Engineering Applications of Polymers

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Questions and Answers

What is the primary property of elastomers that allows them to regain their original shape after deformation?

Elasticity (correct)

Amorphous structure

Chemical resistance

High tensile strength

Which of the following is NOT an application of the material described that provides electrical insulation?

Insulating material for high voltage cables

Cation-exchange resins

Bonds in grinding wheels

Inner tube for tires (correct)

Which property is a characteristic of Butyl Rubber?

Low abrasion resistance

Excellent resistance to oxidative aging (correct)

High gas permeability

High flexibility at low temperatures

What is the main disadvantage of Nitrile Rubber regarding its chemical resistance?

Less resistance to alkalis Signup and view all the answers

Which synthetic rubber has high temperature stability and solvent resistance due to its chemical structure?

Butyl Rubber Signup and view all the answers

What method is used to synthesize Nitrile Rubber?

Emulsion Polymerization Signup and view all the answers

Which characteristic of elastomers is linked to the coiled nature of their molecular chains?

Elasticity Signup and view all the answers

Which substance is used as a catalyst in the synthesis of Butyl Rubber?

Anhydrous aluminium chloride Signup and view all the answers

What temperature range can this rubber withstand?

-40 oC to 100 oC Signup and view all the answers

Which process involves heating rubber with sulphur to improve its strength?

Vulcanization Signup and view all the answers

What is the primary purpose of compounding in rubber manufacturing?

To mix raw rubber with other substances for specific properties Signup and view all the answers

Which of the following applications is NOT mentioned for the rubber?

Insulation for wiring Signup and view all the answers

What are polymer composites commonly developed for?

Military and aerospace applications Signup and view all the answers

Which characteristic is NOT desirable in an ideal structural material for the aircraft industry?

High density Signup and view all the answers

What is the main purpose of curing in the context of elastomer materials?

To create a stronger, more durable substance Signup and view all the answers

What is true about the properties of strong materials in relation to density and impact strength?

Higher stiffness generally leads to poorer impact strength Signup and view all the answers

What is the primary method for obtaining polyglycolide?

Ring-opening polymerization of glycolide Signup and view all the answers

Which catalyst is commonly used in the ring-opening polymerization of glycolide?

Aluminium isopropoxide Signup and view all the answers

What characterizes the degradation of polyglycolide?

It is characterized by hydrolytic instability Signup and view all the answers

What type of degradation process does polyglycolide undergo?

Erosive degradation in two steps Signup and view all the answers

Which of the following is NOT a commercial application of biodegradable polymers?

Non-biodegradable dental implants Signup and view all the answers

What is released during the degradation of polyglycolide?

Glycolic acid Signup and view all the answers

How does glycolic acid affect the body after degradation?

It enters the tricarboxylic acid cycle Signup and view all the answers

What is the primary role of the matrix in polymer composites?

To bind the fibers and transmit external stress Signup and view all the answers

Which of the following statements about the degradation process of polyglycolide is true?

The polymer chain dissolves after the crystalline regions collapse Signup and view all the answers

Which of the following statements about Kevlar is true?

It can withstand temperatures up to 450 ⁰C Signup and view all the answers

What is the correct chemical process for preparing Kevlar?

Polycondensation between 1,4-phenyl-diamine and 1,4-benzedicarbonyl chloride Signup and view all the answers

How does Kevlar behave at cryogenic temperatures?

It maintains its strength Signup and view all the answers

What is a key characteristic of carbon fibers?

They contain at least 90% carbon Signup and view all the answers

What unique property does Kevlar exhibit when exposed to ignition?

It ignites but burning stops when the heat source is removed Signup and view all the answers

What is one application of Kevlar?

Used in bulletproof vests Signup and view all the answers

What technique is used to determine the weight average molecular mass (Mw)?

Light scattering and ultra centrifugation Signup and view all the answers

Which statement about the properties of polymer composites is true?

The bonding forces between fibers and matrix primarily contribute to strength Signup and view all the answers

What is the formula for calculating number average molecular mass (Mn)?

Mn = ∑ Ni Mi / ∑ Ni Signup and view all the answers

Which statement is true regarding the Poly Dispersity Index (PDI)?

PDI is the ratio of Mw to Mn. Signup and view all the answers

What characterizes a monodisperse polymer?

All molecules have the same molecular mass. Signup and view all the answers

What is the relationship between Mw and Mn for polymers?

Mw is always greater than Mn. Signup and view all the answers

What does a higher Poly Dispersity Index (PDI) imply about a polymer?

The polymer is heterogenous with a wider range of molecular masses. Signup and view all the answers

Which of the following properties is NOT used to determine number average molecular mass (Mn)?

Light scattering Signup and view all the answers

Why is an average molecular mass calculated for polymers?

Individual macromolecules have different degrees of polymerization. Signup and view all the answers

What happens to the glass transition temperature (Tg) of a polymer as its flexibility increases?

Tg decreases due to higher segmental mobility. Signup and view all the answers

How do intermolecular forces influence the Tg of a polymer?

Stronger intermolecular forces increase Tg due to restricted molecular mobility. Signup and view all the answers

What effect does branching have on the glass transition temperature (Tg) of a polymer?

