European Plastic Welder Chapter 1: Plastics

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European Plastic WelderChapter 1 Plastics

• Co ASR, Romanian Welding Society
• P1 CWS, Czech Welding Society ANB
• P2 SLV, Schweisstechnische Lehr- und
  Versuchsanstalt SLV Duisvurg, Niederlassung der
  GSI mbH
• P3 IIS, Italian Welding Institute
• P4 EWF, European Federation for Welding,
  Joining and Cutting
• P5 ISQ, Institute for Welding and Quality

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1.1
Generals on Polymers
Definitions Application of polymers Nomenclature
of polymers Classification of polymers Main
physical properties of polymers
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Introduction to polymers
Term polymer greek poli (many) meros (unit)
many units
Polymers are a large class of materials
consisting of many small molecules (called
monomers) that can be linked together to form
long chains, thus they are known as
macromolecules (term introduced by H. Staudinger
in 1920s). A typical polymer may include tens
of thousands of monomers. Because of their large
size, polymers are classified as
macromolecules. Polymers occur naturally in the
form of proteins, cellulose(plants), starch(food)
and natural rubber. Engineering polymers,
however, are usually synthetic polymers.
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Definitions

• Polymer
• Large molecule consisting of a number of
  repeating units with molecular
• weight typically several thousand or higher
• Repeating unit
• The fundamental recurring unit of a polymer
• Monomer
• The smaller molecule(s) that are used to prepare
  a polymer
• Oligomer
• A molecule consisting of reaction of several
  repeat units of a monomer but not large enough to
  be consider a polymer
• Single repeat unit MONOMER
• Many repeat units POLYMER
• Degree of polymerization
• The number of the repeating units

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Application of polymers
The field of synthetic polymers or plastics is
currently one of the fastest growing materials
industries. The interest in engineering polymers
is driven by their manufacturability,
recyclability, mechanical properties, and lower
cost as compared to many alloys and ceramics.
Also the macromolecular structure of synthetic
polymers provides good biocompatibility and
allows them to perform many biomimetic tasks that
cannot be performed by other synthetic materials,
which include drug delivery, use as grafts for
arteries and veins and use in artificial tendons,
ligaments and joints.
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Application of polymers
INCPEN, Towards greener households, June 2001
p. 580.0400 A of the Chemical Economics Handbook
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Application of polymers
ACCENTURE RESEARCH, Trends in Manufacturing
Polymers Achieving High Performance in a
Multi-Polar World, www.accenture.com
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Nomenclature of polymer
1- Nomenclature Based on monomer source The
addition polymer is often named according to the
monomer that was used to form it Example
poly( vinyl chloride ) PVC is made from vinyl
chloride
-CH2-CH(Cl)- If X is a
single word the name of polymer is written out
directly
ex. polystyrene -CH2-CH(Ph)-
Poly-X
If X consists of two or more words
parentheses should be used
ex , poly (vinyl acetate )
-CH2-CH(OCOCH3)- 2- Based on polymer
structure The most common method for condensation
polymers since the polymer contains different
functional groups than the monomer
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Nomenclature of polymers
PC Polycarbonat PPE Polyphenylether SMA
Styrol-Maleinsäureanhydrid ABS
Acrylnitril-Butadien-Styrol PMMA
Polymethylmethacrylat PS Polystyrol SAN
Styrol-Acrylnitril-Copolymere PVC
Polyvinylchlorid PET Polyethylenterephthalat
(PETP) PBT Polybutylenterephthalat (PBTP) PA
Polyamid POM Polyoxymethylen RF-PP
Resorcin-Formaldehyd-Polypropylen PE-UHMW
Polyethylen-ultra high molecular weight PP
Polypropylen PE-HD Polyethylen hoher Dichte
(High Density) PE-LD Polyethylen niedriger
Dichte (Low Density)
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Classification of polymers

• Main classifications of the polymers
• by origin
• by Monomer composition
• by chain structure
• by thermal behaviour
• by kynetics or mechanism
• by application

A. Classification by Origin

• Synthetic organic polymers
• Biopolymers (proteins, polypeptides,
  polynucleotide, polysaccharides, natural rubber)
• Semi-synthetic polymers (chemically modified
  synthetic polymers)
• Inorganic polymers (siloxanes, silanes,
  phosphazenes)

