Photochemical stabilization of linear low-density polyethylene/clay nanocomposites: Towards durable nanocomposites

This article reports a study of the chemical modifications of LLDPE/nanoblend nanocomposites exposed to UV light in conditions of artificially accelerated ageing and natural weathering. Analysis by infrared spectroscopy of the chemical modifications produced by photoageing shows that the presence of an organo-clay leads to the decrease of the oxidation induction time of the polymer (LLDPE), which results in lower durability of the nanocomposites. Protection against photooxidation was tested with different kinds of UV stabilizers and with a metal deactivator. It is shown that the metal deactivator is very efficient in stabilizing the nanocomposite since it totally cancels the prodegradant effect of the organo-clay. This confirms the role played by iron impurities in natural clays. The use of a metal deactivator offers a new insight into the stabilization strategy for nanocomposites.     

Influence of montmorillonite nano-dispersion on polystyrene photo-oxidation

UV photo-oxidative degradation of polystyrene/montmorillonite nanocomposites (PS/o-MMTs) and microcomposite (PS/Na/MMT), obtained via in situ bulk polymerization, has been studied in accelerated conditions. Imidazolium or standard alkylammonium surfactants were used to modify MMT. The chemical modification resulting from photo-oxidation has been followed using infrared spectroscopy (FT-IR). The rate of photo-oxidation of PS/o-MMT and PS/Na/MMT was faster than that of pristine PS. The results suggest that the photo-oxidative instability could be related to the degree of exfoliation and then to the presence of catalytic active sites on the MMT layer surface.     

Photo-oxidation behaviour of polyethylene/multi-wall carbon nanotube composite films

The resistance to accelerated photo-oxidation of polyethylene/multi-walled carbon nanotubes (MW-CNTs) composite films was compared with the photo-oxidation behaviour of pristine polyethylene film. The polyethylene/MW-CNTs films containing different CNTs loading were subjected to accelerated UV-B exposure. At short exposure time, i.e. under 200 h, the rates of carbonyl formation are very similar to that observed for pristine polyethylene film but at longer irradiation times the carbonyl formation increases for lower MW-CNTs contents (0.1, 0.2 and 0.5% wt./wt.), and decreases for higher MW-CNTs contents (1 and 2% wt./wt.). By adding a UV-stabilizer to the films their photo-oxidation rates are drastically decreased also at low MW-CNTs concentration. Addition of a metal deactivator (MD) produced no observable effect.     

聚酰胺6/蒙脱石纳米复合材料的紫外光老化

聚合物 /层状硅酸盐纳米复合材料的研究十分活跃 [1～ 4 ] .聚酰胺 6/蒙脱石 ( PA6/MMT)纳米复合材料与纯聚酰胺 6( PA6)相比 ,模量和强度明显提高 ,耐热性能提高尤为显著 .光氧化行为材料科学领域的重要研究课题 .Admas等 [5]报道在紫外光照射下 ,聚丙烯 /粘土纳米复合材料的氧化速度要比纯聚丙烯的快 .对于 PA6/MMT纳米复合材料的光老化研究尚未见报道 .本文以傅里叶变换红外光谱定量研究手段 ,对比分析了 PA6/MMT纳米复合材料与 PA6的紫外光氧化性能 .1　实验部分　　采用熔体插层技术 ,将 PA6( Honeywell B1 0 0 MP)和有机蒙…     

负载卤化镍(NiX2/HD)催化MMA的原子转移自由基聚合

以负载卤化镍(NiX2/HD)为催化剂合成聚甲基丙烯酸甲酯(PMMA),具有反应可控、后处理简单且催化剂可以反复使用的优点。研究结果表明:卤原子、催化剂、钝化剂的类型和含量、反应温度等条件对该体系的聚合速率及可控性有重要影响。在相同条件下,NiCl2较NiBr2的催化速率快;钝化剂卤化铜/三-(N,N-二甲基氨基乙基)胺(CuX2/Me6TREN)对聚合产物分子量分布的可控性要优于卤化铁/三-(N,N-二甲基氨基乙基)胺(FeX3/Me6TREN);增大钝化剂的含量,聚合速率降低,且含量为1%时聚合的可控性较好;温度升高聚合速率加快,分子量分布指数(PDI)增大。顺磁共振检测中观察到钝化剂中过渡金属的化合价发生改变。     