A small amount of branching reduces Tg, while a high degree of branching increases it. Signup and view all the answers

What is the effect of molecular weight on the glass transition temperature (Tg) up to 20,000?

Tg increases with increasing molecular weight. Signup and view all the answers

What role do plasticizers play in relation to the glass transition temperature (Tg)?

They decrease Tg by diluting intermolecular forces. Signup and view all the answers

Which polymer is likely to have the highest Tg value based on structural characteristics?

Polystyrene with Tg of 100 °C. Signup and view all the answers

Which configuration of a polymer is considered to be the least symmetric?

Atactic Signup and view all the answers

What is the effect of adding hydrogen bonding polar groups to a polymer chain?

It increases Tg due to restricted molecular mobility. Signup and view all the answers

Signup and view all the answers

Study Notes

Polymers for Engineering Applications

Polymers are essential components of everyday items and have diverse industrial applications, including paints, adhesives, fibers, and elastomers.
Molecular weight is a crucial property, measured by number average (Mn) and weight average (Mw) molecular weights, with the polydispersity index (PDI) signifying the homogeneity of the polymer.
PDI is the ratio of mass average molecular weight (Mw) to number average molecular weight (Mn). Monodisperse polymers have a PDI of 1, while polydisperse polymers have a PDI greater than 1.
Polymers' properties are significantly influenced by glass transition temperature (Tg), flexibility, intermolecular forces, branching, and molecular weight.
Higher flexibility generally corresponds to lower Tg values.
Intermolecular forces, such as hydrogen bonding, increase Tg.
Branching decreases Tg, while cross-linking increases it.
Higher molecular weight generally corresponds to higher Tg values.
Plasticizers lower Tg, improving flexibility.
Stereoregularity of polymers affects their Tg values (isotactic > syndiotactic > atactic).
Tensile strength, density, and melt viscosity are important mechanical properties, influenced by molecular weight.
Crystallinity, degree of crystallinity, and stereo-regularity influence polymers' properties, such as melting point, solubility, and permeability.

Plastics

Plastics are organic materials characterized by high molecular weights, moldability with heat and pressure, and a catalyst.
They exhibit lightness, corrosion resistance, and thermal/electrical insulation.
Different types of plastics exhibit varying resilience to specific chemical attacks or solvents.
The degree of crystallinity significantly impacts the chemical resistance of a plastic.
Resins are crucial components of plastics and provide the basis for molding and shaping.

Polymethyl Methacrylate (PMMA)

PMMA is synthesized via suspension polymerization and is rigid with a high softening point (~130-140°C).
It displays good optical clarity, dimensional stability, and shape-forming properties, but has low resistance to hot acids and alkalis.
PMMA applications include lenses, windows, and transparent fixtures.

Urea-Formaldehyde (UF) Resins

UF resins are produced through the condensation of urea and formaldehyde, forming cross-linked polymers through curing.
They demonstrate good tensile strength, electrical insulation, chemical resistance (except organic solvents), and shape integrity.
UF resin applications include bonding agents in grinding wheels, cation exchange resins, and binders in composites.

Elastomers

Elastomers are high-molecular-weight polymers that exhibit significant elasticity and recover their initial shape when the stress is released.
Butyl rubber is made by mixing isobutylene with isoprene, utilizing a methyl chloride solvent and anhydrous aluminum chloride catalyst at 80°C.
Nitrile rubber synthesis involves emulsion polymerization of butadiene and acrylonitrile in the presence of a water solvent and H2O2, culminating in a vulcanized product.
Nitrile rubber possesses excellent resistance to heat, sunlight, oils, fats, and organic solvents, though it is less resistant to alkali.
Nitrile rubber applications include tires, hoses, and various industrial parts.

Polymer Composites

Composite materials are composed of two or more components (e.g., matrix and fiber), combined to enhance properties compared to individual materials.
Polymer composites typically utilize a strong fiber embedded within a matrix to improve strength and other properties in structural applications.
Materials often utilized in composite materials include glass, carbon fiber, and Kevlar.
Kevlar is a high-strength, high-modulus aromatic polyamide fiber.
Carbon fiber is a strength and light-weight material of carbon content exceeding 90% obtained through pyrolysis.
Applications of composites encompass military, aerospace, and construction sectors.

Conducting Polymers

Conducting polymers are organic polymers with delocalized pi-electron systems exhibiting electrical conductivity approaching that of metals.
Polyacetylene is synthesized by reacting acetylene over a Ziegler-Natta catalyst.
The conductive properties in these polymers can be enhanced through doping (oxidative or reductive).
Examples include polyacetylene, polypyrrole, and polyaniline.

Biodegradable Polymers

Biodegradable polymers undergo hydrolysis or enzymatic degradation, forming soluble products.
Polyglycolide (PGA) is a biodegradable polymer produced through ring-opening polymerization of glycolide.
Biodegradable polymers have applications in controlled drug delivery, tissue engineering, and temporary implants, due to their biocompatibility.

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Description

This quiz explores the fundamental concepts of polymers and their engineering applications. Topics include molecular weight, the polydispersity index, and how properties like glass transition temperature and intermolecular forces affect polymer behavior. Test your knowledge of essential polymer science principles!