Lab#7 Polymer Cross - travel through it, thus high...

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Densities of Unknown Liquids and Solids
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Results and Discussion An experiment was performed in order to determine the effect of cross-linking on polymer viscosity. Borate ion [B(OH) 4 - ] was used to cross-link strands of the polymer poly(vinyl alcohol). The reactions used in the experiments are: (1) Na 2 B 4 O 7 10H 2 O 2B(OH) 3 (aq) + 2Na + (aq) +2B(OH) 4 - (aq) +3H 2 O(l) (2) 2B(OH) 4 - (aq) + H 2 SO 4 (aq) 2B(OH) 3 (aq) + SO 4 2- (aq) + 2H 2 O(l) The data from this lab is tabulated in the table below: Table 1 : Viscosity of different states of PVA solution. Substance Viscosity Observations PVA t=0.35s to travel the 20ml graduated cylinder Not visually viscous Borate ion Did not travel, therefore, no viscosity Cross polymer- very viscous gel 3M H 2 SO 4 t=0.45s to travel the 20 ml graduated cylinder Removal of cross polymers 1.0M NaOH Did not travel at all Resurrection of Cross-linking Gel Conclusion The viscosity was determined relative to the time is takes to travel through a substance that gives it a resistance. The higher the resistance, the slower that time it takes to
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Unformatted text preview: travel through it, thus high viscosity, and vice versa. PVA contains a large number of OH groups, one for every two carbon atoms in the polymer chain which makes PVA soluble in water. PVA did not change the viscosity of the solution. PVA can also form hydrogen bonds with borate ions to form cross link between strands of the polymer, producing a mixture consisting of a three-dimensional network of polymer strands that are hydrogen bonded to borate ion and entrapped water molecules. This cross-linking polymer caused the solution to change into a gel substance with really high viscosity. Sulfuric acid reacts with borate ion to break up the cross-links which reverts the solution back into a non-vicious material with a viscosity similar to PVA. Lastly, NaOH neutralized the acid, restoring the cross-linking and gel substance with really high viscosity. Cross- linking significantly increases viscosity....
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This note was uploaded on 03/08/2008 for the course CHEM 2070 taught by Professor Chirik,p during the Fall '05 term at Cornell University (Engineering School).

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Lab#7 Polymer Cross - travel through it, thus high...

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