Polymers Flashcards
describes the ability of a material to be molded or formed
plastic
tends to be used to describe finished parts
plastic
tends to describe the raw material and is used by the scientific community
polymer
created when a large number of identical repeating monomer units are joined together to make a single large polymer molecule
polymer
smallest repetitive unit in a polymer and is based on the carbon atom
mer
polymers can be grouped into two chemical classes:
thermoplastic and thermoset
terms that describe how polymers behave when heated
thermoplastic and thermoset
two economic groups of polymers
commodity polymers and engineering polymers
the estimated amount of petrochemicals used by all the plastics industries ranges from
5% to 7%
is Dow Chemical’s trade name for an expanded polystyrene material used primarily by the construction industry
Styrofoam
was a trade name coined in the 1930s to market a regenerated cellulose product
Cellophane
It was the first clear plastic wrapping material used in quantity by the packaging industry
cellophane
polymer’s properties depend primarily on:
- the elements that make up the polymer molecule
- the polymer molecule’s polarity
- the size or molecular weight of the molecule
- the molecule’s shape
- the polymer’s thermal history
- mechanical history
only 2 packaging polymers are predominantly nonpolar
polyethylene and polypropylene
is that material property that stops or reduces the permeation of gas through the material
barrier
occurs where highly polar surfaces attract one another
friction (“stickiness”)
the packaging industry uses either ______ or _______ to impart polarity to the surface of low-polarity plastics
flame treatment or corona discharge treatment
the individual structural unit of a polymer is a
monomer
describes the chemical reaction that joins monomer units together to form complex polymeric structures
polymerization
the exceptions which are made by condensation polymerization
polyethylene terephthalate & polyamide
family of molecules variously called
olefins, polyolefins, or hydrocarbons
the simplest possible combination of hydrogen and carbon is
methane
a polymer that is built up from one type of monomer
homopolymer
contain two different monomer types
copolymers
contain three monomer types
terpolymers
Has ine of the lowest melting points of all the packaging polymers
Nonpolar polyethylene
Molecules also develop varying degrees of attraction for one another through a group of weaker electrical attractions generally referred to as
Van der Waals’ forces
The polarity, or “dyne” level , of a plastic surface is indirectly measured by
Noting the contact angle of a drop of water on the surface or by determining which solution in a set of solutions of known dyne level will be able to wet the surface.
Is one where the individual monomer units simply add onto themselves to form chain-like structures.
Addition polymerization
A mixture of low-molecular-weight prepolymer components is an
Oligomer
this molecular drag or resistance to flow is observed as
viscosity
the chain at about 1,500 carbons long would be classified as
low-molecular-weight polyethylene
for any given polymer, as molecular weight increases:
- melting point increases
- tensile strength, stiffness, and hardness increase
- barrier properties will be higher
- solubility in solvents decreases
highly branched molecular chains cannot pack closely together and, hence, produce a
LPDE (low-density polyethylene)
highly linear polyethylene molecules can be closely packed and result in a
high-density polyethylene (HDPE)
a third variant has short controlled side branches
linear low-density polyethylene (LLDPE)
LDPEs are polyethylenes with relative densities between
0.910 and 0.925
HDPEs have densities between
0.941 and 0.959
the density of the plastic relative to water
relative density
the most common polyamides are
polyamide 6 and 66
are a reaction product of polyisocyanate and polyhydroxyl groups
urethanes
highly ordered molecular arrangements are said to be
crystalline
completely random arrangements are
amorphous
the degree of crystallinity depends partly on
the polymer chain’s shape
with its long linear chains, is predisposed to high levels of crystallinity
high-density polyethylene
with its many randomly arranged branches, has an irregular geometry and tends to be amorphous
low-density polyethylene
will tend to freeze the polymer chains in this random state
rapid cooling
allows time for the molecules to realign themselves into a more ordered crystalline state
slow cooling
affects the physical properties of most plastics
degree of crystallinity
as a polymer’s crystallinity increases:
- stiffness increases
- heat tolerance increases
- barrier properties improve
- loss of clarity likelihood increases
is a material, usually a synthetic polymer, that has high elongation properties, defined as being able to return to its original length when the stress is released
elastomer
to describe a highly elastic thermoplastic material
plastomer
deformation of plastics under load is variously referred to as
creep and cold flow
is most commonly observed as loss of torque with plastic closures
cold flow
is the temperature at which a polymeric material changes from a rigid solid state to a soft, rubbery or elastic state
Glass transition temperature
refers to a marked directionality in how a particular molecule is arranged
orientation
orientation can be carried out in directions
monoaxial and biaxial
is used in such packaging products as plastic strapping, where a maximum of tensile strength is required in one direction
monoaxial orientation
most packaging films are
biaxially oriented
is soft, has high elongation and low tensile strength
unoriented polypropylene film
is stiff and has low elongation, and its tensile strength increases three- or four-fold.
biaxially oriented film
is used to produce shrink film
a combination of thermal and mechanical history
the degree of shrinkage is controlled by the
degree of stretching
have thermal expansion coefficients ten times or more than that of metals
plastic materials
occurs when the large size of groups within a
molecule prevents chemical reactions that are observed in related molecules with smaller groups.)
Steric hindrance
Typical thermal analysis methods
DTA -thermal analysis
DSC - scanning calorimetry
DMA - mechanical analysis
