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.     

硬脂酸铁加速LDPE膜光降解作用的研究

本文合成了硬脂酸铁(FeSt_s),用等离子体发射光谱、热分析仪、紫外光谱、红外光谱等分析手段进行了表征,研究了它对光氧化低密度聚乙烯(LDPE)薄膜羰基指数和粘均分子量的影响,并探讨了它的作用机理.结果表明:在LDPE膜中加入0.1%～0.3?St_s,即可控制可分解LDPE膜的使用寿命;羧酸铁在光解LDPE膜中的敏化活性依次递减如下:硬脂酸铁>月桂酸铁>辛酸铁;月桂酸铁和辛酸铁的光敏催化活性较低;二苯甲酮不是LDPE的有效光敏剂,能阻滞LDPE的光降解作用;高温下UV光降解LDPE膜的光降解速率高于低温下的光降解速率.     

Degradation behavior of linear low‐density polyethylene films containing prooxidants under accelerated test conditions

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 ± 5 μ thickness were prepared by a film‐blowing technique. The films were subjected to xenon arc weathering and air‐oven aging tests (at 70°C) 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. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Comparative effects of cobalt carboxylates on the thermo‐oxidative degradation of LDPE films

This article reports the effect of three cobalt carboxylates—cobalt stearate (CoSt₃), cobalt palmitate (CoPal₃), and cobalt laurate (CoLau₃)—on the thermo‐oxidative degradation of low‐density polyethylene (LDPE) films prepared by sheeting process. The carboxylates were blended with LDPE in the concentration range of 0.05–0.2% (w/w). The degradation was monitored by techniques such as FTIR spectroscopy, change in the mechanical properties (tensile strength and elongation at break), viscometry, surface electron microscopy, melt flow index measurements, and apparent density measurements. Studies indicate that films containing these additives are highly susceptible to thermo‐oxidative degradation. Oxygen containing functionalities such as carbonyl and vinyl species are generated on the surface of polyethylene because of thermo‐oxidation, as indicated by FTIR studies. This oxidative process is accelerated in the presence of cobalt carboxylates. The degradation of LDPE was found to increase proportionally with concentration as well as with increasing chain length of the cobalt carboxylate, and follow the order CoSt₃ > CoPal₃ > CoLau₃. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3758–3765, 2007     

表面改性Mg(OH)_2/LDPE复合材料性能的研究

以硬脂酸钠为改性剂,将采用湿法表面改性后的氢氧化镁(Mg(OH)2)填充到低密度聚乙烯(LDPE)中。考察Mg(OH)2用量对Mg(OH)2/LDPE复合材料阻燃性能和力学性能的影响,并对比改性前后力学性能及阻燃性能的差异。结果表明:Mg(OH)2可提高Mg(OH)2/LDPE复合材料的阻燃性和耐热性,但降低了复合材料的力学性能;经硬脂酸钠表面改性的Mg(OH)2可使复合材料力学性能的减弱趋势变得平缓。     

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.     

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     

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     

Physicomechanical,optical, barrier,and wide angle X‐ray scattering studies of filled low density polyethylene films

Series of low density polyethylene (LDPE) films filled with different fillers such as silica, mica, soya protein isolate, potassium permanganate, and alumina were processed using a single screw extruder. The filled LDPE films were characterized for physicomechanical properties like tensile strength, percentage elongation at break, and tear strength, optical properties like percent transmission and haze. The barrier properties such as water vapor transmission rate and oxygen transmission rate of the filled LDPE films have also been reported. Microcrystalline parameters such as crystal size (〈N〉) and lattice distortion (g) of the filled LDPE films obtained using wide angle X‐Ray scattering method have been reported. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2781–2789, 2006     

含羧酸铈光敏剂及其配合体系的LDPE地膜的应用

研究了羧酸铈光敏剂及其配合体系的各组分的协同关系和作用，讨论了其与合体系对聚乙烯地膜断裂伸长率，羰基指数和相对分子质量的影响，并进行了农田地膜覆盖应用试验，结果表明，含羧酸铈光敏剂配合体系的聚乙烯地膜具有良好的使用性能和可控光降解性能。     

The effect of transition metal stearates on the photodegradation of polyethylene

The effect of a series of transition metal (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) stearates on the photodegradation of a high-density polyethylene was examined mainly by changes in the carbonyl IR absorption of the sample films. Electron spin resonance (ESR) and luminescence spectra of the samples containing the copper stearate were measured. The photochemical reaction of the copper stearate was examined by IR and UV-visible spectroscopies. The iron stearate was the most effective at an early stage of the photodegradation of the polymer, and vanadium and manganese stearates accelerated it, while the copper stearate retarded it. The other metal stearates showed no applicable effect on the photodegradation. The relative intensity of the ESR spectra of the photoirradiated samples and that of the emission spectra of the unirradiated samples at ca. 350 nm decreased with increasing concentration of the copper stearate. An absorption peak at 1580 cm^?1 decayed, and a new peak at 1740 cm^?1 appeared with photoirradiation of the copper stearate. Absorption peaks of the copper stearate at 252 and 665 nm decayed also rapidly with photoirradiation of the copper stearate in THF solution. The results suggest that one of the main retardative functions of the copper stearate in the photodegradation of polyethylene was an ultraviolet absorber.     

