intro to polymers

2/16/2004 1

Introduction to PolymersIntroduction to Polymers

Seth Bates and A. LopezSan Jose State University

12/22/2003 Lecture 1 – Intro to Polymers Tech 140 2

What is a Polymer?What is a Polymer?� Strictly speaking:

– A substance composed of molecules which have long sequences of one or more species of atoms or groups of atoms linked to each other by primary bonds. (Introduction to Polymers: Second Edition, by Young and Lovell. Page 3)

� Informally speaking:– Long chains of carbon based molecules linked by

covalent bonds (imagine a bead necklace several hundred feet long)


General Classes of PolymersGeneral Classes of Polymers� Thermoplastics

– Can be repeatedly melted upon the application of heat, considered recyclable because of this

� Elastomers– Rubbery materials that can stretch many times their original length;

they do not melt upon application of heat, they will degrade if heated to high enough temperature

� Thermosets– Generally rigid materials that can withstand higher temperatures

than elastomers, they do not melt and will degrade if heated to high enough temperature

� As with all classifications, there are sometimes exceptions to the rules when describing the behavior of polymers


Poly(tetrafluoroethylene) and Mica Composite Poly(tetrafluoroethylene) and Mica Composite 150X Magnification150X Magnification


Historical SummaryHistorical Summary� The search for a material replacement of horn

sparked the modern plastics industry– Horn was not of uniform quality – Horn was difficult to work with and had very limited mold-

ability, but it had unique properties and esthetic appeal� By the 1800’s Horn was being replaced by other

natural polymers– Shellac; insects

� found use as a coating for furniture and molded into boxes, buttons, combs and electrical insulators and later into phonograph records

– Gutta percha: palaquium tree� Found largest use as an electrical insulator (first transatlantic

cable insulated with gutta percha) and billiard balls


Historical Summary Historical Summary (p1)(p1)� Some natural polymers became useful only when

modified chemically– Rubber was one of the earliest and most important

discoveries in the polymer industry� Charles Goodyear discovered vulcanization of natural rubber

– Celluloid was another early modified polymer; the first polymer truly capable of imitating the esthetics of horn and shell

� Celluloid was clear and could be colored to imitate the patternsof horn and shell

� One of its unique applications was in the film industry, where it was used as the substrate for the first motion picture film


Historical Summary Historical Summary (p2)(p2)

� The physical properties and quality of modified natural polymers were still a barrier for many applications outside of fashion accessories and knickknacks– Bakelite, a product of phenol and formaldehyde, was

introduced in 1909; it was the first fully synthetic thermoset polymer

– With the introduction of phenolic polymers started to be used in structural, electrical and chemical applications not previously considered for polymers


Serendipitous DiscoveriesSerendipitous Discoveries

� History – Development by Accident– Poly(ethylene) – Discovered in 1933 by Fawcett and

Gibson during a botched experiment – Teflon® was invented accidentally by Dr. Roy Plunkett

at Dupont in 1938 when experimenting with Freon® coolants under pressure.

– Silly Putty – Trying to invent a substitute for natural rubber, James Wright combines silicon oil with boric acid, instead of substitute for rubber he gets a fun play toy


Major Consumer PlasticsMajor Consumer Plastics

� The use of plastics is increasing around the world, in the U.S sales of plastics between 1984 and 1994 increased by about 5% annually.– 82% of sales were of the following resins:

LDPE HDPEPVC PPPS PUPET Phenolic


Most Common Process MethodsMost Common Process Methods� LDPE

– Film: bags and shipping wrap

� HDPE– Blow molding and extrusion: containers, tubing,

electrical insulation

� PVC– Extrusion: pipe, shaped profiles, patent leather

� PP– Extrusion and injection molding: fibers, sheet, molded

parts


RecyclingRecycling

� This has become a hot environmental topic for many reasons– Most polymers are not biodegradable– Most polymers are made from petroleum and

other non renewable resources– Polymer processing requires many

environmentally harmful solvents� See the introduction and article in Science Magazine

Vol. 297 No. 5582, pages 798 and 803 respectively, on “Green” chemistry


Recycling Consumer PlasticsRecycling Consumer Plastics

� Thermoplastic recycling process:


Recycling of ThermosetsRecycling of Thermosets� While most thermosets are not recycled

there are methods of reusing some of these polymers– Many thermosets can be chopped and used as

filler– Powdered phenolic can be added to the raw

material stream– Depolymerization can be used in some cases to

break down thermosets into their component parts for reuse


Why Can Thermoplastics be Why Can Thermoplastics be RemeltedRemelted??

� Chemical bonding in thermoplastics polymers allows this…– The “backbone” of polymers is chemically bonded

through covalent bonds– Separate polymer chains (macromolecules) in the bulk

are attracted to each other by Van der Waal’s and/or dipole forces in addition to entanglement

– Heating thermoplastics inputs thermal energy into the material causing excitation of the molecules and subsequent motion, allowing macromolecules to slip past each other (melt)


Why Can Thermosets NOT be Why Can Thermosets NOT be RemeltedRemelted??

� Chemical bonding in Thermosets– As in thermoplastics, the backbone of most thermosets

is covalently bonded– In contrast to thermoplastics, there are no individual

macromolecules� Thermosets consist of a continuous crosslinked network of

covalently bonded molecules

– Thermosets are “locked” into their molecular structure by strong covalent bonding, which does not allow polymer chains to move freely with the application of heat


Disposal of PlasticsDisposal of Plastics

� Dumping plastics in a land fill takes up a tremendous amount of space; most plastics do not degrade readily

� Incineration of plastics has an especially controversial issue since the 1970’s when Federal clean air regulations were put in place– PVC in particular has been a concern for incineration

because it releases dioxins a suspected carcinogen� Biodegradable plastics have started to be used that

break down in the presence of sunlight, water, and microorganisms


End ofIntroduction to Polymers

For more information, check the polymer and composites links at the tech 140 web page

intro to polymers

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