Accumulation Of Carbonyl Groups Research Articles

Effect of oxygen-containing functional groups on the micromechanical behavior of biodegradable plastics and their formation of microplastics during aging

Biodegradable plastics (BPs) are more prone to generate harmful microplastics (MPs) in a short time, which have always been ignored. Oxygenated functional group formation is considered to be a key indicator for assessing microplastic formation, while it is difficult to characterize at a very early stage. The micromechanical properties of the aging plastic during the formation of the MPs are highly influenced by the evolution of oxygen-containing functional groups, however, their relationship has rarely been revealed. Herein, we compared changes in the physicochemical properties of BPs and non-degradable plastic bags during aging in artificial seawater, soil, and air. The results showed that the oxidation of plastics in the air was the most significant, with the most prominent oxidation in BPs. The accumulation of carbonyl groups leads to a significant increase in the micromechanical properties and surface brittleness of the plastic, further exacerbating the formation of MPs. It was also verified by the FTIR, 2D-COS, AFM, and Raman spectroscopy analyses. Furthermore, the increased adhesion and roughness caused by oxygen-containing functional groups suggest that the environmental risks of BPs cannot be ignored. Our findings suggest that the testing of micromechanical properties can predicate the formation of the MPs at an early stage.

Sulfated exopolysaccharides from Porphyridium cruentum: A useful strategy to extend the shelf life of minced beef meat

Sulfated exopolysaccharides (EPS) from Porphyridium cruentum strain were extracted and their antioxidant and anti-bacterial potentials were evaluated based on DPPH free radical, ABTS•+ radical cation and DNA nicking assays, and against four foodborne pathogenic bacteria, respectively. They showed also interesting functional, foaming and emulsion properties. Moreover, microbiological and chemical effects of EPS at 0.5, 1 and 2% on refrigerated minced beef meat were undertaken. Chemical analyses revealed that the treated meat underwent significant decrease (P < 0.05) of primary and secondary lipid oxidation. By the end of the storage period, exopolysaccharides at 2% reduced the metmyoglobin and carbonyl group accumulation compared to control samples and were more efficient (P < 0.05) against microflora proliferation. Furthermore, two multivariate exploratory techniques namely Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) were applied successfully to all obtained data describing the main characteristics attributed to refrigerated meat samples. Overall, these findings indicated that EPS from P. cruentum are worthy being developed as functional and bioactive components for the meat industry.

Effect of oxidative modification by reactive oxygen species (ROS) on the aggregation of whey protein concentrate (WPC)

The effects of reactive oxygen species (ROS) on the oxidative aggregation of whey protein concentrate (WPC) were studied. Increasing the oxidation time resulted in the accumulation of carbonyl groups, a decrease in α-helix structures, an increase in disordered structures and the aggregation of secondary structures. The surface hydrophobicity decreased and the zeta potential increased at the beginning of oxidation, indicating that electrostatic interactions were the cause of the noncovalent aggregation of the whey protein. Covalent aggregates were examined in terms of the sulfhydryl/disulfide content (total SH/SS), molecular weight and carbonyls, with the results implying that covalent interactions included protein-protein cross-linking, carbonyl cross-linking, and aromatic side chain cross-linking but excluded the cross-linking of sulfur-containing amino acid residues. The solubility and stability of initial aggregations were high due to flexible structures, while upon further oxidation, the solubility and stability worsened, consist with the soluble protein content and stability index.

Sodium nitroprusside application regulates antioxidant capacity, improves phytopharmaceutical production and essential oil yield of marjoram herb under drought

Nitric oxide (NO) represents a crucial signal particle that plays a pivotal function in plant development, but its roles in improving drought tolerance in marjoram still unknown. The protective roles of foliage-spraying NO (as sodium nitroprusside, SNP; 0, 30, and 60 μM) on inducing drought tolerance in marjoram herb was evaluated by measuring the antioxidant defense system and phytopharmaceutical characteristics in an outdoor pot experiment. Under well-watered, SNP (30 and 60 μM) application significantly enhanced growth, essential oil (EO) yield, up-regulating antioxidant system, and improved water use efficiency (WUE) compared to untreated plants (0 μM SNP). Drought significantly inhibited marjoram growth, WUE, EO yield, catalase, and peroxidase activity as well as herbal extract reducing power and reflective index, whereas oxidative biomarkers (hydrogen peroxide, lipid peroxidation, protein carbonyl group accumulation, and electrolyte leakage) and EO specific gravity were drastically amplified relative to well-watered plants in the absence of SNP. Alternatively, under drought, SNP application mitigated drought induced-oxidative burst and improved WUE that associated with increasing plant biomass and EO assimilation relative to those in drought-affected herbs only. Phytopharmaceuticals of herbal extract (ascorbic acid, total soluble phenol, anthocyanin, and flavonoid) were significantly improved by drought and/or SNP foliar application. The promotive roles of SNP in moderating the depressing effect of drought on marjoram was attributable to up-regulating antioxidant capacity, improving secondary metabolite assimilation, and increasing WUE that accelerate drought tolerance and EO yield as well as improved EO fractions. The existing outcomes open innovative opportunities for obtaining precious natural antioxidants and phytopharmaceuticals by using arid regions.

