Adhesives chemically reactive

Many of these features are interrelated. Finely divided soHds such as talc [14807-96-6] are excellent barriers to mechanical interlocking and interdiffusion. They also reduce the area of contact over which short-range intermolecular forces can interact. Because compatibiUty of different polymers is the exception rather than the rule, preformed sheets of a different polymer usually prevent interdiffusion and are an effective way of controlling adhesion, provided no new strong interfacial interactions are thereby introduced. Surface tension and thermodynamic work of adhesion are interrelated, as shown in equations 1, 2, and 3, and are a direct consequence of the intermolecular forces that also control adsorption and chemical reactivity. 

Conceivably, many compounds of inorganic elements have chemical reactivity that could contribute to improved adhesion to mineral surfaces. A fairly wide range of compounds, not restricted to any particular group in the periodic table, have been proposed as coupling agents as is shown in the following list ... 

Improve adhesion of dissimilar materials such as polymers to inorganic substrates. Also called primers. Primers generally contain a multifunctional chemically reactive species capable of acting as a chemical bridge. In theory, any polar functional group in a compound may contribute to improved bonding to mineral surfaces. However, only a few organofunc-tional silanes have the balance of characteristics required... 

The adhesion of thermoplastic to glass cannot be explained by copolymerization of the coupling agent with the matrix. The polymers have essentially fully reacted. Chemical reactivity on the polymer backbone is now of interest. The picture is also more complex in that the number of polymers to be reinforced is much larger than for the thermosetting materials. Virtually every polymer which is being injection molded is also being used in its reinforced form. 

Reactive diluents can be used to reduce the modulus and increase the elongation of the cured waterborne epoxy formulations just as they are often used for 100 percent solids and solvent-borne epoxy adhesives. The reactive diluents become codispersed in the formulation with mechanical and chemical stability similar to that of the base epoxy emulsion. Polyglycidyl ether of caster oil, phenyl glycidyl ether, and diglycidyl ether of neophenyl glycol are examples of mono- and difunctional reactive diluents that have been used to improve flexibility and increase the tack-free time of waterborne epoxy adhesives. 

Considerable research activity has been directed toward producing wood composite adhesives from lignin, and this has been accompanied by very little practical success in terms of commercial implementation. By themselves, and regardless of source, lignins offer no advantages in terms of chemical reactivity, product quality, or color when compared to conventional wood composite adhesives. At low replacement levels (10 to 30%), lignins can and will continue to be employed as extenders for UF and PF resins. When they are used as extenders, best results are obtained when chemically activated (e.g., by methylolation). 

The adhesive may be solvent or water-based, hot-melt, coldseal or heatseal and pressure sensitive or chemically reactive. So the solidification process may occur via drying of water or solvent-based adhesives, by cooling of hot-melt and heat-seal adhesives, or by curing of chemically-reactive systems. With two notable exceptions - self-adhesive labels used on items of fruit or vegetables, and heat-sealable layers on packaging films - adhesives are in general not intended to touch the packaged food directly. 

Sampathkumar S-G, Li AV, Jones MB, Sun Z, Yarema KJ. Metabolic installation of thiols into sialic acid modulates adhesion and stem cell biology. Nat. Chem. Biol. 2006 2 149-152. Mahal LK, Yarema KJ, Bertozzi CR. Engineering chemical reactivity on cell surfaces through oligosaccharide biosynthesis. Science 1997 276 1125-1128. 

The bisphenol moiety offers outstanding properties such as toughness, rigidity and good high-temperature performance. Chemical resistance is provided by ether linkages adhesive and reactive properties are imparted by the hydroxyl and epoxy groups. 

Polymer blends and alloys have more complex behavior in the presence of fillers than the binary mixtures of polymer and filler. The same factors, such as filler distribution, filler-matrix interaction, filler-matrix adhesion, particle orientation, nucleation, chemical reactivity, etc. have influence on properties, but this influence is complicated by the fact that there are two or more polymers present which compete for the same filler particles. These complex interactions result in many interesting phenomena discussed below. 

Thus, it appears that chemical reactivity or ionic-cross interactions could lead to in situ compatibilising or miscibility enhancement during melt-mixing. However, several questions remain. How does the reactivity modify the thermodynamic balance, the reciprocal miscibility or the rheological behaviour of the melt Or, how the covalent or ionic bonding influence the interfacial adhesion processability and final mechanical properties of the immiscible blends ... 

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