Nonstaining

In dental appHcations gallium aUoys are nonstaining and used in the fabrication and repair of dental protheses. These aUoys exhibit a sufftcientiy high solder temperature enabling presoldering of the aUoy without distortion of the restoration (56) (see Dental materials). 

Solvenol monocyclic terpenes processing aid nonstaining reclaim oil and solvent swells and penetrates mbber dissolves and disperses heavy oils... 

In general, the amines are more active than the phenoHcs which are in turn more active than the phosphites. Amine antioxidants, however, often cause staining problems and are therefore used mainly in black stocks. The phenoHcs and phosphites are relatively nonstaining and are normally used ia light-colored mbbers. 

Stilbenequiaones such as (5) absorb visible light and cause some discoloration. However, upon oxidation phenolic antioxidants impart much less color than aromatic amine antioxidants and ate considered to be nondiscoloring and nonstaining. 

Stabilization of Elastomers. Polyunsaturated elastomers are sensitive to oxidation. Stabili2ers are added to the elastomers prior to vulcani2ation to protect the mbber during drying and storage. Nonstaining antioxidants such as butylated hydroxytoluene (1),... 

It should persist ia the mbber over its entire life cycle. For noncarbon black filled mbbers, the antiozonant must be nondiscoloring and nonstaining. The antiozonant should have a low toxicity and should be nonmutagenic, and, the antiozonant should be acceptable economically, eg, have low manufactufing and end use costs. 

Phenidone, l-phenyl-3-pyrazolidone (738) (B-76M140404), has been used as a nonstaining, high contrast photographic developer. New optical brighteners containing 2-pyrazolines (739) and pyrazoles (740) have been synthesized recently and their properties and applications reviewed (75AG(E)66s). 

Stabilizers. Antioxidants provide protection against UV light and thermal oxidative degradation. Hindered phenols are the most common nonstaining antioxidants. For SBR latices, two additional type of stabilizers must be used. 

Ivan et al. [95] reported that 3,5-di-tert-butyM-hydroxybenzylcyanoacetate is a nonstaining antiozonant that affords similar protection to NR and to cw-polyisoprene compounds such as N-isopropyl-N -phenyl-para-phenylenediamine does (see Figure 15.12). This product lasts longer than conventional nonstaining antiozonants, like the styrenated phenols. 

The most prevalent approach to achieve long-lasting and nonstaining ozone protection of rubber compounds is to use an inherently ozone-resistant, saturated backbone polymer in blends with a diene rubber. The ozone-resistant polymer must be used in sufficient concentration (minimum 25 phr) and must also be sufficiently dispersed to form domains that effectively block the continuous propagation of an ozone-initiated crack through the diene rubber phase within the compound. Elastomers such as ethylene-propylene-diene terpolymers, halogenated butyl mbbers, or brominated isobutylene-co-para-methylstyrene elastomers have been proposed in combination with NR and/or butadiene rubber. 

Naphthenic oils give good processability and compatibihty in diene elastomers and the resulting vulcanizates are relatively nonstaining. 

Clear unsaturated oils are vulcanised at room temperature with sulphur monochloride to give a white, friable solid which is nonstaining and suitable for use in coloured compounds. Crosslinking using sulphur monochloride produces a white factice, but care had to be taken in its use, for if not used when fresh it develops a high level of acidity which affects compound cures severely. The acidity can be removed by steaming the factice just prior to use. Modem white factices contain a small addition of alkali to counteract any developed acidity. 

Light. Ultraviolet (uv) light promotes free-radical oxidation at the mbber surface which produces discoloration and a brittle film of oxidized mbber (35). This skin cracks in random directions to form a pattern called crazing, which can be prevented by the addition of carbon black fillers or uv stabilizers. Black stocks are more resistant to uv light than are gum or light-colored stocks. Nonblack compounds require larger quantities of nonstaining antioxidants which should bloom to the surface as the surface uv stabilizers deplete. 

The solvent should be nonstaining, and at least in fog form, noncorrosive to paint, metals, plastics, and fabrics. 

Cosmetics and Soaps. Ultramarine pigments are widely used in cosmetics. Pink is not recommended for toilet soaps because of the color shift to violet. Advantages are complete safety, nonstaining, and conformance to all major regulations. 

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