Polymers

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• Polymers
• Substances containing a large number of
  structural units joined by the same type of
  linkage.
• These substances often form into a chain-like
  structure.
• Polymers in the natural world have been around
  since the beginning of time.
• Starch, cellulose, and rubber - possess
  polymeric properties.
• Man-made polymers studied since 1832.
• Today, the polymer industry has grown to be
  larger than the aluminum, copper and steel
  industries combined.

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• WHAT ARE POLYMERS?
• Tiny molecules strung in long repeating chains
  form polymers.
• Why should you care?
• Our body is made of them. DNA, the genetic
  blueprint that defines people and other living
  things, is a polymer.
• The proteins and starches in the foods we eat,
  the tires on our bikes and cars, the wheels on
  skateboards and skates.
• Surrounded by polymers every day, everywhere we
  go.
• Another great reason to learn about polymers.
• Understanding their chemistry enables in wisely
  using them.
• Once familiar with the varieties of polymers that
  people make, such as plastics, we can recycle
  many of them and use them again.
• Thats good for the environment.

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• Polymers at Home

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What makes all these different? Each connects
with a different kind of human-made polymer that
we encounter in our homes every day.
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• Water-resistant paints and varnishes derive from
  a family of synthetic polymers called acrylics.
  You can also paint yourself warm with acrylics
  Spun acrylics find their way into fiberfill
  jackets and bedtime comforters.

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• In 1907 Leo Baekeland patented a revolutionary
  new material.
• Could mold it at high temperatures and it would
  retain its shape when cooled, could dye it with
  brilliant colors.
• Baekeland named it Bakelite after himself.
• Soon everything from telephones and radios to
  auto parts, furniture, and jewelry was being made
  from Bakelite.

• In a cover story on Leo Baekeland in 1924, Time
  magazine proclaimed that in a few years
  Bakelite will be embodied in every mechanical
  facility of modern civilization. From the time
  that a man brushes his teeth in the morning with
  a Bakelite handled brush, until the moment he
  falls back on his Bakelite bed ...all that he
  touches, sees, uses, will be made of this
  material of a thousand uses.

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• World War II pushed plastics production into
  high gear.
• Japanese submarines made it impossible for Allied
  nations such as Great Britain and the United
  States to import latex, the basis of most natural
  rubber, from Asian plantations.
• Industrial chemists rose to the challenge,
  devising economical means of producing synthetic
  rubber in huge volumes.
• They also created new polymers for use in
  airplanes, ships, and tanks under fire.
• Silk without silkworms? Practically. The
  plastic nylon replaced the silk in hosiery in
  1938.
• Many of the airborne troops in World War II
  floated to earth beneath nylon parachutes.
• Other synthetic fibers such as polyester made the
  fashions of the 1970s possible.

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• Natural rubber from latex, made balls that could
  bounce.
• But it became hard and brittle when it got too
  cold, a sticky mess when it got too warm.
• In 1839 Charles Goodyear discovered that latex
  heated with sulphuror vulcanizedwould remain
  elastic at a wide range of temperatures.
• Sulphur made bridges between the long chain
  polymers in rubber to keep them from sliding past
  one another or contracting into knots
• Carriages, cars, trucks, and buses have traveled
  billions of miles on tires made from vulcanized
  rubber and synthetic substitutes.

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• Polystyrene foam - made into cartons to protect
  eggs or into packing peanuts to cushion fragile
  objects for shipping.
• Insulates - as cups and coolers to keep the warm
  ones warm and the cold ones cold.
• Placed behind walls and ceilings in homes,
  polystyrene foam helps keep the weather outside
  at bay.
• Chlorofluorocarbons (CFCs), containing both
  chlorine and fluorine, were sometimes used to
  make foam products. This was found to damage the
  earths protective ozone layer-hence phased out
  their use in the creation of foam packaging and
  most other types of polystyrene foam.

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Polymers in Nature

• Everything we see in nature-
• What do all these have in common?
• They contain polymers!
• You can find different plants, animals, and
  natural objects that make or contain polymers.
• You can build a miniature world of your own.

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• Rosin
• Dead wood and pulp from pine trees contain a
  polymer called rosin, which is used to make
  varnish and soap. Violinists rub rosin on the
  horsehairs in their bows to make them slide
  smoothly across the strings. Gymnasts and
  baseball players use rosin to improve their
  grips.
• Animal Horns
• Antelope, buffalo, sheep, cattle, and rhinos all
  have horns. Unlike a deers antlers, made of
  bone, horns are made of the polymer keratin.
• Parts of ours are made of keratin too
  -ingredient in our hair and fingernails. Keratin
  in the outermost layer of our skin makes it
  waterproof like other mammals, so one doesnt get
  waterlogged the moment he dives in the pool.

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• Range of applications
• Far exceeds that of any other class of material
  available to man.
• Extend from
• adhesives, coatings, foams, and packaging
  materials to textile and industrial fibers
• composites, electronic devices, biomedical
  devices, optical devices, and precursors for many
  newly developed high-tech ceramics.

