The document discusses crystallinity in polymers. It defines crystalline and amorphous regions in polymers, and explains that polymers exist as a mixture of crystalline and amorphous phases. It describes how polymer chains fold and organize into crystalline lamellae and spherulites. The degree of crystallinity affects various material properties, and can be measured using techniques like DSC and X-ray diffraction. A higher crystallinity leads to properties like increased hardness, strength and barrier properties.

1. Crystallinity in polymers
Manjinder Singh
SC16M072

2. CONTENT :
• SOLIDS
• INTRODUCTION
• DEGREE OF CRYSTALLINITY
• CRYSTALLISABLITY
• POLYMER CRYSTALLISATION
• HELICAL STRUCTURES
• SPHERULITES
• LAMELLAR STUCTURES
• FOLDING OF CHAINS DURING CRYSTAL FORMSTION
• CRYSTALLIZATION MECHANISMS
• POLYMER CRYSTALLINITY MEASUREMENTS
• PROPERTIES AFFECTED BY CRYSTALLINITY

3. SOLIDS
• CRYSTALLINE SOLIDS :
A crystal or crystalline solid is a solid
material whose constituents (such as atoms,
molecules or ions) are arranged in a highly
ordered microscopic structure, forming
a crystal lattice that extends in all
directions.
• AMORPHOUS SOLIDS : An amorphous
solid is any non-crystalline solid in which
the atoms and molecules are not organized
in a definite lattice pattern. Such
solids include glass, plastic, and gel.

4. BASIC DIFFERENCES
CRYSTALLINE SOLIDS AMORPHOUS SOLIDS
They have characteristic geometrical
shape
Solids that don't have definite
geometrical shape
T hey have sharp melting point They melt over a wide range of
temperature
Physical properties of crystalline
solids are different in different
directions. This phenomenon is
known as Anisotropy.
Physical properties of amorphous
solids are same in different
direction. amorphous solids are
isotropic.
When crystalline solids are rotated
about an axis, their appearance does
not change. This shows that they are
symmetrical.
Amorphous solids are
unsymmetrical.
Crystalline solids cleavage along
particular direction at fixed cleavage
planes.
Amorphous solids don't break at
fixed cleavage planes.

5. INTRODUCTION
• Properties of textile fibers are determined by their chemical
structure degree of polymerization, orientation of chain
molecules, crystallinity, package density and cross linking
between individual molecules. Polymer crystallinity is one
of the important properties of all polymers. Polymer exists
both in crystalline and amorphous form.

6. • Figure shows how the arrangement of polymer chain
forming crystalline and amorphous regions. It can be
seen that part of molecules are arranged in regular
order, these regions are called crystalline regions. In
between these ordered regions molecules are arranged
in random disorganized state and these are called
amorphous regions.
• Crystallinity is indication of amount of crystalline
region in polymer with respect to amorphous content.

7. DEGREE OF CRYSTALLINITY
• The degree of crystallinity is defined as the fractional amount of
polymer that is crystalline and it is either expressed in terms of the
mass fraction or the volume fraction.
• For semi-crystalline polymers, the degree of crystallinity is one of its
most important physical parameters since it reflects the sample’s
morphology and determines various mechanical properties, such as
the Young modulus, yield stress as well as the impact strength.
• Differential scanning calorimetry is widely used to determine the
amount of crystalline material. It can be used to determine the
fractional amount of crystallinity in a polymer sample. Other
commonly used methods are X-ray diffraction, density measurements,
and infrared spectroscopy.

8. CRYSTALLISABLITY
• Crystallisabilty is the maximum crystallinity that a polymer
can achieve at a particular temperature, regardless of the
other conditions of crystallization.
• Crystallisablity at a particular temperature depends on the
chemical nature of the macromolecular chain, its geometrical
structure, molecular weight and molecular weight
distribution.

9. POLYMER CRYSTALLISATION
• Crystallization of polymers is a process associated with partial
alignment of their molecular chains.
• These chains fold together and form ordered regions
called lamellae, which compose larger spheroidal structures
named spherulites.
• Polymers can crystallize upon cooling from the melt,
mechanical stretching or solvent evaporation. Crystallization
affects optical, mechanical, thermal and chemical properties of
the polymer.

