Modification of poly(ethylene terephthalate) by combination of reactive extrusion and followed solid‐state polycondensation for melt foaming

A combination of reactive extrusion and followed solid‐state polycondensation (SSP) was applied to modify the virgin fiber grade poly(ethylene terephthalate) (v‐PET) and recycled bottle‐grade PET (r‐PET) for melt foaming. Pyromellitic dianhydride (PMDA) and triglycidyl isocyanurate (TGIC) were chosen as the modifiers for the reactive extrusion performed in a twin‐screw extruder. For comparison, commercially available chain extender ADR JONCRYL ADR‐4370‐S was also used. The characterizations of the intrinsic viscosity, i.e., [η], and rheological properties whose changes were correlated to the long chain branches introduced in the molecular structure were performed on the modified PET to evaluate their chain extension extent. The results revealed that the [η] of 1.37 dL/g was obtained for PMDA modified v‐PET while that of 1.15 dL/g for TGIC modified r‐PET. Such difference was attributed to the different reactivity of the two chain extenders with the two types of PET. Increases in shear viscosity and storage modulus, and the high pronounced shear thinning behavior were also observed in the modified PET. Finally, the foamability of the certain modified PET was verified by the batch melt foaming experiments. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42708.     

Neural network modeling of the preparation process of a siloxane‐organic polyazomethine

Although apparently simple, the polycondensation reaction leading to polyazomethine is difficult to control because of its equilibrium character, the conversion degree being influenced by a series of parameters. The reaction between a siloxanediamine, 1,3‐bis(3‐aminopropyl)tetramethyldisiloxane, and terephthalaldehyde was performed here in solution (in tetrahydrofuran) without by‐products removal and in absence of any catalyst or pH modifier. Different conditions (co‐monomers ratio, dilution, and temperature), considered as input parameters for the process modeling, were varied according to a pre‐established experimental program. The viscosity of the reaction mixture was chosen as output parameter, being monitored with a Haake Viscotester 7 Plus‐L. The process modeling was performed using a hybrid combination of artificial neural networks and differential evolution algorithm, the last one having the role of developing the neural model in an optimal form. The simulation results showed that the methodology provides accurate results, the model predictions being in close correlation with the experimental data. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42552.     

Gelation and crosslinking characteristics of photopolymerized poly(ethylene glycol) hydrogels

The gelation and crosslinking features of poly(ethylene glycol) (PEG) hydrogels were scrutinized through the UV polymerization processes of poly(ethylene glycol) methacrylate (PEGMA) and poly(ethylene glycol) dimethacrylate (PEGDMA) mixtures. The real‐time evolutions of the elastic moduli of the prepolymerized mixtures with different crosslinking ratios of PEGMA and PEGDMA and the photoinitiator concentrations were measured during photopolymerization. The rheological properties were compared with other properties of the PEG hydrogels, including the relative changes in the C?C amounts in the mixtures before and after UV irradiation, water swelling ratio, gel fraction, mesh size, and mechanical hardness. As the portion of PEGDMA as a crosslinker increased, the final elastic modulus and gel fraction increased, whereas the swelling ratio and scratch penetration depth at the hydrogel film surface decreased because of the formation of compact networks inside the hydrogels. These results indicate that there was a good correlation between the rheological analysis for predicting the crosslinking transition during photopolymerization and the macroscopic properties of the crosslinked hydrogels. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41939.     

Significance of polymer on emulsion stability in surfactant‐polymer flooding

The influence of polymer on stability and shear rate on droplet size of emulsion is evaluated in the laboratory, microstructure of the emulsion is observed under a microscope, and the pore distribution of the cores is analyzed through mercury injection experiments. In the process of surfactant‐polymer (SP) flooding, the thickness of polymer absorbed on the surface of the rock is calculated by a mathematical model. The experiments show that the polymer is good for the stability of emulsion, with the increase of shear rate, stability becomes better, and droplet size gets smaller. Due to the adsorption of polymer, the pore throat turns narrow, seepage velocity is increasing, and also the emulsion becomes more stable with the smaller‐size droplets. During the single emulsifier flooding, the emulsion is easy to coalescence for its instability, and the seepage channel can be easily blocked, which leads to the high injection pressure. Consequently, the polymer plays an important role on emulsion stability in SP flooding. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42171.     

Characterization of extensional rheological filament stretching with a dual‐mode Giesekus model

A new, simple, formulation that describes capillary thinning as predicted by a two‐mode Giesekus model is derived, and its application in analyzing data from extensional rheometry (capillary thinning) experiments is discussed. An algorithm is presented that can be used to fit the expressions obtained from the Giesekus model to extensional rheometry data. Examples of data fitting are given for an idealized data set, for measurements obtained for aqueous solutions of 6 wt % 900,000 molecular weight polyethylene oxide, and for biological fluids obtained from pitchers of Nepenthes Rafflesiana. Good fits to the data were obtained, with coefficients of determination in excess of 0.98. For each data set, it was possible to calculate values of extensional viscosity and relaxation time for each of the two modes, allowing quantitative comparison of different fluids or of the same fluid as it ages. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2188–2199, 2016     

Solution behavior of water‐soluble poly(acrylamide‐co‐sulfobetaine) with intensive antisalt performance as an enhanced oil‐recovery chemical

