Content Of Oxygen-containing Functional Groups Research Articles

Role of pigments in the stability of polyethylene systems

The photodegradation processes of high-density polyethylene (HDPE) films containing either a phthalocyanine-based pigment, or a rutil (TiO 2 )-based pigment, as well as of the unpigmented films stabilised differently were investigated during photo-ageing, applying mechanical, gel content and XPS measurements. The phthalocyanine pigment-containing film showed degradation characteristics (abrupt decrease of elongation at break after short irradiation period, no gel formation, high concentration of oxygen-containg functional groups on the surface) similar to those of the films containing a low amount of stabiliser. The behaviour of the TiO 2 -containing film and that of the unpigmented films containing a higher amount of stabiliser were also similar (slow decrease of elongation at break, increase of gel content, lower amount of oxygen-containing functional groups on the surface). The concentration of oxygen-containing functional groups in samples pigmented with phthalocyanine increased remarkably with increasing processing temperature. The results suggest that the phthalocyanine pigment influences the photostability indirectly, through reduction of the thermal stability of polymer due to the adsorption of the thermal stabiliser by the phthalocyanine pigment. Coating the surface of phthalocyanine with reactive surfactant improved the photostability of the HDPE film.

Oxidation with air of cyclohexanone to carboxylic diacids on carbon catalysts

Carbons derived from phenolic resins were used as catalysts for the aqueous phase oxidation of cyclohexanone at 140°C under air pressure. The reaction yielded mainly adipic, glutaric and succinic acids. The samples were modified by heat treatments in CO2, air or N2 at different temperatures and characterized to determine their surface area and porosity and to evaluate the functional groups on the surface. Treatments under CO2 or air increased the oxidation activity. The selectivity to adipic acid was maximum (33%) after activation in air which greatly increased the surface concentration of oxygen-containing functional groups. However, it was not possible to attribute the selectivity to specific acidic, neutral or basic groups present at the surface of carbons.

The composition of lignite humic acids

Humic acids from lignite deposits in Bulgaria were characterized with respect to the concentration of oxygen-containing functional groups. The following ranges were determined, in mequiv g −1: total acidity 5.1–6.8; carboxylic groups 3.5–4.5; phenolic OH groups 1.6–2.3; ketone groups 1.0–2.0; quinone groups 1.0–1.3; and methoxyl groups 0.3–1.3. Yields of high- and low-molecular fractions were monitored by g.p.c. on Sephadex G-50. The molecular mass for the lower molecular fraction was ~ 4000u. On the basis of the elemental composition, molecular mass and distribution of oxygen in functional groups, a concept for lignite humic acid structure was developed.

A comparative chemical-structural study of fossil humic acids and those extracted from urban wastes

Chemical-structural features of commercial humic acids (HAs) from leonardite or lignite were studied and the data obtained were compared with those of humic acids extracted from composted urban wastes. The greatest differences showed by the elemental analysis between the three HAs were in N and H contents, both of which diminished with the oxidation degree of the starting materials. Unlike the HA from the more oxidized material HAL1 showed the highest content of oxygen-containing functional groups. FTIR spectra did not show differences between HAs from evolved materials such as leonardite or lignite. However, differences were found between these HAs and those extracted from composts of urban wastes, which showed a greater aliphatic character and a more pronounced peak in the absorption band attributed to secondary amides and in that of carbohydrates. The 13C-NMR spectra were similar for both HAs from leonardite regardless of their oxidation degree. The percentage of aromaticity of these HAs was 45%. HALi showed a low percentage of aromaticity, probably due to the addition of non-humified carbon to this HA during its industrial extraction, which would cause an enlargement of the peak appearing at 30 ppm, thus decreasing the peaks indicative of aromaticity. The spectra of compost HAs showed a low aromaticity degree for these HAs as a consequence of the pronounced peak appearing at 73 ppm corresponding to carbon of carbohydrates and/or polyalcohols and aminoacids. Py-GC revealed a high content of benzene and toluene in all the commercial HAs. The values of these fragments as well as those of the ratios between pyrolitic fragments, used as humification index for soils, were the highest in the HA extracted from the more oxidized leonardite.

