Elastomer typical

Valuable reviews and books of structural analysis of elastomers have been published by several authors [1-6]. Some of these reviews provide excellent explanation on the basic theory of sequence distribution of copolymer and NMR techniques applicable to elastomers. Typical high-resolution 3H- and 13C-NMR spectra of various vulcanisates and raw rubbers are depicted in a book written by Kelm [6]. The assignments and references shown for each rubber are very useful for structural studies of elastomers. In view of recent progress in the hardware and software of NMR, this chapter describes some of the more recent applications of high-resolution NMR to the structural characterisation of elastomers, after a brief description on the fundamental structural features of elastomers. 

The addition of an elastomer (typically a high butadiene content SBS) to SBC will serve to enhance further the elastomeric properties of the SBC. One key feature mentioned previously was improvement in hinge life properties. SBS copolymers can also be added to thermoformed sheet in blends of SBC and crystal polystyrene. The SBS does cause some loss of clarity, but gives more impact resistance to the sheet. Selection of the proper SBS can result in minimal loss of clarity, typically at 3-10% loadings. Styrene-isoprene copolymers (SIS) have also been tested with SBC and can give similar results in impact property improvement. 

In particular, the elastic recovery of the bitumen has remarkably improved when modified with elastomers. Typical values of 25% to 35%, at 25°C, for conventional bitumen can be increased, so as to reach elastic recovery values higher than 95%. As a consequence, the strain developed when bitumen is loaded is recovered to a large extent and plastic (permanent) deformation is minimised. 

Some adhesives will bond cured elastomers. Typically, a thin layer (0.0025 mm thickness) of the activator is applied to one of the adherends and a layer of the adhesive (0.026-0.26 mm) is placed on the other adher-end. The two substrates are then pressed together and secured until adequate handling strength develops. Most acrylic adhesives cure to this point in 2-20 minutes, but some cure in as little as 10 seconds. In all cases, cure is completed within 24 hours. These adhesives provide excellent shear, peel, and impact strengths at temperatures ranging from -107°C to -i-121 °C. These adhesives can withstand short exposures up to 177°C. ... 

Elastomers typically found in complex composite structures such as tires tend to be blends to obtain specific properties in order that the ultimate product may function according to the required mission profile. Several compounding references that the reader may find of value are provided in the References at the end of... 

This esterification does not require the use of catalysts, though catalysts based on the organic-metallics of titanium or zirconium, e.g. tetrabutyl titanate, are often used to reduce reaction times. However, the trace residues of some of these catalysts can have adverse effects on the hydrolytic stability of the final urethane elastomer. Typical polyester structures are shown in Table 1.3. 

All manufacturing processes for ABS involve the polymerization of styrene and acrylonitrile monomers in the presence of an elastomer (typically polybutadiene or a butadiene copolymer) to produce SAN that has been chemically bonded or grafted to the rubber component termed the substrate. ... 

The new elastomers are particularly relevant to the automotive industry because they offer better properties - particularly heat, oil and fuel resistance - than the established materials such as natural and synthetic rubber and plasticized PVC. Among the most important types are PUR elastomers, PBT block copolymers, EPDM olefinic terpolymers and ethylene-acrylic elastomers. Typical applications are the traditional rubbery ones of gaskets, seals, gaiters and cable covers, but set in the aggressive underbonnet environment of today s performance vehicles. Beyond this, however, there are examples where these materials are sufficiently versatile to have been selected, sometimes with reinforcement, as engineering components in their own right. 

Thermal-oxidative degradation of elastomers typically causes the following changes ... 

Typical Use Plastics and elastomers. Typical Use Metals and other materials. ... 

Post-elastic stiffiiess, Kj Elastomer (typically low-damping rubber) Stmcture stiffiiess reduction Structure fundamental frequency reduction... 

In quite a variety of applications, thermoplastic elastomers have replaced conventional thermoset elastomers. Typical uses for TPEs include automotive exterior trim (bumpers, fascia, etc.), automotive underhood components (electrical insulation and connectors, and gaskets), shoe soles and heels, sporting goods (e.g., bladders for footballs and soccer balls), medical barrier films and protective coatings, and components in sealants, caulking, and adhesives. 

Finally, it is important to compare relative measures of cost of the various oil-resistant elastomers. Typically, the pound-volume cost method is used which is simply the cost of the compoimd multiplied by the specific gravity. This gives the true cost of the amount of compoimd needed to fiU a given volume such as a mold cavity. This is shown in Table 3.1 along with the upper high-temperature limits of the various materials. While Acrylic elastomers, ACMs and AEMs, are cost effective for use up to 150°C, the HNBRs are much tougher, more abrasion-resistant materials. The Huorocarbon, FKM, and Fluorosilicone, FVMQ, materials have excellent upper temperature limits, but the pound-volume costs are heavily influenced by the relatively... 

Most oil-field elastomers must also be oil resistant, and oil-resistant elastomers typically have poor low-temperature properties. When a polymer type is selected for its oil resistance and does not have acceptable low-temperature properties, plasticizers can be added to provide better low-temperature properties for the compound. Addition of plasticizers reduces modulus and changes other properties. Changing other compound ingredients, however, wiU help to compensate for these changes. 

Assemblies bonded with cyanoacrylate have shown entirely satisfactory long-term performance in a variety of applications particularly where at least one of the substrates is an amorphous thermoplastic or an elastomer. Typically, accelerated testing is done at high temperatures and extreme conditions to predict whether long-term bond performance will be acceptable. 

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