Retardation Processes

The first known fire-retardant process found durable to laundering was developed in 1912 (4). A modification of an earlier process (5), this finish was based on the formation of a tin(IV) oxide [18282-10-5] deposit. Although the fabric resulting from treatment was flame resistant, afterglow was reputed to be a serious problem, resulting in the complete combustion of the treated material through smoldering. 

Ammonia—Gas-Cured Flame Retardants. The first flame-retardant process based on curing with ammonia gas, ie, THPC—amide—NH, consisted of padding cotton with a solution containing THPC, TMM, and urea. The fabric was dried and then cured with either gaseous ammonia or ammonium hydroxide (96). There was Httle or no reaction with cellulose. A very stable polymer was deposited in situ in the cellulose matrix. Because the fire-retardant finish did not actually react with the cellulose matrix, there was generally Httle loss in fabric strength. However, the finish was very effective and quite durable to laundering. 

Since the stress is constant, it follows that so also is the creep rate. The creep compliance at time t, 7, can be considered to consist of three terms, an instantaneous compliance, Jq, a term covering a variety of retardation processes, xj/it), and a viscous term, t/rj. These are related by ... 

One of the reasons that it took so long for the acid retardation process to become... 

There is indeed a striking similarity between the salt separation processes discussed here and the acid retardation process. Consequently, it was possible to use the same basic process flow-sheet and equipment for these salt purification processes that have been extensively used for over 20 years for APU systems. 

Note 3 Examples of additives are antioxidants, plasticizers, flame retardants, processing aids, other polymers, colorants, UV absorbers, and extenders [7]. 

Relevance of Polymer Stabilization to Flame-Retardant Processes.34... 

RELEVANCE OF POLYMER STABILIZATION TO FLAME-RETARDANT PROCESSES... 

The rates of relaxation and retardation processes above the glass temperature are strongly dependent on the viscosity and thus on the fraction of free volume present. Because the viscosity not only depends on temperature but also on static pressure (the glass transition temperature increases approximately 1 °C per 20 bar of pressure) it is not surprising that pressure also affects the viscoelastic processes. A qualitatively relation analogous to Eq. (13.121) can be readily derived (Ferry, 1980) ... 

Like other retardation processes, the strength of the mechanical glass-rubber relaxation can, in principle, be determined by means of the empirical Havriliak-Negami equation (34)... 

Fe" porphyrins (hemes) are air sensitive and easily oxidized to the p-oxo dimer [Fe "(Por)]20 (Scheme 17). However, the irreversible oxidation can be prevented by a large excess of the axial ligand (retards process A), at a low temperature (< — 50 C, retards process D), or by protection of the O2 binding site (prevents process C). The third approach has been intensively studied in relation to the biological oxygen carriers, myoglobin (Mb) and hemoglobin (Hb). 

When studying a polymer on a large frequency/time scale, the response of a given material under a dynamic stimulus usually exhibits several relaxations. Moreover, the peaks are usually broad and sometimes and are associated with superposed processes. The relaxation rate, shape of the loss peak, and relaxation strength depend on the motion associated with a given relaxation process [41]. In general, the same relaxation/retardation processes are responsible for the mechanical and dielectric dispersion observed in polar materials [40]. In materials with low polarity, the dielectric relaxations are very weak and cannot be easily detected. The main relaxation processes detected in polymeric systems are analyzed next. 

For a Hookean solid, say a metal, the load will produce a deformation that stays constant over time. On the other hand, for a polymeric material the same load will produce an initial deformation, followed by a slow and constant deformation up to a certain value (creep). This is an illustration of a retardation process, where the final response of the material to the load is retarded. On the other hand, one can also visualize an experiment where a constant strain is imposed to both, a Hookean solid and a viscoelastic solid. Under these experimental conditions, a constant stress is developed in the first case, whereas in the second case, the stress is nonconstant it starts at an initial value and then decreases up to a zero value. This experimental behavior constitutes a relaxation process. 

During the 50 years that have passed since the pubhcation of these classical studies, numerous research groups examined the salt and, in particular, acid retardation processes in ion exchanger, but no new ideas have been suggested for the explanation of the non-trivial phenomenon of electrolytes discrimination. Interestingly, a more or less adequate mathematical description of experimental data is possible both in terms of selfassociation of acids in the homogeneous resin phase and association of acid molecules with the functional groups of the resin [122] and in frames of a two-phase model of the resin bead [123]. However, both approaches are based on the above ideas that have been formulated, considered, and rejected by the pioneers of the method. Indeed, mathematical models may well fit experimental data into equations, but they do not prove the reality of the concept they are based on. 

The first phenomenon has never been discussed in chromatography, while the second, although exploited in the acid retardation process, did not find an acceptable explanation. 

The above-discussed acid retardation and base retardation in the immobiUzed Uquid phase could be compared with the so-called salting-out effects. However, this term is hardly applicable to the case of salt retardation, the first example of which was demonstrated by a successful removal of small amounts of NH4CI from a concentrated brine of (NH4)2S04. This practically important problem arises in the manufacture of caprolactam, where large amounts of sulfuric acid are converted into ammonium sulfate used for the preparation of the crystalline fertilizer. The new process of ISE on nanoporous NN-381 resin allowed an effective purification of very large volumes of concentrated sulfate brine, due to the fact that small ions of NH and Cl are efficiently squeezed into and retained in the finest pores of the sorbent [172]. We consider this salt retardation process as a convincing proof of our interpretation of the mechanisms of the new electrolyte separation process. 

We usually apply the technique originally developed for the acid retardation process, namely loading the colrrmn with the feed solution from the bottom up, and then eluting its content with water pumped in the opposite direction. This approach has helped to reveal all details and... 

Processing rather concentrated mixtures of hydrochloric, nitric, or sulfuric acids with their metal salts, resulting, for example, from metal acid pickling, has been the successive niche of the acid retardation process [115]. The latter actually presents a very fortunate experimental finding, the physical sense of which remained obscure tiU our days. For this reason its application was limited to the partial recovery of excess acid from its mixtures with salts by frontal chromatography on strong anion exchanging resins. 

First, the technique turned out to be applicable to any types of electrolyte mixtures, including mixtures of two acids, two salts, two bases, or a salt and a base, rather than just mixtures of a salt and its parent acid, as was the subject of the acid retardation process. The prerequisite of successful separation is the size difference of the largest ions of the two electrolytes to be separated. (Fractionation of mixtures composed of more than two components is also possible.)... 

Polyphenylene oxide (PPO) HDT, rigidity, flame retardancy Processability, impact strength... 

Maxwell bodies are obtained if Hookean and Newtonian bodies are connected in series (Figure 11-11). The Kelvin or Voigt model, on the other hand, contains Hookean and Newtonian bodies in a parallel arrangement (Figure 11-11). The Maxwell body is a model for relaxation phenomena and the Kelvin body is a model for retardation processes. 

Here, the indices e and rj are again omitted because the strain is the same in both elements. In Equation (11-57), 700 is a constant and /ret the retardation time. As a rule, there is usually a whole spectrum of retardation times in the retardation processes also. Retardation and relaxation time distributions are similar, but they are not identical since they pertain to different models of the deformation behavior. 

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