC) and epoxidized natural rubber (ENR) were prepared in a Brabender plasticorder by the melt blending technique. The melt flow behavior of these blends with respect to blend ratio and temperature has been examined using a melt flow indexer and capillary rheometer. ENR decreases the Brabender torque, increases the melt flow index (MFI), and decreases the melt viscosity of PVC in the blends. Arrhenius plots were used to study the effect of temperature on melt flow index (MFI) and viscosity. Moreover, the flow behavior index (n′) obtained from capillary rheometer data was found to be dependent on temperature and blend ratio.     

聚丙烯/丙烯-乙烯共聚物共混体系的流变行为研究

采用毛细管流变仪和旋转流变仪研究了聚丙烯(PP)纤维专用料/丙烯-乙烯共聚物(PEC)共混体系的流变行为,探究了剪切速率、温度、共混物组成对熔体流变行为的影响。结果表明,随着剪切速率的增加,PP、PP/PEC和PEC均表现出"剪切变稀"行为;随着温度的升高,聚合物的表观黏度逐渐降低,特别是在低剪切速率下的这种现象更明显;随着PEC含量的增加,体系的非牛顿指数增加,黏流活化能降低,黏度对温度的敏感性降低,熔体剪切模量增加,熔体弹性增加。     

转矩流变仪表征熔融聚合物的流变性能

采用温度校正后的转矩流变模型,研究了结晶与非晶聚合物的流变性能,并将流变结果与毛细管流变仪进行对比。结果表明,在非牛顿指数及流动活化能测量方面,转矩流变仪与毛细管流变仪测量结果差异较小;由于黏滞耗散作用,转矩流变仪在进行流变表征时需要进行转矩的温度校正;转子等效半径与几何结构有关,而与物料种类及加工条件无关;转矩流变仪测量的剪切速率范围较窄。     

Adjustable Twin‐Slit Rheometer for Shear Viscosity Measurement of Extruded Complex Starchy Melts

An online rheometer with an innovative system of height‐adjustable and independently temperature‐controlled slits was designed to measure the shear viscosity of extruded wheat bran fiber‐containing starchy materials. The range of melt pressures and temperatures, obtained with a die, could be covered by the rheometer. A close ingredient thermomechanical history in the extruder was achieved both with the die and the rheometer, while covering an apparent shear rate from 5 to 30 s^–1. Although minor technical problems remained, first rheological data were obtained and showed a pseudoplastic flow behavior for all recipes. The flow curves were fitted by a power law model. Wheat bran fiber addition influenced both the K‐ and n‐values, leading to more shear‐thinning melt behavior and an increase in true shear viscosity. Only a limited effect on these values was found in these preliminary experiments when further increasing the fiber content.     

Effects of extrusion conditions on rheological behavior of acrylonitrile–butadiene–styrene terpolymer melt

The influence of temperatures and flow rates on the rheological behavior during extrusion of acrylonitrile–butadiene–styrene (ABS) terpolymer melt was investigated by using a Rosand capillary rheometer. It was found that the wall shear stress (τ_w) increased nonlinearly with increasing apparent shear rates and the slope of the curves changed suddenly at a shear rate of about 10³ s^?1, whereas the melt‐shear viscosity decreased quickly at a τ_w of about 200 kPa. When the temperature was fixed, the entry‐pressure drop and extensional stress increased nonlinearly with increasing τ_w, whereas it decreased with a rise of temperature at a constant level of τ_w. The relationship between the melt‐shear viscosity and temperature was consistent with an Arrhenius expression. The results showed that the effects of extrusion operation conditions on the rheological behavior of the ABS resin melt were significant and were attributable to the change of morphology of the rubber phase over a wide range of shear rates. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 606–611, 2002     

Rheological Behavior and Mechanical Properties of Blends of Poly(vinyl chloride) with CP-POSS

In this work, a polyhedral oligomeric silsesquioxane which contains 3-chloropropyl groups (CP-POSS) was synthesized. The rheological behavior of CP-POSS/PVC blends was investigated by torque rheometer and capillary rheometer. Mechanical properties were investigated by electronic material tester. Influences of blending composition, shear rate and shear stress on melt apparent viscosity and non-Newtonian index (n) were discussed. The results show that the plastic time decreases and melt viscosity increases with increasing content of CP-POSS. CP-POSS has a good compatibility with PVC. The blend has the best impact strength when the content of CP-POSS is 7 wt%. The CP-POSS can be used as a processing aid and impact-resistant aid for PVC.     

