Lab 4. Tensile Test Plastic

Question 1

polymer is

Answer 1

an organic substance composed of molecules with large molecular mass composed of repeating structural units……

Question 2

what is a polymer connected by

Answer 2

covalent bonds… may contain hundreds or thousands of repeat units

Question 3

what is small definition of polymer.

Answer 3

many chains.

Question 4

name two forces that hold polymer chains together

Answer 4

covalent molecules and van-der-waals

Question 5

Difference between monomer and repeat units

Answer 5

A monomer is a single molecule, a polymer is a long chain of monomers, repeating units are a simplified method of drawing a polymer, whose chain may extend for a long time.

Show example

Question 6

name some natural polymers

Answer 6

proteins, enzymes, starches, and cellulose

Question 7

where are natural polymers important

Answer 7

biological and physiological processes in plants and animals

Question 8

plastics

Answer 8

are materials that have some structural rigidity under load, and are used for general-purpose applications

Question 9

elastomers-

Answer 9

polymer which contributes to rubber, fibers, adhesives, films and foams

Question 10

name some plastics

Answer 10

polyethylene, polypropylene, polystyrene, fluorocarbons, epoxies,

Question 11

what are the two types of polymers/plastics

Answer 11

thermoplastics and thermosetting

Question 12

qualities of thermoplastics

Answer 12

high molecular weight, soften or liquid when heated, harden when cool, process is reversible regardless of repeated cycles

Question 13

qualities of thermosettings

Answer 13

(polymers that cure, through the addition of energy/heat to a stronger forms by a cross-linkage process)

harden or solidify when heated

irreversible process (thermoset materials cannot be easily melted and re-shaped after i is cured

Question 14

crosslinkage of thermoplastic

Answer 14

little to none

Question 15

crosslinkage of thermoset

Answer 15

alot network

Question 16

what are factors the influence properties of polymers/plastics

Answer 16

Molecular weight
degree of polymerization
molecular structure

Question 17

linear polymers

Answer 17

van der waals bonding between chains.

Question 18

branched polymers

Answer 18

chain packing efficiency is reduced compared to linear polymers lower density

Question 19

cross-linked polymers

Answer 19

chains are connected by covalent bonds. often achieved by adding atoms or molecules that form covalen links between chains. many rubbers have this strucuture

Question 20

network polymers

Answer 20

3D networks made from trifunctional mers.

Question 21

give in the direction of increasing strength, the type of crosslinkage

Answer 21

linear, branched, crosslinked, network

Question 22

how are amorphous plastics bonds

Answer 22

they have no strong bonds between molecular chains

Question 23

how are bondings with crystalline plastics

Answer 23

they have strong bonds between molecular chains

Question 24

an amorphous/semi crystalline plastic will exhibit….

Answer 24

a glass transition temperature TvG

Question 25

below glass transition temperature molecules have….

Answer 25

little relative mobility

Question 26

above glass transition temperature molecules have….

Answer 26

great mobility

Question 27

what is the glass transition temperature usually around

Answer 27

.5-.8 of the melting temperature….

Question 28

glass transition temperature-

Answer 28

often define the maximum service temperature of plastics and control very important processing parameters

Question 29

like metals,….

Answer 29

plastics yeild at the end of the elastic region

plastics also start necking

Question 30

what happens during necking?

Answer 30

the molecule chains stretch from agglomerated polymers to aligned polymers

Question 31

plastics can endure….

Answer 31

significant strain after the onset of necking

Question 32

brittle deformation

Answer 32

does not cause to much molecular stretches and plastic region during the failure. it is usually seen in thermosetting and glassy polymers

Question 33

plastic deformation

Answer 33

is defined by the interaction between crystalline and amorphous regions, and it is partially reversible

Question 34

crazes

Answer 34

are regions of very localized plastic deformation, which lead to the the formation of small and interconnected microvoids

Question 35

as the tensile stress enlarges a craze, the stress introduced…

Answer 35

will be distributed over an increasing volume which means that force peaks are avoided.

Question 36

.what are some advantages of plastics

Answer 36

good electrical insulation
good thermal insulation

high specific strength..strength/weight per unit volume

can be recycled

low density
application in composite materials

Question 37

disadvantages of plastics

Answer 37

low toughness
less resistance to abrasion

can produce hazaradous fumes when burned

in general, cannot be used in high temperature applications

although special utlra high temperature resistant plastic is available.