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• Applications
• Industry
• Automobile parts, windshields for fighter
  planes, pipes, tanks, packing materials,
  insulation, wood substitutes, adhesives, matrix
  for composites, and elastomers
• Agriculture and Agribusiness
• Polymeric materials -in and on soil to
  improve aeration, provide mulch, and promote
  plant growth and health.
• Medicine
• Many biomaterials, - heart valve
  replacements and blood vessels, are made of
  polymers like Dacron, Teflon and polyurethane.
• Consumer Science
• Plastic containers of all shapes and sizes
  are light weight and economically less expensive
  than the more traditional containers.
• clothing, floor coverings, garbage disposal
  bags, and packaging.
• Sports
• Playground equipment, various balls, golf
  clubs, swimming pools, and protective helmets

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• Medical Therapeutic apheresis -a treatment
  process that enables substances which cause
  disease to be safely removed from the blood while
  it is outside the body.
• A Germany-based medical technology company
  Fresenius Medical Care developed a technology
  called DALI (Direct Adsorption of Lipoproteins)
  especially for the treatment of patients with
  severe lipometabolic disorders. It enables LDL
  cholesterol, also known as bad cholesterol
  because of its influence on vascular
  calcification, to be extracted from the blood.
• -An adsorber filled with a special material
  electrostatically bonds the LDL cholesterol. For
  the housing of the adsorber system, a
  fracture-resistant plastic was required.
  Makrolon 2458 developed by Polycarbonates
  Business Unit of Bayer Material Science AG.
• This polycarbonate is sufficiently tough and
  stiff, which protects it from becoming easily
  damaged in the often hectic everyday hospital
  environment.
• Withstands the pressurized hot-steam
  sterilization of the DALI adsorber, where
  temperatures reach at least 121 C for over 20
  minutes.

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Plastics in the medical technology sector
                                                            

• Polycarbonate adsorber housings
• Robust in everyday hospital use, suitable for
  hot-steam sterilization
• The housing of the DALI adsorber system is made
  from the fracture-resistant polycarbonate
  Makrolon 2458. This withstands pressurized
  hot-steam sterilization, where temperatures reach
  at least 121 C for over 20 minutes.

In the DALI treatment, the patient's blood is
removed from an arm vein and passed through the
adsorber where the LDL cholesterol sticks to the
adsorber globules. The cleaned blood reenters the
patient's body via another arm vein
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• A further benefit of the polycarbonate is its
  high transparency which allows continuous visual
  monitoring of the blood treatment by hospital
  personnel and therefore enhances patient safety.
  Makrolon 2458 meets the requirements of the
  American standard US-Pharmacopeia, Class VI,
  relating to the biological compatibility of
  plastics. Like all medical technology products
  from Bayer MaterialScience, it also complies with
  international standard ISO 10993-1 regarding the
  biocompatibility of plastics that are in contact
  with body fluids and tissue for up to 30 days.

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• Future Trends
• Nature has used biological polymers as the
  material of choice, Mankind chose polymeric
  materials as the choice material.
• From the Stone Age, through the Bronze, Iron, and
  Steel Ages into its current age, the Age of
  Polymers.
• An age in which synthetic polymers are and will
  be the material of choice.
• Potential for exciting new applications in the
  foreseeable future.
• Areas as conduction and storage of electricity,
  heat and light, molecular based information
  storage and processing, molecular composites,
  unique separation membranes, revolutionary new
  forms of food processing and packaging, health,
  housing, and transportation.
• Polymers will play an increasingly important role
  in all aspects of our life.
• The large number of current and future
  applications of polymeric materials has created
  need for persons specifically trained to carry
  out research and development in Polymer Science
  and Engineering-
• can expect to achieve both financial reward and
  personal fulfillment.

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• Scientific Principles
• The field is so vast and the applications so
  varied
• Important to understand how polymers are made and
  used
• There are over 60,000 different plastics
  knowledge of this important field can truly
  enrich our appreciation of this wonder material.
• Companies manufacture over 30 million tonnes of
  plastics each year, spend large sums on RD, and
  more efficient recycling methods.
• Some of the scientific principles involved in the
  production and processing of these fossil fuel
  derived materials known as polymers are

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• Polymerization Reactions
• The chemical reaction in which high molecular
  mass molecules are formed from monomers is known
  as POLYMERIZATION
• Two basic types of polymerization
• chain-reaction (or addition) polymerization.
• step-reaction (or condensation) polymerization.

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1. Chain-Reaction (addition) Polymerization

• A three step process involving two chemical
  entities.
• The first, known simply as a monomer, can be
  regarded as one link in a polymer chain. It
  initially exists as simple units. In nearly all
  cases, the monomers have at least one
  carbon-carbon double bond.
• Initiation
• Propagation
• Termination

Ethylene is one example of a monomer used to
make a common polymer
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• The other chemical reactant is a catalyst.
• In chain-reaction polymerization, the catalyst
  can be a free-radical peroxide added in
  relatively low concentrations. A free-radical is
  a chemical component that contains a free
  electron that forms a covalent bond with an
  electron on another molecule. The formation of a
  free radical from an organic peroxide is
• In this chemical reaction, two free radicals
  have been formed from the one molecule of R2O2.
• With the chemical components identified, a look
  at the polymerization process

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• Step 1 Initiation
• The first step, initiation, occurs when the
  free-radical catalyst reacts with a double bonded
  carbon monomer, beginning the polymer chain. The
  double carbon bond breaks apart, the monomer
  bonds to the free radical, and the free electron
  is transferred to the outside carbon atom in this
  reaction.