Chemical characterization of humic substances extracted from organic-waste-amended soils

Humic substances were extracted from a soil treated, in a 4-year experiment, at different rates with a sludge from anaerobic treatment of combined civil and industrial wastes, and with agricultural manure. Elemental and chemical analyses, molecular weight (MW) distribution and infrared (IR) spectroscopy were performed on the purified humic acids (HA). Organic wastes significantly increased the HA content of the treated soils and improved CEC. The C/N, C/H and C/O ratios of HA extracted from the original wastes showed a higher degree of humification for sludge than for manure. This difference was also noticed for the C/N ratio of soil humic extracts, indicating a faster humification process for the sludges in soil. The content of oxygen-containing functional groups was lower than the ‘model’ HA reported in the literature, and even more so for HA from sludges, reflecting their anaerobic formation. MW distribution and E 4/E 6 ratios showed that the sludge material had a higher molecular complexity than manure, supporting the high degree of humification attributed to the former. HA extracted from sludge-treated soils revealed a molecular dimension increasing with the application doses of waste material. Infrared spectra showed that HA formed in soils after waste additions reflected the chemical composition of the original organic material, which was rich in aliphatic groups and peptides for sludge and in carbohydrates for manure. On the basis of this study, it is concluded that not only are organic waste additions able to build up the HA content in soils but the HA formed assume the chemical characteristics and the degree of humification of the original material.

Evolution of organic oxygen bonds during pyrolysis of coal

Five Czech coals of different rank (70.2, 71.5, 74.5, 75.0 and 83.3 wt% carbon) were heated at different temperatures in the range 250–850 °C and the contents of oxygen-containing functional groups (OH, COOH, CO, OCH 3) were determined in the coals and carbonization residues. The coals and residues were subjected to pyrolysis chromatography at 740 °C and the yields of phenol produced were measured. The dependence of the oxygen functions and the phenol yield on temperature and coal rank is discussed. In the coals studied, the most resistant oxygen groups appear to be hydroxyl and methoxyl; carboxyl and carbonyl oxygen are eliminated below 550 °C.

Chemically modified carbon fibre electrodes part II. Characterization of trimethylsilanized carbon fibres by reduction of adsorbed o-nitrophenol

Bulk-functionalized carbon fibres [1], i.e. distorted carbon fibres with a high concentration of oxygen-containing functional groups not only on their surface but also in their bulk, were tested as a precursor for the preparation of chemically modified carbon electrodes. Reactivity and concentration of the functional groups were characterized by trimethylsilanization as a model reaction. Trimethylsilanized areas are highly hydrophobic—they can be discriminated from non-modified areas via electrochemical reduction of strongly adsorbed o-nitrophenol (o-NPh). It is concluded that trimethylsilanized electrodes based on bulk-functionalized carbon fibres are not only covered with o-NPh on their surface but also contain it on “internal sites”. In contrast, conventional high-temperature surface oxidation of carbon fibres and subsequent trimethylsilanization is not very effective, as this modification technique is mainly restricted to the few edge-sites of the graphite-like carbon layers.

Chemically modified carbon fibre electrodes: Part II. Characterization of trimethylsilanized carbon fibres by reduction of adsorbed o-nitrophenol

Bulk-functionalized carbon fibres [1], i.e. distorted carbon fibres with a high concentration of oxygen-containing functional groups not only on their surface but also in their bulk, were tested as a precursor for the preparation of chemically modified carbon electrodes. Reactivity and concentration of the functional groups were characterized by trimethylsilanization as a model reaction. Trimethylsilanized areas are highly hydrophobic—they can be discriminated from non-modified areas via electrochemical reduction of strongly adsorbed o-nitrophenol ( o-NPh). It is concluded that trimethylsilanized electrodes based on bulk-functionalized carbon fibres are not only covered with o-NPh on their surface but also contain it on “internal sites”. In contrast, conventional high-temperature surface oxidation of carbon fibres and subsequent trimethylsilanization is not very effective, as this modification technique is mainly restricted to the few edge-sites of the graphite-like carbon layers.

