The study covers the fundamental relationships between the nature of aprotic polar solvents [N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF) and dimethylsulfoxide (DMSO)] used for casting solution preparation and the structure and performance of poly(amide-imide) (PAI) ultrafiltration membranes. It was found that the distinctive feature of the ternary systems PAI-poly(ethylene glycol) (PEG-400, Mn = 400 g mol−1) solvent is gel formation upon the increase in PEG-400 concentration in the solution. The PEG-400 addition to the casting solution was shown to increase pure water flux of the PAI membranes prepared from the casting solutions in different solvents. However, different patterns of the change of pure water flux when gel point is exceeded in PAI-PEG-400-solvent system were revealed. The PAI membranes obtained from the ternary systems PAI-PEG-400-solvent were found to combine high pure water flux at P = 0.1 MPa (130 L m−2 h−1 for DMSO, 120 L m−2 h−1 for DMA and 70 L m−2 h−1 for NMP) and high poly(vinylpyrrolidone) (PVP) rejection coefficients: 98–99% for PVP with Mn = 40000 g mol−1 and 86–95% for PVP with Mn = 10000 g mol−1. SEM studies reveal the significant difference in the PAI membrane structure when different solvents are used for casting solution preparation. The structure of the membranes obtained from 20 wt% PAI solutions in NMP and DMA consists of the thin selective layer supported by substructure pierced by elongated macrovoids. Meanwhile, when DMSO and DMF are used as solvents the addition of PEG-400 yields the suppression of macrovoid formation and anisotropic sponge-like membrane structure is obtained.

Effect of the solvent nature on the structure and performance of poly(amide-imide) ultrafiltration membranes

The effect of the addition of triblock copolymer polyethylene glycol (PEG)–polypropylene glycol (PPG)–polyethylene glycol (PEG) (Pluronic F127) and polyethylene glycol (PEG-4000, Mn = 4000 g mol−1) to the polysulfone (PSF) casting solution on the membrane structure and performance was studied. The phase state, viscosity and turbidity of PSF solutions in N,N-dimethylacetamide (DMAc) with the addition of block copolymer Pluronic F127 were investigated. It was found that 18–22 wt.% PSF solutions in DMAc with Pluronic F127 content ≥ 5 wt.% feature a lower critical solution temperature (LCST). Membrane structure was investigated using scanning electron and atomic force microcopies. It was revealed that average pore size and pore amount on the surface of the membrane selective layer increase and pore size distribution becomes wider with an increase in Pluronic F127 content in the casting solution. It was found that the average surface roughness parameters of the membrane selective layer for PSF/Pluronic F127 membranes significantly exceed those for PSF/PEG-4000 membranes. It was shown that the increase in the membrane flux and the decrease in polyvinylpyrrolidone (PVP K-30, Mn = 40,000 g mol−1) rejection are a result of the addition of both Pluronic F127 and PEG-4000 into the casting solution. It was revealed that PSF/Pluronic F127 membranes are characterized by higher pressure resistance in ultrafiltration process, a lower total flux decrease during ultrafiltration of bovine serum albumin solutions. The antifouling performance of PSF/Pluronic F127 membranes was found to exceed significantly the antifouling performance of PSF/PEG-4000 membranes.

Modification of polysulfone ultrafiltration membranes using block copolymer Pluronic F127

Hot embossing is the most promising method for surface micropatterning of low-value-added products made of cheap polymers such as acrylonitrile butadiene styrene (ABS). In hot embossing, a polymeric part is compressed with a micropatterned mold at a temperature slightly above the glass transition temperature (Tg), held at this temperature for some time, and then cooled below Tg for demolding. However, through this study, we demonstrate that using this conventional strategy to replicate 1 µm structures on a large area on ABS results in defective replicas or damaged molds. We propose a viscous embossing strategy, wherein the polymer is embossed far above its Tg and demolded shortly thereafter in the viscous state. The absence of cooling is the key for damage-less demolding of 1 µm structures on a large area. Yet, an excessive increase of the temperature and time results in the formation of a thermally-induced tensile skin on the polymer surface, as evidenced by the experimental and theoretical analyses performed in this study. In this study, 100 million 1–6 µm wide high-aspect-ratio (1–4) holes were embossed on a smartphone-sized area on the ABS polymer in a few seconds. This proposed strategy exhibits several advantages such as highly precise and more productive replication, which are not observed in the conventional hot embossing technique. 

