Mixing Of Polymer Blends Research Articles

Study of polycarbonate–polystyrene interfaces using scanning transmission electron microscopy spectrum imaging (STEM‐SI)

AbstractPolymer blends are important for both commercial utility and scientific understanding. The degree of interfacial mixing in polymer blends is important since it influences the blends' mechanical properties. Understanding bulk properties in multiphase polymeric materials requires knowledge of the interfacial properties of the materials. The characterization of the interface, in terms of its width and composition profile, provides insight about the bulk behaviour of the material. Chemical microscopy through electron energy‐loss spectroscopy (EELS) in a transmission electron microscope is gaining popularity to characterize narrow polymer–polymer interfaces. In this work, we show how scanning transmission electron microscopy spectrum imaging, a spatially resolved energy‐loss spectroscopy, can be employed to calculate the interfacial width in a pair of immiscible polymers, taking a polycarbonate–polystyrene (PC‐PS) bilayer as an example. By mapping peaks unique to each of the blend constituents at several points across the interface, we show how the interfacial profile concentrations can be determined. With this method we calculated the interfacial width in the PC‐PS bilayer sample to be approximately 32 nm, even utilizing low resolution spectrometers, which are more widely available. Using the technique described with higher resolution EELS instruments having a better signal‐to‐noise ratio, a higher spatial resolution can be achieved. Using EELS chemical fingerprints of polymers that have been developed earlier, the technique presented here has the potential for effective visualization and morphological measurements of phase‐differentiated polymer blends. This paper is an attempt to enable a new user to characterize polymer–polymer interfaces using chemical microscopy. © 2022 Society of Industrial Chemistry.

(Invited) Conjugated Polymers in Redox Active Devices: Electrochromism As a Case Study

Conjugated polymers provide a unique encompassing set of structurally tunable optical, electronic transport, and redox properties that allows their present and potential use in a host of applications which span, field effect transistors, light emitting diodes, solar cells and photodetectors, electrochromism, along with batteries and supercapacitors. Processing of these materials is carried out using a variety of solution methods including spin-coating, spray-coating, blade-coating, slot die coating and ink jet printing. In this lecture, we demonstrate how the optical absorbance spectra of electron-rich pi-conjugated polymers can be tuned to yield electrochromic materials of all colors that can be switched to highly transmissive forms as desired for absorptive/reflective (display type) and absorptive/transmissive (window type) devices. We will demonstrate how structural design and synthesis of fully conjugated polymers, along with mixing in polymer blends, has been used to complete the color palette of electrochromic polymers (ECPs) needed for subtractive color mixing. Colorimetric tuning (using the L*a*b* color space) using a combination of electron rich and poor units, in conjunction with employing subtle changes in steric strain or relaxation, allows for the enhancement of the neutral form color vibrancy, and the transmissivity of the oxidized forms. We have developed a set of fast switching, high contrast black and brown ECP blends. We use these brown blends to demonstrate the attractiveness of ECPs in window-type electrochromic devices (ECDs) as active materials in color changing eyewear.

THE EFFECT OF TYPE ZEOLITE ON THE GAS TRANSPORT PROPERTIES OF POLYIMIDE-BASED MIXED MATRIX MEMBRANES

The permeation rates of O2, N2, CO2 and CH4 has been studied for polyimide-polyethersulfone (PI/PES) blends-zeolite mixed matrix membranes synthesized in our laboratory. The study investigated the effect of zeolite loading and different zeolite type on the gas separation performance of these mixed matrix membranes. Frequency shifts and absorption intensity changes in the FTIR spectra of the PI/PES blends as compared with those of the pure polymers indicate that there is a mixing of polymer blends at the molecular level. Differential scanning calorimetry measurements of pure and PI/PES blends membranes have showed one unique glass transition temperature that supports the miscible character of the PI/PES mixture. The PI/PES-zeolite 4A mixed matrix membrane with 25 wt % zeolite loading produced the highest O2/N2 and CO2/CH4 selectivity of around 7.45 and 46.05, respectively.

