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Questions and Answers
Which characteristic distinguishes thermosetting polymers from thermoplastics during heating?
What happens to thermosetting polymers when they are reheated?
What percentage of the tonnage of all synthetic polymers produced do thermoplastics account for?
Which of the following is an example of a thermosetting polymer?
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Which of the following polymers is NOT classified as a thermoplastic?
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How do thermoplastics and thermosets compare in terms of market share?
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What is the typical specific gravity of polymers?
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What is the key symbol used to represent thermosetting polymers?
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What characteristic of thermoplastics makes them suitable as electrical insulators?
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Which of the following statements is true regarding the usage of polymers compared to metals?
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What is a key feature of thermosetting polymers?
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Which of the following is NOT a commercial form of thermoplastic products?
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Which property of thermoplastics is typically higher than that of metals and ceramics?
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How are starting plastic materials for thermoplastics typically supplied to fabricators?
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What happens to a thermosetting polymer during the curing process?
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Which thermoplastic product is commonly used for protective covering?
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What is a significant reason why polymers are important in manufacturing?
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Which characteristic is typical of thermoplastic polymers?
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How does branching in polymer structures affect their properties?
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In terms of energy production, polymers are generally:
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Which of the following statements is true regarding the cost-effectiveness of polymers?
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What property is NOT associated with plastics used in manufacturing?
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What is a defining feature of tightly cross-linked or networked polymer structures?
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When comparing polymers to metals, which of the following is generally true?
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What is the primary function of the reinforcing phase in composite materials?
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Which of the following is an example of a Ceramic Matrix Composite (CMC)?
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What role does the matrix material play in composite materials?
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Which of the following shapes is NOT commonly found in the reinforcing phase of composite materials?
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Which type of composite is formed from polymer resins embedded with reinforcing agents?
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How does the matrix material behave under applied load?
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What is a key characteristic of Metal Matrix Composites (MMCs)?
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What is the generic term often used for the secondary phase in composite materials?
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What is one primary benefit of using a sandwich structure with a foam core?
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Which of the following best describes FRPs?
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What is a common use for printed circuit boards?
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What is one advantage of using honeycomb cores in sandwich structures?
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Which component is NOT typically found in the composition of automotive tires?
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What property do laminated composite structures such as windshield glass provide?
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Which material is commonly associated with sandwich structures for enhancing lightweight design?
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What is a significant characteristic of laminar composite structures?
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Study Notes
Thermosetting Polymers (TS)
- Characterized by highly cross-linked, three-dimensional, covalently bonded structures.
- Chemical reactions during cross-linking are called curing or setting.
- After curing, the formed part becomes one large macromolecule.
- Always amorphous and exhibit no glass transition temperature.
- Symbolized by 'TS' and cannot tolerate repeated heating cycles.
Market Shares
- Thermoplastics dominate commercially with around 70% of the market share.
- Thermosets and elastomers share the remaining 30%, with a slight advantage for thermosets.
- Polymers exceed metals in volumetric use.
Examples of Polymers
- Thermoplastics include:
- Polyethylene
- Polyvinylchloride
- Polypropylene
- Polystyrene
- Nylon
- Thermosets include:
- Phenolics
- Epoxies
- Certain polyesters
Reasons Why Polymers are Important
- Plastics can be molded into complex shapes, often with no further processing.
- On a volumetric basis:
- Polymers are cost-competitive with metals.
- Polymers generally require less energy to produce than metals.
- Some plastics are translucent or transparent, making them competitive with glass for some applications.
Polymer Structures
- Linear structure is the fundamental type for thermoplastics.
- Branched structure is another common type found in thermoplastics.
- Tightly cross-linked or networked structure is characteristic of thermosets.
Effect of Branching on Properties
- Thermoplastics have linear or branched structures, or a mixture of both.
- Branching increases entanglement among molecules, leading to:
- Increased strength in the solid state.
- Increased viscosity at a given temperature in the plastic or liquid state.
Physical Properties of Thermoplastics
- Thermoplastics have lower densities than metals or ceramics.
- Polymers have a specific gravity of around 1.2.
- Ceramics have a specific gravity of around 2.5.
- Metals have a specific gravity of around 7.0.
- Thermoplastics have a higher thermal expansion coefficient than metals or ceramics:
- Approximately five times the value for metals and ten times the value for ceramics.
- Thermoplastics have a much lower melting temperature than metals and ceramics.
- Thermoplastics are electrically insulating.
- Thermoplastics have a higher specific heat than metals and ceramics.
Commercial Thermoplastic Products and Raw Materials
- Thermoplastic products include:
- Molded and extruded items.
- Fibers and filaments.
- Films and sheets.
- Packaging materials.
- Paints and varnishes.
- Starting materials are typically supplied to the fabricator in powder or pellet form.
Composite Materials
- Composites are materials made of two or more distinct phases, resulting in a material with properties different from its constituent parts.
- The primary phase is the bulk of material and serves as the base.
- The secondary phase is often called a reinforcing agent as it strengthens the material.
- Common types of composites include:
- Metal Matrix Composites (MMCs)
- Ceramic Matrix Composites (CMCs)
- Polymer Matrix Composites (PMCs)
Functions of the Matrix Material
- The primary phase provides the bulk form of the composite product.
- It holds the reinforcing phase in place, often concealing it.
- It shares the load with the reinforcing phase, sometimes deforming to transfer stress to the reinforcement.
The Reinforcing Phase
- Reinforcement phase strengthens the primary phase.
- Most common shapes:
- Fibers
- Particles
- Flakes
Other Laminar Composite Structures
- Automotive tires: Multi-layered rubber layers bonded with reinforcing agents.
- Fiber-reinforced plastics (FRPs): Multi-layered panels for aircraft, boats, etc.
- Printed circuit boards (PCBs): Layers of reinforced copper and plastic for electrical conductivity and insulation, respectively.
- Snow skis: Layers of metals, particle board, and phenolic plastic.
- Windshield glass: Two layers of glass sandwiching a sheet of tough plastic.
Sandwich Structure
- Foam Core: Thick core of low-density foam bonded to thin sheets of a different material.
- Honeycomb Core: Alternative to foam core.
- Both foam and honeycomb cores achieve high strength-to-weight and stiffness-to-weight ratios.
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Description
Test your knowledge on thermosetting polymers, including their characteristics, market shares, and examples. Understand the differences between thermoplastics and thermosets, and learn about their significance in various applications.