Pre-irradiation method

Araki et al. (117) have described a so-called dry-state grafting procedure in which the cellulose is boiled with water and then the water is replaced by various alcohols, also by boiling. The cellulose was then dried and grafted with styrene using both mutual and pre-irradiation methods. The treatment was effective with cotton but only to a small extent with rayon fibers. The order of effectiveness of the solvents used was butanol as the most effective and methanol, water, higher alcohols and ketones as considerably less effective. This is a different order from... 

Armstrong, and Rutherford have reported extensive studies on the vapor phase grafting of vinyl monomers to cellulosic fibers both mutual and pre-irradiation methods have been used (97, 120). Again, water or another swelling agent was found to be necessary for effective grafting to rayon and cotton for all the monomers studied. In the case of cellulose acetate water was helpful but not necessary except for styrene. Acetic acid and methanol vapors were also found to be effective promotors of vapor phase grafting to cotton and cellulose acetate fibers. 

Scheme 4 SimplifiecI representation of the pre-irradiation method ("step aJ applied to the grafting reaction of glycidyl methacrylate (GMA) onto polypropylene fstep W for the functionalization of the material by reaction...

Acryhc acid was grafted onto PP fabric by a pre-irradiation method using a cobalt-60 gamma ray. The effects of absorbed dose, the reaction temperature, reaction time, storage time, as well as the addition effect of ferrous... 

The radiation grafting of TFS onto various fluorine-containing base polymers, such as LDPE, ETFE, PEA, FEP, and PTFE has been accomphshed by the pre-irradiation method [105]. A proper examination of the swelling properties and solubility parameters of these polymer films in pure TFS showed that LDPE yielded the highest, and PTFE led to the lowest graft levels. This is because of the fact that the sorption of hquid in polymer depends on the affinity between the hquid and the polymer film. 

Simultaneous radiation grafting is, therefore, a single step process while the pre-irradiation method involves two steps [ 170,177). The lifetime of irradiated PVDF at room temperature is about one year [ 179). 

With adequate swelling vinyl monomers can be satisfactorily grafted to cellulose and its derivatives by the three main methods developed for other polymers (98). These are (1) the mutual or direct method where the polymer is irradiated in the presence of the monomer or monomer vapor, (2) the pre-irradiation (sometimes called post-irradiation grafting) method where the polymer is first irradiated and then brought into contact with the monomer, and (3) the peroxide method in which the polymer is irradiated in air and the resulting polymeric peroxide used to initiate graft polymerization. 

Radiation grafting [83, 84, 85, 86, 87, 88, 89] is a very versatile and widely used technique by which surface properties of almost all polymers can be tailored through the choice of different functional monomers. It covers potential applications of industrial interest and particularly for achieving desired chemical and physical properties of polymeric materials. In this method, the most commonly used radiation sources are high-energy electrons, y-radiation, X-rays, U.V.-Vis radiation and, more recently, pulsed laser [90], infrared [91], microwave [92] and ultrasonic radiation [93]. Grafting is performed either by pre-irradiation or simultaneous irradiation techniques [94, 95]. In the former technique, free radicals are trapped in the inert atmosphere in the polymer matrix and later on the monomer is introduced into... 

The sensitivity of the method is extremely high so that no problems with build-up of products of the radiolysis are likely. Conversely, however, problems with impurities will be serious. The radiolytic method allows the possibility of pre-irradiation as a partial cure. 

Other NAA methods involve the chemical separation of interfering ions (Blotcky et al., 1976) in these the short half-life (2.24 minutes) of AI makes post-irradiation separations a problem. Pre-irradiation separation techniques have potential problems of contamination and losses during the separation phase. 

Many methods of radiation grafting can be used, but for synthetic fibers such as PET and PP, pre-irradiation technique in an inert atmosphere (vacuum or N2) have been used. Radiation on PET or PP fibers in an inert atmosphere producing trapped radicals which is still exist for a long time at room... 

The simplest technique is pre-saturation in which the solvent is subjected to CW irradiation for a short time at a level sufficient to saturate the solvent without affecting other solute peaks. The saturating field is removed immediately before the observation pulse so that the solvent peak has no opportunity to relax. Several solvent peaks can be saturated if rapid frequency switching can be performed during the saturation period. If proton exchange between solvent and solute occurs, for example exchange of OH and NH with H2O, the solvent saturation can be transferred to the solute. However, this is rarely a problem in synthetic polymers, and because of its ease of application the pre-saturation method is the preferred method. 

In some extremely demanding cases, pre-irradiation chemical concentrations are carried out together with postirradiation separations, combining the advantages and the drawbacks of both techniques. This method, referred to as PC-RAA, can provide the highest possible sensitivity of trace element analysis among the AA techniques. 

Dang et al. (2000) increased the sensitivity of NAA for Th by separating the indicator radionuclide, Pa, using co-predpitations with manganese dioxide and barium sulfate and determined Th in total diet samples. A similar postirradiation procedure was coupled to the following pre-irradiation separation and concentration of Th (PC-RNAA) by H5llriegl et al. (2005) to increase the sensitivity of the method for the determination of urinary Th excretions. The pre-concentration procedure consisted of phosphate and caldum oxalate coprecipitations. The detection limit of Th in the urine sample was about 10 pg (0.04 jiBq). 

Glover et al. (1998, 2001) developed an ultra-sensitive method for the analysis of Th in bioassay and environmental samples and pre-concentration radiochemical neutron activation analysis (PC-RNAA) was applied. In the pre-irradiation procedure, Th was concentrated using... 

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