In-process rheometry as a PAT tool for hot melt extrusion

Real time measurement of melt rheology has been investigated as a Process Analytical Technology (PAT) to monitor hot melt extrusion of an Active Pharmaceutical Ingredient (API) in a polymer matrix. A developmental API was melt mixed with a commercial copolymer using a heated twin screw extruder at different API loadings and set temperatures. The extruder was equipped with an instrumented rheological slit die which incorporated three pressure transducers flush mounted to the die surface. Pressure drop measurements within the die at a range of extrusion throughputs were used to calculate rheological parameters, such as shear viscosity and exit pressure, related to shear and elastic melt flow properties, respectively. Results showed that the melt exhibited shear thinning behavior whereby viscosity decreased with increasing flow rate. Increase in drug loading and set extrusion temperature resulted in a reduction in melt viscosity. Shear viscosity and exit pressure measurements were found to be sensitive to API loading. These findings suggest that this technique could be used as a simple tool to measure material attributes in-line, to build better overall process understanding for hot melt extrusion.     

Growth parameters on the defects formation in a grown silicon crystal

The growth of macroscopically dislocation-free Czochralski silicon crystals, various defects such as D defects and microdefects causing oxidation-induced stacking faults can form. The effects of growth parameters such as pulling speed or cooling rate of the crystal on the formation of these defects is examined. From an experiment on the continuous cooling of a silicon crystal from 1400 °C, it is found that there is an intermediate cooling rate range in which the nucleation of OISFs is enhanced. The impact of the presence of OISFs on the electrical properties of the silicon crystal is examined with a minority lifetime mapper, and the resistivity is measured with a four-point probe. A higher pulling speed of the crystal from the melt results in a higher density of particles on the polished silicon wafers. This implies that many of the particles present on the polished silicon wafers are related to solidification of the silicon crystal. Slower pulling from the melt followed by controlled cooling thereafter is suggested as a means of lowering these grown-in defects in Czochralski silicon crystals. © 1998 Kluwer Academic Publishers     

不同熔体流动速率的SA型透明尼龙的流变性能

采用固相后缩聚方法制备了一系列熔体流动速率不同的SA型透明尼龙(SATN),采用毛细管流变仪对其流变性能进行了研究,并讨论了熔体流动速率对其流变性能的影响。研究结果表明,SATN熔体属假塑性流体,表观黏度随着剪切速率的升高而降低;随着熔体流动速率的减小,SATN的非牛顿性增强,熔体黏度增大,对剪切速率的敏感性增强,但是对温度的敏感性减弱。     

In-situ observation of faceted growth of benzophenone single crystals

Melt growth of benzophenone was in-situ observed under various cooling rate and temperature gradient. The melt growth experiments were performed for various cooling rate of melt and various temperature gradients. The movement of growth interface with time was measured for various growth faces such as (001), (101) and (011) and the growth rates of the respective faces were calculated. It was found that the growth rate of all the faces increased with cooling rate of the melt. Steady state growth was observed in the experiments with low temperature gradient while, the steep gradient leads to unstable growth of crystal. The observed growth rate variation was explained using the attachment energy model.     

白榴石增强的牙科饰面瓷研究现状

回顾了白榴石微晶玻璃在制备方法、热稳定性和力学性能3个方面的研究进展。与传统的玻璃析晶法相比,先制备白榴石晶体,然后将其与低软化点玻璃混合烧结,这种方法在控制白榴石晶体尺寸方面更具优势。烤瓷温度和时间会影响微晶玻璃中白榴石晶体的含量,进而影响微晶玻璃的热膨胀系数,因此需要严格控制。微晶玻璃中白榴石晶体的直径应该小于4μm,这样可以将微晶玻璃中微裂纹的影响减少到最小。作者制备的一种白榴石微晶玻璃在950℃保温60 min后析晶完成,并且白榴石晶体的尺寸在1μm左右。     

