Copolymer melt rheograms from melt flow index

Available literature data on the variation of melt viscosity with shear rate are shown to coalesce together to give unique curves for each copolymer type, independent of temperature and copolymer grade, based on a normalising technique using the Melt Flow Index. The unified curves obtained are useful for estimating the flow curves of the copolymers at the temperature of interest if the Melt Flow Index of the copolymer at the specific temperature is known. Coalesced curves are presented for a number of commonly known copolymers such as acrylonitrile-butadiene-styrene, styrene-butadiene-styrene. vinyl chloride-vinyl acetate, ethylene-vinyl-acetate, polyester elastomer and an olefinic-tyype thermoplastic elastomer.     

Rheograms of filled polymer melts from melt-flow index

Polymers filled with extending fillers, such as calcium carbonate or talc, or with reinforcing fillers, such as glass fibers or mica, are increasingly being used in a number of applications. The addition of fillers to a polymer changes the melt rheological behavior of the polymer. A knowledge of the viscosity vs. shear-rate flow curves of the filled system at various temperatures and as a function of filler parameters (such as filler type, shape, and amount) is necessary for process design, optimization, and trouble shooting. The generation of such rheological data is ezpensive and cumbersome in view of the broad range of fillers and the large numbers of filler parameters. In the present article, a unifying approach is proposed that coalesces the flow curves of filled systems of a polymer at various temperatures into a master curve that is independent of the filler parameters. An effective methods is presented to estimate the rheograms of filled systems with the use of a master curve, characteristic of a genetic resin type, knowing the melt-flow index and glass-transition temperature of the system. Master curves have been reported for filled system of low-density polyethylene, high-density polyethylene, poly-propylene polystyrene, nylons, poly(ethylene terephthalate), and polycarbonate.     

Estimation of the melt rheology of polymer waste from melt flow index

The need for recycling of polymeric waste has been well recogmized as a result of the escalating prices of the petrochemical feedstocks and the growing awareness to curtail solid waste that causes environmental pollution. During processing, the molecular weight of the polymer is reduced due to thermal and shear degradation. Since the melt rheology of the processed material is sensitive to the changes in molecular structure, knowledge of the complete flow curve depicting the variation of melt viscosity with shear rate at processing temperatures is a useful tool for assessing the reprocessibility of waste material and for specifying the conditions of reprocessing. In the present paper, an effective method is proposed to generate the melt flow curves of polymer waste from knowledge of its melt flow index. The method makes use of a master curve that can be obtained by plotting the available viscosity data in terms of modified functions based on the melt flow index. The master curves characteristic of the particular generic resin type are presented for low-density polyethylene, polypropylene and polystyrene.     

Reversible melt flow rate increase of branched acetal polymers

Continued shearing of molten long-chain branched acetal polymers raises their melt flow rates manyfold. The increase is not due to molecular degradation, as evidenced by constancy of inherent viscosity, and by the ability to reverse the increase by dissolving and reprecipitating the polymer. Shearing was found to have only a relatively small effect upon the melt viscosity but a very large effect upon the entrance correction for capillary flow. It is suggested that crystallization of branched polymers from solution creates an exceptionally strong entanglement network, and that the observed rheological changes reflect the disruption by shear of this network.     

Effect of the melt flow index and melt flow rate on the thermal degradation kinetics of commercial polyolefins

In this study, several polyolefins, including different grades of polypropylene (PP), high‐density polyethylene, linear low‐density polyethylene, and low‐density polyethylene, were tested by thermogravimetric analysis (TGA), and the relationships of their melt flow index (MFI) and melt flow ratio (MFR) values to the thermogravimetry (TG) curves, differential thermogravimetry (DTG) curves, and activation energy of thermal degradation were investigated. Kinetic evaluations were performed by Friedman and Kissinger analysis methods, and the apparent activation energy values for the overall degradation of different grades of polyethylenes (PEs) and PPs were determined. We found that for the samples with lower MFIs, the thermograms shifted to higher temperatures. Meanwhile, a higher activation energy was needed for their thermal degradation. Also, for samples with higher values of MFR, as a means of molecular weight distribution, a lower activation energy was needed for their thermal degradation, and their TGA thermograms shifted to lower temperatures. The breadth of the DTG curves depended on the MFR in the PEs, although MFR had little effect on the DTG curves in the studied PP grades. Among all of the samples studied, the injection‐molding grades with medium MFIs and low MFRs degraded at higher temperatures and showed better thermal stability. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012     