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• Step 2 Propagation
• Propagation, is a repetitive operation in
  which the physical chain of the polymer is
  formed. The double bond of successive monomers is
  opened up when the monomer is reacted to the
  reactive polymer chain. The free electron is
  successively passed down the line of the chain to
  the outside carbon atom.

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• This reaction is continuous because the energy in
  the chemical system is lowered as the chain
  grows.
• Thermodynamically speaking, the sum of the
  energies of the polymer is less than the sum of
  the energies of the individual monomers.
• Simply put, the single bounds in the polymeric
  chain are more stable than the double bonds of
  the monomer.

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• Step 3 Termination
• Termination occurs when another free radical
  (R-O.), left over from the original splitting of
  the organic peroxide, meets the end of the
  growing chain.
• This free-radical terminates the chain by
  linking with the last CH2. component of the
  polymer chain.
• This reaction produces a complete polymer
  chain. Termination can also occur when two
  unfinished chains bond together.

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These termination types are as below.
Other types of termination are also possible.
This exothermic reaction occurs extremely fast,
forming individual chains of polyethylene often
in less than 0.1 second. These polymers have
relatively high molecular weights. branches or
cross-links with other chains also may occur
along the main chain.
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• 2. Step-Reaction (condensation)Polymerization
• Another common type of polymerization.
• This method produces polymers of lower
  molecular weight than chain reactions and
  requires higher temperatures to occur.
• Unlike addition polymerization, step-wise
  reactions involve two different types of
  di-functional monomers or end groups that react
  with one another, forming a chain.
• Condensation polymerization also produces a
  small molecular by-product (water, HCl, etc.).
• EgFormation of Nylon 66, a common polymeric
  clothing material, involving one each of two
  monomers, hexamethylene diamine and adipic acid,
  reacting to form a dimer of Nylon 66.

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The polymer could grow in either direction by
bonding to another molecule of hexamethylene
diamine or adipic acid, or to another dimer. As
the chain grows, the short chain molecules are
called oligomers. This reaction process
theoretically can continue until no further
monomers and reactive end groups are available.
The process is relatively slow and can take up
to several hours or days. This process breeds
linear chains that are strung out without any
cross-linking or branching, unless a
tri-functional monomer is added.
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• Polymer Chemical Structure
• The monomers in a polymer can be arranged in a
  number of different ways.
• Both addition and condensation polymers can be
  linear, branched, or cross-linked. Linear
  polymers are made up of one long continuous
  chain, without any excess appendages or
  attachments. Branched polymers have a chain
  structure that consists of one main chain of
  molecules with smaller molecular chains branching
  from it. A branched chain-structure tends to
  lower the degree of crystallinity and density of
  a polymer. Cross-linking in polymers occurs when
  primary valence bonds are formed between separate
  polymer chain molecules.
• Chains with only one type of monomer are known as
  homopolymers. If two or more different type
  monomers are involved, the resulting copolymer
  can have several configurations or arrangements
  of the monomers along the chain.
• The four main configurations are depicted below

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Copolymer configurations
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• Polymer Physical Structure
• Segments of polymer molecules can exist in two
  distinct physical structures.
• CRYSTALLINE or AMORPHOUS forms.
• Crystalline polymers are only possible if there
  is a regular chemical structure (e.g.,
  homopolymers or alternating copolymers), and the
  chains possess a highly ordered arrangement of
  their segments. Crystallinity in polymers is
  favored in symmetrical polymer chains, but never
  100. These semi-crystalline polymers possess a
  rather typical liquefaction pathway, retaining
  their solid state until they reach their melting
  point at Tm.

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• Amorphous polymers do not show order.
• The molecular segments are randomly arranged and
  entangled.
• - Do not have a definable Tm due to their
  randomness. At low temperatures, below their
  glass transition temperature (Tg), the segments
  are immobile and the sample is often brittle.
• As temperatures increase close to Tg, the
  molecular segments begin to move. Above Tg, the
  mobility is sufficient (if no crystals are
  present) that the polymer can flow as a highly
  viscous liquid.
• The viscosity decreases with increasing
  temperature and decreasing molecular weight.
• There can also be an elastic response if the
  entanglements cannot align at the rate a force is
  applied (as in silly putty). This material is
  then described as visco-elastic.
• In a semi-crystalline polymer, molecular flow is
  prevented by the portions of the molecules in the
  crystals until the temperature is above Tm. At
  this point a visco-elastic material forms.
• These effects are as in the specific volume
  versus temperature graph.

