Sati N. Bhattacharya

Extensional rheology of polypropylene melts from the Rheotens test

Abstract In recent years the “Rheotens” melt strength test has emerged as one of the most important tools for comparing the drawability of polymer melts. This paper examined whether a reliable set of test conditions could be obtained to determine a true and accurate melt strength of a polymer. The influence of various extrusion and drawing parameters on the extensional rheological performance of two polypropylenes are discussed. Using this knowledge an attempt was made to estimate the transient extensional viscosity from the Rheotens test. An analytical Wagner model in the linear region of the Rheotens test was used for the first time to calculate the transient extensional viscosity from the Rheotens test. These results were compared to the transient extensional viscosity obtained from a constant strain rate Rheometrics melt extensional rheometer (RME). The results agree within measurement accuracy with those measured from an RME. Consequently, the viscosity determined from the Rheotens experiment can be used to estimate transient extensional viscosity. The influence of different Rheotens test conditions on transient extensional viscosity are also discussed.

Rheology of LLDPE, LDPE and LLDPE/LDPE blends and its relevance to the film blowing process

The relevance of polymer melt rheology in film blowing process for linear low-density polyethylene (LLDPE) and its blends with three different low-density polyethylenes (LDPEs) has been discussed. The effect of different LDPE components as well as their concentration on shear and elongational viscosity has been investigated. A good correlation has been observed between the extensional rheological parameters of LDPEs measured by different experimental techniques. The molecular structure of parent polymers as well as blend composition play an important role in the rheology of these blends and consequently their performance in the film blowing process. © 2000 Society of Chemical Industry

Melt strength and film bubble instability of LLDPE/LDPE blends

The relevance of measuring the melt strength of low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and their blends to their performance in terms of bubble stability in the film blowing process has been investigated. A good correlation between the melt strength values for two series of LLDPE/LDPE blends and the size of the operating window for stable film bubble formation has been established. Both the macromolecular structure of the parent polymers, and melt morphology play an important role in the performance of these blends in the film blowing process. © 1999 Society of Chemical Industry

Molecular-dynamics simulation of model polymer nanocomposite rheology and comparison with experiment

The shear-rate dependence of viscosity is studied for model polymer melts containing various concentrations of spherical filler particles by molecular-dynamics simulations, and the results are compared with the experimental results for calcium-carbonate-filled polypropylene. Although there are some significant differences in scale between the simulated model polymer composite and the system used in the experiments, some important qualitative similarities in shear behavior are observed. The trends in the steady-state shear viscosities of the simulated polymer-filler system agree with those seen in the experimental results; shear viscosities, zero-shear viscosities, and the rate of shear thinning are all seen to increase with filler content in both the experimental and simulated systems. We observe a significant difference between the filler volume fraction dependence of the zero-shear viscosity of the simulated system and that of the experimental system that can be attributed to a large difference in the ratio of the filler particle radius to the radius of gyration of the polymer molecules. In the simulated system, the filler particles are so small that they only have a weak effect on the viscosity of the composite at low filler volume fraction, but in the experimental system, the viscosity of the composite increases rapidly with increasing filler volume fraction. Our results indicate that there exists a value of the ratio of the filler particle radius to the polymer radius of gyration such that the zero-shear-rate viscosity of the composite becomes approximately independent of the filler particle volume fraction.

Reactive processing of polyolefins with MAH and GMA in the presence of various additives

This paper describes the initial results obtained on the study of the reactive processing of polyolefins (LLDPE, PP) with maleic anhydride (MAH) and glycidyl methacrylate (GMA) in the presence of styrene, dimethyl sulfoxide (DMSO), and dimethylacetamide (DMAC). The investigation of the processing torque obtained from the grafting reaction showed that the torque could be used as an indicator for some product properties such as gel content and percentage of grafting. Addition of a monomer such as styrene and electron donor compounds such as DMSO and DMAC showed significant improvement in processing properties in comparison with additive-free systems.

Analysis of gas permeability characteristics of poly(lactic acid)/poly(butylene succinate) nanocomposites

Gas permeability and morphological properties of nanocomposites prepared by the mixing of poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and clay was investigated. While the composition of PLA and PBS polymers was fixed as 80% and 20% by weight, respectively, for all the nanocomposites, clay contents varied from 1 to 10wt%. From the morphological studies using both wide angle X-ray diffraction and transmission electron microscopy, the nanocomposite having 1wt% of clay was considered to have a mixed morphology of intercalated and delaminated structure, while some clusters or agglomerated particles were detected for nanocomposites having 3 and more than 3wt% of clay content. However, the average particle size of the dispersed PBS phase was reduced significantly from 7 µm to 30-40nm with the addition of clay in the blend. The oxygen barrier property was improved significantly as compared to the water vapor. A model based on gas barrier property was used for the validation of the oxygen relative permeabilities of PLA/PBS/clay nanocomposites. PLA/PBS/clay nanocomposites validated the Bharadwaj model up to 3wt% of clay contents only, while for nanocomposites of higher clay contents the Bharadwaj model was invalid due to the clusters and agglomerates formed.