Photo-oxidation and ozonization of poly(3-hexylthiophene) thin films as studied by UV/VIS and photoelectron spectroscopy

The kinetics and the mechanisms of degradation of thin P3HT layers have been investigated quantitatively for ozonization and photo-oxidation. Both, decay kinetics and product evolution of the polymer degradation are monitored by in situ UV/VIS and X-ray photoelectron spectroscopy (XPS). The degradation pathways of ozonization and photo-oxidation of P3HT turn out to be significantly different. Ozone attacks the thiophene units mainly by direct addition to the double bonds, leading to the loss of UV/VIS absorption, while the aliphatic side chains [1] are hardly affected. During photo-oxidation, the polymer is primarily attacked at the alkyl side chain which leads to the formation of reactive peroxide species. These subsequently cause the oxidation of sulfur and concomitantly the destruction of the thiophene ring, resulting in the loss of absorption. From the kinetics of the blue shift of the optical absorption it is concluded that the polymer is mainly attacked at the terminal thiophene rings the case of photo-oxidation whereas ozone attacks positions more or less randomly distributed along the chain. The rate of photo-oxidation under AM 1.5 conditions is at least one order of magnitude faster than the decomposition of P3HT by ozone.     

Effect of different nanoparticles on HDPE UV stability

In the present study different series of HDPE nanocomposites were prepared by melt mixing on a Haake-Buchler Reomixer, containing 2.5 wt% of multiwall carbon nanotubes, pristine and modified montmorillonite, and SiO₂ nanoparticles. Nanocomposites in the form of thin films were exposed to UV irradiation at 280 nm at constant temperature (25 °C) and constant relative humidity (50%) for several times. From tensile strength and Young’s Modulus measurements it was verified a high increase with initial UV irradiation times (till 100 h) and a slight reduction thereafter. The increase was higher in nanocomposites compared with neat HDPE, except these containing MWCNTs, and was attributed to the crystallinity increase in the particular samples. The mechanical properties reduction at higher UV irradiation times was attributed to the extensive macromolecular chain scission causing irregularities and holes in film surfaces. However, from FTIR study it was found that SiO₂ and organically modified montmorillonite cause a serious effect on HDPE during UV degradation. New chemical compounds containing carbonyl, vinyl and hydroxyl groups were formed. It seems that these nanoparticles have an accelerating effect acting as catalysts to HDPE photo-oxidation. This was also verified from micro-Raman analysis. Untreated montmorillonite has also a small influencing effect while neat HDPE and nanocomposites containing multiwall carbon nanotubes have the highest UV stability.     

Aspects of the thermal and photostabilisation of high styrene-butadiene copolymer (SBC)

