Solvent-based adhesives compatibility

New copolymers based on a copolymerization of isobutylene and p-methyl-styrene with improved heat resistance have been reported [64]. Once copolymerization was accomplished, the polymer was selectively brominated in the p-methyl position to yield a terpolymer called EXXPO. In contrast to butyl and halobutyl, the new terpolymer has no unsaturation in the backbone and therefore shows enhanced thermal stability and resistance to oxidation. Useful solvent-based adhesives can be formulated using the new terpolymer in combination with block copolymers [65]. The hydrocarbon nature of the new terpolymer results in excellent compatibility with hydrocarbon resins and oils. 

An appreciable amount of resin is required to modify the elastomer s rheological properties sufficiently have "good" tack. If one plots resin content versus a specific adhesive property such as tackr the curve increases sharply to a maximum, then decreases sharply to very low levels. The drop in properties occurs when the resin becomes the dominant or continuous phase in a distinctly two-phase system or when the modulus of the composition is sufficiently high to prevent it from wetting the substrate in other systems. The level of resin at the maximum tack value depends upon the solubility and/or compatibility of the particular resin chosen with the particular elastomer used. In solvent-based adhesives this level has been on the order of 60% resin to 40% elastomer. 

Compatibility is an issue of relevance in a number of aspects of adhesion. Perhaps, the most obvious is the selection of solvents in the making of a Solvent-based adhesive, or for Solvent welding of thermoplastics. In both cases, solubility parameters can be employed. 

The adhesive must be compatible with the surfaces being bonded. Polystyrene foam is attacked by some solvent based adhesives. Also, plasticizers can migrate between adhesive and vinyls, or other plastic substrates. 

Hydroxyalkyl lignin derivatives were crosslinked with diisocyanates or with melamine in both solvent and aqueous emulsion-based adhesive formulations for wood products (51) (Figure 7). Adhesive performance was found to be related to component solubility and compatibility (51), The use of kraft lignin in aqueous alkali and that of lignin sulfonates in water has been explored in combination with emulsifiable diisocyanates (52) in wood adhesives. Satisfactory strength properties were reported. 

Wide surface compatibility The high polarity of the base elastomer aids in developing adhesion to virtually all high polarity surfaces. Solvent-based products often develop good adhesion to low polarity surfaces such as polyolefins and other plastic substrates. 

The use of plasticizers is relatively uncommon in solvent-based pressure-sensitive adhesives, especially for use on tapes. Where plasticizers are included, their compatibility with the substrate should be considered, to ensure that plasticizer migration will not lead to transfer of the adhesive. Where plasticizing of block copolymers is intended, plasticizers should be selected that are compatible with the diene midblocks rather than with the polystyrene domains. 

Applications of NBR adhesives are based on the excellent elastomeric properties of the polymer coupled with its polarity, which provides good solvent resistance and compatibility with other polymers. Organic solutions of NBR are the most common adhesives, although water-borne and pre-cast films can also be nsed. 

A further interfacial factor can be the presence of non adsorbable or non desorbable contaminating films (as previously mentioned above) at the interface. Such materials can be oils, fatty acids, plasticisers from the rubber and metal processing oils from inadequately cleaned metal components. Some of these lubricants can be absorbed by the adhesive if it is solvent-based but in the case of the new waterborne rubber to metal systems this absorption cannot take place, for the systems are neither miscible or compatible with oils. These new waterborne systems have a critical tolerance level for surface contamination of the metal and if this is exceeded then wetting out of the metal by the adhesive will not, at the worst be possible, or at the best complete. 

Nitrile polymers have found a varied number of applications in the adhesive area. These applications are based on the excellent elastomeric properties of the polymer coupled with its polarity which gives the material good solvent resistance and compatibility with other polar materials. The various commercially available physical forms of nitrile polymers (slab rubber, crumb rubber, liquid rubber and latex) have also increased the ease of processing of the material and broadened the application base. In an attempt to review this broad area, the applications have been subdivided into three parts. In the first section applications involving solely nitrile rubber as the base polymer as well as miscellaneous nitrile rubber blends are reviewed. Due to the large number of applications involved, nitrile rubber/pheno-lic blends have been separated into the second section. For the same reason, nitrile rubber/ epoxy blends are covered separately in the third section. 

A study of column extraction of metals was carried out using pre-packed columns available from Polymer Laboratories (now a part of Varian, Inc.) [6]. Trace metals in these monomers would have a detrimental effect on the stability of anaerobic adhesive products and must be absent prior to use. The columns used are specially coated macroporous polystyrene products that are compatible with polar, non-polar, protic and aprotic solvents. They are designed to remove metals from solvents and monomers. The metal removing SPE product is approximately 45 pm and based on a mono-dispersed macroporous polymeric material. 

There is not a best adhesive for universal environments. For example, an adhesive providing maximum resistance to acids, in all probability, will provide poor resistance to bases. It is difficult to select an adhesive that will not degrade in two widely differing chemical environments. In general, the adhesives that are most resistant to high temperatures usually exhibit the best resistance to chemicals and solvents. Table 2.9 provides the relative compatibilities of s)mthetic adhesives in selected environments. 

Epoxies Low shrinkage, compatible with a wide variety of modifiers, veiy long storage stability, moderate viscosity, cure under adverse conditions Excellent adhesion, high strength, available clear, resistant to solvents and strong bases, sacrifice of properties for high flexibility... 

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