Challenging multiphase complex fluids for applications

Modern processing technology is calling the scientific understanding of dynamic processes, where the science of complex fluids plays a central role. We summarize our recent efforts using the generic approaches of multi-scale physics of complex fluids on apparently irrelevant processes, i.e. the mixing of polymer blends, the processing of thermoplastic(TP) toughened thermosetting(TS) composites using phase separation of TP in TS, as well as the enhanced oil recovery using polymer soft gel. It is emphasized that the thorough physical understanding in multi-scales of time and space through the joint efforts of experiment and theory in each scale is the key issue for the modeling of various processes.

Nonrandom mixing in polymer blends: Implications for phase behavior

Nearest-neighbor pair distribution functions are computed from the semiflexible chain lattice cluster theory (LCT) for binary polymer blends and are compared with the predictions of simple random mixing theory. The LCT treats lattice model polymers with structured monomers and with variable chain flexibility by allowing the monomers to extend over several lattice sites and by introducing trans ↔ gauche bending energies. Comparisons with Monte Carlo simulations for polymer melts enable further tests for the accuracy and limitations of the LCT, while computations of nearest-neighbor pair distribution functions for a variety of binary polyolefin blends provide a link between the phase behavior of these blends and the microscopic local correlations induced by packing constraints and energetic interactions. Altering monomer structures leads to subtle changes in pair distribution functions but profound variations in phase behavior. The calculations of the nearest-neighbor pair distributions provide a simple microscopic explanation for the LCT predictions of the pressure dependence of blend phase diagrams. Variations of the nearest-neighbor pair distribution functions with chain stiffness, van der Waals interactions, temperature, polymerization indices, etc., are correlated with trends in phase behavior and other physical properties. The semiflexible chain LCT is used for further tests towards developing a computationally convenient thermodynamically equivalent linear semiflexible chain model to mimic the melt and blend properties of experimental (or theoretical) structured monomer chains.

Heat of mixing in polymer blends based on poly(vinyl acetate)

Knowledge of the heat of mixing is very important in order to evaluate the interaction parameter, according to the Patterson theory. In this work we illustrate the results regarding some polymer blends, based on poly(vinyl acetate) and some polyacrylates with different substituent groups. In this way it is possible to understand the effect of the lateral group hindrance, as it will be illustrated in the paper.

Predicting the effect of viscosity ratios on the mixing of polymer blends using the boundary element method

AbstractMixing or blending two or more fluids of different viscosities is an important and complex issue in the polymer industry. Simulating these types of processes leads to a better understanding of the flow phenomena that take place during mixing. The boundary element method is ideal to simulate mixing flows, because of the large deformations and moving boundary nature of internal batch mixers and extruders. This paper presents a boundary element simulation of the flow of multi‐viscous polymer blends inside extruders and internal mixers. In addition, the governing equations, boundary integrals, and their numerical implementation for creeping flows are presented. The simulation is used to predict the mixing quality of polymer blends in realistic mixing processes. A model describing the relationship of drop strain to matrix strain as a function of viscosity ratio is also presented. The flow simulation results are in good agreement with analytical and experimental results.

Analysis of the Phase Structure Development during the Melt Mixing of Polymer Blends

The paper presents analysis of the phase structure development in polymer blends, where a minor component is dispersed in the matrix consisting of a major component, during the melt mixing, Problems of modelling of the flow field in mixing devices are briefly discussed. Relevant results of theoretical and experimental studies of the droplet breakup and coalescence are summarized. Theories dealing with the competition between droplet breakup and coalescence are discussed in detail. Their results are compared with experimentally determined dependences of the size of dispersed droplets on mixing conditions, properties of the components, and blend composition.

Enthalpies of Mixing in Polymer Blends of Chlorinated Polymers: Application of a Group Contribution Method

A modified Guggenheim quasichemical method (MGQ) has been applied to calculate enthalpies of mixing in mixtures based on chlorinated polymers such as poly(epichlorohydrin) (PECH) or poly(vinyl chloride) (PVC). The required parameters have been determined from experimental heats of mixing in mixtures of model compounds. Using the MGQ method, enthalpies of mixing of PECH/ester containing polymer mixtures and PVC/polyoxide blends have been simulated. In PECH/ester containing polymer blends, the MGQ method gives an adequate picture of the evolution of the miscibility with the polyester CH 2 /CH 2 COO ratio. Similarly, in PVC/polyoxide blends, the variation of the heat of mixing along the polyoxide family seems to agree with the miscibility window of these blends. However, in PVC/poly(ethylene oxide) blends, the MGQ method was not able to predict accurately the experimentally observed dependence of the miscibility on the composition.