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Members of the Polymer Family

• Separated into two different groups depending on
  their behavior when heated.
• Polymers with linear molecules are likely to be
  thermoplastic.
• These are substances that soften upon heating
  and can be remolded and recycled. They can be
  semi-crystalline or amorphous.
• The other group of polymers is known as
  thermosets. These are substances that do not
  soften under heat and pressure and cannot be
  remolded or recycled. They must be remachined,
  used as fillers, or incinerated to remove them
  from the environment.

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Thermoplastics

• Generally carbon containing polymers synthesized
  by addition or condensation polymerization.
• This process forms strong covalent bonds within
  the chains and weaker secondary Van der Waals
  bonds between the chains.
• Usually, these secondary forces can be easily
  overcome by thermal energy, making thermoplastics
  moldable at high temperatures.
• Thermoplastics will also retain their newly
  reformed shape after cooling.
• Applications of thermoplastics include parts for
  common household appliances, bottles, cable
  insulators, tape, blender and mixer bowls,
  medical syringes, mugs, textiles, packaging, and
  insulation.

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• Thermosets
• Have the same Van der Waals bonds that
  thermoplastics do.
• Also have a stronger linkage to other chains.
• Strong covalent bonds chemically hold different
  chains together in a thermoset material.
• The chains directly bonded to each other or
  bonded through other molecules. This
  "cross-linking" between the chains allows the
  material to resist softening upon heating.
• Thermosets must be machined into a new shape if
  they are to be reused or they can serve as
  powdered fillers.
• Difficult to reform, but have many distinct
  advantages in engineering design applications
  including
• High thermal stability and insulating properties.
  
• High rigidity and dimensional stability.
• Resistance to creep and deformation under load.
• Light-weight.
• Applications for thermosets include epoxies
  (glues), automobile body parts, adhesives for
  plywood and particle board, and as a matrix for
  composites in boat hulls and tanks.

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Unit Operations in Polymer Processing

• Thermoplastic and thermoset melt processes may be
  broken down into

• Preshaping
• Shaping
• Shape Stabilization

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Unit Operations in Polymer Processing

• Preshaping steps
• Solids handling and conveying most processes
  usually involve feed in particulate form
• Plastication The creation of a polymer melt from
  a solid feed.
• Mixing often required to achieve uniform melt
  temperature or uniform composition in compounds
• Pumping The plasticated melt must be
  pressurized and pumped to a shaping device
• Shaping
• The polymer melt is forced through the shaping
  devices to create the desired shape.
• The flow behavior (rheology) of polymer melts
  influences the design of the various shaping
  devices, the processing conditions and the rate
  at which the product can be shaped.
• Shape stabilization
• Involves the solidification of the polymer melt
  in the desired shape, through heat transfer

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Polymer Processing

• Five basic processes to form polymer products or
  parts.
• They are
• Injection molding,
• Compression molding,
• Transfer molding,
• Blow molding, and
• Extrusion
• Compression molding and transfer molding are used
  mainly for thermosetting plastics.
• Injection molding, extrusion and blow molding are
  used primarily with thermoplastics.

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Injection Molding

• Common process for forming plastics- involves
  four steps
• Powder or pelletized polymer is heated to the
  liquid state.
• Under pressure, the liquid polymer is forced into
  a mold through an opening, called a sprue. Gates
  control the flow of material.
• The pressurized material is held in the mold
  until it solidifies.
• The mold is opened and the part removed by
  ejector pins.
• Advantages of injection molding include rapid
  processing, little waste, and easy automation.
• Molded parts include combs, toothbrush bases,
  pails, pipe fittings, and model airplane parts.

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Diagram of injection molding
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Injection Molding

• Injection molding is the most important process
  used to manufacture plastic products. It is
  ideally suited to manufacture mass produced parts
  of complex shapes requiring precise dimensions.
• It is used for numerous products, ranging from
  boat hulls and lawn chairs, to bottle cups. Car
  parts, TV and computer housings are injection
  molded.
• The components of the injection molding machine
  are the plasticating unit, clamping unit and the
  mold.

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Injection Molding Cycle

• Injection molding involves two basic steps
• Melt generation by a rotating screw
• Forward movement of the screw to fill the mold
  with melt and to maintain the injected melt under
  high pressure
• Injection molding is a cyclic process
• Injection The polymer is injected into the mold
  cavity.
• Hold on time Once the cavity is filled, a
  holding pressure is maintained to compensate for
  material shrinkage.
• Cooling The molding cools and solidifies.
• Screw-back At the same time, the screw retracts
  and turns, feeding the next shot in towards the
  front
• Mold opening Once the part is sufficiently cool,
  the mold opens and the part is ejected
• The mold closes and clamps in preparation for
  another cycle.

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Injection Molding Cycle

• The total cycle time is tcycletclosingtcooling
  tejection.

