Oxidation and biodegradation of polyethylene films containing pro-oxidant additives: Synergistic effects of sunlight exposure, thermal aging and fungal biodegradation (original) (raw)
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Comparison of the biodegradability of various polyethylene films containing pro-oxidant additives
Polymer Degradation and Stability, 2010
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 þ iron or manganese þ iron þ cobalt) was studied. Abiotic pre-treatment consisting of photooxidation and thermal oxidation corresponding to about three years of outdoor weathering (including 3e4 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 1 H 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
Polymer Degradation and Stability, 2008
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 AE 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.
Degradation of polyethylene film samples containing oxo- degradable additives
The introduction of the so called oxo-biodegradable additives in the Argentine market motivated the assessment of the effects of abiotic and biotic factors on the structure and mechanical behavior of polyethylene (PE) with oxo-degradable additives (PE+AD). Samples of oxo-degradable packaging films found in local shops together with polyethylene films with and without d 2 w ® additive were annealed at different temperatures between 50 and 110ºC and submitted to ultraviolet radiation at different irradiances (0,35; 0,45; 0,89 and 1,20 W/m 2). Furthermore, aged oxo-degradable films were set in a controlled compost bioreactor in order to evaluate their biodegradation ability. Experimental results showed that elongation at break was the mechanical property more sensitive to the polymeric degradation. The structural changes determined by FT-IR remarked the importance of the UV degradation time over the irradiation rate; the carbonyl index of the degraded samples pointed out that chain scission was a thermally activated process. Regarding degradation due to UV radiation, at the same dose, the elongation at break is lower at lower irradiance both in PE and PE+AD samples. On the other hand, thermal degradation of PE without additive is more susceptible to degradation than PE + AD. At the beginning of the biodegradation tests, PE + AD showed a higher CO 2 production rate with respect to PE; however, this rate reduced along the first 30 days, reaching the CO 2 production of PE without additive. The maximum biodegradation observed for both PE and PE+AD samples was 24 % after 90 days of incubation.
2013
The biodegradability of two polypropylene films with low content of ethylene (a statistical copolymer (PPs) and a block copolymer (PPb) with balanced additions of phenolic antioxidant and pro-oxidants based on Mn, Mn/Fe or Co was studied. Abiotic pre-treatments by accelerated artificial photooxidation and thermooxidation representing about 3e4 years of outdoor weathering, including 3e4 months of exposure to daylight and 3 years in soil were followed by FTIR and SEC measurements. When a controlled oxidation was reached in the films, they were inoculated, in a second step, with the strain Rhodococcus rhodochrous in mineral medium and incubated up to 180 days. The metabolic activity of bacteria was evaluated by measuring ATP content, ADP/ATP ratio and cell viability. Complementary 1 H NMR experiments were conducted on the incubation media, with and without cells, in order to monitor the consumption of soluble compounds excreted from the oxidized polymers by R. rhodochrous cells. The main conclusions are that the Co derivatives (with Co content ! 150 ppm) must be considered toxic for R. rhodochrous. PP films containing pro-oxidants based on Mn and Mn þ Fe give positive results for the biotest (low ADP/ATP ratio, post-development in Petri dishes). However the biodegradability of oxidized PP films is less efficient in comparison to oxidized PE films (see paper published in this journal). This observation may be correlated with the accumulation in the incubation media of oxidized oligomers that cannot be metabolized rapidly by the bacterial cells and/or by the residual crystallinity of PP derivatives.
Polymer Composites, 2017
Nano-TiO 2 particles were modified with poly(ethylene glycol) (PEG) and used as pro-oxidant additives for degradable low-density polyethylene (LDPE) films. The photo-oxidation and biodegradation of polyethylene films containing modified nano-TiO 2 particles were examined by exposure to UV irradiation for 370 hr followed by their incubation with mature compost and fungal strains isolated from soil. It is found that films with pro-oxidant additives showed an obvious decrease in molar mass, molecular weight, and mechanical properties and an increase in their carbonyl index during the photo-oxidation. In addition, the degradation rate under UV irradiation could be controlled by an addition of small amount of hindered amine light stabilizer. Furthermore, a profuse growth and colonization of fungal mycelia and spores on the photo-oxidized TiO 2 /PEG/LDPE composite films were observed while no colonization of fungal mycelia on the photo-oxidized LDPE films and photooxidized TiO 2 /LDPE composite films. The hydrophilic modification of TiO 2 by PEG facilitates the photooxidation LDPE into small molecular weight residues which was easily consumed by fungal mycelia, leading to enhanced biodegradation.
