Surface and bulk modification of polyolefins by functional aryl nitrenes as highly reactive intermediates

Aromatic azides with hindered amine light stabilizer (HALS) residues or hydrophilic groups such as glucose, sucrose and dextrine residues were synthesized and used for surface modification of polyolefins. By UV‐irradiation nitrenes were formed, which are able to react with polyolefin surfaces. By photochemical immobilization of the carbohydrates hydrophilicity of PE and PP was strongly increased (surface tensions > 44mN/m). Light stability of PP surfaces modified with HALS azides was comparable with PP, stabilised with Tinuvin 770. Bulk modification of ethylene‐propylene and ethylene‐octene copolymers was achieved by grafting nitrenes formed by thermal decomposition of azido benzoic acid. In a circulating air oven up to 1.55 wt% amino benzoic acid residues could be bonded covalently to ethylene‐propylene‐copolymers, less than half of it to ethylene‐octene‐copolymers. Reactive extrusion resulted in grafting yields of more than 50% for both types of copolymers.     

Degradation of polymer blends—II. Oxidative radiolysis and stabilization of blends of low-density polyethylene and styrene-butadiene-styrene copolymers

The solubility, infra-red and mechanical properties have been studied for LDPE-SBS blends irradiated with γ-rays in the presence of oxygen. The results have been compared with those obtained for the oxidative radiolysis of pure LDPE and for the photo-oxidation of the same LDPE-SBS blend. The oxidative degradation mainly occurs in the polybutadiene part of the blend. Efficient stabilization by hindered amines Tinuvin 770 is reported.     

The mechanism of u.v. stabilization of polypropylene films by 2-hydroxy-4-octyloxybenzophenone

The rates of oxygen absorption by unstabilized and u.v.-stabilized polypropylene (PP) films irradiated with a high-pressure mercury lamp have been determined as a function of the light intensity (I). The induction time is nearly proportional to I^?0.5 for unstabilized PP and for PP stabilized with Tinuvin P, and proportional to about I^?0.9 for PP stabilized with 2-hydroxy-4-octyloxybenzophenone (HOBP). The change in concentration of HOBP in PP during the photo-oxidation is determined with radioactive HOBP. During the induction time, the observed decrease obeys zero-order kinetics even when the starting concentration of HOBP is as low as 0.008%. The decrease is caused by reaction of HOBP with the polymer and by fragmentation into gaseous products. These results are interpreted on the basis of the same reaction scheme as that worked out for the uninhibited and inhibited autoxidation of PP. It is concluded that HOBP acts not only as a u.v. absorber or as an excited-state quencher, but also as a scavenger of free radicals.     

光交联聚乙烯材料的光稳定性研究

本文中用紫外光敏化的方法对低密度聚乙烯进行了交联,并利用ESCA和ATR-IR等手段研究了交联后材抖的光稳定性及其改进办法。     

Detection of tinuvin 770, a light stabilizer of plastic materials from dialysis membranes, by high-performance liquid chromatographic analysis

Tinuvin 770 [bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate] is a pharmacologically active agent used worldwide as a light stabilizer for plastic materials. In vitro studies show that it is an L-type Ca(2+) channel and neuronal nicotic acethylcholine receptor blocker. Hypotension, vegetative dysfunction, and neurological symptoms are frequently observed during a haemodialysis treatment. The release of Tinuvin 770 from plastic materials applied in haemodialysis may play a part in the development of clinical signs. In our study, four different commonly used haemodialysis membranes (polysulphon, cuprophan, and two types of hemophan) are examined. The polymers are soaked for 72 h in physiological saline solution. Isolation is carried out using a Waters Oasis SPE column for solid-phase extraction and by high-performance liquid chromatography (HPLC) with electrospray ionization-mass spectrometric detection. Tinuvin 770 release is detected from all examined membranes. Validation studies show a satisfactory selectivity, linearity, accuracy, and recovery of this method. Our results suggest that Tinuvin 770 could have specific toxicological and therapeutic importance related to haemodialysis treatment. The developed HPLC method is suitable for the detection of Tinuvin 770.     

