Melt rheology of polyarylate/polybutylene terephthalate blends

The viscosity, the activation energy of flow, and the exchange reactions of bisphenol A 50/50 isophthalic/terephthalic acid and poly(butylene terephthalate) blends are studied by means of an extrusion capillary rheometer, covering a range of 10 s^?1 to 300 s^?1 shear rate and 280°C to 300°C temperature. The results are interpreted in terms of compatibility and free volume additivity. The decrease in viscosity with time is explained as a result of transesterification rather than degradation.     

Melt fracture behavior of polypropylene‐type resins with narrow molecular weight distribution. I. Temperature dependence

Polypropylene (PP)‐type resins with narrow molecular weight distribution, such as PP‐type thermoplastic elastomer PER and controlled‐rheology PP (CRPP) made by peroxide degradation of high molecular weight PP, have a problem of easy generation of skin roughness at extrusion. To examine the present state, the occurrence of skin roughness in PER and CRPP at extrusion was investigated with a capillary rheometer in a shear rate range of 12–6100 s^?1 and a temperature range of 180–280°C. A homo‐PP (HPP) and a block‐PP (BPP) with usual molecular weight distributions were used for comparison. HPP and BPP with usual molecular weight distributions show smooth extrudates at low shear rates and abruptly generate severe skin roughness “elastic failure” originating at the die entrance at a higher shear rate. PER and CRPP with narrow molecular weight distributions easily generate “sharkskin” melt fracture originating at the die exit, from a shear rate nearly one decade lower than rates of elastic failure of HPP and BPP. The sharkskin becomes more severe, with increasing shear rate, and attains to the elastic failure. The critical shear rate at which sharkskin occurs increases with increasing extrusion temperature. The critical shear rate is about 20 s^?1 at 180°C and about 120 s^?1 at 280°C, which is in the range encountered by the molten resin at extrusion processing. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2111–2119, 2002     

Flow and crystallization of saturated fatty acid methyl esters and their binary mixtures

Demand for biodiesel has increased due to being a more environmentally-friendly fuel. Cold weather operation of biodiesel is challenging due to fatty acid methyl ester (FAME) content in biodiesel. Saturated FAMEs crystallize at relatively high temperatures, increase the viscosity of biodiesel, and can clog fuel lines. Here, several factors altered crystallization temperature (CT) of FAMEs, including composition, shear rate, and cooling rate. The crystallization of pure and binary mixtures of methyl palmitate, methyl myristate, and methyl stearate were studied under shear flow and static conditions. Static phase CTs of pure methyl palmitate, methyl myristate, and methyl stearate were 26, 14, and 35°C, respectively. In binary mixtures, CTs were depressed up to 7°C, which agreed with freezing point depression theory. Increasing shear rate up to 100 s⁻¹ decreased CT by 2°C compared to static conditions. Decreasing cooling rate from 1 to 0.1°C/min increased CT less than 2°C. Overall, FAME composition altered CT more than shear flow or cooling rate for pure and binary mixtures of three FAMEs.     

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.     

In situ composites from blends of polycarbonate and a thermotropic liquid‐crystalline polymer: The influence of the processing temperature on the rheology,morphology, and mechanical properties of injection‐molded microcomposites

