Evaluation of the rate of abiotic and biotic degradation of oxo-degradable polyethylene

The recent introduction of oxo-degradable additive in the Argentinean market has motivated the study of the effect of abiotic (temperature and ultraviolet (UV) radiation) and biotic (aerobic in compost) degradation on the structure and mechanical behavior of films of polyethylene (PE) and oxo-degradable polyethylene (PE+AD).Physico-chemical tests show that the failure strain and the carbonyl index of degraded PE and PE+AD samples depend on the UV irradiation dose. Furthermore, the additive plays a crucial role in the degradation and subsequent decay of the molecular weight.It was observed that, for the same dose, the most deteriorated material was the one exposed to the lowest irradiance, emphasizing the importance of the time of exposure to UV radiation. The ratio between the irradiance and the critical dose, is a characteristic time associated to the sharp decay on the failure strain. The critical dose decreases significantly when increasing the temperature of the photo-degradation assay.PE is more susceptible to thermal degradation than PE+AD; the latter only degrades under thermal aging at the highest temperature.Initially biotic degradation in compost showed an increasing production of carbon dioxide for both previously UV-degraded and untreated PE+AD. It is also remarkable that UV-degraded samples of PE and PE+AD with differences in their abiotic degradation level, reached the same final biotic degradation level. It was observed that although the additive increased the abiotic photodegradation, the molecular weight reduction in compost was not enough to reach the maximum biotic degradation level established by international standards for biodegradable materials.     

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.     

The influence of biotic and abiotic factors on the rate of degradation of poly(lactic) acid (PLA) coupons buried in compost and soil

Poly(lactic) acid (PLA) is a compostable biopolymer and has been commercialised for the for the manufacture of short-shelf life products. As a result, increasing amounts of PLA are entering waste management systems and the environment; however, the degradation mechanism is unclear. While hydrolysis of the polymer occurs abiotically at elevated temperature in the presence of water, potential catalytic role for microbes in this process is yet to be established. In this study, we examined the degradation of PLA coupons from commercial packaging at a range of temperatures (25°, 37°, 45°, 50° and 55 °C) in soil and compost and compared with the degradation rates in sterile aqueous conditions by measuring loss of tensile strength and molecular weight (Mw). In addition, in order to assess the possible influence of abiotic soluble factors in compost and soil on degradation of PLA, degradation rates in microorganism-rich compost and soil were compared with sterile compost and soil extract at 50 °C. Temperature was determined to be the key parameter in PLA degradation and degradation rates in microorganism-rich compost and soil were faster than in sterile water at temperatures 45° and 50 °C determined by tensile strength and Mw loss. Furthermore, all tensile strength was lost faster after 30 and 36 days in microorganism-rich compost and soil, respectively, than in sterile compost and soil extract, 57 and 54 days, respectively at 50 °C. Significantly more Mw, 68% and 64%, was lost in compost and soil, respectively than in compost extract, Mw, 53%; and in soil extract, 57%. Therefore, degradation rates were faster in microorganism-rich compost and soil than in sterile compost and soil extract, which contained the abiotic soluble factors of compost and soil at 50 °C. These comparative studies support a direct role for microorganisms in PLA degradation at elevated temperatures in humid environments. No change in tensile strength or Mw was observed either 25° or 37 °C after 1 year suggesting that accumulation of PLA in the environment may cause future pollution issues.     

A scanning electron and atomic force microscopy study of the surface morphology and composition of CsI films as affected by evaporation rate and humid-air exposure.

Evaporation rate and subsequent exposure to humid air affect the surface morphology and composition of cesium iodide (CsI) films and, in turn, their photoemissive efficiency when used as photocathodes. The surface morphology and elemental composition of 300-nm-thick CsI films grown at two different rates (1 nm/s and 0.04 nm/s), both freshly evaporated and after 24-h exposure to humid air were investigated by means of atomic force microscopy and scanning electron microscopy/electron diffraction spectroscopy. The CsI film freshly evaporated at a slow rate exhibited a granular surface presenting circular holes or craters where the CsI material was moved from the center to the boundaries. After 24-h exposure to humid air, this film coalesced in large grain showing a marked increase of surface roughness. Conversely, the CsI film grown at a fast rate mostly retained its original surface uniformity and homogeneity with no presence of holes and craters after 24-h exposure to humid air. Further, surface roughness and average peak height decreased, but the surface coalesced in large grains spaced by small fractures where the CsI coverage was almost lost. In conclusion, the films grown at a fast evaporation rate were affected by 24-h exposure to humid air less than those grown at a slow rate, and are thus expected to possess a greater long-term stability.     

