Composition formulation, adhesive solvents

The formulated adhesives are generally available as films or solvent solutions. They are commonly used as laminating adhesives for film or metallic foil because of their high peel strength. A composition consisting of a plasticized polyvinyl chloride copolymer and an epoxy resin can be cured with an aliphatic polyamine, which will crosslink by reacting with both resins. This adhesive possesses excellent adhesion to metals. 

TG is frequently used for analysing the composition of adhesives by quantifying the amount of moisture which is present and the amount of volatiles associated with a reaction. Fast heating rate TG allows detection of very low levels of volatiles in small samples. TG is also used for the quantitative determination of solvents in polymeric additives used as pour-point depressants and flow improvers [220], PET moisture analysis by means of TG can be carried out at ppm level [221]. Thermogravimetry (eventually combined with GC or IR and subambient DSC) is very useful for the determination of residual solvents or for the study of interactions of water with polymers (important for modified release formulations for which swelling or gel formation of polymeric excipients is relevant). TGA has also been employed to measure the continuous desorption of sorbed SCCO2 in polymeric materials [222]. 

Nonreactive resins with a variety of compositions are of considerable importance in the formulation of adhesives. In some cases, they are used on their own in solvent adhesives, so-called resin adhesives, but generally in combinations with polymers, in which they perform various functions. Above all, they increase tack, improve adhesion, influence viscosity, fluidity, and scalability, and, in some cases, also act as plasticizers. The most important applications for nonreactive resins are in pressure-sensitive adhesives, contact adhesives, hot-melt adhesives, solvent adhesives, and emulsion-based adhesives. In this context, the term resin covers materials differing very widely in their composition ... 

Alkenyloxystyrene monomers such as 4-allyloxystyrene are useful components of photocured cationically polymerizable compositions. Used alone or in combination with divinyl ethers they provide low viscosity formulations, which are excellent solvents for commercial onium salt photoinitiators. Photocuring rates are comparable to vinyl ether monomers and the initially photocured alkenyloxystyrene polymers may be further heat processed to yield crosslinked phenolic type resins having outstanding thermal resistance properties. The new materials have good adhesive properties and are potentially useful where a combination of ease of processability and high performance is required. 

Radiation curing adhesives are generally applied as solvent-free liquids. High-solids EB and uv curing liquid adhesives have been formulated from a variety of resins and elastomers. They include epoxy acrylates, epoxies, other acrylates, polyesters, blends of acrylate monomers with elastomers, and other compositions. 

Structural adhesives are solvent-free compositions and can be formulated to give varying pot-lives, making them suitable for temperate as well as tropical climatic conditions. A long pot-life makes the adhesive suitable for use with form work or where additional steel reinforcement has to be fitted. 

It was not until the commercialization of synthetic plastics resins in the 1930s that an almost unlimited variety of base materials became available for compounding into adhesives and sealants. Most of the thermoplastic resins were soluble in organic solvents and were used as solvent adhesives for molded plastic articles of the same base composition and sometimes for other materials. Poly(vinyl chloride) (PVC), a thermoplastic developed in 1927, is used today in solvent formulations to bond PVC articles such as coated fabrics, films, foams, and pipe. In the early 1930s, phenolics came into importance as adhesive resins. Before that time they were used as coating varnishes [9, p. 239). About 1931 development of the use of a new phenolic resin for plywoods and veneers began [9, p. 239]. 

Although not included in this discussion, these compositions may be formulated to be developed in what is known as a semiaqueous solvent [26], where an organic solvent, such as butanol, at levels between 5 and 20%, is present in the aqueous developer. Formulations developed in this manner have been shown to have resolution equivalent to the all-aqueous developers with, in some instances, superior adhesion to the substrate. 

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