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Molding Processes

• Molding techniques for polymers involve the
  formation of three-dimensional components within
  hollow molds (or cavities)
• Injection Molding
• Thermoforming
• Compression Molding
• Blow Molding
• Rotational Molding

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Compression Molding

• This type of molding was among the first to be
  used to form plastics. It involves four steps
• Pre-formed blanks, powders or pellets are placed
  in the bottom section of a heated mold or die.
• The other half of the mold is lowered and is
  pressure applied.
• The material softens under heat and pressure,
  flowing to fill the mold. Excess is squeezed from
  the mold. If a thermoset, cross-linking occurs in
  the mold.
• The mold is opened and the part is removed.
• For thermoplastics, the mold is cooled before
  removal so the part will not lose its shape.
  Thermosets may be ejected while they are hot and
  after curing is complete. This process is slow,
  but the material moves only a short distance to
  the mold, and does not flow through gates or
  runners. Only one part is made from each mold.

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Compression Molding

• Compression molding is the most common technique
  for producing moldings from thermosetting
  plastics and elastomers.
• Products range in size from small plastic
  electrical moldings and rubber seals weighing a
  few grams, up to vehicle body panels and tires.
• A matched pair of metal dies is used to shape a
  polymer under the action of heat and pressure.

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• Transfer Molding
• This process is a modification of compression
  molding. It is used primarily to produce
  thermosetting plastics. Its steps are
• A partially polymerized material is placed in a
  heated chamber.
• A plunger forces the flowing material into molds.
  
• The material flows through sprues, runners and
  gates.
• The temperature and pressure inside the mold are
  higher than in the heated chamber, which induces
  cross-linking.
• The plastic cures, is hardened, the mold opened,
  and the part removed.
• Mold costs are expensive and much scrap material
  collects in the sprues and runners, but complex
  parts of varying thickness can be accurately
  produced.

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• Blow Molding
• Blow molding produces bottles, globe light
  fixtures, tubs, automobile gasoline tanks, and
  drums. It involves
• A softened plastic tube is extruded
• The tube is clamped at one end and inflated to
  fill a mold.
• Solid shell plastics are removed from the mold.
• This process is rapid and relatively inexpensive

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Blow Molding

• Blow molding produces hollow articles that do
  not require a homogeneous thickness distribution.
  
• HDPE, LDPE, PE, PET and PVC are the most common
  materials used for blow molding. There are three
  important blow molding techniques
• Extrusion blow molding
• Injection blow molding
• Stretch-blow processes
• They involve the following stages
• A tubular preform is produced via extrusion or
  injection molding
• The temperature controlled perform is transferred
  into a cooled split-mould
• The preform is sealed and inflated to take up the
  internal contours of the mould
• The molding is allowed to cool and solidify to
  shape, whilst still under internal pressure
• The pressure is vented, the mold opened and the
  molding ejected.

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Extrusion Blow molding

• In extrusion blow molding, a parison (or tubular
  profile) is extruded and inflated into a cavity
  with a specified geometry. The blown article is
  held inside the cavity until it is sufficiently
  cool.

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Injection Blow Molding

• Injection blow molding begins by injection
  molding the parison onto a core and into a mold
  with finished bottle threads. The formed parison
  has a thickness distribution that leads to
  reduced thickness variations throughout the
  container. Before blowing the parison into the
  cavity, it can be mechanically stretched to
  orient molecules axially (Stretch blow molding).
  The subsequent blowing operation introduces
  tangential orientation. A container with biaxial
  orientation exhibits higher optical clarity,
  better mechanical properties and lower
  permeability.

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• Extrusion
• This process makes parts of constant cross
  section like pipes and rods. Molten polymer goes
  through a die to produce a final shape. It
  involves four steps
• Pellets of the polymer are mixed with coloring
  and additives.
• The material is heated to its proper plasticity.
• The material is forced through a die.
• The material is cooled.
• An extruder has a hopper to feed the polymer and
  additives, a barrel with a continuous feed screw,
  a heating element, and a die holder. An adapter
  at the end of an extruder blowing air through an
  orifice into the hot polymer extruded through a
  ring die produces plastic bags and films.

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The Single Screw Plasticating Extruder

• Regions 1, 2, 3 Handling of particulate solids
• Region 3 Melting, pumping and mixing
• Region 4 Pumping and mixing
• Regions 34 Devolatilization (if needed)

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Cast Film Extrusion

• In a cast film extrusion process, a thin film is
  extruded through a slit onto a chilled, highly
  polished turning roll, where it is quenched from
  one side. The speed of the roller controls the
  draw ratio and final film thickness. The film is
  then sent to a second roller for cooling on the
  other side. Finally it passes through a system of
  rollers and is wound onto a roll.
• Thicker polymer sheets can be manufactured
  similarly. A sheet is distinguished from a film
  by its thickness by definition a sheet has a
  thickness exceeding 250 mm. Otherwise, it is
  called a film.

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Sheeting Dies

• One of the most widely used extrusion dies is
  the coat-hanger or sheeting die. It is used to
  extrude plastic sheets. It is formed by the
  following elements
• Manifold evenly distributes the melt to the
  approach or land region
• Approach or land carries the melt from the
  manifold to the die lips
• Die lips perform the final shaping of the melt.
• The sheet is subsequently pulled (and cooled
  simultaneously) by a system of rollers

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Blown Film Extrusion

• Film blowing is the most important method for
  producing Polyethylene films (about 90 of all PE
  film produced)
• In film blowing a tubular cross-section is
  extruded through an annular die (usually a spiral
  die) and is drawn and inflated until the frost
  line is reached. The extruded tubular profile
  passes through one or two air rings to cool the
  material.
• Most common materials LDPE, HDPE, LLDPE

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Coextrusion

• In coextrusion two or more extruders feed a
  single die, in which the polymer streams are
  layered together to form a composite extrudate.

