EBB 427

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EBB 427

• Commodity and Engineering Plastics

UNIVERSITI SAINS MALAYSIA
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Types of Thermoplastics

• Various possible classification scheme for
  polymers
• Crystalline vs non crystalline
• Properties or end-use
• Form (fibers, coatings, foam, etc.)
• Polymerization process
• response of the polymer to heat and solvent

UNIVERSITI SAINS MALAYSIA
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Commodity Plastics

• Examples
• Polyethylene (PE)- plastic bag, hot-melt glue gun
• Polyvinylchloride (PVC)- pipe
• Polystyrene (PS)-toys, disposable drinking glass

Engineering Plastics

• Examples
• Polyamide (PA)- unlubricated gear, sji boots
• Polycarbonate (PC)- compact disc, motorcycle
  helmet
• Ultrahigh molecular weight PE pen tips

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Thermoplastic Materials (Commodity Plastics)

• All of the commodity plastic which will be
  considered here are made by addition
  polymerization method
• The differences between the monomers used to make
  these commodity tplastics are the functional
  groups attached to the carbon

In all cases, three hydrogens are attached to the
carbon-carbon double bond
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Steric Hindrance

• Steric effects arise from the fact that each atom
  within a molecule occupies a certain amount of
  space.
• The substitution of one functional group on the
  carbon-carbon double bond, relates to steric
  hindrance(interference because of size)
• When the functional groups are small (such as
  hydrogen), little steric hindrance
• Steric hindrance increases, as larger functional
  group are substituted onto the C-C double bond-
  results of restricted polymer motion, less
  ability to pack densely, and change in physical,
  mechanical and chemical properties

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• PP and PE are often given a special name,
  polyolefins
• Polyolefins means oil like refer to oily and
  waxy feel these materials have
• Consists of only carbon and hydrogen, they are
  all aliphatic groups

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Polyethylene (PE)

• PE is the simplest of all polymers, with 2 C and
  4 H in the basic polymer repeating unit
• High molecular weight, relatively insensitive to
  most solvent (used for chemical reaction vessels
  or pipe)
• However joining is a problem because of solvent
  resistance of PE (overcome by using bonding
  technique that melt the surface of the PE parts)
• The thermal conductivity is good, however Tm of
  PE is low - limited applications at high temp.

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Polyethylene (PE)

• Low cost and ease of manufacture
• Applications packaging, container, toys and
  houseware
• The major differences of PE molecules occur
  during polymerization process- formation of
  branching
• Branching- formation of side chain off the basic
  polymer backbone
• Number of side chain and length of side chain-
  effect the properties

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Classification of polyethylenes

• Polyethylene is classified into several different
  categories based mostly on its density and
  branching. The mechanical properties of PE depend
  significantly on variables such as the extent and
  type of branching, the crystal structure, and the
  molecular weight.
• UHMWPE (ultra high molecular weight PE)
• HMWPE (high molecular weight polyethelyene)
• HDPE (high density PE)
• HDXLPE (high density cross-linked PE)
• PEX (cross-linked PE)
• MDPE (medium density PE)
• LDPE (low density PE)
• LLDPE (linear low density PE)
• VLDPE (very low density PE)

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Classification of polyethylenes

• UHMWPE is polyethylene with a molecular weight
  numbering in the millions, usually between 3.1
  and 5.67 million. The high molecular weight
  results in less efficient packing of the chains
  into the crystal structure as evidenced by
  densities less than high density polyethylene
  (e.g. 0.935 - 0.930). The high molecular weight
  results in a very tough material.
• HDPE is defined by a density of greater or equal
  to 0.941 g/cc. HDPE has a low degree of branching
  and thus stronger intermolecular forces and
  tensile strength.
• PEX is a medium- to high-density polyethylene
  containing cross-link bonds introduced into the
  polymer structure, changing the thermoplast into
  an elastomer.

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Classification of polyethylenes

• MDPE is defined by a density range of 0.926 -
  0.940 g/cc.
• LLDPE is defined by a density range of 0.915 -
  0.925 g/cc. is a substantially linear polymer,
  with significant numbers of short branches
• LDPE is defined by a density range of 0.910 -
  0.940 g/cc. LDPE has a high degree of short and
  long chain branching, which means that the chains
  do not pack into the crystal structure as well.
• VLDPE is defined by a density range of 0.880 -
  0.915 g/cc. is a substantially linear polymer,
  with high levels of short chain branches

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Branching Mechanism for PE
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Effect of Branching on Several Polymer Properties
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LDPE, HDPE, LLDPE
What is the relationship between brance of PE
with the density???
Relate the properties of LDPE, HDPE LLDPE with
the structure!!!
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Relationship Between Density and Molecular Weight
in PE

• Overall trend, increases in molecular weight,
  result in increase in crystallinity and density

• Molecular weight distribution (MWD)
• Narrow MWD results in sharp melting point
• Broad MWD melting occur at a wide range of
  temp.
• (low molecular weight melt first, act as a
  lubricant for
• Higher molecular weight)

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PE

• Crosslinked PE- can be done by electron
  irradiation or by chemical methods
• Electron irradiation is more effective in
  amorphous region than crystalline region
• Crosslinking changes thermoplastic to thermoset
  materials

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PE

• Depending on the crystallinity and molecular
  weight, a melting point and glass transition may
  or may not be observable. The temperature at
  which these occur varies strongly with the type
  of polyethylene.
• For common commercial grades of medium-density
  and high-density polyethylene, the melting point
  is typically in the range 120-130 degrees C. The
  melt point for average commercial low-density
  polyethylene is typically 105-115 degrees C. Most
  LDPE, MDPE, and HDPE grades have excellent
  chemical resistance and do not dissolve at room
  temperature because of the crystallinity.
• Polyethylene (other than cross-linked
  polyethylene) usually can be dissolved at
  elevated temperatures in aromatic hydrocarbons
  (i.e. toluene, xylene) or chlorinated solvents
  (i.e. trichloroethane, trichlorobenzene).

