MATERIALS AND AGES

Adapted from “Understanding Materials Science” by Rolf. E. Hummel

Polymeric MaterialsAdapted from “Understanding Materials Science” by Rolf. E. Hummel

FibersWool (2 million years)Hemp (First cultivated plant, 6500 years)Flax (5400 years - Eygypt)Cotton (5000 years - India)Silk (5000 -4500 years – China and Japan) Artificial Silk (1880’s – regenerated cellulose (a complex carbohydrate) fibers later known as Viscose or Rayon)

Rubber Mayan Culture Brought to Europe in 1496 The “milk” (Latex) used for water proofing in 1615. Rubber items such as air mattresses, potable bath tubs and “mackintoshes” in 1800’s. Charles Goodyear in 1830’s discovered ‘Vulcanization” – treating with sulfur and curing rubber to make it durable and pliable at low temperatures.

Wood, Leather, Cork, Sponges, etc.

Polymeric MaterialsAdapted from “Understanding Materials Science” by Rolf. E. Hummel

Paper Paper-making: China, A. D. 105

Plastics Schönbein (Germany, 1846): Nitrocellulose or cellulose nitrate – a Thermoplastic material, i.e. it will become pliable with heating.

L. H. Baekeland (Amero-Belgian, 1906): Bakelite – the first fully synthetic organic polymer which is a Thermoset plastic, i.e. it remains hard at elevated temperatures.

Goodyear (USA, 1842): Vulcanized rubber – an Elastomer.

Polymeric Materials – Chapter 14

Hydrocarbons: Many organic materials are made of hydrogen and carbon atoms.

Mol

ecul

ar w

eigh

t in

crea

ses

Isomerism:

For example:

Butane

Isobutane

C C

H H

HHEthylene

“mono-mer”

+R.

An “initiator”The dot symbolizes an unpaired electronKnown as a “free radical”

For example: H – O – O – H + Heat 2 HO.

CC.

H H

HH

R + C C

H H

HH

C C

H H

HH

R CC.

H H

HH

+ C C

H H

HH

……..

Polyethylene- a macromolecule

poly-mer

Polymer MoleculesPolymers are gigantic molecules (macromolecules) that are composed of repetition of the structural entity “mer”.

Molecule chain

n = Degree of polymerization

Weight of polymer chainWeight of a “mer”

=

Common Polymer Molecules

C C C C C CHHHHHH

HHHHHH

Polyethylene (PE)

mer

ClCl Cl

C C C C C CHHH

HHHHHH

Polyvinyl chloride (PVC)

mer

Polypropylene (PP)

CH3

C C C C C CHHH

HHHHHH

CH3 CH3

mer

Trash bags, Milk jars, Toys,Packaging films and containers

Pipes, Bottles, Toys,Car mats and seats

Containers with internal hinges, fibers,Microwave containers

Low Cost Polymers

Common Polymer Molecules

= aromatic ring

Polystyrene (PS)Foamed insulations, cups and other containers

PolycarbonatesHigh-impact windows, Impact automobile parts, small household appliances

PolyesterSoda bottles, Film for cassette and videos,

Automobile trims, Fibers for carpets and clothes

Polymer Chains

Polymers consist of chains of various sizes!

Average Molecular Weight

See Example 14.1 in your book!

smaller Mw larger Mw

Number Average: Mn = (Mi)(xi), Mi = mean molecular weight of the size range “i”, xi = fraction of the chains within the size range “i”.nn = Degree of polymerization = Mn / mExperimentally the Mn is calculated by knowing the total weight of a polymer (Mtotal) in a solution and measuruing the number of chain ends (nend): Mn = 2Mtotal / nend

The size distribution is evaluated by Size Exclusion Chromotography (SEC)

Weight Average:MW = (Mi)(wi), wi = weight fraction of the chains within the range “i”.nw = Degree of polymerization = Mw / m

Molecular Structure of Polymers

Increasing Strength

Polymer molecules are three dimensional!

Branched Cross-Linked NetworkLinear

secondarybonding