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MM091372
POLYMER AND COMPOSITE MATERIALCredit: 3 SKS
Semester: 7
LECTURE 7DEPARTMENT OF MATERIALS AND METALLURGICAL ENGINEERING
FACULTY OF INDUSTRIAL ENGINEERINGINSTITUT TEKNOLOGI SEPULUH NOPEMBER (ITS) SURABAYA
Dr. Eng. Hosta Ardhyananta, S.T., M.Sc.
NIP. 19801207 2005 01 1 004
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MEASUREMENT OFMOLECULAR WEIGHT AND SIZE
Molecular weights of polymers can be determinedby chemical or physical methods of functional-groupanalysis, by measurement of the colligativeproperties, light scattering, or ultracentrifugation, orby measurement of dilute-solution viscosity
Absolute measurement: molecular weights can becalculated without reference to calibration by
another method
Dilute solution viscosity is not a direct measure ofmolecular weight
Require solubility of the polymer
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To understand the size of polymer : explain theschematic illustration below
small ???
BIG ???
light ???
HEAVY ???
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End group analysis
Require known number of determinable groups permolecule
The long chain limits
Count the number of molecules in a given weight
It yield number-average molecular weight
Insensitive at high molecular weight
Condensation polymers: End-group analysisinvolves chemical methods for functional groups.Carboxyl groups titrated with base. Amino groupstitrated with acid. Hydroxyl groups by reagent orinfrared spectroscopy. Limited by insolubility of the
polymer
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Addition polymers: no general procedure becausevariety of type and origin. Analysis may be made for
Initiator containing identifiable functional groups,elements, or radioactive atoms, vinyl group
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Colligative property measurement Activity equal to its mole fraction
Colligative property based on vapor-pressure
lowering, boiling-point elevation (ebulliometry),freezing-point depression (cryoscopy), osmoticpressure (osmometry)
Number-average molecular weight: typical polymersconsist of mixtures of many molecular species,molecular weight yield average values
=
=
=
==~
1
~
1
~
1 i
i
i
ii
i
i
n
N
NM
N
wM
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Concentration dependence of the colligativeproperties is developed in terms of the osmotic
pressure Vapor-phase osmometry: temperature difference
from different rates of solvent evaporation andcondensation
Ebulliometry: boiling point of the polymer solution iscompared with pure solvent
Cryoscopy: freezing-point depression
Membrane osmometry: osmotic pressure
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Light scattering
The scattering of light occurs whenever a beam oflight encounters matter
Determination of polymer molecular weights by lightscattering
Refractive index , n
The amplitude of the scattered light is proportionalto the polarizability and mass of the scatteringparticle
The intensity of scattering is proportional to thesquare of the particle mass
The heavier molecules contribute more to the
scattering than the light ones
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i
i
i
i
ii
i
ii
i
ii
w
MN
MN
Mwc
Mc
M
=
=
=
====
1
1
2
1
1
Weight-average molecular weight
Average-Mw is greater than average-Mn
Average-Mw/Mn is a measure of polydispersity
Average-Mw is sensitive of high-molecular-weight
species
Average-Mn is influenced at the lower end of themolecular weight distribution
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Sample preparation
Calibration
Treatment of data
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Ultracentrifugation
Determining the molecular weight of high polymer
Protein molecule, biological material
Centrifugation by high speed rotation
The concentration of polymer is determined byoptical methods based on measurements of
refractive index or absorption Solvents must be chosen for difference from the
polymer in both density (to ensure sedimentation)
and refractive index (to allow measurement)
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Solution viscosity and molecular size
Measure the size or extension in space of polymermolecules
Molecular weight for linear polymers
Comparing efflux time , t , flow
Viscosity of a polymer is proportional to its molecular
weight Viscosity-average molecular weight
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Gel Permeation Chromatography
Gel permeation chromatography is a powerful new
separation technique Discovery by Moore 1964
The separation takes place in a chromatographic
column filled with beads of a rigid porous gel ; highlycrosslinked porous polystyrene and porous glass ;the pores in gels are the same size as thedimensions of polymer molecules
A sample of a dilute polymer solution is introducedinto a solvent stream flowing through the column
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The dissolved polymer molecules flow past theporous beads, they can diffuse into the internal pore
