Effect Of Melt Viscosity Research Articles

Effects of melt viscosity on enrichment and separation of primary silicon from Al–Si melt

The effects of melt viscosity on the enrichment and separation of Si crystals from Al–Si melt during an electromagnetic solidification process were investigated. Both the enrichment efficiency and the separation were found to be strongly dependent on the melt viscosity. A high melt viscosity was beneficial to the enrichment of primary silicon, whereas a low melt viscosity facilitated the separation process. A new enrichment mechanism was proposed in order to clarify the influence of melt viscosity, and an improved process for achieving high-efficiency enrichment of Si crystals via control of the melt viscosity was also proposed. Additionally, the morphology of Si crystals was found to change from spheroidal to plate-like in shape owing to the difference in viscosities in different regions.

The effect of melt viscosity on thermal efficiency for single screw extrusion of HDPE

In this work, a highly instrumented single screw extruder has been used to study the effect of polymer rheology on the thermal efficiency of the extrusion process. Three different molecular weight grades of high density polyethylene (HDPE) were extruded at a range of conditions. Three geometries of extruder screws were used at several set temperatures and screw rotation speeds. The extruder was equipped with real-time quantification of energy consumption; thermal dynamics of the process were examined using thermocouple grid sensors at the entrance to the die. Results showed that polymer rheology had a significant effect on process energy consumption and thermal homogeneity of the melt. Highest specific energy consumption and poorest homogeneity was observed for the highest viscosity grade of HDPE. Extruder screw geometry, set extrusion temperature and screw rotation speed were also found to have a direct effect on energy consumption and melt consistency. In particular, specific energy consumption was lower using a barrier flighted screw compared to single flighted screws at the same set conditions. These results highlight the complex nature of extrusion thermal dynamics and provide evidence that rheological properties of the polymer can significantly influence the thermal efficiency of the process.

Effect of melt viscosity on the crystallization kinetics of pre-sheared metallocene polyethylene melts

This work aims to verify the impossibility mentioned in the literature of saturating the crystallization kinetics of pre-sheared metallocene polyethylene melts. Similarly to results reported for other materials, and contrary to other published works, an acceleration of crystallization kinetics with the increase of shear strain and its saturation at large strain values was found. Similar strain values, with the same temperature variation, were evaluated with independent experiments using different devices, which allowed us to identify the steady state as the melt state responsible for the saturation of crystallization kinetics. Since this is a partially disentangled melt state, with viscosity lower than that of fully entangled (relaxed) melts, we assign the acceleration of crystallization kinetics by application of shear, and its saturation, mainly to the facilitated diffusion of chain segments to the lamellae growth front. This conclusion is supported additionally with the experimental results of other authors.

Viscosity measurements of melts at high temperatures using ultrasonic guided waves

This paper describes an experimental procedure using ultrasonic waves propagating in a rod to simultaneously measure the viscosity and temperature of melts at high temperatures using a very small amount of sample and without any mechanical rotating equipment. This method has applications in laboratory tests as well as for process monitoring in industries. A refractory material is used as buffer rod in the experiment to transfer the ultrasonic vibrations from a piezoelectric transducer into the melt, which is water cooled to protect the transducer from high temperatures. The sensor is based on the effect of melt viscosity on ultrasonic guided wave reflections from the solid–fluid interface. The difference in the time of flight of the ultrasonic wave in the buffer rod at two different temperatures is used to measure the temperature. The results from the measurement of melt viscosity using the proposed method, on three different glass samples, are in agreement with the values provided by the National Institute of Standards and Technology, USA. This method offers advantages in reduction in the amount of sample, cost, complexity in experiments, experimental time.

