Plastics Flashcards
Define thermoplastics
A thermoplastic is a resin that is solid at room temperature but becomes plastic and soft upon heating, flowing due to crystal melting or by virtue of crossing the glass transition temperature (Tg)
Thermoplastics can be processed and reshaped multiple times through heating.
What are the main processing methods for thermoplastics?
- Injection-moulding
- Blow-moulding
- Extrusion
- Thermoforming
These methods take advantage of the reversible nature of thermoplastics.
List three common examples of thermoplastics.
- Polyethylene (PE)
- Polycarbonate (PC)
- Polyvinyl chloride (PVC)
These materials exhibit distinct properties suitable for various applications.
How do thermosets differ from thermoplastics?
Thermosets cannot be softened by reheating and undergo a chemical change during the initial process, creating a crosslinked structure
This crosslinked structure makes thermosets rigid and strong.
What is the melting point characteristic of thermoplastics?
Melting point lower than the degradation temperature
This allows thermoplastics to be reshaped upon heating.
Give examples of thermosets.
- Polyester resin
- Fiberglass systems
- Bakelite
- Urea-formaldehyde foam
- Epoxy resin
Each example serves specific industrial and consumer purposes.
What is the characteristic structure of elastomers?
Elastomers have loosely crosslinked polymers that provide flexibility and elasticity
Rubber and neoprene are common examples.
Define composites in the context of materials.
Composites, or fibre-reinforced polymers (FRPs), are made from a polymer matrix reinforced with fibres or other materials
The fibres provide strength, while the matrix protects them.
What does anisotropic mean in relation to composites?
Anisotropic means the material properties change depending on the placement and number of layers of reinforcement material
This allows for tailored engineering properties.
What is tensile strength?
Tensile strength refers to the amount of stress a material can handle before it breaks or deforms
Measured in megapascals (MPa), it varies by material.
What is shear strength?
Shear strength describes how well a material can resist strain when layers shift or slide
It is critical for understanding how materials behave under different loading conditions.
What is compressive strength?
Compressive strength indicates how a material performs under compression or flattening pressure
Composites generally show higher tensile strengths than compressive strengths.
List examples of composites.
- MDF
- Plywood
- Glass reinforced plastic (GRP)
- Carbon fibre reinforced plastic (CRP)
These materials are engineered for specific strength and performance characteristics.
True or False: Thermoplastics can be recycled by applying heat.
True
This is due to their ability to melt and be reshaped.
Fill in the blank: Thermosets are _______ and cannot be softened by reheating.
inflexible
This characteristic is due to their crosslinked molecular structure.
