Polymer-diluent Systems Research Articles

Straightforward determination of equilibrium heat of fusion and interaction parameter for a Polymer-Diluent system

Straightforward determination of equilibrium heat of fusion and interaction parameter for a Polymer-Diluent system

A criterion of diluent selection for the polymeric membrane formation via thermally induced phase separation process based on Hansen solubility parameter theory

The Hansen solubility parameter (HSP) theory, which includes the Hansen dispersion (D), polar (P), and hydrogen (H) components and a derivative ‘solubility parameter distance, Ra’ parameter, was adopted to evaluate the interaction between different polymers and their various diluents, so as to obtain a valuable and feasible criterion for the diluent selection of the thermally induced phase separation (TIPS) process for the preparation of polymeric membranes. Firstly, a full-scale database of the four HSP parameters of typical polymer-diluent systems was obtained based on a complete literature review about the phase separation process of all the polymer/diluents systems that have been applied to prepare polymeric membranes via TIPS and our additional exploratory experiments for membrane formation mechanism, in which two different phase separation processes including solid to liquid and liquid to liquid were distinguished. Relationships between the Ra parameter and the phase separation behavior were figured out to get a criterion for selecting the single diluent for the typical polymers. Moreover, the diluent selection was extended by adding a second diluent, and a schematic three-dimensional phase diagram was drawn to provide a feasible understanding of the TIPS process of the polymer-binary diluent system. Taking polypropylene (PP) as the representative example, plenty of exploratory experiments for the membrane formation mechanism based on a literature review were conducted to propose a guide based on the Hansen polar and hydrogen solubility component parameters to help select a proper binary diluent system.

Solid–liquid–liquid phase envelopes from temperature-scanned refractive index data

Abstract A novel method for estimating the upper critical solution temperature (UCST) of N,N-diethyl-m-toluamide (DEET)-polyethylene systems was developed. It was validated using data for the dimethylacetamide (DMA)-alkane systems which showed that refractive index mixing rules, linear in volume fraction, can accurately predict mixture composition for amide-alkane systems. Furthermore, rescaling the composition descriptor with a single adjustable parameter proved adequate to address any asymmetry when modeling the DMA-alkane phase envelopes. This allowed the translation of measured refractive index cooling trajectories of DEET-alkane systems into phase diagrams and facilitated the estimation of the UCST values by fitting the data with an adjusted composition descriptor model. For both the DEET- and DMA-alkane systems, linear behavior of UCST values in either the Flory–Huggins critical interaction parameter, or the alkane critical temperature, with increasing alkane molar mass is evident. The UCST values for polymer diluent systems were estimated by extrapolation using these two complimentary approaches. For the DEET-polyethylene system, values of 183.4 and 180.1 °C respectively were obtained. Both estimates are significantly higher than the melting temperature range of polyethylene. Initial liquid–liquid phase separation is therefore likely to be responsible for the previously reported microporous microstructure of materials formed from this binary system.

Investigation on the membrane formation process of polymer–diluent system via thermally induced phase separation accompanied with mass transfer across the interface: Dissipative particle dynamics simulation and its experimental verification

A new dissipative particle dynamics (DPD) simulation methodology was established to investigate the membrane formation process via thermally induced phase separation (TIPS) accompanied with mass transfer across the interface between the polymer solution and the coagulation bath, taken into account polyvinylidene fluoride–diphenyl carbonate (PVDF–DPC) system. The simulation results indicated that the polymer solution mainly underwent spinodal decomposition and if the coagulation bath medium had a good compatibility with the diluent, diluent and bath particles could engulfed or ejected across the polymer solution–coagulation bath interface, which caused a thin and dense polymer layer was formed near the interface. In addition, as the coagulation temperature decreased, the spinodal decomposition became faster and the coagulation bath had a less effect on the membrane formation process. Second as the compatibility between the diluent and coagulation bath declined the mass transfer got indistinct and the polymer layer disappeared gradually. To verify above simulation results, experiments were performed, whose conclusions were consistent with the simulations. The observation and conclusion in this study are beneficial to the understanding of the membrane formation of polymer–diluent system via TIPS.