Impregnation of thermoplastic resin in jute fiber mat

Impregnation rate of thermoplastic resin (polypropylene) in jute fiber mat and influence of relative factors on impregnation were studied, aiming to develop the continuous melt impregnation technique and to investigate the effect of impregnation rate and temperature on processing conditions and mechanical properties of natural fiber mat-reinforced thermoplastics. Influence of pressure on porosity of fiber mat and effect of melt viscosity on impregnation rate were also investigated. The modified capillary rheometer was used as apparatus and experimental data were analyzed based on the one-dimension Darcy’s law. Results showed that at a given pressure, the impregnation rate is inversely proportional to melt viscosity and jute fiber mat has higher porosity than glass fiber mat. The architecture, compressibility, permeability and fiber diameter of jute fiber mat were compared with those of glass fiber mat and their effects on impregnation were discussed further. It could be seen that the average diameter of jute fiber is much bigger; the porosity of jute fiber mat is significantly higher and inner bundle impregnation does not exist in jute fiber mat. Therefore, it is not difficult to understand why the impregnation rate in jute fiber mat is 3.5 times higher and permeability is 14 times greater. Kozeny constants of jute and glass fiber mats calculated based on the capillary model are 2950 and 442, respectively.

Effect of molecular weight and molding conditions on the replication of injection moldings with micro‐scale v‐groove features

AbstractInjection molded optical plastic parts require accurate replication of micro‐scale features. The effects of melt viscosity and molding conditions on replication of microscopic v‐groove features in injection molded parts were examined for PC with different molecular weight. The micro‐scale feature size was a continuous v‐groove with 20 μm in depth and 50 μm in width. For injection molding conditions, melt temperature, mold temperature, injection velocity and holding pressure were varied in three levels. As the result, the mold temperature had significantly affected replication for all polymers with different molecular weight. Additionally, the molding conditions that lower melt viscosity led to improved replication. In the case of polymer with high molecular weight, the viscosity decreased with increasing melt temperature. It has been found that high replication of micro‐scale features could be achieved by higher mold temperature and higher melt temperature even with high viscosity PC. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Melt viscosity effects in ethylene–propylene copolymers

One of the key factors to a better understanding of the phase morphology of high-impact ethylene–propylene (EP) copolymers is the knowledge of the rheological behaviour of the various phases in these complex systems. Next to the molecular weight distribution, the comonomer content also affects the viscosity, as could be demonstrated in a systematic study of a wide range of compositions. More specifically, this means that for a given average molecular weight, the zero shear viscosity of the disperse phase consisting of amorphous ethylene–propylene ‘rubber’ (EPR) and crystalline polyethylene (PE) of such an impact copolymer are up to orders of magnitude higher than the respective polypropylene (PP) phase. This has a significant effect on the phase morphology and ultimately the mechanical performance of these compositions.

Effects of melt viscosity and silica activity on the rate and mechanism of quartz dissolution in melts of the CMAS and CAS systems

The dissolution rate of quartz in melts of the CMAS and CAS systems at 1,600°C and 1.5 GPa is a function of both the silica activity of the melt and its viscosity. In melts with low silica activity quartz dissolves more quickly than in higher aSiO2 melts regardless of viscosity. For melts with equal aSiO2, dissolution is faster in the low viscosity melt. Quartz dissolution is controlled by interface kinetics in three of the four melts used in this study for times much greater than predicted by the model of Zhang et al. (in Contrib Mineral Petrol 102:492–513 1989). One melt which was previously shown to adhere to the predicted behaviour at lower temperature shows a significant activation time at higher temperature. All the dissolution data indicate that there are likely to be three distinct domains of dissolution behaviour, although the details of why a particular melt falls in any one domain require further study. Although the current database is small, the relationship between quartz solubility and the dissolution constant indicate that solubility may be a useful parameter for predicting dissolution rates, particularly if silica activity and melt viscosity are also known.

