Acquired biodegradability of polyethylenes containing pro-oxidant additives

Biodegrability of high density polyethylene film (HDPE) and low density polyethylene film (LDPE) both containing a balance of antioxidants and pro-oxidants was studied with defined microbial strains particularly with Rhodococcus rhodochrous and Nocardia asteroides in mineral medium. After an abiotic pre-treatment consisting of photooxidation and thermo-oxidation corresponding to about 3 years of outdoor weathering the samples were inoculated, incubated up to 200 days and during the period their metabolic activities were followed by measuring adenosine triphosphate content. Simultaneously the cultures were also monitored by optical microscopy and FTIR spectroscopy. The first initial phase of fast growth caused by the presence of low molecular extractable compounds was followed by a long period of stabilized metabolic activity suggesting that microorganisms continued to gain energy from the substrate but evidently at a much slower rate. Complementary analysis performed at the end of incubation revealed that during the experiment time biodegradation processes probably affected surface layer of materials only.     

Comparison of the biodegradability of various polyethylene films containing pro-oxidant additives

The biodegradability of high density polyethylene films (HDPE), low density polyethylene films (LDPE) and linear low density polyethylene films (LLDPE) with a balanced content of antioxidants and pro-oxidants (manganese + iron or manganese + iron + cobalt) was studied. Abiotic pre-treatment consisting of photooxidation and thermal oxidation corresponding to about three years of outdoor weathering (including 3-4 months of exposure to daylight) was monitored by FTIR and SEC measurements. The oxidized samples were then inoculated with the strain Rhodococcus rhodochrous in mineral medium, and incubated up to 180 days. The metabolic activity of the bacteria was assessed by measuring adenosine triphosphate content (ATP) and the viability of the cells. Complementary experiments were performed by ¹H NMR spectroscopy to monitor the biodegradation of soluble molecules excreted from the polymer in the incubation medium. Finally SEM was used to visualize the formation of a biofilm at the surface of the polymer. Three samples among the 12 tested were investigated in compost and soil environments. The results show that the main factor controlling the biodegradability of the polyethylene films is the nature of the pro-oxidant additive and to a lesser extent that of the matrix. Except for the samples containing very high content of cobalt additive, the various polymer films were used as substrates by the bacteria.     

Degradation of abiotically aged LDPE films containing pro-oxidant by bacterial consortium

The degradation of abiotically aged low density polyethylene (LDPE) films containing trace quantities of a representative pro-oxidant (cobalt stearate) was investigated in the presence of well defined enriched microbial strains namely, Bacillus pumilus, Bacillus halodenitrificans and Bacillus cereus in Basal salt medium. The films were initially subjected to an abiotic treatment comprising UV-B irradiation, and subsequently inoculated with the bacterial strains. The degradation in the polymeric chain was monitored by changes in the mechanical, morphological, structural and thermal properties. The abiotic treatment led to the formation of extractable oxygenated compounds as well as unoxidised low molecular weight hydrocarbons, which was confirmed by GC-MS studies. These were utilized by the bacterial consortium in the subsequent biotic phase and led to a mass loss of the polymer (8.4 ± 1.37%), which was also accompanied by an increase in the bacterial count. A decrease in the surface tension of the cell free medium was observed, which indicates that the bacterial consortium produced extracellular surface active molecules in order to enhance the bioavailability of the polymeric fixed carbon. The spectroscopic investigations reveal that the bacteria preferentially consume the oxygenated products leading to a decrease in the Carbonyl Index (CI), which in turn leads to an increase in the initial decomposition temperature as observed in the TGA traces. The morphological investigations reveal a biofilm formation on the surface, which was found to be scattered in certain regions and not uniform on the polymeric surface.     

