Ultra-violet irradiation

It is the simplest compound containing the -N = N- chromophore, but is of no practical importance since it lacks affinity for fibres. Normally it exists in the most stable trans form, but may be converted to a less stable, bright red as form, m.p. 71 -S C by ultra-violet irradiation. Cis to irans isomerization occurs rapidly on heating. 

Intensive technologies are derived from the processes used for the treatment of potable water. Chemical methods include chlorination, peracetic acid, ozonation. Ultra-violet irradiation is becoming a popular photo-biochemical process. Membrane filtration processes, particularly the combination microfiltration/ultrafiltra-tion are rapidly developing (Fig. 3). Membrane bioreactors, a relatively new technology, look very promising as they combine the oxidation of the organic matter with microbial decontamination. Each intensive technique is used alone or in combination with another intensive technique or an extensive one. Extensive... 

Majrich found that light has a negligible effect on cyclonite. T. Urbanski and Malendowicz [26] reported that under the influence of ultra-violet irradiation cyclonite changes colour from white to pale yellow, but undergoes no other alteration. In particular, unlike nitric esters, neither NO, nor N02 is evolved from cyclonite. 

Slow decomposition of lead azide takes place under the influence of ultra-violet irradiation, as demonstrated by the investigations of Garner and Maggs [84] and Tompkins etal. [22, 85], but if the irradiation is very intense, explosion may occur, as was shown by Berchtold and Eggert [86] and Meerkamper [87]. In another paper Eggert [88] reported that the light intensity required to cause the explosion of lead azide is 2.0 J/cm2 when the electrical energy of the flash is 240 J, and the half-life of the flash 0.8 msec. 

Like lead azide, silver azide decomposes under the influence of ultra-violet irradiation. If the intensity of radiation is sufficiently high the crystals may explode (cf. p. 171). 

Anhydrous hydrazine burns in air. On heating hydrazine above boiling point, thermal decomposition of gaseous hydrazine takes place at 250-310°C (Elgin and Taylor [44] Askey [45]). Bamford [46] ascertained that hydrazine is decomposed by an electrical spark, while Elgin and Taylor established that hydrazine vapour is decomposed by ultra-violet irradiation (also Wenner and Beckmann [47]). 

As shown by Mine [92], the reduction in viscosity of collodion cotton, nitrogen content 11.2%N, dissolved in acetone by ultra-violet irradiation is greater, the higher the concentration of nitrocellulose in the solution. 

Intramolecular nitrene insertion of pyranoside azides is a further route to oxazepanes <95JCS(Pl )1747>. Thus thermolysis of the diazide (94) affords the tetrazolooxazepane (95) in high yield. When the rearrangement is carried out under ultra-violet irradiation the yield of (95) is reduced when it is also accompanied by small amounts of the isomer (96). 

Ultra- Violet Irradiation. In this method the items first are coated with a specific adhesion promoter, then passed under sources of ultra-violet light of specific... 

Benzene and naphthalene are nitrated with nitrogen dioxide at 18-20°C to yield mononitro derivatives. At 60°C polynitro compounds are obtained as well. Ultra-violet irradiation does not affect the nitration yield. 

Benzil has frequently been used as a means of generating free radicals in polymerization systems subjected to ultra-violet irradiation 11, 16, 56—58). In studies of the benzil-photoinitiated polymerizations of methyl methacrylate, and vinyl acetate, Melville (16) assumed that initiation was brought about by fragmentation of photoexcited benzil into two benzoyl radicals. However a survey of the photochemistry of benzil 34) indicates that such a cleavage does not in fact take place in solution studies of the products formed on irradiation of benzil in cyclohexane (59), cumene and isopropanol (60) can be rationalised on the basis of initial hydrogen abstraction from solvent by photoexcit i benzil, e.g. 

The percentage recoveries obtained by the above digestion followed by atomic absorption spectrometric determination are given in Table 1. The recoveries obtained by the same method when applied to arsenic spiked water samples are shown in Table 2. Figure 1 shows the effect of ultra-violet irradiation as a function of time for triphenylarsine oxide, disodium methanearsonate and dimethylarsinic acid. The extent of arsenic recovery using... 

Ultra-violet irradiation (both continuous and flash photolysis X > 300 nm) of solutions of a,(3-unsaturated ketones (including 4-mentha-6,8-dien-2-one (carvone), verbenone,... 

