Accelerating aging humidity

Accelerated aging and crystal transformation rates have also been traced to high residual moisture content. Ando et al. studied the effect of moisture content on the crystallization of anhydrous theophylline in tablets [9]. Their results also indicate that anhydrous materials convert to hydrates at high levels of relative humidity. In addition, if hygroscopic materials (e.g., polyethylene glycol 6000) are also contained in the formulation, needle-like crystals form at the tablet surface and significantly reduce the release rate of the theophylline. 

Nalidixic acid is stable up to five years under reasonable conditions of temperature and humidity. Pawelczyk and Plotkowiakowa(17) subjected sodium nalidixate solutions to accelerated aging, but were unable to identify decomposition products. Detzer and Huber(lS) studied the photolysis and thermolysis of nalidixic acid in the presence of oxygen. Photolysis produced de-carboxylated nalidixic acid, structure A, and a diketone product, structure B, as well as carbon dioxide and ethylamine. 

Vacuum-Steam-Pressure Test. A special aging test which has been used successfully in the USA to accelerate aging to produce the effects of 6-month tropical exposure on certain types of sealed fuzes. It is primarily a development test which can be used during production The test consists of subjecting bare fuzes to 1000 fifteen-minute consecutive cycles in a vacuum-steam-pressure environment. The 1000 cycles takes about 10 days of continuous running time. The basic cycle consists of temperature-humidity cycling superimposed on pressure cycling in a test chamber with a salt laden atmosphere. Representative curves of temperature and pressure are shown in Fig 1... 

The Effect of Variations in Relative Humidity on the Accelerated Aging of Paper... 

A Thermotron programmable humid oven was employed for the accelerated aging experiments. The temperature of the oven was held steadily at 90 0.2°C throughout this series of experiments. The... 

Accelerated Aging. After treatment with deacidifying agents, three naturally aged fabrics ( 11-13 in Table I) and the chlorine bleached fabric were exposed to acclerated aging in the dark at 100% relative humidity (RH), and 100°C for 15 days in a closed environment. 

Accelerated Aging. The Cellophane samples were artificially aged In a Thelco forced-draft oven at 90, 110, and 140 °C. The relative humidity varied, but was less than 2Z at all temperatures. Samples were sandwiched between a glass fiber screen and glass microscope slides to prevent curling. After removal from the oven, samples were... 

Absorption coefficient description, 82 physical interpretation, 84 Accelerated aging of paper, effect of variations in relative humidity, 63-78 Acid degradation, effective means of book protection, 23-24 Acid formation in paper aging characteristics, 16 chief source, 16... 

Environmental and accelerated ageing tests were performed on the indoor dye modules described in Sect. 7.6 in order to detect failure mechanisms. Contrary to expectations, many modules survived humidity/freeze cycling tests (10 cycles, 85%, 20 h at 55°C per cycle) without major degradation, demonstrating the capability of the sealing concept (see Fig. 7.8). This was also true for temperature cycling (between —5 and 55°C). However, it has... 

Environmental aging is usually less severe in service (laboratory tests tend to accelerate aging so that the testing can be completed in a reasonable time). However, the effects of the actual service environment are generally more complex. For example, there may be simultaneous exposure to cyclic stress, cyclic temperature, and humid environments. 

There is a striking difference, however, in the action of various alkaline materials. Neutralizing acid paper with sodium carbonate, as is shown later, prolongs its life. Alkalizing paper to pH 10 with sodium carbonate causes paper to darken, to oxidize, and to degrade. The effects are most pronounced in humid-oven accelerated aging, less so in the dry-oven aging. 

While Barrow solved the main problem, there are other modes of degradation which must be considered. As an organic material, cellulose and paper can be easily oxidized. Very small amounts of the transition metals, compounds of iron, copper, and cobalt, under humid conditions can accelerate oxidation and embrittlement of paper. This type of degradation, as is shown later, does not show up in the dry-oven accelerated aging which Barrow used. Thus his alkaline papers, if they contained the oxidation catalysts, may not always have been permanent. 

Since Washington summers are known for high temperature and humidity levels, it might be said that the collections at the Library of Congress have suffered from a natural accelerated aging process. The majority of nineteenth and twentieth century books and unbound items that are brittle in the Library of Congress, and no doubt other collections,... 

It had been suggested that accelerated aging in ovens supplied with ambient air is unnatural in that the moisture content of paper under such conditions is much lower than in papers under normal conditions and that the validity of heat aging would be increased by controlling the relative humidity of the aging environment at some level comparable with natural conditions. At the Barrow Laboratory, papers have been aged at a variety of humidities and temperatures in three different kinds... 

For each paper, both Foldur Kraft and newsprint, there were ten sample sets and one unwashed set, which was used as a control. The air dried samples were subjected to accelerated aging in humid (90°C/50% relative humidity) and dry (100°C) circulating air ovens for one, two, three, and five weeks. At regular seven-day intervals one sheet from each sample set was removed and tested. 

Relative Humidity 90°C Humid Oven Accelerated Aging ... 

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