Chapter 4 L09

Question 1

What is a thermoplastic?

Answer 1

They are a type of plastic that:
- Their processing is reversible
- No cure requiered

Question 2

Name the main strucutral difference between thermoplastics and thermosets. How do the properties change?

Answer 2

• Thermoplastics bonds are linear polymere chains
• Thermosets bonds are crossed-linked polymere chains
  Therefore thermoplastics are more viscous and they can be melted as often as desired

Question 3

What are the 3 classifications of thermoplastics?

Answer 3

• Standard (cheaper, more production )
• Engineering (applied in engineering machines)
• High performance (expensive, low production)

Question 4

How are polymers classified according to order their structure is?

Answer 4

• Amorphous: Formed by amorphous and non-crystalline structures
• Semicrystalline: Formed by amorphous and crystalline structures

Question 5

How do viscosity and the shear modulus behave with temperature changes?

Answer 5

As temperature increases, thermoplastic’s viscosity increases and the shear modulus decreases

Question 6

What is the difference between PE-HD and PE-LD. Sketch them.

Answer 6

Polyethylene(High/Low density) have different size chain lengths. PE-HD has short side chains and PE-LD has long chain lengths. Skecth: “Notes”

Question 7

Name two transparent thermoplastics.

Answer 7

PP (polypropylene) and PC (polycarbonate)

Question 8

Name two thermoplastics used in a foamed (espuma) form.

Answer 8

PS (polystyrene) and PE-LD (polyethylene low-density)

Question 9

How does water absortion affect the mechanical properties of PA (polyamide) ?

Answer 9

It lowers the glass transition temperature and increases the toughenss

Question 10

What are the main building groups of polyaryletherketones as well as the properties?

Answer 10

P.a.e.k. are made of ether, ketones and aryl groupes. This provides a extermely high mechanical, thermal and chemical properties

Question 11

Advantages and disadvantages of thermoplastics in aerospace

Answer 11

Advantages: No cure needed, rapid processing
Disadvantages: ↑ Processing temperatues ↑ Viscosity

Question 12

Are thermoplastics used under or above the glass transition temperature? Why?

Answer 12

During the manufacturing process they are used above the glass transition temperature, as the viscosity flow increases, facilitating its manufacturing