Ozone Degradation Research Articles

IMPACT OF ENHANCED SIMULATED SOLAR ULTRAVIOLET RADIATION UPON A MARINE COMMUNITY

Abstract—There is evidence to indicate that an increased exposure to solar radiation in the UV‐B region (specifically, 290–320 nm) may occur as a result of anthropogenic degradation of stratospheric ozone. The fact that present levels of solar UV radiation can detrimentally affect marine organisms led to experiments to quantify the impact of increased UV radiation upon a marine community. Two 720–l seawater chambers (continuous flow‐through design) were exposed to simulated solar UV radiation. Fluorescent sunlamps filtered by a 290 nm cutoff filter (a 0.13 mm thickness of cellulose triacetate film) were used as the radiation source. Utilization of three different weighting factors for the spectral irradiances at the surface of the chambers yielded differences of 18%, 35% and 40% in biologically effective fluence rate between the two chambers. Analysis of attached forms of algae at various depths demonstrated that a surface exposure of 1.4W/m2 in the 290–315nm waveband as contrasted with the chamber receiving a surface exposure of 1.0W/m2 resulted in depressed Chl a concentrations, reduced biomass, increased autotrophic indices, and decreased community diversity. These results indicate a potential for adverse effects of increased solar UV‐8 radiation: decreased community diversity, community structure shifts, and decreased productivity.

Study on ozone treatment of water‐soluble polymers. II. Utilization of ozonized polyethylene glycol by bacteria

AbstractA bacterium capable of utilizing polyethylene glycol of low molecular weight (less than 300) was isolated from soil and identified as Pseudomonas aeruginosa by biologic characteristics (named P. aeruginosa PEG‐K). The effect of ozone degradation on the utilization of polyethylene glycol of high molecular weight by the bacterium was studied on the basis of the measurement of oxygen uptake by Warburg manometer and of bacterial growth. The polyethylene glycol, which can never be utilized at all because of high molecular weight, became utilizable by the bacterium as a result of ozonization, while the formaldehyde produced by the ozonization inhibited the utilization of the ozonized polyethylene glycol by the same bacterium. However, such inhibition disappeared by treating the aldehyde with hydrogen peroxide. From the results of gas chromatography and measurement of chemical oxygen demand, P. aeruginosa PEG‐K was found to utilize ethylene glycol, diethylene glycol, and triethylene glycol, which were produced by the ozonization.

Study on ozone treatment of water‐soluble polymers. I. Ozone degradation of polyethylene glycol in water

AbstractPolyethylene glycol (molecular weight 8000) was degraded by ozone in 1% aqueous solution of pH 12. Chemical oxygen demand of the solution decreased with increasing ozone consumed. Intrinsic viscosity of the solution lowered exponentially as a result of the ozonization. The number of breaks calculated from the viscosity indicated that two molecules of ozone were consumed for one cleavage of the polymer chain. The molecular weight distribution obtained by gel permeation chromatography was very broadened and molecular weight was lower as well, and the polymer chain was found to be cleaved randomly by ozone. The production of formic ester, ethylene glycol, diethylene glycol, triethylene glycol, and hydrogen peroxide was confirmed by IR, NMR, gas chromatography, and chemical analysis. These observations could be accounted for by electrophilic attack of ozone on the ether bond.

An investigation on the chain‐folding structure of an ethylene–propylene copolymer by selective degradation

AbstractA renewed explanatory study is reported on the fold structure and branch location in single crystals of an ethylene–propylene copolymer by means of the ozone degradation method. By analogy with concurrent studies on linear polyethylenes a distribution of fold lengths is inferred, this distribution being broader, more uniform, and spreading deeper into the crystal interior in the case of the copolymer than for the linear polyethylene. Perhaps the most salient points of the work is that in contrast to nitric acid the oxidation by ozone does not obscure then characteristic CH3 infrared absorption band enabling the branch content to be followed during degradation. The single exploratory experiment of the present work reveals that while there is a certain amount of preference for the branches to accumulate near the fold surface, a substantial portion of them can still be located in the crystal interior. The potential of the present method for a more systematic study is indicated.

Association of the reaction products in the ozone degradation of polyethylene and its relevance to the study of the fold surface structure

AbstractAn association of reaction products was observed in the course of GPC analysis of ozone treated chain‐folded single crystals of polyethylene which, however, could be eliminated by washing with water. This recognition proved to be important for quantitative studies of the fold surface relying on oxidative fold cutting and should be of interest for studies of oxidative degradation phenomena for their own sake. With the association products appropriately removed, the random fold cutting mechanism could be more closely verified than was possible before. Anhydride linkages are suspected as the source of the association.