In the process of oilfield development, salt tolerance is an important property for enhanced oil‐recovery (EOR) chemicals. In this study, we synthesized two acrylamide‐based sulfobetaine copolymers containing 2‐hydroxy‐3‐[(3‐methacrylamidopropyl)dimethylammonio]propane sulfonate (SHPP) or 3‐(4‐acry‐loyl‐1‐methyl‐piperazinio)‐2‐hydroxypropane sulfonate (SHMP). The interactions between these two copolymers and inorganic salts were compared, and the apparent viscosity (η_app) behaviors of copolymer–salt solutions at different shear rates and temperatures were investigated. We found that the η_app of PAPP and PAMP showed intensive antisalt performance, exhibiting an excellent antipolyelectrolyte effect. The η_app retention value of 30,000 mg/L PAMP in brine was 86.47 mPa s at 510 s^?1, and when the temperature was increased to 90 °C, it was 99.73 mPa s; this was better than that of PAPP under the same conditions. Therefore, PAMP was more applicable as an EOR chemical that have outstanding salt tolerance and temperature resistance. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46235     

Morphology and performance of poly(vinylidene fluoride) flat sheet membranes: Thermodynamic and kinetic aspects

In this study, poly(vinylidene fluoride) (PVDF) membranes were prepared using two different solvents with various polymer concentrations to investigate the predominant kinetic or thermodynamic aspects of membrane preparation in a phase separation process. For this purpose, dimethyl sulfoxide (DMSO) as a weak solvent and N‐2‐methylpyrrolidone (NMP) as a strong solvent were used with polymer concentrations between 8 and 15 wt %. Scanning electron microscopy and water content, contact angle, and pore size measurements were used to assess the factors affecting the physicochemical properties of the prepared membranes. The results showed that in the case of NMP, the membrane structure is mainly controlled by thermodynamic parameters, while when using DMSO, kinetic parameters are predominant. According to the results, the prepared PVDF‐based membranes with DMSO exhibited a relatively denser top layer and less permeation compared to the NMP/PVDF membranes. The difference between the viscosities of the casting solutions with equal polymer concentrations in DMSO and NMP was considered to be the main effective factor in solvent/nonsolvent exchange, resulting in denser top layers in the DMSO/PVDF membranes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46419.     

Study on the interactions between SDBS/SOE‐60 mixed surfactant and PVP in solution

The interactions between the mixed surfactants sodium dodecyl benzenesulfonate (SDBS) and modified oil ethoxylate (SOE‐60) with polyvinylpyrrolidone (PVP) were studied at 25 ± 1 °C using a surface tension meter, Ubbelohde viscometer, and fluorescence spectrophotometer. Interaction mechanisms of SDBS/SOE‐60‐PVP systems were explained by the “necklace and bead” model. The results showed that the interaction could be divided into three parts by two characteristic concentrations: the critical aggregation concentration (cac) and the polymer saturation point (psp). The interaction mechanisms of SDBS/SOE‐60‐PVP systems are consistent with the “necklace and bead” model. The binding mixing surfactant micelles, formed by free SDBS and SOE‐60 molecules, were bound to PVP chains by hydrophobic and ion–dipole interactions. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46717.     

Thermoreversible rheological responses of biscarbamates and tricarbamates in uncured epoxy composite pastes caused by their self‐assembly in an epoxy matrix

We investigated the rheological behaviors of diglycidyl ether of bisphenol A (epoxy resin) composite pastes with fumed SiO₂, biscarbamates, and tricarbamates with the same terminal alkyl chains of C₁₆, respectively. The rheological measurement results show that the rheological responses of both carbamates in the epoxy composite pastes were stronger than that of fumed silica at the same concentrations, especially at low concentrations, and the rheological behaviors of the epoxy composites with them were thermally reversible and concentration dependent. IR, thermal, differential scanning calorimetry, and polarized microscopic analyses demonstrated that their different excellent rheological responses in epoxy composite pastes came from their different self‐assemblies in the epoxy matrix, which were caused by the different intermolecular interactions, mainly including hydrogen‐bonding and van de Waals interactions, and the intermolecular interactions for carbamates were closely related to their molecular structures. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46032.     

A method based on the time–temperature superposition principle to predict pressurization time in compression molding

The quality of epoxy composites reinforced by glass fibers and manufactured by compression molding is affected by the pressurization time. Traditional methods, including differential scanning calorimetry and dynamic thermomechanical analysis, cannot be reliably used to predict pressurization time in the scenario of continuous production and inconstant circumstances seen in industry. In this paper, the rheological behaviors of epoxy under constant temperature were investigated and analyzed to verify if the time–temperature superposition (TTS) principle, which defines the relation between time and temperature in the deformation and relaxation response of a viscoelastic material, could be suitably applied to describe them. The results show that the TTS principle could indeed be used to predict resin viscosity by the horizontal shift factor. A new method based on the TTS principle and written into a program to forecast pressurization time in compression molding is proposed. The uniform surface color and the qualified thickness of the composite components using the program indicate that the program works well and that this method is feasible for predicting pressurization time during compression molding. The results of tensile and short‐beam shear strength tests show that pressurization time affects the mechanical properties of the final product. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45308.