Moisture pickup

MoistureResista.nce, Plastic foams are advantageous compared to other thermal insulations in several appHcations where they are exposed to moisture pickup, particularly when subjected to a combination of thermal and moisture gradients. In some cases the foams are exposed to freeze—thaw cycles as well. The behavior of plastic foams has been studied under laboratory conditions simulating these use conditions as well as under the actual use conditions. 

Moisture pickup and freeze—thaw resistance of various insulations and the effect of moisture on the thermal performance of these insulations has been reported (207). In protected membrane roofing appHcations the order of preference for minimizing moisture pickup is... 

The hygroscopic and humectant properties of com symps are of great importance in many apphcations. Depending on the type of symp and on the specific conditions of temperature and humidity, the products may either resist or facihtate moisture loss or moisture absorption. The abihty to attract moisture or retard its loss increases with increasing DE value. Prevention of moisture pickup is more characteristic of symps having low DE values. 

Protective packaging is primarily required to prevent moisture pickup. The flavor quaUty of regular instant coffee changes very tittle during storage. However, the powder is hygroscopic and moisture pickup can cause caking and flavor impairment. Moisture content should be kept below 5%. 

In ordinaiy heating and coohng operations, during which there is no moisture pickup, continuous recirculation of the conveying gas is frequently employed. Also, solvent-recovery operations employing continuously recirculated inert gas with intercondensers and gas reheaters are carried out in pneumatic conveyors. 

Where folding cartons are to contain a product which is sensitive to moisture pickup, barriers are available which can be incorporated into the carton construction. An example of this is polyethylene laminated to paperboard. In some cases an insert bag is used instead, but this requires an additional operation and is usually accomplished by a form-fill-seal machine that makes a bag which is then inserted by another machine into the folding carton. 

Disadvantages of the phenolic resins are the necessary longer press times compared to UF-resins, and the dark color of the glue line and the board surface. There is also the possibility of a higher moisture pickup of the boards when stored at higher relative humidity due to the hygroscopicity of the high alkali content of the resin. 

Chemical compounds that contain methylol groups (-CH2 OH) form stable, covalent bonds with cellulose fibers. Those compounds are well known and widely used in textile chemistry. Hydrogen bonds with cellulose can be formed in this reaction as well. The treatment of cellulose with methylolmelamine compounds before forming cellulose unsaturated polyesters (UP) composites decreases the moisture pickup and increases the wet strength of reinforced plastic [48,49]. 

Reducing the number of cellulose hydroxyl groups that are available for moisture pickup. 

The resin is more than 90% DGEBA with the remaining material predominately at n=1. The curing agent, nadic methyl anhydride (NMA), is manufactured by Allied Chemical. The catalyst was benzyl dimethylamine (BDMA). All materials were stored in a desiccator to minimize moisture pickup. 

XRD Characterization The powder x-ray diffraction of the mechano-chemically milled complex borohydride has been carried out by the Philips X pert diffractometer with Cu-Koi radiation of X= 5.4060 A. The incident and diffraction slit width used for the measurements are 1° and 2° respectively. The sample holder was covered with Polyethylene tape (foil) with an O-ring seal in an N2 filled glove box in order to avoid or at least minimize the 02/moisture pickup during the XRD measurements. The diffraction from the tape was calibrated without the actual sample and found to be occurring at 29 angles of 22° and 24°, respectively. The XRD phase identification and particle size calculation has been carried out using PANalytical X pert Highscore software, version l.Of. 

Plastic foams are advantageous compared lo other thermal insulations in several applications where lhey are exposed lo moisture pickup, particularly when subjected to a combination of thermal and moisture gradients. 

Approximately 1 g of the sample (weight to the nearest 0.1 mg) that has been pulverized to pass through a No. 60 sieve (ASTM D-2013) is placed in a cold muffle furnace and heated at such a rate that the temperature reaches 450 to 500°C (842 to 932°F) after 1 hour. The heating is continued so that a final temperature of 700 to 750°C (1292 to 1382°F) is reached by the end of the second hour, and heating is continued at this temperature for an additional 2 hours. At the end of the heating period, the sample is removed from the furnace, covered, allowed to cool under conditions that minimize moisture pickup, and weighed. The yield of ash is determined by the formula... 

The moisture pickup and hydrolysis tests were carried out at room temperature and 80 R.H. to simulate storage. The results are shown in the following table. 

Film thickness will also affect the rate of moisture pickup. Films of thickness up to 150 ppm take 12 h to reach equilibrium whereas films of thickness 175, 200, and 250 pm have not reached equilibrium in 15 h. Films of lower thickness... 

The moisture uptake rates (MUR) can simply be obtained by weighing the sample after a given time (six days), but in such a case it is assumed that the moisture uptake is still in the linear phase. If, for instance, the weight gain is 5 mg per 10-g sample in six days, then the MUR is 5/(10 x 6) = 0.083 mg/g/day. If the MUR values are plotted versus relative humidity (RH) and the curve that intercepts the x axis at 20% RH is obtained from a straight line, the compound can be stored without moisture pickup in atmospheres of less than 20% RH. In addition, the hygroscopicity of materials is indicated as follows ... 

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