乙酰基丙酮钴的合成及其光敏化效果的研究

本文研究了乙酸基丙酮钴的合成、性能表征及其对ＬＤＰＥ的光氧化降解作用。结果表明，乙酰基丙酮钴对ＬＤＰＥ的光氧化效果明显优于硬脂酸铁。     

含铁络合物类光敏剂降解塑料性能的研究

合成了以二硫代氨基甲酸为配体的一系列铁络合物以及硬脂酸铁光敏剂。通过人工加速紫外光降解试验和自然暴露试验,研究了含光敏剂的LDPE膜的力学性能、粘均分子量、红外线吸收及羰基指数的变化,比较讨论含上述铁盐光敏剂的LDPE的光降解性能     

EVA对农膜再生料的力学性能及流变性能的影响

用熔融共混法制备了EVA与农膜再生料（RPE）的共混材料,研究了EVA对农膜再生料的改性作用,并与新料低密度聚乙烯（LDPE）进行了对比研究。对再生料、改性材料和新料进行了力学性能分析、旋转流变分析、转矩流变分析和形貌分析。结果表明,EVA可以显著提高农膜再生料的断裂伸长率,对拉伸强度影响不大,当EVA用量为50%时,改性材料的断裂伸长率和拉伸强度都和新料相当。EVA可以提高再生料的相容性,改善其流变性能和加工性能,使再生料的流变行为接近新料,更容易加工。     

The low temperature response of slit-seals in low density polyethylene thin films

The low temperature mechanical strength and the modes of failure of low density polyethylene (LDPE) films and hot air slit-seals have been assessed. Seven different LDPEs were blown into thin films (～30μm) and slit-sealed on-line, both the extrusion and sealing being undertaken using commercial equipment. When pulled in tension transverse to the extrusion direction, both the films and the slit-seals exhibited a ductile response at the higher temperatures, while at lower temperatures brittle failures were seen. The ductile-to-brittle transition temperatures were reasonably well defined with the slit-seal embrittling at significantly higher temperatures. The low temperature mechanical performance of LDPE films containing slit-seals is thus controlled by the seal. However, by using seven different LDPE resins with a range of melt flow rates, it was seen, that the low temperature response was enhanced with the low melt flow rate resins. Informed materials selection can therefore enable manufacturers to produce LDPE products containing slit-seals with good low temperature strength.     

Fe-Sr2Bi2O5光催化降解低密度聚乙烯膜

采用共沉淀法合成的新型光催化剂(Fe-Sr₂Bi₂O₅)与低密度聚乙烯(LDPE)通过熔融共混制备了一种新型光催化降解复合膜(Fe-Sr₂Bi₂O₅/PE)。通过力学性能、接触角、傅里叶变换红外光谱(FT-IR)和场发射扫描电镜(FESEM)等表征手段研究了该催化剂在室温条件下固相光催化降解LDPE复合膜的性能变化。结果表明:Fe-Sr₂Bi₂O₅在紫外光和可见光条件下对LDPE均具有较好的光催化降解能力,其中,紫外灯照射10 d后,Fe-Sr₂Bi₂O₅/PE复合膜断裂伸长保留率低于5%,拉伸强度保留率低于40%,接触角降低22.52°,已完全脆化;同时,LDPE复合膜中出现明显的羰基等降解特征吸收峰和降解孔洞;与Sr₂Bi₂O₅和TiO₂相比,Fe-Sr₂Bi₂O₅对LDPE具有更好的降解效果。综上所述,在紫外光和可见光条件下,Fe-Sr₂Bi₂O₅对LDPE具有明显的光催化降解作用,为未来光催化降解聚乙烯(PE)提供了一定的新依据。     

Low molecular weight paraffin,as phase change material,in physical and micro-structural changes of novel LLDPE/LDPE/paraffin composite pellets and films