用熔体流动指数仪研究三元乙丙橡胶熔体的流变性能

用熔体流动指数仪研究了三元乙丙橡胶(EPDM)熔体的流变性能,建立了实验条件下EPDM的熔体流动指数(MFI)与流变参数、门尼黏度之间的关系。结果表明,EPDM 70的非牛顿指数和活化能比EPDM 80的大,2种橡胶熔体的剪切速率与MFI成线性关系,剪切黏度与MFI成乘幂关系。     

Rheology of poly(vinyl chloride) formulations from melt flow index measurements

A knowledge of the complete flow curve, or rheogram, of a PVC formulation depicting the variation of the melt viscosity over industrially relevant ranges of shear rate and temperature is essential in the design of polyer-processing equipment, process optimization, and troubleshooting. These data are generated on sophisticated rheometers that are beyond the financial and technical means of most PVC processors. The only flow parameter that can be readily measured on an inexpensive apparatus is the melt flow index of the resin-mix. In the present work, a method has been proposed to estimate the rheograms of a PVC formulation at temperatures relevant to its processing conditions with the use of a master curve, knowing the melt flow index and glass-transition temperature of the formulation. A master curve that coalesces rheograms of different PVC formulations at various temperatures has been generated and proposed as a tool for estimating the flow curve.     

Effect of carbon black on time dependence of the melt flow index

Time dependence in the melt indexing of polyolefins stabilized against thermally induced changes is well known, the prevalent effect being an increase in melt index toward a steady-state value. The melt index of polyethylenes compounded with carbon black has been found to decrease, in some cases radically, although oxygen uptake data show no evidence of thermal instability. The melt index–time plot can be restored to its normal shape by adding excess quantities of a standard thioether antioxidant. Data are rationalized by assuming that polyethylene adsorbs on the available pigment surface, forming a crosslink network. The thioether antioxidant, however, may adsorb preferentially, thereby restoring the normal response of the polymer to forces resulting in its capillary extrusion. The results emphasize the contribution of chain orientation effects to the time dependence of melt index.     

Upgrading the melt flow index to rheogram approach in the low shear rate region

The unified viscosity function curves proposed earlier by the authors have an inherent limitation in the low shear rate region. This limitation is the effect of using the melt flow index as a normalizing factor to obtain the coalesced curves, which itself is insensitive to molecular parameters such as molecular weight distribution. A single integral constitutive equation of the BKZ type is used to derive the viscosity function which would be useful in generating unified curves based on the melt flow index but devoid of the limitation of molecular weight distribution effects in the low shear rate region.     

Adsorption of water-soluble,nonionic polymers onto cellulosic fibers

The adsorption of 12 different nonionic water-soluble polymers, methylcellulose (MC), hydroxypropylcellulose (HPC), polygalactomannan (PGM), polyglycidol (PGD), polyacrylamide (PAAm), methylolated polyacrylamide (MPAAm), polymethacrylamide (PMAAm), three differently hydrolyzed poly(vinyl acetate)s (PVAs), poly(vinyl) methyl ether (PVME), and poly(vinyl pyrrolidone) (PVP) onto bleached kraft pulp (BK), unbleached kraft pulp (UK), and a groundwood pulp (MP) has been investigated under aqueous conditions with attention to the functional groups in the polymers and the chemical character of the pulps. It was found that the adsorption was often selective toward one of the pulps. In order to gain some additional information on these interactions, some adsorption experiments were also performed on acetylated pulps. Some polymers (PGD, PAAm, MPAAm, and PVA 124) having both proton donating and accepting capability were not adsorbed onto any of the pulps. This was attributed to intramolecular hydrogen bonding in these polymers. Some polymers (PVA 224, PVME, and PVP) were strongly adsorbed onto UK but not at all onto BK. It was suggested that in these cases the adsorptive interaction was between phenolic and/or catecholic groups in the lignin on the UK and proton accepting sites on the polymers. However, for three polymers (MC, PGM, and PMAAm), a more general type of hydrogen bonding interaction was considered. For some polymers (HPC, PMAAm, and PVA 420) having hydrophobic groups, it was suggested that hydrophobic interactions were important for the adsorption.     

Hydrodynamic stability of yarn spinning from a melt of flexible-chain polymers

Conclusions Empirical relationships have been obtained which describe satisfactorily the effect of basic spinning parameters on nonuniformity in the diameter of the undrawn yarns; these make it possible to calculate optimum parameters which ensure an assigned level of yarn nonuniformity in diameter.It has been found that increasing the melt viscosity decreases the region of stable spinning.A connection has been found between nonuniformity of the undrawn yarn and the strength of the finished yarn: the strength of the drawn yarn is increased proportionately to the decrease in nonuniformity of the undrawn yarn in its diameter.Translated from Khimicheskie Volokna, No. 5, pp. 16–18, September–October, 1984.     

