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The viscosity evolution for different temperatures was studied experimentally. A time-varying viscosity model was derived and the influence of the initial temperature on gel time was analyzed. The experimental results show that the viscosity of polymer grout increases exponentially with time. It can be divided into two phases. Before gelation, the viscosity variable quantity is very small. At the gel point, there is a sudden increase in viscosity. The initial viscosity and gel time decrease with the increasing initial temperature within a certain range, The study contributes to deepening understanding of the rheological properties of polymer grout, which can provide some references for polymer grouting construction.

In this paper, a novel ethylene-vinyl acetate copolymer (EVA)/amino-functionalized polymethylsilsesquioxane (PAMSQ) composite wax inhibitor (WI) was prepared through melt blending, and the rheological and wax depositing properties of the doped crude oil were studied. The EVA/PAMSQ composite can strongly crystallize with wax molecules and trigger the formation of compact wax flocs, which greatly improve the rheological properties of crude: compared to the pure EVA at the same dosage, the composite can further decrease the gel point and apparent viscosity (25 °C) by 14.6 °C and 92.0%, respectively. The wax deposition can also be inhibited by adding the composite: adding EVA inhibits the mass of the wax deposit at 24 h by 62.3%, and this number is suppressed by 77.9% after adding the EVA/PAMSQ composite, but the wax molecule diffusion is accelerated and the wax content in the wax deposit rises because of the improved crude oil rheological characteristics. Here, we develop the gel structure theory to consider the wax deposition process affected by the WI. Adding the WI contributes little to the wax precipitation temperature but decreases the gel structural strength of the oil a lot, and thus, the oil near the pipe wall can only form the wax deposit with a higher wax content to resist the pipe wall shearing. Therefore, the crude oil added EVA/PAMSQ composite possesses not only the lowest wax deposit rate and the highest aging rate but also the highest wax content in the wax deposit.

The alkali-catalyzed alcoholysis of polyethylene vinyl acetate (EVA) was used to obtain the product ethylene-vinyl alcohol copolymer (EVAL), and the grafting product poly(ethylene-vinyl alcohol)-graphene oxide (EVAL-GO) was prepared in the form of chemical grafting by utilization of the groups on the surface of GO and EVAL through the esterification reaction. The products were analyzed by Fourier transform infrared (FTIR), 1H nuclear magnetic resonance (NMR) and Thermogravimetric (TG). The rheological properties of the oil sample and changes in the morphology of wax crystals were characterized by Advanced Hybrid Rheometer and polarized optical microscopy (POM) respectively. The degree of alcoholysis of EVAL reached 74.51%, and the grafting rate of EVAL-GO (0.5%) was 36.18%. Reduction of pour point and gel point of nanocomposite treated crude oil was 12 °C and 4 °C from undoped crude oil at the optimum additive concentration of 1000 mg/kg. Moreover, it decreased the viscosity and yield value of virgin crude oil by 99.5% and 78.3%, respectively. From the morphological analysis, it was indicated that EVAL-GO could make the wax crystals form sphere-like crystals, and the increased void space promoting more liquid oil to be released thus significantly improving the low-temperature fluidity of Daqing waxy crude oil.

The gel point is the lowest solids content at which a fibre suspension forms a continuously connected network and is related to the fibre aspect ratio. In this paper we firstly investigated the conditions required to accurately measure a gel point using sedimentation. We found that very heavily treated cellulose nanofibres can produce anomalous sedimentation data, due to the electrostatic repulsion from fibre surface charges dominating the gravity driven sedimentation. Screening the anionic surface charges by adding high levels of Na+ or Ca2+ ions reduced the electrostatic interactions between the fibres and allowed them to settle normally. Gel point measurement was then used to probe the development of nanofibre quality with increasing energy input for three different feedstocks: eucalypt kraft pulp, commercial microfibrillated cellulose and de-lignified, bleached spinifex pulp. By combining the data of the aspect ratio and average diameter, determined from SEM and TEM, we were able to compare the differences in feedstock processability. The aspect ratio of all three feedstocks increased with increasing homogenisation energy, showing that the fibre delamination dominated over fibre shortening. The slope of the aspect ratio versus energy consumption showed the ease of processing of each sample. The spinifex fibres had the fastest rate of aspect ratio increase and therefore were the most processable. Gel point is an excellent tool to track quality development of nanocellulose through processing and to compare the potential of different feedstocks for nanocellulose production.

