Elongational viscosity at a constant elongational strain rate of polypropylene melt

The measurement of elongational viscosity has been carried out with an improved elongational rheometer, sensitive to small elongational forces and measuring simultaneously the diameter of elongating samples. Force distribution was evaluated for various conditions. The method of reduced variables, successful in linear viscoelastic properties, can be applied to the temperature dependence of elongational viscosity only at small elongational strain rate. For large elongational strain rates, the elongational viscosity was found to be non-linear and a new method characterizing non-linearity was proposed. The non-linearity parameter in elongational viscosity was independent of elongational strain rate and almost independent of temperature. Non-linearity in elongational viscosity is discussed in terms of a structural change in the polymer melt.     

The dynamic viscosity of polypropylene melt

The dynamic viscosity of polypropylene melt was determined as a function of frequency and temperature. The temperature-shift Arrhenius energy was calculated in several ways. The influence of temperature on the elastic and viscous components was quantitatively discussed.     

The effect of melt history,pressure, and crystallization temperature on spherulite size in bulk isotactic polypropylene

Melt history, pressure, and crystallization temperature are three variables that may be used to vary spherulite size in polymer systems. In this study, bulk polypropylene samples were given various melt treatments and then isothermally crystallized under constant pressure. Spherulite size was found to increase with increasing severity (i.e., increased temperature or time at temperature) of melt treatment, explained by the thermal deactivation of nucleation sites. Spherulite size also increases with increasing crystallization temperature, owing to a smaller driving force for nucleation and the deactivation of increasing numbers of nuclei at higher crystallization temperatures. An analogous effect of pressure was also found, and a simple model to compare increased pressure and decreased crystallization temperature was derived.     

Dependence of the orientation strengthening of polypropylene fibers on temperature and rate of deformation

Conclusions The mean deformation rate rather fully characterizes the kinematics of polypropylene fiber stretching. It can be used as a norming parameter to obtain generalized temperature-rate characteristics of this process.The degree of orientation in stretching polypropylene fibers, like that for previously studied polymers, is determined by the magnitude of the accumulated highly elastic deformation.Translated from Khimicheskie Volokna, No. 4, pp. 24–25, July–August, 1983.     

The effects of melt history,crystallization pressure,and crystallization temperature on the crystallization and resultant structure of bulk isotactic polypropylene

A study of the effects of constant-pressure isothermal crystallization on polymer structure was conducted in bulk isotactic polypropylene. The investigation was designed to determine the influence of pressure, temperature, and melt history variables on the structure of this bulk polymer. Results demonstrate that the effects of pressure and crystallization temperature can be quite adequately combined into one processing parameter, undercooling (defined as the melting temperature minus the crystallization temperature), by use of the Clausius-Clapeyron equation. This parameter is demonstrated to be important in determining the kinetics of crystallization and the resultant structure. The moderate to high undercoolings involved in this study are representative of commercial injection-molding processes, and a number of conclusions regarding commercial processing are made based on these laboratory investigations.     

Elongational viscosity in the isothermal melt spinning of polypropylene

The elongational viscosity of polypropylene has been investigated by isothermal melt spinning, carried out over a range of experimental conditions. The filament diameter and the elongational force were measured for running filaments and the relationship between elongational viscosity and elongational strain rate reported. The elongational viscosity was observed to decrease in the vicinity of the spinneret and then remained constant before increasing along the thread line. An increase in elongational viscosity did not occur within the isothermal zone until the elongational flow was fully developed. The onset of an increase in elongational viscosity was determined from the constant total elongational strain. The degree of molecular orientation was also studied by birefringence measurements and was investigated as a function of elongational stress. At a high elongational stress, the relation between birefringence and elongational stress departed from linearity and exhibited a rapid increase which can be related to the increase in elongational viscosity.     

聚丙烯熔体流动指数与分子量及其分布的关系

研究了聚丙烯(PP)的熔体流动指数(MI)与聚合物不同分子量之间的关联性,对于分子量分布较窄的PP,数均分子量(Mn)、重均分子量(Mw)和粘均分子量(Mv)均能较好的关联;反之,MI与Mn关联性下降,而MI与Mn和Mv的关联性仍很好,尤其是MI与Mv的关联性受分子量分布的影响很小;MI与Z均分子量的关联性很差。同时．确定了MI与各种分子量之间的关联式,该式用于本体PP工艺反应器内氢气浓度的计算和MI的预测,与实验测量结果吻合良好。     

Dependence of melt temperature on screw speed and size in extrusion

Melt temperature in an extrusion process can significantly influence production rate, product quality, and yield. However, prediction of melt temperature is extremely difficult because errors in the predictions of output rate, screw power, and heat transfer, which are used to calculate melt temperature, cumulatively cause a very large error in the prediction of melt temperature. This paper analyzed the overall energy balance of an extruder and developed a simple equation to predict the melt temperature of a projected extruder in scale-up as a function of screw diameter, depth, and speed based on the experimental results of an experimental extruder and the polymeroperties. The predicted melt temperatures agreed reasonably with the measured values reported in a previous scale-up study.     

