chapter 9. analysis and testings of polymer 9.1. chemical...
TRANSCRIPT
Sem 1 2006/2007
Fisika Polimer
Ariadne L. Juwono
Chapter 9. Analysis and testings of polymer
9.1. Chemical analysis of polymers
9.2. Spectroscopic methods
9.3. X-Ray diffraction analysis
9.4. Microscopy
9.5. Thermal analysis
9.6. Physical testing
Sem 1 2006/2007
Fisika Polimer
Ariadne L. Juwono
9.1. Chemical analysis of polymers
There are 2 common techniques for analyzing low-molecular-weightpolymers of reactions of polymers.
Mass spectroscopy
The polymer is reacted to form low-molecular-weight fragments that are condensed at liquid-air temperature. Then, the fragments are Volatilized, ionized, and separated based on the mass and charge by the action of electric and magnetic fields in a typical mass spectrometer analysis.
Gas Chromatography
A method of separation in which gaseous or vaporized components are distributed between a moving gas phase and a fixed liquid phase or solid absorbance. The components pass through chromatography column and are detected their number, nature, and amounts.
Sem 1 2006/2007
Fisika Polimer
Ariadne L. Juwono
9.2.1. Infrared spectroscopy (IR)
9.2. Spectroscopic methods
Infrared spectroscopy works because chemical bonds have specific frequencies at which they vibrate corresponding to energy levels. The resonant frequencies or vibrational frequencies are determined by the shape of the molecular potential energy surfaces, the masses of the atoms and, eventually by the associated vibronic coupling. In order for a vibrational mode in a molecule to be IR active, it must be associated with changes in the permanent dipole.
Thus, the frequency of the vibrations can be associated with a particular bond type.Simple diatomic molecules have only one bond, which may stretch.
Sem 1 2006/2007
Fisika Polimer
Ariadne L. Juwono
More complex molecules may have many bonds, and vibrations can be conjugated, leading to infrared absorptions at characteristicfrequencies that may be related to chemical groups. The atoms in a CH2 group, commonly found in organic compounds can vibrate in six different ways, symmetrical and asymmetrical stretching, scissoring, rocking, wagging and twisting.
In order to measure a sample, a beam of infrared light is passedthrough the sample, and the amount of energy absorbed at each wavelength is recorded. This may be done by scanning through thespectrum with a monochromatic beam, which changes in wavelength over time, or by using a Fourier transform instrument to measure all wavelengths at once.
Sem 1 2006/2007
Fisika Polimer
Ariadne L. Juwono
From this, a transmittance or absorbance spectrum may be plotted, which shows at which wavelengths the sample absorbs the IR, and allows an interpretation of which bonds are present. This technique works almost exclusively on covalent bonds, and as such is of most use in organic chemistry. Clear spectra are obtained from samples with few IR active bonds and high levels of purity. More complexmolecular structures lead to more absorption bands and more complex spectra. The technique has been used for the characterization of very complex mixtures however.
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Fisika Polimer
Ariadne L. Juwono
• Gaseous samples require little preparation beyond purification, but a sample cell with a long pathlength (typically 5-10 cm) is used as gases show relatively weak absorbances.• Liquid samples can be sandwiched between two plates of a high purity salt (commonly sodium chloride, or common salt, although a number of other salts such as potassium bromide or calcium fluorideare also used). The plates are transparent to the infrared light and will not introduce any lines onto the spectra. Some salt plates are highly soluble in water, and so the sample, washing reagents and the like must be anhydrous (without water).
Sample preparation
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Fisika Polimer
Ariadne L. Juwono
• Solid samples can be prepared in two major ways.
The first is to crush the sample with a mulling agent (usually nujol) in a marble or agate mortar, with a pestle. A thin film of the mull is applied onto salt plates and measured.
The second method is to grind a quantity of the sample with a specially purified salt (usually potassium bromide) finely (to remove scattering effects from large crystals). This powder mixture is then crushed in a mechanical die press to form a translucent pellet through which the beam of the spectrometer can pass.
Sem 1 2006/2007
Fisika Polimer
Ariadne L. Juwono
Sem 1 2006/2007
Fisika Polimer
Ariadne L. Juwono
Sem 1 2006/2007
Fisika Polimer
Ariadne L. Juwono
Sem 1 2006/2007
Fisika Polimer
Ariadne L. Juwono
9.2.2. Nuclear magnetic resonance spectroscopy (NMR)
Nuclear magnetic resonance (NMR) is a physical phenomenon based upon the magnetic properties of an atom's nucleus. All nuclei that contain odd numbers of nucleons and some that contain even numbers of nucleons have an intrinsic magnetic moment. The most commonly used nuclei are hydrogen-1 and carbon-13, although certain isotopes of many other elements nuclei can also be observed. NMR studies a magnetic nucleus, like that of a hydrogen atom (protium being the most receptive isotope at natural abundance) by aligning it with a very powerful external magnetic field and perturbing this alignment using an electromagnetic field. The response to the field by perturbing is what is exploited in nuclear magnetic resonance spectroscopy and magnetic resonance imaging.