The thermal and photo-oxidative stabilisation of high styrene-butadiene copolymer (SBC) with high styrene content (K-Resin) has been studied using a variety of analytical and spectroscopic methods including yellowness, luminescence and FT-IR spectroscopy coupled with hydroperoxide analysis in order to understand the nature and effectiveness of the processes involved. The next stage of the program was to evaluate the effects of various chemical/solvent treatments on the role of metal ions/residual catalysts and hydroperoxides in the thermal and photostabilisation of SBS as well as combinations of phenolic antioxidants and phosphites/phosphonites. Other additives, such as HALS and a metal deactivator, were also added to the combinations of phenolic and phosphite antioxidants in order to study their behaviour and efficiency. The chemical treatments appeared to stabilise SBS against thermal oxidation to a greater or lesser extent. Phosphoric acid treatment via reflux and zinc dithiocarbamate treatments showed better performances than the rest of the treatments, the latter was particularly effective at inhibiting the discolouration. During photo-oxidation, on the other hand, chemical treatments involving phosphoric acid and pre-thermal effects showed the importance of catalyst effects. The addition of phenolic antioxidants, phosphites/phosphonites, metal deactivator and HALS was found to stabilise the SBS against thermal and photo-oxidation. In thermal oxidation, the combination of Irganox^® 1010/Irgafos^® 168 was found to effectively stabilise the polymer when the finalisation of the polymerisation was with adipic acid. When the same antioxidants were used, but with polymer finalised with BHT, strong yellowing was observed and a higher amount of hydroperoxides and oxidation products. Increasing the amount of antioxidants did not increase the stabilisation efficiency. The stabilisation efficiency of Irganox^® 1010 combined with Alkanox^® P-24 was found to be more effective than when it was combined with Irgafos^® 168. The formulations containing Irgafos^® 168/Irganox^® 1010 and Irgafos^® 168/Irganos^® 1330 were more effective in colour protection and retarding the formation of oxidation products than the combinations of Irgafos^® 168/Irganox^® 3114 and Irgafos^® 168/Lowinox^® 1790. The effect of the addition of HALS, such as Tinuvin^® 770, Tinuvin^® 622 and Chimassorb^® 944, and a metal deactivator, such as Irganox^® MD 1024, to the combination of Irgafos^® 168/Irganox^® 1010 was found to be antagonistic. In photo-oxidation, a combination of Irganox^® 1010/Irgafos^® 168 protected the polymer efficiently, when the polymerisation of the polymer was finalised with adipic acid. When the polymerisation was finalised with BHT, a higher amount of hydroperoxides and oxidation products was found. An increase in the amount of antioxidants did not enhance the stability of the polymer. The addition of Alkanox^® P-24 exhibited an opposite effect to that seen in thermal oxidation, as the stabilisation efficiency was less effective than with Irgafos^® 168. The formulation containing Irgafos^® 168/Irganox^® 1010 was found to be the most efficient compared with the other phenolic antioxidants. The addition of Tinuvin^® 770 to the formulation Irgafos^® 168/Irganox^® 1010 was found to have a synergistic effect. The addition of polymeric HALS or Irganox^® MD 1024, a metal deactivator, had an antagonistic effect on the stabilisation of the polymer. Disruption of the excimer sites in the styrenic phase also correlated with stabilisation effects.     

UV‐curing synthesis of sulfonated polyaniline‐silver nanocomposites by an in situ reduction method

Sulfonated polyaniline‐silver (SPAni‐Ag) hybrid nanocomposites have been synthesized by the in situ reduction using a UV‐curing polymerization method without using any reducing or binding agent. An aqueous solution of aniline and orthoanilinic acid (OA) comonomers, a free‐radical oxidant and silver metal salts were irradiated by UV rays. Reduction of the silver salt in aqueous aniline and OA leads to the formation of silver particles which in turn catalyze the oxidation of comonomers to sulfonated polyaniline (SPAni). The resultant SPAni‐Ag nanocomposites were characterized by using different spectroscopy analyses like UV–visible (UV–Vis), X‐ray diffraction (XRD) and infrared spectroscopy. The absorption bands were revealed to be optically active and the peaks blue‐shifted due to the presence of metallic silver within the SPAni matrix. The XRD patterns displayed both the broad amorphous polymeric and sharp metallic peaks. Scanning electron microscopy and transmission electron microscopy of the nanocomposites showed a uniform size distribution with spherical and granular morphology. Thermogravimetric analysis revealed that the nanocomposites had a better thermal stability than the bulk SPAni. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of compatibilizer and Irganox MD 1024 on the thermo-oxidative stability of PP/PP-g-MA/OMMT nanocomposites

