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Activity

Making glue

Summary: 
Make glues made from household ingredients and test how long they can hold a marble to a piece of cardboard. Understand some of the ways that glues work on a molecular level.
Science content (2016 curriculum): 
Chemistry: States of Matter, Properties of Materials (K-7)
Chemistry: Physical Changes, Solutions, Mixtures and Separating (2, 4, 5, 6)
Materials: 
  • labelled containers of flour, cornstarch, milk powder, icing sugar
  • small scoops e.g. 1/8 or 1/4 teaspoon measures
  • squeeze bottle of water
  • stir sticks e.g. wooden coffee sticks
  • trays with small compartments e.g. paint trays or ice cube trays
  • optional: worksheet (see attached)
  • marbles
  • strips of cardboard e.g. cut up cereal box
  • waste tub
Procedure: 

This activity adapted from https://www.acs.org/content/dam/acsorg/education/resources/k-8/science-a...

Give students tubs of glue making materials, scoops, water bottles, trays, stir sticks.
Ask them to make the best glue possible - they should test their glue by putting a blob of it on a cardboard strip, pushing a marble into it, then hanging the strip upside down. They can time how long it takes for the marble to fall off - the longer, the better glue. (This activity does not take into account the drying process of glues - commercial glues need dry time to reach maximum strength.)
Distribute worksheets for students to record the glue recipes they create, as well as how long the glue holds the marble to the cardboard.

Discuss how glues work (only a partially understood process):
The molecules of a glue need to be good at sticking to each other and to the material(s) it is glueing together. There are several molecular processes at work.
Adsorption - the glue and the material have charged molecules that attract each other. It is a weak attraction, but with many of these bonds they can hold the glue and surfaces of the material together.
Mechanical - the long molecules of the glue creep into the tiny holes in the surface of the material(s) and hold them together.
Charged molecule attraction and long molecules are the easiest explanations for this activity.

Other glue mechanisms:
Diffusion theory. The adhesive can diffuse into the surface and vice-versa, with molecules swapping over at the join and mingling together.
Chemisorption - there is a chemical reaction between the glue and the material. (not the mechanism for the glues made in this activity)
From www.explainthatstuff.com/adhesives.html

Attached documents: 
Grades taught: 
Gr 5
Teacher: 
Ingrid
Teaching site: 
ingridscience afterschool