Test 2

Polyethylene and Poly Propylene ( in the melt) Will: - form hydrogen bonds with one another - interact strongly due to polar forces - Only interact weakly through secondary inter-molecular forces

only interact weakly through secondary inter-molecular forces

Which one of the following are characteristics of thermosetting polymers: - Heavily branched cross - linked polymer - Linear slightly branched long chain molecules - Become infusible on molding so cannot be reused - Soften on heating and harden on cooling, can be reused

- Heavily branched cross-linked polymer - Become infusible on molding so cannot be reused

Which one of the following factors affects the strength of a thermoplastic polymer: - molecular weight - Crystallinity - Polar atom - All of the above

All of the above

Kevlar is commercial name for: - Glass fibers - Aramid fibers - Carbon Fibers=

Aramid Fibers

Fibers made up of aromatic polyamide are known as

Aramid fibers of Kevlar

Describe how compressive stresses are introduced in pre-tensioned prestressed concrete?

Compressive stresses are introduced in pre-tensioned prestressed concrete by first stretching the tendon and then pouring concrete on the tendon

The number of anions surrounding the central cation in an ionic solid is known as

Coordination number

the total number of neighbours of a central atom in a molecule or ion.

Coordination number

A combination of 2 or more polymers is known as

Copolymer

High density polyethylene cooled slowly from 160 C to room temperature: - still amorphous - Crystallizes - a mixture where some regions are rubbery and some region are glassy

Crystallizes

What thermal processes occurs during ceramic processing. Glass generally melts before ceramic. How does the addition of glass affect the thermal processing of ceramics.

Drying, sintering and vitrification are some of the thermal processes which occur during ceramic processing. Glass is liquify and fills the pores, and forms a solid in the pores. It also makes the absorption of water lower as the glassy bond increases

Which ones of the following descriptions would not be applicable to ceramics: - mixed ionic and covalent bonding - Brittle - Hard - Ductile - Structure comprising metal cations with non-metallic anions

Ductile

These polymers, primarily consist of coil - like polymer chains - Thermoplastics - Thermoset - Elastomers - All polymers

Elastomers

Addition of a plastic fiber will decrease....

False

Since ceramics are non-metallic in nature, they are covalently bonded only

False

Strength of a thermoplastic polymer can be increased by removal of a highly polar atom from the main carbon chain

False

The melting point of a polyester (thermosetting polymer) is 200 C.

False

Wooden block posses excellent strength in the direction perpendicular to the cellulose fibrils

False

Cooling a non-crystallizable ( amorphous) polymer liquid below TG results in the formation of a: - Ordered solid - Glass - Less Viscous material - Opaque material

Glass

Type of safety glass processed by thermal or chemical treatment that increase the strength of the glass

Glass tempering

What is a tempered glass? Describe briefly how is it produced, and how a tempered glass considered stronger than annealed glass. Give applications

Glass that is heated to near surface softening point and rapidly air cooled. The surface cools first while the interior is still warm. When the interior cool and contracts, the surfaces are rigid, and so tensile stresses are created in the interior of the glass and compressive stresses on the surface. It is stronger because the applied tensile stress must surpass the compressive stresses on the surface before a fracture occurs. Some Applications are in auto side windows and safety glass for doors

One of characteristic property of thermoplastic polymeric materials: - High temperature stability - High Mechanical strength - High Elongation - Low hardness

High Elongation

If a tennis racket is made up of wood. Would you orient the woods fiber direction parallel to the axis of the shaft of the the racket or perpendicular to it? Explain with sketch

I would orient the woods fiber direction parallel to the axis of the shaft. In the longitudinal direction, the strength of the wood is due to the strong covalent bonds of the cellulose microfibrils that are oriented mainly longitudinally.

Graphite cannot be classified as: - Conducting solid - Network solid - Covalent solid - Ionic Solid

Ionic Solid

The Word Polymer meant for a material made from: - Single monomer - Two Monomers - Multiple Monomers

Multiple monomers

Describe how the addition of sodium oxide to a regular glass will affect the silica glass network structure, and why are they added to silica glass?

NaO2 is added to glass, and the oxide breaks the glass network. The oxide once added to glass increases the workability. It is added because it decreases the melting point of which silica melts.

__________are the oxides that break up the glass network and improve glass processability

Network modifers

_______ and _________ would be 2 examples of polymers

Nylon and Polyethylene

Which one of the following statements are correct about ceramics: - All of the above - Only 1 - 1 and 3 - Only 3

Only 3

A simple molecular compound that can be covalently bonded together to form long molecular chains

Polymers

A polymer engineer wants to use low density polyethylene. Which one of the following property is not related with low - density polyethylene. - Tough - Hard - Poor conductor of electricity - Highly branched structure

Poor conductor of electricity

Atactic Polystyrene (Tg = -160 C) quenched from 120 C to room temperature: - rubbery temperature - Crystallizes - Is a glassy material

Rubbery Material

a process of compacting and forming a solid mass of material by heat or pressure below the melting point

Sintering

Elastic Deformation in polymers is due to: - Slight adjust of molecular chains - Slippage of molecular chains - Straightening of molecular chains - Severe deformation of covalent Bonds

Slight adjust of molecular chains

Molecules that have the same chemical composition but different structural arrangements

Stereoisomers

In selecting a material for the windshield of automobiles, what types of glass would you use? Purpose a process that would keep glass shards from dispersing if the glass fractures.

Tempered glass, use a layer of laminate sandwiched between two layers of glass. Laminate gives windshield their extra strength to help maintain structural integrity and it allows the glass to break into small pieces

What is the difference between high density polyethylene and low density polyethylene? How does the structure account for different behavior and nature, hence the use a polymer?

The high density polyethylene is more rigid, has a good impact strength and stress crack resistance and chemical resistance. Low density polyethylene is flexible, has high impact strength, good water vapor and alcohol barrier properties

Why are the layers of graphite able to slide past each other easily?

The layers slide over each other because the bonding between layers is weak which makes graphite slippery

Consider two transitions from the solid to the liquid or rubbery state shown below on a plot of specific volume vs temperature: - The transition X is a Tg while transition Y is a crystalline melting point - Y is the Tg while X is the Tm - X and Y are melting points, but X is the Tm of a semi-crystalline material and Y is the Tm of an almost perfect crystal

The transition X is a Tg while transition Y is a crystalline melting point

In general, strongest polymer group is: - Thermoplastics - Thermoset - Elastomers - All Polymers

Thermoset

The glass transition temperature of a polymer can be change using a plasticizer

True

to change or make into glass or a glass structure through heat fusion

Vitrification

ABABABABAB Is an example of____________ copolymer

alternating

The role of a plasticizer is: - increase the molecular weight of the polymer - decrease the melting point of the polymer - increase the glass transition temperature - decrease the brittle - ductile transition temperature

decrease the brittle-ductile transition temperature