Rubber is Ablative

Ablation means removal of material from the surface of an object by vaporization, chipping, or other erosive processes. The term occurs in Space Physics [5]. In space vehicle design, ablation is used to both cool and protect mechanical parts and/or payloads that would otherwise be damaged by extremely high temperatures. A low-density EPDM rubber is a fire stopping and fire proofing product that can be ablative in nature. 

---

The transition of dispersed particles from the rubbery to glassy state defines the lowest temperature at which the incorporated rubber is able to reduce the matrix jdeld stress and accoimt for significant toughening (280,281). The effect of added rubber usually fades away at temperatures 10-20 K above its which is manifested as a sharp drop in the fracture energy (256). An equation was derived for the brittle-ductile transition temperature as a function of the particle... 

High temperature. The rubber is able to relax even in the rapidly forming stress field ahead of the travelling crack. Stress whitening occurs over the whole of the fracture surface. Bucknall and Smith [128] report similar results for other rubber-modified impact polymers. 

Intermediate temperature. The rubber is able to relax during the relatively slow build-up of stress at the base of the notch, but not during the fast crack propagation stage. Stress... 

Drilco Rubber Type. See Figure 4-169 and Table 4-102 [56]. Shock is absorbed by an elastometer situated between the inner and outer barrels. This shock absorbing element is vulcanized to the barrels. The torque has to be transmitted from the outer into the inner barrel. This tool is able to absorb shocks in axial or in radial directions. There is no need to absorb shocks in the torque because the drill string itself acts like a very good shock absorber so the critical shocks are in axial directions. These tools cannot be used at temperatures above 200°F. Though they produce a small stroke the dampening effect is good [56]. 

Very frequent are the cases of stress-induced crystallizations. A typical case is that of slightly vulcanized natural rubber (1,4-m-polyisoprene) which, under tension producing a sufficient chain orientation, is able to crystallize, while it reverts to its original amorphous phase by relaxation [75],... 

The Vinyloop process is based on the selective dissolution of PVC used in composites applications like cable insulation, flooring, tarpaulins, blisters, etc. After removal of insoluble parts like metals, rubber or other polymers, the PVC is reprecipitated with all additives by introduction of a non-solvent component whieh will form with the seleetive solvent an azeotropie mixture. By using typical conditions, the process is able to reeover a pure PVC eompound powder ready for use without any additional treatment like melt filtration or a new pelletisation (speeific characteristics of the powder are average diameter of 400 microns and bulk density above 600 kg/ eub.m). All the solvents used are eompletely reeyeled and reused. PVC compounds recovered in the Vinyloop process can be reused in a closed-loop recycling scheme... 

The efficiency of Crabtree s catalyst as a catalyst for small molecule hydrogenation has been known for many years. Unlike many homogeneous hydrogenation catalysts, Crabtree s catalyst is able to reduce hindered olefins at favourable rates.7 It has never been reported as a catalyst for the hydrogenation of rubber except for its use in the hydrogenation of bulk PBD.8 This paper describes the first use of Crabtree s catalyst in the hydrogenation NBR. Kinetic data are presented and analyzed to understand the underlying chemistry. 

A. I believe that this statement of Goering s, especially regarding oil and rubber, is true. Without these products, the country would not be able to wage war. With rubber the situation was exactly the same in the United States. I believe that these were measures of military economy under the idea of a defensive war which, of course, was what the United States was thinking of, too. 

An atactic structure is in both cases not crystallisable. Atactic PP is because of its glass-rubber transition temperature (Tg = -15 °C) rubbery and technically of no use. Isotactic PP is able to crystallise and can, therefore, be used in practice. For PS atacticity is no objection its properties as a glassy polymer are retained up to its Tg (95 °C). 

It appears from the evolution of the adhesion index that a distinction has to be made between the interactions carbon blacks are able to have with unsaturated or with saturated (or near-to-saturated) elastomers. Thus, the adhesion index of butyl rubber is enhanced upon oxidation of the black, while the reverse is observed with polybutadiene 38). The improvement of the reinforcing ability of carbon black upon oxidation, in the former case, has been interpreted by Gessler 401 as due to chemical interactions of butyl rubber with active functional groups on the solid surface. Gessler, relating the reinforcing characteristics of the oxidized carbon black for butyl rubber to the presence of carboxyl groups on the surface of the filler, postulated a cationic... 

