Resin cross-linkage

Resin type and nominal percent cross-linkage Minimum wet capacity, mequiv mL Density (nominal), g mL Comments... 

Dg remains constant over a wide range of resin to liquid ratios. In a relatively short time, by simple equilibration of small known amounts of resin and solution followed by analysis of the phases, the distribution of solutes may be followed under many different sets of experimental conditions. Variables requiring investigation include the capacity and percent cross-linkage of resin, the type of resin itself, the temperature, and the concentration and pH of electrolyte in the equilibrating solution. 

Fig. 2. Total capacity vs cross-linkage for polystyreae sulfonic acid resin in the form where A and B correspond respectively to dry and wet weight capacity in meq/g of resin, and C represents wet volume capacity in meq/mL of wet setded resin.

Uncured resins are oligomers of relatively low molecular weight that may be a liquid or a solid. Before epoxy resins can become useful products, they must be cured, with the addition of a curing agent. Curing involves the cross-linkage by polymerization of the reactive epoxy groups into a three-dimensional matrix. 

The first packing materials used in a HPLC were beads of organic gel permeation resins used for size separations. These were commercially available resins and no attempt was made to optimize them for high pressure, except to select for a high degree of cross-linkage to prevent crushing. 

Resin Beads. The resin beads are prepared from commercially available Dowex 50W-X8, a sulfonic acid cation exchange resin. The 8% cross-linked resin was chosen because it does not shrink or expand excessively in acid-water systems and because it is readily available. Resin cross-linkage had no detectable effect on the final oxide products in the development test runs. The resin is hydraulically classified to produce a size fraction that is predominately 60-80 m in diameter. The classified resin is washed with 6 M HC1 to remove contaminants such as iron and rinsed thoroughly with water. 

Complete cross-linkage between fiber and resin at temperatures between 270 and 290F. 

Table 4-3. Effects of Increasing Cross-Linkage in Polystyrene or Phenolic Resins...

Although original water samples can apply for some techniques, the isolation procedure is essential for better HS characterization with most analytical techniques. The traditional HS isolation method probably is XAD adsorption, which has been widely used for decades in the HS isolation from waters, soils, and organisms. This method can not only isolate HS, but also further separate HS into two fractions (humic acid and fulvic acid). Detailed isolation procedures have been reviewed in previous articles.XAD resins are styrene-divinylbenzene or methyl methacrylate polymer with various hydrophobicities and cross linkages. The resins adsorb dissolved organic matter mainly by hydrophobic binding or weak interactions such as Van Der Waals force, but the exact mechanism of adsorption is still unknown. 

The insoluble polymeric resin is synthesised by the suspension-radical copolymerisation of styrene with divinylbenzene (DVB) (see Figure 4.3). The polymerisation results in a three-dimensional column framework which is porous in character and can thus allow diffusion of ions to take place through it. By conducting the polymerisation in an aqueous medium beads of definite size can be produced. The extent of cross-linkage and hence pore size can be varied by altering the proportion of DVB. 

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