Rheology and microstructure of myofibrillar protein-plant lipid composite gels: Effect of emulsion droplet size and membrane type

Composite gels were prepared from 2% myofibrillar protein (MP) with 10% imbedded pre-emulsified plant oils (olive and peanut) of various particle sizes at 0.6 M NaCl, pH 6.2. Dynamic rheological testing upon temperature sweeping (20-70 °C at 2 °C/min) showed substantial increases in G′ (elastic modulus) of MP sols/gels with the addition of emulsions, and the G′ increases were inversely related to the emulsion droplet size. Furthermore, gels containing emulsified olive oil had a greater (P < 0.05) hardness than those containing emulsified peanut oil. Regardless of oil types, MP-coated oil droplets exhibited stronger reinforcement of MP gels than Tween 80-stablized oil droplets; the latter composite gels had considerable syneresis. Light microscopy with paraffin sectioning revealed a stable gel structure when filled with protein-coated oil droplets, compared to gels with Tween 80-treated emulsions that showed coalesced oil droplets. These results suggest that rheological characteristics, hardness, texture, and water-holding capacity of MP gels were influenced by type of oils, the nature of the interfacial membrane, and the size of emulsion droplets.     

Sweetness and texture perception in mixed pectin gels with 30% sugar and a designed rheology

Pure low-methoxyl (LM) pectin and mixtures of LM and high-methoxyl (HM) pectin in different ratios were used to produce gels with control over the rheological parameter storage modulus (G′). The gels either had similar pectin concentrations and different G′ values, or different pectin concentrations and similar G′ values. All gels were prepared with 30 g/100 g sugar, in the presence of 0.1 g/100 g CaCl₂, at pH 3.5; these are conditions that favour gel formation of both LM and HM pectin.The gels were compared for their sensory characteristics; specifically sweetness, sourness, thickness, and glueyness. Sweetness was found to increase with increasing storage modulus (G′) in pectin gels of similar pectin concentration, but different G′ values. Gels with higher proportions of LM pectin were perceived as sweeter than those with low LM pectin ratios. These gels also had increasing loss modulus (G″), and increasing differences between G′ and G″, which indicates that diffusion has a bearing on the perception of sweetness in pectin gels. Thickness and glueyness were mostly determined by total pectin concentration. Thickness also increased with increasing LM pectin concentration while glueyness increased with increasing HM pectin concentration.     

Tough organogels based on polyisobutylene with aligned porous structures

Macroporous gels with aligned porous structures were prepared by solution crosslinking of butyl rubber (PIB) in cyclohexane at subzero temperatures. Sulfur monochloride was used as a crosslinker in the organogel preparation. The reactions were carried out at various temperatures between 20 and −22 °C as well as at various freezing rates. The structure of the gel networks formed at −2 °C consists of pores of about 100 μm in length and 50 μm in width, separated by polymer domains of 10-20 μm in thickness. The aligned porous structure of PIB gels indicates directional freezing of the solvent crystals in the direction of the temperature gradient. The size of the pores in the organogels could be regulated by changing the freezing rate of the reaction solution. The results suggest that frozen cyclohexane templates are responsible for the porosity formation in cyclohexane. In contrast to the regular morphology of the gels formed in cyclohexane, benzene as a crosslinking solvent produces irregular pores with a broad size distribution from micrometer to millimeter sizes due to the phase separation of PIB chains at low temperatures. Macroporous organogels prepared at subzero temperatures are very tough and can be compressed up to about 100% strain without any crack development. The gels also exhibit superfast swelling and deswelling properties as well as reversible swelling-deswelling cycles in toluene and methanol, respectively.     

油田用聚合物凝胶相对强度表征方法研究

实验研究了动力粘度η、动态储能模量G’、转变压力Pt（TGU值）测量3种方法用于表征油田用特别是提高采收率用聚合物凝胶（弱凝胶和较强凝胶）相对强度的适宜性和准确性。在η和G’测定了使用了3种代表性凝胶：（1)聚合物浓度不同的HPAM／Cr^3 凝胶,即柔性链聚合物弱凝胶;（2）组成固定的PAM／木素磺酸钠／Cr^3 凝胶,为较强凝胶;（3）组成固定的黄胞胶／Cr^3 凝胶,即刚性链聚合物脆性凝胶。在Pt测定中使用聚合物浓度不同的另一种HPAM／Cr^3 凝胶。得到的结论如下。对于柔性链聚合物弱凝胶（1）,当G＜0.1Pa时,η值是相对强度的良好表征值,G’越小,则η测定的重现性越好,G’测定的重现性越差。对于较强凝胶[(2),G‘＞0.1Pa]和刚性链聚合物形成的脆性凝胶（3）,η测定的偏差很大,凝胶越强,则G’测定的重现性越好。对于结构易破坏的脆性凝胶,振荡法测量（G’、G”、η＊）是表征相对强度的适当方法。Pt(TGU值）测定的重现性很差且有不少困难问题。因此不能用作凝胶性能的基础数据。     

影响胶态分散凝胶成胶性能因素研究

研究了各种因素对聚合物（ＨＰＡＭ）／柠檬酸铝／盐体系胶态分散弟胶（ＣＤＧ）的形成（通过成胶时间测定）和性能（通过孔隙阻力因子的测定）。孔隙阻力因子ＦＰＲ为相同聚合物浓度的ＣＤＧ和ＨＰＡＭ溶液分别流过填砂滤层所需的时间之比,可代表ＣＤＧ在多孔介质中的相对强度。研究结果表明：ＣＤＧ的性能随所用ＨＰＡＭ分子相对质量提高而;ＮａＣｌ的存在（≤７０００ｍｇ／Ｌ）可促进ＣＤＧ的形成;在下列条件下可形成稳定的Ｃ     