Scanning electron microscopy study on reverse osmosis membranes prepared from Indian cellulosic polymers

Five different reverse osmosis (RO) membranes were prepared from indigenous cellulosic polymers under optimised conditions. A scanning electron microscope was used to study their morphology by examining the top layers and cross sections in detail. RO performance results of the membranes are discussed to correlate the morphology and it is inferred that if impurities are minimised and a highly ordered texture of the top layer and the inner matrix is attained, the desalination performance will improve.     

聚乙烯熔体流动速率的测定及有关参数的研究

通过聚乙烯多种牌号熔体流动速率MFR值的测定,根据高聚物熔体的流变行为和poiseuille方程,用MFR值对粘度η_切进行了定量计算;借助高分子理论,指出以MFR值表征分子量及分布的可行性;利用参数之间的依赖性,阐述了熔体流动速率对聚乙烯树脂在加工成型中的意义。     

Prediction of melt viscosity flow curves at various temperatures for some olefin polymers and copolymers

A knowledge of the variation of melt viscosity of thermoplastic polymers with both shear rate and temperature is of considerable importance to plastics engineers as well as to polymer rheologists. The actual measurement of melt viscosity at a large number of temperatures and shear rates is frequently a tedious and time-consuming task. A technique has been developed, based upon the applicability of shear rate-temperature superposition, for predicting the flow curves of a number of olefin polymers and copolymers at various temperatures from experimental data obtained at one temperature for the material in question. The experimental validity for superimposing log shear stress—log shear rate curves at different temperatures along the log shear rate axis has been established for both high and low density polyethylenes, polypropylene, polybutene-1, and poly (ethylene vinyl acetate) copolymers. The temperature dependence of the resultant shift factors has been determined for each system, and the method of utilizing this information to predict viscosities as a function of temperature and shear rate is discussed.     

The measurement of melt flow and melt stability

The melt flow of a plastic as measured by the standard method (ASTM D-1238) is at a high enough stress so that the flow is non-Newtonian. If the die in the plastometer is replaced by a nonstandard, tapered die of large orifice, a lower stress can be used and the flows are shown to be comparable to Newtonian viscosities measured in a cone and plate rheometer. Under these conditions the plastometer can be used as a sensitive measure of the melt stability of a plastic.     

Modeling of melt electrospinning for semi-crystalline polymers

A comprehensive model for the stable jet region in electrospinning of crystallizing polymer melts has been presented. First, the conventional flow-induced crystallization (FIC) model by Ziabicki was coupled with the non-isothermal melt electrospinning model. The modeled initial jet profiles were compared to digitized experimental images of the stable Nylon-6 melt jet near the spinneret. The final jet diameters were also compared to the average thickness of collected fibers. The results were in good agreement with the flow visualization experiments for various melt temperatures and flow rates. The modeled crystallinity predictions were also in agreement with experimental data from collected fiber mats. Then, a new FIC model that can provide microstructure information, such as crystallite number density and average size, has been proposed and validated under isothermal and non-isothermal conditions in the bulk as well as in the confined geometry of the polymer melt jet in electrospinning. Nylon-6,6 was used as the model polymer in this crystallization study, and the results are in good agreement with the widely-used Ziabicki FIC model.     

聚合物熔融接枝技术研究进展

综述了聚合物熔融接枝改性影响因素的研究新进展,包括接枝单体类型、第3单体、引发剂、反应温度和时间、设备及工艺等,分析了各因素对接枝反应的接枝率、接枝效率及副反应的影响,指出了聚合物熔融接枝未来的发展之路。     

Polypropylene during crystallization from the melt as a model for the rheology of molten-filled polymers

Polarized light microscopy shows that polypropylene crystallizes from the melt into a well-distinguished spherulitic structure. Therefore, it provides a useful model for molten-filled polymers, where the growing spherulites are considered to be filler particles dispersed in a matrix fluid. Although spherulites are randomly dispersed in the space, two dispersion models (simple cubic and centered cubic) are discussed to correlate the transformed fraction α(t) with the volume fraction of filler ϕ(t). The combination of these results with those of differential scanning calorimetry (DSC) shows that the transformed fraction α(t) is a direct indication of the volume fraction of filler ϕ(t). The rheological study, using oscillatory experiments coupled with DSC results, shows the relative sensitivity of the rheological functions to structural changes of the liquid during crystallization. Furthermore, they reveal the existence of a yield effect above a certain criticl value of the filler content (ϕ_c = 0.4). In the absence of this yield effect, a model is proposed to predict the variation of the rheological functions with the filler content. This model shows not only a variation of the plateau modulus, but also the modification of the characteristic times of relaxation of the polymer matrix, whereas the shape of the relaxation spectrum remains unchanged. © 1996 John Wiley & Sons, Inc.