Bend Test Determinations of Various Polymer Coatings

TEACHER NOTES

Objectives:

Students will:

• test coating bendability by the bend test.
• determine which coatings have the best and worst bendability property.
• compare bendability properties of coatings to other properties.

Applicable Science Concepts:

• Following testing proceedures
• Comparing and contrasting results
• Bending can rate how well a substrate will endure manufacturing bending and abuse during service, and the ability to resist cracking when elongated.

Supplies:

• Coating samples in their original containers
• Heavy Duty aluminum foil
• Cylinders of various diameters
• We used:

Safety:
Manufacturers provide instructions for the use of their products, and these instructions should be followed completely. Protective gloves and lab coats should be used when preparing and handling the glass slides with coatings, and safety glasses should be used at ALL times.

Activity:
Taken from the ASTM Standard Test Method for Mandrel Bend Test of Attached Organic Coatings: ASTM D 522 - 88 http://www.astm.org/cgi-bin/SoftCart.exe/BOOKSTORE/COMPS/CONTENTS/71.html?L+mystore+mhth9641

Preparation:

• Each group will need one aluminum foil panel of each coating obtained from the teacher.
• A set of objects with various diameters should be ready to use.

Investigation Procedures:

• Place the test panel over the largest diameter.
• Using a steady pressure with your fingers, bend the panel approximately 180° around the diameter.
• Remove and examine the panel immedialtely for cracking visible to the unaided eye.
• If cracking has not occurred, repeat the procedure using successively smaller diameter objects on another area of the foil until either cracking occurs or the smallest diameter has been used.
• This procedure can be applied as a “pass/fail” test by determining whether cracking is produced by a specified diameter size.
• The resistance to cracking value for a coating is taken as the diameter greater than that at which cracking occurs. So, the last diameter where cracking does NOT occur.

Report:

• The objects and their diameters used in the test. (If need be, you can calculate diameter by wrapping a sheet of paper around the object, marking where the paper overlaps, laying the paper flat and measuring it with a ruler, and then finding the diameter from the equation “Circumference (perimeter) = 2πr = πd” by dividing the length of the paper by π.)
• The value at which cracking occurs and the value before it cracks.

Conclusions:
Have groups of students share their data with other groups by putting their data either on the board or on an overhead. Students should discuss why bendability is important. Where would you use stiff or flexible coatings? Why? They can then compare the results of the bendability test to other physical characteristics they have already observed.

OUR TEST RESULTS (Diameter in.(mm)):

Polymer Science Learning Center | Department of Polymer Science | University of Southern Mississippi
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