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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.

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.

Waxy crude oil pipelines are pigged periodically to scrape the adhered wax deposit from the pipe wall and remove it from the pipeline. If wax deposition on the pipe wall is not too severe and there is not much change in pipeline throughput due to wax deposition in winter, a pigging operation in winter is inadvisable because a “paraffin blockage” may occur during pigging due to a lower operating temperature. Seasonal pigging of this pipeline is advisable if the crude oil is piped at ambient temperature in summer and the wax deposit on the pipe wall accumulated during winter is eroded by the oil flow. The pipeline should be pigged during high temperatures in summer rather than in winter. A semi-empirical wax deposition model developed by our laboratory is used to predict the wax deposit distribution along the pipeline in different seasons and the volume of pre-pigging deposit on the pipe wall, and a seasonal pigging program is recommended. An experimental method consisting of determination of the gel point of wax-contaminated oil ahead of the pig is developed to calculate the volume of wax deposits removed by the pipeline pigging operation under actual field conditions to test the model. The wax content in the crude oil is determined from the gel point. The relative discrepancy between the predicted and the field experimental pigging operation data is 12.3%.

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.

A semi-empirical spectrum model is proposed to describe the experimental data of the steady shear properties of a Shengli waxy crude oil near its gel point, where sophisticated structural effects become apparent due to the existence of waxy crystals in the crude oil. The model, consisting of a time spectrum, can well fit the steady shear viscosities of the waxy crude oil over the whole experimental shear rate region from 10−4 to 102 s−1. Two other experiments on complex fluids reported recently in the literature are also well described by this model demonstrating the applicability and accuracy of the model.

The homogeneity of PAN/DMSO/H2O spinning dopes with conventional PAN molecular weight and comparative high PAN concentration have been investigated using rheology method. The rheological results show that G′ and G″ of these solutions increase with increasing oscillation frequency. At lower temperature and higher H2O content, higher viscous modulus and elastic modulus are observed, too. The homogeneity of PAN/DMSO/H2O systems is reflected through the logG′-logG″ plots as well as gel point temperatures. The theoretical analysis indicates PAN/DMSO/H2O spinning solutions with conventional PAN molecular weight are close to homogeneous systems, which are very suitable for gel spinning.

The evolution of native egg yolk undergoing a thermal-induced sol-gel transition was studied by using temperature controlled small amplitude oscillatory shear measurements. The critical gel point was determined according to Winter’s criterion: 1) from the measurements of storage and loss moduli as a function of heating time at different frequencies, and 2) from the exponents of the power law mechanical spectra obtained after cure experiments performed up to a maximum temperature (60–90 °C) followed by a sudden decrease in temperature up to 20 °C. Differential Scanning Calorimetry (DSC) was performed in order to investigate thermal transitions in egg yolk. Microstructure of gels was evaluated by Transmission and Scanning Electron Microscopy. The results obtained were discussed in terms of the processes involved in protein gelation: change in the protein system, aggregation of partially denaturated protein molecules and association of aggregates. As a result, an elastic gel network was always obtained. The influence of frequency, heating rate, solids concentration and maximum temperature of processing, was analysed. Most of the transformations found during thermal processing were found to be basically irreversible, even at the sol state and gel point. However, some reversible phenomena were detected during constant temperature processing depending on the maximum temperature performed.

Dynamic oscillatory experiments are used to monitor the gelation of the borosilicate systems prepared through the sol-gel process from metal alkoxides. The rheological experiments show that tan δ = G”/G’ is independent of frequency at the gel point in agreement with the results of others on organic gelling systems. The dynamic moduli at the gel point followed power-law behavior with respect to frequency. The power-law exponent is found to be ∼0.70. The apparent fractal dimension, dp, of the network cluster at the gel point is determined. The dF values for the samples ranged from 2.5 to 3.8 depending on the final structure of the evolved products at the gel point. The large values (dF > 3) exclude a simple geometric interpretation of the results. The effect of processing parameters, such as composition of reactants and temperature, on the resulting microstructures near the gel point is discussed.