10. CRYSTALLIZATION
MECHANISMS
• Crystallization by stretching
• Crystallization from solution

11. CRYSTALLIZATION BY STRETCHING
• Crystallization occurs upon extrusion used in making fibers
and films.
• In this process, the polymer is forced through, e.g., a nozzle
that creates tensile stress which partially aligns its molecules.
Such alignment can be considered as crystallization and it
affects the material properties.
• Anisotropy is more enhanced in presence of rod-like fillers
such as carbon nanotubes, compared to spherical fillers.
• Polymer strength is increased not only by extrusion, but also
by blow molding, which is used in the production of plastic
tanks and PET bottles.

12. • Some polymers which do not crystallize from the melt, can be
partially aligned by stretching.
• Some elastomers which are amorphous in the unstrained state
undergo rapid crystallization upon stretching.

13. CRYSTALLIZATION FROM
SOLUTION
• Polymers can also be crystallized from a solution or upon
evaporation of a solvent. This process depends on the degree of
dilution.
• In dilute solutions, the molecular chains have no connection
with each other and exist as a separate polymer coils in the
solution.
• Increase in concentration which can occur via solvent
evaporation, induces interaction between molecular chains
and a possible crystallization as in the crystallization from the
melt.
• Crystallization from solution may result in the highest degree
of polymer crystallinity.

14. • The crystal shape can be more complex for other polymers,
including hollow pyramids, spirals and multilayer dendritic
structures.
• The rate of crystallization can be monitored by a technique
which selectively probes the dissolved fraction.

15. HELICAL STRUCTURES
• To facilitate closer packing of molecules in the crystalline
phase , many polymers tend to assume a helical structure.
• Isotactic vinyl polymers has helical structures.
• Helical structure has a special significance in polymers of
biological origin.
• DNA structure also have helical structures.
• This DNA structures was determined by Watson and Crick.
• Hydrogen bonding plays an important role in the formation of
the double helix of the DNA molecules.

16. DOUBLE HELIX OF THE DNA MOLECULE BY WATSON-CRICK

17. SPHERULITES
• Spherulites are spherical semicrystalline regions inside non-
branched linear polymers.
• Their formation is associated with crystallization of
polymers from the melt and is controlled by several parameters
such as the number of nucleation sites, structure of the polymer
molecules, cooling rate, etc.
• Spherulites are composed of highly ordered lamellae, which
result in higher density, hardness, but also brittleness of the
spherulites as compared to disordered polymer.
• The lamellae are connected by amorphous regions which provide
certain elasticity and impact resistance.

18. • Alignment of the polymer molecules within the lamellae
results in birefringence producing a variety of colored
patterns.
• Birefringence is the optical property of a material having
a refractive index that depends on the polarization and
propagation direction of light.
• If a molten polymer such as polypropylene is made into thin
film between to hot glass plates and cooled, it is seen that,
from different nucleation centres, spherulites start developing.

19. SPHERULITES FORMATION IN SELF-
NUCLEATED TRIGONAL ISOTACTIC POLY
(1-BUTENE)

20. • Mechanical properties : Formation of spherulites affects many
properties of the polymer material; in particular,
crystallinity, density, tensile strength and Young's modulus of
polymers increase during spherulization. This increase is due
to the lamellae fraction within the spherulites, where the
molecules are more densely packed than in the amorphous
phase.
• Optical properties : Spherulites can scatter light rays and
hence the transparency of a given material decreases as the
size of the spherulites increases. Alignment of the polymer
molecules within the lamellae results
in birefringence producing a variety of colored patterns when
spherulites are viewed between crossed polarizers in
an optical microscope.

21. LAMELLAR STRUCTURE
• Lamellar structures or microstructures are composed of
fine, alternating layers of different materials in the form
of lamellae.
• Such conditions force phases of different composition to
form but allow little time for diffusion to produce those
phases equilibrium compositions.
• Fine lamellae solve this problem by shortening the
diffusion distance between phases, but their high surface
energy makes them unstable and prone to break up
when annealing allows diffusion to progress.

