Module 6 None-Metallic Materials Objective Three

Question 1

Thermoplastic polymers

Answer 1

formed through chain growth polymerization
covalent bonds along length of chain
adjacent bonds are weak
low melting range- soft and deformable-molecules slide past each other

Question 2

Glass transition temperatures (Tg)

Answer 2

low temp threshold where polymers exhibit a drop in impact toughness
above Tg polymer chains can slide past each other
below Tg polymers are more brittle, slide is more difficult

Question 3

Copolymers

Answer 3

mixtures of different monomers within long chains

Question 4

Polyethylene PE

Answer 4

uses: clear sheets, bottles, tubing, cups, packaging, electrical insulation

Question 5

Polyvinyl Chloride PVC

Answer 5

uses: floors, fabrics, films, hoses, wire coating

Question 6

Polypropylene PP

Answer 6

uses: sheet, pipe, coverings

same uses as PE except its less dense

Question 7

Polstyrene

Answer 7

uses: containers, styrofoam, molded products, packaging

Question 8

Acrylonitrile Butadiene Styrene ABS

Answer 8

uses: pipe, luggage, telephones

Question 9

Acrylics (Polymethylmethacrylate, Lucite, Plexiglass)

Answer 9

uses: windows, transparent sheet, aircraft windows

Question 10

Polycarbonates (Lexan, Makrolon)

Answer 10

uses: DVD, laminated bullet proof windows, eyeglasses

Question 11

Increasing Chain Lengths

Answer 11

significantly changes the properties of a polymer chain

greater number of carbon atoms in the chain, the more rigid the chain

Question 12

Degree of polymerization

Answer 12

the larger (n) number of carbon atoms in the chain
the greater the n value, the greater the strength/ stiffness and melting point of the polymer

Question 13

Branching

Answer 13

adding side chains during polymerization

increases strength and stiffness as individual molecules become intertwined and bonded

Question 14

Crosslinking

Answer 14

enhances polymer strength by linking chains with strong covalent bonds
ex: vulcanization

Question 15

PE crosslinking: Peroxide

Answer 15

peroxides are heat-activated chemicals that generate free radicals for crosslinking (Engel Process)

Question 16

PE crosslinking: Moisture-cured Vinyl Silane

Answer 16

a reactive silane molecule is grafted to the backbone of the polyethylene, the silane becomes reactive with the addition of water, and crosslinking occurs across silicon and oxygen molecules to form the bridge

Question 17

PE crosslinking: Beta Irradiation

Answer 17

PE is subjected to high energy electrons, knocks off individual hydrogen atoms, and underlying carbon bonds with neighbouring chain (PEX-C)

Question 18

PE Crosslinking: Chain Stiffening

Answer 18

similar to branching, adding large pendent groups like benzene to the polymer backbone, which prevents flexing and increases stiffness

Question 19

PE Crosslinking: Polar Groups

Answer 19

increase the electrostatic charge between chains, by adding electronegative side groups (things like Cl, which forms vinyl)

Question 20

PE Crosslinking: Add fillers

Answer 20

creates a composite, by adding wood fibers, glass fiber, etc, increases hardness

Question 21

PE Crosslinking: Increase Crystallinity

Answer 21

stretches the polymer, which lines the molecules in the stretching direction, increases strength along the stretch, but can split easily along the other directions

Question 22

Polyamides

Answer 22

occurs when an acid reacts with an amine (condensation copolymer)
ex: Nylon, Kevlar

Question 23

PTFE (Polytetrafluoroethylene or Teflon)

Answer 23

Non-reactive due to the replacement of hydrogen atoms by fluorine atoms in a ethylene molecule

Question 24

Thermosetting Polymers

Answer 24

formed by step growth polymerization. All the bonds between monomers are primary covalent bonds in a network configuration. They become hard rigid and brittle when heated, don’t soften

Question 25

Phenolics:

Answer 25

uses: electrical equipment, metallurgical mounting resin

Question 26

Polyurethane

Answer 26

uses: sheet, tubing, foam, elastomers, fibres

Question 27

Amino resins

Answer 27

uses: dishes, laminates

Question 28

Polyesters

Answer 28

uses: fibreglass composite, coating

Question 29

Epoxies

Answer 29

uses: adhesives, fibreglass composites, coatings

Question 30

Cyanoacrylate

Answer 30

uses: Adhesives (Super glue)

Question 31

Elastomers (Rubber)

Answer 31

spring-like linear molecules, usually thermoplastic polymers that have crosslinks between linear portions, the amount of crosslinking controls rigidity

Question 32

Dienes

Answer 32

monomers with two double bonds

Question 33

Vulcanization

Answer 33

mixing sulfur (1-5%) with the elastomer and then heating it within a mold. The sulfur breaks a few of the double bonds, causing bridges between chains

Question 34

Isoprene

Answer 34

the simplest diene that can be used to make an elastomer

2-methylbuta-1, 3-diene

Question 35

Natural rubber

Answer 35

basically isoprene with naturally occurring impurities

Question 36

Latex

Answer 36

the milky emulsion from rubber trees

Question 37

Butadiene Styrene (SBR)

Answer 37

copolymer of butadiene and styrene

Question 38

Nitrile Rubber (NBR)

Answer 38

a copolymer of butadiene and acrylonitrile developed for resistance to petroleum base oils and hydrocarbon fuels
more acrylonitrile (18-48%) higher resistance to oils

Question 39

Polychloroprene (Neoprene)

Answer 39

synthetic rubbers that are produced by polymerization of chloroprene
The chlorine makes it very chemically inert

Question 40

FKM fluorocarbon Elastomer

Answer 40

copolymers of hexafluoropropylene (HFP) vinylidene fluoride (VDF/VF2) and sometimes tetrafluoroethylene (TFE)
Fluorine replaces roughly 70% of hydrogen, which gives good chemical resistance, low compression set, high operating temp, and low strength

Question 41

Silicones

Answer 41

inorganic polymers that consist of a silicon and oxygen backbone
Thermally stabile, high melting/boiling points, low reactivity