Effects of Process Variables Flashcards
As temperature__________, the molecules of
the polymer move faster and their kinetic
energy ______________. This can cause the
polymer to _____, and its shape to change
increases, increases, expand
Substances that are made up
of long chains of repeating molecules. The
behavior of polymers can be affected by
__________ changes
Polymers, temperature
At _____________, certain polymer chains
may break down and degrade, resulting in a
loss of material
high temperatures
Solid polymers that tend to form
ordered regions are termed
crystalline polymers
Polymers that have no crystals at
all are called
amorphous
A real polymer is ___________
crystalline, and the extent of
crystallization is characterized by
the ____________.
never completely ; percentage of crystallinity
In the amorphous region of the polymer,
at lower temperature, the molecules of
the polymer are in frozen state, where the
molecules can vibrate slightly but are not
able to move significantly.
glassy state
In __________ state, the polymer is brittle, hard, and rigid analogous to glass
glass
shows hard, rigid, and
brittle nature analogous to a crystalline
solid with molecular disorder as a liquid.
glassy state
When the polymer is heated, the polymer
chains are able to wiggle around each
other, and the polymer becomes soft and
flexible similar to rubber.
rubbery state
The temperature at which the glassy
state makes a transition to rubbery state
is called the
glass transition temperature Tg
There is a diffuse transition zone between
the rubbery and liquid states for
crystalline polymers; the temperature at
which this occurs is called the
flow temperature, tf
______________is the
property of the amorphous region of the
polymer, whereas the crystalline region is
characterized by the ________________
glass transition temperature
melting point temperature
Polymer with highest Tg; lowest
Polycarbonate, LDPE
The glass transition temperature depends on the
mobility and flexibility of the polymeric chains
ease of the chain segment to rotate along
the chain backbone
flexibility
If the
polymeric chains can move easily, then the glassy state
can be converted to the rubbery state at _________, that is the glass transition temperature is ________
lower temperature, lower
If somehow the mobility of the chains is restricted, then
the glassy state is more __________ and it is difficult to break
the restriction causing the immobility of the polymer
chains at the lower temperature, because ______ is
required to make the chains free.
stable; more energy
Factors Affecting the Glass
Transition Temperature
intermolecular forces
chain stiffness
cross linking
pendant groups
plasticizers
molecular weight
Strong intermolecular forces cause _______ Tg
higher
The presence of the stiffening groups such as ______ in the polymer chain reduces the _________ of the chain
amide, sulfone, carbonyl, p-phenylene; flexibility, higher Tg
restrict
rotational motion and raise the glass transition
temperature.
cross linking
The presence of __________ can change
the glass transition temperature.
pendant groups
types of pendant groups
bulky
flexible
limits the packing of the chains and hence
increases the rotational motion, tending to less Tg
value
flexible pendant groups
can
restrict rotational freedom, leading to higher
glass transition temperature.
bulky pendant groups
Low molecular weight
and non-volatile materials added to
polymers to increase their chain
flexibility
plasticizers
Plasticizers reduce ________ between polymer chains, which ________ Tg
intermolecular cohesive forces, decrease
Tg is _______________with
the molecular weight.
increased
The modulus of a polymer __________ with
increasing temperature.
decreases
When _______ is applied to a polymer, it can cause the chains to
become more tightly packed together, leading to an increase in
___________
pressure; density
The specific effects of pressure on a polymer depend on the type of ___________ which it is subjected to pressure
polymer and the conditions
defined
as the pressure exerted by a fluid
at equilibrium at any point of time
due to the force of gravity.
hydrostatic pressure
Hydrostatic pressure is
____________ to the depth
measured from the surface as the
weight of the fluid ___________
when a downward force is
applied.
proportional; increases
is the
pressure exerted by a liquid on a
solid surface
Hydrostatic pressure
Effect of Pressure on the
Mechanical Properties of Polymers
elastic modulus
Yield strength
Fracture properties
is the unit of measurement of an
object’s or substance’s resistance to being
deformed elastically
elastic modulus
measure of a material’s
stiffness or resistance to deformation under an
applied load.
elastic modulus
Elastic modulus describes the ratio of
change in length or volume of a material to the
change in length or volume of the applied load.
