the pva always shrinks when it is in high MW, is there any method to improve the deformation of the film?
Dear Marwa,
Preparation of Films PVA films were produced by a casting evaporation technique from aqueous polymer solutions. Accurate weights of PVA powders with different weight ratios were added into distilled water and left to hydrate overnight. The next day, the dispersions were heated in a water bath at 80—90 °C for 30—60 min and then made up to 8% PVA solutions. The solutions were left to stand until trapped air bubbles were removed, and then cooled to ambient temperature. Different amounts of the polymer solutions (10, 15, 20 g) were poured into glass petri dishes (diameter 10 cm) and oven-dried at about 50 °C for 24 h. The dried films were peeled from the
petri dishes and stored in a desiccator at room temperature. Before permeation
studies and tensile tests, dried films were cut into circular test sections with area of 19.625 cm2 and rectangular test sections with size of 137 cm2, respectively. The thickness of the films was measured by using a micrometer (Mitutoyo, No. 293-721-30 CE, Japan). At least five thickness readings at different regions were taken for each test section and the results averaged.
Determination of Apparent Solubility of Films. Rectangular pieces, each of area of 137 cm2 , were cut from the PVA films and oven-dried until constant weights were obtained. Each piece was immersed in 40 ml of distilled water contained in a boiling tube. The boiling tube was then placed in a shaker water bath at 37 °C. After 24 h, the piece was removed and spread on a clean petri dish and oven dried at about 50 °C to constant weight. The percentage weight loss, W%, expressed as the percentage of decrease in the weight of film after dissolution, represented the apparent solubility of film. For each film, at least five determinations were made and the average W% obtained.
Evaluation of Swelling Property of Films. Square pieces, area 1 cm2 were cut from the PVA films. The dimensions of each piece were accurately measured by using a caliper (Mitutoyo, No. 500-216, Japan) before introducing into a test tube containing 5 ml distilled water. The tube was placed in a shaker water bath at 37 °C. After 5 h, the piece was removed and spread on a clean petri dish. Accurate measurements of the dimensions were made immediately. The swelling index was defined as the percentage increase in the dimensions of the film after swelling. For each film, at least five determinations were made and the results averaged.
For more information, please see the following link:
http://cpb.pharm.or.jp/cpb/199910/C10_1412.pdf
Hoping this will be helpful,
Rafik
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