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

Polymeric Materials Adapted from “Understanding Materials Science” by Rolf. E. Hummel  Fibers  Wool (2 million years)  Hemp (First cultivated plant, 6500 years)  Flax (5400 years - Eygypt)  Cotton (5000 years - India)  Silk ( 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  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 Materials Adapted 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. Molecular weight increases Isomerism: For example: Butane Isobutane

CC HH HH Ethylene “mono-mer” + R.R. An “initiator” The dot symbolizes an unpaired electron Known as a “free radical” For example: H – O – O – H + Heat2 HO. C C.C. HH HH R+ CC HH HH C C HH HH R C C.C. HH HH + CC HH HH …….. Polyethylene- a macromolecule poly-mer Polymer Molecules Polymers are gigantic molecules (macromolecules) that are composed of repetition of the structural entity “mer”. Molecule chain n = Degree of polymerization Weight of polymer chain Weight of a “mer” =

Common Polymer Molecules CCCCCC HHHHHH HHHHHH Polyethylene (PE) mer Cl CCCCCC HHH HHHHHH Polyvinyl chloride (PVC) mer Polypropylene (PP) CH 3 CCCCCC HHH HHHHHH 3 3 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 Polycarbonates High-impact windows, Impact automobile parts, small household appliances Polyester Soda 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! Number Average: M n =  (M i )(x i ), M i = mean molecular weight of the size range “i”, x i = fraction of the chains within the size range “i”. n n = Degree of polymerization = M n / m Experimentally the M n is calculated by knowing the total weight of a polymer (M total ) in a solution and measuruing the number of chain ends (n end ): M n = 2M total / n end The size distribution is evaluated by Size Exclusion Chromotography (SEC) Weight Average: M W =  (M i )(w i ), w i = weight fraction of the chains within the range “i”. n w = Degree of polymerization = M w / m

Molecular Structure of Polymers Increasing Strength Polymer molecules are three dimensional!