A stiffer material will have a ________elastic
modulus.
higher
force causing the
deformation divided by the area to which the
force is applied
stress
ratio of the
change in some parameter caused by the
deformation to the original value of the
parameter
strain
ensile and compressive
elasticity, or the tendency of an object to deform along an axis
when opposing forces are applied along that axis
Young modulus
Young modulus is defined as the ratio of __________
tensile stress to tensile strain
describes an
object’s tendency to shear (the deformation of shape at
constant volume) when acted upon by opposing forces
Shear modulus/ Modulus of rigidity
Shear modulus is defined as
shear stress over shear strain
Types of elastic modulus
Bulk
Flexural
describes volumetric elasticity, or the
tendency of an object to deform in all directions when
uniformly loaded in all directions
bulk modulus K
extension of Young’s
modulus to three dimensions
Bulk modulus K
Bulk modulus is defined as _______________ and is the inverse of ____________
volumetric stress over volumetric strain ;
compressibility
describes the object’s tendency to flex
when acted upon by a moment.
flexural modulus
Elastic modulus of polymers ___________with increasing hydrostatic pressure in tension, compression, and shear
increases
One of the main reasons for the increase in the elastic modulus with increasing pressure is the effects of
finite deformations on the polymer
_______ hydrostatic pressure can also cause the glass
transition in a polymer to shift to higher temperatures.
High
a material property and
is the stress corresponding to the yield point at which the
material begins to deform plastically
yield strength or yield stress
often used to determine the maximum
allowable load in a mechanical component, since it
represents the upper limit to forces that can be applied
without producing permanent deformation.
yield strength
The yield strength of polymers also ___with
applied hydrostatic pressure
increases
appearance of a crack or complete
separation of an object or material into two or more pieces
under the action of stress.
fracture
occurs due to the development
of certain displacement discontinuity surfaces within the solid
fracture of a solid
If a displacement develops perpendicular to the surface, it is
called a
normal tensile crack/crack
If a displacement develops tangentially, it is called a
shear crack, slip band, or dislocation
stress at
which a specimen fails
via fracture.
fracture strength
Fracture strength is
usually determined for a
given specimen by a ______, where the final recorded point is the _________
tensile test; fracture strength
of the polymers always increased
with increasing hydrostatic pressure.
ultimate tensile strengths
The fracture strength increased
proportionally to the
yield strength
The ___________ tends to
increase for ductile polymers
but decrease for some brittle
polymers
tensile strength
In some brittle polymers like
PS, ______________________
is induced beyond a certain
critical pressure
brittle-ductile transition
substance that accelerates
chemical reactions without being consumed in
the process.
catalyst
can help to speed up the
polymerization process, reduce the
temperature required for polymerization, or
control the structure of the resulting polymer.
catalysts
quantity that measures
the extent to which the reaction has proceeded
extent of reaction
the degree of crosslinking or bonding between
the monomers in a polymer chain
extent of reaction
________ increases the rigidity and strength of
the polymer, while the ___________ can
affect its flexibility and solubility.
cross linking; extent of bonding
The extent of the reaction can be controlled
through
temperature, time, and the type and
concentration of the crosslinking agents used.
general expression, relating
average functionality (f),extent of reaction (p), and average
degree of polymerization ത 𝑋𝑛for polycondensation reaction
carried out for a period t.
Carother’s equation
s defined as the fraction of
functional groups/monomers that have reacted at time t.
Extent of Reaction
defined as equal to
the total number of bifunctional initially added, No, divided by
the remaining number of molecules Nafter time t.
Average degree of polymerization
implied the formation of essentially infinitely large
polymer network in the reaction mixture.
gelation
The sudden onset of gelation marks the division of the
mixture into two parts
gel; sol
soluble in all non
degrading solvents
gel
soluble and
can be extracted from the gel.
sol
As polymerization proceeds beyond the gel point, the
amount of gel ___________ at the expense of the sol, and the
mixture rapidly transforms from a viscous liquid to an
elastic material of ______________
increases; infinite viscosity
can help in determining the critical
extent of reaction at which gelation or cross-linking would
commence
Carother’s reaction
It is thus essential to
stop the polymerization reaction before the onset of
________
gelation.
It can be clearly seen that at the point of a _______, when the reaction is complete, the
polymer being formed in the polycondensation system gets
cross-linked and, hence, turns into insoluble, infusible gelled
mass.
theoretical extent of reaction