Photodegradation of polypropylene/polystyrene blends: Styrene-butadiene-styrene compatibilisation effect

The mutual influence between the PP/PS polymer blend components during UV photodegradation was studied. Polypropylene (PP) and polystyrene (PS) have different photodegradation mechanisms, due to the larger UV absorption of polystyrene and formation of more stable tertiary carbon radicals. To compare the stabilities the kinetics of carbonyl formation was measured in different blend compositions. The results show that polystyrene presented a faster carbonyl formation than polypropylene, while the blends display faster kinetics than the isolated components. The kinetics of carbonyl formation of the blends was a function of polypropylene content. This result is unexpected if one considers the behaviour of each component alone. The kinetics and mechanism of UV degradation can be only explained taking into account the interaction between the blend components. PS absorbs UV light and energy is transferred to PP, which produces more reactive tertiary carbon free radicals. The effect of the interaction between the domains is enhanced when a compatibiliser is used, corroborating the hypothesis of energy transfer.     

Aerobic biodegradation of calcium carbonate filled polyethylene film containing pro-oxidant additives

Two low density polyethylene films, which contained pro-oxidant additives, where investigated, one of them containing micro-milled calcium carbonate filler. Both materials were subjected to controlled thermal oxidation, the oxidation was obviously retarded in the filler-containing sample. Following this, the biodegradability of samples pre-oxidized for 40 and 80 days was investigated. The levels of carbon mineralization reached 13% and 16% for the 40 and 80 days pre-oxidized polyethylene containing filler, respectively, after approximately 16 months in a soil environment at 25 °C, and both types of sample were mineralized to about 19% in compost environment at 58 °C during the same period. The sample not containing filler was mineralized to about 7% in soil after 13 months, and about 23%, after 8 months in compost. Scanning electron microscopy revealed dense colonization of the sample surfaces in both soil and compost. The data presented here provide clear quantitative evidence that part of the polyethylene material was biodegraded.     

Characterization of oxidation progress by chemiluminescence: A study of polyethylene with pro-oxidant additives

Non-isothermal chemiluminescence measurements in nitrogen and isothermal measurements in oxygen were used for the evaluation of degradation in pre-oxidized polyethylene either pure or containing Mn-based pro-oxidant additives. The results were compared with infrared spectroscopy data. Chemiluminescence measurements of pure polyethylene and polyethylene with additive made it possible to calculate the set of rate constants, based on the Bolland-Gee oxidation scheme. The oxidation rate constants of polyethylene with additive were significantly higher, while the activation energy of the process appeared lower (65 kJ mol⁻¹), than those of pure polyethylene. The method provides an access to study oxidation processes during the induction period of oxidation when infrared spectroscopy cannot provide sufficient information.     

Abiotic and biotic degradation of oxo-biodegradable polyethylenes

Conventional polymeric materials accumulate in the environment due to their low biodegradability. However, an increase in the biodegradation rate of these polymers may be obtained with the addition of pro-degrading substances. This study aimed to evaluate abiotic and biotic degradation of polyethylenes (PEs) using plastic bags of high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE) formulated with pro-oxidant additives as test materials. These packaging materials were exposed to natural weathering and periodically analyzed with respect to changes in mechanical and structural properties. After a year of exposure, residue samples of the bags were incubated in substrates (compost of urban solid waste, perlite and soil) at 58 °C and at 50% humidity. The biodegradation of the materials was estimated by their mineralization to CO₂. The molar mass of the pro-oxidant-activated PE decreased and oxygen incorporation into the chains increased significantly during natural weathering. These samples showed a mineralization level of 12.4% after three months of incubation with compost. Higher extents of mineralization were obtained for saturated humidity than for natural humidity. The growth of fungi of the genera Aspergillus and Penicillium was observed on PE films containing pro-oxidant additives exposed to natural weathering for one year or longer. Conventional PE films exposed to natural weathering showed small biodegradation.     

Photodegradation of rhodamine B over semiconductor supported gold nanoparticles: The effect of semiconductor support identity

Rhodamine B (RB) is a toxic dye used extensively in textile industry, which must be remediated before its drainage to environment. In the present study, supported gold nanoparticles on commercially available titania and zincite were successfully prepared and then their activity on the photodegradation of RB under UV A light irradiation was evaluated. The synthesized photocatalysts were characterized by ICP, BET, XRD, TEM and EDX. Kinetic results showed that Au/TiO₂ was a photocatalyst inferior to Au/ZnO. This observation could be attributed to the strong reflection of UV irradiation by gold nanoparticles over TiO₂ support.     