Total luminescence intensity (TLI) offers superior early oxidation detection in unstabilised polyethylene but is no better than FT-IR for stabilised polyolefins

In an earlier study, we have shown that chemiluminescence (CL) and the total luminescence intensity (TLI) method are highly sensitive to oxidation in degradable PE. In this study, stabilised PE and PP were characterised with CL in an inert (TLI) and in an oxygen atmosphere (CL-OIT) and the results were compared to those obtained by the commonly used techniques, FT-IR (carbonyl index (CI)) and thermal analysis (DSC-OIT). PE was aged at a low temperature (80 °C) and PP was aged at temperatures between 60 and 120 °C. Non-Arrhenius behaviour was observed in the oxidation of PP. This showed the importance of aging at a low temperature to obtain realistic results. TLI and CI of stabilised PP and most of the stabilised PE gave comparable results with the same sensitivity for oxidation detection. This was in contrast to our previous results for degradable PE. However, TLI of unstabilised PE showed earlier oxidation detection than CI, which agreed with our earlier results. TLI of PE had a higher sensitivity than CL-OIT, and both TLI and CI of PP were sufficiently sensitive to detect the effect of aging at different temperatures, whereas DSC-OIT was not.     

Role of the UV absorber as a matrix in matrix‐assisted laser desorption/ionization mass spectrometric analysis of a mixture of a UV absorber and a stabilizer

A mixture of a UV absorber (Tinuvin 234 or Tinuvin 329) and a UV stabilizer (Tinuvin 770) was analyzed using matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) without any matrix. Fragmentation patterns of the UV absorbers and stabilizer were also investigated. The mass spectra showed the [M+H]⁺ ions and some fragment ions. Tinuvin 234, Tinuvin 329, and Tinuvin 770 generated three (m/z 119, 370, 432), one (m/z 252), and two (m/z 124 and 140) fragment ions, repectively. These fragment ions can be used to identify the chemical structures of the UV absorbers and stabilizer. Since the UV absorber performed a role as the matrix, the ion abundance of the UV stabilizer was enhanced by mixing with the UV absorber. When organic materials extracted from polypropylene (PP) containing the UV absorber and stabilizer were directly analyzed using MALDI‐MS without any matrix, the protonated molecule of the UV stabilizer was detected in abundance but the product ions of the UV absorber were not observed. When 2,5‐dihydroxybenzoic acid was used as a matrix, the protonated molecule of the UV absorber was observed. Copyright © 2010 John Wiley & Sons, Ltd.     

Vacuum-ultraviolet induced oxidation of the polymers polyethylene and polypropylene

The emission from low-pressure microwave plasmas in the vacuum-ultraviolet (VUV) region (λ < 200 nm) was investigated in order to use these plasmas as light sources for the study of the VUV photochemistry of polyethylene (PE) and polypropylene (PP) as part of the study of plasma-polymer interaction. These polymers, immersed in low-presure oxygen, were exposed to radiation with wavelengths down to 112 nm, the cut off of magnesium fluoride used as a window to separate the polymer specimen from the plasma light source. Total oxygen incorporation in the surface [O], and the formation of hydroxyl, carbonyl, and carboxyl groups were measured using XPS in combination with chemical derivatizations, particularly their dependence upon the radiation spectrum and the oxygen pressure around the sample. In most experiments the surface oxygen concentration [O] attained a constant value that appears to be related to the initial oxidation rate; this suggests a competition between oxygen incorporation and chain scission reactions, followed by the removal of volatile oxidation products. PE is usually oxidized to a higher level than PP, the latter appearing to be more susceptible to reaction with atomic oxygen than PE. A general initiation mechanism for the VUV experiments is proposed that allows us to explain the observed differences in behavior between PE and PP, and the results obtained under different irradiation conditions. The nature of oxidation products is in both cases very similar to what is observed after direct plasma treatment of the polymers. We conclude that short wavelength radiation contributes very appreciably to the observed surface modification effects during plasma treatment of PE and PP. © 1995 John Wiley & Sons, Inc.     

