morphology of polymer

1. CHAPTER FOUR
crystalline and amorphous
morphology of polymer

2. Amorphous polymer Morphology
 The bulk state, sometimes called the condensed or solid
state, includes both amorphous and crystalline polymers
 Morphology : is a term used to describe the form or structure
of the polymer chains of thermoplastic materials when they
are in their frozen or solid state.
 For thermoplastic resins, there are two basic morphologies:
AMORPHOUS and SEMI-CRYSTALLINE
 Amorphous polymers appear random and jumbled when
allowed to cool in a relaxed state. They appear very
similarly to their molten state, only the molecules are closer
together.
 They can be described as being similar to a large pot of
spaghetti noodles.

3. Amorphous polymer Morphology
Amorphous materials are like cooked ramen noodles in
that there is a random arrangement of the molecules and
there are no crystals present to prevent the chains from
flowing

4. Amorphous polymer Morphology
 It is important to remember that both materials have the
random, unordered arrangement when molten.
 amorphous polymers exhibit different physical and
mechanical behavior.
 Depending on temperature and structure, At low temperatures,
glassy, hard, and brittle. As the temperature is raised, they go
through the glass–rubber transition.
 Above Tg, cross-linked amorphous polymers exhibit rubber
elasticity. An example is styrene–butadiene rubber (SBR)
 An amorphous polymer does not exhibit a crystalline X-
ray diffraction pattern, and it does not have a first-order
melting transition.

5. Amorphous polymer Morphology
Example :
Polyvinyl Chloride (PVC)
General Purpose Polystyrene (GPPS)
Polycarbonate (PC)
Polymethylmethacrylate (PMMA or Acrylic)
Acrylonitrile Butadiene Styrene (ABS a terpolymer)

6. Amorphous polymer Morphology
 Older literature referred to the amorphous state as a
liquid state.
 However, polystyrene or poly(methyl methacrylate) at
room temperature are glassy.
 Today, amorphous polymers in the glassy state are better
called amorphous solids.
 >Tg, if the polymer is amorphous and linear, it will flow,
albeit the viscosity may be very high.
 For most materials, we are concerned with the melting
point and boiling point.

7. Glass Transition Temperature (Tg)
 The glass transition temperature (Tg) is defined as the
temperature at which the polymer softens because of the onset
of long-range coordinated molecular motion.
 For thermoplastic materials, we are concerned with:
o Glass Transition Temperature
o Melting Temperature
 In amorphous materials, it is the temperature at which
material behaves more rubber-like than glass-like. Above Tg:
 The material stretches further when pulled (more ductile)
 The material absorbs more impact energy without fracturing
when struck
 When the material does fail, it fails in a ductile manner as
opposed to a brittle manner

8. The sample experienced a brittle
failure The material broke like glass
The sample broke in a ductile manner.
The material yielded (stretched) before
failure. The material behaved more
like a rubber

9. Glass Transition Temperature (Tg)
example: Polyethylene and Polypropylene both have low
Tg’s. They are way below room temperature. That is why
milk jugs and yogurt containers are flexible when you take
them out of the refrigerator.
Amorphous materials don’t truly have a Tm. They just
continue to soften more until they behave more like a liquid.
The molecules absorb enough energy and move far
enough apart (increase the free volume) that the material
can flow.

10. Amorphous polymer

11. Melt Temperature (Tm)
 When we refer to the melt temperature for amorphous materials, it
is usually the temperature at which we can process it.
 For S/C materials, the Tm is the temperature at which the crystals
melt.
 If the polymer is crystalline Tm>Tg
ideal temperature for
growing crystals
is approximately 2/3
of the way between the Tg
and the Tm.
 Not in all cases, but in
many, the degradation temperature for S/C materials is not
much higher than the melt temperature.

12. Melting vs. Glass Transition Temp.
What factors affect Tm and Tg?
Both Tm and Tg increase with
increasing chain stiffness
 Regularity (tacticity) affects
Tm only

13. • The mechanical properties of polymers are
sensitive to temperature changes
Figure 1 Modulus versus temperature for an
amorphous thermoplastic

14. Figure 2. Modulus versus temperature for crystalline
thermoplastics

15. Figure 3. Modulus versus temperature for thermosetting
resins

16. Figure 4 Modulus versus temperature for a reinforced
crystalline thermoplastic

17. crystalline state
• Both amorphous and crystalline areas in can exist in
the same polymer.
• Areas in polymer where chains packed in regular
way.
• X-ray scattering and electron microscopy have shown
that the crystallites are made up of lamellae which,in
turn, are built-up of folded polymer chains
Schematic representation of
(a) fold plane showing regular chain folding,
(b) ideal stacking of lamellar crystals,
(c) interlamellar amorphous model
(d) fringed micelle model of randomly distributed crystallites
(Plastic Technology Handbook)