Sem 1 2006/2007
Fisika Polimer
Ariadne L. Juwono
NMR spectroscopy is one of the principal techniques used to obtain physical, chemical, electronic and structural information about a molecule. It is the most powerful technique that can provide detailed information on the three-dimensional structure of biological molecules in solution. Also, nuclear magnetic resonance is one of the techniques that has been used to build elementary quantum computers.
Spin angular momentum is a vector quantity. The z component of which, denoted Iz, is quantized:
This magnetic moment is intrinsically related to I with a proportionality constant γ, called the gyromagnetic ratio:
Sem 1 2006/2007
Fisika Polimer
Ariadne L. Juwono
The energy of a magnetic moment µ when in a magnetic field B0:
The frequency of electromagnetic radiation required to produce resonance of a specific nucleus in a field B is:
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Ariadne L. Juwono
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Chemical shifts of NMR
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9.2.2. Electron paramagnetic resonance spectroscopy (EPR/ESR)
Electron Paramagnetic Resonance (EPR) or Electron Spin Resonance (ESR) is a spectroscopic technique which detects species that have unpaired electrons, generally meaning that the molecule in question is a free radical, if it is an organic molecule, or that it has transition metal ions if it is an inorganic complex. Because most stable molecules have a closed-shell configuration without a suitable unpaired spin, the technique is less widely used than nuclear magnetic resonance (NMR).
The basic physical concepts of the technique are analogous to those of NMR, but instead of the spins of the atom's nuclei, electron spins are excited. Because of the difference in mass between nuclei and electrons, weaker magnetic fields and higher frequencies are used, compared to NMR. For electrons in a magnetic field of 0.3 tesla, spin resonance occurs at around 10 GHz.
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Fisika Polimer
Ariadne L. Juwono
EPR is used in solid-state physics, for the identification and quantification of radicals (i.e., molecules with unpaired electrons), in chemistry, to identify reaction pathways, as well as in biology and medicine for tagging biological spin probes.
Since radicals are very reactive, they do not normally occur in high concentrations in biological environments. With the help of specially designed nonreactive radical molecules that attach to specific sites in a biological cell, it is possible to obtain information on the environment of these so-called spin-label or spin-probe molecules.
Sem 1 2006/2007
Fisika Polimer
Ariadne L. Juwono
An electron has a magnetic moment. When placed in an external magnetic field of strength B0, this magnetic moment can align itself parallel or antiparallel to the external field. The former is a lower energy state than the latter (this is the Zeemaneffect), and the energy separation between the two is ∆E = geµBB0, where ge is the gyromagnetic ratio of the electron (see also the Landég-factor) the ratio of its magnetic dipole moment to its angular momentum, and µB is the Bohr magneton. To move between the two energy levels, the electron can absorb electromagnetic radiation of the correct energy:
∆E = hν = geµBB0
The paramagnetic centre is placed in a magnetic field and the electron caused to resonate between the two states; the energy absorbed as it does so is monitored, and converted into the EPR spectrum.
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Fisika Polimer
Ariadne L. Juwono
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Ariadne L. Juwono
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9.3. X-ray diffraction (XRD)
X-ray crystallography is a technique in crystallography in which the pattern produced by the diffraction of X-rays through the closely spaced lattice of atoms in a crystal is recorded and then analyzed to reveal the nature of that lattice. This generally leads to an understanding of the material and molecular structure of a substance. The spacing in the crystal lattice can be determined using Bragg's law. The electrons that surround the atoms, rather than the atomic nuclei themselves, are the entities that physically interact with the incoming X-ray photons. This technique is widely used in chemistry and biochemistry to determine the structures of an immense variety of molecules, including inorganic compounds, DNA, and proteins. X-ray diffraction is commonly carried out using single crystals of a material, but if these are not available, microcrystalline powdered samples may also be used, although this requires different equipment, gives less information, and is much less straightforward.
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Bragg's Law
nλ = 2d sinθ
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X-ray diffraction pattern from a layered structure vermiculite clay.
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9.4. Microscopy
9.4.1. Light microscopy
9.4.2. Electron microscopy
9.4.3. Scanning electron microscopy (SEM)
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Ariadne L. Juwono
9.5. Thermal analysis
9.5.1. Differential scanning calorimetry (DSC)
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9.5.2. Thermogravimetric analysis (TGA)
9.5.3. Thermomechanical analysis
A method of measuring the weight change of a sample as a function oftemperature, using a sensitive balance. Some application of TGA in the assessment of thermal stability anddecomposition temperature, curing in condensation polymers, composition in distribution in copolymers, and composition of filledpolymers.
