Carbon filled rubbers

Mechanics of Generation of Great Tensile Properties IN Carbon-Filled Rubber... 

Although we made no attempt to elucidate the mechanism of friction decreases in rubbers after surface fluorination, it seems to us that apart from the substitution of H atoms to F in the polymer macromolecule, which forms a fluoropolymer on the surface, there is another phenomenon that makes a significant contribution to the friction decreases, i.e., fluorination of carbon black, which is used in rubber recipes for reinforcement. It appears that when the carbon black in the surface of the rubber is fluorinated it produces a lubricating effect, followed by blooming on the surface of the treated rubber while it is under a friction load. So, in our opinion, two effects contribute to friction decrease of carbon-filled rubbers fluorination of the rubber macromolecules and fluorination of the carbon black rubbers that do not contain carbon black show a much smaller decrease in friction after XeF2 treatment. 

Dynamic mechanical analysis of filled systems confirms analytical observations. The thickness of the restricted mobility region in carbon filled rubber is proportional to the activity of the carbon black. 

In spite of the often large contribution of secondary filler aggregation effects, measurements of the time-temperature dependence of the linear viscoelastic functions of carbon filled rubbers can be treated by conventional methods applying to unfilled amorphous polymers. Thus time or frequency vs. temperature reductions based on the Williams-Landel-Ferry (WLF) equation (162) are generally successful, although usually some additional scatter in the data is observed with filled rubbers. The constants C and C2 in the WLF equation... 

ATR may also be used to study solids which cannot easily be examined using mulls or KBr discs. The sample should ideally be quite plastic so that contact with the crystal is better effected. Carbon-filled rubber is an example of a material with a spectrum which is almost imposssible to record using conventional transmission. Fibres and films, such as wrappers, are usually easier to examine with ATR than with transmission. A weight, or sprung pressure pad attached to the ATR assembly, will help ensure good contact. 

Macaione et al [235] have used TG for the characterisation of SBR, BR and NR in mono-, di-, or triblend rubber systems and carbon-filled rubber composites and determined the percentage of highly volatile organics, elastomer(s), carbon-black, and inorganic residue for each sample. Lochmiiller et al [194] applied factor analytical methods to evaluate TG results of a series of rubber blends and mixtures composed of chloroprene rubber, NBR, and common rubber additives. TG and measurements of toluene extractable matter of cured siloxane rubbers thermally aged in inert gas atmosphere at 80° C showed a build-up of low-MW fragments in the rubber network with age [244]. 

Commercial pyrolyzers are available for the controlled thermal degradation of materials which are difficult to prepare for transmission spectroscopy because of toughness, surface texture, or composition, including certain polymers and rubbers.Carbon-filled rubbers are best identified by this technique. The condensate from the destructive distillation process can be collected on a plate and run by transmission or internal reflection techniques or the gas formed in the chamber can be run directly. The condensate spectra from pyrolysis should be compared with a library of pyrolyzates since they may differ somewhat from that of the starting material. Polymer pyrolyzates, for example, may show new monomer bands whereas any inorganic fillers originally present will be missing. 

Extraneous molecules in solid phase polymer systems are not limited to plasticizer molecules or even exclusive to substances deliberately added. Impurities wdien present often affect the dielectric behaviour of pol mers and water in particular often has very significant effects on the dielectric spectrum. Poly(niethyl methacrylate) poly(oxymethylene) , and nylons to mention a few are influenced by moisture in this way. The influence of moisture on dielectric relaxation can be the result of interfacial polarization as well as dipolar mechanism. Further, this complication is not restricted to additives such as water but may occur whenever a combination of phase boundary and bulk or sur ce conductivity to or over the botmdaiy can take place. The proof that a relaxaticu is the result of interfacial polarization is not easy to establish, but there is evidence that mie of the relaxations in nylons and pol3 urethanes) are of this type. As expected, conductive fillers will introduce interfacial polarization and this effect has been well documented, especially in carbon filled rubbers . Indeed, as we shall disci later, electronic conductance when localized by interfacial boundaries does result in a form of interfacial polarization. Here, because of its large magnitude the phenomenon has been termed hyperelectronic polarization. 

Filled polymers are sensitive to deformation. The effect can be large in carbon-filled rubbers, particularly for compositions near the percolation threshold. This effect has been used to make selfregulating heaters, since, as the temperature increases, the filled polymer expands and the conductivity falls sharply, resulting in a drastic reduction in current and heat output. A novel application of filled polymers follows from the fact that the percolation threshold depends on sample thickness. 

Applications of pyrolysis generally inclnde samples of crossUnked polymers that are very difficult to sample by other techniques. Other t5q)es of problems might include identifying the elastomer in carbon-filled rubbers or the binder in a grinding wheel. As Wake has indicated, care must be taken to remove additives by extraction prior to pyrolysis. 

These have largely been explained under Section 4.3.5 and have most application for materials whose modulus is observed to be highly strain dependent, carbon-filled rubbers for... 

Scragging Carbon-filled rubbers are normally conditioned or scragged before testing by exposing them to a high strain. This affects filler/rubber interaction (see Section 4.3.5). 

This technique has been studied by Washall and Wampler [6]. Pyrolysis of polymer samples enables IR spectra to be obtained from the vapourised polymer. Many polymers are difficult to analyse by more conventional Fourier transform infrared (FT-IR) sampling techniques due to additives that cause scattering. Carbon-filled rubbers are examples of this type of problem. By dissociating the bonds of the polymer backbone, polymer functionality and structure can be determined much like Py-GC. 

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