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B. Classification by Monomer Composition

• Homopolymers
• Copolymers
• Block
• Graft
• Alternating
• Statistical

Homopolymers Consist of only one type of
constitutional repeating unit (A)
AAAAAAAAAAAAAAA
Homopolymer
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Copolymers Consist of two or more constitutional
repeating units (A-B )

• Several classes of copolymer are possible
• Statistical copolymer (Random)
• ABAABABBBAABAABB
• two or more different repeating unit
• are distributed randomly
• Alternating copolymer
• ABABABABABABABAB
• are made of alternating sequences
• of the different monomers
• Block copolymer
• AAAAAAAAABBBBBBBBB
• long sequences of a monomer are followed
  
• by long sequences of another monomer
• Graft copolymer
• AAAAAAAAAAAAAAAAAA
• B B B
• B B B
• Consist of a chain made from one type of
  monomers with branches of another type

Statistical
Alternating
Block
Graft
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c. Classification by Chain structure (molecular
architecture)

• Linear chains a polymer consisting of a single
  continuous chain of repeat units
• Branched chains a polymer that includes side
  chains of repeat units connecting onto the main
  chain of repeat units
• Hyper branched polymer consist of a
  constitutional repeating unit including a
  branching groups
• Cross linked polymer a polymer that includes
  interconnections between chains
• Net work polymer a cross linked polymer that
  includes numerous interconnections between chains

Linear
Cross-linked
Network
Branched
Direction of increasing strength
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d. Classification by Thermal Behavior

• Polymers may be classified as follows, according
  to the mechanical response at elevated
  temperatures
• Thermoplasts
• Thermosets.
•  
• a) Thermoplasts
• Thermoset polymers soften when heated and harden
  when cooled. Simultaneous application of heat and
  pressure is required to fabricate these
  materials.
• On the molecular level, when the temperature is
  raised, secondary bonding forces are diminished
  so that the relative movement of adjacent chains
  is facilitated when a stress is applied.
• Most Linear polymers and those having branched
  structures with flexible chains are
  thermoplastics.
• Thermoplastics are very soft and ductile.
• The commercial available thermoplasts are
• Polyvinyl Chloride (PVC) and Polystyrene
• Polymethyl methacrylate
• Polystyrene

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Classification by Thermal Behavior

• b) Thermosets
• Thermosetting polymers become soft during their
  first heating and become permanently hard when
  cooled. They do not soften during subsequent
  heating. Hence, they cannot be remolded/reshaped
  by subsequent heating.
• In thermosets, during the initial heating,
  covalent cross-links are formed between adjacent
  molecular chain. These bonds anchor the chains
  together to resist the vibration and rotational
  chain motions at high temperatures. Cross linking
  is usually extensive in that 10 to 15 of the
  chain mer units are cross linked. Only heating to
  excessive temperatures will cause severance of
  these crosslink bonds and polymer degradation.
  Thermoset polymers are harder, stronger, more
  brittle than thermoplastics and have better
  dimensional stability.
• They are more usable in processes requiring high
  temperatures
• Most of the cross linked and network polymers
  which include
• Vulcanized rubbers
• Epoxies
• Phenolic
• Polyester resins
• are thermosetting polymers.
• Thermosets cannot be recycled, do not melt, are
  usable at higher temperatures than
  thermoplastics, and are more chemically inert

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e. Classification Based on Kinetics or Mechanism