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Process Thermoplastic (TP) or Thermoset (TS) Advantages Disadvantages
Inj TP, TS It has the most precise control of shape and dimensions, is a highly automatic process, has fast cycle time, and the widest choice of materials. It has high capital cost, is only good for large numbers of parts, and has large pressures in mold (20,000 psi).
Comp TS It has lower mold pressures (1000 psi), does minimum damage to reinforcing fibers (in composites), and large parts are possible. It requires more labor, longer cycle than injection molding, has less shape flexibility than injection molding, and each charge is loaded by hand.
Trans TS It is good for encapsulating metal parts and electronic circuits. There is some scrap with every part and each charge is loaded by hand.
Blow TP It can make hollow parts (especially bottles), stretching action improves mechanical properties, has a fast cycle, and is low labor. It has no direct control over wall thickness, cannot mold small details with high precision, and requires a polymer with high melt strength.
Extru TP It is used for films, wraps, or long continuos parts (ie. pipes). It must be cooled below its glass transition temperature to maintain stability.
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Product Shaping / Secondary Operations
EXTRUSION
Final Product (pipe, profile)

• Secondary operation
• Fiber spinning (fibers)
• Cast film (overhead transparencies,
• Blown film (grocery bags)

Shaping through die

• Preform for other molding processes
• Blow molding (bottles),
• Thermoforming (appliance liners)
• Compression molding (seals)

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Annular (Tubular) Dies

• In a tubular die the polymer melt exits through
  an annulus. These dies are used to extrude
  plastic pipes. The melt flows through the annular
  gap and solidifies at the exit in a cold water
  bath.

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Profile dies

• Profiles are all extruded articles having
  cross-sectional shape that differs from that of a
  circle, an annulus, or a very wide and thin
  rectangle (such as flat film or sheet)
• To produce profiles for windows, doors etc. we
  need appropriate shaped profile dies. The
  cross-section of a profile die may be very
  complicated

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Secondary Shaping

• Secondary shaping operations occur immediately
  after the extrusion profile emerges from the die.
  In general they consist of mechanical stretching
  or forming of a preformed cylinder, sheet, or
  membrane. Examples of common secondary shaping
  processes include
• Fiber spinning
• Film Production (cast and blown film)

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Fiber Spinning

• Fiber spinning is used to manufacture synthetic
  fibers. A filament is continuously extruded
  through an orifice and stretched to diameters of
  100 mm and smaller. The molten polymer is first
  extruded through a filter or screen pack, to
  eliminate small contaminants. It is then extruded
  through a spinneret, a die composed of multiple
  orifices (it can have 1-10,000 holes). The fibers
  are then drawn to their final diameter,
  solidified (in a water bath or by forced
  convection) and wound-up.

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Fiber Spinning

• Melt spinning technology can be applied to
  polyamide (Nylon), polyesters, polyurethanes and
  polyolefins such as PP and HDPE.
• The drawing and cooling processes determine the
  morphology and mechanical properties of the final
  fiber. For example ultra high molecular weight
  HDPE fibers with high degrees of orientation in
  the axial direction have extremely high stiffness
  !!
• Of major concern during fiber spinning are the
  instabilities that arise during drawing, such as
  brittle fracture and draw resonance. Draw
  resonance manifests itself as periodic
  fluctuations that result in diameter oscillation.

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Thermoforming

• Thermoforming is an important secondary shaping
  operation for plastic film and sheet. It consists
  of warming an extruded plastic sheet and forming
  it into a cavity or over a tool using vacuum, air
  pressure, and mechanical means. The plastic sheet
  is heated slightly above the glass transition
  temperature for amorphous polymers, or slightly
  below the melting point, for semi-crystalline
  polymers. It is then shaped into the cavity over
  the tool by vacuum and frequently by plug-assist.

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Thermoforming

• Thermoforming is used to manufacture refrigerator
  liners, shower stalls, bathtubs and various
  automotive parts.
• Amorphous materials are preferred, because they
  have a wide rubbery temperature range above the
  glass transition temperature. At these
  temperatures, the polymer is easily shaped, but
  still has enough melt strength to hold the
  heated sheet without sagging. Temperatures about
  20-100C above Tg are used.
• Most common materials are Polystyrene (PS),
  Acrylonitrile-Butadiene-Styrene (ABS), PVC, PMMA
  and Polycarbonate (PC)

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• Recycled polymers Eg A typical park.
• Recycling gives new life to the things we use.
• It can - conserve valuable resources landfill
  space, energy, raw materials.
• But recycling also takes effort. One place to
  start is looking at the recycling codes on
  different packages. The numbers and letters by
  the triangle will help to sort plastics for
  recycling.
• Get trash to the recycling center as well.
• Community offers curbside recycling. If not,
  maybe we need to set up a recycling center near
  us.

