Effect of pro‐oxidants on biodegradation of polyethylene (LDPE) by indigenous fungal isolate,Aspergillus oryzae

Proxidant additives represent a promising solution to the problem of the environment contamination with polyethylene film litter. Pro‐oxidants accelerate photo‐ and thermo‐oxidation and consequent polymer chain cleavage rendering the product apparently more susceptible to biodegradation. In the present study, fungal strain, Aspergillus oryzae isolated from HDPE film (buried in soil for 3 months) utilized abiotically treated polyethylene (LDPE) as a sole carbon source and degraded it. Treatment with pro‐oxidant, manganese stearate followed by UV irradiation and incubation with A. oryzae resulted in maximum decrease in percentage of elongation and tensile strength by 62 and 51%, respectively, compared with other pro‐oxidant treated LDPE films which showed 45% (titanium stearate), 40% (iron stearate), and 39% (cobalt stearate) decrease in tensile strength. Fourier transform infrared (FTIR) analysis of proxidant treated LDPE films revealed generation of more number of carbonyl and carboxylic groups (1630–1840 cm⁻¹ and 1220–1340 cm⁻¹) compared with UV treated film. When these films were incubated with A. oryzae for 3 months complete degradation of carbonyl and carboxylic groups was achieved. Scanning electron microscopy of untreated and treated LDPE films also revealed that polymer has undergone degradation after abiotic and biotic treatments. This concludes proxidant treatment before UV irradiation accelerated photo‐oxidation of LDPE, caused functional groups to be generated in the polyethylene film and this resulted in biodegradation due to the consumption of carbonyl and carboxylic groups by A. oryzae which was evident by reduction in carbonyl peaks. Among the pro‐oxidants, manganese stearate treatment caused maximum degradation of polyethylene. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Study of ultraviolet photooxidative degradation of LDPE film containing cerium carboxylate photosensitizer

The carbonyl indices (CI) of photooxidation of low-density polyethylene (LDPE) films containing cerium carboxylate (CeCar₃) with/without aromatic ketones (AK) were determined by infrared (IR) spectroscopy. The effects of these photosensitizers on the rates of ultraviolet (UV) photooxidation of LDPE films and their mechanism in sensitizing photooxidative degradation are studied. Results show that CeCar₃ can cause the accelerated photooxidative degradation of LDPE films, but CeCar₃ in combination with AK may bring about the accelerated or retarded photooxidative degradation of LDPE films to varying degrees. After UV irradiation, followed by long duration storage, LDPE films containing these photosensitizers continued storage oxidative degradation at the storage oxidative rates similar to the past, except for the Michler ketone.     

LDPE‐based blends and films stabilized with nonreleasing polymeric antioxidants for safer food packaging

Several novel random copolymers of ethylene and 1‐olefin counits bearing a highly efficient phenolic antioxidant moiety placed at different distances from the polymerizable double bond were prepared in the presence of a metallocene catalyst. These copolymers were melt‐blended with an antioxidant‐free LDPE in an internal batch mixer to obtain innovative materials containing nonreleasing polymeric antioxidants suitable for safer food packaging applications. Blends and films, obtained by compression molding, were tested for their thermal and thermo‐oxidative stability by thermogravimetric analysis both in dynamic and isothermal conditions. Films containing the macromolecular antioxidants showed a longer induction time before O₂ uptake starts and, consequently, a higher degradation temperature than neat LDPE or LDPE containing a low molecular weight commercial additive. Aging tests demonstrated that the new polymeric antioxidants also exert a valid protection against photo‐oxidation. Eventually, migration tests demonstrated the absence of any trace of products containing the antioxidant moiety when the films were kept in contact with a food simulant. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Kinetic approach on stabilization of LDPE in the presence of carnosic acid and related compounds. I. Thermal investigation