铋粉对PP熔融流变性能及成纤性能的影响

采用熔融共混法制备铋/聚丙烯共混材料(Bi/PP),利用旋转流变仪对其熔融流变特性进行测试分析。再通过熔融纺丝法制备初生纤维,采用扫描电镜、单纤维强力仪等对初生纤维的结构及性能进行表征。研究表明:共混材料表现非牛顿流体特性;共混材料的表观黏度与温度及剪切速率呈负相关;相同温度下,随铋粉含量增加,共混物的表观黏度也相应上升,铋粉在PP基体中的分散性较好但团聚增多,初生纤维内部孔隙结构增多,力学性能有所降低。     

Rheological behavior of short sisal fiber-reinforced polystyrene composites

The rheological behavior of short sisal fiber-reinforced polystyrene composites containing short sisal-fiber has been studied using an Instron capillary rheometer. The effect of fiber length, fiber loading, shear rate, shear stress and temperature on the rheological behavior of the composites was studied. Unlike other short fiber-reinforced thermoplastics at lower temperature the melt viscosity of polystyrene(PS)-sisal composites are lower than that at higher temperatures. At 180°C the viscosity of the composite is governed by wall-slip, which decreases the viscosity and at 190°C the viscosity is governed by fiber melt interaction that increases the viscosity. The morphology of the extrudate was studied using optical and electron microscopy.     

Melt flow properties of polypropylene/EPDM/glass bead ternary composites

The flow properties of polypropylene(PP)/ethylene-propylene-diene monomer copolymer(EPDM)/glass bead (GB) ternary composites were measured in a wide scope of shear rates by using a Rosand capillary rheometer. The apparent shear rates varied from 10 to 10⁵ s^–1, and the test temperature was from 210 to 240°C. The results showed that the flow behavior of the composite melts may be considered to approximate that of a power law fluid although the slope of the melt flow curves somewhat varied around shear rate of 700 s^{– 1}. The dependence of the melt shear viscosity on the test temperature was roughtly consistent with the Arrhenius expression. The melt shear viscosity increased dramatically with increasing the volume fraction (_g) of GB under lower shear rate level, white it increased gently with an addition of _g under higher shear rate level. Furthermore, there were certain effects of the filler surface treatment on the melt shear viscosity and its sentivity to the filler content at higher concentration of the beads at lower shear rates.     

Control of spontaneous nucleation in flux growth

Factors considered important in controlling nucleation in flux growth have been investigated in comparative studies of pseudobinary cross-sections of several ternary systems. The pairs of pseudobinaries differed with respect to the acid:base concentration in each melt. It is shown that the number of crystals obtained by spontaneous nucleation depends mainly on the acid:base ratio and that the viscosity, solubility, relative supersaturation and supercooling are less important. A mechanism is presented to show how the presence of smaller complex ions, resulting from a higher concentration of basic oxide, can account for fewer crystals being obtained. Experimental evidence is reported which shows that fewer crystals nucleate when a modified cooling programme is adopted.     

Heat transfer studies for a crystal in a synchrotron radiation beamline

Heat load studies have been performed for the first crystal of a double crystal monochromator to be installed in a beamline of the 2·5 GeV synchrotron radiation source Indus-2. Finite element analysis (FEA) has been used to calculate the temperature distribution and the mechanical distortions on these crystals. Several cases of cooling schemes and heat loads have been studied. Based on these FEA results, the analytical relationships available in the literature have been modified. It is shown that modified analytical results compare well with the empirical results obtained from FEA. The optimisation of the cooling conditions can be achieved by doing FEA calculations for only one case. All other cases can then be calculated by using analytical relations proposed here. The proposed analytical equations are generic in nature and can be applied for any source—crystal combination and therefore would be useful for performance prediction of any new monochromator on a new synchrotron source without taking recourse to time consuming, computation-intensive FEA.     

