Testing the Physical Properties of the Cross-Linkage Between Polyvinyl Alcohol and Sodium Borate

Introduction:

Polyvinyl alcohol is a polymer that is odorless, nontoxic, soluble, and biodegradable. When cross-linked with sodium borate, PVA can be used as a packing material. Cross-linking occurs when polymers are bonded to each other by covalent or ionic bonds. Sodium borate was the cross-linking agent that bonded the PVA polymers together. Other examples of cross-linking are epoxy resins, polycarbonates, and the vulcanization of rubber as shown in the figure below.

The objective of this lab was to test the reaction of PVA and ¬¬sodium borate to determine its ability as a packaging material for baby food. Cross-linking between PVA and sodium borate occurs where Boron covalently bonds to Oxygen as seen below.

Testing the physical properties of the cross-linked polymers with different concentrations of sodium borate was done to determine which the most effective packaging material was. We hypothesized that if more sodium borate was added to the PVA, then the solution would become more viscous and less elastic.

Procedure:

Polyvinyl alcohol (PVA) and sodium borate were provided and utilized, along with 3 plastic beakers, 3 wooden stirring sticks, gloves, a ruler, and 3 plastic bags. 30 mL of PVA was poured into each of the 3 plastic beakers and labeled solutions 1, 2, and 3. Sodium borate was added to each beaker in quantities of 5mL, 10mL, and 15mL, respectively. Each solution in the experiment was stirred vigorously with a wooden stick to compare physical properties after the solutions were completely mixed. For the first test, the mixtures were stretched and measured with a ruler to compare elasticity. Next, viscosity of each solution was tested and compared. The boiling point of each solution was tested by separating 5g of each solution into glass beakers and heated on a warmer until the first sign of boiling occurred, then measured using a thermometer. Strength and durability was tested by quickly pulling apart the substances and comparing the ease by which each one broke.

Results:

Polyvinyl alcohol was mixed with sodium borate in 3 separate trials to determine how different amounts of sodium borate affected the physical properties of the resulting solution. PVA was held constant at 30mL per solution and sodium borate was controlled in quantities of 5mL, 10 mL, and 15mL for solutions 1, 2, and 3, respectively, making it the independent variable. The resulting physical properties measured were the dependent variables.

Observations of the solutions