Ozone Degradation in Packed Columns

Ozone is being considered increasingly as an alternate disinfectant to chlorine for use in water and wastewater systems. Owing to its low solubility, the design of efficient contact systems is imperative for economic use of ozone in this respect. Even with the most efficient system, however, there inevitably will be some release of the gas to the atmosphere at some pint. This release may be unacceptable in certain situations, especially urban areas, and may have to be minimized by specific procedures. Such procedures may involve adsorption into potassium iodide solution, thermal degradation in a flare or decomposition, catalytic or otherwise, in a packed column. A technique by which ozone decomposition in a packed column may be evaluated by reaction zone analysis will be described.

Crystallinity and the effect of ionizing radiation in polyethylene. II. Crosslinking in chain‐folded single crystals

AbstractIn order to ascertain whether the crystal core of irradiated polyethylene single crystals is free from crosslinks—as would follow from the results of Part I—the fold surface of irradiated single crystals was shaved off with ozone and the resulting product examined by GPC for molecular weight. It was found that on ozone degradation the entire material, which had been insolubilized by radiation‐induced crosslinking, has become soluble hence became available for the GPC analysis. The chromatograms displayed the same peaked development with degradation as the unirradiated crystals leading eventually to single traverse dicarboxylic acids. This proves the absence of crosslinks within the crystal interior of the material as examined by GPC. The appearance of some additional low molecular weight material, is attributed to scission at the radiation‐induced double bonds due to ozone which eliminates the possibility of the existence of crosslinks within the lattice such as might provide scission sites for ozone. The conclusion could therefore be reached that, to the extent assessable by our GPC test, there are no radiation‐induced crosslinks within the crystal lattice, hence the crosslinks produced must be entirely confined to the fold surface region of the crystals.

Fold surface of polyethylene single crystals as assessed by selective degradation. I. Ozone degradation method

AbstractOzone has been used as a selective oxidizing agent for degrading polyethylene single crystals at room temperature in order to confirm and extend results on surface structure obtained by use of fuming nitric acid at temperatures above 60°C. The surfaces of the crystals were rendered highly accessible to the ozone gas by preparing the crystalline material in a highly expanded form; the solvent in which the crystals were suspended was removed by sublimation from the solid state. The extent and nature of the reaction were studied by measuring the increase in weight and in density, by direct chemical analyses, and by making use of infrared spectroscopy and gel‐permeation chromatography. It was found that the surfaces of the crystals are attacked at room temperature by ozone, with resulting chain scission, and the broad features of the chemical reaction were established. Some folded chains are found to be as long as the original thickness of the crystal, and once folds have been cut, continuing reaction shortens the chains. In the early stages of the degradation, during which most of the weight increase takes place, the density of the crystals increases, and the magnitude of the increase is that expected from the increase in weight alone, i.e., assuming no increase in effective volume.

Phospholin-derivate—II : Untersuchung über die lage der doppelbindung in phospholinen

1-Oxo-1-alkoxy-3-phospholenes are obtained from alcohols and 1,1,1-tribromo-3-phospholenes, 1-oxo-1-alkoxy-2-phospholenes from 1,1,1,-trichloro-3-phospholenes. The position of the CC-double bond was proved by spectroscopic methods and in two cases by ozone degradation. Sulfur dioxide treatment of 1,1,1-tricholoro-3-phospholenes yields a mixture of isomeric 1-oxo-1-chlorophospholenes containing over 90% of 2-phospholene. A synthesis of the pure isomers of 1-oxo-1-chlorophospholenes is described, starting from the corresponding 1-oxo-1-alkoxyphospholenes and phosgene. The position of the CC-double bond in 1-oxo-1-phenyl- and 1-oxo-1-(β-chloroalkoxy)-phospholenes was determined. Both the 1-oxo-1-ethoxy-3-phospholene and the 1-oxo-1-ethoxy-2-phospholene were converted into mixtures with their double bond isomers by alkaline treatment.

On the mechanism of ozone degradation of SBR

AbstractThe reaction mechanism of the ozone attack of SBR copolymers was studied to obtain information for use in the development of elastomeric materials having improved resistance to deterioration in service. Techniques of ultracentrifugation and viscometry were utilized to follow molecular changes induced by ozone. Chemical changes were investigated by measuring variations in active oxygen group concentration. Results suggest that the autocatalytic degradation of uninhibited SBR was initiated by a random ozone attack at a double bond on the unozonized chain, producing an ozonide which decomposed spontaneously, forming small segments with activated chain‐ends. This primary reaction, in the presence of oxygen, activated an α‐methylenic chain cleavage process which was terminated when the molecules were degraded to a limiting size, where no more R. radicals were formed from α‐methylenic groups. The reaction was also terminated when oxygen was removed from the system.

Chemical Inhibition of Ozone Degradation of SBR

Abstract The standard rubber antioxidant types which are capable of imparting ozone resistance to SBR vulcanizates are summarized. The 6-ethoxy-l,2-dihydro-2,2,4-trimethylquinoline and para phenylenediamines are shown to represent the most active structures. Steric, mesomeric, and resonance effects are shown to be important in imparting high levels of antiozone activity. When electronegative groups are substituted in an active structure, antiozone effectiveness is greatly reduced. Antiozonant activity is attributed to efficient stopping of ozone-induced free radical chain reactions in the polymeric structure.