改性聚乙烯醇体系熔体的流变性能

采用HAAKE RHEOCORD－90挤出式毛细管流变仪测定了改性PVA体系的流变性能。结果表明，改性PVA熔体是对剪切速率敏感的假塑性流体，非牛顿指数n较小，熔体偏离牛顿流体的程度较大。在相同温度及剪切速率下，随水含量增加，改性PVA体系的表观粘度下降。改性PVA体系的粘流活化能随剪切速率提高和水含量减少而降低，即温度敏感性降低。     

Rheological properties of poly(trimethylene terephthalate) in capillary flow

The shear viscosity, extensional viscosity, and die swell of the PTT melt were investigated using a capillary rheometer. The results showed that the PTT melt was a typical pseudoplastic fluid exhibiting shear thinning and extensional thinning phenomena in capillary flow. There existed no melt fracture phenomenon in the PTT melt through a capillary die even though the shear rate was 20,000 s^?1. Increasing the shear rate would decrease the flow activation energy and decline the sensitivity of the shear viscosity to the melt temperature. The molecular weight had a significant influence on the flow curve. The flow behavior of the PTT melt approached that of Newtonian fluid even though the weight‐molecular weight was below 43,000 s^?1 at 260°C. The extensional viscosity decreased with the increase of the extensional stress, which became more obvious with increasing the molecular weight. The sensitiveness of the extensional viscosity to the melt temperature decreased promptly along with increasing the extensional strain rate. The die swell ratio and end effect would increase along with increasing the shear rate and with decreasing the temperature, which represented that the increase of the shear rate and the decrease of temperature would increase the extruding elasticity of the PTT melt in the capillary die. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 705–709, 2005     

熔融缩聚法合成的聚乳酸熔体的流变性能研究

采用锥板流变仪研究聚L-乳酸(PLLA)的流变性能,并对直接法熔融缩聚制备的聚乳酸进行了测试。结果表明:PLLA熔体属于切力变稀流体;PLLA熔体的表观粘流活化能较高,其表观黏度对温度的敏感性高。     

聚乳酸/氯化钠共混物的流变性能

利用动态流变仪和毛细管流变仪,分别测试了聚乳酸(PLA)及PLA/NaCl(70/30)共混物的复数黏度和剪切黏度,得到了两种熔体的非牛顿指数(n)和流动活化能(ΔEη)。结果表明:PLA熔体的n随温度的升高以斜率为0.002线性地增大,而PLA/NaCl(70/30)共混物熔体的n随温度的升高以斜率为-0.01线性地减小;在剪切速率为1s-1时,PLA熔体的ΔEη为135.92kJ/mol,PLA/NaCl(70/30)共混物熔体的ΔEη为119.57kJ/mol,表明PLA熔体的黏度对温度的敏感性比PLA/NaCl(70/30)共混物熔体的黏度对温度的敏感性高。     

Effects of Extrusion Rate,Temperature, and Die Diameter on Melt Flow Properties During Capillary Flow of Low-Density-Polyethylene

The melt flow properties of a low-density polyethylene were measured at test temperatures varying from 140 to 170°C and in a wide range of extrusion rates by means of a capillary rheometer, to identify the influence of extrusion conditions (such as temperature, shear rate, and die diameter) on the melt flow behavior in the present paper. The results showed that the entry pressure drop increased nonlinearly with an increase of the piston speeds, and it decreased with an addition of the die diameter. The melt shear flow obeyed roughly the power law and the melt shear viscosity decreased approximately linearly with an increase of the true shear rates in a bi-logarithmic coordinate system. The dependence of the melt shear viscosity on temperature accorded approximately the Arrhenius expression. Under these experimental conditions, the entrance pressure drop increases as an exponential function with an addition of the channel contraction ratio.     

