Desiccator method

Two important, but often under emphasized, aspects of measuring c/w values and isotherms in foods are accuracy and repeatability. Variation in and isotherm values can be due to inherent variation in biological materials, as well as differences in measurement methods, protocols, and equipment employed. Wolf et al. (1985) presented the results of a COST 90 Project on the standardization of saturated salt solution isotherm measurement methodology and Lewicki and Pomaranska-Lazuka (2003) discussed errors in the static desiccator method. 

Lewicki, P.P. and Pomaranska-Lazuka, W. 2003. Errors in static desiccator method of water sorption isotherms estimation. Int. J. Food Prop. 6, 557-563. 

Methods for determination of the total moisture in coal have been placed into the following categories (1) thermal methods that often include distillation methods (2) a desiccator method (3) distillation methods, which often include extraction and/or solution methods (5) chemical methods and (6) electrical methods. 

Describes two cup methods, one a Desiccant Method and the other a Water Method. Periodic weighings are made in both methods. 

Tentative Test Method for Emission of Formaldehyde from Wood Products - 24 Hour Desiccator Method" National Particleboard Association, 1980. 

Very often the protective ability of inhibited film materials is estimated by laboratory desiccator methods. 

For a number of years the following desiccator method of corrosive tests was used at MPRI NASH [49-51,98]. Metallic samples in the form of plates 50 X 50 X 2 in size are wrapped in an inhibited film and placed into the desiccator inside which 98 2% relative air humidity is maintained by aqua solution of glycerin, and are subjected to cyclic heating-cooling. One cycle consists of the endurance of the samples in the same humidity at a temperature of 55 2°C for 8h and at a similar humidity and a temperature of 20 2°C for 16 h. The protective ability of the films is estimated by the corrosion resistance of metallic samples after 21 test cycles (Table 1.11). 

Water-Vapor Transmission. Primary Film Test Method ASTM E96. The primary test method for the determination of water-vapor transmission through plastics less than 32 mm thick is ASTM E96. (See Fig. 4.) There are two basic methods the Desiccant Method and the Water Method. Agreement between the two methods should not be expected. The method selected should be the one which most nearly approaches the conditions of use. 

Desiccant Method A desiccant covered by the film to be tested and placed in a humid chamber. Moisture from the chamber permeates the film and is picked up by the desiccant. After a measured period of time the test dish is reweighed and the water vapor transmission rate (WVTR) of the material is calculated. 

ASTM D96 (Discontinued Test Method) Standard test method for determining water vapor transmission of materials such as paper, plastic film and sheeting, fiberboards, wood products, etc., that are less than 31 mm in thickness. Two basic methods, the Desiccant Method and the Water Method are used. The specimens have either one side wetted or one side exposed to high humidity and another to low humidity. In the Desiccant Method, the... 

Formaldehyde emission tests were performed on the hoards glued with the most promising formulations. Two boards per formulation type were tested. The emissions were measured according to the specifications of the JIS A 1460 2001 standard [9]. The determination of the formaldehyde emitted by the boards was done by the desiccator method. The emitted quantity of formaldehyde was obtained from... 

Figure 4. Formaldehyde emission test results (mg/1) using the desiccator method according to JIS A 1460 2001 standard [9], F designation formaldehyde emission <0.3 mg/f corresponding to the emission of natural wood.

JIS A 1460 2001, Building boards, determination of the formaldehyde emissions — desiccator method (2001). 

The tannin/hexamine binders alone produced panels with zero formaldehyde emission when tested by the desiccator method [33]. 

Pleated filter Platinum or glass dish Drying cabinet Analytical balance Desiccator Method... 

Figure 9 Water adsorption curves generated from desiccator method and DVC methods.

There are two types of standard cup methods the desiccant method (dry cup) and water methods (wet cup). In the desiccant method (eg, methods A, C, E in ASTM E96, ISO 15496), the specimen is sealed to an open mouth of a test dish containing a descant, and the assembly is placed in a controlled atmosphere. The dishes are periodically weighed to determine the rate of water vapour transfer through the specimen into the desiccant. In the water method (eg, methods B, D, and BW in ASTM E96, BS 7209), the dish contains distUled water, and the weight of the dishes are examined in a certain time interval to determine the rate of water vapour transfer through the specimen to the controlled atmosphere. The vapour pressure difference is nominally the same in both methods except when testing conditions are with the extremes of humidity on opposite sides. 

Various standard cup methods include ASTM E96 (Upright cup for water permeable fabric, and inverted desiccant and water cup methods for water impermeable fabric), BS 7208 (upright water cup method in a turning table), JIS L 1099 (Upright cup for water permeable fabric. Inverted desiccant method for water impermeable fabric (for single membrane method), and Inverted desiccant cup for water permeable or water impermeable fabric (for double membrane method)), ISO 15496 (Inverted Desiccant method for water permeable or water impermeable fabric (double membrane method)), and ISO 2528 (Desiccant method) ... 

The water vapor transmission test is used to determine values of water vapor transfer through permeable materials. Two basic methods, the desiccant method and the water method, have been developed. The desiccant method generally yields lower results than the water method. 

In the laboratory, anhydrous forms of the gas are particularly useful for generating chloride-based Lewis acids, which must be absolutely dry for their Lewis sites to function. It can also be used to dry the corresponding hydrated forms of these materials by passing it over as they are heated the materials would otherwise fume HCl(g) themselves and decompose. Neither can these hydrates be dried using standard desiccator methods. 

The two methods yield results of a similar magnitude, but the calculated WVTRs for the desiccant method tend to be slightly lower. 

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