Static ozone resistance

The requirements for static ozone resistance vs. dynamic ozone resistance are very different, so that choiee of antiozonant depends greatly on the expected service of the rubber produet. Static protection is provided by petroleum waxes, usually paraffin and/or microcrystalline waxes. The waxes work by blooming to the rubber surface to form a physical barrier to ozone attack. The choice of wax or wax blend is based upon migration temperature where mobility and solubility of the wax in the rubber are balanced so that sufficient bloom occurs for optimum protection. Because the wax film is inextensible, it will rupture under deformation and expose the elastomer. Waxes protect only under static conditions. 

Note Optimization = 2 factor, 2 and 3-level full factorial design—12 compounds and experiments. Responses (properties) to be measured Static ozone resistance dynamic ozone resistance flex-fatigue resistance extrusion processing high temperature, pressure pulse simulated application test of hose sample. 

Note Optimization=4 factor, 2,2,2 and 2-level full factorial design—16 compounds and experiments. Responses (properties) to be measured Abrasion resistance static ozone resistance resistance to spill fluids, 70 h at 125°C tack for ply build-up extrusion processing heat resistance 1008 h at 125°C. 

In dynamic testing of ozone resistance, a fabric-backed vulcanized rubber specimen is continuously flexed in the ozone chamber over a roller. The fabric backing is in the form of a belt. Any protective chemical films (e.g., certain waxes and antiozonants) that might build up on the surface of the specimen in static testing are quickly broken by the continuous flexing. ASTM test method D 1149 covers static testing and D 3395 covers dynamic testing in a controlled ozone atmospheres. 

Ethylene propylene diene terpolymers (EPDM) can be used to improve the ozone resistance of bromobutyl/natural rubber binary polymer blends, eliminating the need for chemical antiozonants. Addition of 10 phr of EPDM (with a high ethylidene norbornene, ENB, content of9%) to a 50/50 bromobutyl rubber/natural rubber blend results in a compound vdth good static and dynamic ozone resistance. EPDM with a 5.7% ENB level is another suggested grade of polymer. 

Dynamic and static moduli Kinetic energy Creep and set Tensile properties Mechanical stability Abrasion resistance Elastic modulus Peel tests Ozone resistance... 

Substitutes for wax to provide protection of tyre sidewalls against static ozone cracking are examined. The use of low levels of wax or its complete elimination in the tyre sidewall by combinations with dialkyl paraphenylene diamine (77PD) or 2,4,6-tris - (N-1,4 dimethyl pentyl-p-phenylene diamino) 1, 3, 5 triazine (TAPDT) is discussed for the long term resistance to dynamic ozone crack resistance. In addition, a mechanism is proposed to explain how ozone reacts with antiozonants, which involves a scavenging function. 5 refs. 

ISO 7326 [452] Rubber and plastics hoses - Assessment of ozone resistance under static conditions... 

In addition to the weathering tests for elastomers described in Section 2.2, testing ozone resistance is significant for rubber products. Here, parts molded from rubber are stored statically (tensile strain) or dynamically (alternating strain) in an ozone chamber at a specified strain, temperature, humidity, and ozone concentration. Subsequently, their ozone resistance is evaluated based on the resulting crack formation. 

The static ozone chamber test permits adjustment of ozone concentration (0.5 to 2.0 ppm) and temperature (20 to 50°C) as well as relative humidity (10 to 90%) besides numerous strain levels for the rubber specimens the typical loading time ranges from 2 to 96 hours. The corresponding materials and product standards provide recommendations for the use of certain testing conditions the atmospheric conditions in the ozone chamber should, however, be tuned as closely as possible to the crack resistance of the particular elastic material short-term loading at a low ozone concentration and temperature in the case of crack prone materials, a high ozone concentration and temperature over several days for relatively ozone resistant rubbers. 

Polybutene/polyisobutylene 5% Good adhesion low shrinkage excellent UV/ozone resistance low cost good water resistance Dirt pickup low cohesive strength poor solvent resistance can stain substrate for static joints... 