Recycling of crate material: Weatherability of stabilised recycled high density polyethylene

The uv stabilising effect of various stabilisers added to degraded, yellow-pigmented, high density polyethylene (HDPE) crate material originating from crates that have been in use for 10–13 years was investigated. For that purpose, outdoor and Xenotest-1200 exposure tests were carried out, and rates of oxygen absorption during photo-oxidation were determined. The uv stability of the degraded HDPE could be considerably improved—in particular, by the addition of a hindered amine type stabiliser (Tinuvin 770). The uv stability attainable is such that reuse of recycled crate material for the production of new crates is, after upgrading, a realistic possibility.A comparison of the results of outdoor and accelerated ageing showed that the acceleration factors strongly depend on the type of stabiliser applied. This can be attributed to the different mechanisms of stabilisation by which the various additives act.The uv stability of the recycled polymer appeared to be almost independent of the degree of degradation of the crates before recycling. This implies that it is not necessary to exclude from recycling heavily degraded crates which had failed due to brittle fracture.     

EFFECTS OF ORGANIC COLORANTS ON PHOTO-INITIATED CROSSLINKING AND PHOTO-OXIDATION DEGRADATION OF POLYETHYLENE AND RELATED MECHANISM

The effects of three organic colorants on photo-initiated crosslinking and photo-oxidation degradation of polyethylene (PE) samples irradiated by microwave excited (MWE) UV lamp in the melt and the related mechanism have been studied by gel content and thermal extension rate determinations,X-ray photoelectron spectroscopy (XPS),mechanical property tests,UV spectroscopy,and light microscope.The data from the gel content and thermal extension rate determinations of photo-crosslinked polyethylene (XLPE) sam...     

Effect of Oxygen Concentration on Photo-oxidation and Photosensitizer Bleaching in Butter

The effect of headspace oxygen concentration and color of light on photo-oxidation and degradation of photosensitizers in butter was studied. Butter samples were stored under 0%, 0.4%, 0.8%, 1.6%, 3.0%, 5.0%, 21% oxygen, and exposed to violet, green or red light. Storage time was 36 h. Degree of photo-oxidation was measured by a trained sensory panel. Photobleaching of six different photosensitizers was estimated based on front face fluorescence excitation and emission landscapes and spectral curve resolution (parallel factor analysis). The higher oxygen concentration, the more sensory degraded were the samples. Violet light resulted in slightly higher degrees of photo-oxidation than green and red light for low oxygen concentrations. Bleaching rate and course as function of O₂ concentration differed between the photosensitizers. It is suggested that the rate of photobleaching is a balance between type I and type II photoreactions.     

Surface-Anchored Hindered-Amine Light Stabilizers for Improved UV Stability of Polyolefins

Abstract

Hindered-amine light stabilizers (HALS) were surface anchored to polyolefin films by reacting the HALS, namely, 1,2,2,6,6-pentamethyl-4-piperidinol and 1,2,2,6,6-pentamethyl-4-aminopiperidine, with succinic anhydride functionalized polyolefin surfaces. The photostability of polyolefin films with surface-anchored HALS were compared with films stabilized with commercial HALS (Tinuvin 770) by melt blending. It is shown that the photostabilizing efficiency of surface-anchored HALS is superior that of melt-blended polyolefins.     

Study of the thermal oxidation of polyolefines—IX: Some differences in the oxidation of polyethylene and polypropylene

In the thermal oxidations of polyethylene (PE) and polypropylene (PP), both similarities and differences are found. In the initial stage, the ratio of the hydroperoxide formed and the amount of oxygen absorbed is independent of both the nature of the polymer and the actual reaction conditions. With increased conversion, however, this ratio decreases to a greater extent in the case of PE than for PP. Most of the carbonyl groups formed in the PE chain during oxidation are ketones and carboxyls, but in PP there are also carbonyls with different structure. The amount of carbonyl groups in PE is approximately 1.5 times that observed for PP. The number of scissions involving considerable molecular weight decrease is higher for PE than for PP: for identical conversions, the ratio of scissions is S_PE/S_PP ～ 6.     

Photochemical behaviour of fire-retarded polymers

The influence of a non-halogenated intumescent fire retardant on the photooxidation of polypropylene is reported. The photooxidation of polypropylene stabilised with a phenolic antioxidant and two redox antioxidants (HALS), without and with the flame retardant has been studied. The chemical modifications resulting from UV-light exposure with wavelengths above 300 nm in the presence of oxygen were followed by IR and UV-visible spectroscopies. Special attention was given to the influence of each component on the rate of oxidation of the polymeric matrix. The photooxidation of the fire-retarded polymer can be described by two independent phenomena: the photooxidation of the intumescent agent and the photooxidation of the polymer. The results obtained offer new insight in the formulation of stabilised fire-retarded PP for outdoors applications.     