Gutta-percha, the trans 1,4-isomer of natural rubber, is hard and brittle at room temperature. The reason for the difference in properties between the cis and trans isomers readily can be seen by inspecting molecular models. The chains with trans double bonds are able to lie along side of each other, forming a semicrystalline array, as shown in Figure 13-2. This ordered arrangement cannot be deformed easily, hence the material is hard and brittle. However, when the double bonds are cis, steric hindrance prevents the chains from assuming a similar ordered structure and the bulk of the material exists in a... 

Both behaviours can be accounted for by considering the effect of the co-operativity of the p transition motions. Indeed, it is precisely in this temperature range that a precursor motions develop (as described in [ 1], Sect. 8.1.6). Thus, the occurrence of such cooperative motions is able to generate large chain motions, analogous to those involved in the glass-rubber transition, in... 

We have also recently discovered that added calcium laurate is able markedly to enhance the mechanical stability of natural rubber latex (2.). This observation is surprising, partly because of the low solubility of calcium laurate in water, and partly because calcium ions are known to be powerful destabilisers of natural rubber latex (j ). It indicates that the stabilising effect of the laurate anion is much greater than the destabilising effect of the calcium cation. 

In 4.3 we have already seen that polymers, in the rubber or fluid condition, crystallize much more rapidly when their chains are oriented. Therefore a stretched rubber, if stereospecific in its molecular structure, is able to crystallize at a temperature considerably above its equilibrium thermodynamic melting point. Also a thermoplast such as polyethylene, when in the molten state or in solution, can crystallize spontaneously when the chains are being orientated in elongational flow. The latter case is utilized when polyethylene is spun from a diluted solution (gel spinning process), resulting in fibres of super-high strength and stiffness ( Dyneema fibres). 

The double bonds of the rubber molecules all have the cis, or Z, configuration. This causes bends in the chains that make the molecules less able to crystallize. To prevent the molecules from slipping past each other when the rubber is stretched, the molecules are cross-linked by treatment with sulfur in a process called vulcanization. Although the exact details of vulcanization are not known, links between different chains are formed by one or two sulfur atoms ... 

When only spectroscopic methods are used, they are able to identify polymer components with respect to their chemical nature. However, in many cases, they are unable to answer the question whether two chemical structures are combined to yield a copolymer or a blend or both. For example, analyzing a rubber mixture one is able to identify styrene and butadiene as the monomer units. However, using FTIR or NMR it is impossible to decide if the sample is a mixture of polystyrene (PS) and polybutadiene (PB),or a copolymer of styrene and butadiene, or a blend of a styrene-butadiene copolymer and PB. For the latter case, even the copolymer composition cannot be determined just by running a FTIR or NMR spectrum. 

In the case of mass ABS, the variety of rubber particle morphology is less diverse. Typical examples of morphology are shown in Figure 14.6. If polybutadiene rubber is used (linear or star), cellular particles are obtained with SAN occlusions. In the case of styrene-butadiene block rubber (typically 30% styrene) also cellular particles are obtained but besides the SAN occlusions, polystyrene domains are clearly visible in the particles. To be able to make the other morphologies that are possible in HIPS, the interfacial tension has to be manipulated. Controlling the grafting reaction is a way to achieve this but the possibilities are limited with the tools (mainly initiator) that are currently available. 

This substance has extensive lipid solubility and is absorbed immediately by the skin. Additionally, DMM is able to penetrate many materials including plastic and rubber compounds such as latex, polyvinyl chloride, and neoprene in a matter of seconds. In permeability tests, a Silver Shield glove of a flexible, plastic-laminate, offered skin protection from DMM for 4h. This chemically resistant glove, when worn under an outer glove that is resistant to abrasion and tears, may provide limited protection for direct handling of DMM. 

---