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Plastic Composite > Chapter 4A > Flashcards

Chapter 4A Flashcards

1
Q

What is adhesion?

A

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.

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2
Q

What are the requirements for a material to be an adhesive?

A

It must wet the surface, adhere to surfaces, develop strength, and remain stable.

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3
Q

What are the primary theories of adhesion?

A

Mechanical interlocking, adsorption theory, electrostatic theory, and diffusion theory.

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4
Q

Explain the mechanical interlocking theory.

A

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

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5
Q

What does the adsorption theory state?

A

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.

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6
Q

Describe the electrostatic theory of adhesion.

A

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.

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6
Q

What is the diffusion theory?

A

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.

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7
Q

What are the four main classifications of adhesives?

A

Rubber, thermosets, thermoplastics, and natural adhesives.

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8
Q

What are the types of rubber adhesives?

A

Natural rubber, styrene-butadiene rubber (SBR), nitrile, and silicone.

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9
Q

Polymer characteristic for adhesives application.

A
  • 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.
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10
Q

What are the advantages of natural rubber adhesives?

A
  • To improve the strength and temperature resistance.
    -Excellent tack (ideal for pressure sensitive adhesive formulations, good strength, resilience, and moisture resistance.
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11
Q

What is the primary limitation of Natural rubber.

A
  • Poor resistance to organic solvents
  • Does not bond well to metals
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12
Q

What is SBR adhesives?

A

Formed via random copolymerization of styrene and butadiene.
- Adherent: fabrics, foils, rubber and sponge rubber, wood
- Application: pressure sensitive adhesive & laminating

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13
Q

Advantages of SBR

A
  • Better aging properties than natural rubber and reclaimed rubber
  • Bond strength similar to reclaimed rubber.
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14
Q

Why are nitrile adhesives widely used?

A
  • 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
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15
Q

Disadvantages of nitrile

A
  • 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
16
Q

What is a notable advantage of silicone adhesives?

A
  • 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
17
Q

Disadvantages of silicone

A
  • Poor cohesive strength
  • Slow curing
  • Corrosive
  • High cost
18
Q

What are the two main types of thermoplastic adhesives?

A

Polyvinyl acetate (PVAc) and polyamide.

19
Q

What are the key properties of PVAc adhesives?

A

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.

20
Q

Advantages, Disadvantages and Uses PVAc

A

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

21
Q

Advantages, Disadvantages and Uses Polyamide

A

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

22
Q

What are examples of thermosetting adhesives?

A

Epoxy and urea formaldehyde.

23
Q

Advantages, Disadvantages and Uses Epoxy

A

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

24
Q

Advantages, Disadvantages and Uses Formaldehyde

A

A: - More economical
- For composite wood products
- Light color
- Suitable for manufacture of decorative product
D: - Lack of durability
- Unsuitable for service conditions which are extreme high humidity
- Unsuitable for exterior
U: - Mainly for production of particle board
- Light wood, plywood furniture

25
Q

What are examples of natural adhesives?

A

Animal glues, starch, and cellulose derivatives.

26
Q

Advantages, Disadvantages and Uses Animal glue

A

A: - Good resistance to boiling water
- Ageing properties are moderate
- Suitable for interior use only
D: - Low moisture resistance
- Inconvenient to use and must be applied at the proper temperature
U: - Furniture construction

27
Q

Advantages, Disadvantages and Uses Starch

A

A: - Inexpensive
- Have relatively long pot life
- Joint strengths are low compared to other but adequate for certain applications
D: - Poor resistance to water
- Poor resistance to biodeterioration
U: - Paper, bottle labelling
- Stationery
- Formerly used in interior grade plywood fabrication

Plastic Composite (12 decks)

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