The thermo-oxidative stability of polymeric materials reinforced with mineral fillers, such as clays, may be lower than that of pristine polymers, due to the presence of metallic ions and compatibilizing agents. In this paper, an effort was made to understand the influence that a compatibilizing agent and a metal deactivator bonded to a primary stabilizer has on the thermal stability of polypropylene/polypropylene-grafted maleic anhydride/organic montmorillonite (PP/PP-g-MA/OMMT) nanocomposites. At the first stage of this work, the organically modified montmorillonite clay is chemically analyzed by Inductively Coupled Plasma Atomic Emission Spectrometry to quantify the metals present in the clay. TGA, DSC, OIT, and dynamic OIT were used to assess the degradation of the nanocomposites. The results showed that the use of compatibilizing agents has a positive effect on the stability of nanocomposites in the initial steps of degradation, but has a degradative effect at higher temperatures, as indicated by the decreasing T_max for compatibilized nanocomposites. In relation to Irganox MD 1024, an increase in all the parameters for assessing the stability of nanocomposites was observed; however, the most significant change was the delay in the temperature at which the occurrence of exothermal reactions begins. Use of this additive is responsible for delaying the beginning of the exothermic reaction until a higher temperature, as a function of its concentration, as well the differences between the beginning of volatile release and the exothermal reactions. Also was discussed the influence of Irganox MD1024 concentration on T_max, and the difference of temperature between the beginning of heat releasing and the initial weight loss, which decreases as the stabilizer concentration is increased. Thanks to the association of dynamic OIT and TGA results from experiments performed with identical conditions. This complementary use of these techniques is a powerful tool for assessing the stability in the polymeric system.     

Fabrication,characterization of polyaniline intercalated NiO nanocomposites and application in the development of non-enzymatic glucose biosensor

Determination of glucose plays very important part in diagnostics and management of diabetes. Nowadays, determination of glucose is necessary in human health. In order to develop the glucose biosensor, polymer modified catalytic composites were fabricated and used to detect glucose molecules. In this work, NiO nanostructure metal oxide (NMO) was fabricated via thermal decomposition method and polyaniline (wt% = 2, 4 and 6) assisted nanocomposites (NiO/PANI) were also prepared. The morphology and structure of synthesized nanocomposites were characterized by UV–visible diffusion reflectance spectroscopy (UV–vis-DRS), Fourier transform- infra red spectroscopy (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and N₂ adsorption-desorption isotherm measurement. The modified NiO/6%PANI/GCE had higher catalytic activity toward the oxidation of glucose than NiO/GCE, PANI/GCE, NiO/2%PANI/GCE and NiO/4%PANI/GCE. This is due to the larger surface area of NiO/6%PANI nanocomposites provide a ploform for faster electron transfer to the detection of glucose. The constructed glucose biosensor have been exhibited a high sensitivity of 606.13 µA mM⁻¹ cm⁻², lowest detection limit of 0.19 µM, high selectivity, stability, simplicity and low cost for the quick detection of glucose in real sample as well.     

Quantitation method of N,N ′‐disalicylidene‐1,2‐propanediamine by comprehensive two‐dimensional gas chromatography coupled to a nitrogen chemiluminescence detector

Metal deactivator additives (MDAs) have been used for over 60 years to prevent metal catalyzed reactions in petroleum products; a commonly used metal deactivator is N,N′‐disalicylidene‐1,2‐propanediamine. The quantitation of low MDA concentrations in fuels is challenging due to the complexity of the sample matrix. In this work, this difficulty was overcome using GC × GC hyphenated with a nitrogen chemiluminescence detector. The high resolution power of GC × GC avoided co‐elution between the MDA and other sample matrix compounds; while the enhanced sensitivity of GC × GC and the use of a nitrogen chemiluminescence detector supplied a high sensitivity and specificity for nitrogen compounds. For the analysis, the MDA additive was derivatized with the silylation agent N,O‐bis (trimethylsilyl)trifluoroacetamide at room temperature and its quantitation was based on an external calibration curve; good linear response was obtained in the 1.4–8.6 ppm range.     

Photodegradation: a solution for the shopping bag “visual pollution” problem?