Poly (L-lactic acid)/layered silicate nanocomposite blown film for packaging application: thermal, mechanical and barrier properties

In an attempt to alleviate the global solid waste disposal problem and to reduce the dependence on petroleum-based plastics for packaging materials, biodegradable and compostable thermoplastic polymers are required. Polylactic acid (PLLA) is a highly versatile biodegradable polymer derived from 100% renewable resources. Three types of PLA nanocomposites containing 1, 3 and 5 phr of nanoclay were compounded in a co-rotating twin screw extruder, to study the effect of nanoclay content on film processibility of composites as well as properties of blown films. Differential scanning calorimetry CDSC) showed that the cold crystallization and melting temperatures were influenced by the presence of nanoclay. The thennogravimetric analysis (TGA) showed increase in the decomposition temperature for all of the nanocomposites. Mechanical properties of the nanocomposite film showed that the elongation (%) increased up to 3 phr of clay whereas tensile strength and modulus increased only up to 1 phr of the nanoclay. N anocomposite films showed an improvement in oxygen barrier and water vapor barrier in comparison to the neat PLA up to 3 phr of nanoclay.

Molecular simulation of thermophysical properties of aromatic polymers containing oxetane ring in the main chain

Molecular simulation techniques have been applied to newly synthesized aromatic polymers, containing oxetane rings in the main chain, to characterize the shape of rod-like macromolecules. Single chains and periodic unit cells of a series of aromatic polymers with degree of polymerization 15 were used in the simulations, in accordance with the experimentally obtained one. The total potential energy was minimized and then NVE and NPT molecular dynamics simulations were performed for 1,000 ps at 11 temperatures between 10 and 1,000 K. The coefficient of asymmetry was calculated from the computer-generated structures. The predictive capability of the NPT molecular dynamics simulation and Polymer Properties modules of Cerius2 were used to estimate the orientational properties (order parameter), glass transition temperature, cohesive energy, and decomposition temperature of the polymers simulated. In general, there is a good-to-excellent agreement between simulated results and available experimental data of the above investigated properties.

The effect of temperature on the viscoelastic properties of model and industrial dispersions

This paper discusses the effect of temperature on the dynamic rheological properties of both the model polystyrene gelatin and the industrial photographic coupler dispersions. The time temperature superposition (TTS) was used to bring experimental data at various temperatures together into single master curves. An Arrhenius-type TTS principle, rather than the Williams–Landel–Ferry equation, was used in this work to bring all dynamic moduli and dynamic viscosity curves at different temperatures into single master curves. The present investigation verified that the TTS principle, which was developed for polymeric materials, could also be used for model and industrial photographic coupler dispersions as well. Furthermore, not only was the TTS principle suitable for the dispersions in the sol state, but it could also be used for the data in the gel-like state as well. The TTS allowed the estimation of the rheological properties of the dispersions over the frequency range which is otherwise inaccessible to the range of experimental measurement. Therefore, the linear viscoelastic properties of these model and photographic coupler dispersions at very low frequency (which is useful in predicting the stability of the product), as well as properties at very high frequency (or large deformation, e.g., during coating or pumping processes), could be estimated.

Molecular simulation of aromatic polyesters containing oxetane rings in the main chain

Abstract Molecular simulation is a powerful research tool for gaining new insights into polymer chemical structures and processes. This paper presents a computational conformational analysis of some aromatic polyesters containing either an oxetane ring or propylene moieties in the main chain. The studied polyesters were synthesised by phase transfer catalysis using 3,3-bis-(chloromethyl)-oxetane, 1,3-dibromopropane and various aromatic diacids. The computational analysis and calculations were performed using the Cerius2 program (version 3.5), molecular simulation software for material science, designed by Molecular Simulations Incorporated. This study elucidates some aspects and properties dependent upon supramolecular arrangement of the macromolecular chains. In order to verify the agreement between simulated and experimental results the coefficient of asymmetry, order parameter and glass transition temperature were calculated for each studied aromatic polymer.