Cold and hot water extracted polysaccharides (CP and HP) were isolated from Plantago ovata seed husk at 25 and 85 °C, respectively. Their rheological properties were systematically investigated and compared. Different concentrations and temperatures were studied to evaluate the viscoelastic properties of the two fractions. It was found that CP solutions behaved as viscous fluids, while HP solutions preferred to exhibit as gel-like structure. The sol-gel transition process of HP was evaluated and the gel point was determined to be 4.8 mg/mL by Winter-Chambon method in water at 25 °C. The steady flow sweep investigated the viscosity properties of CP solutions and two critical concentrations were found, which locating the transition from the dilute to semi-dilute region, and from the semi-dilute to concentrated region. In addition, the two fractions could form thermo-reversible weak gels, and the gelation temperatures of them increased with the increase of concentration. It is evident that both polysaccharides have significant potential for application in food industry.

The yield stress and pour point are two important parameters related to flow assurance problems in waxy crude oil pipelines. The yield stresses at temperatures below the pour points of five waxy crude oils after heating to different temperatures have been investigated in the present paper. Both the experimental results in this work and data from the literature show that the yield stress values increase exponentially with the decreasing measurement temperature. The experimental results show that the heating temperature has an obvious influence on the yield stress and the pour point. However, it was noted that the yield stress values at the gel point temperature, defined as the highest temperature at which the movement of the sample cannot be observed during the quiescent pour point testing process, are approximately the same for a waxy crude oil after heating to different temperatures. An exponential relationship exists between the yield stress and the difference between the measurement temperature and gel point that is independent of the heating temperature. To explore this phenomenon, the relative magnitudes of the gravitational stress and the structural strength of the wax crystal network during the gel point test has been analyzed, and it was found that the yield stress value at the gel point has a favorable linear relationship with the oil density.

The characterization of the thermo-gelation mechanism and properties of ethyl cellulose/canola oil oleogels was performed using rheology and thermal analysis. Thermal analysis detected no evidence for thermal transitions contributed to secondary conformational changes, suggesting a gelation mechanism that does not involve secondary ordered structure formation. Rheological analysis demonstrated a relationship between the polymer molecular weight and the final gel strength, the cross-over behavior as well as the gel point temperature. Increasing polymer molecular weight led to an increase in final gel strength, the modulus at cross-over, and the gel point temperature. Cooling/heating rates affect gel modulus only for the low molecular weight samples. A decrease in gel strength with increasing cooling rate was detected. The cross-over temperature was not affected by the cooling/heating rates. Cooling rate also affected the gelation setting time where slow cooling rates produced a stable gel faster.

This article discusses the effect of water fraction on the rheological properties of waxy crude oil emulsions including gel point, yield stress, viscosity, and thixotropy. The experimental results reveal that the rheological behaviors of the w/o emulsion samples all intensify with the increase of water volume fraction within 60%. Of more significance is that a correlation for w/o emulsions between yield stress and water volume fraction is put forward with an average relative error of 6.75%. In addition, some mainstream viscosity prediction models of w/o emulsions are evaluated, and Elgibaly model is the best-fit for the emulsions in this study.

Cellulose nanofibre aspect ratio controls the properties of sheets made from nanofibres and processing conditions, but aspect ratio is very difficult to measure. In this paper, aspect ratio was estimated from the gel point of a cellulose nanofibre suspension, the solids concentration at which the transition from a dilute to a semi-dilute suspension occurs. Four batches of cellulose nanofibres were tested. Two were produced from softwood fibres using ball milling. Commercially produced microfibrillated cellulose material was also used, both in as supplied form and after removal of the larger fibres by filtering. The average diameter measured from SEM images of fibres ranged from 33 to 73 nm. One sample was too heavily treated and an average dimension could not be measured. The gel-point was measured both from the height of a layer of cellulose nanofibres sedimented from a dilute suspension or from the lowest solids concentration at which a yield stress could be measured using a vane rheometer. The two methods were closely in agreement for all samples. Aspect ratio was then calculated using either the effective medium (EMT) or crowding number (CN) theories. Aspect ratio calculated with an assumed fibre density of 1,500 kg/m3, using the CN theory ranged from 155 to 60. Use of the EMT theory reduced the calculated aspect ratio by between 11 and 23 %. Reducing the assumed density in suspension from 1,500 to 1,166 kg/m3 reduced the calculated aspect ratio by 12–14 %. The heavily treated sample had by far the lowest aspect ratio.