18. crystalline state
• The crystalline state is defined as one that diffracts X-
rays and exhibits the first-order transition known as
melting.
A first-order transition normally has a discontinuity in the volume–
temperature dependence
crystalline
region
amorphous
region

19. crystalline state
 Polymers crystallized in the bulk, however, are never
totally crystalline, a consequence of their long-chain
nature and subsequent entanglements.
 Crystallinity occurs when linear polymer chains are
structurally oriented in a uniform three dimensional
matrix.
 Three factors that influence the degree of crystallinity
are:
i) Chain length
ii) Chain branching
iii) Interchain bonding
iv) the rate of cooling during solidification

20. Melting temperature observing
 Non regularity of structure first decreases the melting
temperature and finally prevents crystallinity.
 crystalline materials have sharp X-ray pattern
characteristic at Tm
 Ideally, the melting temperature constitutes a first order
phase change, should give a discontinuity in the volume,
with a connected sharp melting point.
 Due to polymer imperfections or very small size of the
crystallites in bulk most polymers melt over a range of
several degrees

21. Specific volume–temperature relations for linear polyethylene

22. The melting temperature is usually taken as the
temperature at which the last trace of crystallinity
disappears.
melting temperature can be determined thermally.
using the differential scanning calorimeter (DSC)
gives the heat of fusion as well as the melting
temperature
Specific volume–temperature relations for linear polyethylene. Open
circles, specimen cooled relatively rapidly from the melt to room
temperature; solid circles, specimen crystallized at 130°C for 40
days, then cooled to room temperature

23. methods for determining the percent
crystallinity
 most crystallizing polymers are semicrystalline; that is, a
certain fraction of the material is amorphous, while the
remainder is crys-talline
 The reason why polymers fail to attain 100% crystallinity
is kinetic, resulting from the inability of the polymer
chains to completely disentangle and line up properly in
a finite period of cooling or annealing.
1. Determination of the heat of fusion of the whole sample
by calorimetric methods such as DSC

24. DSC of a commercial isotactic polypropylene sample
scanning calorimetry (DSC) which measures the heat flow
into or from a sample as it is either heated, cooled
heat of fusion ∆Hf is the area under the peak

25. 2. Determination of the density of the crystalline portion via
X-ray analysis of the crystal structure, and determining
the theoretical density of a 100% crystalline material.

26. ρ exptl experimental density
ρ amorph density
ρ100% cryst crystalline portions density

29. Semi-Crystalline polymer
summery

30. METHODS OF DETERMINING CRYSTAL
STRUCTURE
 There are four basic methods in wide use for the study of
polymer crystallinity: X-ray diffraction, electron
diffraction, infrared absorption, and Raman spectra
X-Ray Methods
 crystalline substances must to act as a three-dimensional
diffraction grating for X-rays
Bragg equation :
By considering crystals as reflection gratings.
λ the X-ray wavelength
θ the angle between the X-ray beam and these atomic planes
n the order of diffraction

31. X-Ray Methods
 d and λ are of the order of 1 Å. Such an analysis from a
single crystal produces a series of spots.
 However, not every crystalline substance can be
obtained in the form of macroscopic crystals. This led to
the Debye–Scherrer
 for powdered crystalline solids or polycrystalline
specimens.
 The crystals are oriented at random so the spots become
cones of diffracted beams.
 can be recorded either as circles on a flat photographic
plate or as arcs on a strip of film encircling the specimen

32. X-Ray Methods

33. The angle RSX is 2θ, where θ is the angle of incidence
on a set of crystal plane
X-Ray Methods

34. X-Ray Methods
Diffraction spot or line depends on
the scattering power of the individual atoms( the
number of electrons in the atom)
the arrangement of the atoms with regard to the
crystal planes
the angle of reflection
the number of crystallographically equivalent sets
of planes contributing
the amplitude of the thermal vibrations of the
atoms.
 intensities of the spots or arcs and their positions are
required to calculate the crystal lattice

35. Electron Diffraction of Single Crystals
 Electron diffraction studies utilize single crystals.
 Since the polymer chains in single crystals are most
often oriented perpendicular to their large flat
surface, diffraction patterns perpendicular to the 001
plane are common.
 Tilting of the sample yields diffraction from other
planes. The interpretation of the spots obtained
utilizes Bragg’s law in a manner identical to that of
X-rays.