This work was aimed at understanding how the injection‐molding temperature affected the final mechanical properties of in situ composite materials based on polycarbonate (PC) reinforced with a liquid‐crystalline polymer (LCP). To that end, the LCP was a copolyester, called Vectra A950 (VA), made of 73 mol % 4‐hydroxybenzoic acid and 27 mol % 6‐hydroxy‐2 naphthoic acid. The injection‐molded PC/VA composites were produced with loadings of 5, 10, and 20 wt % VA at three different processing barrel temperatures (280, 290, and 300°C). When the composite was processed at barrel temperatures of 280 and 290°C, VA provided reinforcement to PC. The resulting injection‐molded structure had a distinct skin–core morphology with unoriented VA in the core. At these barrel temperatures, the viscosity of VA was lower than that of PC. However, when they were processed at 300°C, the VA domains were dispersed mainly in spherical droplets in the PC/VA composites and thus were unable to reinforce the material. The rheological measurements showed that now the viscosity of VA was higher than that of PC at 300°C. This structure development during the injection molding of these composites was manifested in the mechanical properties. The tensile modulus and tensile strength of the PC/VA composites were dependent on the processing temperature and on the VA concentrations. The modulus was maximum in the PC/VA blend with 20 wt % VA processed at 290°C. The Izod impact strength of the composites tended to markedly decrease with increasing VA content. The magnitude of the loss modulus decreased with increasing VA content at a given processing temperature. This was attributed to the anisotropic reinforcement of VA. Similarly, as the VA content increased, the modulus and thus the reinforcing effect were improved comparatively with the processing temperature increasing from 280 to 290°C; this, however, dropped in the case of composites processed at 300°C, at which the modulus anisotropy was reduced. Dynamic oscillatory shear measurements revealed that the viscoelastic properties, that is, the shear storage modulus and shear loss modulus, improved with decreasing processing temperatures and increasing VA contents in the composites. Also, the viscoelastic melt behavior (shear storage modulus and shear loss modulus) indicated that the addition of VA changed the distribution of the longer relaxation times of PC in the PC/VA composites. Thus, the injection‐molding processing temperature played a vital role in optimizing the morphology‐dependent mechanical properties of the polymer/LCP composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Semiconductor‐Insulator Transition in Undoped Rutile,TiO2, Ceramics

The electrical conductivity of undoped rutile ceramics is very dependent on sample processing conditions, especially the temperature and atmosphere during sintering and the subsequent cooling rate. Samples become increasingly semiconducting when quenched from temperatures above ~700°C without the need for a reducing atmosphere. Thus, samples quenched from 1400°C in air have conductivity ~1 × 10^?2 Scm^?1with activation energy ~0.01(1) eV over the temperature range 10–100 K, whereas similar samples that are slow cooled or annealed in air at 300°C–500°C are insulating with activation energy 1.67(2) eV and conductivity, e.g., 1 × 10^?7 Scm^?1 at 400°C. The very wide range of electrical properties is attributed to variations in oxygen content which are too small to be detected using thermogravimetry. Impedance analysis shows that, depending on cooling rate, partially oxidized samples may be prepared in which samples retain a semiconducting core, but have an oxidized outer layer.     

Effect of CO2 Bubbles on Crystallization Behavior of Anhydrous Milk Fat

A study was designed to observe the effect of bubbles created from dissolved CO₂ (0–2000 ppm) on crystallization and melting behavior, fat polymorphs, microstructure, and hardness of anhydrous milk fat (AMF) under nonisothermal crystallization conditions. Calculated amounts of dry ice were added to generate 2000 ppm CO₂ at low partial pressure, and an ultrasound (205 kHz, 10 s; US) treatment was delivered at 35 °C through a noncontact metal transducer on the molten AMF to generate bubbles (~500 nm) of CO₂. The generated CO₂ bubbles were found to induce a higher onset of crystallization temperature during cooling from 35 to 5°C at the rate of 0.5°C min⁻¹. The changes in crystallization behavior owing to the generation of a smaller and significant number of TAG crystals also increased the hardness of the AMF at room temperature and refrigerated conditions. The work suggested the potential use of CO₂ nanobubbles derived from the dry ice with the emission of low power US to control the crystallization behavior and thereby the physical properties of milk fat-containing dairy products.     

