CH 15 - Characteristics, Applications & Processing of Polymers Flashcards Preview

MSE 104 > CH 15 - Characteristics, Applications & Processing of Polymers > Flashcards

Flashcards in CH 15 - Characteristics, Applications & Processing of Polymers Deck (26):
1

How does fracture strength & deformation strains of polymers compare to that of metals?

-fracture strength of polymers roughly 10% of those for metals
-deformation strains for polymers > 1000%
-deformation strains for most metals

2

What is drawing?

-stretches the polymer prior to use
-aligns chains in the stretching direction

3

What are the results of drawing?

-increases the elastic modulus in the stretching direction
-increases the tensile strength in the stretching direction
-decreases ductility

4

What is the effect of annealing after drawing?

-decreases chain alignment
-reverses effects of drawing (reduces E and TS, enhances %EL)

5

What is a thermoplastic?

-little crosslinking
-ductile
-soften with heating
EX: polyethylene, polypropylene, polycarbonate, polystyrene

6

What is a thermoset?

-significant crosslinking
-hard & brittle
-don't soften w/heating
EX: vulcanized rubber, epoxies, polyester resin, phenolic resin

7

What is the influence of temp on thermoplastics?

decreasing temp:
-increases E
-increases TS
-decreases %EL

8

What is the influence of strain rate on thermoplastics?

increasing strain rate:
-increases E
-increases TS
-decreases %EL

9

What things increase chain stiffness?

presence of:
-bulky sidegroups
-polar groups or sidegroups
-chain double bonds and aromatic chain groups

10

What is the stress relaxation test?

-strain in tension to e-knot and hold
-observe decrease in stress with time

11

What is craze?

formation prior to cracking

12

What happens during craze?

-plastic deformation of spherulites
-formation of microvoids and fibrillar bridges

13

What are the two types of polymer formation?

-addition (chain) polymerization
-condensation (step) polymerization

14

What are the three steps of addition/chain polymerization?

(1) initiation
(2) propagation
(3) termination

15

What are types of polymer additives?

fillers, plasticizers, stabilizers, lubricants, colorants, flame retardants

16

What is the benefit of adding fillers to a polymer?

-improve tensile strength & abrasion resistance, toughness, decrease cost
-EX: carbon black, silica gel, wood flour, glass, limestone, talc

17

What is the benefit of adding plasticizers to polymers?

-added to reduce the glass transition temp below room temp
-presence of plasticizer transforms brittle polymer to a ductile one

18

What are examples of stabilizers?

antioxidants, UV protectants

19

How are thermoplastics processed?

-can be reversibly cooled and reheated (recycled)
-heat until soft, shape as desired, then cool

20

How are thermosets processed?

-when heated forms a molecular network
-degrades (doesn't melt) when heated
-prepolymer molded into desired shape, then chemical reaction occurs

21

What are the characteristics of fibers?

-high tensile strengths
-high degrees of crystallinity
-structures containing polar groups
-formed by spinning

22

What is spinning?

-extrude polymer through a spinneret
-spun fibers are drawn under tension
-leads to highly aligned chains

23

What are the types of polymers?

fibers, coatings, adhesives, films, foams

24

What is a polymer coating?

-thin polymer films applied to surfaces
-protects from corrosion/degradation
-decorative (improves appearance)
-can provide electrical insulation

25

How are films produced?

produced by blown film extrusion

26

How are foams produced?

gas bubbles incorporated into plastics