An experimental rheometric investigation is performed to assess the utility of various gelation point determination methodologies. Controlled shear stress and controlled shear rate methods are developed to investigate gelation processes in waxy oils. The nonoscillatory rheological method exhibits high reproducibility for model wax oils as well as for real crude oils. In addition, the nonoscillatory methods are in good agreement with standard oscillatory gel point determination methods. The effect of imposed shear stress, imposed shear rate, and cooling rate on gelation point is investigated with two types of model oils: 5 wt % macrocrystalline wax in Primol 352 and 5 wt % macrocrystalline wax in dodecane. In addition, the effect of wax content on gel temperature of macrocrystalline wax in dodecane is investigated. Moreover, the effect of additives (A3 and A4) on gelation point of a real crude oil UL-YS1 is investigated. Finally, the gelation temperatures of 5 wt % macrocrystalline wax in Primol 352, crude...

Wax deposition causes serious problems during oil production and transportation through pipelines. In this study, the influence of disulfide oil (DSO), ethylene vinyl acetate (EVA) copolymer as pour point depressant (PPD), SiO2 and clay nanoparticles on rheological properties of waxy oils are investigated. The viscoelastic modulus, viscosity, pour point, surface tension and yield stress of different waxy oil samples were measured. It was observed that the gel point, pour point, viscosity, gel strength, and yield stress decreased upon addition of these additives to waxy oil. It was found that rheological properties of oil samples improved by increasing SiO2 and clay nanoparticles up to 0.2 wt% in nanohybrid PPD (NPPD) and decreased at higher concentrations. Also, results indicated that SiO2 nanoparticles had better performance for wax prevention compared to clay, EVA, and DSO. Our measurements showed that yield stress decreased to 0.049 Pa by adding 0.12 wt% of SiO2 nanoparticle into NPPD whereas it was 54.3 Pa for blank oil. Also, pour point and surface tension of oil doped with SiO2 NPPD significantly reduced by increasing nanoparticle concentration. Moreover, it was found that DSO as a waste by product of gas refinery has a performance similar to EVA for wax prevention.

The thermal-induced gelation process in a polyacrylonitrile (PAN) solution containing different amounts of water was investigated through both dynamic and steady-state rheologic measurements. During the cooling process, the storage modulus G 0 was found to intersect with the loss modulus G 00 at a temperature which can be considered as the incipient gel point Tig. This crossover point increased with the water content in the PAN solution. On the basis of the power law G 0 ~ G~ v n and the relation tan d ¼ GðvÞ=G 0 ðv Þ¼ tanðnp=2 Þ¼ const, the loss tangent tan d was traced with decreased temperature at various oscillation frequencies, and a crossover point was observed at the temperature a little higher than the Tig above for all PAN solutions. The water content might affect the value of the relaxation exponent n via two different mechanisms, that is, hydration decoupling of the pendant nitrile groups in PAN at low water content (2wt% water) and molecule aggregation at high water content (4 and 6wt%). Nevertheless, the slight difference in the n values reflects the unique structure of the critical gels irrespective of the water level. The apparent viscosity ha of either the PAN solution or the PAN gel was found to rise with increased water content and both showed pronounced shear-thinning behavior. Compared with temperature, the water effect on the apparent viscosity ha is more significant due to the water-induced aggregation of the molecular chains. Copyright 2010 John Wiley & Sons, Ltd.