Radical high pressure polymerization of ethylene with stable initiators

In order to assess the suitability of stable initiators for the high pressure polymerization of ethylene, polymerization tests were carried out in a stirred autoclave in continuous operation. The pressure used was 1700 bar, the average residence time 30 seconds and the temperature was adjusted to between 200 and 360°C. The initiator concentration in the ethylene feed varied between 4 and 40 mol ppm. Di-tert-butyl peroxide, di-tert-amyl peroxide, tert-butyl hydroperoxide, and 3,4-di-methyl-3,4-di-phenyl hexane, a C? C labile compound, were chosen for use as stable initiators. The level of conversion and the specific initiator consumption were determined. The polymers obtained were characterized by measuring their density, average molecular weight, and melt flow index. The stable initiators used were all characterized by a very low level of consumption. In the case of dialkyl peroxides and alkyl hydroperoxide, the optimum application temperature is substantially above 200°C and above 300°C in the case of the C? C labile initiator. Under these conditions, polymers with a low density, a low molecular weight, a narrow molecular weight distribution and a high melt flow index were obtained.     

High-pressure polymerization of ethylene using methyl isobutyl ketone peroxide as initiator

An investigation was carried out into the suitability of methyl isobutyl ketone peroxide (MIKP) as initiator for the high pressure polymerization of ethylene. For this purpose, polymerization tests were carried out in a stirred autoclave at a pressure of 1000 to 2000 bar and a temperature of 195 to 310°C. The initiator concentration of the feed was varied between 6.5 and 42 mol ppm while the residence time was kept at a constant 30 s. Apart from the rate of polymerization, the conversion and the initiator consumption were also determined. The characteristic properties of polyethylene (PE) were determined by measuring the melt flow index, the density and, in some cases, the molecular weight distribution. Conversion levels of 5 to 27% were achieved with rates of polymerization between 1 and 5.5 kg PE l^?1 h^?1. The initiator consumption at 1700 bar was in the region of 1 to 2 g I kg^?1 PE^?1 over a temperature range of 220 to 315°C. In view of these results, MIKP can be considered as suitable to initiate ethylene high pressure polymerization at 220 to 310°C, particularly in the tubular reactor. The density of the polyethylene thus prepared is ranging between 0.910 and 0.927 g ml^?1. Without the addition of modifiers or cross-linking agents, the melt flow index varies considerably. The polydispersity of the polymers prepared at a pressure of 1700 to 2000 bar was between 6 and 8 and therefore within the range to be expected for stirred autoclaves. Reducing the pressure to 1000 bar resulted in surprisingly low polydispersity values of 2.4 to 3.7.     

Crystallization and fiber/matrix interaction during the molding of PEEK/carbon composites

The objective of this work was to investigate the effects of molding conditions (molding temperature, residence time at melt temperature, and cooling rate) on the crystallization behavior and the fiber/matrix interaction in PEEK/carbon composites made from both prepreg and commingled forms. In order to investigate the crystallization behavior of the PEEK matrix, the molding process was simulated by differential scanning calorimetric analysis, DSC. The results show that the prepreg and commingled systems do not have the same matrix morphology; prepreg tape was found to be at its maximum of crystallinity, whereas the commingled system was found to be only partially crystalline. The results show that processing must be carried out at a temperature sufficiently high to destroy the previous thermal history of the PEEK matrix; this is an essential requirement to produce efficient fiber/matrix adhesion in the commingled fabric system. Optical microscopic observations also suggest that matrix morphology near the fibers is dependent on the melting conditions; a well-defined transcrystalline structure at the interface is observed only when the melt temperature is sufficiently high. However, the high temperature of molding can easily result in degradation of the PEEK matrix such as chain scission and crosslinking reactions. Thermal degradation of the matrix during processing is found to affect the crystallization behavior of the composites, the fiber/matrix adhesion, and the matrix properties. This effect is more important in the case of a commingled system containing sized carbon fibers because the sizing agent decomposes in the molding temperature range of PEEK/carbon composites. This produces a decrease of the matrix crystallinity and an elimination of the nucleating ability of the carbon fibers. A transition between cohesive and adhesive fracture is observed when the cooling rate increases from 30°C/min to 71°C/min for the composite made from the commingled fabric. This critical cooling rate is found to closely correspond to a change in the mechanism of crystallization of the PEEK matrix.     

