Swell ratio testing

Another important parameter is the swelling ratio. A sample is placed in a solvent and the variation of its height is monitored as a function of time through a contact probe. A relationship between sample and solvent allows for the evaluation of the cross-link density and the chain length between cross-links. The technique is named swell ratio testing (SRT) in the American ASTM F2214-02, or hot set test (OST) in the German DIN 57472 Standard. " ... 

Swell Ratio Testing Mechanical Property Characterization... 

In addition, if the swelling of the extrudate is measured in each of these two tests then the swelling ratio using the long die will be Bsr and the swelling ratio using the short die will be Ber (see Section 5.6). Using equation (5.44) and (5.47) this enables the shear and tensile components of the recoverable strains to be calculated and from them the shear and tensile moduli. 

It can be concluded that it is very difficult to predict the result from a polymer macrostructure, but it is relatively easy to measure the secondary species generated on irradiation by using known analytical techniques, such as measuring swelling, tensile tests, analysis using nuclear magnetic resonance (NMR), etc. The yield is then expressed by the G value, which represents the number of cross-links, scissions, double bonds, etc., produced for every 100 eV (1.6 X 10 J) dissipated in the material. For example, G (cross-links), abbreviated G(X), = 3.5 means that 3.5 cross-links are formed in the polymer per 100 eV under certain irradiation conditions. Similarly, the number of scissions formed is denoted by G(S). In order to determine the number of crosslinks or G(X), the number of scissions or G(S), etc., it is necessary to know the dose or dose rate and the time of exposure for these irradiation conditions. From the product yields it is possible to estimate what ratio of monomer units in a polymer is affected by irradiation. ... 

The coupled chemo-electro-mechanical formulation is a quite powerful tool for capturing the behaviour of the chemical, electrical and mechanical unknowns. In order to compare numerical results with experimental results, the numerically obtained relative swelling ratio q versus the prescribed concentration in the solution is depicted in Fig. 17. The initial state of the test cases discussed in Sect 2 has been taken as reference value. 

Die swell ratio is defined as the ratio of the diameter of the extrudate to the diameter of the capillary die (see Fig. 10 in Section 3.6). The inerease in diameter can be expressed as a percentage of die diameter. Whether the measurements are at room temperature or test temperature is also part of the definition. Die swell can be measured using capillary rheometers from either measurement of diameter after the cooling of a piece of extrudate of specified length or by noncontact optical or photographic means of the hot extrudate as it issues from the die. 

ASTM D3835/2000 test method measures rheological properties of thermoplastic (and thermosetting) melts by using a capillary rheometer [4], The test method includes measurements of viscosity, shear rate, shear stress, swell ratio, and percent of extrudate swell. Assuming a newtonian fluid, to calculate melt viscosity j, use... 

The term gel has different meanings in the polymer extrusion industry. The term gel is used as gel content in crosslinked polymers. Determination of gel content is described in ASTM D2765, standard test methods for determination of gel content and swell ratio of crosslinked polyethylene plastics [163]. The gel content (insoluble fraction) produced in ethylene plastics by crosslinking is determined by extracting with solvents such as decahydronaphthalene or xylenes. 

ASTM D2765, Standard Test Methods for Determination of Gel Content and Swell Ratio of Crosslinked Polyethylene Plastics... 

In recent years, with the development of model networks it has been possible to prepare networks of controlled and junction functionality These are prepared by endlinking functionalized prepolymers with cross-linking agents of known functionality. Therefore, by choosing the appropriate molecular weight distribution of the prepolymers it is possible to prepare unimodal and bimodal networks. Mark and coworkers (5-11) have performed extensive studies on model networks to test the various theories of rubber elasticity. In the case of unimodal networks they find that the macroscopic properties such as stress or swelling ratios can be described reasonably well by the Flory-Erman theory (12,13). 

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