Investigating the role of metal oxidation state on the degradation behaviour of LDPE

Transition metal stearates have been reported to act as effective pro-oxidants for polyethylene, even at trace concentrations. This study is an attempt to investigate the effect of the oxidation state of a metal on its pro-oxidant nature. Three metal stearates, namely manganese, iron and cobalt, in their common oxidation states (+2 and +3), were synthesized and their effect on the photo-oxidative and thermo-oxidative degradation of low-density polyethylene (LDPE) films has been investigated. Films of 70 ± 5 μ were prepared by film blowing technique, exposed to xenon arc weatherometer and air oven at 70 °C for extended time periods. The chemical and physical changes induced by this exposure were followed by monitoring the changes in mechanical properties (tensile strength and elongation at break), carbonyl index (CI), molecular weight (viscometry), MFI, density, and thermal properties. The results were analysed to explain the structural and chemical modifications taking place in the polymeric matrix as a result of aging. The studies reveal that the oxidation state of the metal did not affect its ability to initiate and accelerate degradation. The thermo-oxidative degradation in the presence of metal stearate was found to follow the order: cobalt > manganese > iron. However, iron stearate was capable of initiating photo-oxidative degradation to the same extent as cobalt and manganese, in the concentration range investigated. The results indicate that iron is primarily an effective photo-oxidant, while cobalt and manganese can act both as photo-oxidant as well as thermo-oxidant.     

Effect of environment on the degradation of starch and pro-oxidant blended polyolefins

The aim of this study was to understand the rate of degradation of commercial pro-oxidant blended and starch blended High Density Polyethylene (HDPE), pro-oxidant blended Low Density Polyethylene (LDPE), and starch blended polypropylene in three different environments, namely under direct sunlight, buried in soil and immersed in marine waters for a period of 150 days. The bio-fouling parameters were also monitored in the case of polymers deployed in sea water. Exposure to sunlight showed highest weight loss (>10%) and samples buried in soil showed the lowest (∼1%). Pro-oxidant blended HDPE showed higher weight loss when compared to starch blended (22.7 as against 11%). Scanning electron microscopy revealed surface deterioration and decrease in contact angle indicated reduction in surface hydrophobicity. Increase in the carbonyl and hydroxyl groups in the infra-red spectrum of the exposed samples suggested abiotic degradation. Starch blended PP exposed to sunlight showed the highest thermo gravimetric weight loss (63.8%) followed by the same polymer buried in soil (46.1%).     

Post-irradiation oxidation of different polyethylenes

The radiation-induced oxidative degradation of polyethylenes (PEs) with different degrees of crystallinity was characterized after electron-beam irradiation and during storage at room temperature.UHMWPE, HDPE, LDPE, LLDPE and an ethylene-octene copolymer (Engage) were e-beam irradiated to 30 or 60 kGy in vacuum or in air and stored at room temperature in air. EPR spectroscopy was used to investigate macro-radicals produced during irradiation and their post-irradiation changes. FTIR spectroscopy was used to monitor changes in the polymer structure, induced by irradiation, and to follow post-irradiation oxidation.We found that the crystallinity and the size of the crystalline lamellae, in particular, play a major role on the post-irradiation effects. The low-crystallinity polyethylenes showed no oxidation or oxidation only to a small extent, even when irradiated and stored in air. On the contrary, development of post-irradiation oxidation was observed in HDPE and UHMWPE. We attribute these results to a different reactivity of the macro-alkyl radicals formed upon irradiation in the amorphous or in the crystalline phase. While the radicals formed in the amorphous phase decay in short time, the migration time of the radicals trapped in the crystalline phase to the amorphous one is a key factor, governing the oxidation process.     