Three-dimensional analysis of membrane formation via thermally induced phase separation by dissipative particle dynamics simulation

The effects of polymer molecular weight (polymer chain length), polymer molecular weight distribution (polymer chain length distribution) and diluent structure on the membrane formation of polymer–diluent system via the thermally induced phase separation (TIPS) method were analyzed on the basis of a dissipative particle dynamics (DPD) simulation platform. The simulation platform was extended into three-dimensions (3-D) to make sure that the results were more comprehensive. The simulation results proved that both the polymer chain length and polymer chain length distribution had significant influences on the phase separation process. As the polymer chain length increased, phase separation rate first increased when the polymer chain was relatively short and then decreased when the polymer chain length was larger. In addition, as the chain length distribution got wider, the phase separation rate decreased gradually at the middle and last stages of the phase separation process. It was also demonstrated that the interaction between polymer and diluent could be regulated by changing the interaction of the polymer and diluent local part by the local modification on the diluent molecular structure, which was beneficial to the membrane preparation. The information obtained from this study is consistent with the experimental results in literatures, proving that the simulation method could be widely applied in dynamics analysis of the membrane formation process.

Dissipative particle dynamics simulation on the membrane formation of polymer–diluent system via thermally induced phase separation

Dissipative particle dynamics (DPD) simulations are carried out to study the structure and kinetics of membrane formation via thermally induced phase separation, taking into account the polypropylene–diphenyl ether (PP/DPE) system with neutral substrate on the mesoscale. According to the Flory–Huggins–DPD phase diagram, the interaction parameter between polymer and diluent in DPD is regulated to control the temperature. We investigate the effect of the deep and shallow quench on the membrane formation from early stage to late stage, including the corresponding membrane morphology. The results of the structure factor on the mesoscale indicate that the phase separation undergoes spinodal decomposition. Moreover, they are in accordance with the light scattering experiment results and the linear Cahn–Hilliard theory in the early stage. The domain size first reduces with time and then increases, which corresponds to that the number of the interfaces between polymer and diluent first increases, and then decreases to minimize the total free energy. In addition, our results show that the domain size has a more rapid growth in the intermediate stage. The information we gain from this study may benefit to understand the formation of membrane on the mesoscale.

Rheology behavior of high‐density polyethylene/diluent blends and fabrication of hollow‐fiber membranes via thermally induced phase separation

AbstractThe phase‐separation behavior of high‐density polyethylene (HDPE)/diluent blends was monitored with a torque variation method (TVM). The torque variation of the molten blends was recorded with a rheometer. It was verified that TVM is an efficient way to detect the thermal phase behavior of a polymer–diluent system. Subsequently, polyethylene hollow‐fiber membranes were fabricated from HDPE/dodecanol/soybean oil blends via thermally induced phase separation. Hollow‐fiber membranes with a dense outer surface of spherulites were observed. Furthermore, the effects of the spinning temperature, air‐gap distance, cold drawing, and HDPE content on the morphology and gas permeability of the resultant membranes were examined. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Phase behavior of polymer/diluent/diluent mixtures and their application to control microporous membrane structure