• Step-growth
• Chain-growth

f. Classification by Application

• Plastics
• Fibers
• Elastomers
• Coatings
• Adhesives

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Main physical properties of polymers
1-Primary bonds the covalent bonds that
connect the atoms of the main chain 2- Secondary
bonds non covalent bonds that hold one
polymer chain to another including hydrogen bond
and other dipole dipole attraction 3-Crystalline
polymer solid polymers with high degree of
structural order and rigidity 4- Amorphous
polymers polymers with a low degree of
structural order 5-Semi crystalline polymer
most polymers actually consist of both
crystalline domains and amorphous domains with
properties between that expected for a purely
crystalline or purely amorphous polymer 6-Glass
the solid form of an amorphous polymer
characterized by rigidity and brittleness 7
Crystalline melting temperature (Tm) temperature
at which crystalline polymers melt
8 - Glass transition temperature (Tg )
temperature at which an amorphous polymer
converts to a liquid or amorphous domains of a
semi crystalline polymer melt 9 Thermoplastics
(plastics( polymers that undergo thermally
reversible Interconversion between the solid
state and the liquid state 10- Thermosets
polymers that continue reacted at elevated
temperatures generating increasing number of
crosslinks such polymers do not exhibit melting
or glass transition 11- Liquid crystalline
polymers polymers with a fluid phase that
retains some order 12- Elastomers rubbery ,
stretchy polymers the effect is caused by light
crosslinking that pulls the chains back to
their original state
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Amorphous
Crystalline
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1.2
Polymers in the Solid State
Glass Transition Temperature Crystalline Structure
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POLYMERS IN THE SOLID STATE
Amorphous
Semi-crystalline
Glassy
Rubbery
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Glass Transition Temperature

• The glass transition, Tg, is temp. below which a
  polymer OR glass is brittle or glass-like above
  that temperature the material is more plastic.
• The Tg to a first approximation is a measure of
  the strength of the secondary bonds between
  chains in a polymer the stronger the secondary
  bonds the higher the glass transition
  temperature.
• Polyethylene Tg 0C
• Polystyrene 97 C
• PMMA (plexiglass) 105 C.
• Since room temp. is lt Tg for PMMA, it is brittle
  at room temp.
• For rubber bands Tg - 73C.

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Crystallinity

• Crystallization in linear polymers achieving a
  very regular arrangement
• of the mers
• Induction of crystallinity
• cooling of molten polymer
• evaporation of polymer solution
• annealing ? heating of polymer at a specific
  temperature
• drawing ? stretching at a temperature above Tg

Effects

• Increased Density
• Increases Stiffness (modulus)
• Reduces permeability
• Increases chemical resistance
• Reduces toughness

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Crystalline polymers (vs amorphous polymers)

• tougher, stiffer (due to stronger interactions)
• higher density, higher solvent resistance (due
  to closely packing morphology)
• more opaque (due to light scattering by
  crystallites)

• Crystalline morphologies
• Spherulite ? aggregates of small fibrils in a
  radial pattern (crystallization under no stress)
• Drawn fibrillar ? obtained by drawing the
  spherulitic fibrils
• Epitaxial ? one crystallite grown on another
  lamella growth on long fibrils the so-called
  shish-kebab morphology (crystallization under
  stirring)

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1.3
Characteristics of polymers. Behaviour in
exploitation
Maximum service temperature Coefficient of
friction Flammability Tensile strengh at
break Coefficient of linear expansion Thermal
guidelines
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1.4
Polyethylene
Principal Olefin Monomers Mechanical Properties
of Polyethylene Physical Properties of
Polyethylene
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Principal Olefin Monomers

• Ethylene

• Propylene

Poly n
Poly n

• 4-Methylpentene

• Butene-1

Poly n
Poly n
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Mechanical Properties of Polyethylene

• Type 1 (Branched) Low Density of 0.910 - 0.925
  g/cc
• Type 2 Medium Density of 0.926 - 0.940 g/cc
• Type 3 High Density of 0.941 - 0.959 g/cc
• Type 4 (Linear) High Density to ultra high
  density gt 0.959

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Physical Properties of Polyethylene

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1.5
Polypropylene
Polypropylene Structure Advantages/Disadvatages
of Polypropylene Mechanical Properties of
Polypropylene Physical Properties of Polypropylene
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Polypropylene Structure

• Propylene
• Isotactic- CH3 on one side of polymer chain
  (isolated). Commercial PP is 90 to 95 Isotactic

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Advantages/Disadvatages of Polypropylene

• Advantages
• Low Cost
• Excellent flexural strength
• Good impact strength
• Processable by all thermoplastic equipment
• Low coefficient of friction
• Excellent electrical insulation
• Good fatigue resistance
• Excellent moisture resistance
• Service Temperature to 126oC
• Very good chemical resistance