Plastic bags pose a “visual pollution” problem as they have a high surface-to-volume ratio and because they are often brightly coloured. Enhanced photo-oxidation is a possible route to accelerate the mineralisation of such litter. Thus we evaluated the effect of selected metal complexes and an anti-oxidant on the accelerated weathering of blown polyethylene and polypropylene films in a QUV tester. It was found that the additives were more effective in polypropylene than in polyethylene. The transition metal complexes, particularly ferric stearate, were very effective photodegradants. Copper stearate provided a measure of UV protection to polyethylene but not to polypropylene. Poly (1,2-dihydro-2,2,4-trimethylquinoline), a commercial anti-oxidant, also caused accelerated UV degradation. This is significant as its use as a prodegradant is not expected to adversely affect the recyclability of the polymers.     

Photo-stabilising action of metal chelates in polypropylene—Part II: Photolysis versus photo-sensitised oxidation under monochromatic irradiation

The photo-stabilising action of three metal chelates in unprocessed and processed polypropylene is examined using normal and second order derivative ultraviolet and infra-red spectroscopic techniques and hydroperoxide analysis. The effects of photolysis with 254 nm light versus photo-sensitised oxidation with 365 nm light are compared. For each exposure condition the rate of carbonyl formation in the polymer is compared with the rate of decomposition of the metal complex. On photolysis, carbonyl growth commences well before the complete destruction of the complexes and none offers protection to the polymer. In fact, all three chelates behave as photo-sensitisers, indicating that stabiliser photolysis products are photo-active. On photo-sensitised oxidation, while the initial hydroperoxide concentration appears to control the onset of carbonyl growth in the polymer, the rate of decomposition of the complexes shows no dependence on hydroperoxide concentration. Solution experiments indicate that there are no dark reactions with hydroperoxides apart from one of the nickel chelates (Cyasorb UV 1084) at high concentrations (～ 10^?2m) only. Essentially, the metal chelates operate by scavenging macroalkyl radical species (P·) and not alkoxy (PO·) and hydroxy radicals (·OH) during photo-oxidation. They also inhibit hydroperoxide formation during processing and one of the nickel chelates (UV 1084) gives products during the early stages of photo-oxidation which appear to operate as effective stabilisers.     

Photo-oxidation of proteins and its role in cataractogenesis.

Proteins comprise approximately 68% of the dry weight of cells and tissues and are therefore potentially major targets for photo-oxidation. Two major types of processes can occur with proteins. The first of these involves direct photo-oxidation arising from the absorption of UV radiation by the protein, or bound chromophore groups, thereby generating excited states (singlet or triplets) or radicals via photo-ionisation. The second major process involves indirect oxidation of the protein via the formation and subsequent reactions of singlet oxygen generated by the transfer of energy to ground state (triplet) molecular oxygen by either protein-bound, or other, chromophores. The basic principles behind these mechanisms of photo-oxidation of amino acids, peptides and proteins and the potential selectivity of damage are discussed. Emphasis is placed primarily on the intermediates that are generated on amino acids and proteins, and the subsequent reactions of these species, and not the identity or chemistry of the sensitizer itself, unless the sensitizing group is itself intrinsic to the protein. A particular system is then discussed--the cataractous lens--where UV photo-oxidation may play a role in the aetiology of the disease, and tryptophan-derived metabolites act as UV filters.     

Dependence of ultraviolet absorbers' performance on ultraviolet wavelength

So far, ultraviolet absorbers (UVA) have been discussed mainly on the basis of the extinction coefficient (?), and the light degradation of polymeric materials is explained by photolysis of hydroperoxides and Norrish reactions of ketones. This study focuses on the photo-antioxidant ability as characteristic which UVA must possess for the light stabilization, and examines the dependence of the photo-initiation by oxidation products on UV wavelength range. As a result, it has been made clear that UV rays ranging 290-320 nm trigger photo-oxidation (degradation) by photolysis of hydroperoxides and Norrish reactions of ketones, and α-diketone derived from further oxidation of the ketones, for example, initiates photo-oxidation at a surprisingly higher velocity under UV rays above 350 nm. UV rays in the range of 320-350 nm participate in the photo-initiation by an enone (CCCO) structure in addition to the above-mentioned oxidation products, in which the initiation velocity is the medium between the velocities for the above two wavelength ranges. That is to say, the longer the UV rays wavelength range, the faster the photo-initiation velocity. Finally, it is concluded that excellent UVA are judged based on λ_max rather than ?, and that UVA absorbing longer wavelength UV rays can more control the photo-oxidation.     