Rechargeable battery separators containing controlled pores were fabricated via the thermally-induced phase separation (TIPS) process. Based on the idea that pores could be manipulated by controlling the liquid–liquid phase separation temperature in the TIPS process, phase boundaries of the polymer–diluent systems were controlled by using diluent mixtures. Phase behaviors of the polymer/diluent/diluent ternary blends consisting of polyethylene (PE) as polymer, and soybean oil (SBO) and dioctyl phthalate (DOP) as diluents were explored. PE/SBO and PE/DOP binary blends, and PE/SOB/DOP ternary blends exhibited typical upper critical solution temperature (UCST) type phase behaviors, and the phase separation temperatures of the PE/SBO blends were higher than those of the PE/DOP blends. When the mixing ratio of the polymer and diluent-mixture was fixed, the phase separation temperature of the PE/SBO/DOP blend initially increased with increasing SBO content in the diluent-mixture passing through a maximum centered at about 80 wt% SBO and decreased beyond this point. Furthermore, the phase separation temperature of the PE/diluent-mixture blend was always higher than that of the PE/SBO blend when the diluent-mixture contained more than or equal to 50 wt% SBO. To understand the observed phase behavior of the blends, thermodynamic analyses based on the lattice-fluid theory were performed. Larger pore membranes were fabricated from the blend when higher phase separation temperatures of the blend were exhibited.

Effect of diluents on hydrophilic ethylene-acrylic acid co-polymer membrane structure via thermally induced phase separation

Abstract Hydrophilic microporous membranes were prepared via the thermally induced phase separation process using three types of hydrophilic ethylene-acrylic acid co-polymers (EAA) with different co-unit contents. The effects of diluents on the structure of membranes were also investigated. The experimental results showed that the phase diagrams of these polymer diluent systems were typical diagrams of semi-crystalline polymer diluents with weak interaction. The cloudpoint curve shifted to the lower temperature, while the crystallization temperature was not influenced so much by the type of diluents. The pore sizes of EAA membranes prepared from different diluent systems at 30 wt% polymer concentration were about 4.98 μm, 1.80 μm, 1.72 μm, 1.57 μm, and 0.59 μm for the systems of EAA3003/diphenyl ether (DPE), EAA3003/soybean oil, EAA3003/dioctyl phthalate (DOP), EAA3003/sesame oil, and EAA3003/peanut oil, respectively. The microstructure of EAA3003-soybean oil system was leafy, while other systems were cellular. Pore sizes and porosities of three EAAs with different co-unit contents decreased in the order of EAA1410/DOP, EAA3002/DOP and EAA3003/DOP.

Vapor−Liquid Equilibrium for Polymer−Diluent Systems from Melting Point Depression

A novel approach for determining vapor-liquid equilibrium (VLE) for polymer-diluent systems is described. The concentration- and temperature-dependence of diluent-polymer Flory-Huggins interaction parameter X ij is first estimated from depression in polymer melting point as a function of monomer (diluent) concentration. VLE for the polymer-diluent binary system is then obtained using an activity coefficient model and equation of state model with Aspen Polymer Plus. The technique is validated for the syndiotactic polystyrene-toluene and syndiotactic polystyrene-methyl ethyl ketone and is extended to polybutylene terephthalate - with various diluents such as butanediol, tetrahydrofuran, isophorone, 1-methylnaphthalene, and benzonitrile, systems hitherto not reported in the literature.

Fabrication of poly (ECTFE) membranes via thermally induced phase separation

Poly (ethylene chlorotrifluoroethylene) (ECTFE) is a 1:1 alternating copolymer of ethylene and chlorotrifluoroethylene with an excellent combination of chemical, thermal and mechanical properties. Although the lack of a suitable solvent for ECTFE precludes membrane casting by conventional room-temperature processes of immersion precipitation or evaporative casting, thermally induced phase separation provides an attractive pathway for membrane fabrication. We have successfully identified three possible latent solvents for ECTFE and have studied the ECTFE-dibutyl phthalate (DBP) polymer-diluent system. ECTFE membranes were fabricated using a TIPS-casting apparatus that allowed control of several important process parameters. ECTFE membranes were characterized via scanning electron microscopy (SEM), porometry and permeation techniques. Results indicated that membranes with continuous pores having diameters in the microfiltration range (0.1–0.5 μm) could be reliably fabricated.