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.     

Rheology of thermoplastic starch: Effects of temperature,moisture content,and additives on melt viscosity

The melt viscosity of thermoplastic starch has been investigated as a function of temperature, moisture content, and processing conditions. The effects of various low molecular weight additives have also been studied. Starch melts exhibit power law behavior over the range of shear rates studied. Melt viscosity decreased with increasing temperature and moisture content (MC). The power law index m increased with increasing temperature. The consistency K decreased with increasing temperature and increasing moisture content. Moisture content during the pelletizing step influenced melt viscosities measured after equilibration to different MCs. All additives studied except glycerol monostearate (GMS) significantly lowered the melt viscosity of starch, some more effectively than water relative to starch with 15% MC. Starch with GMS had viscosities essentially the same as, or slightly higher than, starch/water. This behavior may be due to the presence of unmelted helical inclusion complexes of starch and GMS. Starch formulations at 160°C exhibited melt visocosities similar to an LDPE of melt index 1.8.     

The effect of TLCP melt structure on the bulk viscosity of high molecular mass polyethylene

A thermotropic liquid crystalline polyester (TLCP), denoted as TCLP3 and based on hydroxybenzoic acid, hydroquinone and sebacic acid, was used as a processing aid in the extrusion of high molecular mass polyethylene (HMMPE). This TLCP is in the nematic phase at 179.6–182°C. Capillary rheometry experiments were carried out at two processing temperatures: 190°C and 230°C. At 190°C TLCP3 is predominantly nematic and at 230°C it is predominantly isotropic. It is an effective processing aid for HMMPE, particularly at 190°C, with viscosity reductions in excess of 90% with a 1 wt% TLCP3/HMMPE blend. The rheological characteristics of the blends have been linked to the optical textures of the TLCP3 using hot-stage optical microscopy. From the experimental observations speculations are made about the mechanisms of viscosity reduction. Initial viscosity reductions are caused by TLCP3 structure effects (fibrillation and phase change), giving rise to fibrillation-induced molecular orientation in the neighboring HMMPE phase. This is only effective when nematic structures are present. Above a critical wall shear stress value the lubrication effect due to TLCP3 migration is dominant.     

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.     

Effect of temperature and shear rate on polyisoimide solution viscosity

The following models describe the effect of temperature and shear rate on the viscosity of polyisoimide solutions. Data was obtained for 20, 30, and 40% polyisoimide solutions in 20:80 tetrahydrofuran/diglyme and for a 30% solution in N-methyl-pyrrolidone at temperatures of 25°, 35°, 55°, and 75°C. The measurements were taken on a Brookfield cone and plate viscometer at shear rates ranging from 9.59 to 383.4 reciprocal seconds. Experimental data fits model (1) reasonably well. In some cases, model (2) provides a better fit. This model accounts for temperature dependencies in the power law shear-thinning exponent. The coefficients β depend on the material lot that is being tested even though the lot molecular weights are very close. Slight differences in acid functional group concentrations for this particular material are a possible explanation.     

Manufacturing and foaming of high melt viscosity of polypropylene by using electron beam radiation technology

The high melt viscosity of polypropylene was studied by grafting bifunctional monomers, 1,6‐hexanediol diacrylate (HDDA) and tripropylene glycol diacrylate (TPGDA), onto homopolypropylene (HPP) and random ter‐polypropylene (RTPP) under electron‐beam irradiation. Creation of the high‐melt‐viscosity polypropylene was possible at low radiation dosage and low monomer content, under a prohibition of both radiation degradation and homopolymerization. TPGDA monomer was more effective in increasing the melt viscosity of HPP compared with RTPP, whereas HDDA monomer was more effective for enhancing the melt viscosity of RTPP. Such different effects of monomers on melt viscosity may arise from different monomer structures, namely, TPGDA has additional three methyl groups, but HDDA has no methyl groups. Electron‐beam radiation technology, on an increase of the melt viscosity, was much more effective in HPP than RTPP, when compared with virgin polymers. Modified RTPP and HPP with high melt viscosity were capable of foaming with numerous fine cells, of which the modified HPP with 1.5 mmol TPGDA and 0.5 kGy could create more spherical foam cells and its bending strength was 1.5 times more than that of the foamed RTPP. POLYM. ENG. SCI., 46:431–437, 2006. © 2006 Society of Plastics Engineers.     

