POLYMERS by fjzhangweiyun

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									    POLYMERS
         “Plastics”



        Third Generation
   CAPT Science Preparation for
Strand II: Chemical Structures and
            Properties
         What is a Polymer?
Any of numerous natural and synthetic
 compounds of usually high molecular
 weight consisting of up to millions of
 repeated linked units (monomers), each a
 relatively light and simple molecule.
              Polymerization

   Polymerization is the process of combining
    many small molecules known as
    monomers into a covalently bonded chain.
            Natural Polymers
             (Biopolymers)

Examples:
   Cellulose
   Shellac
   Amber
   Proteins
   Nucleic Acids
            Synthetic Polymers

Examples:
   Nylon
   Neoprene
   PVC
   Polystyrene
   Silicone
   Silly Putty ®
                            Some Common Addition Polymers
Name(s)                         Formula                  Monomer               Properties                      Uses

Polyethylene                                             ethylene
                                –(CH2-CH2)n–                                   soft, waxy solid                film wrap, plastic bags
low density (LDPE)                                       CH2=CH2

Polyethylene                                             ethylene                                              electrical insulation
                                –(CH2-CH2)n–                                   rigid, translucent solid
high density (HDPE)                                      CH2=CH2                                               bottles, toys

Polypropylene                                            propylene             atactic: soft, elastic solid    similar to LDPE
                                –[CH2-CH(CH3)]n–
(PP) different grades                                    CH2=CHCH3             isotactic: hard, strong solid   carpet, upholstery

Poly(vinyl chloride)                                     vinyl chloride
                                –(CH2-CHCl)n–                                  strong rigid solid              pipes, siding, flooring
(PVC)                                                    CH2=CHCl

Poly(vinylidene chloride)                                vinylidene chloride
                                –(CH2-CCl2)n–                                  dense, high-melting solid       seat covers, films
(Saran A)                                                CH2=CCl2

Polystyrene                                              styrene               hard, rigid, clear solid        toys, cabinets
                                –[CH2-CH(C6H5)]n–
(PS)                                                     CH2=CHC6H5            soluble in organic solvents     packaging (foamed)

Polyacrylonitrile                                        acrylonitrile         high-melting solid              rugs, blankets
                                –(CH2-CHCN)n–
(PAN, Orlon, Acrilan)                                    CH2=CHCN              soluble in organic solvents     clothing

Polytetrafluoroethylene                                  tetrafluoroethylene                                   non-stick surfaces
                                –(CF2-CF2)n–                                   resistant, smooth solid
(PTFE, Teflon)                                           CF2=CF2                                               electrical insulation

Poly(methyl methacrylate)                                methyl methacrylate                                   lighting covers, signs
                                –[CH2-C(CH3)CO2CH3]n–                          hard, transparent solid
(PMMA, Lucite, Plexiglas)                                CH2=C(CH3)CO2CH3                                      skylights

Poly(vinyl acetate)                                      vinyl acetate
                                –(CH2-CHOCOCH3)n–                              soft, sticky solid              latex paints, adhesives
(PVAc)                                                   CH2=CHOCOCH3

cis-Polyisoprene                                         isoprene                                              requires vulcanization
                                –[CH2-CH=C(CH3)-CH2]n–                         soft, sticky solid
natural rubber                                           CH2=CH-C(CH3)=CH2                                     for practical use

Polychloroprene (cis + trans)                            chloroprene                                           synthetic rubber
                                –[CH2-CH=CCl-CH2]n–                            tough, rubbery solid
(Neoprene)                                               CH2=CH-CCl=CH2                                        oil resistant
              Resin Identification Code
Symbol   Abbreviation Polymer Type

         PET or PETE   Polyethylene Terephthalate

         HDPE          High Density Polyethylene

         PVC           Polyvinyl Chloride or Vinyl

         LDPE          Low Density Polyethylene

         PP            Polypropylene

         PS            Polystyrene

         Other          Polymers or blends of
                       polymers that do not fall into
                       the other 6 classifications.
        Properties of Polymers

   Polymers can be very resistant to
    chemicals.

   Polymers can be both thermal and
    electrical insulators.

   Generally, polymers are very light
    in weight with significant degrees
    of strength.
      Properties of Polymers cont.
   Polymers can be processed in various
    ways.