Ozone Deterioration of Elastomeric Materials. Preliminary Results of a Study by Infrared Spectroscopy

Abstract The work described consists of explorative studies with the ultimate objective of developing an accelerated ozone aging test for elastomers based primarily on compositional changes rather than on the conventional variation in physical characteristics. Infrared spectrographic techniques were found to be admirably suited for the reflection of accumulation or depletion of specific structural linkages in polymer molecules undergoing ozonization. Purified gum specimens of Hevea, GR-S, nitrile rubber, Neoprene, and GR-I were dissolved in chlorinated hydrocarbon solvents such as ethylene dichloride or o-dichlorobenzene, and subjected to a stream of ozonized oxygen containing approximately 50 p.p.m. of ozone. Infrared spectrograms of films cast from the treated solutions show progressive intensification of clearly defined absorption bands at 2.9 and 5.8 mµ, reflecting the functional groups hydroxyl and carbonyl, respectively. Methods for quantitating these changes by calibration against reference compounds are described. A means is available for following ozone degradation of polymers in terms of specific variations in molecular structure. Basic information of this nature is potentially useful in the development of an accelerated ozone aging test correctable with aging under conditions of actual service.

Determination of Unsaturation in Butyl Rubber

Abstract In a recent publication on unsaturation in Butyl rubber it was pointed out that, of the various methods that had been examined, ozone degradation at the double bonds appears to give the most reliable unsaturation data, the values based on the limiting viscosity of the degraded polymer being in reasonably good agreement with those determined by end-group analyses. This paper describes in some detail the analytical method, together with certain modifications that have been introduced with the aim of facilitating routine work. It was recognized that the earlier procedure had the disadvantage of being too time-consuming, owing mainly to the steps in which the degraded polymer solution is evaporated to dryness, and the residue redissolved in diisobutylene before the viscosity measurement. An obvious possible improvement was to develop a procedure whereby the polymer solution could be ozonized and the viscosity of the degraded solution determined directly, thus eliminating evaporation and transfer to a second solvent. It was first necessary, however, to perform the experiments described below; their significance will be explained in the sequel. A further simplification was introduced through the use of carbon tetrachloride of ordinary reagent grade instead of the highly purified solvent. While this substitution usually leads to viscosity-time curves displaying a small negative slope in the region where the purified solvent gives unchanged viscosity values, a simple extrapolation to zero time gives viscosity data that are satisfactory within the limits inherent in the method. In view of the practical requirements of the method and the magnitude of the experimental error, the extra time and effort involved in further purification of the solvent appear to be unwarranted.

Unsaturation of Polyisobutylenes and Butyl Rubber. Reactions with Nitrosobenzene, Thiocyanogen, Iodine Monochloride, and Ozone

Abstract Table III summarizes unsaturation values obtained for the various polymers. The ranges indicated are, in most cases, extreme values of determinations made with two or more different samples of a given polymer type. Taking into consideration the small amounts of unsaturation involved, the values based on end-group determinations are in reasonably good agreement with one another and with the values based on the viscosity of the degraded polymer. Higher values are observed for the nitrosobenzene determinations, but these are considered to be less reliable because of the ease with which oxidation phenomena can occur with this reagent. The thiocyanogen values are the lowest of all; on the basis of values obtained by the other methods as well as of experimental evidence not included in this paper, these values are believed to result from incomplete reaction. As a class the iodine monochloride methods give considerably higher values than those obtained with the other reagents. This may be attributed to the substitution reaction that readily occurs with that reagent. The effect is perhaps most marked in the data obtained for polyisobutylene sample 2 with 0.1 N Wijs reagent; the upper value (0.4) is far greater than can be explained on the basis of the knowa molecular weight of this polymer and the corresponding terminal double bond contribution. Furthermore, since this polymer sample was fractionated in such a way as to remove all species of viscosity-average molecular weight less than about 50,000, the high value cannot be ascribed to the presence of dimers, trimers, or other small molecules formed during polymerization. In view of the data and the above considerations, it is believed that the unsaturation values based on ozone degradation are correct within the limits of experimental error, and that this reagent makes possible a relatively good estimation of the number of double bonds in polymers such as have been described. A modified procedure more suitable for rapid evaluations is the object of a current investigation.

Structure of Copolymers of Isobutylene and Isoprene

Abstract By means of ozone degradation experiments it has been shown that the isoprene units in copolymers of isoprene and isobutylene unite in the 1,4 positions. This conclusion is based on negative evidence. Since no evidence was found that would indicate a tendency for the isoprene units to occur in sequences, it is concluded that one isoprene unit cannot exert any directing influence on another, as far as their relative positions along the polymer chain are concerned. The existence of such an influence would necessitate the assumption of unprecedented long-range forces. Hence, the isoprene units must enter the chain in a random manner.