Інтенсивність вільнорадикальних процесів у плазмі крові щурів за впливу гістаміну і кверцетину

The content of products of lipoperoxidation and oxidative modification of proteins in rat blood plasma under the action of quercetin and histamine was investigated. Quercetin was used at concentrations of 0.1; 0.3; 0.5; 1; 3; 5 mm, and histoma - 0.01; 0.1; 1; 10 μm. It was found that quercetin in the blood plasma of rats causes a slight increase in the content of hydroperoxides and TBA-positive products, except the concentration of 0.5 mm, at which the content of secondary products is reduced and the content of primary remains within the control. Histamine at concentrations of 0.01; 0.1; 1; 10 µM leads to an increase in the content of hydroperoxides and a decrease in the number of TBK-positive products. The combined effect of histamine and quercetin causes a significant increase in primary lipoperoxidation products, whereas TBK-positive lipid peroxidation products decrease. Quercetin in the concentration range of 0.1÷1 mM intensifies the accumulation of carbonyl groups of proteins of basic and neutral nature, while flavonoid at concentrations of 3.5 mM – slows down. Histamine at all tested concentrations leads to an increase in the content of carbonyl groups of proteins, except the concentration of 0.1 μm. Against the background of high concentration histamine, quercetin reduces the intensity of oxidative modification of proteins. The simultaneous action of low concentration histamine and quercetin at a concentration of 0.5 and 5 mm leads to the accumulation of carbonyl groups of proteins of a neutral nature, as well as to the main only when exposed to quercetin at a concentration of 5 mm. According to the analysis of variance, it was found that quercetin has a maximum effect on the accumulation of TBA-positive products and carbonyl groups of proteins of basic character. Histamine is strongly influenced by the accumulation of lipid hydroperoxides. Quercetin at concentrations of 0.1; 0.3; 0.5; 1; 3 mm determines between the indices of free radical processes under study, in the blood plasma of rats, a strong interconnectedness, and a bioflavonoid at a concentration of 5 mm leads to the formation of interconnections of average strength. Histamine at concentrations of 10; 1; 0.1 µM causes a close correlation of the mean strength between the individual indices of free radical oxidation. Histamine at a concentration of 0.01 μm causes a significant increase in the correlation between the parameters of sex and oxidative modification of proteins. The combined effect of quercetin at a concentration of 0.1 mm and histamine at a concentration of 0.01 μm causes a change in the nature of the correlation dependence, which becomes strong between most of the studied parameters.

Development and mining of a database of historic European paper properties

A database of historic paper properties was developed using 729 samples of European origin (1350–1990), analysed for acidity, degree or polymerisation (DP), molecular weight of cellulose, grammage, tensile strength, as well as contents of ash, aluminium, carbonyl groups, rosin, protein, lignin and fibre furnish. Using Spearman’s rank correlation coefficient and principal component analysis, the data were examined with respect to methods of manufacture, as well as chemical stability of paper. Novel patterns emerged related to loss of DP and accumulation of carbonyl groups and acidity with time and the role of lignin and rosin, as well as rate of degradation (k = 10−5 year−1) at room conditions. In-depth understanding of long-term degradation of lignin and rosin is needed to better understand the relationships between composition and degradation of historic paper. This study highlights the importance of mining significant volumes of analytical data, and its variability, obtained from real historic objects.