Strain rate dependency on stress–strain relations of polypropylene

True constant strain rate tensile tests of polypropylene up to 2% initial strain were performed to investigate the strain rate dependency of the initial stress–strain gradient dσ/dε with the aid of “slack grip.” The experimental results fairly agree with even the simplest mechanical model analysis with three parameters, showing the conspicuous strain rate dependency on the initial stress–strain gradient dσ/dε. The limiting cases corresponding to zero strain rate and strain rate of infinite magnitude, both predicted by the analysis, were experimentally verified.     

Effects of temperature and strain rate on the tensile behavior of polypropylene composites insulator coatings used in offshore deepwater pipelines

Polypropylene (PP) composites are being increasingly used as thermal insulation coatings in both onshore and offshore pipelines. In this study, the direct tensile behavior of pure PP, PP with glass microsphere filler, and PP with 65% glass filler were investigated at 22, 60, and 90 °C temperatures at various strain rates from 0.003/min to 0.300/min. Fourier transform infrared spectroscopy and scanning electron microscope studies were used to characterize the materials. Stress–strain relationships of the materials were nonlinear in the elastic and inelastic domains. Addition of glass fiber to the PP increased the elastic modulus, but the yield strength and yield strain were reduced along with the ductility. Based on the experimental results, constitutive models coupling the strain rate and temperature have been developed to predict the yield strength, the initial elastic modulus and secant modulus at yield for the PP composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45209.     

间歇式聚丙烯装置产品熔体流动指数的控制

针对间歇式液相本体法聚丙烯装置的生产特点,根据实际生产经验,从原料、催化剂的选择与配方、升温操作、氢调、设备维护等对如何控制聚丙烯粉料熔体流动指数进行了分析。结果表明:只要控制得当,间歇式聚丙烯装置产品的熔体流动指数可以控制在(n±1.5)g/10min(n为预定值)的稳定范围。     

Dependence of viscosity of suspensions of ceramic nanopowders in ethyl alcohol on concentration and temperature

ABSTRACT: This work presents results of measurements of viscosity of suspensions including Yttrium Oxide (Y2O3), YAG (Y3Al5O12) and Magnesium-Aluminum spinel (MgAl2O4) nanopowders in ethanol. Nanoparticles used in our research were either commercially available (Baikowski) or nanopowders newly developed in the Institute of Ceramics and Building Materials (ICBM) in Warsaw, Poland. The study was conducted in a wide range of shear rates (0,01 s1 to 2000 s1) and temperature interval from 15 degreesC to 20 degreesC. A rheometer Haake Mars 2 from Thermo-Fisher, Germany was used in Biophysics Laboratory at Rzeszow University of Technology (RUT). Most of the samples show non-Newtonian behavior. It was conrmed with Rheo-NMR system from Bruker, Germany, that 10% by weight (wt.) of Y2O3 suspension is non-Newtonian uid. In this work we also report, for the rst time, a unexpected behavior of the viscosity of some samples (Y2O3 and Y3Al5O12) due to the sedimentation effect.     

The influence of molecular weight distribution on melt viscosity,melt elasticity,processing behavior and properties of polystyrene

The influence of molecular weight and molecular weight distribution on the melt rheological behavior of two polystrenes of approximately the same weight average molecular weight, but of widely different molecular weight distribution, was determined. Then, using a series of capillaries with different length-to-diameter ratios in an Instron Capillary Rheometer, the entrance correction methods of E. B. Bagley and the relationships of W. Philippoff and F. H. Gaskins, the recoverable shear strain (S_R) in the melt at the capillary wall for these mono- and polydisperse polystyrenes was determined. Shear modulus (G) and normal stress (P_N) were calculated using the relationships: G = τ_RC/S_R and P_N = 2τ_RC S_R, where τ_RC is the corrected shear stress at the capillary wall. These are compared to values obtained using a Weissenberg Rheogonimeter. These two polystyrenes were also injection molded into an ASTM specimen mold over a wide range of stock temperature, using a 12 OZ . in-line reciprocating screw injection press, and evaluated for mechanical property values. The effects of the elasticity parameters (S_R G & P_N) and their magnitude on the rheology, processability and mechanical properties of these polystyrenes are discussed.