Elastomers component

Rubber-Modified Copolymers. Acrylonitrile—butadiene—styrene polymers have become important commercial products since the mid-1950s. The development and properties of ABS polymers have been discussed in detail (76) (see Acrylonitrile polymers). ABS polymers, like HIPS, are two-phase systems in which the elastomer component is dispersed in the rigid SAN copolymer matrix. The electron photomicrographs in Figure 6 show the difference in morphology of mass vs emulsion ABS polymers. The differences in stmcture of the dispersed phases are primarily a result of differences in production processes, types of mbber used, and variation in mbber concentrations. 

Where the polyurethane comprises <30% of the blend, the polyurethane remains in discrete droplets within the polyacetal matrix. In this range the particle size and particle size distribution of the elastomer particles are of importance. Where the elastomer component is in excess of 30%, interpenetrating polymer networks exist in the sense that there are two interpenetrating continuous phases (as opposed to two cross-linked interpenetrating polymer systems). 

Most mechanical and civil engineering applications involving elastomers use the elastomer in compression and/or shear. In compression, a parameter known as shape factor (S—the ratio of one loaded area to the total force-free area) is required as well as the material modulus to predict the stress versus strain properties. In most cases, elastomer components are bonded to metal-constraining plates, so that the shape factor S remains essentially constant during and after compression. For example, the compression modulus E. for a squat block will be... 

By far the largest group of small to medium elastomer components comprises seals and gaskets. Relaxation phenomena, which would result in loss of sealing ability, can become important. 

Figure 6. Sketch of expected variation of the initial (c0) and residual (cr) concentration of functional groups, reaction conversion , and the ratio ve/Te in end-linked networks as a function of molecular weight of elastomer component M. For discussion see text.

Next 129Xe experiments on an EPDM terpolymer, which is present as the elastomer component in a composite material with carbon black will be discussed. The question investigated for these materials is whether the existence of any polymer-filler interaction can be detected by 129Xe NMR. This interaction influences the mobility of the elastomer chains in a relatively large shell around the filler particles. This fraction is called the bound rubber fraction. It is generally believed that the bound rubber fraction influences the mechanical and frictional properties of the filled elastomer [17, 18]. 

The results of Figure 12.25 show very little difference between the two samples for Xe diffusion. The presence of large spherulites in the untreated sample does not seem to affect the diffusion of Xe. The reason maybe that for the copolymer investigated here the spherulites are only partly crystalline because the block chain lengths [12] dictate that the spherulites also contain the elastomer component. 

In the switch from CFC to the more polar HFA propellants, one of the major problems has been inadequate solubility of the surfactants (used to stabilize the micronized drag particles) in the HFA. Solubility can be adjusted within the CFC propellant, e.g. CFC 12 is a far better solvent than CFC 11. However, for HFAs, blends do not exist and so solvency can only be addressed by using a cosolvent such as ethanol. It must be remembered that changing the solvency of the propellant will almost certainly affect the all-important vapor pressure and thus the MM AD, the particle velocity and the deposition site. Alternative stabilizers have been investigated and include PVP, fluorinated surfactants and Poloxamers. In addition to solubility effects, difficulties associated with the use of HFAs also include incompatibility with elastomer components in the metering valves. 

With both the PEA/P(S-co-MMA) and PB/PS IPN s, an important variable is the ratio of elastomer to plastic in the final material. When the plastic component predominates, a type of impact-resistant plastic results. In this manner the PB/PS IPN s are analogous to the impact-resistant graft copolymers. When the elastomer component predominates, a self-reinforced elastomer results, the behavior resembling that of the ABA-type block copolymers (thermoplastic elastomers) described in Section 4.4. When the overall compositions of both the PB/PS and the PEA/P(S-co-MMA) series are close to 50/50, the materials behave like leathers. 

Raman microimaging is used to estimate the effect of the silica filler on phase separation in binary polymer blends composed of BIMS and BR. The domain sizes, relative concentration of polymer components within domains, and distribution of particulate silica filler and zinc stearate curative are characterised for blends of different compositions and history of ageing treatments. The presence of increased concentrations of precipitated silica results in better polymer morphology since domain sizes are reduced. Increased temperature treatment also decreases domain sizes up to about 150 deg.C, but treatment at 200 deg.C appears to induce separation of the elastomer components. Silica is usually found near the centres of the BIMS domains. There is little difference in silica distribution before and after curing. 6 refs. 

PMMA sheets with an added elastomer component offer optical clarity and are resistant to crazing impacts, ageing and weathering. Acrylic sheets are the top surface layer of baths and other bathroom wares. 

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