What is adhesion?
Adhesion is the process by which two similar or dissimilar surfaces are held together in close contact by surface attachment interfacial forces of attraction and mechanical interlocking.
What are the requirements for a material to be an adhesive?
It must wet the surface, adhere to surfaces, develop strength, and remain stable.
What are the primary theories of adhesion?
Mechanical interlocking, adsorption theory, electrostatic theory, and diffusion theory.
Explain the mechanical interlocking theory.
Adhesion occurs when an adhesive penetrates into pores or holes of a substrate and locks mechanically.
- Not only wet the substrate, but also have right rheological properties to penetrates pores.
- wood, paper, textile
What does the adsorption theory state?
Adhesion arises from intermolecular contact between two materials, and involves surface forces that develop between the atoms.
Surface forces: Van der Waals forces, acid-base interactions, and hydrogen bonds.
Describe the electrostatic theory of adhesion.
Adhesion is due to electron transfer across the interface, creating an electrostatic attraction between positive and negative charges. The difference in electronegative of adhesive materials.
What is the diffusion theory?
It explains adhesion through interdiffusion of adhesive and adherend polymers, dependent on compatibility, temperature, and contact time.
Both adhesives and adherend are capable of movement.
What are the four main classifications of adhesives?
Rubber, thermosets, thermoplastics, and natural adhesives.
What are the types of rubber adhesives?
Natural rubber, styrene-butadiene rubber (SBR), nitrile, and silicone.
Polymer characteristic for adhesives application.
- Broad molecular weight distribution better than narrow one.
- Smaller MW fractions, higher mobility.
- Large MW fractions; precipitate in their own bulk or phase-separate. Contribute greatly to the development of cohesive strength in the adhesive layer.
What are the advantages of natural rubber adhesives?
- To improve the strength and temperature resistance.
-Excellent tack (ideal for pressure sensitive adhesive formulations, good strength, resilience, and moisture resistance.
What is the primary limitation of Natural rubber.
- Poor resistance to organic solvents
- Does not bond well to metals
What is SBR adhesives?
Formed via random copolymerization of styrene and butadiene.
- Adherent: fabrics, foils, rubber and sponge rubber, wood
- Application: pressure sensitive adhesive & laminating
Advantages of SBR
- Better aging properties than natural rubber and reclaimed rubber
- Bond strength similar to reclaimed rubber.
Why are nitrile adhesives widely used?
- excellent resistance to oil and hydrocarbon solvents
- versatile for applications like automotive gaskets and seals.
Uses: - Automotive gasket and seals - Consumer shoe products, flooring
- Adherent: rubber, metal, vinyl, plastics
Disadvantages of nitrile
- Tack range: lower than natural rubber
- Not bond well to natural rubber or butyl rubber
- Unsuitable for structural applications under continuous loading exceed 0.7 mpa
What is a notable advantage of silicone adhesives?
- excellent temperature resistance and adhesion to glass
- solvent free
- UV curing formulations available
-making them ideal for automotive and marine applications.
Uses: - Pressure sensitive tape for electrical winding and coil. - Automotive sealing, marine and appliance
- Adherent: Metals, glass, paper, plastics and rubber
Disadvantages of silicone
- Poor cohesive strength
- Slow curing
- Corrosive
- High cost
What are the two main types of thermoplastic adhesives?
Polyvinyl acetate (PVAc) and polyamide.
What are the key properties of PVAc adhesives?
Environmentally friendly, strong, clear-drying, good adhesion to a variety of surface but
- poor moisture resistance
- Joints with thick glue lines tend to creep under sustained loads.
- Inappropriate for structural applications.
Advantages, Disadvantages and Uses PVAc
A: - Tastless
- Ordourless
- Good resistance to oil and grease
- Low cost
D: - Low resistance to weather and moisture
- Poor resistance to solvents
- Creep under sustained load
- Not suitable for structures.
U: - Woodworking adhesives
- Furniture assembly
- Bookbinding
Adherent: Porous or non porous, paper, cloth, leather, glass, plastic
Advantages, Disadvantages and Uses Polyamide
A: - Tough, High cohesive strength
- Good tensile strength and elongation are retained after exposure to high T
- good low T performance (below -50)
- Moderate resistance to water, oil and grease.
D: - Poor resistance to alcohol
- Oxidizing acids and alkali
U: -Footwear industry
- Automotive (metal to metal)
- Structural bonding of wood, metal, plastics
What are examples of thermosetting adhesives?
Epoxy and urea formaldehyde.
Advantages, Disadvantages and Uses Epoxy
A: - Versatile
- High cohesive
- Good toughness
- Cure can be accelerated by heat
- Good temperature and solvent resistance
D: - Exothermic reaction
- Two part system requiring exact measuring and mixing
- One part systems require heat cure
- long cure time
U: - Structural adhesives
- Container and housing manufacture
- Aluminum constructions
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Chapter 120
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G1-5 SCL34
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Chapter 2: Molding, Extrusion, Calendering42
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Radiation, Ingredients29
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Chapter 6A13
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Chapter 5A16
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Chapter 5B13
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Chapter 5C21
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Chapter 4A28
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Chapter 4B23
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Chapter 9 Final20
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Chapter 8 Final16
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Chapter 7 (2) Final19
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Chapter 3 Final34
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Chapter 2 Final (blow molding focused)16
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Chapter 6B21
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Chapter 3D Thermoforming13