Mn2Al-LDH- and Co2Al-LDH-stearate as photodegradants for LDPE film

The layered double hydroxides (LDH) Mn₂Al-LDH-stearate and Co₂Al-LDH-stearate were prepared by a surfactant-assisted intercalation of the corresponding precursor LDH-CO₃ forms. These compounds were evaluated as potential photodegradant additives in low density polyethylene films with a thickness of ca. 40 μm. They were incorporated into blown polyethylene films via a 10% masterbatch. The films were subjected to accelerated ageing in a QUV weatherometer. The machine was fitted with A320 lamps and operated on a dry cycle at 63 °C and an irradiance of 0.67 W/m². It was found that 100 h of QUV exposure was sufficient to cause mechanical embrittlement of films containing as little as 0.1% of either active additive.     

Photodegradation of some ethylene-norbornene random copolymers

We investigated the photodegradation of specific ethylene-norbornene random copolymers (ENRC) - a group of substances which has been attracting much attention in recent years. ENRCs having various contents of norbornene were studied. After irradiation, each sample was separated into chloroform-insoluble and soluble portions. The chloroform-insoluble portion was weighed and analyzed by FTIR. The chloroform-soluble portion was analyzed by size elimination chromatography (SEC), FTIR and ¹H NMR. The yield of the chloroform-insoluble portion increased with increased irradiation time. Formyl, formate, acyl, hydroxy groups and a carbon-carbon double bond were formed by photo-irradiation. Apparently, hydrogen atoms bound to the tertiary and secondary carbon atom in the parent ENRCs are abstracted. From these results, it is suggested that auto-oxidation results from photo-irradiation of the ENRCs. In ENRCs with similar stereoregularity, the degree of photodegradation increases with increasing norbornene content.     

Photodegradation of polycaprolactone/poly(vinyl chloride) blend

The photodegradation of a 1:1 w/w blend of polycaprolactone and poly(vinyl chloride) has been studied by following carbon dioxide emission during UV exposure. Similar measurements were performed for polycaprolactone and poly(vinyl chloride) homopolymers which were prepared and irradiated in the same way. It was found that the blend gave lower CO₂ emission than either of the two homopolymers, indicating that the interaction of the two components in the blend provided a beneficial reduction of photodegradation. It is therefore deduced that the detailed morphological characteristics of the blend have a controlling influence over the photo-oxidation.     

Photodegradation of bisphenol A polycarbonate

When bisphenol A polycarbonate is subjected to weathering conditions this polymer shows two different degradation mechanisms depending on the used irradiation wavelengths, i.e. photo-oxidation and photo-Fries rearrangement. The relative importance of these mechanisms in outdoor exposure conditions is still unknown. In this study bisphenol A polycarbonate is exposed to simulated weathering conditions. Different analysing techniques show that photo-oxidation is the most dominant degradation reaction. However, fluorescence spectroscopy shows that small amounts of photo-Fries rearrangement products are formed. With model compounds blended in polypropylene it is shown that the photo-Fries reaction increases the photo-oxidation rate, thus in PP the photo-Fries reaction can proceed through radical intermediates. However, this is not the case in PC, ageing at condition causing an increased photo-Fries reaction rate did not result in a higher oxidation rate. This implies that in PC the photo-Fries reaction does not initiate its oxidation and thus does not proceed through radicals.     

Photodegradation study of some triazine-type herbicides

Triazines are amongst the most widely used herbicides. Since triazines can be found in many environmental compartments, their fate in ecosystems and the characterization of their degradation pathways in the environment are to be determined. In this paper we report on a study intended to investigate the photodegradation of some triazine-type herbicides: atrazine, cyanazine, terbuthylazine and terbutryn. The rate of photodegradation process was determined, and degradation schemes were outlined for the compounds studied. Moreover, experiments with different degrading energies were carried out in order to gain information about the effect of total degrading energy on the photodegradation process. The most significant processes of photodegradation of triazines are the partial or complete loss of side-chains, or rather the substitution of the heteroatom-containing side-chain to hydroxyl-group. Besides consecutive processes, loss of the different side-chains takes place parallely also, thus, different metabolites will be formed having mixed side-chains, until the cyanuric acid and 2-amino-4,6-dihydroxy-1,3,5-s-triazine are formed by losing all the side-chains. The presence of the dimer products could be detected during the degradation of all triazines. This proves the radical character of processes occurring during the photodegradation. Increasing the degradation energy (15 to 125 W) has raised the degradation rate by 2-5, and the chlorine containing metabolite—which was still present in the completely degraded mixture during the low-energy experiments—has completely disappeared from the mixture, thus, the increased degrading energy is favorable to the formation of less dangerous, nature identical metabolites.     