Carnosic acid and similar compounds exhibit antioxidant behavior in a polyethylene matrix. Thermal resistance of LDPE was investigated at three temperatures (190, 200, and 210°C) by isothermal chemiluminescence. The main kinetic parameters: oxidation induction period (t_i), half oxidation time (t_1/2), maximum oxidation time (t_max), and propagation rate of oxidation (v_ox^max) were calculated. The inhibition of thermal degradation is proved by the values of these parameters relative to unstabilized polymer: the induction times of stabilized low density polyethylene are of one order of magnitude greater that raw polyethylene, and half oxidation periods are three to five times longer than initial LDPE. Thermal aging of protected low density polyethylene occurs at a much slower rate in comparison with unmodified LDPE. The depletion of stabilizers was also evaluated and the kinetic characteristics (the half‐life and the rate constant of consumption for each antioxidant) at three concentrations of all tested additives (0.125, 0.25, 0.50, and 0.75% w/w) were determined. The effectiveness of stabilization was depicted by two values of activation energies calculated from oxidation induction times and maximum oxidation periods. Some considerations on stabilizing mechanism are presented. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1571–1577, 2005     

Characterization of surface phenomena: probing early stage degradation of low‐density polyethylene films

Photo‐oxidative degradation of polyethylene triggers significant deterioration in the polymer properties. Much interest is aimed at characterizing and possibly predicting photo‐oxidative damages, at early stages, prior to the occurrence of profound changes in mechanical properties. Herein, we study the degradation of low‐density polyethylene (LDPE) films, focusing on surface deterioration processes. Thin films of various molecular weights are exposed to accelerated weathering while their chemical, mechanical and morphological characteristics are monitored throughout by apparent contact angle (CA) measurements, Fourier‐transform infrared spectroscopy (FTIR), tensile test, and electron microscopy. A significant decrease in the films' CA during degradation is observed. CA is highly sensitive to two simultaneous phenomena with opposing effect: nanoscale surface roughening and composition changes. We found the latter (specifically the evolution of polar groups) to be the dominant parameter affecting the CA behavior. Consequently, simple CA measurements coincide well with conventional FTIR analysis, and are more sensitive to changes occurring at early stages of degradation. The deterioration in the mechanical properties is also characterized and is found to present poor sensitivity and high variability at these early aging stages. Thus, simple CA measurements could potentially be used as a qualitative indicator for evaluating the aging impact on LDPE. POLYM. ENG. SCI., 59:E129–E137, 2019. © 2018 Society of Plastics Engineers     

Determination of some physical and mechanical properties of laminated veneer lumber impregnated with boron compounds

The viability of producing environment‐friendly blends of HDPE and LDPE with a commercial biodegradable masterbatch containing starch and polyethylene was studied. The service life of these blends was simulated by means of a thermo‐oxidative treatment, and their further disposal in landfill was modeled using an accelerated soil burial test. Characterization was carried out in terms of their calorimetric and thermogravimetric properties. Thermo‐oxidative treatment causes an increase in the crystalline content of both components of the blends, and promotes a segregation of the crystallite sizes of polyethylene. The soil burial test leads to changes in the crystalline content of the biodegradable material, which is influenced by the polyolefinic matrix used. The kinetics of the thermal decomposition of these blends was studied using the Hirata and the Broido models. Thermogravimetric results reveal that the thermo‐oxidative treatment causes a decrease in the activation energy of the thermal decomposition process of both components in the blends, regardless of the type of polyethylene used. The thermo‐oxidative treatment mainly modifies the thermal properties of starch during the degradation process in soil, especially in the LDPE blends. Synergetic degradation of these blends is a complex process that is dependent on the polyolefinic matrix used and mainly causes morphological changes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Rice bran‐filled biodegradable low‐density polyethylene films: Development and characterization for packaging applications

Rice bran was incorporated into low‐density polyethylene (LDPE) at different concentrations by compounding in a twin‐screw extruder and blown into films of uniform thickness. The rice bran incorporation influenced physical, mechanical, barrier, optical, thermal properties, and biodegradation of LDPE. The mechanical and optical properties decreased as the percentage of rice bran increased. The effect of rice bran on the morphology of LDPE blends was examined using scanning electron microscopy. Oxygen transmission rate and water vapor transmission rate increased with the increased content of rice bran. Addition of rice bran did not alter the melting temperature (T_m) of the blends; however the thermal stability decreased, while glass transition temperature (T_g) increased. Kinetics of thermal degradation was also investigated and the activation energy for thermal degradation indicated that for up to 10% filler addition, the dispersion and interfacial adhesion of rice bran particles in LDPE was good. Aerobic biodegradation tests using municipal sewage sludge and biodegradation studies using specific microorganism (Streptomyces species) revealed that the films are biodegradable. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4514–4522, 2006     

