Additives natural rubber adhesives

Wi is the weight fraction of the elastomer, W2 the tackifier, W3 a further compatible additive, such as an oil, and so forth, for the remaining components in the formulated PSA. Application of the Fox equation to the poly (/-butylstyrene) tackified natural rubber adhesive (cited above) gives a value of —11°C, in good agreement with the interpolated value of — 13°C. 

A true synthetic natural rubber was introduced in the mid-1960s with the exact same chemical structure as latex tapped from a tree. The difference is that natural rubber comes with a variety of other ingredients in the latex that can both add and detract from performance, while polyisoprene is considered relatively pure. In addition, there are some differences in molecular weight distribution that impact performance. Available in both latex and solid forms, this elastomer can be directly substituted for natural rubber in many applications. Adhesives which are not cured tend to have higher creep values than natural rubber, but also exhibit lower tack and green strength properties. Vulcanized adhesive products perform equal to cured natural rubber adhesive products. 

Reviews on the subject of brass-plated steel cord-natural rubber adhesion have been written by van Ooij who has done much of the work in the field. Van Ooij [46] has given a model for rubber-brass adhesion, in which a copper sulfide layer forms on the brass before the onset of crosslink formation. The thin film of copper sulfide has good adhesion and cohesion. In addition, the film is so porous that rubber molecules can become entangled with it. It is not required that the film forms simultaneously with the formation of crosslinks during vulcanization but, rather, it is required that the copper sulfide film be completely formed before crosshnking starts. Indeed, adhesion between brass-plated steel and natural rubber can frequently be improved by the use of the retarder, CTP [4] or by using a more delayed action accelerator such as N-dicyclohexylbenzothiazole-2-sulfenamide (DCBS) [47]. 

Formulation. Unlike the natural rubber pressure sensitive adhesives, acrylic adhesives are often supplied in a ready-to-use form. Natural rubber adhesives require time-consuming and costly mastication of the rubber followed by dissolving in solvent. In addition, they must be formulated with a tackifier resin and antioxidants, neither of which is required with an acrylic adhesive. The acrylic adhesives are known for their good UV and oxidative stability while the rubber-based adhesives, because of their chemical unsaturation, are poor in these properties. In general, tackifiers are not required with acrylic adhesives as tack can be designed into the polymer by the proper choice of... 

Among the different pressure sensitive adhesives, acrylates are unique because they are one of the few materials that can be synthesized to be inherently tacky. Indeed, polyvinylethers, some amorphous polyolefins, and some ethylene-vinyl acetate copolymers are the only other polymers that share this unique property. Because of the access to a wide range of commercial monomers, their relatively low cost, and their ease of polymerization, acrylates have become the dominant single component pressure sensitive adhesive materials used in the industry. Other PSAs, such as those based on natural rubber or synthetic block copolymers with rubbery midblock require compounding of the elastomer with low molecular weight additives such as tackifiers, oils, and/or plasticizers. The absence of these low molecular weight additives can have some desirable advantages, such as ... 

Other polymers used in the PSA industry include synthetic polyisoprenes and polybutadienes, styrene-butadiene rubbers, butadiene-acrylonitrile rubbers, polychloroprenes, and some polyisobutylenes. With the exception of pure polyisobutylenes, these polymer backbones retain some unsaturation, which makes them susceptible to oxidation and UV degradation. The rubbers require compounding with tackifiers and, if desired, plasticizers or oils to make them tacky. To improve performance and to make them more processible, diene-based polymers are typically compounded with additional stabilizers, chemical crosslinkers, and solvents for coating. Emulsion polymerized styrene butadiene rubbers (SBRs) are a common basis for PSA formulation [121]. The tackified SBR PSAs show improved cohesive strength as the Mooney viscosity and percent bound styrene in the rubber increases. The peel performance typically is best with 24—40% bound styrene in the rubber. To increase adhesion to polar surfaces, carboxylated SBRs have been used for PSA formulation. Blends of SBR and natural rubber are commonly used to improve long-term stability of the adhesives. 

Standard-grade PSAs are usually made from styrene-butadiene rubber (SBR), natural rubber, or blends thereof in solution. In addition to rubbers, polyacrylates, polymethylacrylates, polyfvinyl ethers), polychloroprene, and polyisobutenes are often components of the system ([198], pp. 25-39). These are often modified with phenolic resins, or resins based on rosin esters, coumarones, or hydrocarbons. Phenolic resins improve temperature resistance, solvent resistance, and cohesive strength of PSA ([196], pp. 276-278). Antioxidants and tackifiers are also essential components. Sometimes the tackifier will be a lower molecular weight component of the high polymer system. The phenolic resins may be standard resoles, alkyl phenolics, or terpene-phenolic systems ([198], pp. 25-39 and 80-81). Pressure-sensitive dispersions are normally comprised of special acrylic ester copolymers with resin modifiers. The high polymer base used determines adhesive and cohesive properties of the PSA. 

The earliest courses which considered polymeric materials dealt with them on an empirical basis, with recipes directing additions of specified amounts or treatments of materials being typical rather than the exception. These early courses concentrated on adhesives, oils and coatings, resins, textiles, paper and pulp and natural rubber. Specific examples are given in the following sections. 