Latent heat storage system by phase change materials is an effective method to achieve high density energy storage. A novel composite pellet consisted of a blend of linear low density polyethylene and low density polyethylene (LLDPE/LDPE) with low molecular weight paraffin (a phase change material, at 25 and 50 wt%) has been developed and coated by calcium silicate to prevent paraffin leakage. Three-layer coextruded films containing the paraffin composites as the middle layer have been prepared from each group for application as plastic film cover to control undesirable temperature variations during the storage of agricultural crops. The Melt Flow Index and thermal properties of the pellets as well as the quantity of paraffin leakage were studied. Thermal/morphological and permeation properties of the coextruded films have been investigated. The results showed that the LLDPE/LDPE polymer matrix provided an appropriate structural morphology for low molecular weight paraffin (n < 18) entrapment with good miscibility and low paraffin leakage (< 5%). Based on differential scanning calorimetry (DSC) thermographs, this type of paraffin may promote the compatibility between linear and low-density polyethylene. A dispersion-type morphology was observed in the micrograph of LLDPE/LDPE film, where the sizes of the spherical micro-domains were reduced as evident in the microscopic images of the paraffin-containing composite films. At storage temperatures below the phase change temperature (T < 25 °C), the oxygen permeability was substantially decreased because of the combined effects of paraffin crystallites and calcium silicate.     

Structure and dynamics of polyethylene/clay films

The relationships between structure and rheology of polyethylene/clay hybrid composite blown films were investigated through rheological tests both in shear and elongational flow. Two polymer matrices (low density polyethylene, LDPE and linear low density polyethylene, LLDPE) with different relaxation kinetics were used. Independently from the matrix, morphological analyses (TEM, XRD, and SEM) indicate that the hybrid structures are similarly constituted of delaminated platelets or tactoids having a relevant degree of orientation along the draw direction. This strongly affects the rheological behavior of materials. However, despite the similarities emerged from morphological analyses, both shear (steady shear and oscillatory) and elongation measurements show a negligible effect upon the rheology of LDPE‐based nanohybrids. Conversely, relevant increases of shear viscosity, dynamic moduli and melt strength of LLDPE‐based nanohybrids have been detected. The effects of homopolymer relaxation kinetics have been investigated by means of stress relaxation tests. The results obtained seem to be consistent with the existence of a roughly bimodal population of dynamical species: a matrix component behaving like the homopolymer, and a fraction interacting with the filler, whose rheological behavior is controlled by the particles and their interactions with the polymer. Mechanical properties of hybrid films were also investigated. Differently from what happens in the melt state, the solid‐state properties mainly depend on the filler amount. The relative increases of tensile modulus and melt strength are of the same order of magnitude for both the matrices used, indirectly confirming the similarities in hybrids structures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4749–4758, 2006     

Immobilization of antioxidant on nanosilica and the antioxidative behavior in low density polyethylene

Nanosilica was firstly modified with an aminosilane coupling agent (AEAPS) and then reacted with the reactive antioxidant, 3,5-di-tert-butyl-4-hydroxycinnamic acyl chloride (AO-Cl), to form a nanosilica-immobilized antioxidant, AO-AEAPS-silica. FT-IR, XPS and TGA measurements confirmed that the reactive antioxidant was chemically immobilized onto the nanosilica surface. SEM observation showed that the nanosilica-immobilized antioxidant was homogeneously dispersed into the matrix of low density polyethylene (LDPE). It has been found that the antioxidative efficiency of AO-AEAPS-silica was superior to the corresponding low molecular counterpart (AO), based on the measurement of the oxidation induction time (OIT) of the LDPE/AO-AEAPS-silica and the LDPE/AO compounds containing equivalent antioxidant component. The release of the antioxidant from LDPE films was evaluated by monitoring the OIT change upon water extraction, demonstrating that AO-AEAPS-silica retained high stability against migration.     

Study of the effect of gamma irradiation on the structure and properties of metallocene linear low density polyethylene containing hindered amines

The changes in the carbonyl index, the melt flow rate, the crystalline content and the ultimate tensile properties of metallocene linear low density polyethylene (mLLDPE) films subjected to gamma irradiation from 10 to 800 kGy, were investigated with and without hindered amine stabilizer (HAS). For comparative purposes, unstabilized and HAS stabilized low density polyethylene (LDPE) were also studied. The results indicated that under gamma irradiation, the HAS stabilizer did not have any influence on the oxidative stability of mLLDPE films as compared with unstabilized ones due probably to complexation reactions between the nitroxyl radicals of the stabilizer and the metallocene catalysts leading to inert species. Moreover, higher increases in melt flow index and crystalline content with a fast drop in ultimate tensile properties were observed for higher doses indicating the occurrence of chain scission. It was also found that the metallocene LLDPE structure had no significant effect on the radiation induced oxidative degradation kinetics when compared to LDPE. Whereas, the addition of HAS to LDPE significantly lowered the formation rates of carbonyls and subsequently improved the durability of the material by doubling the half-value-dose.