Synchronised interrelationship between lipid/protein oxidation analysis and sensory attributes in refrigerated minced beef meat formulated with Punica granatum peel extract

SummaryMicrobiological, chemical and sensory effects of pomegranate peel ethanol extract (EE) at 0.1, 0.5 and 1% (w w−1) on refrigerated minced beef meat were undertaken. Chemical analyses revealed that the treated meat underwent significant decrease (P &lt; 0.05) of primary and secondary lipid oxidation. By the end of storage, EE at 1% reduced the MetMb, carbonyl group accumulation and the disappearance of sulphydryl proteins by 56.68, 65.71 and 59.69% respectively, compared with control samples. EE at 1% showed also the highest scores for colour, appearance, odour and overall acceptability (OA) attributes using a 9‐point hedonic scale. Chemometric approaches showed that lipid/protein oxidation analysis, sensory attributes and storage time allowed the samples discrimination. Oxidative stability parameters were equally used to predict OA by linear regression analysis. The reported data provide an approach to strengthen the interpretation of sensory quality and how they are affected by chemical changes in newly formulated meat products.

Enterocin BacFL31 from a Safety Enterococcus faecium FL31: Natural Preservative Agent Used Alone and in Combination with Aqueous Peel Onion (Allium cepa) Extract in Ground Beef Meat Storage.

Safety aspects and probiotic properties of Enterococcus faecium FL31 strain producing an enterocin, named BacFL31 were previously demonstrated. Taking into account its originality, the enterocin BacFL31 was added alone at 200 AU/g or in combination with the aqueous peel onion (Allium cepa) extract (APOE) at 1.56 ± 0.3 mg/mL to ground beef meat. Its biopreservative effect was evaluated by microbiological, physicochemical and sensory analyses during 14 days at 4°C. The APOE was characterized for its phytochemical content: total phenolic (TPC), flavonoids (TFC) and tannins contents (TAC), its antioxidant capacity using the in vitro 1,1-diphenyl-2-picrylhydrazyl (DPPH) and its antilisterial activity. APOE had a high TPC, TFC and TAC respectively with 140 ± 2.05 (mg GAE/g), 35 ± 0.5 (mg QE/g) and 20.6 ± 1.4 (mg CE/g). Equally, APOE showed a potential radical scavenging activity compared to the butylated hydroxytoluene (BHT), with an anti-radical power (ARP) of 46 ± 1.5. During 14 days of storage at 4°C, the combination between APOE and BacFL31 limited the microbial deterioration (P < 0.05), led to a decrease in thiobarbituric acid reactive substances (TBARS) values and slowed down the metmyoglobin (MetMb) and carbonyl group accumulation and delayed the disappearance of sulfphydryl proteins (P < 0.05). The combination was also efficient (P < 0.05) against microflora proliferation, decreased primary and secondary lipid oxidation (P < 0.05), reduced protein oxidation and enhanced significantly (P < 0.05) the sensory attributes. Thus, the enterocin BacFL31 use from a safe Enterococcus faecium combined with APOE as a potential natural preservative to biocontrol ground beef was promising as it was effective at low concentration. The data lay bases for new tests to be carried out in other food matrices.

Relationships Between Textural Modifications, Lipid and Protein Oxidation and Sensory Attributes of Refrigerated Turkey Meat Sausage Treated with Bacteriocin BacTN635

In this study, bacteriocin “BacTN635” was used to maintain quality and extend shelf life of refrigerated turkey meat sausage. Connections between lipid and protein oxidations and instrumentally textural changes using Bayesian networks during storage of turkey meat sausage were also studied. BacTN635 slowed down metmyoglobin and carbonyl group accumulation and delayed the disappearance of sulphydryl proteins (P < 0.05) in turkey meat sausage. This bacteriocin led to a decrease in primary and secondary lipid oxidation (P < 0.05) and enhanced texture characteristics of sausage by reducing hardness (P < 0.05) and controlling the elasticity lose during refrigeration. We have also investigated the correlations between protein and lipid oxidation and instrumentally measured the parameters of turkey meat sausage treated by BacTN635. The developed model, based on Bayesian network techniques, can automatically learn emerging models in data to explain protein and lipid oxidation and texture modification relationships. Equally, sensorial parameters were used for constructing regression models to predict overall acceptability. In conclusion, BacTN635 could be a promising tool for extending the safety and quality of refrigerated turkey meat sausage. This bacteriocin could be a strong candidate for future applications in a wide range of meat products.