Crystallization mechanism of regioregular poly(3‐alkyl thiophene)s

AbstractThe crystallization properties of three regioregular poly(3‐alkyl thiophene)s (P3ATs) are studied: poly(3‐hexyl thiophene) (P3HT), poly(3‐octyl thiophene) (P3OT), and poly(3‐dodecyl thiophene) (P3DDT). The morphology of the isothermally crystallized samples is a whisker type. The values of the enthalpy of fusion of ideal crystals (ΔH), determined from the melting point depression in the polymer–diluent system, are 99, 73.6, and 52 J/g for P3HT, P3OT, and P3DDT, respectively. The values of the equilibrium melting point (T), determined from the Hoffman–Weeks extrapolation procedure, are 300, 230, and 180 °C for P3HT, P3OT, and P3DDT, respectively. From the linear extrapolation of the P3AT data, the T and ΔH values of unsubstituted polythiophene are predicted to be 400 °C and 139 J/g, respectively. The crystallization kinetics of these polymers are studied with differential scanning calorimetry, and the Avrami exponents vary between 0.6 and 1.4, indicating one‐dimensional heterogeneous nucleation with linear growth. As the P3AT whiskers are produced from the chain‐folding process, the Lauritzen–Hoffman growth rate theory is applied to analyze the temperature coefficient of the crystallization rate data. Graphical plots indicate a transition from regime I to regime II during isothermal crystallization for all the P3ATs studied. The fold surface energy and the work of chain folding calculated from the slopes of the graphical plots decrease with an increase in the number of carbon atoms of the side chain. The primary crystallization process of the side‐chain crystallization is very fast and is attributed to the zipping effect of the main‐chain crystals. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2073–2085, 2002

Phase behavior of polymer–diluent systems characterized by temperature modulated differential scanning calorimetry

The thermodynamic phase behavior of a polymer–diluent system (atactic polystyrene–1-dodecanol) forms the fundamental basis of the description of thermally-induced demixing processes. In this paper, we demonstrate that temperature modulated differential scanning calorimetry (TMDSC) can accurately detect the liquid–liquid demixing transition. This transition can be clearly observed in the modulus of the complex heat capacity signal and in the phase angle. The phase angle shift is very small during liquid–liquid demixing so liquid–liquid demixing of a polymer–diluent system takes place at time scales instantaneously in comparison with the modulation period of TMDSC. In addition, the glass transition temperature of the polymer-rich phase and the crystallization temperature of the diluent can be determined as well within the same TMDSC experiment.

Kinetic studies of thermally induced phase separation in polymer-diluent system

Thermally induced phase separation was studied by the light scattering in polypropylene/methyl salicylate system. Data could be well fitted with the linear Cahn theory for spinodal decomposition (SD) in the early stage of phase separation. Characteristic properties of the early stage of SD, such as an apparent diffusion coefficient and an interphase periodic distance, were obtained. The periodic distance ranged from 3 μm to 4 μm. The growth of the phase-separated structure obeyed power-law scaling in the later stage, and the structure factor could be scaled into a universal time-independent form. Domain sizes obtained from the light-scattering measurements were consistent with the optical microscope measurements. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1028–1036, 2000

Cryogenic induced phase separation of chitosan solution

The chitosan porous membrane was prepared by extending the principle of thermally induced phase separation (TIPS) for the polymer-diluent system to the polymer solution at arnbient temperature to carry out the cryogenic induced phase separation (CIPS). The porous membrane obtained was characterized by scanning electron microscopy (SEM) and gas permeability. It was found that a specific lacy pore structure morphology corresponding to the TIPS’ solicd-liquid phase separation was formed in the demixing process and the porosity could be more than 70%. The research of demixing mechanism and membrane-formation process showed that the membrane was stacked through porous lamella. The porosity of membrane increases and the pore diameter decreases with increasing solidtfying temperature. Both the porosity and pore diameter decrease with the chitosan concentration increase.