ISO 1431-1 2004 Rubber, vulcanized or thermoplastic - Resistance to ozone cracking -Part I Static and dynamic strain testing... 

Contacting ozone gas with water can be achieved with every kind of gas diffuser, which is made of a material resistant to ozone. Ring pipes, porous diffusers and porous membranes, injector nozzles as well as static mixers can be employed. The different types of diffusers are mainly characterized by the diameter of the bubbles produced, e. g. micro (dB = 0.01 — 0.2 mm), small (dB 1.0 mm) or big (dB - 2.5 mm) bubbles (Calderbank, 1970 Hughmark, 1967). 

Particulates packed in reactor beds are subjected to the static pressures of the bed height and thus must be sufficiently strong to resist crushing. Monoliths, particularly when used in a stacked mode, for example, in stationary pollution abatement, must resist crushing axially. For vehicular use, for example, auto exhaust and ozone... 

Viton A. Manufactured by Du Pont, Viton A is also an elastomer, and has a safe working temperature range of -50°C to 250°C. It is resistant to many chemicals, to steam, ozone and faming nitric acid, but not to ketones. Viton A has a low permeability to gases and is good for high vacuum and static vacuum systems. 

For completeness, resistance to ozone cracking under static conditions, which can be classed as ageing, will be considered at this point. The principle of ozone generation. 

ISO. 3011, Determination of resistance to ozone cracking under static conditions. 1997. 

Ethylene-acrylic elastomers are highly resistant to the damaging aspects of weather, ie, sun, water, oxygen, and ozone. Vulcanizates have shown little change in tensile properties and no visible signs of surface deterioration after exposure to the elements in Florida for 10 years. Samples imder 20% tensile strain (static) displayed no cracks after one week s exposnre to 100 ppm ozone in air, a concentration 100 times greater than is usually specified in qualifying tests. 

Under pressure, these Thiokol rubbers distort, although Thiokol ST is superior to FA. However, they are resistant to petroleum solvents, esters and ketones, aromatic fuels, oils, greases and lacquer thinners, ozone, sunlight and ultraviolet light. This makes them very useful for static seals where no other material will serve. 

Vulkanox 4010 NA/LG antiozoneuit excels in antiflexcracking properties and is used in tires and mechanical goods subjected to dyneunic stress, e.g. conveyor belts, hoses, spring components and elastic couplings. In static applications and in cables and seals, its main function is resistance to ozone cracking, which can be further improved by the simultaneous use of an ozone protective wax. Use should be restricted to dark colored rubber articles where staining and discoloration are of no concern. 

Photo-oxidation proceeds relatively slowly. That is why elastomers made from chlo-roprene rubber exhibit considerably better resistance to ozone attack and weather influences than those made from NR, SBR, and NBR. Moreover, chloroprene rubbers respond well to anti-aging and antiozonant agents so that they can be recommended for use under difficult climatic conditions, e.g., in the tropics. By extrapolating mechanical property changes after several years of weathering in ozone-rich atmosphere, the current technology allows the prediction that chloroprene rubber products will exhibit sufficient strain for most static applications even after 50 years in service [697]. 

Blends of petroleum waxes are commonly used as antiozonants in the rubber industry. Just as 6PPD gives excellent protection against ozone attack of the surface of the rubber under dynamic conditions, waxes will bloom to the surface of the rubber to impart excellent resistance to ozone attack under static conditions. The wax actually exudes (or blooms) to the surface of the rubber article to create a physical protective barrier to protect the rubber surface against ozone attack, which can create cracking of the rubber. 

Responses (properties) to be measured Heat resistance fixrm 125 C to 150 C static and dynamic ozone ... 

The fuel, ozone, low temperature, and weathering resistance of epichlorohydrin are ideal properties for a curb pump hose. In addition, the static dissipative properties, especially when a conductive carbon black is used, add to the safety of the hose. The EPA low-fuel vapor transmission requirements may dictate an FKM veneer lining, to which GECO will adhere, as well as being a low fuel transmission elastomer itself. Hose components are shown in Table 7.25. 

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