Differential physiological and antioxidative responses to drought stress and recovery among four contrasting Argania spinosa ecotypes

ABSTRACTOur study was undertaken to ascertain whether the change of the water status and the activation of superoxide dismutase and their isoenzymes in Argan tree can support edaphic drought tolerance and its recovery under rehydration. An experiment was conducted on four contrasting ecotypes of Argania spinosa plants: two contrasting coastal ecotypes (Admine (Adm) and Rabia (Rab)) and two contrasting inland ecotypes (Aoulouz (Alz) and Lakhssas (Lks)). Drought stress significantly decreased the leaf water potential and stomatal conductance in the four contrasted ecotypes. In terms of biochemical responses, significant accumulation of carbonyl groups, hydrogen peroxide and superoxide radical has been recorded in the leaves of stressed plants reflecting oxidative stress. In parallel, the activities of total superoxide dismutase (SOD) and their isoenzymes Cu/Zn-SOD, Cu/Zn-SOD and Fe-SOD were also found to have increased to scavenging ROS and protecting the cell against induced oxidative stress. The recovery kinetics of A. spinosa, as a response to rehydration, were significant and rapid. According to the traits having the most discriminating power, both inland ecotypes (Lks and Alz) showed a better upregulation of its protective mechanisms compared to coastal ecotypes (Rab and Adm). All these adaptive traits make the inland ecotypes as an elite resource of drought tolerance and might become the new focus of domestication research of argan tree in arid and semi-arid environments.

Performance of a phenolic antioxidant introduced by different procedures into polyethylene containing dispersed fillers

The performance of Irganox 1010 phenolic antioxidant was studied in relation to the procedure of its introduction into a stock of the polymer and dispersed filler powders. Three procedures were used for introducing the antioxidant: the antioxidant was deposited onto the surface of filler (procedure I) or polymer powder (procedure II) particles prior to mixing the components, or it was deposited after mixing the polymer and filler powders (procedure III). We studied mixtures with an inert filler (aluminum oxide) and with fillers active in polymer oxidation and regeneration of the phenolic antioxidant (dispersed zinc, zinc oxide). The film samples for the studies were prepared from powder stocks by hot pressing. The antioxidant performance was evaluated by the induction period of oxidation, which was determined from the time dependences of accumulation of carbonyl groups in the polymer structure.

EFFECT OF APPLE POLYPHENOL ON OXIDATIVE STABILITY OF SLICED COOKED CURED BEEF AND PORK HAMS DURING CHILLED STORAGE

ABSTRACT The effects of apple polyphenol (AP) on color, lipid and protein oxidation in sliced cooked cured hams (SCCHs) made of pork and beef during chilled storage were investigated. SCCH samples with no antioxidant added and those treated with vitamin C were used as controls. The results indicated that addition of 500 ppm AP to the samples significantly inhibited discoloration in pork SCCH, but not in beef; all the AP treatments (with 300, 500 and 1,000 ppm AP) successfully inhibited lipid oxidation of both pork and beef SCCHs with the lipid of pork SCCH more effectively protected than that of beef SCCH. However, no effect on protein oxidation as measured carbonyl group accumulation was observed in both pork and beef SCCH treated with AP at the dose used in this study. AP was generally an effective antioxidant. PRACTICAL APPLICATIONSThe results of the present study indicate that apple polyphenol (AP) may be used to retain the quality of hams in chilled storage and of other meat products in quality storage. However, different concentrations of AP have different effects on stored meat products, and the same concentration of AP may produce different effects on different meat products. Therefore, a test should be performed before application of AP to a specific meat product in meat industry.

Oxidative Stress, Induced by 6-Hydroxydopamine, Reduces Proteasome Activities in PC12 Cells: Implications for the Pathogenesis of Parkinson's Disease

Mutations in familial Parkinson's disease (PD) have been associated with the failure of protein degradation through the ubiquitin-proteasome system (UPS). Impairment of proteasome function has also been suggested to play a role in the pathogenesis of sporadic PD. We examined the proteasome activity in PC12 cells treated with 6-hydroxydopamine (6-OHDA), the dopamine synthetic derivate used in models of PD. We found that 6-OHDA treatment increased protein oxidation, as indicated by carbonyl group accumulation, and increased caspase-3 activity. In addition, there was an increase in trypsin-, chymotrypsin-, and postacidic-like proteasome activities in cells treated with 10-100 microM 6-OHDA, whereas higher doses caused a marked decline. 6-OHDA exposure also increased mRNA expression of the 19S regulatory subunit in a dose-dependent manner, whereas the expression of 20S- and 11S-subunit mRNAs did not change. Administration of the antioxidant N-acetylcysteine to 6-OHDA-treated cells prevented the alteration in proteasome functions. Moreover, reduction in cell viability owing to administration of proteasome inhibitor MG132 or lactacystin was partially prevented by the endogenous antioxidant-reduced glutathione. In conclusion, our data indicate that mild oxidative stress elevates proteasome activity in response to increase in protein damage. Severe oxidative insult might cause UPS failure, which leads to protein aggregation and cell death. Moreover, in the case of UPS inhibition or failure, the blockade of physiological reactive oxygen species production during normal aerobic metabolism is enough to ameliorate cell viability. Control of protein clearance by potent, brain-penetrating antioxidants might act to slow down the progression of PD.