Type and distribution of chemical groups from controlled photo-oxidation of gyroid nanoporous 1,2-polybutadiene

Photo-oxidation of nanoporous polymers is little studied. The high UV penetration depth and high surface concentration in these materials give unprecedented possibilities both in fundamental work on surface photochemistry and in nanotechnological applications related for example to patterned hydrophilicity or refractive index. This is a quantitative study of the photo-oxidation products of nanoporous gyroid 1,2-polybutadiene in air. Irradiation of the porous sample with UV in the wavelength range of 300-400 nm enables tuning of the hydrophilicity of the nanoporous polymer through formation of hydrophilic chemical groups, carboxyl and hydroxyls, mainly onto the large air-polymer interface. The nature and abundance of the chemical groups induced by photo-oxidation is identified by solid-state ¹³C-NMR and FTIR spectroscopy. The distribution of photo-oxidation groups, both relative to the nanometre-scale polymer-air interface, and as a function of irradiation depth in the sample, is studied by gravimetry, titrimetry, ATR-FTIR and energy dispersive X-ray spectroscopy in scanning electron microscopy.     

Durability of a starch-based biodegradable polymer

The photo-oxidation and the photo-stabilization of a commercial biodegradable polymer have been investigated in order to establish the possibility of using this polymer as raw material for films for agriculture. The degradation has been followed by measuring the mechanical properties as a function of photo-oxidation time and in particular by following the elongation at break. The virgin polymer, made from maize starch and a synthetic biodegradable polyester, shows poor resistance to the UV irradiation as observed by the fast decay of the elongation at break, but the presence of small amounts of conventional UV stabilizers strongly improves the durability of this polymer. The UV stabilizers remarkably extend the induction time without modifying the photo-oxidation kinetics.Among the investigated stabilizers, the benzophenone compound seems to work slightly better than the benzotriazoles, than the triazine and than the sterically hindered amine. This behaviour has been attributed to the larger absorbance in the UV range of the biodegradable polymer.     

TiO2和ZnO表面CO光催化氧化活性研究

在TiO2和ZnO表面CO光催化氧化研究中发现,365 nm紫外光照下TiO2表面无活性,而ZnO表面却有明显的CO光催化氧化活性.研究表明,主要是由于紫外光照下,ZnO光分解而TiO2没有光分解,从而在表面产生不同吸附形态的氧所致.而且,ZnO表面CO光催化氧化反应活性可在27 h内保持稳定,暗示气相光催化反应中,ZnO不会因为光腐蚀而使其催化活性降低.     

Surface engineering of nanoparticles for highly efficient UV‐shielding composites

Overexposure to ultraviolet (UV) with high energy can not only hurt human skin but also accelerate the degradation of organic matter. Hence, the preparation of polymer‐based UV‐shielding nanocomposites has attracted substantial attention due to the low cost, easy processing and wide applications. Notably, the highly efficient UV‐shielding polymer nanocomposites are still hindered by the agglomeration of inorganic anti‐UV nanoparticles (Nps) in polymer matrix and the narrow absorption range of UV‐shielding agents. To overcome the aforementioned bottlenecks, surface engineering of anti‐UV Nps including organic modification and inorganic hybridization has been extensively employed to enhance the UV‐shielding efficiency of composites. Herein, to deliver the readers a comprehensive understanding of the surface engineering of anti‐UV Nps, we systematically summarize the recent advances in surface organic modification and inorganic hybridization related to anti‐UV Nps. The UV‐shielding mechanism and the factors affecting UV‐shielding efficiency of polymer nanocomposites are also discussed. Finally, perspectives on remaining challenges and future development of highly efficient UV‐shielding composites are outlined.