Solvent-based system

Natural and synthetic rubber and synthetic resins are soluble in organic solvents, resulting in cements, resin solutions, or lacquers. In addition, there are many cellulose derivatives, such as nitrocellulose, ethyl cellulose, and cellulose acetate butyrate, used in preparing solvent-based adhesives. Solvent-based adhesives are also prepared from eyelized rubber, polyamide, and polyisobutylene. Low-moleeular-weight polyurethane and epoxy compounds can be used with or without solvent On the other hand, high-molecular-weight types or prepolymers require solvent to make application possible.  

Solvents, or solvents containing small amounts of bodying resin, are used for bonding thermoplastic resins and film adhesives. An example is toluol, which can be used to soften and dissolve polystyrene molded articles to allow joining the softened pieces. Ketones can be used to bond PVC films in a similar manner. A small amount of resin can be used to thicken the solvent, so that a sufficient amount stays in place to dissolve the substrate. However, that solvent welding of molded plastics can cause stress cracking and weakening of the structure as the parts age should be noted. 

Another class of solvent-based dispersion is the organosols. In this case, vinyl chloride copolymer resins are dispersed in suitable nonvolatile plasticizers and solvent. The solvent is evaporated and the remaining film is heated to approximately 177 °C. The heat helps dissolve the resin in the plasticizer, and a tough, flexible film is obtained upon cooling to room temperature. The major polymers used for solvent-based adhesives are listed in Table 8.10. 

Solvent-based adhesives are more expensive than water-based products. They usually make bonds that 

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Recovery and Purification. AH processes for the recovery and refining of maleic anhydride must deal with the efficient separation of maleic anhydride from the large amount of water produced in the reaction process. Recovery systems can be separated into two general categories aqueous- and nonaqueous-based absorption systems. Solvent-based systems have a higher recovery of maleic anhydride and are more energy efficient than water-based systems. 

Bonding properties of water-based contact adhesives are similar to those of solvent-based systems, but are free of flammabihty ha2ards. However, drying times are longer and the bond is sensitive to moisture. 

The original hot carbonate process developed by the U.S. Bureau of Mines was found to be corrosive to carbon steel (55). Various additives have been used in order to improve the mass transfer rate as well as to inhibit corrosion. Vetrocoke, Carsol, Catacarb, Benfteld, and Lurgi processes are all activated carbonate processes. Improvements in additives and optimization of operation have made activated carbonate processes competitive with activated MDEA and nonaqueous solvent based systems. Typical energy requirements are given in Table 9. 

Compounding is quite different for the two systems. The solvent base system is dependent on magnesium oxide and a /-butylphenoHc resin in the formulation to provide specific adhesion, tack, and added strength. Neither of these materials have proven useful in latex adhesive formulations due to colloidal incompatibihty. In addition, 2inc oxide slowly reacts with carboxylated latexes and reduces their tack. Zinc oxide is an acceptable additive to anionic latex, however. Other tackifying resins, such as rosin acids and esters, must be used with anionic latexes to provide sufficient tack and open time. 

Owing to governmental regulations, considerable research has been expended to develop systems suitable for substitution of solvent-based systems, particularly for automobile and container appHcations. In the switch from solvent-based to waterborne systems, epoxies are successfully bridging the gap largely by adaptation of conventional resins. 

Table 7.1. Values of H for Some Representative Solvent-Base Systems"...

Mixed solvent systems containing water are included below even in case water is only a minor constiment, molten salts are listed after liquid solvent-based systems. 

In the nonaqueous organic solvent-based systems used for lithium batteries, the conductivities are of the order of 10 —10 S/cm k Compared to water, most organic solvents have a lower solvating power and a lower dielectric constant. This favors ion pair formation, even at low salt concentration. Ion pair formation lowers the conductivity as the ions are no longer free and bound to each other. Organic electrolytes show lower conductivities and much higher... 

Waterborne polyurethanes that have the performance of solvent-based systems can be made via tailored emulsion polymerization (Hagernrother and Ruttmann, 1990). 

In the case of organic derivatives such as zirconium acetate, direct bonding of the carboxyiate to the zirconium is found. Similar structures are also found in solvent-soluble, water-insoluble carboxylates such as zirconium propionate. Zirconium alkoxide derivatives tend to be monomeric in solvent-based systems but hydrolyse rapidly with ambient water to give polymeric species. 

Both of these in situ devices use substantially less solution (volumes of solution samples for each kinetic run are usually of the order of a few cm3) than a typical piston-cylinder apparatus. The pill-box cell method has the advantage that the cell can be filled in an appropriate glove box for oxygen-sensitive samples or for nonaqueous solvent-based systems that are sensitive to moisture. Temperature control is exerted by fluid circulating through the metal block. 

Conventional solvent-based systems 30-80% solids Acid, Anhydrides 0.28— 0.50/lb glycols alcohols 0.25-0.50/lb 1 day Fusion cook (8-16 hr) or 1 day Solvent cook (A) 200-300°C (B) 100-200°C (A) High energy input (B) Low energy input ... 

Efficiency-Superior to chlorinated paraffins Cost-Cost/performance advantage over chlorinated paraffins Compatibility-Compatible in both water and solvent based systems... 

There are, however, still several applications where the necessary performance can be achieved only by using solvent-based systems. Research is continuing to further reduce solvent content while retaining its beneficial properties. 

The ever increasing emphasis on reducing air pollution and on health considerations emphasized by OSHA has provided a strong impetus for adhesive manufacturers to develop water-based emulsion polymer systems to replace the organic solvent-based systems on which the industry was founded. This has been a difficult process. 

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