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• Recycling Today's Challenge, Tomorrow's Reward
• Overview
• Consumer waste poses a challenge to everyone.
• Waste solid materials can be grouped into the
  following categories
• metals - aluminum, steel, etc.
• glass- clear, colored, etc.
• paper - newsprint, cardboard, etc.
• natural polymers- leather, grass, leaves, cotton,
  etc.
• synthetic polymers - synthetic rubbers,
  polyethylene terephthalate, polyvinyl chloride,
  etc.

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• Plastics constitute between 14 and 22 of the
  volume of solid waste.
• One possible answer to this problem is recycling.
  
• In 1990, 1 to 2 of plastics, 29 of aluminum,
  25 of paper, 7 of glass, and 3 of rubber and
  steel as post consumer wastes were recycled.
  Obviously, increasing the amount of plastics
  recycled would appear to be the answer. However,
  a major handicap in the reuse of plastics is that
  reprocessing adds a heat history, degrades
  properties and makes repeat use for the same
  application difficult. For example, the 58 gram,
  2-liter polyethylene terephthalate (PET) beverage
  bottle consists of 48 g of PET, the rest being a
  high density polyethylene (HDPE) cup base, paper
  label, adhesive, and molded polypropylene (PP)
  cap. The cup base, label, adhesive and cap are
  contaminants in the recycling of the PET.

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• contaminants issue in plastic recycling, plastic
  products designed "reuse-friendly". Products
  made with recyclability as a viable means for
  disposal. PET for cost effective recycling.
  plastic beads are being used to remove paint from
  aircraft employing a "sand blasting" type method.
  In place of harsh, environmentally unfriendly
  chemical solvents use.
• Another reason for not discarding plastics is the
  conservation of energy. The energy value of
  polyethylene (PE) is 100 of an equivalent mass
  of 2 heating oil. Polystyrene (PS) is 75, while
  polyvinyl chloride (PVC) and PET are about 50.
  With the energy value of a pound of 2 heating
  oil at 20,000 B.T.U., land filling plastics
  results in a waste of energy. Some countries,
  notably Japan, tap into the energy value of
  plastic and paper with waste-to-energy
  incinerators.

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• Another factor is the economic trend of
  progressively increasing tipping fees at
  landfills. As the cost of land filling of solid
  waste increases, so does the incentive to
  recycle. When the cost of land filling exceeds
  the cost of recycling, recycling will be a
  practical alternative to land filling.
• Tipping fees, the charge to the waste hauler for
  dumping a load of solid waste, have been
  increasing regularly. Municipalities have imposed
  restrictions and/or have banned the startup of
  new landfills within their boundaries. As an
  example, 50 of New Jersey's solid waste is
  shipped out of state for landfill burial.
• These factors led to certain recommendations by
  the United States Environmental Protection
  Agency. EPA's recommendations are source
  reduction, recycling, thermal reduction
  (incineration), and land filling. Each of these
  is not without its problems. Source reduction
  calls for the redesigning of packaging and/or the
  use of less, lighter, or more environmentally
  safe materials. The trade-off could mean reduced
  food packaging with the possibility of higher
  food spoilage rates. There would be fewer
  plastics, but more food in solid waste to be
  disposed. Whatever disposal method is chosen, the
  choice is complex. Whatever the costs, the
  consumer will bear them.

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• Today, consumers are using more products and,
  therefore, producing more solid waste. As time
  goes by, we find ourselves with less space to put
  this waste. Eighty percent of all solid waste is
  buried in landfills. Today there are one third
  fewer landfills in operation than the 18,500
  available a decade ago, making land-filling much
  more expensive.
• The amount which synthetic polymers contribute to
  the weight of solid waste will continue to go up
  as the use of plastics increases

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• Recycling of Different Plastics
• PET (Poly Ethylene Terephthalate)
• In 1989, a billion pounds of virgin PET were used
  to make beverage bottles of which about 20 was
  recycled. Of the amount recycled, 50 was used
  for fiberfill and strapping. The reprocessors
  claim to make a high quality, 99 pure,
  granulated PET. It sells at 35 to 60 of virgin
  PET costs.
• The major reuses of PET include sheet, fiber,
  film, and extrusions. When chemically treated,
  the recycled product can be converted into raw
  materials for the production of unsaturated
  polyester resins. If sufficient energy is used,
  the recycled product can be depolymerized to
  ethylene glycol and terephthalic acid and then
  repolymerized to virgin PET.

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• HDPE (high density polyethylene)
• Of the plastics that have a potential for
  recycling, the rigid HDPE container is the one
  most likely to be found in a landfill. Less than
  5 of HDPE containers are treated or processed in
  a manner that makes recycling easy. Virgin HDPE
  is used in opaque household and industrial
  containers used to package motor oil, detergent,
  milk, bleach, and agricultural chemicals.
• There is a great potential for the use of
  recycled HDPE in base cups, drainage pipes,
  flower pots, plastic lumber, trash cans,
  automotive mud flaps, kitchen drain boards,
  beverage bottle crates, and pallets. Most
  recycled HDPE is a colored opaque material, that
  is available in a multitude of tints.

