Adhesives have played a crucial role in human civilization for thousands of years. The oldest known glue, dating back over 8,000 years, was discovered in a cave near the Dead Sea. This ancient adhesive, crafted from a blend of animal bones and plant materials, was used to waterproof baskets and construct utensils. As time progressed, plants and animals continued to be the primary sources of adhesives, binding human societies together.
Today, the variety of tapes and glues available allows us to build and repair almost anything. But what exactly gives these adhesives their stickiness, and how do they differ in strength? Adhesives can be derived from both synthetic molecules and natural substances such as vegetable starch dextrin, milk protein casein, and tree resin terpenes. For adhesives to function effectively, they require both adhesive and cohesive bonds.
Adhesive bonds form between the molecules of the adhesive and the surface it adheres to, while cohesive bonds occur within the adhesive itself, holding it together. Most glues consist of adhesive polymers dissolved in a solvent, which prevents them from sticking inside the bottle. The strong odor of many glues is due to the solvent, which evaporates upon exposure to air. Some glues utilize water as a solvent, while others use chemicals that may be harmful if inhaled. Glues with multiple components that chemically react, rather than just drying, can create stronger bonds.
While both adhesive and cohesive bonds in glue are strong, the drying process renders them irreversible. This means that once a glued surface breaks, it cannot be reattached without new glue. In contrast, tape forms weaker, reversible bonds, allowing it to be peeled off and reused. These weak bonds, known as Van der Waals forces, can occur between any two materials, provided they are extremely close together.
Tape typically consists of a backing coated with a rubber or rubber-like component and a tackifier, which provides the stickiness. The stickiness of tape is determined by the ratio of elastic component to tackifier, the thickness of the adhesive layer, and the type of backing material. Unlike glue, no chemical reaction occurs when tape is applied to a surface. Instead, the adhesive flows into the surface’s cracks and grooves, a property known as viscoelasticity. Once the adhesive fills these microscopic crevices, it forms Van der Waals forces.
There is no definitive answer to what constitutes the world’s strongest adhesive. In terms of absolute adhesive bond strength, glue surpasses tape. However, no single adhesive is suitable for all situations. Among glues, cyanoacrylates, or super glues, may create the strongest bonds, but two-component epoxy glues offer greater resistance to heat and shearing and are compatible with a wider range of surfaces. For example, while super glue might be ideal for suspending an anvil, epoxy would be preferable in high-temperature environments like an active volcano.
When selecting adhesives, engineers must consider various factors, such as the heat resistance required inside an engine. While duct tape’s adhesive bonds cannot match the strength of epoxy glues, its instantaneous stickiness is advantageous in emergencies. Although glue is essential for launching rockets into space, duct tape is preferred for extraterrestrial repairs, as liquid glues do not function in zero gravity.
Gather materials like animal bones (or a substitute like gelatin) and plant materials. Follow a simple recipe to create your own ancient glue. Document the process and compare the effectiveness of your glue with modern adhesives. Discuss how ancient people might have discovered and used these materials.
Collect different types of adhesives, such as various glues and tapes. Design an experiment to test their strength by sticking objects together and measuring how much weight they can hold before breaking. Record your findings and create a chart to compare the adhesive and cohesive strengths of each product.
Use common household items to demonstrate adhesive and cohesive bonds. For example, use a piece of tape to show adhesive bonds by sticking it to different surfaces. Then, use a glue stick to show cohesive bonds by observing how the glue holds together within itself. Explain the differences and why each type of bond is important.
Research the components of tape, such as the backing material, rubber component, and tackifier. Create a design for a new type of tape that balances stickiness and reversibility. Present your design to the class, explaining the choices you made and how they affect the tape’s performance.
Investigate how adhesives are used in different engineering fields, such as aerospace, automotive, and construction. Create a presentation or poster that highlights specific examples, such as the use of epoxy in high-temperature environments or duct tape in space missions. Discuss the factors engineers must consider when selecting adhesives for various applications.
Adhesives – Substances used to stick objects or materials together. – Adhesives are often used in construction to hold different materials in place.
Glue – A type of adhesive that is usually liquid and used for sticking things together. – We used glue to attach the pieces of our science project.
Tape – A long, thin strip of material with a sticky side that is used to hold things together. – I used tape to secure the wires in my electronics project.
Bonds – The connections that hold atoms or molecules together in a substance. – Chemical bonds are important because they determine how substances interact with each other.
Strength – The ability of a material to withstand force or pressure without breaking. – The strength of the bridge was tested to ensure it could hold heavy vehicles.
Polymers – Large molecules made up of repeating units, often used in plastics and other materials. – Many toys are made from polymers because they are flexible and durable.
Solvent – A liquid that dissolves a substance, forming a solution. – Water is a common solvent used in many chemical reactions.
Viscosity – A measure of a fluid’s resistance to flow; thicker fluids have higher viscosity. – Honey has a higher viscosity than water, making it flow more slowly.
Materials – Substances used to make objects or structures. – Engineers choose the right materials to ensure their designs are safe and effective.
Engineers – Professionals who design, build, and maintain structures, machines, and systems. – Engineers work on projects like bridges and airplanes to solve complex problems.