Photodegradation Behavior of Polycaprolactone-Poly(ethylene glycol) Block Copolymer

Polycaprolactone-poly(ethyleneglycol)(PCE)blockcopolymerisabiodegradablepolymer.ThebiodegradationcharacterisationinvitFoandinvivoofthePCEwasreported"'.ItwasfoundthatthedegradationrateofthePCEwasincreasedwithincreasingpoly(ethyleneglycol)content,temperature,acidityandalkalinityanditwasacceleratedbythepresenceofenzyme.Thefastestdegradationratewasobservedinthephysiologicalconditionofthesamplebeingimplantedinthebodyofanimals.SoPCEcopolymerpossessesagoodprospecttobebio-medicalmaterials3.Mostp…     

Photodegradation of isotactic poly(1-butene): Multiscale characterization

The effect of photodegradation in isotactic poly(1-butene) (PB-1) have been investigated using rheology, differential scanning calorimetry and infrared spectroscopy. Two commercially available grades of PB-1 with different average molecular weight were chosen. Specimens prepared by compression moulding were UV irradiated in the interval from 0 to 70 h. UV-induced changes in molecular structure have been followed by evolution of rheological properties, thermal properties and degradation by-products. Thermal analysis showed significant changes in crystallization behaviour influencing morphology and resulting thermal properties. Moreover it has been confirmed that the degradation significantly retards the phase transformation. Rheological measurement has been found as an effective method for determination of early stages of photodegradation of PB-1.     

Photodegradation of Selected Organophosphorus Insecticides Under Sunlight in Different Natural Waters and Soils

In this work photodegradation of four organophosphorus insecticides (ethyl-parathion, methyl-parathion, fenitrothion, fenthion) in different natural waters and soils was studied under sunlight. The origin of the waters was from the region of Ioannina (underground, lake, and river water) and from Preveza (sea water) in Northern-West Greece. The soils used had different percentages of organic matter (0.9-3.5%) and their characterization were SCL, CL, and SL respectively. The photodegradation kinetics of these insecticides were followed by GC-FTD. The identification of the photodegradation by-products was made by using GC-MS. The half-lives of the organophosphorus insecticides vary from 0.4 to 35.4 days in natural waters and from 3.4 to 21.3 days in soils. The humic substances and the other components of these environmental matrices seem to influence the degradation kinetics. The use of GC-MS allowed the identification of some important photodegradation by-products such as: fenthion sulfone, fenthion sulfoxide, fenoxon, 4-methylthio-3,5-dimethyl phenol, O , O , O -triethyl phosphorothioate, paraoxon, 4-nitrophenol, aminoparathion.     

Photochemical-chemiluminometric determination of aldicarb in a fully automated multicommutation based flow-assembly

A sensitive and fully automated method for determination of aldicarb in technical formulations (Temik) and mineral waters is proposed. The automation of the flow-assembly is based on the multicommutation approach, which uses a set of solenoid valves acting as independent switchers. The operating cycle for obtaining a typical analytical transient signal can be easily programmed by means of a home-made software running in the Windows environment. The manifold is provided with a photoreactor consisting of a 150 cm long × 0.8 mm i.d. piece of PTFE tubing coiled around a 20 W low-pressure mercury lamp. The determination of aldicarb is performed on the basis of the iron(III) catalytic mineralization of the pesticide by UV irradiation (150 s), and the chemiluminescent (CL) behavior of the photodegradated pesticide in presence of potassium permanganate and quinine sulphate as sensitizer. UV irradiation of aldicarb turns the very week chemiluminescent pesticide into a strongly chemiluminescent photoproduct. The method is linear over the range 2.2-100.0 μg l⁻¹ of aldicarb; the limit of detection is 0.069 μg l⁻¹; the reproducibility (as the R.S.D. of 20 peaks of a 24 μg l⁻¹ solution) is 3.7% and the sample throughput is 17 h⁻¹.