Symmetric shear test of glass-ceramic sealants at SOFC operation temperature

Glass-ceramics of the BaO–CaO–Al₂O₃–SiO₂ system are frequently used in planar solid oxide fuel cells (SOFC) stacks to seal the fuel and air compartments and to join non-conductively the individual components. Due to the thermal mismatch of the ceramic and metallic materials in the stack, the seals experience predominantly shear stresses. A symmetric shear test has been developed to characterize the critical shear stress of the glass-ceramic at SOFC operation temperature. Specimens representative for the seal situation in an SOFC stack were prepared, using the glass-ceramic to join a center piece of a NiO-YSZ anode covered by yttria-stabilized zirconia (YSZ) electrolyte layers on both surfaces between two Crofer22APU interconnect steel blocks. Shear stress and based on a rheological model, shear modulus and viscosity of the sealant were determined. The investigations showed that the sealant exhibits viscous shear deformation at 800 °C, a temperature typical for SOFC operation. The influence of increasing crystallization on the shear deformation is demonstrated.     

An acoustic study of the relaxation properties of ZhK-1282 nematic liquid crystals in the vicinity of the nematic-isotropic phase transition

The viscous and elastic properties of a ZhK-1282 nematic liquid crystal (NLC) were studied in a temperature interval from 290 to 360 K by method of ultrasonic spectroscopy in the 3–63 MHz frequency range. The temperature dependences of the NLC density and shear viscosity are presented. The results of measurements of the velocity and attenuation of ultrasound and the shear viscosity were used to calculate the volume viscosity coefficient, the moduli of dilatation and isothermal compressibility, the relaxation times of the elastic and viscous properties, and the corresponding critical characteristics of the given NLC.     

氯化原位接枝改性CPVC流变行为的研究

采用氯化原位接枝技术制备了苯乙烯(St)、甲基丙烯酸甲酯(MMA)、丙烯酸-2-羟基乙酯(HEA)、丙烯酸-2-羟基丙酯(HPA)和丙烯酸丁酯(BA)等五种单体改性的CPVC.用毛细管流变仪测定了它们的流变行为.讨论了CPVC和改性CPVC的熔体粘度与剪切速率、剪切应力以及温度的关系.结果表明:CPVC和改性CPVC熔体均为假塑性流体,改性CPVC的假塑性增强,熔体表观粘度低于CPVC的熔体表观粘度.在190～205℃温度范围,两者的对数表观粘度与1/T呈非线性关系.CPVC-g-PMMA对温度和剪切应力更加敏感,CPVC-g-PHEA熔体的流动性明显高于CPVC及其他四种单体改性的CPVC.     

Squeeze flow characterisation of thermoplastic polymer

New manufacturing concepts developed by the CRC-ACS involve co-curing a thermoplastic polymer layer onto the surface of a composite component. The layer can be reshaped to alter the dimensions of the laminate locally. A major physical phenomenon involved in these uses is squeeze flow of the thermoplastic polymer.

In the present work, the squeeze flow of a selected thermoplastic at high temperature and under given pressure was studied. A power-law model for viscosity variation with shear rate was assumed to describe the non-Newtonian behaviour of the thermoplastic at high temperatures. Based on the viscosity model, a fluid mechanics model was derived for the squeeze flow between approaching parallel plates of infinite length. The model relates the plate approaching speed to the applied pressure, thermoplastic geometry (both thickness and width) and power-law viscosity model parameters.

An experimental method and data analysis procedure were developed to determine the parameters of the power-law model that describes the viscosity of the thermoplastic material. Tests were conducted under isothermal conditions by squeezing composite laminates with integrated thermoplastic films. The transient thickness of the thermoplastic film was continuously measured and used to calculate the power-law model parameters for each test. A temperature range of 180–200 °C was investigated to establish the dependence of the power-law model parameters upon temperature.

Using the squeeze flow model, and experimentally determined power-law viscosity model parameters, the effect of various process conditions on the thermoplastic thickness was investigated. Predictions were found to be valid for situations where the shear rate range matched that achieved during the power-law viscosity model parameters tests.     

Effect of addition of polycarbonate on sheared flow of red mud-filled isotactic polypropylene

Different volume fractions of polycarbonate (PC) were incorporated to improve thermal stability of red mud (RM) filled polypropylene (PP). Effects of PC addition in RM filled PP on shear stress, melt viscosity, and melt elasticity have been determined under different shear rates by using a capillary rheometer. With the increase in shear rate, addition of PC in RM-filled PP reduced its shear stress and melt viscosity. However, recoverable shear strain increased with PC content in the blend.     

