When oxygen is present, this vast source of free radical initiators is responsible for the greatly increased rate. Measurement of Molar Absorptivities After consideration of some of the data obtained in the preceding irradiation studies and reported in Chapter III, it was considered desirable to measure the molar absorptivities of the 5. In order to determine the effect of these modifiers on the rate of degradation, films of about the same t h ickness of Resins A, B, and C Table 1 were prepared an d irradiated in a dry nitrogen atmosphere at 70 2C. Use of the calibration curve permitted rapid evaluation of the thickness of films whose thickness was on the order of cm. The band observed earlier at 5. Films were prepared for study by dissolving the resin in a volatile solvent. A somewhat thicker film was used this time in the hope that any degradation products might be formed in sufficient quantities to make their identification possible.
With all their versatility, however, alkyd resins have one rather serious shortcoming as a beautifying and protective coating. Matching notches were cut in the stationary adapter and the rotating holder which allowed the samples to be positioned in the beam very reproducibly from one spectrum to the next. The sodium chloride cells used in infrared an a lysis were calibrated by two independent methods. The Model B Infracord was employed for wholly qualitative examination of the 2. The sodium chloride cells used in infrared analysis were calibrated by two independent methods. In manufacture of phthalic anhydride by the oxidation of naphthalene was 1 PAGE 8 2 begun and products made from this formerly expensive chemical assumed new commercial attractiveness.
It was reasoned that chain scission at this point would result in formation of small fragments which could be removed from the film either as gases or as water soluble compounds leaving behind phthalic acid or related free radicals which might further decompose with evolution of carbon dioxide. As expected, Resin C was degraded at a noticeably faster rate than were the other resins. Because of the difficulty of transferring ether solutions quantitatively, several solutions were prepared by weighing samples of the anhydride and dissolving them and then running the spectra as soon as possible to avoid concentration changes due to evaporation.
Apparently the shielding layer of anhydride is not formed in this case.
A study of some factors affecting the degradation of alkyd resins
The curve was obtained by casting films in metal spacers of known thickness and pressing between two sodium chloride plates. Eesin ordinary rubber stopper drilled for inlet and exhaust tubes and a thermometer served as a top. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Oxygen was bubbled through trap B, which, in this case, was filled with water, and then passed through the irradiation cell and out through mercury trap M, adjusted to maintain the pressure in the system at about 10 mm.
This item may be protected by copyright but is made available here under a claim of fair tnesis 17 U. Peter Edward Morrisett is married to the former Suzanne Hamrick and is the father of two daughters. This was done by measuring the absorbance of solutions of known concentration in cells of known thickness.
Infrared Spectrum of Phthalic Anhydride. Swern, Daniel, et al. This data in addition to the known ability of alkyds, modified only with pigments, to chalk rapidly seemed to indicate some degradation of the C-C-C ester linkage in addition to other effects studied in the modified alkyds. It was known that a series of peroxy esters of phthalic and benzoic acids have their carbonyl absorptions in the region of 5.
A set of films of Resin A was irradiated in a nitrogen atmosphere which was saturated with thesiw. However, if film thicknesses should change, aklyd would expect about equal amounts to be eroded away from each.
The con clu s ion to which the author is forced, in the light of this result, is that the degradation process consists of an initial photolytic cleavage of the polymer at the site of the ester linkage.
During the first 50 hours of the irradiation, Log A a and therefore the log of anhydride concentration, is proportional to time. To further eliminate errors due to solvent absorption, a cell of approximately the same rewin as the sample cell was alkdy with the solvent mixture and placed in the reference beam of the spectro photometer.
Dugan, Beadle and Henick have used infrared spectrophotometry to follow the autoxidation of methyl linoleate by studying the 2. On the apkyd that much of this scattering was the result of non-reproducible positioning of the samples on the spectrophotometer, a new sample holder was constructed which largely eliminated this source of error.
With all allkyd versatility, however, alkyd resins have one rather serious shortcoming 8. Chalking is objectionable for two major reasons: The films were usually prepared in two classes as indicated in irradiation Experiment I.
Comparison of’ Figure 12 and the curve shown in Figure 6, indicates that the initial rate of’ thrsis in nitrogen is the same regardless of’ the presence or absence of’ moisture since their slopes are equal. The change of slope near 50 hours, it is felt, indicates the build-up of a layer of phthalic anhydride on the surface of the film.
A study of some factors affecting the degradation of alkyd resins
After the initial cleavage of the ester, the alcohol portion of the molecule is probably oxidized to aldehydes, ketones, or even carbon dioxide and water. Using the new sample holder, Resin A was again irradiated in dry nitrogen at In order to avoid the increased complexity introduced by the linseed oil degradation and because samples of the unpigmented resin were more easily prepared for irradiation, Resin A was chosen for exclusive use in the remainder of this work.
The resin used was an reain glycerol phthalate which will be designated as Resin A throughout the remainder of this paper. Determination of Molar Absorptivity of Phthalic Anhydride Matching notches were cut in the stationary adapter and the rotating holder which allowed the samples to be positioned in the beam very reproducibly from one spectrum to the next.
However, the absence of a change of slope in Figure 12 indicates that when water vapor is present the layer of phthalic anhydride, suggested earlier, does not form and the degradation continues at the same rate. All the chemicals used in this study were C.
To test the hypothesis that hydrogen peroxide or ozone was reacting with the polymer to form a peroxy ester, it was decided to repeat the irradiation under conditions which would prevent formation of either oxidizing agent. At this temperature, the thinner film was rapidly eroded to the extent that the carbonyl band at 5.