Ultra-violet irradiation of polychloropinene in moist soil produces CO, COj and HCl, along with some phosgene (a somewhat surprising result, since moist soil catalyses the hydrolysis of phosgene. Section 9.10.3.1) [1862]. 

Aliphatic polyamides (PA) and products on their base are polymers with low stability to ultra-violet irradiation and under the effect of solar radiation they destruct less than in a year [1]. In natural conditions ultra-violet part of solar spectrum with wave-length 290-350 nm is more dangerous for these polymers, though aliphatic PAs in this field have very weak absorption of chromophore amide group [2, 3], That is why while examining the problem of PA phototransformations, unlike other polymers, both possibility of light absorption by impurities and self-absorption should be taken into consideration [4],... 

Electron - microscopic photographs of dyed and undyed PCA fibres before and after ultra-violet irradiation were obtained to clarify possible effect of bis-aroilenbenzimidazole derivatives on supermolecular structure of PCA fibres by the method of raster electronic microscopy (REM) with increase of 12000 times. Any specific details of the structure were not observed in the initial sample. After irradiation the initial sample undergoes great... 

Thus, it is seen that thermostable dye XLY bis-(naphthoilenbenzimidazole) oxide facilitates hardenening of PCA-fibres at ultra-violet irradiation when it is introduced into PCA mass. 

Data on effect of DTCU concentration on viscosity characteristics and change of PCA molecular mass before and after ultra - violet irradiation are given in Table 12. 

Table 12. Dependence of viscosity characteristics of PCA on DTCU content before and after ultra-violet irradiation...

Figure 2.14. Kinetics of Isoramnetine consumption (1) and change of its rate at ultra-violet irradiation (2).

Durability of polymer has been studied as the criterion of the effect of oligomer and polymer schififs base on the mechanical properties of CA-film in the process of ultra-violet irradiation. 

Figure 2.27. Effect of preliminary ultra-violet irradiation on CA durability. Additives in % a - 1, b - 3. o - non-irradiated CA, x - CA+BA irradiated, A -CA+XXXIV irradiated, A - CA+XXXV irradiated,...

Table 23. Ultra-violet irradiation effect on the conservation of specific viscosity of 0,5 CDA solutions...

Table 24. Effect of cellulose diacetate films ultra-violet irradiation on conservation of viscosity characteristics. Distance from the irradiation source is 30cm, time of exposure is 24 hours...

Table 25. Effect of ultra-violet irradiation on mechanical properties of the films of modified and initial CDA...

Figure 2.39. EPR - spectra of dyes LIX (a) and LXIII (b) after 4 hours ultra-violet irradiation.

Presence of the processes of structurization in undyed film during the first period of irradiation may be observed while investigating viscosity of irradiated PVA-films, that proves some increase in intrinsic viscosity (see Figure 2.41). Such increase in intrinsic viscosity is not observed in dyed films. Probably PVA structurization after ultra-violet irradiation takes place by recombination radicals of polymer adjacent chains. The rate of radicals accumulation in dyed PVA-films is less (Figure 2.41) and at the same time probability of structurization by recombination PVA macroradicals decreases. 

Figure 2.40. Kinetic of free radicals formation at ultra-violet irradiation 1 - PVA covalently linked with LIX 2 - PVA covalently dyed by LXI 3 - PVA, dyed by LX 4 - PVA, dyed by LXII 5 -undyed PVA.

Figure 2.41. Kinetic of intrinsic viscosity change at ultra-violet irradiation of PVA a) -undyed b)-dyed I c)-dyed II.

Considerable changes take place in PETP structure at ultra-violet irradiation. So M.S. Kuligin with his research workers found increase of absorption bonds intensity in the region 1620 cm in infrared spectra of irradiated PETP, characterizing the presence of double bonds... 

Triphenylphosphate, igranox, diglycol phosphate, trimethyl borate [265], benzotriazole [266] are used as light stabilizers. Fibres modified by such substances exceed goods from compositions produced by traditional method to a far greater extent as to their resistance to ultra-violet irradiation. 

Use of lowmolecular stabilizers has essential disadvantages they do not provide duration of protective effect under service conditions, since they are quickly consumed at ultra-violet irradiation, washed-out from the polymer and are lightly volatile. In this connection there arises the question about possible use of highmolecular stabilizers. 

---