Properties of crosslinked polylactides (PLLA & PDLA) by radiation and its biodegradability

Crosslinked materials derived from poly(lactide) (PLA) have been produced by radiation modification in the presence of a suitable crosslinker (triallyl isocyanurate) (TAIC). The crosslinking structure introduced in PLA films has not only much improved the heat stability but also their mechanical properties. The properties of crosslinked samples are governed by crosslinking density and these improvement seemed to increase with radiation dose. This implied that the three dimensional networks have been introduced in material by radiation and the crosslinking density depended on the structure and length of PLA chains. Biodegradability of PLA was also determined by an enzymatic degradation test and burying in compost at 55 °C. Differing with PLLA, PDLA was insignificantly degraded by proteinase K. The degradation rate of PLA in compost was postponed with the introduction of crosslinks.     

TiO2光催化降解聚乙烯薄膜

TiO2光催化降解聚乙烯薄膜;纳米TiO2;固相光催化;聚乙烯塑料;降解     

Comparative Studies on Degradation of Methyl Orange by Nanostructured Zinc and Zinc Oxide Films

Nanostructured zinc and zinc oxide films were prepared by magnetron sputtering processes and succeeded air annealing treatments. Comparison of reductive degradation rate of methyl orange (MO) by zinc films and photocatalytic degradation rate of MO by zinc oxide films was carried out. Both reductive degradation and photocatalytic degradation process of MO by zinc and zinc oxide films can be described by first order kinetic model. It was found that although MO liquid was most quickly decolorized by metallic zinc films, the mineraliza-tion of MO was not thorough. Observation of extra ultraviolet absorption peaks indicated the formation of aromatic intermediates. On the other hand, although the photocatalytic degradation rate of MO liquid by ZnO films was only as about 1/4 large as the reductive degradation rate by zinc films, no signs of aromatic intermediates were found. Moreover, it was found that partially oxidized zinc oxide film showed higher photocatalytic efficiency than the totally oxidized ZnO films. Synergy effect between zinc and zinc oxide phase in the partially oxidized films was considered to be responsible for the higher photocatalytic efficiency.     

Biodegradation of poly(lactic acid) and its nanocomposites

PLA nanocomposites based on organically modified montmorillonites at 5% w/w loading were prepared by melt blending using an internal mixer and then degraded in a commercial compost. The addition of nanoclays was found to increase the PLA degradation rate, especially for the highest dispersed clay in the polymer matrix. Biodegradation by microorganisms isolated from the compost showed the bacterium Bacillus licheniformis as one of the responsible for PLA biodegradation in compost. It was also found that clays can influence the polymer bacterial degradation depending on their chemical structure and affinity of the bacterium towards the clay.     

Surface modification of polymers. IV. UV initiated degradation of polymers with stabilizers grafted onto the surface

Polypropylene (PP), Polyethylene (PE), and polystyrene (PS) films were grafted with glycidylmethacrylate in thin surface layers. To the oxiran groups thus grafted onto the surface three UV stabilizers were attached, 4-amino-2,2,6,6-tetramethylpiperidine (AP), 2,4-dihydroxybenzophenone (DHBP), and phenyl 4-aminosalicylate (PAS). The amount of stabilizer grafted onto the surface varied between 25 and 40 nmol/cm² depending on the polymer substrate. The samples were exposed to UV radiation in air, and the degradation and oxidation of the polymers were studied with IR, UV, and ESCA spectroscopy and by stress–strain measurements. PP grafted with AP exhibited a near 20-fold increase in lifetime compared with the unprotected PP, AP did not stabilize the PE or PS samples. DHBP was an efficient stabilizer of PE, the oxidation rate of the grafted sample being 1/2 to 1/3 of the ungrafted. A similar effect was observed when DHBP was grafted onto PP and PS. PAS underwent a rearrangement reaction when irradiated with UV light, and had only a slight stabilizing effect.     

Stress and Moisture-Sorption in Ozone-Annealed Films of Zirconium Oxide Obtained from Sol-Gel

The stress development in zirconium oxide films prepared by sol-gel and annealed under ozone-enriched oxygen has been investigated. The organic compounds are mostly oxidized at 200°C with ozone and the stress rises up to higher values than the stress in films annealed with pure oxygen between 200 to 400°C. During exposure to humid air of films annealed at 150°C under pure or ozone-enriched oxygen chemical transformations of organic compounds have been observed. The moisture-induced stress change during film exposure to the ambient air also has been investigated. The competition between hydration of ZrO₂, H-bound formation, surface ionization and capillary condensation mechanisms is discussed.     

