Water pickup, determination

Enhancement of Polymer Biocompatibility. Films from about 0.5 g. of polymer were cast as for the water pickup determinations. The dry films were placed in 100 ml. of deionized water and left at ambient temperature. The water was changed every 24 hours for a total of 72 hours. The films were dried in vacuo at 50°C. Then the... 

Determination of Water Pickup. 0.5 g of polymer was dissolved in 10 mL of warm chloroform. The solution was poured into an aluminum container 5 cm in diameter and left for the solvent to evaporate at ambient conditions. The film was removed from the container and dried to constant weight at 50°C in vacuo. The dried film was weighed, immersed in deionized water for 24 hours, removed, blotted dry, and weighed immediately. The percent water pickup for the polymer was calculated from the formula... 

Tack loss occurring during aging of pressure-sensitive adhesives has been traced in some cases to the hydration of ester-type resins in the formulation. Therefore, in case of a tack loss problem, it should be determined whether the loss is oxidative or due to moisture pickup. Where hydration occurs, control of water pickup during manufacture or storage, change in resin type, or the removal of the moisture in a vacuum oven are possible solutions. 

Consider a pool of water in the bed of your pickup truck. If you accelerate from rest, the water will slosh toward the rear, and you want to know how fast you can accelerate (ax) without spilling the water out of the back of the truck (see Fig. 4-4). That is, you must determine the slope (tan ) of the water surface as a function of the rate of acceleration (ax). Now at any point within the liquid there is a vertical pressure gradient due to gravity [Eq. (4-5)] and a horizontal pressure gradient due to the acceleration ax [Eq. (4-23)]. Thus at any location within the liquid the total differential pressure... 

Four types of fabric substrates were cyanoethylated the control, acid hydrolyzed, 50 and 100 Mrad. Fabric specimens 19 X 89 mm were sprayed with a fine mist of 2% NaOH solution using a hand spray bottle until a 100% pickup by weight was achieved. The specimens were then left to air dry until just damp. Six samples were then placed on a rack inside the sealed reaction vessel, which had inlet and outlet connections to permit the acrylonitrile vapor to flow through and around the reactive fabric. This vessel was connected to two bubble bottles containing water and acrylonitrile with which to saturate nitrogen gas as it entered the reaction vessel. The water was necessary to swell the cellulose so the acrylonitrile could penetrate. It was determined that varying nitrogen flow rates and reaction time had little effect on the percent add-on. 

The history of the sample in environmental analysis provides an indication of the chemistry of the atmosphere, water, or soil that can greatly influence the composition of the sample, as well as the status of the analyte(s) to be determined. Of main importance for estimations of uncertainty is knowledge of the exact time, place, method of sample pickup, and the material of the container used for the sample. 

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