The amount of precipitated wax is one of the key factors that governs the flow properties of waxy crudes. Experimental results of 24 crudes have shown that approximately 2 wt% precipitated wax is sufficient to cause a virgin waxy crude gelling. Accordingly, a correlation between the pour point and the temperature at which 2 wt% of wax has precipitated out from a crude oil; i.e., T c (2 wt%), and a correlation between the gel point and T c (2 wt%) have been developed. The proposed correlation of the pour point is in accordance with the correlation developed by Letoffe et al. (1995) on the basis of 14 crudes from eight countries. The development of the gel point correlation and further verification of the pour point correlation indicate that there is a relationship between the gelling of virgin waxy crudes and the amount of precipitated wax. According to these correlations and the amount of precipitated wax, which can be determined only with a little sample by thermodynamic models or Differential ...

A novel approach has been developed to measure in-situ chemical shrinkage of epoxy resins at the temperature of cure, during which the epoxy resins pass through liquid, rubbery and glassy states. A small sample of MY750/HY917/DY073 epoxy resin system, sealed in a thin-walled silicone bag, was suspended in a pot of silicone fluid and weighed independently of the silicone bath. The buoyancy of the sample was monitored as its density increases with respect to the constant density fluid during isothermal cures at three different temperatures. The relationship between the chemical shrinkage and degree of cure was deduced from a cure kinetics model for the resin. The good match of the results for the three different cure cycles suggests that chemical shrinkage is only a function of degree of cure regardless of time and temperature. A bi-linear relationship was fitted to the experimental data. The break point is at a degree of cure of about 28%, with corresponding chemical shrinkage of 3%. This point is linked to the gel point of the resin, which was measured as approximately 25% degree of cure in previous work. Total cure shrinkage of 6.9% for the MY750 resin system was obtained by extrapolating the results to a degree of cure of 100%. The method is sensitive, reliable and keeps the resin stress-free; therefore it should be applicable to a wide range of materials.

Prediction of gel point conversion and network formation is of great importance in polycondensation during synthesis as well as processing. It enables one to estimate the safe conversions for reactor operation without gelation and the cycle time during processing, and plays an important role in controlling the molding parameters used for reinforced reaction injection molding (RRIM), reaction injection molding (RIM) and compression molding. Theories of gelation have been extensively published in the literature and supported by experimental data for various polycondensation systems. However, most such studies relate to unfilled systems. In this work, metal-filled polyurethanes have been synthesized in bulk by reacting toluene di-isocyanate with castor oil and its polyols possessing different hydroxyl values. Metallic aluminum powder (10–40% by weight) was dispersed thoroughly in castor oil and its polyols before reacting at different temperatures (30–60 °C) in a moisture-free, inert environment. The gel point conversions were measured experimentally and an empirical model from the experimental data has been developed to predict the gelation behavior. The proposed model could be of immense importance in the paints, adhesives and lacquers industries, which use castor oil in bulk. From these experiments it was concluded that: (i) fine metal powder gives a rise in viscosity; (ii) metal fillers not only restrict the molecular motion due to the increase in viscosity, but also lower the conversion; (iii) the vegetable oil and its polyols have a number of bulky groups, which also impart the delay tendency in gel time; (iv) there is a change in gelation dynamics at 50 °C – this is due to the change in reactivity of di-isocyanates; (v) the presence of metal filler does not initiate the intermolecular condensation; (vi) there is a gap between theoretical and experimental gel point owing to the unequal reactivity of the secondary alcohol position; (vii) there is an inverse relationship of gel time with the reaction temperature and hydroxyl value of polyols. An empirical model based on process parameters, i.e., hydroxyl value, temperature, shape factor and filler concentration, has been derived and found to be adequate for the metal-filled system. The correlation coefficient on the data is on the lower side in some cases because the following were not taken into account: (i) the first-order kinetics followed by the reaction in the second half while it is tending towards gelation; (ii) the error in observing the gel point viscosity; (iii) errors in assuming the spherical shape of aluminum metal powder; (iv) errors due to failure to maintain the constant speed in agitation. Copyright © 2003 John Wiley & Sons, Ltd.