Stabilization of Organic–Inorganic Perovskite Layers by Partial Substitution of Iodide by Bromide in Methylammonium Lead Iodide

Thin films of the methylammonium lead halides CH₃NH₃Pb(I_1?xBr_x)₃ are prepared on fluorine‐doped tin oxide substrates and exposed to humid air in the dark and under illumination. To characterize the stability of the materials, UV/Vis spectra are acquired at fixed intervals, accompanied by XRD, energy‐dispersive X‐ray spectroscopy, SEM, and confocal laser scanning microscopy. Different degradation mechanisms are observed depending on the environmental conditions. It is found that bromide can successfully suppress the transformation of the perovskite into the monohydrate, presumably owing to stronger hydrogen‐bonding interactions with the organic cation. However, under illumination in humid air, rather rapid decomposition of the perovskites was still observed, which is due to phase segregation. The use of increased bromide content in methylammonium lead halide absorbers is discussed in terms of their application in perovskite solar cells.     

Ageing and thermal degradation of plasma polymerised thin films derived from Lavandula angustifolia essential oil

The ageing and thermal degradation of polymer thin films derived from the essential oil of Lavandula angustifolia (LA) fabricated using plasma polymerisation were investigated. Spectroscopic ellipsometry and Fourier transform infrared (FTIR) spectroscopy were employed to monitor the optical parameters, thickness and chemical structure of the polyLA films fabricated at various RF powers over a period of 1400 h. The bulk of the degradation under ambient conditions was found to occur within the first 100 h after fabrication. The thermal degradation of the polyLA films was also investigated using the ellipsometry and FTIR. An increase in thermal stability was found for films fabricated at increased RF power levels. Between 200 and 300 °C, the properties indicate that a phase change occurs in the material. Samples annealed up to 405 °C demonstrated minimal residue, with retention ranging between 0.47 and 2.2%. A tuneable degradation onset temperature and minimal residue post-anneal demonstrate that the polyLA films are excellent candidates for sacrificial material in air gap fabrication.     

Thermal degradation of polyethylene into fuel oil over silica–alumina by a continuous flow reactor

A continuous flow reactor was operated at 420 °C and feed rate of 0–1.5 kg h⁻¹ for catalytic degradation of polyethylene (PE) over SA-1 silica–alumina in order to investigate the effect of catalyst on the reaction rate and the quantity and quality of degradation products. SA-1 was either mixed with the PE inside reactor or placed in a catalyst cage, the efficiency being slightly higher in the first case. The catalyst did not have a significant effect on the reaction rates but the volatile products clearly had lower molecular weights. More gases were produced on SA-1 compared to thermal degradation, containing higher amounts of C₄ and less amounts of C₂ compounds.     

Fe~(3+)对淀粉/聚乙烯共混物促降解的研究

本文选用Fe3 + 油酸的组合物为降解剂 ,研究它与淀粉、聚乙烯共混体系在模拟堆肥温度 (70℃ )下的热氧化降解行为 ,对其力学性能、分子量下降率及氢过氧化物浓度进行跟踪测试 ,并通过扫描电子显微镜(SEM )及X 射线衍射仪 (XRD)对试样的表面形态和结晶性能进行表征 .实验结果表明 :含有Fe3 +的有机化合物降解剂在实验条件下对试样有明显的促降解作用 ,并且高Fe3 +含量的降解剂催化PE基体降解活性的发挥受环境因素特别是氧气浓度高低的影响不敏锐 ,而低Fe3+含量的降解剂则与之相反 .在上述实验事实的基础上推导出该体系中聚乙烯热氧化降解的动力学方程式 .     

Effect of annealing on hydrophobic stability of plasma deposited fluoropolymer coatings

Fluorinated amorphous carbon (a-C:F) films e.g. plasma polymerised perfluorocyclobutane have long attracted much consideration due to their low surface energy, hydrophobicity, low refractive index, good electrical and thermal insulation and good thermal stability. Although a-C:F films have many advantages, hydrophobic stability over time in air and water remains a major concern. In this study, the effects of weathering conditions on the hydrophobicity of fluorocarbon films prepared from perfluorocyclobutane precursors were examined using water contact angle measurements. It was found that the high initial hydrophobicity of as-deposited films degrades rapidly in humid conditions. The stability of hydrophobicity can be significantly improved when a suitable treatment such as annealing is employed. The mechanism of weathering was explained with the help of a number of morphological and chemical characterisation techniques such as Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). In particular, XPS results demonstrated that a reduction in the overall amount of -CF₃ radical, oxygenation of surface fluorides and the formation of an overlayer all influence the degradation of fluorocarbon in aquatic environment.     

