Compression set resistance

Butadiene—Methacrylic Acid Ionomers. Carboxyl groups can readily be introduced into butadiene elastomers by copolymerization, and the effects of partial neutralization have been reported (63—66). The ionized polymers exhibit some degree of fluidity at elevated temperatures, but are not thermoplastic elastomers, and are very deficient in key elastomer properties such as compression set resistance. 

Compression Set Resistant. One property of fluorocarbon elastomers that makes them uniquely valuable to the sealing industry is their extreme resistance to compression set. Figure 4 plots compression set vs time for compounds prepared especially for compression set resistance (O-ring grades). 

Long-term compression set resistance is described in Figure 4. Lower set values are achievable by use of higher viscosity gumstock at comparable cross-link densities. Compression set resistance is also very dependent on the cure system chosen. The bisphenol cure system offers the best compression set resistance available today, as shown in Table 5. 

Table 5. Effect of Cure System on Processing Safety and Compression Set Resistance for FKM2260 ...

Post-Curing. Post-curing at elevated temperatures develops maximum physical properties (tensile strength and compression-set resistance) in fluorocarbon elastomers. General post-cure conditions are 16 to 24 h at 200 to 260°C. 

Compression-set resistance Very good Good Fair to good Good to excellent... 

Disclosed are ethylene-vinyl acetate/ethylene-styrene interpolymer blends, which are useful in preparing foams exhibiting improved compression set resistance, dimensional stability and rebound resilience at similar foam densities than known foam systems, e.g. EVA. The crosslinked foams are particularly useful in fabricating footwear and gaskets. 

Since NR is non-polar, its vulcanizates can swell to several times their original volume in non-polar solvents such as mineral oils, toluene, gasoline and diesel oil. It has good resistance to polar fluids such as mild acids and bases typically encountered in the mineral and chemical processing industries. The compression set resistance... 

Ability to single-pass Banbury mix Adhesion to metal Tensile strength Compression-set resistance Steam acid resistance... 

Tear strength, hardness, and melting point increase with increasing content of 4GT in the copolymers. Compression set is highest at 30% 4GT content and virtually identical above 40% 4GT. Compression set resistance can be improved by annealing the copolymers at elevated temperature (12). None of the copolymers in this chapter were annealed prior to testing. 

Better high-temperature compression-set resistance than MT, but less reinforcing and poorer in processing and tensile strengdi/elongation. 

Weight loss and hardening of polymer Loss of compression set resistance and some polymer volatihsation Formation of a trace amount of acidity Formation of lead mercaptide segment in the polymer chain when PbOj is used as a curing agent... 

Cumene Hydroperoxide Copper Ions cupric resinate). Amines H.O, Cupric resinate in Cumene hydroperoxide, excess of. 07% by weight in liquid form, is useful for of LP polymer pourable compositions with compression set resistance. Metallic oxides (ZnO or MgO) neutralize acid byproducts. Amount recommended per 100 parts of polysulfide polymer 8.0 ... 

VFa/HFP/TPE Reactivity. It is well known to those f2miliar wi the characteristics of fluoroelastomers that polymers of unusu dly high fluorine content, e.g., VF2/HFP/TFE terpol rs tAiich contain about 45 wt% VF2 and about equal amounts of HFP and TFE, exhibit some compromise in cure rate and high-temperature compression set resistance in order to achieve their increased fluid resistance. In order to determine idiether there are discernible chemical reasons for these differences, the behavior of VF2/HEP/IFE polymers toward bases in solution was investigated. 

Elastomers derived from isoprene and butadiene are readily crosslinked by peroxides but many of the vulcanizate properties are inferior to those of accelerated-sulfur vulcanizates. However, peroxide vulcanizates of these diene rubbers may be desirable in applications where improved thermal aging and compression set resistance are required. 

D)mamic properties Thermal stability Compression set resistance... 

Compression set resistance Flex fatigue strength Resilience... 

Abrasion resistance Electrical properties Compression set resistance Tear resistance Tensile strength Adhesion to metals Adhesion to fabrics Rebound, cold and hot Resistance to heat aging and flame... 

Compression set is a measure of a compound s resistance to flow while in a compressed state. Unreacted curative will contribute to poor compression set resistance because it continues to react while the sample is in the compressed state. These new cross-links then prevent the stock from returning to its original shape. If peroxide formulations are cured to the cure plateau, 7 to 10 half-lives, no further curing is possible and compression set resistance is at a maximum for that particular compound. Compression set resistance in stocks cured in this manner varies directly with state of cure (or the quantity of peroxide in the formulation). Figure 1 shows the typical response of an elastomer fully cured with various levels of peroxide. The isolated point on the curve shows the result of undercuring a stock and utilizing only 50% of the peroxide added. 

Figure 3 shows typical 300% modulus, tensile strength, and compression set resistance response to cure time. Tensile strength rapidly attains a satisfactory value. Modulus rises rapidly at first and slowly comes to a plateau when all of the... 

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