Effect of Melt Viscosity on the Ejection Force in Injection Moulds

Effect of Melt Viscosity on the Ejection Force in Injection Moulds

Morphology and Physical Properties of ABS/NBR: The Effect of Melt Viscosity of SAN and the Content of NBR

In several acrylonitrile-butadiene-styrene (ABS) copolymers, some amounts of polybutadiene (PB) laTeX grafted with styrene-acrylonitrile (SAN) copolymer were replaced by acrylonitrile-butadiene rubber (NBR) copolymer, and the variations of morphology, mechanical properties, and rheological properties were examined. The impact strength of ABS, with a bimodal distribution of rubber size, was improved by the presence of the NBR, which distributes coarsely in the SAN matrix. Yield behavior in the rheological response due to the presence of rubber particles in the SAN matrix was enhanced by the coarser NBR particles, especially at high temperature.

Physico-chemical aspects of polyethylene processing in an open mixer 4. Comparison of PE-LLD and PE-HD with PE-LD

Melt-oxidation of various polyethylene samples has been compared at 150 and 180°C. Comparison of different low-density polyethylene (PE-LD) samples at 180°C shows mainly the impact of the polymer melt flow (MF) on the initial rate of hydroperoxide formation. The comparison of a series of linear low-density polyethylene (PE-LLD) samples at 150°C shows also the effect of melt viscosity. However, the conclusions are not as straightforward. Melt-oxidation of different polyethylene types indicates that the broadness of the molecular mass distribution might also be an important factor. All these results point to the possible role of shear for initiation of polyethylene oxidation in open mixers. The kinetics of formation of the different functional groups for the various polyethylene types examined are roughly the same as those deduced previously for PE-LD. This is especially so if induction times depending on temperature and particular polyethylene are taken into account. The present investigation also shows the importance of the presence of small amounts of transition metals such as various catalyst residues. In this respect, Cr-catalyst residues in Phillips-type high-density polyethylene (PE-HD) are especially effective for hydroperoxide decomposition. Nonetheless, even Ti-catalyst residues seem to have significant influence on formation of functional groups such as alcohols and carbonyl compounds.

Effects of viscosity on cellular structure of foamed aluminum in foaming process

The effects of melt viscosity on the foaming process and the structures of foamed aluminum have been examined. Methods for measuring the melt viscosity, pore structure, and foaming process are introduced. To increase the stability of the foaming melt and get the sample with a uniform pore distribution, a proper viscosity is needed. Further, the structure of foamed aluminum can be controlled by adjusting the Ca addition and other process parameters.

Effects of melt viscosity and thermal stability on polymer gasification

The effects of melt viscosity and thermal stability of a polymeric material on gasification rate under external radiant fluxes from 1.7 to 3.9 W/cm 2 are studied. The effects of melt viscosity are determined by using two different initial molecular weight polystyrene (PS) samples (about a factor of 2 difference in molecular weight); the combined effects of thermal stability with melt viscosity are determined by using two different initial molecular weight poly (methylmethacrylate) (PMMA) samples (about a factor of 4 difference in molecular weight). The results show that thermal stability affects gasification rate but that the transport process of the in-depth degradation products through the molten polymer to the sample surface does not significantly affect gasification rate except at low external radiant flux. The global heat of gasification is sensitive enough to differentiate the effects of thermal stability of the sample, but its value also depends on external radiant flux; in addition, it decreases with an increase in exposure time. This indicates that the global heat of gasification is not a unique quantity for a polymeric material.

Effect of melt viscosity and surface tension of polymers on the percolation threshold of conductive-particle-filled polymeric composites

Abstract The electrical conductivities of carbon-black-filled low-density polyethylene (LDPE), poly(methyl methacrylate) (PMMA), and poly(vinyl chloride)-vinyl acetate (PVC/ VAc) copolymer were measured as functions of carbon content and melt viscosity of the matrix at the temperatures at which the composites were prepared. Sharp breaks in the relationship between the carbon filler content and the conductivity of composites were observed in all specimens at some content of the carbon filler. The conductivity jumps as much as 10 orders of magnitude at the break point. This phenomenon has been known as the “percolation threshold”. The critical carbon content corresponding to the break point

Several effects of melt viscosity on the nature ofC p ?T data aboveT g for acrylate, methacrylate, and hydrocarbon polymers

