This is not to say that subsequent reactions in the overall degradation process are not of the thermal type. It was first observed after about 90 hours of irradiation. The Experimental section of this paper is reported in the chronological order in which the work was done. The films were usually prepared in two classes as indicated in irradiation Experiment I. Upon weathering, paints formulated from these resins are observed to “che.. These films failed to show any interference fringes due to irregularities in the thickness. Use of the calibration curve permitted rapid evaluation of the thickness of films whose thickness was on the order of 10O3 cm.
The number of fringes and the wave lengths between which they are observed are related to cell thickness by the equation where bis cell thickness in microns and n is the number of fringes observed between the wave lengths Al and A 2 also measured in microns. Fitzgerald has reported the rate of evolution of carbon dioxide upon irradiation of a linseed oil alkyd. This initial reaction is probably free radical in nature. The equations fitting these data are: Formulation of Alkyd Resins. Farmer and other workers have investigated in great detail the mechanism of the autoxidation of these unsaturated chains. The composition of these resins is shown in Table l o The irradiation was carried out first in dry nitrogen at
It was reasoned that if all the ester which disappeared from the film were converted to anhydride and no other aromatic products were formed, then the following general equation would hold: However, due to adsorption of the film on the liquid surface and the fragile nature of the film, it was impossible to remove the film from the surface. Among these products were the various modified glyceryl phthalate resins which made great strides both as surface coatings and as binders for molded products and by the actual commercial production of these alkyds was in excess of 34 million pounds yearly.
Kienle in coined the name “alkyd” and which in his words, “include the complexes resulting from the reaction of polyhydric alcohols and resinifying carboxylic organic acids such as 14 the polybasic acids and their anhydrides. Beer’s law plots of absorbance versus the product of cell thickness and concentration are shown in Figures l In manufacture of phthalic anhydride by the oxidation of naphthalene was begun and products made from this formerly expensive chemical assumed new commercial attractiveness.
This method was checked by weighing a film of known area and calcu lating thickness from the weight, area, and density.
One thess predict qualitatively that the rates of degradation of Resins A and B should be approximately equal and the rate for Resin C should be somewhat greater due to attack at the sites of unsaturation in the linseed oil portion of the polymer.
Dugan, Beadle and Henick4 have used infrared spectrophotometry to follow the autoxidation of methyl linoleate by studying the 2. It was found that the course of the reaction could be followed by infrared spectrophotometry by observing the rates of change of absorbance of the ester carbonyl at 5.
During the first 50 hours of the irradiation, Log Aa’ and therefore the log of anhydride concentration, is proportional to time. Grassie, Norman, Chemistry of High Pol: Carbonyl Absorbance of Resin A. The Experimental section of this paper is reported in the chronolo g ical order in which the work was done. The degradation of poly-ethylene terephthalate has been studied thesos as a photolytic and as a thermal PAGE 11 5 process without any agreement upon a mechanism or even the products of the reaction.
PAGE 51 45 In all four of these cases the results were the same. Having earlier observed a radical difference in the rate of anhydride formation when the atmosphere surrounding the samples during irradiation was changed from water saturated oxygen to dry nitrogen, experiments were conducted which were intended to separate, if possible, the effects of water vapor and oxygen on the rate of degradation. This type of holder necessitated transfer of each sodium chloride plate with its film from the irradi ation holder to a sampling holder designed to fit the reskn spectrophotometers.
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 10O3 cm. It was known that a series of peroxyesters of phthalic and benzoic acids have their carbonyl absorptions in the region of 5.
Cell thicknesses were measured by measuring interference fringes produced by the empty cell. This is not to say that subsequent reactions in the overall degradation process are not of the thermal type. The intensity of this band was only 5 per cent greater than that of the background.
All the chemicals used in this study were C. Miller used infrared spectrophotometry in conjunction with other optical techniques for study of the degradation of a linseed oil alkyd and has su g gested that peak intensities provide a method of measurement of functional group concentrations which, thou g h only thesid approximation, yield interesting and useful results which are not in disagree ment with data obtained from analysis of gaseous degradation pro d ucts and reflectance studies.
Upon opening the irradiation cell, the characteristic odor of ozone was observed during the present work.
A study of some factors affecting the degradation of alkyd resins
Instruments and Chemicals The following commercial instruments were used in this work: To further eliminate errors due to solvent absorption, a cell of approximately the same thickness as the sample cell was filled with the solvent mixture and placed in the reference beam of the theiss. 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.
The apparatus used for irradiation in all the following experiments is shown diagramatically in Figure 2. Renz showed that titanium IV oxide reacts photochemically with glycerol, generating carbon dioxide and titanium III oxide.
A study of some factors affecting the degradation of alkyd resins
Analytical Procedures and Techniques The spectra recorded on the Perkin-Elmer, Model tehsis, were run under the following conditions: Once again a variety of concentrations and cell thicknesses were used.
Examination of the literature indicated that cyclic anhydrides were known to show at least two carbonyl absorptions in the 5. Film Thickness for cm.