Measurement of the Swelling

Discontinuous measurements of the dimensions, or volume, or weight, necessitate a short interval after the extraction of the sample from the liquid, as the liquid evaporates rather strongly from the rubber sample [6]. Then, the most useful method 

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Increase in dimensions of an elastomer due to the absorption of any organic liquid with which it may come in contact or in which it may be immersed. Measurement of the swelling of vulcanised rubber in solvents can be used to determine state of cure and to assess the suitability of elastomers for such uses as chemical plant lining or oil seals. 

An approximate idea of the degree of swelling (the swelling index) experienced by a coal on carbonization may be obtained from the coke button left after the determination of volatile matter, but in many cases this measure of the swelling power is not sufficiently discriminating, principally because this is not the main function of the test. 

FIG. 3 Setup for the measurements of the swelling ratio (a) image analyzer (b) CCD camera (c) microscope (d) thermometer (e) measuring cell (f) pH meter (g) conductivity meter (h) aqueous phase supply system (APSS) (i) temperature control system (TCS). (From Ref. 27.)... 

Locust bean gum is a nondissociating polysaccharide, and one would expect the influence of pH on the swelling to be rather small. The glycosidic linkages of the gum are easily hydrolyzed by acids and therefore a decreased swelling may be observed at low pH values. The swelling is much increased in an alkaline medium the mechanism of this influence is unknown. Exact measurements of the swelling of the gum have not been published. 

NAG Naguib, H. E., Richards, E. V., Pop-Iliev, R., Xu, X., and Park, C. B., Measurement of the swelling of polypropylene melts with dissolved butane. Annual Technical Conference -Society of Plastics Engineers, 59, Vol. 2, 1537, 2001. 

Crosslinked poly(2-hydroxyethylmethacrylate), PHEMA, has been prepared by radical polymerization in presence of different amounts of water and water-diacetine solutions. While homogeneous samples can be prepared at all water-diacetine content, amounts of water higher than 40% causes the formation of macroporous opaque sponges. Mechanical properties of water swollen samples have been measured and related to the crosslink formation during the polymerization process. From water diffusion kinetics in sorption and desorption experiments at 37 C the diffusion coefficients have been calculated. Measurements of the swelling at equilibrium in water-diacetine mix-res indicate the presence of "cosolvency" phenomenon for the samples studied. 

ASE is a measure of the extent to which the swelling and shrinking tendency has been reduced at an equUibrium condition. 

The gel content (toluene insoluble per cent) of the rubber and the swelling index of the gel (the ratio of the volume of a swollen gel to its unswollen volume). The former is a measure of the amount of cross-linked material and the second a measure of the intensity of cross-linking. It has been found that a sample of medium gel content (5-20%) and a medium swelling index (10-20) gives the best impact strength in the blend. 

The parameters of neutron scattering theory of polymer networks are A, the macroscopic stretching of the sample, or linear degree of swelling, f, the network functionality, K. which accounts for restricted junction fluctuations and a, a measure of the degree to which chain extension parallels the macroscopic sample deformation. The functionality is known from knowledge of the chemistry of network formation, and A is measured. Both K and a must be extracted from experiments. 

Here c is the polymer concentration by weight. < the density of the polymer, a an effective bond length or measure of the coil dimensions, and to the monomeric friction factor. The subscript zero indicates the pure polymer. Since 2 (H), the mean-square end-to-end chain separation, the viscosity will be directly proportional to the polymer concentration unless the plasticizer modifies the coil swelling. At high molecular weight the monomeric friction factor is increased by the factor (MIMf)" and M, is increased relative to the undiluted polymer [equation (55)]. Thus... 

The degree of vulcanisation of a rubber compound is assessed technically by the indefinite terms of undercure, correct cure, optimum cure and overcure. It may be given precision by (a) measurement of stress-strain relationship of a range of cures, (b) measurement of the modulus at 100% elongation, (c) measurement of the volume swelling in benzene, or (d) by the use of instruments such as the oscillating disc rheometer and the moving die rheometer. 

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