Plastics Exam Questions with Correctly Solved
Answers
What are plastics?
Plastics are polymers , large molecules made of repeating units of smaller molecules (monomers)
that are chemically bound together. They include include fibers and elastomers.
What is a thermoplastic?
Polymers that are rigid and solid at room temperature but can be heated to soften or re-melted.
What is a thermoset?
Polymers that can NOT be melted or re melted once formed.
What are some advantages and disadvantages of thermoplastics?
- Wide range of physical properties.
- Requires heat and tooling that can withstand it.
- Many can be recycled or molded again.
What are some advantages and disadvantages of thermosets?
- Can be molded at room temperature.
- Heat does not soften these materials.
- Exothermic when setting.
- Can be brittle is cured too quickly or without reinforcement.
- Cannot be recycled.
What is a crystalline polymer?
,Polymers that have a highly ordered molecular structure. They have a defined and narrow
melting point.
What is an amorphous polymer?
Polymers that have a random molecular structure that does not have a sharp melting point. They
gradually get softer as temperature rises.
What are some examples of a crystalline polymer?
Polyethylene (PE)
PBT
Polypropylene (PP)
Polyamide (Nylon)
What are some examples of an amorphous polymer?
PVC
Polystyrene
Acrylic (PMMA)
ABS
PPO
Polycarbonate (PC)
Polyetherimide
What are some advantages and disadvantages of crystalline polymers?
- Sharply defined melting point.
- High shrinkage and potential warpage after molding.
,- Lower impact strength and lower stiffness than amorphous materials.
- High heat resistance but low heat deflection temperature (HDT).
- Usually opaque due to molecular structure.
- Good fatigue endurance.
- Good lubricity; wear resistance.
- Good chemical resistance.
- Ability to flow in thin walled sections.
What are some advantages and disadvantages of amorphous polymers?
- Wide melting range.
- Low shrinkage after molding with less distortion.
- Better impact and lower chemical resistance than
crystalline polymers.
- Moderate heat resistance.
- Dimensional stability.
- Can be transparent or water clear.
- Superior cosmetics of outer surfaces.
Tg - Glass transition
Material softens
Tm - Melt transition
Material melts
, What are some examples of structural referment in plastics? (Not ribbing or molded
portions)
glass fibers
carbon fibers
metal
fibers
aramid fibers
jute
polyester fibers
What are some examples of fillers in plastics?
glass spheres
talc
mica flakes
ceramic powders
silica sand
carbon black
wood flour
What are some examples of additives in plastics?
Colorants
UV Modifiers
Plasticizers
Impact modifiers
Answers
What are plastics?
Plastics are polymers , large molecules made of repeating units of smaller molecules (monomers)
that are chemically bound together. They include include fibers and elastomers.
What is a thermoplastic?
Polymers that are rigid and solid at room temperature but can be heated to soften or re-melted.
What is a thermoset?
Polymers that can NOT be melted or re melted once formed.
What are some advantages and disadvantages of thermoplastics?
- Wide range of physical properties.
- Requires heat and tooling that can withstand it.
- Many can be recycled or molded again.
What are some advantages and disadvantages of thermosets?
- Can be molded at room temperature.
- Heat does not soften these materials.
- Exothermic when setting.
- Can be brittle is cured too quickly or without reinforcement.
- Cannot be recycled.
What is a crystalline polymer?
,Polymers that have a highly ordered molecular structure. They have a defined and narrow
melting point.
What is an amorphous polymer?
Polymers that have a random molecular structure that does not have a sharp melting point. They
gradually get softer as temperature rises.
What are some examples of a crystalline polymer?
Polyethylene (PE)
PBT
Polypropylene (PP)
Polyamide (Nylon)
What are some examples of an amorphous polymer?
PVC
Polystyrene
Acrylic (PMMA)
ABS
PPO
Polycarbonate (PC)
Polyetherimide
What are some advantages and disadvantages of crystalline polymers?
- Sharply defined melting point.
- High shrinkage and potential warpage after molding.
,- Lower impact strength and lower stiffness than amorphous materials.
- High heat resistance but low heat deflection temperature (HDT).
- Usually opaque due to molecular structure.
- Good fatigue endurance.
- Good lubricity; wear resistance.
- Good chemical resistance.
- Ability to flow in thin walled sections.
What are some advantages and disadvantages of amorphous polymers?
- Wide melting range.
- Low shrinkage after molding with less distortion.
- Better impact and lower chemical resistance than
crystalline polymers.
- Moderate heat resistance.
- Dimensional stability.
- Can be transparent or water clear.
- Superior cosmetics of outer surfaces.
Tg - Glass transition
Material softens
Tm - Melt transition
Material melts
, What are some examples of structural referment in plastics? (Not ribbing or molded
portions)
glass fibers
carbon fibers
metal
fibers
aramid fibers
jute
polyester fibers
What are some examples of fillers in plastics?
glass spheres
talc
mica flakes
ceramic powders
silica sand
carbon black
wood flour
What are some examples of additives in plastics?
Colorants
UV Modifiers
Plasticizers
Impact modifiers
