Latexes, water-based adhesive natural

Bentonite thickening agents are used in various water based adhesives, caulks and sealants including those based on proteins and starch, polyvinyl acetate emulsions, natural rubber latexes, acrylic emulsions, neoprene emulsions, butyl emulsions, nitrile emulsions, and SBR emulsions. 

Another form of water-based adhesive is the emulsion or latex which was mentioned in the first chapter. This is a means of providing water-based products in which the adhesive substance itself is not soluble in water but is dispersed in liquid droplets held in suspension in water. Examples include the natural rubber latex as well as PVA, acrylic emulsions and others. 

Emulsion Adhesives. The most widely used emulsion-based adhesive is that based upon poly(vinyl acetate)—poly(vinyl alcohol) copolymers formed by free-radical polymerization in an emulsion system. Poly(vinyl alcohol) is typically formed by hydrolysis of the poly(vinyl acetate). The properties of the emulsion are derived from the polymer employed in the polymerization as weU as from the system used to emulsify the polymer in water. The emulsion is stabilized by a combination of a surfactant plus a coUoid protection system. The protective coUoids are similar to those used paint (qv) to stabilize latex. For poly(vinyl acetate), the protective coUoids are isolated from natural gums and ceUulosic resins (carboxymethylceUulose or hydroxyethjdceUulose). The hydroHzed polymer may also be used. The physical properties of the poly(vinyl acetate) polymer can be modified by changing the co-monomer used in the polymerization. Any material which is free-radically active and participates in an emulsion polymerization can be employed. Plasticizers (qv), tackifiers, viscosity modifiers, solvents (added to coalesce the emulsion particles), fillers, humectants, and other materials are often added to the adhesive to meet specifications for the intended appHcation. Because the presence of foam in the bond line could decrease performance of the adhesion joint, agents that control the amount of air entrapped in an adhesive bond must be added. Biocides are also necessary many of the materials that are used to stabilize poly(vinyl acetate) emulsions are natural products. Poly(vinyl acetate) adhesives known as "white glue" or "carpenter s glue" are available under a number of different trade names. AppHcations are found mosdy in the area of adhesion to paper and wood (see Vinyl polymers). 

Highly purified diallyl maleate and fumarate in an inert atmosphere, are said to polymerize very rapidly [118], However, trace impurities and atmospheric oxygen substantially reduce the polymerization rate under ordinary circumstances. Naturally with the double bond between the two carboxylate groups and the two allylic double bonds, crosslinking takes place at very low conversion. Even so, in copolymer systems such as in poly(vinyl acetate) emulsion copolymers, the cross-linking of a fumarate or maleate within the latex particles appears not to interfere significantly with film formation properties. As a matter of fact these monomers are incorporated in poly(vinyl acetate) latices used in adhesives and in water-based paints. 

Cold-seal adhesives are members of a general category sometimes termed coadhesive substances that have a great tendency to stick to themselves, but often not to much else. Cold-seal adhesives are typically based on natural rubber, which has been applied in a latex (suspension in water) form. One major application is in plastic packaging for chocolate candy. The seal between the two parts of the wrap can then be activated with pressure, as an alternative to heat-sealing, which is problematic with the low-melting temperature candy. 

Water-based dispersions or emulsions such as polyvinyl acetate, acrylics, polyvinyl chloride and polyvinyl alcohol with plasticizers and tackifiers. In addition, this range can include urea formaldehyde and phenolic adhesives, resins, natural adhesives produced from starch, dextrin, casein, animal glues (see Polyvinyl alcohol in adhesives, Phenolic adhesives single-stage resoles. Phenolic adhesives two-stage novolacs. Animal glues and technical gelatins) and rubber latex (see Emulsion and dispersion adhesives). Solvent-free 100% solids such as polyurethane. Hot melt adhesives include Ethylene-vinyl acetate copolymers, polyolefins, polyamides, polyesters with tackifiers and waxes. More recent additions include cross-linkable systems. 

Water-based dispersion adhesives consist of oligomers dispersed in water with surfactants as dispersing agents and stabilizers. Before dispersions, natural rubber latex and casein were used to manufacture such adhesives. Currently, polyvinyl acetate (PVAc) and polyacrylate serve as synthetic base polymers for water-based PSA, while polychloroprene and thermoplastic polyurethane serve the same purpose for water-based contact adhesives. 

Chem. Desaip. Silicone-based, protein-supported emulsion Uses Dewebber, defoamer, antifoam for natural and syn. latexes in latex dipping industry (mfg. of toys, medical, household, and industrial gloves, anesthesia bags) defoamer for pulp/paper mfg., influent and effluent wastewater treatment, boiler water treatmenL paints, adhesives, and sealants food-contact rubber articles Regiiatory. FDA 21CFR 177.2600... 

The major part of the market for ceramic tile adhesives is held by formulations based on a filled polyvinyl acetate latex, but natural rubber latex is still used as a base, particularly where the adhesive is to perform under damp conditions. Formulations II and III give examples. Tile adhesives need to be stiffer than most other applications, and this effect is provided by the clay filler, which also reduces material costs and imparts gap filling properties. Cost may be further reduced by increasing the level of clay to 250 pphr, although performance will be reduced. The resin serves to improve bond strength and water resistance. 

Envelope sealing adhesives are usually remoistenable, and typically blends of dextrin and compatible polyvinyl aeetate homopolymers as well as all dextrin or all resin types. Some water-borne and hot melt pressure sensitive adhesives based on acryhc or rubber resin liquids and rubber resin hot melts are also used. Natural rubber latex is the basis for self sealing envelopes. 

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