The Kinetics of Melting Crystallization of Poly-L-Lactide

The influence of non-isothermal melt crystallization on thermal behavior and isothermal melt crystallization kinetics of poly-L-lactide (PLLA) were investigated by differential scanning calorimetry (DSC), polarizing micrograph (POM) and x-ray diffraction (XRD). Crystallization performed at lower cooling rates (2°C·min^?1) is accompanied by a variation of the kinetics around 118°C. The glass transition temperature of PLLA decreases with increase of cooling rate, and the crystallinity at the end of crystallization increases with decreasing cooling rate. The size of PLLA spherulites increases with a decrease in the cooling rate, and PLLA becomes almost amorphous cooled at rapid rate (>10°C·min^?1). PLLA exhibits an Avrami crystallization exponent n = 3.01±0.13 in isothermal crystallization in the range from 90°C to 140°C. According to Hoffman-Lauritzen theory, two crystallization regime are identified with a transition temperature occurring at 118°C, and the value of K_g(II)/K_g(III) is 2.17 [K_g(II) = 6.025 × 10⁵K², K_g(III) = 1.307 × 10⁶ K²].     

Structure and properties of polyethylene produced by γ-radiation polymerization in flow system

The radiation-induced polymerization of ethylene was carried out by use of a benchscale plant with a flow-type reactor of 1 liter capacity under the following conditions: pressure, 200–400 kg/cm²; temperature, 30–90°C; irradiation intensity, 3.8 × 10⁵ rad/hr; and ethylene flow rate, 300–3000 nl/hr. The molecular weight of polymer formed was shown to decrease with increasing reaction temperature and to increase with increasing pressure. When the ethylene flow rate increases, the molecular weight decreases in the polymerization at 30–60°C, but it does not change in the polymerization at 75–90°C. Methyl group content, which is a measure of short-chain branching of the polymer, increases with increasing reaction temperature, i.e., ca. 1 CH₃/1000 CH₂ at 30°C and ca. 9 CH₃/1000 CH₂ at 90°C. Methyl content is independent of the ethylene flow rate. The changes in the melt index of polymer with reaction conditions corresponds to the change of the molecular weight. The density, crystallinity, and melting point of polymer decrease with the reaction temperature as the short-chain branching increases, and they are almost independent of ethylene flow rate and pressure.     

Modification of a nicotinic acid functionalized water‐soluble acrylamide sulfonate copolymer for chemically enhanced oil recovery

N,N‐Diallyl nicotinamide (DANA) and acrylic acid (AA) were used to react with acrylamide (AM) and synthesize a novel nicotinic acid functionalized water‐soluble copolymer AM/AA/DANA by redox free‐radical polymerization. Then, the acrylamide/sodium acrylamido methanesulfonate/acrylic acid/N,N‐diallyl nicotinamide (AM/AMS/AA/DANA) was obtained by the introduction of the ? SO₃^? group into AM/AA/DANA after sulfomethylation. The optimal reaction conditions, such as the monomer ratio, initiator concentration, reaction temperature, and pH of the copolymerization or sulfomethylation, were investigated. Both AM/AA/DANA and AM/AMS/AA/DANA were characterized by IR spectroscopy, ¹H‐NMR, scanning electron microscopy, and intrinsic viscosity testing. We found that the AM/AMS/AA/DANA had a remarkable temperature tolerance (120°C, viscosity retention rate = 39.8%), shear tolerance (1000 s^?1, viscosity retention rate = 23.3%), and salt tolerance (10 g/L NaCl, 1.5 g/L MgCl₂, 1.5 g/L CaCl₂, viscosity retention rates = 37.4, 27.5, and 21.6%). In addition, the result of the core flood test showed that the about 13.1% oil recovery could be enhanced by 2.0 g/L AM/AMS/AA/DANA at 70°C. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40165.     

