Solvent Modified Resin Structures

Choice of the Lignin Modification Reaction. The phenolysis reaction was selected as a means of modifying the structure and reactivity of the ammonium lignin sulfonate for three main practical reasons. First, because this lignin derivative is soluble in (and will ultimately be used in conjunction with) liquid phenol itself second, because unreacted phenol, unlike other reaction solvents, would not have to be removed from the phenolated product after reaction and before conversion to the adhesive resin and third, because lignins and carbohydrates are known to react with phenols under acidic conditions (6,7). 

Macroporous resin beads, due to their mode of preparation, consist of a macroporous internal structure and highly cross-linked areas (>5%). The latter impart the resin with rigidity, whereas the porous areas provide a large internal surface for functionalization, even in the dry state. These macroporous polystyrene-based resins are subsequently modified in various manners, which render them compatible with numerous organic solvents. Furthermore, they show high resistance toward osmotic shock, but can be brittle when not manipulated carefully. 

High Solids Coatings, High solids coatings resemble the technology of solvent-free coatings but the compositions contain ca 70% by volume of solid resin and are modified by reactive diluents, low viscosity multiftinctional resins, or backbone structures other than the bisphenol A moiety. 

The epoxy-nitrile adhesives were introduced commercially in the late 1960s. They consisted primarily of DGEBA epoxy resin modified with carboxyl-terminated butadiene nitrile (CTBN) rubber. These first nitrile copolymers were available from B.F. Goodrich under the trade name of Hycar. The most convenient form of epoxy nitrile adhesive, especially when one is bonding large parts (aircraft structures), is a supported film. However, solvent solutions of epoxy-nitrile adhesives have also been commercially available. 

The cation-exchange resins obtained from SDVB copolymers prepared by conventional pearl polymerization technique mostly have the gel structure. The conventional SDVB copolymer has been modified by using a solvent or a linear.polymer in the monomer mixture during the polymerization to make porous SDVB copolymers. 

The characteristic structure of the diluent-modified SDVB copolymers is retained in their sulfonated derivatives. A comparison of the solvent regains of macroporous sulfonic acid resin, conventional sulfonic acid resin, and their parent hydrocarbon matrices is made in Table 1. The sulfonated macroporous product like its parent hydrocarbon copolymer also takes up normally incompatible solvents and the close similarity of their regains in the sulfonated material to the water regain of the hydrocarbon matrices, expressed in compatible units, shows that the macropores have largely survived the sulfonation... 

Some elastomeric adhesives are supplied in film form. Most of these adhesives are solvent dispersions of water emulsions. Temperature environments up to 66-204°C are practical. Elastomeric adhesives never melt completely. Bond strengths are relatively low, but flexibility is excellent. These adhesives are used in unstressed joints on lightweight materials, so they cannot be considered structural adhesives. They are particularly advantageous for joints in flexure. Most of these adhesives are modified with synthetic resins for bonding rubber, fabric, foil, paper, leather, and plastic films. They are also applied as tapes. Examples of elastomeric adhesives are shown in Table 4.3. 

There are a number of types, based on their chemical structure, but the most important and most widely used is nylon 6,6. The best adhesives for bonding nylon to nylon are solvents. Various commercial adhesives, especially those based on phenol-formaldehyde (phenolics) and epoxy resins, are sometimes used for bonding nylon to nylon, although they are usually considered inferior to the solvent type because they result in a brittle joint. Adhesives recommended include nylon-phenoUc, nitrile-phenolic, nitriles, neoprene, modified epoxy, cyanoacrylate, modified phenolic, resorcinol-formaldehyde, and polyurethane. Bonds in the range of 1.7-6.9 MPa, depending on the thickness of the adherends, have been obtained. ... 

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