Swelling measurement

The solubiHty parameter of a polymer is a measure of its iatermolecular forces, and provides an estimate of the compatibiHty of a polymer with another polymer or a polymer with a solvent. Two components are compatible if they have similar solubiHty parameters. The solubiHty parameter can be determined by various methods, such as intrinsic viscosity and swelling measurements. The solubiHty parameters of various polymers and solvents are tabulated ia refereace handbooks (146,147). It also can be estimated from the stmcture of the polymer (148). 

Campion and Morgan developed the technique of reverse solubility parameter spectroscopy (RSPS)" to determine the 8 value for a liquid (e.g., an oU), from a series of swelling measurements using a range of elastomers of known 8. In this way, 8 for cmde Brent oU from the North Sea has been found to be 8.2 (cal cm ). ... 

According to these results, swelling measurements on a series of... 

The application of swelling measurements allows us also to estimate the influence of polyfunctional H-siloxanes 5 (R = H) on the network density. Highest values are achieved in stoichiometric mixtures. With excess of the H-siloxane the network density increases rapidly. 

Equilibrium swelling measurements have been done on B2 and on But 21-27 in benzene. No swelling data is reported for the PCP2 system for the reasons stated later in this paper. 

This is the percentage increase in volume attained by immersing a vulcanised sample of rubber in a specified solvent. Volume swelling measurements are useful in determining the resistance of rubbers to solvents, but are also of value in measuring the crosslink densities of rubber vulcanisates. 

Solvent Swelling and Extraction, The residue samples were extracted with pyridine at the boiling point to obtain the amount and composition of the extract. A portion of the dried, extracted solids was swelled in pyridine in order to estimate the density of crosslinks introduced by the preliquefaction process. The solvent swelling measurements were carried out according to the method of Green et al. (30,31). 

Product Identification was by GC/MS, NMR, and IR. Fundamental crosslinking chemistry was explored using swell measurements on simple solution copolymers and swell and tensile measurements with vinyl acetate (VAc), vinyl acetate/butyl acrylate (VAc/BA) or vinyl acetate/ethylene (VAE) emulsion copolymers. Polymer synthesis 1s described In a subsequent paper (6). Homopolymer Tg was measured by DSC on a sample polymerized In Isopropanol. Mechanistic studies were done 1n solution, usually at room temperature, with 1, 2 and the acetyl analogs 1, 2 (R =CH3). 

Volume swelling measurements have produced erratic results even under the most carefully controlled conditions. One important contribution in this regard is the work of Bills and Salcedo (8). These investigations showed that the binder-filler bond could be completely released with certain solvent systems and that the volume swelling ratio is independent of the filler content when complete release is achieved. Some thermodynamic problems exist, however, when such techniques are used to measure crosslink density quantitatively. First, equilibrium swelling is difficult to achieve since the fragile swollen gel tends to deteriorate with time even under the best conditions. Second, the solubility of the filler (ammonium perchlorate) and other additives tends to alter the solution thermodynamics of the system in an uncontrollable manner. Nonreproducible polymer-solvent interaction results, and replicate value of crosslink density are not obtained. 

Tablets coated with the Eudragit-PEG 400 mixture were made with three different polymer film thicknesses 6, 10 and 15 mg (KET-R, 10 and 15 tablets). For these tablets it was not possible to obtain swelling measurements because this was prevented by the lake coating.

Fitting the swelling curves of Fig. 7a to the form Q(t) — kt yields values of a greater than or equal to 0.8. Thus the swelling must be considered anomalous, or non-Fickian. In the absence of ionic interactions, this would not be expected since BMA/DMA 70/30 is initially not far below its Tg at 25 °C. Indeed, swelling measurements of this copolymer in hexane show kinetics that are nearly Fickian (a 0.55), as shown in Fig. 7b. Therefore, the anomalous swelling observed in Fig. 7a must be attributed to ion transport and binding rates in the gel. We will return to this point later. 

The kinetic theory of rubber elasticity is so well known and exhaustively discussed (17, 27, 256-257, 267) that the remarks here will be confined to questions which relate only to its application in determining the concentration of elastically effective strands. In principle, both network swelling properties and elasticity measurements can provide information on network characteristics. However, swelling measurements require the evaluation of an additional parameter, the polymer-solvent interaction coefficient. They also involve examining the network in two states, one of which differs from its as-formed state. This raises some theoretical difficulties which will be discussed later. Questions on local non-uniformity in swelling (17) also complicate the interpretation. The results described here will therefore concern elasticity measurements alone. 

The n value may also be determined from swelling measurements of slightly cross-linked samples of the polymer (12). This method is based on a theory developed by Flory and Rehner (//). It does not require the polymer to be completely soluble in the plasticizer and avoids the need for osmotic pressure measurements which, even under the most favorable conditions, require considerable skill. 

In the series of PS-DVB gels with crosslink densities from 0.007 to 0.112 (as determined by swelling measurements) it was found that the line widths of aromatic carbons measured in CDC13 increase monotonically with crosslink density. From the log-log plot of these data an empirical exponential relationship between line width (Av) and crosslink density (%) can be made 137) ... 

Dimensional methods having use in the laboratory have been reviewed in connection with swelling measurements.17, 18 The length of cracks can in fatigue tests can be manually measured by conventional methods or continually recorded with a video camera. An electrical method of crack measurement has been used for plastics19 that in principle could be applied to rubbers. 

The shear viscosity can be used for relating the polymer flow properties to the processing behavior, extruder design, and many other high shear rate applications. Elongational viscosity, die swell measurements as well as residence time effects can be estimated. Typical data are shown in Figure 6. 

Run No. Additive Mol additive /60g styrene xl< Initial volume fraction of additive in 2 styrene, xlO V. mol min dm 3H20 xlO3 mol min dm-3HL0 X xlO 5 Relative Rate, % H- mol dm from R P K>> from swelling measurements ... 

Figure 6. Linear shrinkage and swelling measurements of beech-wood after alternating treatments with ammonia and water. Arrow f symbolizes swelling a in ammonia, w after two days of watering. Arrow J, symbolizes shrinkage. Reference values are dimensions in air-dry state.

Figure 6.9 Effects of the addition of 1-allyloxyoctane (AO) and 1,8-diallyloxyoctane (DAO) on crosslink density, estimated from equilibrium swelling measurements in decalin...

At low cure times, only Ale and A2c polysulfidic structures (50 ppm) are observed. At longer cure times, Ale and A2c polysulfidic structures reduce in sulfur rank to monosulfide (45 ppm), and Blc (58 ppm). Bit (64 ppm) and Clc (45 ppm) polysulfidic structures are observed. A small amount of ds-to-trans isomerisation was observed, which increased with sulfur content. The reversion reactions of TBSI-accelerated systems result in a lower degree of sulfurisation as opposed to TBBS-accelerated samples. Based on the equilibrium swelling measurements, TBSI is found to be a less efficient accelerator than TBBS. 

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