Photobiodegradation of low‐density polyethylene/banana starch films

The effects of the starch content, photosensitizer content, and compatibilizer on the photobiodegradability of low‐density polyethylene (LDPE) and banana starch polymer blend films were investigated. The compatibilizer and photosensitizer used in the films were PE‐graft‐maleic anhydride (PE‐g‐MA) and benzophenone, respectively. Dried banana starch at 0–20% (w/w) of LDPE, benzophenone at 0–1% (w/w) of LDPE, and PE‐g‐MA at 10% (w/w) of banana starch were added to LDPE. The photodegradation of the blend films was performed with outdoor exposure. The progress of the photodegradation was followed by determining the carbonyl index derived from Fourier transform IR measurements and the changes in tensile properties. Biodegradation of the blend films was investigated by a soil burial test. The biodegradation process was followed by measuring the changes in the physical appearance, weight loss, and tensile properties of the films. The results showed that both photo‐ and biodegradation rates increased with increasing amounts of banana starch, whereas the tensile properties of the films decreased. The blends with higher amounts of benzophenone showed higher rates of photodegradation, although their biodegradation rates were reduced with an increase in benzophenone content. The addition of PE‐g‐MA into polymer blends led to an increase in the tensile properties whereas the photobiodegradation was slightly decreased compared to the films without PE‐g‐MA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2725–2736, 2006     

Evaluation by IR spectroscopy of the degradation of different types of commercial polyethylene exposed to UV radiation and domestic compost in ambient conditions

Different types of commercial polyethylene films, low-density polyethylene (LDPE), high-density polyethylene (HDPE), and biodegradable polyethylene (BIO-PE), were exposed to UV-B radiation at different exposure time and domestic composting during spring and fall at ambient conditions. The effects of UV-B radiation and domestic composting on LDPE, HDPE, and BIO-PE degradation were characterized by FTIR spectroscopy. LDPE, HDPE, and BIO-PE exposed to UV-B radiation underwent photo oxidation reactions leading to the formation of carbonyl (CO) and vinyl (CH₂CH) groups and hydrophilic surface modification. Also, the exposure of LDPE, HDPE, and BIO-PE to domestic composting at ambient conditions at different seasons suffered biodegradation reactions leading to the formation of polysaccharides. In both different seasons LDPE, HDPE, and BIO-PE underwent partial biodegradation, remaining in the domestic composting as unwanted polymer debris. However, biodegradation in domestic composting is not recommended as feasible disposal routes for nonbiodegradable and commercially labeled as biodegradable PE.     

Modeling of degradation of unstabilized and HALS‐stabilized LDPE films under thermo‐oxidation and natural weathering conditions

Mathematical models are proposed to predict degradation of unstabilized low density polyethylene (LDPE) films and those stabilized with hindered amine light stabilizers (HALS) under both thermo‐oxidation at 90°C and natural weathering conditions. The degradation was measured by change in percent elongation at break (?_r) with time. The mathematical approach developed was multiple linear regression analysis (MLRA). The reliability of the selected models was analysed using four statistical criteria, residual variance, coefficient of determination (r²), Student test and Fisher‐Snedecor test. The linear systems that resulted from the MLRA were resolved by the Cholesky method. The results obtained indicated that the polynomial models developed to predict elongation at break were reliable for both unstabilized and HALS‐stabilized samples under thermo‐oxidation at 90°C and natural weathering conditions. This was also confirmed by the comparison of the half‐life time (HLT) values predicted from the models with those observed experimentally. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3284–3292, 2001     

Highly wettable polyethylene films generated by spontaneous surface enrichment of perfluoroalkylated phosphorylcholines