Carbon dioxide evolution and carbonyl group development during photodegradation of polyethylene and polypropylene

In situ infrared (FTIR) spectrometry has demonstrated that more CO₂ is photogenerated from polypropylene (PP) than from polyethylene (PE) films. Potential applications of the method include investigation of polymer degradation mechanism and ranking of polymer photo-stabilities in as little as 3 h.This study focuses on clarifying the mechanism of this rapid CO₂ formation from PE and PP, and complementary insight was obtained from changes in the IR transmission spectra of films irradiated by UVA for hundreds of hours. A 30 min induction time observed for CO₂ photogeneration from PP, but not PE, was reflected, on a much longer time scale, in the induction time for carbonyl development in PP, but not PE. This suggests that, in PP, the CO₂ induction time is a consequence of the slow development of carbonyl groups, a hypothesis that is supported by the elimination of the PP induction time when, prior to the CO₂ measurements, films are pre-exposed to UVA, to generate carbonyl groups. In addition, more CO₂ is evolved from both PE and PP films if they are pre-exposed.     

Removal and mineralization of toluene under VUV/UV lamp irradiation in humid air: Effect of light wavelength,O2 and H2O

VUV/UV photodegradation is a promising method that utilizes energetic photons and reactive oxygen species (ROS) generated via the photo-dissociation of H₂O and O₂ to degrade VOCs. In the paper, we investigated the efficiency of removal and mineralization in humid air and the effects of key factors. Toluene of 4–20 ppm can be almost completely removed in 60 s and mineralization efficiency is above 55% at 25 min. 185 nm ultraviolet light plays a key role in the rapid removal and mineralization of toluene. Appropriate amount of O₂ and H₂O promote the removal of toluene due to the generation of ROS. Based on the intermediates and degradation pathway analysis, it is found that in the presence of O₂, degradation pathways of toluene are more abundant and fewer linear-chain aldehydes are produced, thus resulting in higher mineralization efficiency. This work highlights the importance of practical application of VUV/UV photodegradation in humid air.     

Mechanism of the conduction of thin composite films of polyethylene and metals

The temperature dependence of the conductivity of thin composite films obtained by means of the simultaneous thermal spray-deposition of a polymer (high-pressure polyethylene, PE) and a filler (a metal, viz., silver, copper, or aluminum) in a vacuum has been investigated. It has been ascertained that the conductivity of the PE + Cu and PE + Al films is determined mainly by the tunneling mechanism for the passage of charge carriers between the filler particles. This mechanism also determines the conductivity of the PE + Ag films at low temperatures; at T > 333 K their conductivity is determined by the conductivity of the polymer matrix.L. V. Pisarzhevskii Institute of Physical Chemistry, Ukrainian Academy of Sciences, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 5, pp. 627–630, September–October, 1991. Original article submitted May 29, 1990.     

Kinetic modelling of stabilization coupled with stabilizer loss by evaporation. Case of dithioester stabilized polyethylene

The thermal oxidation of medium density polyethylene (PE) films stabilized by various weight ratios of DiLaurylThioPropionate (DLTP) or DiStearylThioPropionate (DSTP) has been studied in air at 110 and 120 °C. DSC was used for the measurement of an induction time at 190 °C (directly linked to the concentration of residual stabilizing species) and FTIR spectrophotometry for the measurement of the total concentration of ester groups originating from unreacted and reacted stabilizer molecules. The growth in PE carbonyl groups is also recorded and the induction periods at the exposure temperatures are determined. The results show that the physical loss of these hydroperoxide decomposers cannot be neglected, and also imply that simple evaporation-reaction models are inadequate to predict the kinetic behaviour of these systems. A new model is tentatively proposed. It assumes the coexistence of two stabilizer phases: the insoluble (dispersed) phase as the stabilizer excess relatively to the solubility threshold, and the soluble phase from which evaporative loss and the chemical stabilization can occur. Both phases are in equilibrium where the insoluble phase acts as a reservoir for the soluble one.     

Degradation behaviour of PCL/PEO/PCL and PCL/PEO block copolymers under controlled hydrolytic,enzymatic and composting conditions

Short-term hydrolytic and enzymatic degradation of poly(ε-caprolactone) (PCL), one series of triblock (PCL/PEO/PCL) and the other of diblock (PCL/PEO) copolymers, with a low content of hydrophilic PEO segments is presented. The effect of the introduction of PEO as the central or lateral segment in the PCL chain on copolymer hydrolysis and biodegradation properties was investigated. FTIR results revealed higher hydrolytic degradation susceptibility of diblock copolymers due to a higher hydrophilicity compared to PCL and triblock copolymers. Enzymatic degradation was tested using cell-free extracts of Pseudomonas aeruginosa PAO1, for two weeks by following the weight loss, changes in surface roughness, and changes in carbonyl and crystallinity index. The results confirmed that all samples underwent enzymatic degradation through surface erosion which was accompanied with a decrease in molecular weights. Diblock copolymers showed significantly higher weight loss and decrease in molecular weight in comparison to PCL itself and triblock copolymers. AFM analysis confirmed significant surface erosion and increase in RMS values. In addition, biodegradation of polymer films was tested in compost model system at 37 °C, where an effective degradation of block copolymers was observed.