Small and large deformation viscoelastic behaviour of selected fibre blends with gelling properties

Dietary fibres can be used as valuable functional ingredients in baked goods, as thickeners and gelling agents as a result of their ability to modify the structural properties of the matrix in which they are embedded. Viscoelastic behaviour of 12 selected gel–fibre blends (carboxymethylcellulose, hydroxypropylmethylcellulose, locust bean gum, high ester pectin, fructo-oligosaccharide and gluco-oligosaccharide) prepared at 10% concentration (w/v) was investigated at 25 °C and 95 °C by applying both fundamental and empirical rheological techniques to explore their usefulness/suitability as structural ingredients in diluted and weakened baking systems such as gluten free matrices. Mechanical and thermo-mechanical properties were recorded by using a controlled stress rheometer, measuring the storage modulus (G′), the loss modulus (G″) and the complex viscosity (η*). Textural characteristics were assessed by using a TAXTplus Texture Analyser with different attachments. Penetration and back extrusion tests were used for solid and liquid-like samples, respectively. The overall results indicated that (i) carboxymethylcellulose and pectin formed the strongest and the weakest gels, respectively, and that (ii) temperature had a significant effect on gel strength improvement especially for locust bean gum. A 30% substitution of hydrated fibres (cellulose derivates, galactomanans and high ester pectin) by prebiotics (fructo-oligosaccharides and gluco-oligosaccharides) led to a significant decrease of gel structure rigidity when compared to an identical system without prebiotic addition. Only locust bean gum exhibited an opposite behaviour inducing an increase in values of both dynamic moduli (G′ and G″) and static hardness. Significant relationships between dynamic (rheometry) and static (texture analysis) methods were found. Strengthening and structuring ability of some fibre blend gels endorsed them to be used as promising functional ingredients to make gluten-free bread by using low cost thickeners' agents.     

New aspects of nonlinear elasticity of polymer gels and elastomers revealed by stretching experiments in various geometries

This review focuses on the novel features of nonlinear elasticity for a range of gels and elastomers that were recently revealed through experiments using various types of strain such as uniaxial and biaxial stretching. Particular emphasis is placed on the magnitude of the cross‐effect of strains in different directions which can be characterized by unequal biaxial stretching. The studied materials include (1) markedly swollen hydrogels with a water content of 98%, (2) tetra‐arm poly(ethylene glycol) (Tetra‐PEG) gels with nearly uniform network structures without entanglement couplings of network strands, (3) slide‐ring gels with movable crosslinks along network strands and (4) elastomer foams with low densities of polymer solids. The magnitude of the cross‐effect of strains reflects the structural features of networks and crosslinks as well as bulk compressibility for each material. We also summarize recent results on strain‐driven swelling and the accompanying force reduction phenomena under various types of stretching. Remaining issues to be investigated are presented on the basis of existing results. © 2016 Society of Chemical Industry     

High Polymer Content 3,5‐Pyridine‐Polybenzimidazole Copolymer Membranes with Improved Compressive Properties

Three series of polybenzimidazole (PBI) copolymers (3,5‐pyridine‐r‐2OH‐PBI, 3,5‐pyridine‐r‐para‐PBI, and 3,5‐pyridine‐r‐meta‐PBI) were polymerized and cast into membranes by the polyphosphoric acid (PPA) process. Monomer pairs with high and low solubility characteristics were used to define phase stability‐processing windows for preparing membranes with high temperature membrane gel stability. Creep compliance of these membranes (measured in compression at 180 °C) generally decreased with increasing polymer content. Membrane proton conductivities decreased linearly with increasing membrane polymer content. Fuel cell performances of some high‐solids 3,5‐pyridine‐based copolymer membranes (up to 0.66 V at 0.2 A cm^–2 following break‐in) were comparable to para‐PBI (0.68 V at 0.2 A cm^–2) despite lower phosphoric acid (PA) loadings in the high solids membranes. Long‐term steady‐state fuel cell studies showed 3,5‐pyridine‐r‐para‐PBI copolymers maintained a consistent fuel cell voltage of >0.6 V at 0.2 A cm^–2 for over 2,300 h. Phosphoric acid that was continuously collected from the long‐term study demonstrated that acid loss is not a significant mode of degradation for these membranes. The PBI copolymer membranes' reduced high‐temperature creep and long‐term operational stability suggests that they are excellent candidates for use in extended lifetime electrochemical applications.     

Fabrication of composite microcapsules by drop-on-demand inkjet: Effect of precursor composition on the process limits

The feasibility of using drop-on-demand inkjet technology for the fabrication of calcium alginate hydrogel microcapsules containing dispersed sub-micron solid particles (TiO₂ photocatalyst) was demonstrated. The influence of the printed solution viscosity on the micro-droplet size has been investigated and a study of the effect of solids fraction in the suspension on its printability was carried out. It was found that solutions with viscosities of up to 28 mPa s and solids content of up to 7.8 vol% can be reproducibly printed, resulting in droplets ranging from 45 to 105 μm depending on the inkjet operating conditions. In order to ensure stable and reproducible droplet formation, a pressure difference ranging from −200 to −1800 Pa had to be maintained in the nozzle. A uniform distribution of dispersed solids in the resulting microcapsules was achieved by adjusting pH and viscosity. The relationship between the printhead operating pressure, the fluid viscosity, the solids loading and the final size of the obtained microcapsules was established, allowing rapid prototyping of artificial cell-like structures with internal solid inclusions by the inkjet method.