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Polypropylene (PP)

• Polypropylene or polypropene (PP) is a
  thermoplastic polymer, used in a wide variety of
  applications, including food packaging, textiles,
  laboratory equipment, loudspeakers, automotive
  components, and polymer banknotes. An addition
  polymer made from the monomer propylene, it is
  unusually resistant to many chemical solvents,
  bases and acids. Its resin identification code is

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• level of crystallinity intermediate between that
  of low density polyethylene (LDPE) and high
  density polyethylene (HDPE)
• Although it is less tough than LDPE, it is much
  less brittle than HDPE
• This allows polypropylene to be used as a
  replacement for engineering plastics, such as ABS
  
• Polypropylene has a melting point of 160ºC. Food
  containers made from it will not melt in the
  dishwasher, and do not melt during industrial hot
  filling processes

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Polypropylene (PP)

• Presence of pendent CH3 group- formation of 3
  different types of PP

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Different Types of PP

• Isotactic polymers refer to those polymers formed
  by branched monomers that have the characteristic
  of having all the branch groups on the same side
  of the polymeric chain. The monomers are all
  oriented in the same way If we represent a
  monomer by AB then an isotactic polymer is
  AB-AB-AB-AB-AB-etc.
• Besides Isotactism, there are other two types of
  stereoregularity or tacticity frequently found in
  the scientific literature
• Syndiotactism- The monomers have alternating
  orientations within the polymer chain
  AB-BA-AB-BA-AB-BA-etc.
• and Atactism- The monomers have random
  orientations within the chain e.g.
  AB-AB-BA-AB-BA-BA-BA-AB-etc.

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Polyvinyl chloride (PVC)

• Globally, over 50 of PVC manufactured is used in
  construction. As a building material, PVC is
  cheap and easy to assemble.
• In recent years, PVC has been replacing
  traditional building materials such as wood,
  concrete and clay in many areas.
• The symbol for polyvinyl chloride developed by
  the Society of the Plastics Industry so that
  items can be labelled for easy recycling is

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PVC
PVC pipes
Adhesive for arts craft
Adhesive film
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Rigid PVC

• Compared to PE and PP, unmodiffied PVC is more
  rigid and stronger
• Rigid PVC is used in many applications, fillers
  are often used to reduce the cost of the product,
  stiffness, thermal stability, however reduce
  toughness

Size representations of common pendent groups in
commodity polymers
- The Cl atom is approximately the same size as
the CH3 group - The size of Cl atom is sufficient
to interfere the close packaging
and Crystallization of PVC- resulting largely
amorphous polymer (10 crystallinity)
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Plasticized PVC

• Plastisizers are added to PVC, the plastic become
  flexible than the rigid PVC
• Plasticizers work by embedding themselves between
  the chains of polymers
• Space them apart (increasing of the "free
  volume"), and thus significantly lowering the
  glass transition temperature for the plastic and
  making it softer

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Polystyrene (PS)

• Carbon-carbon double bond to which a benzene ring
  and three hydrogens are attached
• The size of benzene group reduce the ability of
  the polymer chain to bend-prevent
  crystallization-100 crystallinity

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Polystyrene (PS)

• Polystyrene's most common use, however, is as
  expanded polystyrene (EPS). Expanded polystyrene
  is produced from a mixture of about 5-10 gaseous
  blowing agent and 90-95 polystyrene by weight
• Expandable polystyrene is the lightweight
  material of which coffee cups and takeaway food
  containers are made. The voids filled with
  trapped air give expanded polystyrene low thermal
  conductivity. This makes it ideal as a
  construction material and it is used in
  structural insulated panel building systems. It
  is also used as insulation in building
  structures, as molded packing material for
  cushioning fragile equipment inside boxes, as
  packing "peanuts", as non-weight-bearing
  architectural structures (such as pillars), and
  also in crafts and model building, particularly
  architectural models.

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High Impact Polystyrene (HIPS)

• Modification of PS can increase selected
  properties, by creating copolymer and blends
• Pure polystyrene is brittle, but hard enough that
  a fairly high-performance product can be made by
  giving it some of the properties of a stretchier
  material, such as polybutadiene rubber. The two
  materials cannot normally be mixed due to the
  amplified effect of intermolecular forces on
  polymer solubility (see plastic recycling), but
  if polybutadiene is added during polymerization
  it can become chemically bonded to the
  polystyrene, forming a graft copolymer which
  helps to incorporate normal polybutadiene into
  the final mix, resulting in high-impact
  polystyrene or HIPS, often called "high-impact
  plastic" in advertisements. Common applications
  include use in toys and product casings. HIPS is
  usually injection molded in production.

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Acrylonitrile butadiene styrene, (ABS)

• Combination materials called ABS has been
  developed
• Styrene and Acrylonitrile monomer can be
  copolymerized to form random, amorphous
  copolymer- SAN

-ABS is in the middle of triangle. -The
properties changes created by increasing the
concentration of one materials relative to the
other - Noted the presence of HIPS, SAN, ABS
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Glossary-Important Terms

• Blending
• Copolymerization
• Alloying
• Miscible
• Compatibility