Chemiluminescence thermo

The quality of the polymer, its photo-oxidation and thermo-oxidation history expressed in concentration of hydroperoxides, carbonyl groups or of other oxidized structures and terminal groups. The rate of an oxidative attack may then be related to the average molar mass and to its distribution, and to the ratio of amorphous/crystalline structures. Polymers cannot be simply ordered according to the intensity of light emission at a given temperature. The chemiluminescence-time patterns are related with the rate of sample oxidation, but they may differ from one to the next polymer. 

The effect of molar mass and stereoregularity on the thermo-oxidation of polymers and on the chemiluminescence-time patterns has been investigated only rarely [44-46]. 

Apparatus and Method. The fixed-bed coluiiui was a 316 stainless steel tube, with an inside diameter of 1.09cm and a length of 40cm. The temperature of the column was maintained with an electric furnace located at its outer wall. Concentrations of NO and NO2 that exhausted from the bypass line and adsorption coluriui were analyzed by using a chemiluminescent NO, analyzer (Thermo Environmental Instruments Inc., model 42C). 

The recorded chemiluminescence originated from only a thin surface film. The thickness of this film depends on the extent of self-absorption of the emitted radiation and remains unknown at this time. The pseudo-first-order rate of thermo-oxidative reactions responsible for the chemiluminescence is not limited by oxygen concentration. The applied stress decreases the activation energy for thermooxidative reactions, resulting in the observed chemiluminescence increase. As stress-activated bonds in the surface film react, what can be called surface stress relaxation occurs resulting in the observed SCL decrease. 

G. Ahlblad, P. Gijsman, B. Terselius, A. Jansson, and K. Moller, Thermo-oxidative stablility of PP waste films as studied by imaging chemiluminescence, Polym. Degrad. Stab. 2001, 73, 15-22. 

In the course of thermo-oxidative degradation of PAs stabilized with antioxidants, such as phenols and secondary aromatic amines and hindered nitroxy radicals chemiluminescence is observed. This effect is attributed to redox inhibition reactions. 

The intensity of chemiluminescence signal that is frequently used in the assessment of thermo-oxidation stability of a polymer and the kinetics of its change with time or temperature is determined by the following ... 

Polyolefins are susceptible to several degradative mechanisms, out of which thermo-oxidative and thermomechanical are dominant. The PO stability depends on macromolecular configuration and it follows the order HOPE > LLDPE > LDPE > i-PP. Chemiluminescence, FT-IR, mechanical properties, and Ihermogravimetty have been used for detecting and quantifying degradations (Cran 2004). 

The catalytic activity in the SCR of NO was determined in a continuous flow unit. NO conversion was measured with a Thermo Electron Series 44 chemiluminescent analyzer. 

Several applications of polymers placed in contact with metals require detailed study on the effect of this kind of materials upon the durability of plastics. Ozawa and Tsurumi studied by chemiluminescence the consequence of various transition metal stearates (concentration 0.5 phr) on the thermo-oxidative degradation of polypropylene even at low temperature (105 C). They stated the relative decreasing catalytic order of these compounds as follows [8901] ... 

Also the acceleration effect of stearic acid on oxidation of PP was examined by CL [645]. Similarly, the influence of azo dyes on the thermo-oxidative stability of iPP was assessed by chemiluminescence [646]. 

Figure 3.2 Chemiluminescence, measured in a nitrogen atmosphere of two different LDPE samples (a)Thermo-oxidlzed(100°C) A = LDPE B = LDPE + 7.7% starch C = LDPE + 15% MB and D = LDPE + 20% MB (see Reference 10). (b) Biodegraded (Pseudomonas aeruginosa). LDPE with and without Tween-80 biodegraded and undegraded, all samples pre-irradiated for 0,40 and 300 days before ageing.

The most common methods coupled with the three mentioned tests are those also used for evaluating thermal and thermo-oxidative stability, namely measurement of the oxidation induction period by the oxygen uptake test, manometry, DTA, DSC, TG, EGA and EGD in isothermal and nonisothermal (dynamic) conditions oven aging in static or circulating air at 50-150°C, chromatography UV, IR, ESR, NMR spectroscopy, chemiluminescence, viscosimetry, mechanical indices determination, etc. Other criteria refer to discoloration, embrittlement, cracking, loss of elongation, etc. Hydroperoxides concentration can... 

The techniques most commonly used in thermo-oxidative studies on polymers are mainly based on thermal analysis methods such as thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) and on pyrolysis-gas chromatographic studies (particularly if they are linked to complimentary techniques such as mass spectrometry or infrared spectroscopy). Other techniques that have been used to a much lesser extent include chemiluminescence analysis, nuclear magnetic resonance (NMR) spectroscopy, electron spin resonance, and positron annihilation lifetime mass spectrometry. 

Camacho and Karlsson [35] investigated the thermal and thermo-oxidative stability of recycled PP, HDPE and a 20 80 PP/HDPE blend. These samples were subject to extrusion cycles. The oxidation induction time of all three samples decreased with the number of extrusion cycles, as did the temperature of oxidation. Chemiluminescence runs showed two peaks one sharp peak (corresponding to PP) and the other bimodal in shape (corresponding to PE). 

THERMO-OXIDATIVE STABILITY OF PP WASTE FILMS STUDIED BY IMAGING CHEMILUMINESCENCE... 

The SCR activity measurements were carried out on cmshed samples sieved to obtain fractions of 0.18-0.300 mm. These measurements were carried out in a fixed-bed reactor, with 10 mg of the catalyst loaded between two layers of inert quartz wool. The reactant gas composition was 1000 ppm NO, 1100 ppm NH3, 3.5% O2, 2.3% H2O and He balance. The total flow rate was 300 mL/min (ambient conditions), with a continuous monitoring of the NO and NH3 concentration with a Thermo Electron model 17C chemiluminescent NO-NOx gas analyser. The catalytic activity, represented as a first-order rate constant (k), can be calculated from the NO conversion, X, as Eq. 2 ... 

---