Relationship between thickness of polymer films and their oxidation on copper substrate

This research was undertaken to understand how the thickness of polyethylene films oxidized on a copper substrate influences the accumulation of carbonyl groups (measured by an IR-spectroscopy technique) and of metal from the substrate (determined by polarography analysis). It was found that the whole polymer became inhibited by the time the copper stopped transferring into the specimen. Plots of copper concentration versus film thickness have two thickness sections: section I is found between 0 and 70 μm and section II between 80 and 170 μm. Between these two sections the metal concentration varies drastically. This situation can be explained by two schemes by which PE changes to inhibited condition. According to Scheme I (for section I, short oxidation time) this change has only one step: the inhibited layer gradually becomes thicker beginning from the interface and moving toward the outer surface. The second scheme (for section II) shows that the polymer becomes inhibited in two steps. It is typical of thicker films. In this case the oxidation process shifts and localizes in the outer surface because of longer treatment. As a result, transfer of metal and formation of an inhibited layer are interrupted for some time. The metal accumulation in the film only resumes when low-molecular-weight products of thermooxidative degradation—formed in the specimen outer surface—enter the region of adhesional contact. A so-called second transfer stage for metal is realized during which the whole polymer becomes inhibited. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 671–675, 2003

Crosslinking in polyethylene films by oxidation on metals

AbstractThe kinetics of oxidative conversions, such as accumulation of carbonyl groups and crosslinks in polyethylene films that were subjected to oxidation on metallic substrates differing in activity (e.g., copper and aluminum), was investigated. It was learned that the rate and ultimate level of crosslinking in the polymer oxidized on copper were higher than those on aluminum. It is believed that this situation is related to the catalytic effect of the copper compounds transferred into the polymer volume at the regimes of contact oxidation. The amounts of transferred metal were approximately equal in both the soluble and the insoluble fractions of the polymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2776–2783, 2002

Carnosine, the anti-ageing, anti-oxidant dipeptide, may react with protein carbonyl groups

Carnosine (β-alanyl- l-histidine) is a physiological dipeptide which can delay ageing and rejuvenate senescent cultured human fibroblasts. Carnosine's anti-oxidant, free radical- and metal ion-scavenging activities cannot adequately explain these effects. Previous studies showed that carnosine reacts with small carbonyl compounds (aldehydes and ketones) and protects macromolecules against their cross-linking actions. Ageing is associated with accumulation of carbonyl groups on proteins. We consider here whether carnosine reacts with protein carbonyl groups. Our evidence indicates that carnosine can react non-enzymically with protein carbonyl groups, a process termed ‘carnosinylation’. We propose that similar reactions could occur in cultured fibroblasts and in vivo. A preliminary experiment suggesting that carnosine is effective in vivo is presented; it suppressed diabetes-associated increase in blood pressure in fructose-fed rats, an observation consistent with carnosine's anti-glycating actions. We speculate that: (i) carnosine's apparent anti-ageing actions result, partly, from its ability to react with carbonyl groups on glycated/oxidised proteins and other molecules; (ii) this reaction, termed ‘carnosinylation,’ inhibits cross-linking of glycoxidised proteins to normal macromolecules; and (iii) carnosinylation could affect the fate of glycoxidised polypeptides.

Exercise Preconditioning against Hydrogen Peroxide-Induced Oxidative Damage in Proteins of Rat Myocardium

Both regular physical exercise and low levels of H2O2 administration result in increased resistance to oxidative stress. We measured the accumulation of reactive carbonyl derivatives and the activities of proteasome complex and DT–diaphorase in cardiac muscle of trained and untrained rats after chronic i.p. administration of 1 ml t-butyl H2O2 (1 mmol/kg for 3 weeks every second day). Twenty-four rats were randomly assigned to a control group administered with saline, control administered with H2O2, and exercised administered either saline or H2O2. The activity of DT–diaphorase significantly increased in H2O2 administered and exercised groups, indicating that an increase in H2O2 levels stimulate the activity of this enzyme. The cardiac muscle of H2O2 administered nonexercised animals accumulated significantly more carbonyl than control group (P < 0.05). The exercise and H2O2 administration resulted in less oxidatively modified protein than found in nonexercised groups (P < 0.05). The peptide-like activity of proteasome complex was induced by the treatment of H2O2 and exercise and exercise potentiate the effect of H2O2. On the other hand, the chymotrypsin-like and trypsin-like activities were stimulated only by physical training and H2O2 administration. The data suggest that chronic administration of H2O2 after exercise training decreases the accumulation of carbonyl groups below the steady-state level and induces the activity of proteasome and DT–diaphorase. Hence, the stimulating effect of physical exercise on free radical generation is an important phenomenon of the exercise-induced adaptation process since it increases resistance to oxidative stress. Regular exercise training is a valuable physiological means of preconditioning the myocardium to prolonged oxidative stress.