Thermomechanical properties and water uptake capacity of soy protein‐based bioplastics processed by injection molding

The optimization of the processing conditions in the production of soy protein bioplastics by injection molding has been essential in order to develop materials with a great capacity to absorb water while displaying good mechanical properties. Using a 50/50 (wt/wt) soy protein/glycerol mixture, and 40 °C, 500 bar, and 70 °C as reference values for cylinder temperature, injection pressure, and mold temperature, respectively, the effect of those processing parameters over thermomechanical and hydrophilic properties was studied. Processing parameters did not show a great influence over the thermomechanical bending properties within temperatures ranging from ?30 to 130 °C, as most samples displayed a similar response, independently of the parameter studied. On the other hand, when studying tensile and hydrophilic properties, the main effect corresponded to the cylinder and mold temperature values, as pressure did not exert a clear influence when increased from 300 to 900 bar. Samples with a lower water uptake were obtained when processed at higher temperature, as a result of crosslinking promotion. Moreover, a greater extensibility was observed when bioplastics are processed at high mold temperatures. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43524.     

Dynamic compressive behavior of basalt fiber reinforced concrete after exposure to elevated temperatures

This paper investigated the dynamic behavior of basalt fiber reinforced concrete (BFRC) after elevated temperatures by using a 100‐mm‐diameter split Hopkinson pressure bar apparatus. Changes in weight and ultrasonic pulse velocity (UPV) were also studied. The results indicate that the weight losses of BFRC before cooling increase with temperature, while a reduction in weight loss value is observed after water cooling. The UPV values of BFRC decrease constantly as temperature increases, and the measured velocities under the same temperature increase with fiber content as temperature exceeds 200 °C. For a given temperature, the strain rate, dynamic strength, critical strain, and impact toughness of BFRC increase with impact velocity. For a given impact velocity, the increasing temperature generally leads to an increase in strain rate and critical strain and results in a decrease in dynamic strength and impact toughness except in the case of 200 °C. At 200 °C, however, a marginal reduction, even an improvement in dynamic strength is observed, and the impact toughness initially decreases, then increases with loading rate when compared with that at room temperature. Basalt fiber is effective in improving the strength performance, deformation capacity, and energy absorption property of concrete after high temperature. Copyright © 2015 John Wiley & Sons, Ltd.     

Dry Fractionation Approach in Concentrating Tocopherols and Tocotrienols from Palm Fatty Acid Distillate: A Green Pretreatment Process for Vitamin E Extraction

Palm fatty acid distillate (PFAD) is a rich source of vitamin E. As compared to other vegetable oil, PFAD has higher tocotrienol (70–80%) over tocopherol content, which makes it a valuable source for vitamin E extraction. Current vitamin E extraction methods are not sustainable due to the intensive usage of chemical and high operational cost. Hence, the present study investigated for the first time using dry fractionation process as a green and economical pretreatment method for separating solid fraction (stearin) and liquid fraction (olein) in order to concentrate vitamin E from PFAD in olein fraction. We examined the dry fractionation conditions: crystallization ending temperature (36–44 °C), cooling rate (0.3 and 1.5°C min⁻¹), stirring speed (20–125 rpm), and holding time (0–60 min) on the composition of unsaturated and saturated fatty acids as well as vitamin E content in liquid fraction (olein) and solid fraction (stearin) using gas chromatography and high performance liquid chromatography, respectively. In most of these conditions, vitamin E was ultimately higher in olein fraction as compared to stearin fraction, which is correlated with the high degree of unsaturation. Under a cooling rate of 0.3°C min⁻¹, 90 rpm stirring speed, and ending crystallization of 38 °C, the highest vitamin E rich olein fraction was attained with 1479 ± 10.51 ppm in 50 g olein fraction as compared to 1366 ± 7.94 ppm in 500 g of unfractionated PFAD.     