This technique measures the mechanical response of a polymersystem as the temperature is changed. The measurements include dilatometry, heat deflection, torsionmodulus, and stress-strain behaviour.
Sem 1 2006/2007
Fisika Polimer
Ariadne L. Juwono
9.5.4. Thermal properties
The most interesting thermal properties is the softening temperatureof plastics. Some measurements to obtain this property are:• Using an indentor under fixed load to penetrate the plastics,• HDT,• Polymer melt of stick temperature test,• Zero-strength temperature test.
Another test is a flammability test to obtain the burning rate.
Sem 1 2006/2007
Fisika Polimer
Ariadne L. Juwono
9.6. Physical testing
9.6.1. Mechanical properties
9.6.1.1. Stress-strain properties
The most informative mechanical measurement is obtained from stress-strain curve in tension. The tensile test is conducted by measuringforce developed as the sample is elongated at constant rate of extension.Another mechanical tests are flexure, compression, and torsion tests.
9.6.1.2. Fatigue tests
9.6.1.3. Impact tests
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Ariadne L. Juwono
9.6.1.3. Impact tests
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Instron machine
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9.6.1.5. Hardness tests
9.6.1.4. Tear resistance
Barcoll hardness tester
Tear resistance test specimen
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Rockwell hardnesstester
Vickers hardness tester
Brinell hardnesstester
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9.6.2. Optical properties
9.6.2.1. Transmittance and reflectance
Transmittance is the major appearance of a transparent materials.Transmittance is the ratio of the intensities of light passing through andlight incident on the material.
Reflectance is the major appearance of an opaque materials.Transmittance is the ratio of the intensities of the reflected and the incident lights.
A translucent substance is one that transmits part and reflects part ofthe light incident on it.
(units : luminous transmittance and luminous reflectance [flux]).
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GlossGloss is the geometrically selective reflectance of a surface responsible for its shinny of lustrous appearance.
HazeHaze is the percentage of transmitted light that is passing through thespecimen deviates from the incident beam by forward scattering.
TransparencyTransparency is the state permitting perception of objects through or beyond the specimen.A sample of low transparency may not exhibit haze, but objects seen through it will appear blurred of distorted.
These properties are “objective” physical properties that belong to the materials.
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9.6.2.2. Color
Color is the subjective sensation in the brain resulting from the perceptionof those aspects of the appearance of objects that result from thespectral composition of the light reaching the eye.Color depends largely on the spectral power distribution of a light source,the spectral reflectance of the illuminated object, and the spectralresponse curves of the eye.
Color technology includes visual perception, the measurement of colorand color difference, color matching, and the coloring of plastics.
Sem 1 2006/2007
Fisika Polimer
Ariadne L. Juwono
9.6.3. Electrical properties
9.6.3.1. Dielectric constant, dielectric strength and loss factor
Dielectric constant of an insulating material is the ration of the capacitiesof a parallel plate measured w or w/o the dielectric material placed between the plates.
Loss angle, δ, is a phase difference between changes in the field andthe polarization.
Power factor ≡ sin δ, dissipation factor ≡ tan δ.Loss factor ≡ dielectric constant X power factor.
For insulators, high voltage decreases the resistance and deterioratesthe dielectric.
Sem 1 2006/2007
Fisika Polimer
Ariadne L. Juwono
9.6.3.2. Resistivity
In most polymers, the resistance is very high. Both surface and volumeresistivity are important for applications of polymers as insulatingmaterials.
9.6.3.3. Electronic properties
Polymers are possible to produce unusual electronic properties.These include electrical conductivity, charge storage, energy transfer,and, contact electrification (triboelectricity). Examples: PE, PET, PVF
Conductivity of some polymer can have 20 X conductivity usual polymer.Examples: polyacetylene, poly-p-phenylene.
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Ariadne L. Juwono
9.6.4. Chemical properties
9.6.4.1. Resistance to solvent
The effect of solvents on polymers may take several forms:a. Solubility,b. Swelling (inc absorption of water),c. Environmental stress cracking (materials fail by mechanical stress
in the presence of an organic liquid or an aqueous solution),d. Craszing (material fails by the development of small cracks in the
presence of an organic liquid or its vapour, w or w/o mechanicalstress.
9.6.4.2. Vapour permeability
The permeability of a polymer to a gas or vapour is the product of the solubility of the gas or vapour in the polymer and its diffusion
coefficient. Permeability ∝ rate of transfer vapour through unit thicknessof the polymer in film film/m2 and ∆p.
Sem 1 2006/2007
Fisika Polimer
Ariadne L. Juwono
9.6.4.3. Weathering
Artificial weathering → for convenience and reproducibility.The real weathering test takes a long time and expensive.