Preparation and interaction characteristics of exfoliated ABS/organoclay nanocomposite

A series of poly(acrylonitrile‐co‐butadiene‐co‐styrene) (ABS)/organoclays (Cloisite10A, Cloisite25A, and Cloisite30B) nanocomposites are prepared via two different methods: one is a solution blending and the other is a two‐step process where the solution blended mixture is subsequently compounded in the melt state using a torque rheometer (SOAM method). The effect of surfactants on the surface of three different organoclays that are modified with alkylammonium salts in polymer/organoclay nanocomposites is investigated by focusing on two major aspects; Flory‐Huggins interaction parameters and physical (thermal and mechanical) properties. The d‐spacing of both neat organoclays and intercalated/exfoliated organoclays is examined by X‐ray diffraction analysis, and the microstructure of these nanocomposites is examined by FE‐TEM. Solubility parameters of both polymer and organoclays of interest are calculated according to the group contribution method. Viscoelastic behavior of the nanocomposites is also investigated by measuring rheological properties under an oscillatory shear. The increase in the onset temperature of the thermal degradation indicates the enhancement of thermal stability of ABS due to intercalation or partial exfoliation. Mechanical properties, such as, tensile strength, tensile modulus, and elongation at break of the nanocomposites are measured. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Rheological behavior of semi‐aromatic transparent polyamide

The rheological behaviors of semi‐aromatic transparent polyamide (SATPA) melt are investigated using a capillary rheometer. The effects of shear rate, shear stress, and temperature on the apparent viscosity η_a of SATPA are discussed. A correlation of non‐Newtonian index with temperature is obtained. The results show the shear thinning of SATPA; meanwhile η_a decreases with increasing temperature and shear rate, and the viscous flow activation energy is further obtained from temperature dependence of the samples. It was concluded that the apparent viscosity η_a is sensitive to temperature at lower shear rate owing to the higher viscous flow activation energy; on the contrary, the influence of temperature effect on the apparent viscosity becomes minor at higher shear rate due to the lower viscous flow activation energy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1586–1589, 2005     

Ultrasonic Degradation Studies and Its Effect on Thermal Properties of Polypropylene

In this article, the ultrasonic degradation of polypropylene (PP) melt was conducted in a specially designed reactor. Dynamic stress rheometer and gel permeation chromatography (GPC) were used to study the degradation behavior of PP melt. Thermal properties of ultrasonically treated PP were further discussed. The results showed the decrease of complex viscosity, zero shear viscosity, representative relaxation time, viscoelastic moduli as well as cross-over modulus, but an increase of cross-over frequency with introduction of ultrasonic irradiation, due to reduction of weight average molecular weight and increase of molecular weight distribution index of the polymer. The ultrasonic chain scissions of PP melt mainly occurred at the initial 3 min of irradiation and subsequently tended to terminate under our experimental conditions. In addition, the crystallization temperature and melting temperature of PP together got decreased in the presence of ultrasonic irradiation due to the occurrence of lower molecular weight components and some chemical irregularities in PP chain, along with the slight increase of crystallinity.     

The effect of blending temperature,composition, and shear rate on PET/Vectra A900 LCP blend viscosity and morphology

The rheological and morphological properties of several melt-blended compositions of poly(ethylene terephthalate) (PET) and Vectra A900 liquid crystalline polyester were investigated, using blending temperature, composition, and shear rate as variables. Rheological behavior was determined at several shear rates on an Instron capillary rheometer at 300°C, and three-dimensional surface plots of the results were prepared, detailing the effect on melt viscosity of changes in the variables. Scanning electron microscopy was used to examine the internal morphology of selected samples. In the preparation of melt blends containing an isotropic and anisotropic polymer, blending temperature and composition both influence the resulting morphology. These effects are accentuated during extrusion of the blends at low shear rates and diminished at high shear rates.