Pentaerythritol crystallization – Influence of the process conditions on the granulometric properties of crystals

The quality of crystals depends on many factors that determine their granulometric properties. In order to obtain crystals of desired size distribution, proper selection of the operating conditions is of a great importance. Commonly, the unseeded cooling crystallization is controlled by selecting the appropriate cooling profile. The crystallization process can also be controlled by adding a certain number of seed crystals of a uniform size in the crystallizer at the saturation temperature. This paper investigates the influence of the process conditions (mixing intensity, cooling profile, batch time, saturation temperature and seeding) on the granulometric properties of pentaerythritol obtained by batch cooling crystallization. All investigated process conditions influence the crystal size distribution (seeded and unseeded experiments). On the other hand, the shape of crystals was the same for all experimental conditions. Optimal cooling profile, lower retention time, higher mixing rate, and smaller initial seed surface area improves the final crystal size distribution.     

Three‐dimensional finite element solution of gas‐assisted injection moulding

This paper presents a finite element algorithm for solving gas‐assisted injection moulding problems. The filling material is considered incompressible and has temperature and shear rate dependent viscosity. The solution of the three‐dimensional (3D) equations modelling the momentum, mass and energy conservation is coupled with two front‐tracking equations, which are solved for the polymer/air and gas/polymer interfaces. The performances of the proposed procedure are quantified by solving the gas‐assisted injection problem on a thin plate with a flow channel. Solutions are shown for different polymer/gas ratios injected. The effect of the melt temperature, gas pressure and gas injection delay, on the solution behaviour is also investigated. The approach is then applied to a thick 3D part. Published in 2001 by John Wiley & Sons, Ltd.     

冷却槽对自孕育法制备ZA92镁合金组织的细化作用

采用自孕育法制备新型的ZA92镁合金,研究了冷却槽对组织的细化作用,并对其机理进行了分析。结果表明:合金熔体内部的形核与冷却槽的激冷作用、熔体的流动速度及剪切力的大小有关,合适的冷却槽角度有利于晶粒的游离和增殖。熔体在流经冷却槽的过程中,其组织变化趋势为:粗大枝晶→细小枝晶→等轴晶→蔷薇状晶和近球状晶。冷却槽角度较大或较小均不利于组织的细化,当冷却槽角度在30~45°之间时,坯料组织的晶粒分布比较集中且细小,其平均晶粒尺寸在47.5~51.4μm之间。     

Synthesis and characterisation of large chlorapatite single-crystals with controlled morphology and surface roughness

This work describes the synthesis of chlorapatite single crystals using the molten salt method with CaCl₂ as a flux. By manipulating the processing conditions (amount of flux, firing time and temperature, and cooling rates) it is possible to manipulate the crystal morphology from microscopic fibres to large crystals (up to few millimetre long and ~100?μm thick). The crystal roughness can be controlled to achieve very flat surfaces by changing the melt composition “in situ” at high temperature. The Young modulus and hardness of the crystals are 110?±?15 and 6.6?±?1.5?GPa respectively as measured by nanoindentation. Crystal dissolution in Hanks solution starts around the defects. Several in vitro assays were performed; ClAp crystals with different size and shape are biocompatible. Cell apoptosis was very low at 5, 10, and 15?days (Caspase-3) for all the samples. Proliferation (MTT) showed to be influenced by surface roughness and size of the crystals.     

Properties of ceramic injection moulding formulations

The rheological properties of nine ceramic injection moulding compositions based on polypropylene with a fled silicon powder loading were measured. Minor components of the polymer-ceramic blend were shown to have a considerable effect on the properties of the melt. An attempt was made to derive, from capillary rheometer flow curves, the parameters which are thought to influence moulding quality. !n particular, the shear rate dependence of viscosity at the nozzle temperature, fluidity ate shear rate of 100 sec^?1, the temperature dependence of viscosity in the region of the nozzle temperature and at o shear rate of 100 sec^?1 and the yield stress are discussed. !n Part 2 the influence of these variables and other properties of the formulations, on quality of moulding will be considered.