Relationship Between Flame Retardation and Phase Transition Behavior of Polyester Fabrics Treated with a Bromine-Containing Compound

Poly (ethylene terephthalate) (PET) fabrics are treated with meso-1,2,3,4-tetrabro mobutane (TBB) to investigate flame retardation. The limiting oxygen index (LOI) value increases with an increasing amount of absorbed TBB (ATBB) and reaches 28.1 % when ATBB is 10.20% owf. The slope of LOI is 1.14%/% owf from 0 to 4.65% owf of A TBB, and the slope decreases 0.31%/% owf at a region higher than 4.65% owf. The phase transition behavior of treated samples, investigated with differential scanning calorim etry, reveals that the depression of the melting initial temperature ( T m) is directly proportional to the LOI value. Flory's equation for the depression of the melting point in polymer-diluent systems is applied to the PET-TBB system. We conclude that TBB molecules, which have strong affinities for PET segments in the region below 4.65% owf, show greater retardation for flammability.

Isotherinal crystallization of isotactic polypropylene-hexamethylbenzene blends: kinetics analysis

This paper analyses the polymer crystallization kinetics (obtained via differential scanning calorimetry) for a model eutectic-forming polymer-diluent system, isotactic polypropylene (iPP)-hexamethylbenzene (HMB). The Avrami and Hoffman-Lauritzen crystallization theories were applied to iPP crystallization in the presence of HMB. In addition, an experimental-computational method of obtaining the phase diagram for an eutectic-forming system is presented along with a technique for determining the sequence of phase separation events.

Kinetics of Droplet Growth in Liquid–Liquid Phase Separation of Polymer–Diluent Systems: Model Development

A new model is presented for describing the increase in average droplet size as a function of time for systems composed of diluent droplets in a polymer–diluent matrix phase. The new model describes the merging of any two dropletsandaccounts for the effect that two coalescing drops has on neighboring drops. In particular, as two drops coalesce, fluid is expelled from between them. This expelled fluid causes the movement of neighboring drops, which leads to further coalescence of drops. The model predicts a strong influence of the droplet growth rate on the volume fraction of the droplet phase, which corresponds with experimental observations. The model was found to be sensitive to the matrix phase viscosity and the single fitting parameter, and less sensitive to the interfacial tension and Hamaker constant.

Kinetics of droplet growth in liquid—liquid phase separation of polymer—diluent systems: experimental results

Liquid—liquid thermally induced phase separation of the polymer—diluent system isotactic poly(propylene)—diphenyl ether was studied under an optical microscope. It was found that as the system phase separated, droplets of a diluent-rich phase formed within a polymer-rich matrix. These droplets grew in size and decreased in number by a process known as coarsening. The scaling exponent relating droplet diameter and time was determined. The scaling exponent was found to be a strong function of the droplet phase volume fraction, and this strong dependence on volume fraction was relatively insensitive to temperature. The influence of the ratio of interfacial tension between the phases and the viscosity of the matrix phase was less significant on the growth rate of the droplets.

A simple method of extrapolating the coexistence curve and predicting the melting point depression curve from cloud point data for polymer-diluent systems

This paper presents a quick, useful method for obtaining an equilibrium phase diagram (including the melting point depression curve) for a semicrystalline polymer-diluent mixture from cloud point data. Good agreement was obtained between the theoretically predicted and experimentally generated equilibrium crystallization curves in spite of simplifying assumptions. An accurate extrapolation of the coexistence curve to regions in the phase diagram where experimental generation of cloud point data is not possible was also obtained. Flory's original polymer swelling theory was used to determine the complete phase diagram. In the system studied (isotactic polypropylene in diphenyl ether), the interaction parameter was assumed to be a function of temperature only. Cloud points were generated experimentally, and an interaction parameter was determined at each temperature. A melting point depression curve was calculated from the temperature dependent interaction parameter and compared with experimentally determined equilibrium melting points. The resulting phase diagram was used to interpret the morphology of microporous structures prepared by the thermally induced phase separation mechanism.