structure depending on their size and the pore-sizedistribution of the gel
Larger molecules can enter a small fraction of the
internal portion of the gel, or are excluded; smallerpolymer molecules penetrate a larger fraction of theinterior of the gel
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The larger the molecule, the less time it spendsinside the gel and the sooner it flows through thecolumn
The different molecular species are eluted from thecolumn in order of their molecular size asdistinguished from their molecular weight, the
largest emerging first
A specific column or set of column (with gels ofdiffering pore size) is calibrated empirically to give
such a relationship, a plot of amount of soluteversus retention volume (the chromatogram) can beconverted into a molecular-size distribution curve
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Calibration: commercial narrow-distributionpolystyrene
Gel permeation chromatography has valuable forsystem from low to very high molecular weight
Wide variety of solvent and polymer, depending on
the type of gel
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Polyelectrolytes Polymers with ionizable group are termed
polyelectrolytes
Polyacids such as poly(acrylic acid) and hydrolyzedcopolymers of maleic anhydride
Polybases such as poly(vinyl amine) and poly(4-
vinyl pyridine) Polyphosphates, nucleic acids, proteins
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Because of the preponderance of small ions, thecolligative properties of polyelectrolytes in ionizing
solvents measure counterion activities rather thanmolecular weight
In the presence of added salt, correct molecularweights of polyelectrolytes can be measured bymembrane osmometry, since the small ions canequilibrate across the membrane
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ANALYSIS AND TESTING OFPOLYMERS
Methods of physical and chemical analysis ofpolymers
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Chemical analysis of polymers
Spectroscopic methods
X-ray diffraction analysis
Microscopy
Thermal analysis
Physical testing Nuclear magnetic and electron paramagnetic
resonance spectroscopy
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Chemical Analysis of Polymers
The chemical analysis of polymers is not basicallydifferent from the analysis of low-molecular-weight
organic compounds Appropriate modification is made to ensure solubility
or the availability of sites for reaction (e.g., insoluble
specimens should be ground to expose a largesurface area)
Chemical analysis of molecule
Chemical reactions of polymers
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Mass spectrometry: polymer is reacted (as in thermaldegradation) to form low-molecular-weight fragmentswhich are condensed at liquid-air temperature. Then,volatilized, ionized, and separated according to mass
and charge by the action of electric and magnetic fields.From the various ionic species found, the structures ofthe low-molecular-weight species can be inferred
Gas chromatography is a method of separation in which
gaseous or vaporized components are distributedbetween a moving gas phase and a fixed liquid phase orsolid adsorbent. Adsorption or elution steps taking placeat a specific rate for each component, separation isachieved. Chromatographic column. Detector signal isproportional to the concentration of the dilute componentin the gas stream.
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Infrared spectroscopy Emission or absorption spectra arise when
molecules undergo transitions between quantum
states corresponding to two different internalenergies
The energy differenceE between the states isrelated to the frequencyE = hv
Infrared frequencies in the wavelength range 1 50
m are associated with molecular vibration andvibration-rotation spectra
A molecule containing N atoms has 3N normalvibration modes, including rotational andtranslational motions of the entire molecule
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Raman spectrum : frequency of visible light is
altered in the scattering process by the absorptionor emission of energy produced by changes inmolecular vibration and vibration-rotation quantum
states In polymers, the infrared absorption spectrum is
surprisingly simple considering the large number ofatoms involved. This simplicity results first frommany vibration have almost same frequency andappear in the same spectrum; second from the strictselection rules that prevent vibrations from causing
absorptions The approximate wavelengths of some infrared
absorption bands arising from functional group and
atomic vibrations
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Experimental methods Sources : electrically heated silicon carbide or rare
earth oxide rods
Dispersion methods : Both diffraction gratings andprisms of inorganic salts. Prism materials are NaCl
(below 15 m), KBr (below 25 m), CsBr (below 35m), LiF (below 6 m), CaF
2
(below 9 m)
Detectors : sensitive heat detectors such asmultiple-junction thermocouple, pneumatic detector,photocells.
