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Questions and Answers
Which characteristic is essential for fibers used in textiles and composites?
In which forming technique is molten plastic injected into a mold to solidify?
Which term best describes the time-dependent behavior of polymers that exhibit both viscous and elastic properties?
What happens to polymers during the crystallization process?
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Which of the following is NOT a common application of plastics?
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Which forming technique is used to create hollow plastic objects by inflating molten plastic?
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Which property contributes to the mechanical behavior of polymers but does not relate directly to their classification?
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Which technique involves heating a plastic sheet until pliable and then shaping it into a mold?
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Which type of polymer is characterized by having branch points that connect three or more segments?
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What does the term 'degree of polymerization' (DP) refer to?
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What is a consequence of crosslinking in polymers?
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Which of the following statements about linear polymers is true?
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What is the primary composition of most polymers?
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Which type of polymer includes adjacent chains that are attached via covalent bonds?
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How is the molecular weight of a polymer typically expressed?
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What are network polymers primarily characterized by?
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Which polymer structures allow for strong physical properties primarily due to cross-linking?
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What is the effect of molecular shape on polymers?
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Which of the following is an example of a forming technique for elastomers?
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How does dispersity impact polymers?
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What are network polymers primarily characterized by?
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Which of the following is NOT a mechanical property typically associated with vulcanized rubber?
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What characterizes amorphous polymers compared to crystalline polymers?
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Which feature is essential in determining the average molecular weight of polymers?
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Study Notes
Molecular Structure
- The arrangement of a polymer's atoms defines its structure.
- A polymer can be either amorphous or crystalline, with a variety of shapes including linear, branched, or crosslinked.
- Polymer structures impact key properties like rigidity, transparency, thermal properties and how they handle stress.
Polymer Types
- Linear polymers contain repeating units connected end-to-end, like polyethylene, Teflon, and PVC.
- Branched polymers have branch points that connect three or more segments, inhibiting close packing of chains and creating a more flexible structure.
- Crosslinked polymers have adjacent chains linked by covalent bonds and behave differently than linear polymers.
- Network polymers are trifunctional, with three points on their monomer that can react, creating a 3-dimensional network.
Molecular Weight
- Polymers are large molecules with variable chain lengths.
- Average molecular weight is used since chains vary in length.
- The spread of molecular weights is called dispersity, which highlights polymer chain length variation.
Polymer Fracture
- Crazing, similar to Griffith cracks in metals, involves microvoids and fibrillar bridges forming in polymers.
- Spherulites can deform plastically to further enhance the fibrillar structure.
Mechanical Properties
- Viscoelastic deformation is a property of polymers at intermediate temperatures where they behave like a rubbery solid, exhibiting both viscous (fluid-like) and elastic (solid-like) characteristics.
- Time Dependent Deformation is a characteristic of viscoelasticity, polymers exhibit both viscous and elastic behavior when deformed over time.
- Crystallization in polymers is a process of partial molecular chain alignment, forming ordered regions called spherulites.
Elastomers
- Rubber is a natural polymer with cross-links that increase strength.
- Vulcanized rubber is polyisoprene with sulfur cross-links.
- Cross-linked polymers can be classified as network polymers, like epoxies and phenol-formaldehyde polymers, because of their 3D structures.
Forming Techniques of Elastomers
- Extrusion forces elastomer material through a die to create continuous shapes like tubes and hoses.
- Applications include seals, gaskets, and hoses.
Plastics
- Plastics are a wide range of synthetic polymers formed by polymerization, where repeating units (mers) are connected end-to-end.
- Polyethylene, Teflon, and PVC are common examples.
- Plastics are valued for their flexibility, durability, and wear resistance.
Forming Techniques of Plastics
- Injection molding involves injecting molten plastic into a mold where it cools and solidifies.
- Extrusion melts plastic and forces it through a die to create shapes like pipes and sheets.
- Blow molding inflates molten plastic inside a mold to create hollow objects like bottles.
- Thermoforming heats a plastic sheet until pliable and shapes it into a mold.
Fibers
- Fibers are filamentous materials with high surface area to volume ratios, typically used in textiles and composites.
Fiber Forming Techniques
- Weaving interlaces fibers together to create fabric.
- Knitting uses interlooping to create fabric.
- Nonwoven techniques use various methods to create fabric without weaving or knitting, such as needle punching, where needles entangle fibers.
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Description
This quiz covers the fundamental concepts of polymer structure, types, and molecular weight. Learn about amorphous and crystalline arrangements, differences between linear, branched, crosslinked, and network polymers, and the significance of molecular weight in polymers. Test your knowledge on how these properties influence polymer behavior.