Uses Solvent for cellulose acetate, crude rubber, natural resins, nitrocellulose, vinyl resins, waxes, fats, oils, shellac, rubber, DDT, and other pesticides preparation of adipic acid and caprolactum additive in wood stains, paint, PVC paints, lacquers (to prevent blushing or improve flow), and varnish removers degreasing of metals spot remover lube oil additive in PVC adhesives to control evaporation rate leveling agent in dyeing and delustering silk. 

Rubber. The rubber industry consumes finely ground metallic selenium and Selenac (selenium diethyl dithiocarbamate, R. T. Vanderbilt). Both are used with natural rubber and styrene—butadiene mbber (SBR) to increase the rate of vulcanization and improve the aging and mechanical properties of sulfurless and low sulfur stocks. Selenac is also used as an accelerator in butyl mbber and as an activator for other types of accelerators, eg, thiazoles (see Rubber chemicals). Selenium compounds are useful as antioxidants (qv), uv stabilizers, (qv), bonding agents, carbon black activators, and polymerization additives. Selenac improves the adhesion of polyester fibers to mbber. 

Diazoaminobenzene (DAAB) is used as a chemical intermediate, a complexing agent, and as a polymer additive. DAAB has been used to promote adhesion of natural rubber to steel tire cords. It has also been used as a blowing agent in the production of a foamed polymeric material. In addition, DAAB is used in the manufacture of dyes and insecticides. DAAB is present in cosmetics, pharmaceuticals, and food products, as a dye contaminant in D C Red No. 33, FD C Yellow No. 5, and FD C Yellow No. 6. 

Revertex. [Diversified Compounders] High stdids natural rubber latex used for carpet backing, adhesives, cement and asphalt additives. 

In addition to the benefits of low odor and redueed fogging, these adhesives form stronger bonds to low-energy substrates sueh as EPDM rubber, natural rubber, and other difficult-to-bond plastics. This property seems to be a funetion of the solvent action of the uncured adhesive, so care must be taken to avoid stress eraeking when the adhesive is used on sensitive substrates sueh as polyearbonates and polyaerylates. 

Elastomers used in water-based systems include various rubber latices, especially natural rubber and SBR, and occasionally, polychloroprene. The bulk of the market in water-based adhesives is now held by acrylic dispersions. Although these are designed for use without modification, it is normal to formulate, especially by addition of tackifiers. Commonly used tackifying resins include soft resins, or hard resins in solution, which may... 

In addition, it must not lose adhesion as a result of perspiration, but must permit easy and clean removal. Traditional adhesives were based on natural rubber and zinc oxide, but water-based acrylic systems now dominate. 

Chlorinated rubber resins are produced by the chlorination of synthetic and natural rubbers. The chemical structure shown in Fig. 13.3 is synthesized by the addition of chlorine to unsaturated double bonds until the resin contains 65% chlorine. These resins have similar properties to those of vinyl resins. Plasticizers are added to increase elasticity and resin adhesion. These coatings are resistant to water but have poor resistance to sunhght. 

Environmental Toxic to fish nontoxic to bees Precaution Combustible can form explosive mixts. with air > 89 C Hazardous Decomp. Prods. CO, CO2, SO, CS2 Uses Vulcanizing agent, accelerator for rubber preservative for natural rubber latex fungicide insecticide seed protectant/disinfectant animal repellent antioxidant for polyolefins lube oil additive in food-pkg. adhesives accelerator for food-contact rubber articles for repeated use antiseptic antibacterial, antifungal for topical pharmaceuticals Regulatory FDA 21CFR 175.105,177.2600 SARA reportable Manuf./Distrib. Aldrich Atofina Agri Complex Ouimica SA FMC Foret ... 

The proportion of bio-based materials in each of the sectors of elastomers and fibres accounted for almost 40% due to the use of 290 000 t of natural rubber and 300 000 t of cellulosic fibres. The market size for thermoplastics and thermosets amounted to circa 15.8 million t, of which circa 12.5 million t accounted for rigid materials, mainly in packaging, building and construction, automotive and electronics industries as well as for furniture and consumer goods. A volume of 3.3 million t is attributed to adhesives, paints and lacquers, binders and other polymeric additives. In these areas it is estimated that bio-based materials... 

Uses Vulcanizing agent, accelerator for rubber preservative for natural rubber latex fungicide insecticide seed protectant/disinfectant animal repellent antioxidant for polyolefins lube oil additive in food-pkg. adhesives accelerator for food-contact rubber articles for repeated use antiseptic antibacterial, antifungal for topical pharmaceuticals... 

Chlorine treatment of natural rubber gives chlorinated rubber III. Since the products contain up to 65% chlorine, substitution obviously occurs along with addition across the double bonds (since the latter would only lead to a theoretical maximum of 51%C1). As indicated by spectroscopic studies, some cyclization to cyclohexane structures occurs also. Chlorinated rubber solutions are Used as adhesives for diene rubber-metal laminates. 

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