23. LEFT TO RIGHT: SPHERULITES; BLOCK
COPOLYMER MICRODOMAINS; LAMELLAR
CRYSTALS; CRYSTALLINE BLOCK UNIT CELL.

24. FOLDING OF CHAIN DURING
CRYSTAL FORMATION
• For a standard polymer, the lamellar thickness is around 100
Å and the molecular chain length is around 1000 to 10000 Å .
• The accommodation of the long chain into the narrow lamella
is by assuming that chain folding takes place during the
process of crystallization.
• Many experimental techniques such as electron diffraction
prove beyond any reasonable doubt that the chains in a
crystal are folded and oriented perpendicular to the plane of
the polymer crystal lamella.

25. schematic representation of chain folding taking
place during formation of crystal lamella

26. POLYMER CRYSTALLINITY
MEASUREMENTS
• BY DIFFERENTIAL SCANNING CALORIMERTY (DSC)
• BY X-RAY DIFFRACTION (XRD)

27. DIFFERENTIAL SCANNING
CALORIMERTY (DSC)
• DSC can be used to determine amount of crystallinity in a
polymer.
• Instrument is designed to measure amount of heat absorbed or
evolved from sample under isothermal conditions.
• DSC contains two pans, one reference pan that is empty and the
other pan has polymer sample.
• In this method polymer sample is heated with reference to a
reference pan. Both polymer and the reference pan are heated at
same rate.
• The amount of extra heat absorbed by polymer sample is with
reference to reference material

29. • DSC curve of a PET bottle sample

30. %100% 


 
f
obs
f
H
H
ityCrystallin

32. X-RAY DIFFRACTION(XRD)
• X-Ray diffraction is also used to measure the nature of
polymer and extent of crystallinity present in the Polymer
sample.
• Crystalline regions in the polymer seated in well-defined
manner acts as diffraction grating .
• So the Emerging diffracted pattern shows alternate dark and
light bands on the screen.
• X-ray diffraction pattern of polymer contain both sharp as
well as defused bands.
• Sharp bands correspond to crystalline orderly regions and
defused bands correspond to amorphous regions

33. • Schematic diagram of X-ray diffraction pattern

34. • Crystalline structure is regular arrangement of atoms.
Polymer contains both crystalline and amorphous phase
within arranged randomly.
• When beam of X-ray passed through the polymer sample,
some of the regularly arranged atoms reflect the x-ray beam
constructively and produce enhanced intense pattern.
• Amorphous samples gives sharp arcs since the intensity of
emerging rays are more, where as for crystalline samples, the
incident rays get scattered.
• Arc length of diffraction pattern depends on orientation. If the
sample is highly crystalline, smaller will be the arc length.

35. • X-ray diffraction pattern of (a) amorphous sample and
(b) Semi crystalline polymer sample

36. CRYSTALLINITY CALCULATIONS
• The crystallinity is calculated by separating intensities due to
amorphous and crystalline phase on diffraction phase.
• Computer aided curve resolving technique is used to separate
crystalline and amorphous phases of diffracted graph.
• After separation, total area of diffracted pattern is divided into
crystalline (Ac) and amorphous(Aa).
• Small Angle X-ray Scattering (SAXS), Infrared Spectroscopy, can
also be used to measure crystallinity.
• Percentage of crystallinity Xc % is measured as ratio of crystalline
area to total area.
XC = AC /(AC +AA)
AC = Area of crystalline phase
AA = Area of amorphous phase

37. PROPERTIES AFFECTED BY
CRYSTALLINITY
• HARDNESS : The more crystalline a polymer, the more
regularly aligned its chains. Increasing the degree of
crystallinity increases hardness and density.
• YOUNG’S MODULUS : There is steep increase in young's
modulus with increase in amount of crystalline component in
the sample.
• TENSILE STRENGTH : This property is directly proportional
to the crystalline structure of a component.
• PERMEABILITY : Crystalline polymers are far less
permeable than the amorphous variety. It means as the
polymer crystallinity increases with decrease in permeability.