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• PVC (polyvinyl chloride)
• There is much controversy concerning the
  recycling and reuse of PVC due to health and
  safety issues. When PVC is burned, the effects on
  the incinerator and quality of the air are often
  questioned. The Federal Food and Drug
  Administration (FDA) has ordered its staff to
  prepare environmental impact statements covering
  PVC's role in landfills and incineration. The
  burning of PVC releases toxic dioxins, furans,
  and hydrogen chloride. These fumes are
  carcinogenic, mutagenic, and teratagenic. This is
  one of the reasons why PVC must be identified and
  removed from any plastic waste to be recycled.
• .

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LDPE (low density polyethylene)

• LDPE is recycled by giant resin suppliers and
  merchant processors either by burning it as a
  fuel for energy or reusing it in trash bags.
  Recycling trash bags is a big business. Their
  color is not critical, therefore, regrinds go
  into black, brown, and to some lesser extent,
  green and yellow bags.

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• PS (Polystyrene)
• PS and its manufacturers have been the target of
  environmentalists for several years. The
  manufacturers and recyclers are working hard to
  make recycling of PS as common as that of paper
  and metals. One company, Rubbermaid, is testing
  reclaimed PS in service trays and other utility
  items. Amoco, another large corporation,
  currently has a method that converts PS waste,
  including residual food, to an oil that can be
  re-refined.

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• Currently, PVC is used in food and alcoholic
  beverage containers with FDA approval. The future
  of PVC rests in the hands of the plastics
  industry to resolve the issue of the toxic
  effects of the incineration of PVC.
• PVC accounts for less than 1 of land fill waste.
  When PVC is properly recycled, the problems of
  toxic emissions are minimized. Various recyclers
  could reclaim PVC without the health problems.
  Uses for recycled PVC include aquarium tubing,
  drainage pipe, pipe fittings, floor tile, and
  nonfood bottles. When PVC is combined with other
  plastic waste it is used to produce plastic lumber

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• A potential use as plastic lumber.
• Recycled plastic is mixed with wood fibers
  and processed into a replacement for lumber. The
  wood fibers would have become land fill if not
  reused. The end product is called Biopaste. This
  is expected to eventually become a multi-million
  dollar enterprise. R D continue to improve this
  product.
• Recycling is a cost effective means of dealing
  with consumer plastic waste. Research to reduce
  the cost of recycling needs to continue.
  Recycling of plastics is not going to reach the
  level of the recycling programs of paper and some
  metals until lower cost, automatic methods of
  recycling are in place. Fortunately, the
  solutions to these problems are not beyond the
  scope of our technology or our minds.

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Resin Name Common Uses Examples of Recycled Products
(PET or PETE) Soft drink bottles, peanut butter jars, salad dressing bottles, mouth wash jars Liquid soap bottles, strapping, fiberfill for winter coats, surfboards, paint brushes, fuzz on tennis balls, soft drink bottles, film
(HDPE) Milk, water, and juice containers, grocery bags, toys, liquid detergent bottles Soft drink based cups, flower pots, drain pipes, signs, stadium seats, trash cans, re-cycling bins, traffic barrier cones, golf bag liners, toys
(PVC-V) Clear food packaging, shampoo bottles Floor mats, pipes, hoses, mud flaps
(LDPE) Bread bags, frozen food bags, grocery bags Garbage can liners, grocery bags, multi purpose bags
(PP) Ketchup bottles, yogurt containers, margarine, tubs, medicine bottles Manhole steps, paint buckets, videocassette storage cases, ice scrapers, fast food trays, lawn mower wheels, automobile battery parts.
(PS) Video cassette cases, compact disk jackets, coffee cups, cutlery, cafeteria trays, grocery store meat trays, fast-food sandwich container License plate holders, golf course and septic tank drainage systems, desk top accessories, hanging files, food service trays, flower pots, trash cans
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SUPER PLASTICS
The substance (classed as an organic
semiconductor) consists of snowflake-shaped
molecules and can be used in a variety of light-
emitting forms from mobile phone displays to food
packaging. It will also be possible to use the
material to light up wallpaper in a variety of
colours as an alternative to traditional overhead
lighting. The material is also so flexible and
durable that it could be applied to clothing in
everything from school uniforms to sports gear.
Semi conducting plastic can amplify light -
making it one thousand times brighter. This work
could, in the future, make the internet faster.
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• The Future
• Recycling is a viable alternative to all other
  means of dealing with consumer plastic waste.
• In response to the problem of mixed plastic
  waste, a coding system has been developed and
  adopted by the plastic industry. The code is a
  number and letter system. It applies to bottles
  exceeding 16 ounces and other containers
  exceeding 8 ounces. The number appears in the 3
  bent arrow recycling symbol with the abbreviation
  of the plastic below the symbol.
• Western European companies, egHoechst and Bayer,
  have entered the recyclable plastic market with
  success. With a high tech approach, they are
  devising new methods to separate and handle mixed
  plastics waste.