36. Electron Diffraction of Single Crystals
Required:
Evacuated diffraction tube that contains an electron
gun accelerating anode to provide a known energy to
the electrons in the beam
crystalline targets and screen

37. Infrared Absorption
The information that infrared absorption spectra yield about
crystallinity:
1. “crystallization sensitive bands.” The intensities of
these bands vary with the degree of crystallinity and
have been used as a measure of the crystallinity.
2. By measuring the polarized infrared spectra of oriented
semicrystalline polymers, information about both the
molecular and crystal structure can be obtained. Both
uniaxially and biaxially oriented samples can be studied.
3. The regular arrangement of polymer molecules in a
crystalline region can be treated theoretically, utilizing
the symmetry properties of the chain or crystal

38. Raman Spectra
1. Since the selection rules for Raman and infrared spectra are
different, Raman spectra yield information complementary to
the infrared spectra.
example, the S—S linkages in vulcanized rubber and the C=C
bonds yield strong Raman spectra but are very weak or
unobservable in infrared spectra.
2. Since the Raman spectrum is a scattering phenomenon,
whereas the infrared methods depend on transmission, small
bulk, powdered, or turbid samples can be employed.
3. the Raman spectra provide information equivalent to very low-
frequency measurements, even lower than 10 cm-1. Such low
frequency studies provide information on lattice vibrations.

39. Polymer Single Crystals
 crystallization is an allayment of molecular chain and
folding of chain to get order region
polymer single crystal formation
1) From precipitate (from dilute solutions, they form
lamellar-shaped single crystals)
2) From melt

40. Polymer Single Crystals
1) From precipitate
 Ideas about polymer crystallinity start by preparing
single crystals of polyethylene.
 These were made by precipitation from extremely dilute
solutions of hot xylene.
 These crystals tended to be diamond-shaped and of the
order of 100 to 200 Å thick

41. 2. CRYSTALLIZATION FROM THE MELT
usually super cool to greater or lesser extents
crystallization temperature may be 10 to 20°C lower
than the melting temperature
Supercooling arises from the extra free energy required
to align chain segments
spherulites are really spherical in shape only during
the initial stages of crystallization

42. Spherulites of low-density polyethylene

43. Spherulites of low-density polyethylene

44. The evolution of the spherulite

45. KINETICS OF CRYSTALLIZATION
 Lamellae formation from bulk, are organized into
spherulites or their predecessor structures, hedrites
 volume changes on melting; usually increasing
 the isothermal crystallization of poly(ethylene oxide) as
determined dilatometrically:

46. The rate of crystallization increases as the temperature
is decreased.
This follows from the fact that the driving force
increases as the sample is supercooled

47. KINETICS OF CRYSTALLIZATION
 Crystallization rates may also be observed
microscopically :
 by measuring the growth of the spherulites as a function
of time
 The isothermal radial(at 125°C) growth of the spherulites
is usually observed to be linear

48. KINETICS OF CRYSTALLIZATION
 The increase in rate of crystallization as the temperature
is lowered is controlled by the increase in the driving
force
 temperature is lowered still
further, molecular motion
becomes sluggish as the glass
transition is approached, and
the crystallization rate
decreases again.
linear growth rate versus crystallization temperature for poly(ethylene terephthalate) .Tf =
265°C, and Tg = 67°C, at which points the rates of crystallization are theoretically zero.

49. KINETICS OF CRYSTALLIZATION
 Below Tg, the rate of crystallization effectively becomes
zero.
rule-of-thumb
 for determining a good temperature to crystallize a
polymer
 if the melting temperature(Tf) is known. where Tf is in
absolute temperature. At (8/9) Tf the polymer is
supposed to crystallize readily.

50. Free energy of polymer crystallization
 The classic melting temperature is usually taken
where the last trace of crystallinity disappears, point
A in Figure b.

51. ∆Gf The free energy of fusion
∆Hf the molar enthalpy
∆Sf entropy of fusion
 At the melting temperature, ∆Gf equals zero, and
 smaller entropy or a larger enthalpy term raises Tf.
 the relative changes in ∆Hf and ∆Sf in going from the
amorphous state to the crystalline state determine the
melting temperature of the polymer
Free energy of polymer crystallization

52. Properties
Amorphous vs. S/C
 Chemical Resistance
 Optical Properties
 Impact Resistance
 Viscosity
 Weather Resistance
 Shrinkage

53. Chemical Resistance
 Plastic materials are used in virtually and contact with a
wide variety of chemical substances that they need to
resist
As a general rule S/C materials are more resistant to
chemical attack than amorphous materials.
It is more difficult for the chemical media to
penetrate the dense crystalline structure to damage
the polymer chains.
Polyethylene is used to store everything from
detergent to mineral spirits to gasoline.