We report here a new feature for highly wettable polyethylene films prepared by spontaneous surface enrichment of perfluoroalkylated phosphorylcholine (PC) additives via a simple heat‐press technique. Perfluoroalkylated PCs were newly synthesized from monohydroxyethyl ether compounds with hexafluoromethylene (C₆F₁₃PC), octafluoromethylene (C₈F₁₇PC), and decafluoromethylene (C₁₀F₂₁PC) chains. Hexadecyl phosphorylcholine (C₁₆PC) was synthesized as a control. These PC additives were mixed well with low‐density polyethylene (LDPE) microparticles (? = 6 μm), placed between stainless plates, and pressed at 120°C. Perfluoroalkylated PCs effectively improved the surface wettability of the composite film compared with that of the alkylated PC. C₈F₁₇PC is extremely surface active in the LDPE matrix and occupies ～ 95% of the outermost ～ 10 Å. The water contact angle data for the LDPE film was decreased from 94°/81° (θ_A/θ_R) to 28°/8° by the addition of an approximately low concentration of C₈F₁₇PC (3.3% w/w) because of spontaneous enrichment on the surface. When the elongation to break value of the films was slightly reduced with the PC additives, Young's modulus and the tensile strength of the composite films were similar to those of pure LDPE film. In conclusion, fluoroalkylated PCs have good potential as additives to improve the wettablility of thermoplastic polymers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2868–2874, 2006     

Oxidative degradations of oxodegradable LDPE enhanced with thermoplastic pea starch: Thermo‐mechanical properties,morphology, and UV‐ageing studies

The abiotic UV‐degradation behavior of oxodegradable LDPE was investigated in the presence of thermoplastic pea starch (TPPS) in this study. Oxodegradable LDPE was first melt‐blended with thermoplastic pea starch (TPPS) using an internal mixing chamber to enhance the abiotic oxidative degradation of oxodegradable LDPE. Because of their different affinity, maleated polyethylene was added as compatibilizer. Tensile properties, thermal properties, and morphology of resulting melt‐blends were determined at different content in TPPS. High content in TPPS (40 wt %) could be readily added to oxodegradable LDPE without affecting the tensile properties of resulting melt‐blends. UV‐ageing studies on compatibilized TPPS/oxodegradable LDPE melt‐blends were carried out by Attenuated Total Reflectance infrared spectroscopy (ATR‐FTIR), Dynamic Thermomechanical Analyses (DMTA) and Differential Scanning Calorimetry (DSC) under abiotic conditions. These results suggested a synergistic effect on the UV‐ageing of TPPS‐based melt‐blends provided by both components during the first stage of UV‐irradiation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Degradation of polyethylene during extrusion. II. Degradation of low‐density polyethylene,linear low‐density polyethylene,and high‐density polyethylene in film extrusion

The degradation of different polyethylenes—low‐density polyethylene (LDPE), linear low‐density polyethylene (LLDPE), and high‐density polyethylene (HDPE)—with and without antioxidants and at different oxygen concentrations in the polymer granulates, have been studied in extrusion coating processing. The degradation was followed by online rheometry, size exclusion chromatography, surface oxidation index measurements, and gas chromatography–mass spectrometry. The degradations start in the extruder where primary radicals are formed, which are subject to the auto‐oxidation when oxygen is present. In the extruder, crosslinking or chain scissions reactions are dominating at low and high melt temperatures, respectively, for LDPE, and chain scission is overall dominating for the more linear LLDPE and HDPE resins. Additives such as antioxidants react with primary radicals formed in the melt. Degradation taking place in the film between the die orifice, and the quenching point is mainly related to the exposure time to air oxygen. Melt temperatures above 280°C give a dominating surface oxidation, which increases with the exposure time to air between die orifice and quenching too. A number of degradation products were identified—for example, aldehydes and organic acids—which were present in homologous series. The total amount of aldehydes and acids for each number of chain carbon atoms were appeared in the order of C5>C4>C6>C7?C2 for LDPE, C5>C6>C4>C7?C2 for LLDPE, and C5>C6>C7>C4?C2 for HDPE. The total amounts of oxidized compounds presented in the films were related to the processing conditions. Polymer melts exposed to oxygen at the highest temperatures and longest times showed the presence dialdehydes, in addition to the aldehydes and acids. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1525–1537, 2004     