Mechanisms of antioxidant action: Nitrosamines as heat and light stabilisers for polypropylene

N-Nitrosamines are shown to be very effective melt stabilisers for polypropylene and one of these, derived from the hindered amine light stabiliser, Tinuvin 770, is almost twice as effective as the latter. The mechanism is believed to involve the formation of two kinds of nitroxyl radical, the first derived from the amine and the second formed by the reaction of nitric oxide with alkyl, and possibly alkoxyl, radicals. Nitrosamines which do not dissociate to NO are neither melt stabilisers nor uv stabilisers.     

SYNTHESIS AND EVALUATION OF A NEW PHOTOSTABILIZER—2, 2, 6, 6-TETRAMETHYL-4-PIPERIDINYL SALICYLATE FOR POLYMERS

A new photostabilizer--2,2,6,6-tetramethyl-4-piperidinylsalicylate (TMPS) has been syn-thesized by ester-exchange reaction between 2,2, 6, 6-tetramethyl-4-piperidinol and methylsalicylate.The photostabilizing effect of TMPS and Tinuvin 770, PDS on the photodegradation of cis-1,4-polybutadiene has been investigated for comparison. The results observed show that the mosteffective stabilizer of the three is TMPS. The reason of the good photostabilizing effect of TMPSwas discussed by fluorescence spectra.     

Quenching of singlet oxygen by hindered amine light stabilisers. A flash photolytic study

Rate constants for the quenching of singlet oxygen (¹O₂, ¹δ_g) for a series of piperidines, piperidine-N-oxyl free radicals and some commercially used hindered amine light stabilisers (HALS) have been measured by a laser flash photolysis method. Quenching rate constants are in the order: piperidine-N-oxyl free radicals ≤ secondary piperidines < tertiary piperidines. For some commercial HALS, ¹O₂ quenching rate constants and the light protective effect towards polypropylene photo-oxidation have been compared. No correlation has been found between the stabilizing action and the quenching efficiency towards ¹O₂. The data obtained point to little contribution of singlet oxygen to the key steps of polyolefin photo-oxidation.     

苯乙烯-甲基丙烯酸四甲基哌啶醇酯共聚物光防护行为的研究

本文用力学性能、分子量、ESR、IR等测定方法,研究比较了大分子受阻胺PDS和小分子受阻胺Tinuvin-770对聚丙烯的光防护作用。结果表明,二者的光防护作用都是通过形成>NO·稳定自由基机理;并能有效地接枝在聚丙烯上,而PDS还具有“微交联“作用。光氧化监测表明,PDS较耐光分解,其光氧化防护中所产生的>NO·稳定自由基在整个老化过程中保持一定的浓度,加之大分子化改善了PDS的热稳定性,耐抽提性,相容性,因而使PDS具有较高的光防护效率。     

一种新型的高聚物的光稳定剂——4-(水杨酸)2,2,6,6-四甲基哌啶醇酯的合成及其光稳定能力的评价

<正> 自1967年日本Sankyo公司发现2,2,6,6-四甲基哌啶化合物具有良好的光稳定能力以来,对该类化合物的研究与开发工作已取得很大的进展。不同结构的衍生物作为正式商品不断问世,同时作为添加剂已在许多大品种烯类聚合物制品中得到广泛的应用,然而它作为一种光稳定剂其稳定效能在某些方面仍不能令人满意,如对紫外辐射屏蔽作用,由于它在300—350 nm波长范围内只有较小的克分子吸收系数,因此是不够理想     

Quantitative Analysis of Polymer Additives with MALDI-TOF MS Using an Internal Standard Approach

MALDI-TOF MS is used for the qualitative analysis of seven different polymer additives directly from the polymer without tedious sample pretreatment. Additionally, by using a solid sample preparation technique, which avoids the concentration gradient problems known to occur with dried droplets and by adding tetraphenylporphyrine as an internal standard to the matrix, it is possible to perform quantitative analysis of additives directly from the polymer sample. Calibration curves for Tinuvin 770, Tinuvin 622, Irganox 1024, Irganox 1010, Irgafos 168, and Chimassorb 944 are presented, showing coefficients of determination between 0.911 and 0.990.