Transcript Slide 1

UNIVERSITI SAINS MALAYSIA
EBB 427
Commodity and Engineering
Plastics
UNIVERSITI SAINS MALAYSIA
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
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
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 t’plastics are the functional groups
attached to the carbon
In all cases, three hydrogens are attached to the carbon-carbon double bond
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 carboncarbon 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
• 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
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.
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 chaineffect the properties
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)
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.
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
Branching Mechanism for PE
Effect of Branching on Several
Polymer Properties
LDPE, HDPE, LLDPE
What is the relationship between
brance of PE with the density???
Relate the properties of LDPE,
HDPE & LLDPE with the structure!!!
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)
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
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 highdensity polyethylene, the melting point is typically in the range 120130 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).
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
• 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
Polypropylene (PP)
• Presence of pendent CH3 groupformation of 3 different types of PP
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.
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:
PVC
PVC pipes
Adhesive film
Adhesive for arts
& craft
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)
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
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 bendprevent crystallization-100% crystallinity
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.
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 highperformance 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.
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
Glossary-Important Terms
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Blending
Copolymerization
Alloying
Miscible
Compatibility