Nonblack compounds

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. 

Ultraviolet light initiates free radical oxidation at the exposed surface of an elastomeric product to generate a layer of oxidized rubber. Heat, moisture, or high humidity can then initiate crazing of the surface, which subsequently can be abraded off. Such degradation of the surface is more severe with nonblack stocks than with black compounds. Nonblack compounds such as white tire sidewalls thus require higher levels of nonstaining antioxidants than carbon black-loaded formulations. 

Best low temperature brittle point Nonstaining, nondiscoloring Useful for nonblack compounds Good compatibility... 

The use of protective agents is not necessary in EPM compounds. For EPDM compounds, antioxidants are provided, particularly if they are intended for high temperature (150°C or more) service. In black compounds (or when staining is tolerated) aromatic amines (espedally phenylene diamine derivatives) offer the best protection in peroxide cured compounds, TMQ use is recommended. In nonblack compounds, nonstaining antioxidants should be provided addition of... 

Plasticizers Polar plasticizers such as esters decrease surface resistivity of nonblack compounds hydrocarbon secondary plasticizers provide increased levels. Unplasticized PVC without a surface coating of paraffin wax has a surface resistivity of about 10 ohm. Addition of 40 phr of ester plastieizer decreases this to 10 °-10 ohm. Phosphate plasticizers can lower surface resistivity by several orders of magnitude. In addition, the mobility (lowering of glass transition temperature) of the plasticizer is a factor. Low-temperature plasticizers are found to have an increased effect in lowering surface resistivity. When substituting, for example, an adipate or oleate for a phthalate to lower surface resistivity (in cases where the application permits), it must be considered that the former are more available microbial nutrients. 

Although superior to Neoprene and Hypalon , NBR/PVC blends do not have as great resistance to UV light as pure PVC. Thus, nonblack compounds should be protected with titanium dioxide and UV light absorbers. The latter have been commonly chosen from the benzotriazole class. New hindered amine stabilizers have been introduced (e.g., NOR HALS 833 from Ciba), that are resistant to hydrogen chloride. These should be considered for NBR/PVC compounds (except if tin mercaptide stabilizers are used). All NBR/PVC compounds should contain antioxidants of broad compatibility (e.g., Irganox 1076). 

Copolymers of styrene and butadiene with styrene content of 75-90%. They are organic nonblack reinforcing materials and find their greatest application in leather-type shoe soles. They facilitate the easy processing of relatively hard compounds due to a high degree of thermoplastic behaviour. 

Non-benzenoid aromatic compounds, flash vacuum pyrolysis for, 21 148 Non-benzenoid quinones, 21 238 Nonbenzidine-based dyes, 9 448 Nonblack fillers, 21 781... 

Filler dispersion is a property that determines how well the filler partciles in a given rubber compound are dispersed as a result of the mixing process. This relates to carbon black dispersion as well as the dispersion of nonblack fillers such as silica, clay, calcium carbonate, titanium dioxide, etc. Also rubber curatives such as sulfur and accelerators can be poorly dispersed (commonly these ingredients are added late in the mixing cycle). Poor dispersion makes a mixed stock less uniform, and commonly the cured ultimate tensile strength will have more variability. Poor dispersion can affect other important cured physical properties such as abrasion, tear, and fatigue resistance, flexometer heat buildup, and other dynamic properties. 

Zinc oxide, which is formed from the burning of zinc metal, was the first nonblack filler nsed for reinforcement of rubber compounds. Although zinc oxide and magnesinm oxide are still used as reinforcing fillers in some specialty compoimds, particnlarly those that reqnire heat resistance, their role in rubber compoimding in the last several decades is that of an activator for the sulfur cure system or as curatives for chloroprene rubber compounds. 

For comparative purposes, the effects of nonblack fillers, both natural rubber and SBR compounds, are shown in Tables (12) and (13). For example it illustates... 

Surface Treatment. Carbon black remains the particulate filler of choice for rubber articles since the inherent reinforcing effect of the nonblack fillers in hydrocarbon elastomers is not comparable. This is primarily due to the nonbonded interactions established between the particulate filler and polymer functionality (28). Surface chemistry plays an important role in the interaction of the nonblack fillers and the polymer with contributions ranging from electrostatic interactions to covalent bonding to the polymer backbone. However, surface chemistry also strongly affects the interaction of the nonblack filler with other chemicals in the rubber compound, particularly active metal oxides, curatives, and antidegradants. 

CSM compounds possess excellent resistance to ozone attack, oxidation, and weathering, even for nonblack products. Also, these CSM compounds usually possess some oil, water, and chemical resistance. Therefore, CSM compounds are used in environmental applications (especially pond linings), insulation for cables, spark plug boots, coated fabrics, hose covers, single-ply roofing, rafts, and folding kayaks. 

W.H. Waddell, L.R. Evans. Use of nonblack fillers in tire compounds. Rubb. Chem. TechnoL, 69,377-423,1996. 

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