Study of oxo-biodegradable polyethylene degradation in simulated soil
Materials Research, 2014
This study aims to evaluate the influence of pro-oxidant additive and accelerated aging on the degradation of polyethylene (PE) samples in simulated soil, in accordance with ASTM G160-03. Films of polyethylene with and without pro-oxidant additive were studied, before and after 72 hours of accelerated aging. The films were initially characterized by analyses of Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) (to evaluate the Carbonyl Index (CI)). The films were exposed for 30, 60 and 90 days in simulated soil, with controlled moisture and soil pH. The results showed the degradation of polyethylene films through an increase of CI in samples with additive and accelerated aging after 30 days of exposure, and a decrease, after 60 and 90 days, indicating the uptake of material oxidation by-products by microorganisms. The polyethylene films without pro-oxidant additive after accelerated aging showed greater structural and surface modifications, as compared to films with the additive.
Abiotic Oxidation Studies of Oxo-biodegradable Polyethylene
Journal of Polymers and the Environment, 2008
The best approach to induce oxo-biodegradation in polyethylene is the use of special additives known as prooxidants. Pro-oxidants accelerate abiotic oxidation and subsequent polymer chain cleavage rendering the product apparently more susceptible to biodegradation. In this work, the abiotic oxidation is studied to understand how the addition of nanoclay affects the oxidation rate and the degradation mechanism of oxo-biodegradable polyethylene. In order to achieve this, the following materials were used in this study: (1) polyethylene (PE), (2) oxo-biodegradable polyethylene (OPE), (3) polyethylene nanocomposite (PE-Nac), and (4) oxo-biodegradable polyethylene nanocomposite (OPENac). Wide-Angle X-ray scattering (WAXS) and Transmission Electron Microscopy (TEM) studies reveal that grafting in the preparation of composites helps to achieve mixed intercalated/exfoliated morphology in PENac and OPENac. Abiotic oxidation was carried out in an oven for a period of 14 days at 70°C with air supply. The effect of abiotic oxidation was evaluated by measuring the changes in tensile strength, elongation at break, carbonyl index and molecular weight. Results show that OPE and OPENac are more susceptible to oxidation than PENac. The molecular weight distribution data obtained from GPC reveal that the addition of nanoclay does not alter the oxidation mechanism in OPE significantly.
2016
In this study, PP films were modified with an organic pro-degradant in different concentrations (1, 2 and 3 wt.%), exposed in the first step of degradation to natural ageing for 100 days followed by biodegradation in simulated soil in the respirometric test for 100 days. At the end of the combined degradation process the PP samples were characterized according to their morphological and physical properties and the CO 2 generated during the biodegradation in soil was monitored. The CO 2 production by the PP films modified with the organic pro-degradant was proportional to the oxidation rate and weight loss of the samples. The reduction in the average viscosimetric molecular weight could be attributed to chain scission due to the weathering conditions to which the samples were exposed (natural ageing followed by biodegradation in soil). Scanning electron microscopy (SEM) of the PP films revealed surface deterioration of the films with the organic pro-degradant after the combined degra...
Journal of Applied Polymer Science, 2008
This article reports the results of studies on the photooxidative and thermooxidative degradation of linear low-density polyethylene (LLDPE) in the presence of cobalt stearate. Various amounts of cobalt stearate (0.1-0.9% w/w) blended with LLDPE and films of 70 6 5 l thickness were prepared by a film-blowing technique. The films were subjected to xenon arc weathering and air-oven aging tests (at 708C) for extended time periods. We followed the chemical and physical changes induced as a result of aging by monitoring changes in the mechanical properties (tensile strength and elongation at break), carbonyl index, morphology (scanning electron microscopy), melt flow index, and differential scanning calorimetry crystallinity. Cobalt stearate was highly effective in accelerating the photodegradation of LLDPE films at concentrations greater than 0.2% w/w. The kinetic parameters of degradation, as determined by nonisothermal thermogravimetric analysis, were estimated with the Flynn-Wall-Ozawa isoconversion technique, which was subsequently used to determine the effect of cobalt stearate on the theoretical lifetime of LLDPE.
Ultraviolet (UV)-assisted surface modification in the presence of oxygen was used as initial step to achieve controlled degradation of poly(3-hydroxy-butyrate), PHB, films by entomopathogenic fungi. Treated surfaces were investigated by surface analysis techniques (water contact angle, Fourier Transformed Infrared Spectroscopy in Attenuated Total Reflectance mode, X-ray Photoelectron Spectroscopy, Near-edge X-ray Absorption Fine Structure, Gel Permeation Chromatography, Optical Microscopy, Scanning Electron Microscopy, and weight loss). After the UV-assisted treatments, new carbonyl groups in new chemical environments were detected by XPS and NEXAFS spectroscopy. The oxidizing atmosphere did not allow the formation of C@C bonds, indicating that Norrish Type II mechanism is suppressed during or by the treatments. The higher hydrophilicity and concentration of oxygenated functional groups at the surface of the treated films possibly improved the biodegradation of the films. It was observed a clear increase in the growth of this fungus when oxygenated groups were grafted on the polymers surfaces. This simple methodology can be used to improve and control the degradation rate of PHB films in applications that require a controllable degradation rate.