Oxidation of ultra high molecular weight polyethylene (UHMWPE) part 2: Critical examination of the total luminescence intensity (TLI) method for determining hydroperoxides

The validity of the total luminescence intensity (TLI) method for determining the amount of hydroperoxides in a UHMWPE sample has been assessed. Measurements of hydroperoxides with FTIR before and after a TLI run showed that only about 50% of the hydroperoxides were decomposed at 150 °C. It was also found that this value was not constant with ageing time, which means that the TLI value could not be representative of the total number of hydroperoxides in a sample as a function of ageing time. Thermoluminescence was also found to complicate the measurements and could, if care was not taken, give TLI values that were much too high. In addition it was found that the TLI value is actually connected with the build-up of carbonyls rather than the build-up of hydroperoxides. This last finding is consistent with part one of this study, where it was reported that CL from oxidising UHMWPE is a type of activated CL, where carbonyls are the activating species. From all of these results it is concluded that TLI is not a suitable method for determining hydroperoxides in UHMWPE.     

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.     

Chemiluminescence kinetic analysis on the oxidative degradation of poly(lactic acid)

The oxidation of polymers is characterized by the generation of free radicals, and the kinetic parameters depicting the progress of oxidation are specific for each material structure and formulation. The durability of materials depends intrinsically on the molecular structure, and degradation mechanism influences the long-term stability of products. The intimate transformations of macromolecules can be reliably characterized by chemiluminescence (CL), which depicts the evolution of oxidation state by the reaction of free radicals with molecular oxygen. The isothermal and nonisothermal CL spectra are complementary proofs for the interpretation of oxidation behavior involving hydroperoxide as the initiators of oxidation. The degradation of PLA takes place by decomposition and fragmentation to lactide. The values of five kinetic parameters (initial CL intensity, CL intensity at the first peak, temperature corresponding to the first peak, oxidation induction time and oxidation rate) obtained for oxidative degradation of PLA lead to the activation energies ranged between 49 and 99 kJ mol^?1. The evolution of thermal degradation for poly(lactic acid) is an excellent example for the explanation of the decay fate of radical intermediates.     

Chemiluminescence from the thermal oxidation of polyisoprene and polybutadiene I. Influence of oxygen pressure on the chemiluminescence of polyisoprene during its oxidation

The influence of oxygen pressure p (0.016-0.1 MPa) on polyisoprene thermal oxidation at 100 °C has been studied by chemiluminescence (CL). The maximum CL intensity was found to be almost proportional to p, whereas the induction time is influenced in the same way but to a lesser extent. Assuming that the classical mechanistic scheme with initiation by bimolecular hydroperoxide decomposition and termination by bimolecular radical combination, partially studied by Tobolsky and co-workers in the 1950s, is valid, it was established that chemiluminescence originates essentially from hydroperoxide decomposition. A theory which tries to reconcile this result with the most popular hypothesis according to which light is emitted by terminating peroxyl bimolecular combination is proposed.     

Use of 9,10-diphenylanthracene as a contrast agent in chemiluminescence imaging: The observation of spreading of oxidative degradation in thin polypropylene films

Thin films of polypropylene were doped with a chemiluminescence (CL) activator, 9,10-diphenylanthracene (DPA), and were thermally oxidised in a CL imaging apparatus to determine whether heterogeneous oxidation processes such as spreading of oxidation could be observed. The presence of DPA resulted in significantly more intense CL images compared with undoped polymer, due to the efficient chemically induced electron exchange luminescence reaction between DPA and hydroperoxides. Hence, the CL images from DPA-doped PP were used to locate the position of hydroperoxides in the oxidising polymer. For thermal oxidation at 150 and 140 °C hydroperoxides were observed to form in localised regions of the films, whilst other areas remained hydroperoxide free. As the oxidation time increased the concentration of hydroperoxides in these areas increased and they were observed to spread to the remainder of the polymer. Time-resolved line maps from the images indicated that zones with high concentration of hydroperoxides travel through the polymer during oxidation. Integrals of CL images from the thermal oxidation of DPA-doped polymers indicated that a significant degree of oxidation had occurred by the end of the “induction period” for a conventional CL-intensity oxidation-time profile. This is a likely reason why spreading of oxidation has not previously been observed for undoped PP films.     