Samples : solid, liquid or gaseous samples. High orlow temperature. Microscope attachments.Transparency to infrared radiation needs special
window materials. Thin samples
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Application to polymers
Detection of chemical groups : C=C at 6.1 m in naturalrubber, carbonyl at 5.8 m and ether at 8.9 m in PMMA,
aromatic structures at 6.2 , 6.7 , 13.3 , 14.4 m inpolystyrene, C-Cl at 14.5 m in PVC , peptide groups at3.0 , 6.1 , 6.5 m in nylon , C-F2 at 8.2 8.3 m in PTFE
Dichroism : molecular vibration leading to infraredabsorption, there is periodic change in electric dipolemoment. The dipole-moment change can be confined tospecific direction. The use of polarized infrared radiation
leads to absorption which is a function of the orientationof the plane of polarization, which is called dichroism asthe dichroic ratio.
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Crystallinity : the infrared absorption spectra ofpolymer in the crystalline and amorphous state can
differ for two reasons. First, Intermolecularinteractions may exist in the crystalline polymerwhich lead to sharpening or splitting bands; Second,conformations may exist leading to band. PET,
Nylon
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Nuclear magnetic and electron paramagneticresonance spectroscopy
Nuclear magnetic resonance (NMR) spectroscopy
detects the motion of nuclei (such as proton) havingnonzero spin
Electron paramagnetic resonance (EPR)
spectroscopy detects free radical species
NMR spectroscopy
To study the chain configuration Developed technique for observing narrow-line or
high-resolution spectra
To study the position of protons
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magnet
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Experimental methods
NMR utilizes the property of spin (angularmomentum and its associated magnetic moment)
possessed by nuclei. Atomic number and mass number are not both even
Nuclei of isotopes H1, C13, O17, and F19
Application of strong magnetic field splits the energylevels into two, representing states with spin paralleland antiparallel
Transition between the states lead to absorption oremission of an energy
00 2 HhvE ==
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Frequency v0 in the microwave region, field ofstrength H0 of the order of 10,000 gauss , is the
magnetic moment of the nucleus The energy change is observed as a resonance
peak or line
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With an assembly of nuclei, the field on any one ismodified by the presence of the others
HL is the local field with a strength of 5 10 gauss
A distribution of local fields usually exist so that theresonance line becomes broadened
Line width and its second moment
)(2 00 LHHhv +=
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If molecular motion is enhanced by working with asolution and by increasing the temperature, narrowline can be observed
Deuterated solvent used, since contribute noresonance
Scale unit : chemical shifts relative to standard
Two scale :scale, zero ; scale, 10.00
Coupling : neighbor, high magnetic field strength
Double resonance or spin decoupling
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A typical NMR spectrum for a simple compound
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NMR spectrum of polycarbonate
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NMR development, double resonance or spin decoupling
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EPR spectroscopy
Detection of free radical
Magnetic moment, arising from the presence ofunpaired electron
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X-ray diffraction analysis
X-ray diffraction method investigate orderarrangement of atom through the interaction ofelectromagnetic radiation to give interference effectwith structure comparable in size to the wavelengthof the radiation.
The wavelengths of x-rays are comparable tointeratomic distances in crystals
Polymer single crystals are too small for x-raydiffraction experiments. The crystal structure isusually determined from a fiber drawn of the
polymer. Because of the alignment of the crystallineregions with the long axes of the molecules parallelto the fiber axis. Rotation pattern from a single
crystal
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Chain conformations : atoms regularly spaced alonghelices. Helical structures
Chain packing : crystallinity
Disorder in the crystal structure : defect, distortion
Orientation
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Microscopy
Light and electron microscopy
Light microscopy
Reflected-light microscopy for examining the textureof solid polymer
Thin film examining by transmitted light
Polarized microscopy : ability of crystalline materialto rotate the plane of polarized light. Spherulitestructure. Crystalline melting point
Phase-contrast microscopy : involving differences inrefractive index
Interference microscopy : low thickness specimen
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Electron microscopy and electron diffraction
Resolution of smaller object Morphology of crystalline polymer
Light
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Scanning electron microscopy
Beam of electron scanning across the surface of
specimen Conducting film
Secondary electrons, backscattered electrons, x-ray
photons
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Thermal analysis
Traditional calorimetric, differential thermal analysis,thermogravimetric analysis, thermomechanicalanalysis, electrical thermal analysis, effluent gasanalysis
Enthalpy changes associated with heating,
annealing, crystallizing,
Thermall treatment of polymer
Response of system to temperature, including
polymerization, degradation, or other chemicalchanges
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Differential thermal analysis curve
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Thermogravimetric analysis
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Physical testing
Physical properties of polymer
Rheology and viscoelasticity
Stress-strain properties in tension
Measuring force developed as the sample iselongated at constant rate of extension
Modulus or stiffness (slope of the curve), yield stress,strength, elongation at break
F
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Polyethylene
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Tensile stress-strain curves for several types of
polymeric material
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Shear, flexure, compression, torsion
Fatigue tests
Cyclic mechanical stress
Various modes of fatigue testing
Alternating tensile and compressive stress
Cyclic flexural stress
Fatigue failure may arise from the absorption ofenergy in a material which is not perfectly elastic.