54.  But Polypropylene is only slightly less chemically
resistant than Polyethylene.
 Of the amorphous materials PVC is probably the best in
chemical resistance, mainly due to the large chlorine
atom that helps to protect the main polymer chain.
 Polycarbonate, Acrylic, Polystyrene and the other
styrenics are all very susceptible to chemical attack,
especially to mineral spirits and solvents like lacquer and
paint thinners, alcohol, and gasoline.

55. Optical Properties
Amorphous materials have a much higher clarity
than S/C materials. and can be translucent/optical
quality.
If the crystallinity is disrupted by adding a copolymer
or other additive or by quenching the material so
quickly the crystals don’t have enough time to form,
the material may appear somewhat clear.
Amorphous Acrylic more commonly known as
Plexiglas and Polycarbonate used in safety glasses
and optical lenses are far superior in terms of optical
properties

56. Impact Resistance
 The material structure determines the impact resistance,
but as a general rule, S/C materials are more brittle
than Amorphous.
 The chain portions that are folded up in the crystal
restrict the polymer chains as they try to move past one
another when a force is applied making the S/C materials
more brittle.
 Polycarbonate is used in safety glasses, but General
Purpose Polystyrene (GPPS) is very brittle – both are
amorphous, but have different polymer structures.
 On the S/C side, Polyethylene is very ductile at room
temperature because it is above its Tg, but Nylon and
Polyester are brittle at room temperature.

57. Viscosity
 S/C materials by their very nature flow more easily than
Amorphous materials.
 The same mechanism that allows the material to fold up
into dense crystals allows the polymer chains to slide
past one another easily in the melted state.

58. Weather Resistance
 The most damaging aspect of weathering is generally
considered to be Ultraviolet light.
 The UV light breaks down the chains of the polymers
making them more brittle, causing colors to fade or
yellow, and causing additives in the polymers to migrate
to the surface (chalking).

59.  Amorphous polymers have better chemical resistance to
weathering effects than S/C polymers.
 The crystals in the S/C polymers diffract the light so the
UV rays spend more time within the polymer structure
and do more damage.
 The clear amorphous polymers allow the damaging
radiation to pass through doing less damage.

60. Shrinkage
 Because they fold up into crystal structures, S/C
materials have higher shrinkage rates when compared to
Amorphous materials.
 In injection molding most amorphous materials will
shrink between 0.003-0.007 in/in (0.3-0.7%)
 S/C materials shrink differently depending upon the
level of crystallinity that they achieve.
 Some will shrink over 0.025 in/in depending on
processing variables, part thickness, and additives.

61. Broad soflening range
thermal agitation of the molecules breaks down the weak
secondary bonds.
The rate at which this occurs throughout the formless
structure varies producing broad temperature range for
softening
Sharp melting point
the regular close-packed structure results in most of the
secondary bonds being broken down at the same time.

62. Crystalline vs Amorphous Thermoplastics
Crystalline (actually usually semi-crystalline):
Atomic bonds regular and repeated
Have a defined melting point Tm
Can contain some degree of amorphous polymer
Usually translucent to opaque

63. Amorphous
 Extensive chain branching
 All thermosets are amorphous
 Exhibit glass tranistion temperatures Tg
 Below Tg, polymer acts stiff and rigid
 Above Tg, polymer acts soft and rubbery
 Melt or liquefy over extended temperature range near Tg.
 Don’t have distinct Tm like crystalline polymers.
 Thermosetting polymers do not melt but degrade above Tg

65. Examples o amorphous and crystalline
thermoplastics
Amorphous
• Polyvinyl Chloride (PVC)
• Polystyrene (PS)
• Polycarbonate (PC)
• Acrylic (PMMA)
• Acrylonitrile-butadiene-
styrene (ABS)
• Polyphenylene (PPO)
Crystalline
• Polyethylene (PE)
• Polypropylene (PP)
• Polyamide (PA)
• Acetal (POM)
• Polyester (PEW, PBTF’)
• Fluorocarbons (PTFE,
• PFA, FEP and ETFE)