The impact of cupric ion on thermo‐oxidative degradation of chitosan

The thermal degradation of chitosan and chitosan–cupric ion compounds in air was studied using thermogravimetric and differential thermal analyses in the temperature range 30–600 °C. The impact of cupric ion on the thermo‐oxidative degradation of chitosan was investigated. Fourier transform infrared and X‐ray diffraction analyses were utilized to determine the microstructure of the chitosan–cupric ion compounds. Kinetic parameters such as activation energy, pre‐exponential factor, Gibbs energy, and enthalpy and entropy of activation were determined using the Coats–Redfern equation. The results show that the thermo‐oxidative degradation of chitosan and chitosan–cupric ion compounds is a two‐stage reaction. The impact of cupric ion on the thermo‐oxidative degradation of chitosan is significant, and all thermodynamic parameters indicate that the thermo‐oxidative degradation of chitosan and chitosan–cupric ion compounds is a non‐spontaneous process and proceeds via a mechanism involving nucleation and growth, with an Avrami–Erofeev function (A₄) with the integral form [?ln(1 ? α)]⁴. Copyright © 2010 Society of Chemical Industry     

Photodegradation of some low‐density polyethylene–montmorillonite nanocomposites containing an oligomeric compatibilizer

The photo‐oxidation behavior at the exposed surfaces of maleated low‐density polyethylene [LDPE poly(ethylene‐co‐butylacrylate‐co‐maleic anhydride) (PEBAMA)] and montmorillonite (MMT) composites was studied using attenuated total reflection Fourier transform infrared spectroscopy, X‐ray diffraction (XRD), transmission electron microscopy (TEM), and mechanical testing. Two different MMT clays were used with the maleated polyethylene, an unmodified clay, MMT, and an organically modified montmorillonite (OMMT) clay which was significantly exfoliated in the composite. The morphologies of sample films were examined by XRD and TEM. The results were explained in terms of the effect of the compatibilizing agent PEBAMA on the clay dispersion. It was found that the OMMT particles were exfoliated in the polymer matrix in the presence of the PEBAMA, whereas the MMT clay particles were agglomerated in this matrix. Both mechanical and spectroscopic analyses showed that the rates of photo oxidative degradation of the LDPE‐PEBAMA–OMMT were higher than those for LDPE and LDPE‐PEBAMA–MMT. The acceleration of the photo‐oxidative degradation for LDPE‐PEBAMA–OMMT is attributed to the effects of the compatibilizer and the organic modifier in the composite. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40788.     

Photodegradation of low-density polyethylene with prooxidant and photocatalyst

Low-density polyethylene (LDPE) composite films with trisilver phosphate (Ag₃PO₄) and cadmium selenide (CdSe) particles as photocatalysts and manganese stearate as prooxidant were prepared. The film samples were irradiated under UV and visible light and their photodegradation were evaluated using Fourier-transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and differential scanning calorimetry. The carbonyl index of the photocatalyst containing samples was very higher than the pure irradiated LDPE and even prooxidant containing film. The morphologies of the irradiated composite films were completely changed and had many cavities and cracks. The thermal stability of the composites was very lower than the pure polyethylene. However the crystallinity of the LDPE films with photocatalysts was enhanced contrarily the LDPE film with manganese stearate. Generally the results showed that the combination of the prooxidant with photocatalyst have synergistic effect on the photodegradation of the LDPE and can be used to accelerate the degradation of the polyethylene films.     

An Investigation into the UV-Photo-Oxidative Degradation of LDPE by Using Cobalt Naphthenate as Photosensitizer

The effect of cobalt naphthenate on photo degradation of low density polyethylene was studied. The carbonyl index, tensile strength, elongation at break, density and relative crystallinity of the samples were measured. The samples were made of different concentrations of LDPE and cobalt naphthenate. Parts of uniform thickness were cut for testing before and after UV-irradiation at every 30-days interval for 90 days. From the results of FTIR, and other measurements, it was observed that the UV-irradiation affects on the LDPE films and the rate of degradation increased with increasing both the concentration of the photosensitizer and time of irradiation.     