Anomalous behavior of unplasticized PVC compounds in capillary flow

Capillary rheometry was performed over a temperature range of 170°–200°C and a shear-rate range of 3–3000 sec^?1 on an unplasticized poly(vinyl chloride) compound. The data were corrected for the effect of pressure on viscosity, for pressure loss in the barrel and at the capillary entrance, and for the non-Newtonian velocity profile. The pressure coefficient of viscosity was found to be in the same order of magnitude as those previously found with linear polyethylene and butadieneacrylonitrile copolymers. The pressure–shear-rate superposition of the flow curves is valid at least approximately, although the temperature–shear-rate superposition is inapplicable. The shape of flow curves at 180°, 190°, and 200°C are concave downward when they are expressed as log-shear-stress-log-shear-rate. Similar plots at 170° and 175°C, however, are very different; shear stress is independent of shear rate at low shear rates, increases somewhat and becomes independent of shear rate again at high shear rates. There is no detectable temperature dependence of flow behavior at 170° and 175°C. Irregularly shaped extrudates were obtained at higher shear rates. At constant shear rate the irregularity increased with the length of the capillary. The effect of thermal-mechanical history on the particulate and crystalline structure is discussed with possible influence on the reproducibility of the rheological data.     

High-temperature gasification of carbonaceous materials by flash pyrolysis: thermal aspects

Finely divided biomass was pyrolysed in heated tubé reactors at 700–1000 °C and 250–300 K s^{− 1} of the materials. It is concluded that the main thermal parameter is the reactor temperature at various heights. The range 800–900 °C mainly gives a fuel gas, while 900–1000 °C yields a synthesis gas. A secondary thermal parameter is the heating rate, which depends on the reactor temperature and the particle size. The results obtained are as good as at higher rates and can be compared with those under calculated equilibrium conditions. A third thermal parameter is the quenching effect on the entities immediately after formation. This effect depends on the vector gas flow and on the reactor geometry in the hot zone. The complex ‘chemical plasma’ generated by flash decomposition combines almost as fast as it is produced, under conditions which are very far from equilibrium. Generally, the shorter the residence time, the greater the difference from the equilibrium values. At high temperatures, short residence times of gases in the hot zone appear to increase the intensity of thermal shock to the particles, so some characteristics such as gasified carbon can exceed equilibrium values.     

The influence of thermal history on the properties of poly(3-hydroxybutyrate-co-12%-3-hydroxyvalerate)

The influence of thermal history on the properties of commercial P(3HB-co-12%-3HV) was studied. Thermogravimetric analysis and differential scanning calorimetry revealed that the plasticizer evaporated at 140°C or higher. The loss of plasticizer during thermal treatment at 170 and 180°C resulted in a slight increase of the melting temperature of the polymer. The processing time and temperature, as well as the cooling procedure influenced the thermal behaviour of the material. A decrease in molecular weight with time was found at the temperatures investigated and this significantly affected the mechanical properties of the polymer prepared at 180 and 200°C. The rate constant k_d of thermal degradation was slightly higher for samples during a shape-forming process in a Minimax apparatus than during a quiescent heating process (DSC) and its value increased with temperature. Limiting the processing at 170°C to 2 min gave a material with useful properties but increasing the residence time resulted in a decrease in strength, elongation at break, molecular weight and viscosity although it did not significantly influence the modulus of elasticity. Materials prepared at 180 or 200°C were more brittle and longer residence times resulted in a deterioration of the mechanical properties. © 1996 John Wiley & Sons, Inc.     

Effect of proccessing on flow properties of some linear polyethylene resins

Changes in flow properties of polyethylene resins have often been observed during processing operations. Studies in this laboratory show that melt viscosity of polyethylene normally increases when the resin is heated in a compression mold at temperatures below 300°C. At the same time, the solution viscosity actually decreases in some cases. During extrusion, on the other hand, both melt viscosity and solution viscosity are shown to decrease. In addition, the logarithm of melt flow rate is seen to deviate markedly from the expected linear dependence on reciprocal of absolute temperature. The results suggest that both crosslinking and chain-scission reactions occur during processing, the former predominating at low or zero shear, the latter at high shear.