SUBJECTS mastic

The molecular weight of natural rubber (NR) can be altered by mechanical means. Mastication of NR results in a reduction of molecular weight. In the distant past, NR was commonly subjected to mechanical degradation on open mills for extended periods of time to improve processability. 

Applied to rubber which has been subjected to prolonged mastication, often carried out with periods of rest between mastication stages such rubber shows little or no elastic recovery. Deflashing... 

Some mastics are less durable than more traditional concrete materials when subjected to mechanical impact and abrasion. 

Ceresa (78,79) studied in detail the system poly(methyl methacrylate)-acrylonitrile. Figure 25 shows the change in composition with mastication time. A study of gel formation by the block copolymers was made by subjecting the isolated fractions of block copolymers to further mastication. A wide range of block copolymers with varying composition and structure was obtained (Fig. 26). 

Fig. 1 shows, at low magnification, particles of Gouda cheese expectorated after 5 chews. Clearly in this short time span the first subject (top half) has saturated the sample more completely with saliva and caused more extensive melting of the fat, than the second subject (lower half). Such factors may greatly influence the subjects perceptions of the textural character of the cheese. From examination of mastication patterns it may be possible to determine which factors are influential in assessment of food texture. 

A considerable problem for both the food industry and sensory scientists is the degree of individual variation in texture perceptions. The differences in breakdown pathways in the mouth for standard samples may underlie some of the variability. Indeed Brown et al31 have demonstrated an influence of chewing behaviour on texture perceptions in a model food system. Even if all individuals shared a common system for assessing a particular textural characteristic, the differences in the way they masticate a sample may cause them to come to different conclusions regarding its texture. However, there is also the real possibility that subjects may use different measuring systems for assessment of a textural characteristic they... 

Langley, K.R. and Marshall, R.J. (1993). Jaw movement during mastication of fibrous and non-fibrous composite foods by adult subjects. J. Texture Studies 24, 11-25. 

The nature of the flame tests is of the utmost importance in the evaluation of the properties of the fire-resistant mastics. The proper tests are based on careful consideration of the type of combustile or incombustible substrate, the nature of the flame exposure to which these substrates may be subjected in the course of the service, and other requirements which may be needed to meet the desired specifications. 

At the conclusion of the test, the unanchored mastic exhibited the loss of appreciable initial adhesion to the metal. The lath-anchored panel was subjected to the fire only 25 minutes because the extreme heat fused the jets of the burner, necessitating cessation of the test. After cooling, the mastic layer from this panel could not be removed even with application of considerable face. Whenever excellent bondage under fire is desirable, anchorage of the mastic is desirable. 

Asphalt mastic is a heavy duty system that is shop-applied in thicknesses up to 1 in. (25.4 mm). Although asphalt mastics perform well, they are very costly. Their use is usually limited to river crossing and swamp areas. Coal-tar enamel has more than 50 y of successful performance underground, but it is subject to cracking when the temperature is below 20° F (-7°C), and there are environmental constraints. The EPA has shut down applicators in the middle of production because of air pollution. These problems rule out asphalt mastic and coal-tar enamel as feasible materials for most pipelines. In addition, coal-tar enamels are often ruled out because of long-term deterioration. Asphalt enamel is generally considered inferior to coal-tar enamel therefore, its use is limited. Polyvinyl chloride tape is becoming obsolete because of the superior performance of polyethylene tape. 

In the past, many or perhaps most publications on cellular solids in the nonfood literature were the result of interest in their performance at relatively small deformations (strains). In contrast, during their mastication, foods are subjected to very large compressive strains and are then tom apart. Moreover, in engineering and biomechanics applications, the solid foam is expected to be rather inert. Or, if it does interact with the environment, this would be a slow process that takes place on a time scale of months or years. In contrast, cellular foods interact with moisture very rapidly and the resulting changes can be quite unique, depending on the amount of water soluble components in their cell walls. 

Sensations perceived in the mouth during mastication may vary between subjects, but their acceptability will certainly reflect cultural as well as physiological and psychological differences. Tests for sensory assessment of texture aim at understanding how the food feels in the mouth. They may be classified into those where consumers are constrained to record only their perception of in-mouth stimuli (e.g., trained panel assessment) in other words, they are asked to perform as an analytical instrument. Alternatively, consumers are asked to record their judgment against requirements of quality (e.g., preference testing) where perceptions are related to expectation. Sensory assessment of texture is described in many texts, for example, Kilcast (2004). 

Completion of the reaction by transfer of a proton from the solvent to the carbanion will then give a product (3a -f- 3b) of composition corresponding to thermodynamic equilibrium of the anionic species. That this approximates closely to an equilibrated mixture of the alcohols has been confirmed by subjecting some steroid alcohols to equilibration with alkoxide ions, under conditions sufficiently Mastic to allow thermodynamic equilibrium to be attained through a reversible oxidation/reduction process. Reduction of steroidal 20 ketones is of considerable interest in providing a mixture of epimers, each present in considerable proportion. The reduced mixture contains a modest preponderance of the 20a-epimer [34], although recent experiments [34M] confirm indications from molecular models that the 20/ -alcohol is the more stable. Further work is needed to clarifythis situation (see alsop. 139). 

Flavor Release Flavor release is the process whereby flavor molecules move out of a food and into the surrounding saliva or vapor phase during mastication (126, 127). The release of flavors from a food material occurs under extremely complex and dynamic conditions (136). A food usually spends a relatively short period (typically 1 to 30 seconds) in the mouth before being swallowed. During this period, it is diluted with saliva, experiences temperature changes, and is subjected to a variety of mechanical forces. Mastication may therefore cause dramatic changes in the structural characteristics of a food emulsion. 

In sensory evaluation consumers estimate fruit firmness on the basis of the deformation resulting from physical pressure applied by the hand and fingers. The toughness or tenderness of meat is subjectively evaluated in terms of the effort required for the teeth to penetrate and masticate the flesh tissues. Therefore, determination of rheological properties of foodstuffs is important in evaluation of consumer-determined quality by correlating rheological measurements with sensory tests. 

These techniques rely upon high shear to cause bond scissions. Ruptured bonds result in formations of free-radical and ionic species. When this application of shear is carried out in the presence of monomers, block copolymers can form. This approach is exploited fairly extensively. Such cleavages of macromolecules can take place during cold mastication, milling, and extrusion of the polymers in the viscoelastic state. Both homolytic and heterolytic scissions are possible. The first yields free-radical and the second ionic species. Heterolytic scissions require more energy but should not be written off as completely unlikely." Early work was done with natural rubber. It swells when exposed to many monomers and forms a viscoelastic mass. When this swollen mass is subjected to shear and mechanical scission, the resultant radicals initiate polymerizations. The mastication reaction was shown to be accompanied by formation of homopolymers. Later, the technique was applied to many different polymers with many different monomers. ... 

Rosin family s most common form of adhesive is colophony, a hard amorphous substance derived from the oleoresin of the pine tree. This material is applied in solvent solution form as a hot-melt mastic. It has poor resistance to water, is subject to oxidation, and has poor aging properties. Plasticizers are usually added to reduce its brittleness. Bond strengths are moderate and develop rapidly. These materials are used as temporary adhesives in bonding paper and as label varnishes. They are also used as components of PSAs based on styrene-butadiene copolymers and in hot-melt adhesives and tackifiers. These materials have been largely replaced by synthetic-resin adhesives. One specialized form of rosin adhesive is Canada Balsam, covered by the obsolete Military Specification MIL-C-3469C, titled Canada Balsam. This material was intended for cementing optical elements. 

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