Enhanced degradation properties of polypropylene integrated with iron and cobalt stearates and its synthetic application

Synthetic plastic leads to environmental contamination, and a promising solution to this problem is to use prooxidants as fillers within them to speed up the photooxidation and thermooxidation processes. This makes plastics more susceptible to biodegradation. In this study, the degradation properties of the widely used polymer polypropylene (PP) were improved by integration with cobalt stearate (CoSt₂) and iron stearate (FeSt₃) as prooxidants with accelerating weathering degradation. The metal stearates were blended with PP in the concentration range 0.1–0.9% w/w. The properties of the blends were studied by mechanical properties testing, thermogravimetric analysis, differential scanning calorimetry, and water absorption measurement. We performed the degradation properties and thermooxidative studies by conducting an accelerated weathering test on PP–metal salt blends. Fourier transform infrared spectroscopy and scanning electron microscopy analysis of the samples before and after the accelerated weathering test were performed to study the extent of degradation in PP‐based metal salt blends. The results indicate that the tensile strength was inversely proportional to the concentration of metal stearates, and the samples showed an increased degree in polymer crystallinity (PPFe5 > PPCo5), and this led to the degradation of PP in less time. CoSt₂ predominantly enhanced the degradation of PP in comparison to FeSt₃. Food containers and pots were constructed with the tailored polymers of PP in the injection‐molding machine. Thus, metal‐stearate‐integrated polymers have great industrial potential to generate value‐added products. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46028.     

Ecofriendly modification of acetosolv lignin from oil palm biomass for improvement of PMMA thermo‐oxidative properties

The environmentally friendly esterification of acetosolv lignin (AL), obtained from pressed oil palm mesocarp fibers, is described, for the improvement of thermo‐oxidative properties of poly(methyl methacrylate) (PMMA) films. Acetylation of AL was performed in ecofriendly conditions using acetic anhydride in the absence of catalysts. Acetylated acetosolv lignin (AAL) was successfully obtained in only 12 min with a solvent‐free and catalyst‐free microwave‐assisted procedure. Lignins were characterized by Fourier transform infrared spectroscopy, size exclusion chromatography, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC), confirming the efficacy of the methodology employed. AL and AAL as fillers in different concentrations (1% and 5%) were added to PMMA films. The thermal and mechanical properties of the lignin‐incorporated films were analyzed by TGA, DSC, and dynamic mechanical analysis (DMA). The films incorporated with lignin and acetylated lignin presented initial degradation temperature (T_onset) and onset oxidative temperature (OOT) values higher than pure PMMA films, contributing thus to an enhancement of thermo‐oxidative stability of PMMA. The DMA analyses showed that incorporation of AL or AAL increased the storage modulus (E′) of PMMA films, but did not affect their glass‐transition temperatures (T_g). The results indicate the potential use of oil palm mesocarp lignin to enhance the thermo‐oxidative properties of PMMA without compromising its mechanical response. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45498.     

Study on the degradation of low‐density polyethylene in the presence of cobalt stearate and benzil

Degradable polymers are in great demand for a variety of applications such as packaging, agriculture, and medicine. Polyolefins blended with photodegradants/biodegradants are potential candidates for replacing the nondegradable thermoplastics in areas where litter abatement poses problems. In the present article, the effect of metallic photoinitiators like cobalt stearate and a combination of metallic/nonmetallic photoinitiators, i.e., a mixture of cobalt stearate and benzil, on the photooxidative degradation of low‐density polyethylene (LDPE) films have been investigated. Attempts have been made to correlate the results as a function of mixed additives. Films of LDPE containing varying amounts of cobalt stearate and a combination of benzil and cobalt stearate were prepared. The photodegradation of these films has been monitored by various techniques like FTIR spectroscopy, differential thermal analysis, and density and viscosity measurements. Cobalt stearate was highly effective in accelerating the photodegradation of LDPE films at low concentrations. The addition of benzil to cobalt stearate decreased the rate of photodegradation compared to cobalt stearate alone. A retarding effect was observed when benzil alone was added to LDPE. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 236–243, 2006