CHEMICAL CHARACTERISTICS OF A NATURAL SOIL LEACHATE FROM A HUMIC PODZOL

A leachate, collected in the field in a lysimeter placed between the Ae and Bhf horizon of a Humic Podzol in Newfoundland, was analyzed by chemical and spectroscopic methods.About 87% of the dry, ash-free weight of the leachate was fulvic acid, the remainder consisting mainly of polysaccharides and nitrogenous compounds. A comparison of the analytical characteristics of the purified leachate with those of extracted and purified Podzol Bh fulvic acid showed that the main structural features of the two materials were very similar. Judging from its high contents of oxygen-containing functional groups and from its water solubility, the organic matter in the leachate had all the characteristics of an efficient metal–complexing agent, capable of playing a significant role in metal–organic matter interactions in soils.An organic matter–silica sediment was isolated from the leachate, consisting of 47.6% organic matter and of 52.4% of almost pure SiO2∙nH2O. The organic matter in the sediment accounted for about 10% of the organic matter in the leachate. The isolation of the sediment suggests that investigations on interactions between compounds of silicon and humic substances deserve greater attention than they have so far received.

Antioxidant Properties of Carbon Black in Unsaturated Elastomers. Studies with cis-Polybutadiene

Abstract The thermal antioxidant behavior of carbon black was studied in vulcanized cis-polybutadiene and related to the surface chemistry of the black. Continuous and intermittent stress relaxation and oxygen absorption measurements were employed to determine the antioxidant ability of the carbon blacks. The blacks were characterized by the surface concentrations of oxygen-containing functional groups, using methods described in the literature. Antioxidant activity was found to be highest in carbons containing relatively large amounts of bound oxygen. These carbons are also acidic and decompose peroxides by the ionic mechanism. This was demonstrated with cumyl peroxide. However, even though the acidity and ability to decompose cumyl peroxide to phenol and acetone could be destroyed by methylation, this treatment did not seriously impair the antioxidant activity, so that the role of acidic groups appears to be minor. Evidence is presented which suggests strongly that the antioxidant behavior of carbon blacks is due to surface quinones, possibly hydrogen-bonded with adjacent hydroxyl groups. Measurements made on samples vulcanized in peroxide and sulfur curing systems indicate that the antioxidant behavior of carbon black is independent of the method of vulcanization in the absence of other antioxidants. A characteristic feature of the antioxidant action of carbon blacks is their tendency to repress the oxidative crosslinking reactions, the relative amount of compensation of chain scission by crosslinking being smaller than in gum vulcanizates.

Antioxidant properties of carbon black in unsaturated elastomers. Studies with cis-polybutadiene

The thermal antioxidant behavior of carbon black was studied in vulcanized cis-polybutadiene and related to the surface chemistry of the black. Continuous and intermittent stress-relaxation and oxygen absorption measurements were employed to determine the antioxidant ability of the carbon blacks. The blacks were characterized by the surface concentrations of oxygen-containing functional groups, using methods described in the literature. Antioxidant activity was found to be highest in carbons containing relatively large amounts of bound oxygen. These carbons are also acidic and decompose peroxides by the ionic mechanism. This was demonstrated with dicumyl peroxide. However, even though the acidity and ability to decompose dicumyl peroxide to phenol and acetone could be destroyed by methylation, this treatment did not seriously impair the antioxidant activity, so that the role of acidic groups appears to be minor. Evidence is presented which suggests strongly that the antioxidant behavior of carbon blacks is due to surface quinones, possibly hydrogen-bonded with adjacent hydroxyl groups. Measurements made on samples vulcanized in peroxide and sulfur curing systems indicate that the antioxidant behavior of carbon black is independent of the method of vulcanization in the absence of other antioxidants. A characteristic feature of the antioxidant action of carbon blacks is their tendency to repress the oxidative crosslinking reactions, the relative amount of compensation of chain scission by crosslinking being smaller than in gum vulcanizates.