The results of this experiment are shown in Table 2 and in Figures 6, 7, and 8. 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. Almost all the work up to this time, has been directed toward chalking in modified glycerol phthalate resins. Loss of Total Carbonyl from Resin A. The method described above may only be employed when the film is thin enough to allow measurement of the absorbance of the 5.
The Experimental section of this paper is reported in the chronological order in which the work was done. Since that time the word has been generally used as a generic term for these resins and also for their many modifications. A second set of samples was irrradiated in wet oxygen. Fitzgerald has re ported the rate of evolution of carbon dioxide upon irradi ation of a linseed oil alkyd. These predictions are observed to be quite correct. This type of holder necessitated transfer of each sodium chloride plate with its film from the irradiation holder to a sampling holder designed to fit the infrared spectrophotometers. In the preceding four experiments the samples were irradiated in a holder of aluminum and bakelite which prevented the film from contacting the irradiation cell and allowed the atmosphere used in the cell to circulate about the film and its so d ium chloride substrate.
The determination of molar absorptivity rfsin Resin A has previously been described. 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.
The equations fitting these data are: Degradation of Ester Carbonyl in Moist Air at 30c.
A study of some factors affecting the degradation of alkyd resins
In England, Watson Smith first prepared glycerol phthalate in The presence of these strong oxidizing agents and the location of the band introduced the possibility that a peroxy acid or ester might be present. It was submitted to the Dean of the College of Arts and Sciences and to the Graduate Council, and was approved as partial fulfillment of the requirements for the degree of Doctor of Philosophy.
The curve was obtained by casting films in metal spacers of known thickness and pressing between two sodium chloride plates.
The first, ori g in a lly postulated by Renz in2 1 attributes the decomposition of the film to a cyclic oxidation-reduction process involving the pigment. Cell thick nesses were measured by measuring interference fringes produced by the empty cell. In this manner the sample temperature would have a definite effect on the rate of the overall process by determining the rates of such oxidation s That temperature does, in fact, have a marked effect upon the degradation process as a whole is illustrated by Figures 5 and 6.
Use of the calibration curve permitted rapid evaluation of the thickness of films whose thickness was on the order of cm. Chalking is objectionable for two major reasons: Glyceryl phthalate alkyds have been popular in the field of surface coating because of their gloss retention and general pleasing appearance throughout a relatively long protective life.
Under these conditions the rate of degradation PAGE 19 was greatly diminished and after about 48 hours of irradiation three new bands were clearly observable in 13 the carbonyl region. Once again a variety of concentrations and cell thicknesses were used.
In order to examine the effect of temperature on the rate of loss of ester carbonyl intensity and on the rate of formation of the anhydride carbonyl, films of Resin A were irradiated for approximately hours in an atmosphere of dry nitrogen at three different temperatures;, and C. 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.
The initial cleavage of the polymer is thought to occur at the site of the ester linkage and is probably free 54 PAGE 61 radical in nature. A somewhat thicker film was used this time in the hope that any degradation products might be formed in sufficient quantities to make their identifi cation possible.
Degradation of Resin A at 75c. It was also found that concentrations of phthalic acid and phthalic anhydride as low as l and lO-3 molar respectively could be detected by infrared by use of mixed solvent systems of chloroform and absolute ethanol or ether in thick cells, and with a slit width of about microns.
A study of some factors affecting the degradation of alkyd resins
Gropp for continuing advice, assistance, and inspiration. Instruments and Chemicals The following commercial instruments were used in this work: Thesis — University of Florida. The increase in anhydride concentration, and simultaneous decrease in ester concentration, was interpretated as an example of thesie first order kinetics in photons of ultraviolet light of the required energy for bond cleavage.
The first, originally postulated by Renz in21 attributes the decomposition of the film to a cyclic oxidation-reduction process involving the pigment. In order to shed some light on this question, films of Resin A were placed in the irradiation cell but were shielded by aluminum foil thezis the ultraviolet rays.
It was this reasoning thesks stimulated interest in a part of the alkyd molecule, mainly ignored in earlier studies, and which prompted the work described in the following pages, in the hope that analytical methods mi g ht be developed which would aid in the understanding of the degradation process.
Measurement of Film Thickness For films which were on the order of lO-3cm.
A series of standard films, prepared with silver or aluminum, spacers between two plates of sodium chloride, were scanned and absorbance plotted against film thickness to give a calibration curve. This is not to say that subsequent reactions in the overall degradation process are not of the thermal type.
In general these are long chain fatty acids with as many as three carbon-carbon double bonds per carboxylic acid group. A peroxide aliyd adjacent to the carbonyl produces a ressin shift to shorter wave lengths.
Comparison of Figure 12 and the 75 curve shown in Figure 6, indicates that the 42 initial rate of degradation in nitrogen is the same regardless of the presence or absence of moisture since their slopes are rwsin.
These films failed to show any interference fringes due to irregularities in the thickness.