Large-scale hot embossing of 1 µm high-aspect-ratio textures on ABS polymer

Polymer networks crosslinked via non-covalent interactions afford interesting materials for a wide range of applications due to their self-healing capability, recyclability, and tunable material properties. However, when strong non-covalent binding motifs in combination with high crosslink density are used, processing of the materials becomes troublesome because of high viscosities and the formation of insoluble gels. Here, we present an approach to control the processability of grafted polymers containing strong non-covalent interactions by balancing the interplay of intra- and intermolecular hydrogen bonding. A library of copolymers with different degrees of polymerization and content of protected ureido-pyrimidinone-urea (UPy-urea) grafts was prepared. Photo-deprotection in a good solvent like tetrahydrofuran (THF) at low concentrations (≤1 mg mL–1) created intramolecularly assembled nanoparticles. Remarkably, the intrinsic viscosity of these nanoparticle solutions was an order of magnitude lower compared to solutions of the intermolecularly assembled analogues, highlighting the crucial role of intra- versus intermolecular interactions. Due to the strong hydrogen bonds between UPy dimers, the intramolecularly assembled structures were kinetically trapped. As a result, the polymer nanoparticles were readily processed into a bulk material, without causing major changes in the morphology as verified by atomic force microscopy. Subsequent intermolecular crosslinking of the nanoparticle film, by heating to temperatures where the hydrogen-bond exchange becomes fast, resulted in a crosslinked network. The reversibility of the hereby obtained polymer networks was shown by retrieving the intramolecularly assembled nanoparticles via redissolution and sonication of the intermolecularly crosslinked film in THF with a small amount of acid. Our results highlight that the stability and processability of highly supramolecularly crosslinked polymers can be controlled both in solution and in bulk by using the interplay of intra- and intermolecular non-covalent interactions in grafted polymers.

Controlling the Processability and Stability of Supramolecular Polymers Using the Interplay of Intra- and Intermolecular Interactions

Enhanced oil recovery (EOR) techniques are essential to improve oil production, and polymer flooding has become one of the promising technologies for the Brazilian Pre-Salt scenario. Biopolymers offer a range of advantages considering the Pre-Salt conditions compared to synthetic polymers, such as resistance to high salinity, high temperature, and mechanical degradation. In that sense, bulk rheology is the first step in a workflow for performance analysis.
This paper presents a rheological analysis of four biopolymers (Schizophyllan, Scleroglucan, Guar Gum, and Xanthan Gum) in concentrations from 10 to 2,300 ppm, generally suitable for EOR applications, in temperature levels of 25, 40, 50, 60 and 70°C and two brines of 30,100 ppm and 69,100 ppm total dissolved solids, which aim to model seawater and the mixture between injected seawater and reservoir water typical in Pre-Salt conditions. The pseudoplastic behavior, the overlap concentration, and the activation energy were determined for each polymer solution.
The structural differences in the polymers resulted in different rheological behaviors. Schizophyllan is the most promising, as its viscosifying power is higher than synthetic polymers comparable to Xanthan Gum.  Its resistance at high temperatures is higher than that of synthetic polymers. Scleroglucan behaved similarly to Xanthan Gum, with the added advantage of being nonionic. Guar Gum had the lowest viscosities, highest overlap concentrations, and most pronounced viscosity decay among the tested polymers.
To the author’s knowledge, rheological studies of the biopolymers presented here, considering the viscosities and the overlap concentration and activation energy, in the Pre-salt conditions, are not available in the literature and this will benefit future works that depend on this information

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Bulk rheology characterization of biopolymer solutions and discussions of their potential for enhanced oil recovery applications

The viscous flow activation energy and non-Newtonian index properties of polymer based on feature size were studied through a series of experiments on the rheological properties of amorphous polymer polymethyl methacrylate (PMMA), semi-crystalline polymer polypropylene (PP), and crystalline polymer high-density polyethylene (HDPE) using capillary die with hole diameters of φ0.3 mm, φ0.5 mm, φ1.0 mm, and φ2.0 mm. The results show that the viscous flow activation energy of PMMA decreases with the feature size under microscopic scale. And the viscous flow activation energy of PP and HDPE increases with hole diameters of the die. Under macroscopic scale, the difference in viscous flow activation energy of all polymer materials is significantly reduced with hole diameters of the die. For the non-Newtonian index of the three polymer materials, it decreases with the feature size under the microscopic scale while it increases or does not change with the feature size under the macroscopic scale. At the same time, for different high polymer materials, the viscous flow activation energy model (SVAE model) and non-Newtonian index model (SNNE model) based on feature size were established. Finally, the accuracy and effectiveness of the SVAE model and the SNNE model are verified by comparing with the traditional model and reference data. The viscous flow activation energy and non-Newtonian index values of the polymer material can be calculated conveniently and accurately.

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Research on Polymer Viscous Flow Activation Energy and Non-Newtonian Index Model Based on Feature Size

The invention provides an establishment method of a high polymer melt viscous flow activation energy model based on feature size. The method comprises the following steps: establishing a viscous flowactivation energy index model of different materials, feature size and shearing rate; obtaining high polymer melt viscous flow activation energy under different shearing rate through calculation, andobtaining values of coefficients A and B through fitting; based on high polymer melt experiment analysis, obtaining values of the coefficients A and B under different mouth model feature size D, and establishing a relational expression between the model coefficients A and B and the feature size D; according to the melt experiment of different high polymer materials, obtaining a scattering distribution diagram of the coefficients A and B of different high polymer materials about the mouth model feature size D, and obtaining a numerical value of a high polymer material feature parameter throughfitting; introducing a model correction coefficient, and establishing the viscous flow activation energy calculation model. In the technical scheme provided by the invention, different high polymer materials and high polymer melt rheological feature size influence can be considered, and accuracy of high polymer melt viscous flow activation energy calculation is improved.

Wu Gang

Papers

Research on Polymer Viscous Flow Activation Energy and Non-Newtonian Index Model Based on Feature Size

Establishment method of high polymer melt viscous flow activation energy model based on feature size