胶束微观非均相体系与化学发光能量转移

胶束微观非均相体系能提高化学发光的选择性和灵敏度,并且实验操作方便,因此其在化学发光检测技术中的应用已成为研究热点.胶束增敏化学发光是对激发量子效率,荧光量子效率以及反应的速率综合作用的结果.本文综述了正相和反相胶束体系在能量转移型化学发光体系中的应用,同时阐述了胶束与不同发光体系的相互作用.     

CdTe量子点增敏鲁米诺-KMnO4化学发光对间苯二酚的测定

碱性介质中,CdTe量子点能够强烈地增强鲁米诺-KMnO4体系的化学发光,间苯二酚对该体系的化学发光有很强的抑制作用.该文结合流动注射分析法,建立了测定间苯二酚的新方法,并对可能的反应机理进行了探讨.结果表明,在优化实验条件下,间苯二酚在1.0×10-9 ～5.0×10-5 mol/L的浓度范围内与发光强度呈良好的线性关系,检出限(S/N=3)为8.0×10-10 mol/L.对于1.0×10-7 mol/L间苯二酚,测定11次的相对标准偏差为2.6%.将该体系用于水样中间苯二酚的测定,回收率为96% ～104%,相对标准偏差为1.9% ～3.3%.     

雌二醇的流动注射阻抑化学发光法测定

基于碱性介质中雌二醇对N-溴代丁二酰亚胺-钙黄绿素化学发光体系的阻抑作用,建立了雌二醇的流动注射化学发光分析新方法,优化了其分析条件,并初步探讨了该化学发光反应的机理。该方法测定雌二醇的线性范围为0.02~0.1、0.1~8.0 mg/L,检出限为0.008 5 mg/L。对0.1 mg/L的雌二醇标准溶液进行11次平行测定,相对标准偏差为1.2%。将该法用于注射液中雌二醇的测定,结果满意。     

CdTe纳米棒-过氧化氢化学发光体系的研究

在水相中合成了以巯基乙酸和L-半胱氨酸为稳定剂的CdTe纳米棒。研究发现在碱性溶液中H2O2能直接氧化CdTe纳米棒产生强烈的化学发光,化学发光的强度与CdTe纳米棒尺寸大小相关,且一些表面活性剂能强烈敏化该反应。     

ON SOME PROBLEMS CONCERNING INVESTIGATION OF LIQUID-PHASE CHEMILUMINESCENCE

Abstract— Some features of chemiluminescence important for quantitative studies of the phenomenon are discussed. Parallel excitation reactions may lead to several sorts of emitters. Energy transfer from and quenching of excited states may be responsible for the peculiar behaviour of chemiluminescent systems. These points are illustrated by results for a model reaction: thermal decomposition of dicyclohexylperoxydicarbonate (DCHPC) in the presence of O₂ with or without methylethylketone and an activator, 9,10-dibromoanthracene.     

The application of simultaneous chemiluminescence and thermal analysis for studying the glass transition and oxidative stability of poly(N-vinyl-2-pyrrolidone)

A computer-controlled chemiluminescence (CL) instrument incorporating a differential scanning calorimeter was used to simultaneously acquire photochemical and enthalpic data for poly(N-vinyl-2-pyrrolidone) (PVP). Samples were subjected to a linear temperature ramp under nitrogen and their luminescence response recorded. The resultant dynamic CL peak is attributable to the decomposition of hydroperoxide groups and the subsequent mutual termination of secondary polymer peroxyl radicals. It is shown that dynamic CL can be used to characterize the level of oxidation in PVP, which in commercial samples, may be partly related to the level of residual polymerization inititor and to the drying process. The temperature at which maximum CL emission occurs correlates with the glass transition temperature (T_g) of the polymer and increases with increasing molecular weight. A marked increase in the T_g of PVP occurs after it is aged in air for 24 h at 120°C. This is due to the loss of adsorbed moisture from the polymer which was confirmed by thermogravimetric analysis. Oxidation profiles of PVP were obtained by plotting the integrated CL peak area as a function of aging time. The profiles are compared with data obtained from isothermal CL and viscosity measurements. Gas perturbation experiments suggest that when drying PVP under nitrogen at elevated temperatures significant populations of longlived macroalkyl radicals are formed which can peroxidize the polymer on exposure to air. © 1993 John Wiley & Sons, Inc.     

