Oven aging technique

To evaluate antioxidants for polypropylene, various test methods have been developed. Gordon correlates these methods, and Gysling suggests a modified oven-aging technique and shows antioxidant synergist combinations. 

A Modified Oven-Aging Technique for Studying Polymer Antioxidant Systems... 

This chapter will explain the setup and methodology used for the field retrieval study. The physical and chemical analysis techniques used to study the oxidation of the tire rubber, along with the data analysis developed to interpret the results, will also be explained. Then, the development of an oven-aging protocol that attempts to reproduce the mechanism and rate of tire field aging will be described. 

Being cut from tires, the rubber samples in this work cannot always be studied using standard test procedures. The specific techniques used to measure rubber aging have been described in detail elsewhere and are summarized below [2]. The same techniques have been used to evaluate rubber aging in both field and the laboratory oven-aging studies. For reference. Figure 34.2 shows a diagram of the internal components of a radial-ply tire. 

Kohler et al. discussed the potential of the chemiluminescence technique as an industrial test method. Imaging chemiluminescence was used to assess antioxidant performance. An advantage over oven aging was found to be the possibility for evaluation of the oxidative stability of samples with unusual geometries, such as fibres and powder particles [136]. A correlation was also found between oven aging and chemiluminescence measurements on stabilised PP and it was shown that chemiluminescence measurements done at... 

By using very thin samples, the oven aging of polypropylene can be appreciably accelerated. Specimens of definite and reproducible shape and thickness were made by using a microtome. The first phase of the work evaluated the influence of sample thickness from 0.2 to 12 mils on oven life at different temperatures. In the second phase, this modified technique was used to study the effectiveness of three anti-oxidant/DLTDP systems as thermal stabilizers for polypropylene. The results obtained over a wide spectrum of antioxidant/DLTDP combinations are shown in three-dimensional graphs. 

Test methods for assessing thermal oxidative stability include oxygen absorption (30,31,35), thermal analysis (36,37), oven aging (33,38,39), and chemiluminescence (40,41). Such techniques primarily reflect the reactivity of the rubber component in ABS with oxygen. 

Antioxidants are common additives for polymers. Oven ageing and thermal analysis techniques such as DSC and TGA have been used with varying degrees of success to measure both the concentration and effectiveness of antioxidants. In most cases, the failure of these tests to correlate with actual end-use performance is due to the volatility of the antioxidants and other components at test temperatures. Even at a relatively... 

In order to prove the validity of chemiluminescence, a comparison of CL with other analyses techniques was carried out. In comparison with other techniques, such as oven ageing testing, iodometric peroxide determination, UV and FTTR spectroscopy, XPS, x-ray tomography, density and modulus profiling, chemiluminescence offers higher sensitivity, simplicity and quickness. However, care should be exercised in comparing samples with different forms and ageing times. 

There are three primary methods to age catalysts and each addresses different failure modes. The first method is an ex situ thermal aging technique that measures support stability (Stevens et al. 2005). In this method, catalyst powder is weighed and placed in an oven. The weight loss of the powder is monitored over time (Fig. 3a). This technique studies the stability of the support to platinum-catalyzed chemical combustion and is very useful for determining the relative stability of different carbon supports. The second method is an in situ technique to measure the electrochemical... 

Thermal Degradation Techniques. PFAP(II) samples (5.0g) were contained in small glass Petri dishes and placed in forced-air ovens maintained at 135°, 149°, 177°, or 200°C =b 2°C for the specified time intervals. The weight loss of these samples was monitored as a function of aging time. Small portions of these samples were dissolved in acetone for viscosity measurements and in dimethylformamide for GPC studies. 

First and foremost, note that interest is in the nature of intramolecular dynamics of molecules in isolation. That is, observations must be made over a time scale where the molecule does not collide with others in the reaction vessel. Modern techniques allow very low pressures under which such measurements can be made. Most desirable among these methods are beam techniques in which molecules are studied in a low-density beam produced, for example, by vaporizing molecules in an oven. Experiments prior to this T>eam age (circa 1960) often inferred information about intramolecular dynamics from bulk data, which contained effects due to collisions, with resultant loss in accuracy. 

Thermal stability was determined by assessing the color of compression molded films of the polymer. A film sample was held in a convection oven for 4 hours at 200°C. Color and clarity of the aged film varied firom no ehange to yellow for different polymers. Molecular weight of the polymer was assessed by an indi-reet measurement of melt viscosity. A film sample was produeed by applying pressure to 0.5 g of polymer powder at 225°C in a press for 30 seconds. The area of the film formed by this technique was measured as an indieation of the viscosity of the polymer. A lower viseosity, i.e., lower molecular weight, polymer spread into a larger area film sample. Table 5.41 shows a summary of the PVDF polymerization conditions and the polymer properties. The data in Table 5.41 indieate that no reaction took place in the absenee of both iron and surfactant. Polymerization yield was anemie in the presence of only surfactant or iron. 

Several commercial weatherometers provide similar temperatures and provided the UV shorter wavelength cut-off is not less than that experienced in sunshine ( 290 nm) [62], these are realistic practical conditions for plastics that end up on the soil particularly in the sunbelt countries, where they are wisely used. International standards describe the use of typical commercial laboratory techniques. Since ageing and weathering procedures have been standardised for the benefit of manufacturers and users of plastics, it is not considered that the details of the weathering procedure should be part of the standard itself, provided that full reference is made to the standard method chosen. ASTM D 5510-94 [60] describes a convenient heat-ageing oven for degradable plastics. 

Conventional techniques determine long-term heat stability of polymer articles at temperatures below melting conditions, for example, during accelerated aging in circulating air ovens until degradation effects such as discoloration and embrittlement are visible (Figure 28). 

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