Rheological behaviour of silicic acid sols with and without different cations (e.g., Pb2+, Zn2+, Al3+ and Zr4+) was studied by steady shear and oscillatory flow measurements at different ageing periods. From the steady shear flow curves, the changes in viscosity, area of hysteresis of the flow curves and the yield stress were measured with ageing time of the sols. A sharp change of the above parameters (e.g., viscosity, area of hysteresis of the flow curves and yield stress) occurred after a certain time of ageing. It indicated qualitatively the point of gelation of the sols. The gel point of the sols could be quantitatively measured from their oscillatory flow measurement. From the above results it was observed that gel point (the time of gelation) increased in the order of Pb2+

The effect of different salts and surfactant and their doses on the gel temperature of extremely dilute solutions (below 1%) of methyl cellulose (MC) has been studied. The gel temperature decreases non-linearly (concave downward) with increase in MC concentration. The addition of salts like NaCl, (NH4)2SO4 and (Na)2CO3 lowers the gel temperature of MC due to its dehydration. But increase in gel temperature is also observed on addition of 0.5 and 1% NaCl to 0.6 and 0.7% MC solutions, respectively. The addition of 1% sodium carbonate causes appearance of clouds only up to 0.2% MC, cloudy gel followed by clear gel up to 0.3% MC, thereafter phase separation occurs even at room temperature. The effect of addition of a surfactant, sodium lauryl sulphate (SLS) on the process of gelation of aqueous MC solutions has been studied in detail. The gelation process depends on r, the ratio of weight% of surfactant and that of MC present in the aqueous solution. Gels are formed for the limit 0.02

The DEBGA–MHHPA epoxy system has found increasing applications in microelectronics packaging for which the ability to understand and model the cure kinetics mechanism accurately is crucial. The present article reports on the work done to elucidate accurate knowledge of the gel point by rheological methods. To determine the gel point using the G′–G″ crossover method was found not to be accurate, and the gel point obtained by this method was found to be frequency-dependent. Using the point where tgδ was found independent of the frequency can accurately define the gel point at different temperatures. At the gel point determined by this method, G′ and G″ were found to follow the same power law, demonstrating the accuracy of the method in determining the gel point. The scaling exponent obtained was 0.75–0.79. The activation energy for the cure reaction of the system was determined to be 75.1 kJ/mol by the obtained gel times at different temperatures. The steady-shear rheology test was also used to observe the viscosity change at the gel point. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1248–1256, 2000

A superthickening device (solids bed height=5.5–6.0 m) has been examined for potential use in concentrating an alum-based sludge generated during the production of potable water. Initial trials show that, even when flocculated using an appropriate dose of polyelectrolyte, the superthickened sludge settles to a solids content of only 3–4 wt%. This concentration is equivalent to the sludge gel point and indicates that no significant sediment-based compression is taking place. However, when subjected to an in situ low shear rate (1 rpm) stirring treatment, the polyelectrolyte-flocculated sludge consolidates to far higher concentrations, reaching 17 wt% solids after 60 h of thickening. Possible mechanisms underlying this result include the rearrangement and densification of the inter-particle network and suppression of liquid channels in the sediment bed. On a more qualitative level, this study also briefly considers the advantages of superthickeners over conventional mechanical dewatering methods and outlines a number of experimental considerations relevant to future research.

The problems faced by carragenan producers is the optimation of the presipitation ingridients. Presipitation process on the extraction carragenan from seaweeds is very essential since the fraction with higher molecul weight will be separated from the lighter one, and it can influence the gel strength which is one of the important characteristics. Precipitation ingridients used in this experiments consist of methanol, ethanol, and isopropanol. The extraction of carragenan from Eucheuma cottonii in this research follows some steps e.g. extraction with KOH 6%, heating, rinsing, pulping, hot filtering, addition of KCL 5%, precipitation, washing-rinsing, squizing, drying and grinding. Quality parameters observed were gel strength, moisture content, ash content, viscosity, boiling point, and gel point. From these experiments methanol ingridients exhibited the best characteristics of refined carragenan in term of gel strength (1407,83 g/cm 2 ), moisture content (9,96%), ash content (18,7%), viscosity (251 cP), boiling point (27,6 ° C), and gel point (30,3 ° C). In general refined carrageenan processed with these presipitation meet the standard from FAO (Food Agriculture Organization), FCC (Food Chemicals Codex), dan EEC (European Economic Community).