Study on the chemiluminescence behavior of bovine serum albumin with luminol and its analytical application

In this paper, the luminescence behavior of bovine serum albumin (BSA) and luminol was first studied by flow injection chemiluminescence (CL). It was found that the hyperchromic effect of luminol in the presence of BSA led to the acceleration of the electrons transferring rate of excited 3-aminophthalate, which greatly enhanced the CL intensity of luminol/dissolved oxygen reaction. The increments of CL intensity were proportional to the concentrations of BSA with a linear range from 0.01 to 7 nmol L(-1). It was also found that azithromycin could inhibit the CL intensity of luminol/BSA reaction. The decrements of CL intensity were logarithm over the concentrations of azithromycin ranging from 0.1 to 700 ng mL(-1). At a flow rate of 2.0 mL min(-1), a complete analytical process, which included sampling and washing, could be performed within 30s with relative standard deviations of less than 3.1%. This proposed method was successfully applied in assaying azithromycin in pharmaceutical and human serum samples with recoveries from 91.0 to 104.3%. The possible luminescence mechanism of luminol/BSA/azithromycin reaction was discussed in detail by CL, UV and fluorescence methods.     

Simultaneous detection of uric acid and glucose on a dual-enzyme chip using scanning electrochemical microscopy/scanning chemiluminescence microscopy

Scanning electrochemical microscopy (SECM) and scanning chemiluminescence microscopy (SCLM) were used for imaging an enzyme chip with spatially-addressed spots for glucose oxidase (GOD) and uricase microspots. For the SECM imaging, hydrogen peroxide generated from the GOD and/or uricase spots was directly oxidized at the tip microelectrode in a solution containing glucose and/or uric acid (electrochemical (EC) detection). For the SCLM imaging, a tapered glass capillary (i.d. of 1∼2 μm) filled with luminol and horseradish peroxidase (HRP) was used as the scanning probe for generating the chemiluminescence (CL). The inner solution was injected from the capillary tip at 78 pl s⁻¹ while scanning above the enzyme-immobilized chip. The CL generated when the capillary tip was scanned above the enzyme spots was detected using a photon-counter (CL detection). Two-dimensional mapping of the oxidation current and photon-counting intensity against the tip position affords images of which their contrast reflects the activity of the immobilized GOD and uricase. For both the EC and CL detections, the signal responses were plotted as a function of the glucose and uric acid concentrations in solution. The sensitivities for the EC and CL detection were found to be comparable.     

Direct determination of horseradish peroxidase encapsulated in liposomes by using luminol chemiluminescence.

Horseradish peroxidase (HRP) encapsulated in liposomes was directly detected by using luminol chemiluminescence (CL) with H2O2 without lysis of liposomes. At a low concentration of H2O2, the initial rate of HRP-catalyzed luminol CL in liposomes was slower than that of HRP-catalyzed luminol CL in a lipid-free bulk solution. The decrease in the initial rate of the CL reaction in liposomes was due to the membrane permeation of luminol and H2O2. At a high concentration of H2O2, the initial rate of the CL reaction in liposomes was the same as that in a lipid-free bulk solution. The CL measurement conditions in both a lipid-free bulk solution and in liposomes were optimized in the concentrations of luminol and H2O2 by measuring the CL response curves, in which only one peak appeared and the CL intensity was maximal. The CL intensity observed in HRP-catalyzed luminol CL in liposomes was a factor of seven greater than that observed in a lipid-free bulk solution. The CL intensity was dependent on the amount of HRP-encapsulated liposomes used. The detection limit in the direct detection of HRP encapsulated in liposomes was sensitive by a factor of 3 compared with that in HRP-catalyzed luminol CL in a lipid-free bulk solution.     