• Disadvantages
• High thermal expansion
• UV degradation
• Poor weathering resistance
• Subject to attack by chlorinated solvents and
  aromatics
• Difficulty to bond or paint
• Oxidizes readily
• flammable

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Mechanical Properties of Polypropylene

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Physical Properties of Polypropylene-Polyethylene

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Reference

• 1 Billmeyer, F. W., Textbook of Polymer Science,
  3rd ed., Interscience Publishers, 1984 (classic
  book with excellent treatment of polymer
  properties) 2 Barth, H. G. and Mays, J. W.,
  Eds., Modern Methods of Polymer Characterization,
  Wiley, 1991 (covers latest developments at the
  time of most methods) 3 Brady, Jr., R. F.,
  Ed., Comprehensive Desk Reference of Polymer
  Characterization and Analysis, American Chemical
  Society-Oxford, 2003 (survey of characterization
  and analytical methods) 4 Brandrup, J.,
  Immergut, E. H. ,Grulke, E. A., Abe, A, and
  Bloch, D. R., Eds., Polymer Handbook, 4th ed.,
  John Wiley and Sons, 2005 (premier handbook of
  polymer science, listing virtually all polymer
  characteristics for most polymers) 5 Brydson,
  J. A., Plastics Materials, Butterworth Heinemann,
  2000 (comprehensive treatment of plastics, their
  synthesis, properties, and applications) 6
  Bueche, F., Physical Properties of Polymers,
  Krieger Publishing, 1979 (emphasis is on polymer
  physics) 7 Cowie, J.M.G. and Arrighi, V.,
  Polymers Chemistry and Physics of Modern
  Materials, 3rd ed., CRC Press 2008 (excellent
  discussion of physical properties and
  applications) 8 Heimenz, P.C. and Lodge, T.
  P., Polymer Chemistry, 2nd ed., CRC Press, 2007
  (comprehensive treatment of polymer chemistry -
  synthesis and physical chemistry) 9 Mark,
  J.E., Allcock, H. R., and West, R., Inorganic
  Polymers, Oxford, 2005 (physical chemistry and
  properties of inorganic polymers) 10 Mark, J.
  E., Ed., Polymer Data Handbook, Oxford, 1999
  (compilation of major classes of polymers and
  their physical properties)

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• 11 Mori, S. and Barth, H. G., Size Exclusion
  Chromatography, Springer-Verlag, 1999
  (comprehensive treatment of SEC, theory and
  applications) 12 Munk, P. and Aminabhavi, T.
  M., Introduction to Macromolecular Science, 2nd
  ed., John Wiley and Sons, 2002 (emphasis on
  polymer physical chemistry) 13 Nielsen, L. E.,
  Polymer Rheology, Marcel Dekker, 1977
  (introductory text on polymer rheology) 14
  Richardson, T. L. and Lokensgard, E., Industrial
  Plastics Theory and Applications, Delmar, 1996
  (practical overview of some important properties
  and polymer processing) 15 Carraher, Jr., C.
  E., Seymour/Carraher's Polymer Chemistry, 7th
  ed., CRC Press, 2007 (popular introduction to
  polymer chemistry) 16 Seymour, R. B.,
  Engineering Polymer Sourcebook, McGraw Hill, 1990
  (good overview of physical properties of
  engineering polymers) 17 Sperling L. H.,
  Introduction to Physical Polymer Science, 2d d.,
  Wiley-Interscience, 1992 (good treatment of
  polymer physics and properties) 18 van
  Krevelen, D. W., Properties of Polymers, 3rd ed.,
  Elsevier, 1990 (in-depth treatment of polymer
  properties, best resource available) 19
  Whistler, R., Industrial Gums, 2nd ed., Academic
  Press, 1973 (although outdated, gives solid
  background on the chemistry and properties of
  cellulosics and polysaccharides) 20 Wu, C. S.,
  Ed., Handbook of Size Exclusion Chromatography,
  2nd ed., Marcel Dekker, 2003 (covers all aspects
  of this important technique).
• 21 Course Classes of Polymeric Materials, Joe
  Greene, CSU, CHICO
• 22 Course Engineering Thermoplastics, Joe
  Greene, CSU, CHICO

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