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The gel-setting and gel-melting temperatures of aqueous gelatin and agar solutions (0.5 wt% and 1 wt%) were measured by applying a steady state hot-wire method during pressurization up to 200 MPa. Pressurization induced the elevation of both the gel-setting and gel-melting temperatures in proportion to the pressure. The hot-wire method was found to be effective for assessing gelation under pressurized conditions.

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.

A number of scales for sol fraction and irradiation dose have been tested in order to linearize gel-formation kinetics. The logarithm of sol fraction vs square root of irradiation dose has been discovered to be most suitable for the logarithmic-normal distribution. The plots remain reasonably linear up to about 70% gel fraction.

Moulding thermoset resin laminates under autoclave conditions removes the possibility of using resin sampling to determine the gelation point of the resin. The gelation point is critical, since it is then that pressure has to be applied to achieve optimum mechanical properties. This paper describes the use of automatic dielectrometry to monitor the process under autoclave conditions, giving an accurate prediction of the gel point. The need to ‘stage’ the prepreg system is eliminated, and optimum mechanical properties of the resulting laminate can be obtained.

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.

The two constants in the equation log η = A + C′ Mn1/2 (η is the viscosity of molten alkyd and Mn the number average molecular weight) were determined at 110°C for two kinds of alkyd resin prepared with the same formulation but with different cooking schedules. It was found that the magnitude of the slope C′ was larger for the alkyd which was prepared by raising the reaction temperature directly up to 230°C, in comparison with that of the alkyd which was prepared by maintaining the temperature at 170°C for an hour and then raising it up to 230°C. Measurements of η and Mn were carried out until the gelation occurred. Both upward and downward breaks were observed in log η vs. Mn1/2 plot. Based on these viscometric data, the gel point mechanism was discussed. Disagreements between the molecular weight observed and that calculated from the Flory's theoretical equation became more remarkable as the esterification proceeded. This suggested that a large extent of intraesterification reaction is taking place in alkyd synthesis.

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.

Tablets with a methylcellulose coating were found to exhibit lower dissolution profiles than those coated with a hydroxypropyl methylcellulose coating at 37 degrees, and the cause was investigated. The differences are attributed to thermal gelation of the methylcellulose at temperatures near 37 degrees, which creates a barrier to the dissolution process and essentially changes the dissolution mechanism. This mechanism is substantiated by the fact that at temperatures below the gel point and at increased agitation, the effect disappears. The retarded dissolution effect is not peculiar to the drug involved.

From fundamental and technological points of view RIM is a complex process.1 Fast reactions are required to form, in many applications, network materials and the reactions must by synchronised with the process so that the mould is filled with liquid reacting material, the material becoming solid at complete filling. The rates of reaction occurring between the two liquid reactant feeds which are mixed prior to mould filling must be well controlled, as must be the molecular growth process leading to the final, solid material. The important point in the polymerization is the gel point, which in terms of reactant flow defines the point of infinite viscosity.2,3

A high gel point methylcellulose (Methocel HG) was given in single doses to normal healthy young adults. Only minor symptoms were reported, e. g., mild laxative effect, mild constipating effect, and a few instances of commonplace symptoms such as cramping, flatus, headache, and tenesmus which apparently were not related to the ingestion of Methocel HG. Essentially all of the ingested Methocel HG was eliminated in the feces within ninety‐six hours following administration.