Chemiluminescence of polyethylene: The comparative antioxidant effectiveness of phenolic stabilizers in low‐density polyethylene

The thermal stabilizing efficiency of a range of phenolic antioxidants (Lowinox CA22, Lowinox WSP, Lowinox TBP6, Irganox 3114, Irganox 1330, and Cyanox 1790) was determined in polyethylene films with chemiluminescence and hydroperoxide analysis and compared with standard systems based on Irganox 1010 and 1076. Under both nitrogen and oxygen conditions, good correlations were obtained between the two methods, confirming the importance and role of the hydroperoxide functionality and its stability in the oxidative process. Chemiluminescence decay rates correlated well with the initial corresponding hydroperoxide contents, which were measures of the antioxidant efficiencies in the polymer. The antioxidant structure and volatility (melting points) were important parameters to consider in any such correlations and related very much to the methodology and conditions of analysis (i.e., the temperature and atmosphere). Some of the antioxidants themselves under nitrogen exhibited strong chemiluminescence, which appeared to be a legacy associated with their manufacturing history and the partial oxidation of their structures, which gave peroxide functionalities. This was more notable for the complex antioxidant structures. Under oxygen, higher levels of chemiluminescence were observed, and this was indicative of some level of oxidation associated with the antioxidant structures. With temperature‐ramping experiments, the chemiluminescence emission was significant and only observed at temperatures close to the melting points of the additives and/or polymer. Mobility was clearly an essential feature of this reaction emission because chemiluminescence was well observed when the molten state was reached. Under normal practical conditions, such levels of chemiluminescence, because of employed stabilizers, do not contribute significantly to the chemiluminescence emissions of stabilized polymer materials. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3312–3326, 2002     

纳米金催化Luminol-H_2O_2化学发光体系对异烟肼的测定

碱性条件下,纳米金对Luminol-H2O2化学发光体系有增敏作用,而异烟肼对该化学反应具有强烈的抑制作用。基于此,在优化化学发光反应条件的基础上,提出了一种测定异烟肼的新方法,并对其可能的化学发光机理进行了探讨。该方法测定异烟肼的线性范围为0.005~9.0 mg/L,检出限(3σ)为3.0μg/L,相对标准偏差为3.5%(n=11,ρ=0.2 mg/L)。该法已成功用于药物制剂中异烟肼含量的测定。     

A chemiluminescence technique for the evaluation of the thermal oxidative stability of polyethylene

Various polyethylenes (low density, linear low density and high density) were studied by means of chemiluminescence. The emitted light intensity versus time curves produced during isothermal oxidation are characterized by two consecutive S-shaped curves indicative of two-stage oxidation. It is shown that the method developed previously for the evaluation of oxidation parameters from a single sigmoidal curve can be successfully applied to the study of two-stage processes. Results pertaining to the thermal oxidative stability of polyethylene as well as data related to the decomposition of polyethylene hydroperoxide are presented.     

鲁米诺-铁氰化钾化学发光体系对盐酸环丙沙星的测定

环丙沙星对NaOH介质中的鲁米诺-铁氰化钾的化学发光具有较强的增敏作用,据此建立了一种新的测定痕量环丙沙星药物的流动注射化学发光法。讨论了介质浓度、发光试剂浓度等因素的影响,在最佳实验条件下,环丙沙星的质量浓度在2.0×10-5~1.2×10-4g.L-1范围内与发光强度呈良好线性关系,检出限为1.2×10-6g.L-1,11次平行测定4.0×10-5g.L-1环丙沙星的相对标准偏差为3.2%。该方法已用于环丙沙星片剂的测定,所得结果与标示值相符。     

Improvement of α‐tocopherols long‐term efficiency by modeling its heterogeneous natural environment in polyethylene

The natural antioxidant vitamin E (α‐tocopherol) is of interest to use in packaging applications to decrease the amount of toxic products migrating into food and drugs. We have earlier shown that the long‐term efficiency of α‐tocopherol in polyethylene (PE) films is poor. α‐Tocopherol is located in the lipid phase of the cell in vivo and it has been revealed that it is more efficient in a polar substrate. PE is more hydrophobic and homogenous than the heterogeneous and hydrophilic lipid phase. Three different additive systems were investigated to model α‐tocopherols heterogeneous natural environment in PE. Two of these had carboxylic acid groups, EAA and polyTRIM/PAA core‐shell particles (Core), and the third, oat starch, had no carboxylic acid groups. The materials were thermally aged and characterized by chemiluminescence (CL), FTIR, chromatography, and thermal analysis. The EAA system as well as the Core system improved the antioxidant properties of α‐tocopherol in PE, and the Core system had the best performance. We know that starch has stabilizing properties in PE, but it had no effect on the efficiency of α‐tocopherol. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1660–1666, 2006