Thermooxidative degradation of polyolefins in the solid state—4: Heterogeneous oxidation kinetics

Chemical kinetics is an ideal tool to examine reactions in solution. It cannot be applied to the phenomena in solid polymers, especially semi-crystalline polymers, without considerable adjustments. This derives directly from the corresponding polymer model, amorphous domains separated by crystallites. The elementary chemical reactions usually occur in the amorphous domains only. It is the kinetics in these amorphous domains which governs the overall chemistry in the polymer. The elementary reaction kinetics known from solution chemistry need to be adapted to these domains. The main point in this respect is to take into account the fact that for two functional groups on a polymer chain to react with one another, either they must be close enough spatially if they are both part of a high molecular mass fragment or at least one of them must be on a low molecular mass fragment so that it is able to diffuse more or less in the solid matrix. Hence, for example, bimolecular hydroperoxide decomposition can be restricted to a large extent to the associated hydroperoxide groups present in solid polyolefins. The problem of the transposition of the kinetics in the amorphous domains to the kinetics in the observation volume, the only kinetics accessible experimentally, is more complicated. It is usually not possible to transpose directly the experimental macroscopic kinetics to the kinetics of the amorphous domains or vice versa. It is the expression of the kinetic law which determines the possibility or impossibility of direct transposition. Usually, the heterogeneous nature of the polymer has to be taken into account for the passage back and forth. Then there are two main possibilities to be envisaged. The first possibility uses the heterogeneous oxidation model with its mathematical expression. Then the rate law in the amorphous domain can be transformed into the rate law for the observation volume so that the elementary law can be checked. The second possibility envisages the kinetics exclusively in the amorphous domains and calculates it for the observation volume through the use of the spreading equation derived for the heterogeneous oxidation model. This also allows for a check on the agreement with the experimental data and, therefore, the assumptions concerning the elementary kinetics in the amorphous domains. The model permits the interpretation of the experimental kinetics for associated hydroperoxides as well as for free hydroperoxides discussed previously. It also yields a good fit for the accumulation of carbonyl groups on thermal oxidation of PE-LD. Possible improvements are discussed.

Photocatalytic degradation of polyethylene film by incorporated extra-fine particles of titanium dioxide

Low-density and high-density polyethylene (PE) films (thickness 50–170 μm) containing 0·125–1·0 wt% of titanium dioxide (TiO 2) particles were photoirradiated by a high-pressure mercury arc over a period up to 200 h at room temperature in air. During photoirradiation, the transparent film (transmittance of the unirradiated film with 0·5 wt% of TiO 2 was >65%) turned white together with decreases in weight and mechanical properties, e.g. elongation at break and tensile strength. This occurred after characteristic induction periods, while linear accumulation of carbonyl groups in the film was observed just after the commencement of photoirradiation. Carbon dioxide and carbon monoxide were detected as gaseous products. X-ray diffraction analyses revealed a decrease in the proportion of amorphous region in PE during the photocatalytic degradation. Increase in the amount of TiO 2 or a rise in termperature reduced P i . Transmission electron microscopic measurement revealed that voids around the TiO 2 particles, which are predominantly located in the amorphous region of PE rather than the crystalline region, were produced by TiO 2-photocatalytic oxidation, causing the whitening and the decrease of mechanical strength. Control experiments revealed that this type of degradation proceeds only in the copresence of extra-fine particles of TiO 2, molecular oxygen, and photoirradiation.

Structure of photooxidized polypropylene fibres

Photooxidative degradation of polypropylene fibres which differ in the degree of orientation was studied. IR spectroscopy revealed that in the presence of light stabilizers the induction period of oxidation was prolonged and the accumulation of carbonyl groups in the fibre was slowed down. In highly oriented fibres the lowered mobility of chain segments in the amorphous regions after the transition from the spherulitic to fabrillar morphology also showed a stabilizing effect.