Flow and Heat Transfer Simulation of the Mixing of Polymer Blends Using the Boundary Element Method

Abstract In most polymer processes the quality of the final part stems back in great part to the mixing of the polymer blends and the viscous heating that occurs during the process. To date, these processes have been simulated using the finite difference or finite element methods which rely on cumbersome remeshing techniques, restricting the analysis to simple geometries. However, mathematical manipulation of the governing equations results in boundary integrals, allowing the solution of complicated moving boundary problems without domain meshing. The resulting boundary element model and simulation results of flow with heat transfer and the blending of two or more fluids of different viscosity effects during mixing of polymer blends is presented in this paper. The results give insight to the complex phenomena that take place during mixing processes.

Simulating the Non-Isothermal Mixing of Polymer Blends Using the Boundary Element Method

In most polymer processes the quality of the final part stems back in great part to the mixing of the compound and the viscous heating that occurs during the process. To date, these processes have been simulated using the finite difference or finite element methods which rely on cumbersome remeshing techniques, restricting the analysis to sim ple geometries. However, mathematical manipulation of the governing equations results in boundary integrals, allowing the solution of complicated moving boundary problems without domain meshing. The resulting boundary element model and simulation results of the flow and heat transfer effects during mixing of polymer blends is presented in this arti cle. The results are in good agreement with experimental data and give insight to the com plex phenomena that take place during mixing processes.

Fundamentals of polymer compounding: The phase‐inversion mechanism during mixing of polymer blends

AbstractDuring a routine extrusion compounding of a polymer blend of polyarylate resin and ethylene/acrylate rubber, an unexpected powdery product instead of a cohesive mixture was obtained. Also, the 20% rubber component was not well dispersed in the final product. This process problem was studied by simulation with a laboratory internal mixer following the procedure discussed by Shih. The powder formation was successfully reproduced. From the results of continuous video monitoring and analyses of the intermediate samples collected during the simulation experiments, we found that the progression of mixing from solid pellets to a cohesive mixture in a batch mixer or a twin‐screw extruder needs to “climb over” a prolonged transition state where the plastic polyarylate was dispersed in the 20% rubber. The finding led to two successful solutions to the powdering problem. A “phase‐inversion” mechanism is proposed to explain the observed morphological changes. This mechanism appears to have wider applicability in the processing of polymer blends. © 1992 John Wiley & Sons, Inc.

Droplet size of the minor component in the mixing of melts of immiscible polymers

Using a general description of break-up and the Smoluchowski theory of coalescence of droplets, a relation has been derived for the radius of a droplet arising during mixing of polymer blends in the steady state. In a dilute system, the radius of the droplets increases linearly with their concentration. In more concentrated systems, the type of the concentration dependence of the droplet size is affected by the properties of the dispersed phase and of the matrix.

A proton MAS NMR method for determining intimate mixing in polymer blends

A proton MAS NMR method for determining intimate mixing in polymer blends

Polymer-Polymer Interdiffusion

AbstractInterdiffusion of polymer chains plays an important role in establishing good adhesion at polymer interfaces as well as in the kinetics of phase separation and mixing in polymer blends. Reptation, a process in which a given linear chain crawls along a primitive path defined by the topological constraints due to the surrounding chains, is thought to be the most important diffusion mechanism. A reptating chain of Volecular weight M should have a tracer diffusion coefficient given by D =DR =Do M−2, where D depends on the Rouse mobility of the chain and an entang ement molecular weight, Me. Because the topological constraints are assumed to be fixed, DR is independent of the molecular weight P of the polymer into which the M-chains are diffusing. In principle however if M is large enough and P is small enough the M-chain can diffuse by rearrangement of the P-chains surrounding it, a process called constraint release. The D for this process, DCR= αCRDoMe2/(MP3), where αCR is a constant approximately equal to 13, increases strongly with decreasing P. Recent experimental results, which give evidence for both reptation and constraint release, will be reviewed. These results have important implications for the diffusion of nonlinear polymer chains, e.g. stars and rings.