Dynamic Tear Properties

In general, however, the vulcanizates suffer from poor low temperature crystallization performance compared to a conventional sulfur cure, and also have inferior tensile and tear properties. Urethane cross-linking systems (37), eg, Novor 950 (see Table 3) are also extremely heat resistant, but exhibit inferior tensile and dynamic properties compared to conventional sulfur-cured vulcanizates. One added virtue is that they can be used in conjunction with sulfur systems to produce an exceUent compromise according to the ratios used (38). 

ISO 13995 Protective clothing—Mechanical properties—Test method for the determination of the resistance to puncture and dynamic tearing of materials... 

The structure and vulcanisation mechanisms of carboxylated rubbers in general are discussed, and results are presented of a study of the vulcanisation of carboxylated nitrile rubber using four different curing systems. The crosslink density, tensile and dynamic mechanical properties, stress relaxation and tear strength of vulcanised samples were investigated. 22 refs. 

Both tear resistance and hysteresis increase on incorporation of silica, but the effect is less pronounced as compared to the stress-strain properties. Tension set of the ZnO-neutralized m-EPDM system is low (around 20%) and incorporation of filler causes only a marginal increase in set due to chain slippage over the filler surface, as previously discussed. Measurement of physical properties reveal that there occurs an interaction between the filler surface and the polymer. Results of dynamic mechanical studies, subsequently discussed, support the conclusions derived from other physical properties. 

Clay hllers were surface modihed with TMPTA or triethoxyvinyl silane (TEVS) followed by EB irradiation by Ray and Bhowmick [394]. Both the untreated and treated fillers were incorporated in an ethylene-octene copolymer. Mechanical, dynamic mechanical, and rheological properties of the EB-cured unfilled and filled composites were studied and a significant improvement in tensile strength, elongation at break, modulus, and tear strength was observed in the case of surface-treated clay-filled vulcanizates. Dynamic mechanical studies conducted on these systems support the above findings. 

Such effects are likely to be important. The use of SP interactions to create bioinspired material properties (e.g., see Chap. 9) implies that the ultimate yield behavior of SP materials could depend on the mechanical response of supramolecular interactions. Paulusse and Sijbesma (2004) have also shown that ultrasound-generated shear stresses can mechanically tear apart coordination SPs, damage that is subsequently repaired during dynamic equilibration once the shear stresses are removed. The mechanical response of supramolecular interactions within materials has potentially important consequences in the context of self-repairing materials, where the mpture of sacrificial supramolecular interactions protects a permanent, underlying materials architecture. The dynamic repair of the SP component in... 

Before World War II (1939-1945) natural rubber was used for practically all rubber applications. Natural rubber is preferred in many products because of its superior building tack, green stock strength, better processability, high strength in non-black formulations, hot tear resistance, retention of strength at elevated temperatures, better resilience, low heat build-up, fatigue resistance, and better dynamic properties. Rubber products are broadly classified as dry rubber products and latex based products [60]. 

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. 

It should be noted that the standard test methods for tensile stress- strain properties, tear strength, rebound resilience, and other dynamic properties provide for high-temperature measurements, preferably at the recommended temperatures of ISO 471. 

Chem. Descrip. Polypropylene glycol CAS 25322-69-4 EINECS/ELINCS 200-338-0 Uses Polyol for use in coatings, adhesives, sealants, elastomers, epoxy flexiblllzers, and defoamers food pkg. adhesives, paper/paperboard Features Improves tens, str., elong. at break, tear str., resilience, dynamic props. reduces compression set and hysteresis Regulatory FDA 21CFR 175.105,176.180,177.1680 Properties Pt-Co 20 color (50 C) water wh. to si. haze m.w. 4000 sp.gr. 

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