Manifested as heat, leading to a temperature rise, alower modulus, and rapid failure
Impact tests
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p
Rupture may be divided into two classes: brittle andductile
Brittle rupture occurs if the material behaves elasticallyup to the point of failure , does not yield or draw
In ductile rupture, the specimen is permanently distortednear the point of failure
Brittle failure : lack of distortion of the broken parts
Brittle point or temperature at the onset of brittleness Brittle point is roughly related to the glass transition
temperature
Impact strength : energy required to cause the break.Notched specimen to improve reproducibility
Other forms of impact test : falling objects strike thespecimen
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Tear resistance
Film : packaging application Fatigue tests
Tear strength and tensile strength are closelyrelated
Hardness
Resistance to penetration, scratching, marring
Resistance to penetration by an indentor pressedinto the plastic under a constant load
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Abrasion resistance
Scratch test
Degree of abrasion Friction, hardness and abrasion resistance are
related closely to the viscoelastic properties
Th l ti
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Thermal properties
Softening temperature
Observation of temperature : (a) an indentor underfixed load penetrates into the material (Vicat test) (b)
a bar deforms a specified amount (deflectiontemperature of heat distortion test) (c) samplebecome molten and leaves trail when moved across
a hot metal surface (polymer melt or sticktemperature test) (d) fail in tension under its ownweight (zero strength temperature test)
Flammability
Burning rate
Self-extinguishing : removal of an external flame
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heat
O i l i
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Optical properties
Transmittance and reflectance
Transparent : does not scatter light
Transmittance : ratio of the intensities of lightpassing through and light incident on the specimen
Opaque : reflect light , does not transmit it
Reflectance : ratio of the intensities of the reflected
and the incident light
Translucent substance : transmit and reflects light
Transmittance and reflectance may be measured as
a function of the wavelength of light in aspectrophotometer
Luminous transmittance and luminous reflectance
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light light
light
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Color Subjective sensation in the brain resulting from the
perception of the appearance which result from the
spectral composition of the light reaching the eye
Gloss
Geometrically selective reflectance of a surfaceresponsible for its shiny or lustrous appearance
Surface reflectance : specular direction which is the
direction of mirror would reflect light Photoelectric instrument for measuring gloss at a
variety of angles of incidence and reflection
Haze
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Haze
Percentage of transmitted light which in passing throughthe specimen deviates from the incident beam byforward scattering
Hazemeter : light deviating more than 2.5 o from thetransmitted beam direction
The effect of haze is to impart a cloudy or milkyappearance
Transparency
The state permitting perception of objects through or
beyond the specimen Fraction of the normally incident light which is
transmitted without deviation from the primary beamdirection of more than 0.1 o
Electrical properties
Dielectric constant and loss factor
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Dielectric constant and loss factor
Dielectric constant of an insulating material is the ratio ofthe capacities
The difference is due to the polarization of the dielectric
Loss factor is proportional to the energy absorbed percycle by the dielectric from the field
Resistivity
Resistance to the flow of direct current
Dielectric strength
Insulator will not sustain an indefinitely high voltage
As the applied voltage is increased, a point is reachedwhere a catastrophic decrease in resistance takes place,
accompanied by a physical breakdown of the dielectric
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electric electric
Electron conduction
Arc resistance
The surface of polymer may become carbonized andconduct current readily when exposed to an electricaldischarge
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Chemical properties
Resistance to solvents
Effect of solvent on polymer
Solubility, swelling, environmental stress cracking,crazing
Vapor permeability Permeability to a gas or vapor
Rate of transfer of vapor through unit thickness
Weathering
Exposure to weather
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chemical chemical
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MORPHOLOGY AND ORDER INCRYSTALLINE POLYMERS
RHEOLOGY AND THEMECHANICAL PROPERTIES OF
POLYMERS
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