Density Determination of Various Polymer Coatings

Teacher Notes

Objective:

The purpose of this activity is to:

• determine the density of selected coatings such as house paints, epoxies, and waxes
• compare density to impact resistance or hardness for example.
• understand that density is defined as the mass per unit volume and in this activity is expressed in grams per milliliter.

Applicable science concepts:

Density, volume, mass, volume measuring, and mass measuring.

Supplies:

• 20 mL and 1.0 mL syringes,
• coating samples in their original containers,
• electronic balances ,
• paper towels.

Safety:

Manufacturers provide instructions for the use of their products and these instructions should be followed completely. Protective gloves, eye wear, and lab coat should be used when handling the coatings.

Preparation:

Begin the activity with a discussion on coatings. Ask the students to identify the coatings, a covering layer, that they see around them everyday. They should mention paint and waxes among others. Then ask what characteristics they would want in a paint for their car, house, boat, etc. Narrow the list to measurable characteristics and discuss how each would be measured. Next focus on density and direct a discussion on how they would go about finding the density of a liquid such as paint.

Investigation Procedures:

The instructions are inquiry based and directed by you. To find the volume of the syringe mass an empty syringe, fill it with distilled water to the 20.0 mL mark, and mass the filled syringe. Suggest that the students perform the same procedure 3 times. Then students should dry the syringe completely and fill it with the coating to the 20.0 mL mark. Mass the filled syringe being careful to cap the syringe and wipe any excess paint (coating) off the syringe and record all findings. Students can then calculate the density of the coating. If time permits each group could find the density of more than one coating.
Paints can easily be handled in 20.0 mL syringes but waxes would better be handled in 1.0 mL syringe.
Tests results we obtained: Kilz liquid in a can- 1.23 g/mL; Krylon oil enamel- 0.94 g/mL; 100% acrylic latex- 1.07 g/mL; and Armor all car wax- 0.78 g/mL.

Conclusions:

Have teams of students put data on board, overhead or put into a composite power point program. Students should then discuss the importance of this lab and how they might compare each coating with other physical characteristics they observed.

Reference:

American Society for Testing and Materials (ASTM) D 1475-90 Standard Test Method for Density of Paint, Varnish, Lacquer, and Related Products.