Linear low-density polyethylene (LLDPE) was irradiated with electron beam radiation at room temperature and in the melt. It was found that the gel point, as measured by an insoluble fraction in boiling xylene, occurred at a slightly lower radiation dose for melt irradiated samples. The melt radiation-crosslinked samples showed different melt rheological properties from the room-temperature radiation-crosslinked samples, as exemplified by the stress relaxing more slowly in a step strain experiment (relaxation modulus) for the former at a given radiation dose. The relaxation modulus could be fitted to a power-law expression consisting of two parameters, which, when plotted against each other, resulted in a single master curve for both irradiation temperatures. The curve showed two distinct regions of differing slope, which intersect at a point argued to represent a pseudogel point.

Many thickening operations continue to be constrained by their ability to process consolidated underflows with high yield stress and associated rheological characteristics. The application of high molecular weight polymers (flocculants) is a prerequisite to maintain the operation integrity and dynamics of most gravity based solids/liquid separation processes. Such treatments are an effective means of consolidating solids and maximising clean water recovery. Unfortunately polymer/solids interaction at, and beyond, the gel point result in a significant increase the yield stress for a given solids content. BASF is developing a novel flocculant treatment (NFT) by which primary solid/liquid separation efficiency is maintained, and the subsequent consolidation process is enhanced, wherein higher underflow solids are associated with reduced yield stress. This paper will present application data to demonstrate the benefits associated with this NFT.

L'augmentation de la temperature de polymerisation de 80 a 295°C provoque des augmentations du taux de conversion au point de gel differentes pour le phtalate, l'isophtalate et le terephtalate de diallyle. Le rendement en prepolymere precipite juste avant le point de gel est quasi-identique pour les 3 composes quelle que soit la temperature. Des relations empiriques reliant la temperature aux parametres du point de gel sont proposees

Nature allows polymers to pass through the gel point with striking simplicity and elegance. However, what are the rheological properties at the gel point? Is the polymer at the gel point, the ‘critical gel’, at a distinct material state that has its own properties? It seems that these questions, until recently, have not been pursued. The questions might have been avoided since it was well known that the established rheological concepts fail altogether at the gel point: the concept of a viscosity is inapplicable since the viscosity diverges to infinity and the concept of an equilibrium modulus is useless since the modulus is still zero at the gel point. The gel point itself had remained mysterious.

The volume changes of 13 kinds of fish and other meat sol were measured by a dilatometer when the sol of meat paste was converted to gel by heating. The gel point, about 60°C, was ascer-tained by measuring rigidity. The volume change, V/Vsol, where V was the volume of meat paste after heating and Vsol that of sol at 10°C, did not depend on the setting property and the dis-integrating property reported by SHIMIZU et al. and ranged from 1.015 to 1.046. Moreover, the value of V/Vsol was independent of the rigidity.

The rate and extent of solution of polyvinylchloride in ester plasticizers has been measured using infrared spectroscopy. The measurement is based on shifts in the carbonyl stretching frequency of the ester linkage, similar to the familiar infrared solvent shifts commonly observed for low molecular weight materials. Double beam techniques were necessary to record the shifts. The intensity of the shifted band increases up to gelation and the rate of increase depends on the temperature of heating. The intensity of the shifted band is directly proportional to the concentration of polymer dissolved in the plasticizer and can be used to measure this concentration at any time during the gelation process. It is estimated that from 17 to 22 per cent of the polymer was dissolved at the gel point after heating at 65°C. and that about 29 per cent of the polymer was dissolved at the gel point after heating at 75°C., for the plastisols used in this study.

Although some works on changes in viscosity of liquids with gamma-ray dose have been made near the “gel point”, very little works have been done below this point. Changes in viscosities of different-grade silicone fluids below gel point have been measured using a differential viscometer developed in our laboratory, capable of measuring change in viscosities of two liquids directly. Preliminary results on viscosity changes when irradiated with energetic alpha particles will also be reported.

The effect of certain additives on the gel point of various grades of Methocel 4000 solutions has been investigated. Most electrolytes, as well as sorbitol, sucrose, and glycerin depress the gel point while ethanol, propylene glycol, and polyethylene glycol 400 raise the gel point. The effect of propylene glycol in counteracting the gel point depression caused by magnesium chloride or sucrose as examples of electrolytes and nonionic hydrophilic compounds, respectively, is illustrated. The gel point raising effect of ethanol, propylene glycol, and polyethylene glycol 400 has been related to their solvent properties.