   Polymers are materials with a seemingly
    limitless range of characteristics and
    colors.

   Polymers are usually made of petroleum,
    but not always.

   Polymers can be used to make items that
    have no alternatives from other
    materials.
Three factors that influence the degree of
crystallinity (or “stiffness”) are:

    • Chain length


    • Chain branching


    • Interchain bonding


The importance of the first two factors is nicely
illustrated by the differences between HDPE and LDPE.
                    HDPE vs LDPE
   HDPE is composed of very long
    unbranched hydrocarbon chains. These
    pack together easily in crystalline domains
    that alternate with amorphous segments,
    and the resulting material, while relatively
    strong and stiff, retains a degree of
    flexibility.
   In contrast, LDPE is composed of smaller
    and more highly branched chains which
    do not easily adopt crystalline structures.
    This material is therefore softer, weaker,
    less dense and more easily deformed than
    HDPE. As a rule, mechanical properties
    such as ductility, tensile strength, and
    hardness rise and eventually level off with
    increasing chain length.
          Two Plastic Types
         Based on Processing
•Thermoplastic Polymers

•Thermosetting Polymers
           Thermoplastic Polymers
A Thermoplastic is a polymer in which the molecules are held
  together by weak secondary bonding forces that soften when
  exposed to heat and return to its original condition when cooled
  back down to room temperature. When a thermoplastic is
  softened by heat, it can then be shaped by extrusion, molding,
  or pressing.
Examples include milk jugs and carbonated soft drink bottles.
            Thermoset Polymers
A Thermoset is a polymer that solidifies or “sets”
  irreversibly when heated or cured. A thermoset
  polymer can’t be softened once “set”. Thermosets are
  valued for their durability and strength and are used
  extensively in automobiles and construction including
  applications such as adhesives, inks, and coatings.
The most common thermoset is the rubber truck and
  automobile tire.
           The End Life of Polymers
         Durables vs. Non-Durables
   Products with a useful life of three years
    or more are referred to as durables.
    They include appliances, furniture,
    consumer electronics, automobiles, and
    building and construction materials.


   Products with a useful life of less than
    three years are generally referred to as
    non-durables. Common applications
    include packaging, trash bags, cups,
    eating utensils, sporting and recreational
    equipment, toys, medical devices and
    disposable diapers.
       What do we do with Polymers
      when they are no longer useful?
                   Three Options
               and their consequences

1.   Disposal
     in a landfill
2.   Incinerate
3.   Recycle
        Disposal in a landfill
Polymers are fairly resistant to chemicals
 and therefore would take a very long time
 to decompose if just buried in a landfill.

In the meantime, the waste polymers take
  up a lot of space and could possibly
  decompose or react with other materials
  that might eventually result in compounds
  that could be potentially harmful to the
  environment.
                    Incinerate
The burning (combustion) of polymers produces
  harmful gases that are toxic to the environment.
Recycle - The best choice!
    Mechanical Recycling
    Feedstock Recycling

    Source Reduction
       Mechanical Recycling
Once collected, reclamation is the next step where the
 plastics are chopped into flakes, washed to remove
 contaminants and sold to end users to manufacture
 new products such as bottles, containers, clothing,
 carpet, plastic lumber, etc.
        Feedstock Recycling
Pyrolysis (heating without oxygen) and other
  chemical recycling is a special case where
  condensation polymers such as PET or nylon
  are chemically reacted to form starting
  materials.
      Source Reduction Use less!
   Redesign products and packaging that uses less polymer
    material.
   Reduce the amount the amount of polymer products that are
    purchased.
   Clean and Reuse the polymer products that have been
    purchased.
 What is the first question you are asked at
the grocery store checkout: paper or plastic?
   Paper bags can be recycled. Plastic bags are being
    recycled in many places, with about 50% of
    supermarkets now having recycling programs for
    plastic bags.
   However, a stack of 1,000 paper bags is 46 inches
    high and weigh 140 pounds. A stack of 1,000 plastic
    bags is only 4 inches tall and weighs 16 pounds. That
    is a 124 pound savings.





When you translate these weight and volume
 differences into transportation efficiencies, it
 takes seven trucks to haul the same number of
 paper bags as can be hauled by only one truck
 carrying plastic ones.

								
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