Using objective computerized statistical procedures, we have examined high precisionC p data by DSC reported by Wunderlich and Gaur for a series of alkyl acrylate and methacrylate polymers. Although they claimed the data to be linear inT aboveT g , our results do not support the linear model. One or two endothermic slope changes are revealed aboveT g in lowT f polymers (T f < 20 °C) and at least one exothermic slope change in highT f polymers (T f > 20 °C).T f is the flow temperature of Ueberreiter. Both the first endotherm and the first exotherm occur near (1.22 ± 0.07)T g , suggesting aT ll type phenomenon.T ll varies as $$1/\bar M_n $$ . The first exotherm is associated by us with wetting of the DSC pan by molten polymer on the first heating of particulate highT f polymers. The rate of wetting, and presumably the magnitude of the exotherm, depends in part on the ratio,γ/η, whereγ is surface tension andη is melt viscosity of the molten polymer. Sinceγ is relatively constant, the molecular weight and temperature dependence for rate of wetting resides inη, which depends on $$\bar M_w $$ . For $$\bar M_n > > \bar M_c $$ , a second exothermic event caused by sintering, and also controlled by η, may be present. The interactive roles of $$\bar M_n ,\bar M_w ,\bar M_w /\bar M_n $$ ;M c (entanglement molecular weight); particle size, and heating rate onC p —T behaviour are delineated for the first time. LowT f hydrocarbon polymers, namely atactic polyalphaolefins,C 3 ,C 5 ,C 6 ; PIB; and dienes, PBD and cis-PI, exhibit single or double endotherms. Other results on highT f polymers showing exothermic effects, notably PS, PnBMA and polyglycidylmethacrylate are cited.

Studies on binary and ternary blends of polypropylene with SEBS, PS, and HDPE. I. Melt rheological behavior

Studies are reported on melt rheological behavior of some binary and ternary blends of polypropylene (PP) with one or two of the following polymers: styrene–b-ethylene butylene–b-styrene triblock copolymer (SEBS), polystyrene (PS), and high-density polyethylene (HDPE). Blend composition of the binary blends PP/X or ternary blends PP/X/Y were so chosen that the former represent addition of 10 wt % X to PP while the latter represent 10 wt % addition of X or Y to the PP/Y or PP/X blend of constant composition 90:10 by weight, X/Y being SEBS, PS, or HDPE. Measurements were made on a capillary rheometer using both temperature elevation and constant temperature methods to study the behaviors prior to flow and in the flow region. Flow behavior, measured at a constant temperature (200°C) and varying shear stress (from 1.0 to 5.0 × 106 dyn/cm2) to evaluate melt viscosity and melt elasticity parameters, is discussed for its dependence on the nature of the blend. Extrudate distortion, studied as a function of shear stress to evaluate the critical shear stress for the onset of extrudate distortion, showed differences in the tendency for extrudate distortion or melt fracture of these different blends. Also discussed is the effect of melt viscosity and melt elasticity on extrudate distortion behavior at the critical condition, which showed a unique critical value of the ratio (melt elasticity parameter)1/2 (melt viscosity) for all these blends. Blend morphologies before and after the flow through the capillary are investigated through scanning electron microscopy, and their correlations with rheological parameters of the melt are discussed.

Property Modifications in Fibers of Blends Based on Poly(ethylene Terephthalate)

In an effort to apply compatibility rules to the behavior of polymer fibers, tenacity of fibers spun from blends based on poly(ethylene terephthalate) has been studied. Blends containing 5% and 10% of a wide range of added thermoplastics were formulated using as a guide critical surface-tension data and solubility parameters of the components. For blends spun at 325°C a significant correlation was found between tenacity variations and differences in the compatibility parameters, suggesting that these parameters may serve as guides to the selection of compositions displaying superior fiber properties. At lower spinning temperatures melt-viscosity effects, among others, also strongly influence fiber properties. These factors, along with thermal stability effects, must be considered in attempts to optimize the tenacity of multicomponent fiber-formers.