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Subject: 26. Electrochemical Techniques
     
26.1  What is pH?

The pH scale determines the degree of acidity or alkalinity of a solution,
but as it involves a single ion activity it can not be measured directly.

pH = - log10 ( gamma H  x  m H )

where gamma H = hydrogen ion single ion activity coefficient
          m H = molality of the hydrogen ion.

As pH can not be directly measured, it is defined operationally according to
the method used to determine it. IUPAC recommend several standardised methods
for the determination of pH in solution in aqueous solutions. There are 
seven primary reference standards that can be used, including 0.05 mol/kg
potassium hydrogen phthalate as the Reference Value Standard. There is an
ongoing debate concerning the relative merits of having a multiple primary
standard scale ( that defines pH using several primary standards, and their
values are determined using a cell without a liquid junction ) or a single
primary standard ( that requires a cell with a liquid junction ). Interested
readers can obtain further information on the debate in [1]. Bates [2], is a 
popular text covering both theory and practise of pH measurement. 
   
26.2  How do pH electrodes work?     

Contributed by Paul Willems , and slightly modified 
by Bruce Hamilton.

The most common type of pH electrodes are the "glass" electrodes. They
consist of a special glass membrane that is sensitive to variations in pH, 
as pH variation also changes the electrical potential across the glass. In 
order to be able to measure this potential, a second electrode, the 
"reference" electrode, is required. Both electrodes can be present in a 
"combined" pH electrode, or two physically-separate electrodes can be used.

The glass electrode consists of a glass shaft on which a bulb of a special
glass is mounted. The inner is usually filled with 3 Mol/Litre aqueous KCl
and sealed. Electrical contact is provided by a silver wire immersed in the 
KCl.

For "combined" electrodes, the glass electrode is surrounded by a concentric
reference electrode. The reference electrode consists of a silver wire in 
contact with the almost-insoluble AgCl. The electrical contact with the meter
is through the silver wire. Contact with the solution being measured is via
a KCl filling solution. To minimise mixing of the solution to be measured and
the filling solution, a porous seal, the diaphragm, is used. This is usually
a small glass sinter, however other methods which allow a slow mixing contact
can also be used, especially for samples with low ionic strength. Besides the
"normal" KCl solutions, often solutions with an increased viscosity, and 
hence lower mixing rate are used. A gel filling can also be used, which 
eliminates the necessity for slow mixing devices. 

In contact with different pH solutions a typical glass electrode gives, when 
compared to the reference electrode, a voltage of about 0 mV at pH 7, 
increasing by 59 mV per pH unit above 7, or decreasing by 59 mV per pH unit 
below 7. Both the slope, and the intercept of the curve between pH and 
generated potential, are temperature dependent. The potential of the 
electrode is approximated by the Nernst equation :

E = E0 - RT log [H+] = E0 + RT pH
Where E is the generated potential, E0 is a constant, R is universal
gas constant and T is the temperature in degrees Kelvin.

All pH-sensitive glasses are also susceptible to other ions, such as Na or K. 
This requires a correction in the above equation, so the relationship between 
pH and generated voltage becomes nonlinear at high pH values. The slope tends
to diminish both as the electrode ages, and at high pH. As the electrode has
a very high impedance, typically 250 Megohms to 1 Gigohm, it is necessary to
use a very high impedance measuring instrument.

The reference electrode has a fairly constant potential, but it is 
temperature dependent, and also varies with activity of the silver ions in 
the reference electrode. This occurs if a contaminant enters the reference
electrode.

Calibration

From the preceding, it is obvious that frequent calibration and adjustment of
pH meters are necessary. To check the pH meter, at least two standard buffer 
solutions are used to cover the range of interest. The pH meter should be 
on for at least 30 minutes prior to calibration to ensure that all components
are at thermal equilibrium, and calibration solutions should be immersed for
at least a minute to ensure equilibrium. 

First use the buffer at pH 7, and adjust the zero (or the intercept). 
Then, after thorough rinsing with water, use the other buffer to adjust the 
slope. This cycle in repeated at least once, or until no further adjustments 
are necessary. Many modern pH meters have an automatic calibration feature,
which requires each buffer only once.

Errors

People assume pH measurements are accurate, however many potential errors 
exist. There can be errors caused by the pH-sensitive glass, reference 
electrode, electrical components, as well as externally generated errors.

Glass Electrode Errors

The pH-sensitive glass can be damaged. Major cracks are obvious, but minor
damage can be difficult to detect. If the internal liquid of the pH-measuring
electrode and the external environment are connected, a pH value close to 7 
will be obtained. It will not change when the electrode is immersed in a 
known solution of different pH. The electrical resistance of the glass 
membrane will also be low, often below 1 megohm, and it must be replaced.

Similar results occur if the glass wall between the inner and outer part of 
a combined electrode breaks. This may occur if the outer part is plastic.
The inner part can crack without any external signs. The electrical 
resistivity over the glass electrode is intact, but actual measuring between
both electrodes reveals a low resistivity. The electrode must be replaced.

The glass can wear out. This gives slow response times, as well as a lower 
slope for the mV versus pH curve. To rejuvenate, immerse the electrode in a 
3 Molar KCl solution at 55 degrees Celsius for 5 hours. If this does not 
solve the problem, try removing a thin layer of the glass by immersion for
two minutes in a mixture of HCl and KF (be careful, do not breathe the fumes,
and wear gloves). The electrode is then immersed for two more minutes in HCl,
and rinsed thoroughly. As an outer layer of glass has been removed, the new 
surface will be like a new electrode, however the thinner glass will result
in a shorter electrode life. Frequent recalibration will be required for
several days.

The glass can be dirty. A deposit on the glass will slow the response time,
make the response sensitive to agitation and ionic strength, and also give 
the pH of the film, not the sample solution. If the deposit is known, use a
appropriate solvent to remove it, and rehydrate the electrode in 3M KCl.
If the deposit is not known, first immerse the electrode for a few minutes 
in a strongly alkaline solution, rinse thoroughly, and immerse it in a 
strong acid (HCl) solution for several minutes. If this does not help, try 
using pepsin in HCl. If still unsuccessful, use the above HCl/KF method. 

Reference Electrode Errors

The diaphragm of the reference can become blocked. This is seen as unstable
or wrong pH measurements. If the electrical resistivity of the diaphragm is
measured, high values are reported (Most multimeters will give an over-range 
error). The most common reason is that AgS formed a precipitate in the 
diaphragm. The diaphragm will be black in this case. The electrode should be 
immersed in a solution of acidic thiourea until the diaphragm is white, and
then replace the internal filling liquid of the reference electrode 

There is no contact across the diaphragm, due to air bubbles. This appears
as if the diaphragm were blocked, except that the diaphragm is white. Ensure 
that the filling solution level in the reference electrode is always well
above the sample, so that liquid is always slowly flowing from the reference 
electrode towards the sample.

The electrode filling solution is contaminated. This appears as unstable or 
wrong pH measurements. Often the 0mV pH differs considerably from pH 7. The 
diaphragm has its normal colour and the electrical resistivity is normal. 
However, the solution often becomes contaminated due to low filling solution 
levels, and air bubbles may also appear in the diaphragm, which obviously
affects electrical resistivity. Replacing the reference filling solution 
several times should solve the problem, but the electrode may have been 
permanently damaged. The problem can be avoided by choosing gel-filled 
reference electrodes, double-junction electrodes, or ensuring there is an 
outflow of reference filling solution towards the sample.

The electrode was filled with the wrong reference solution. This appears as
as displaced pH measurements. Flush and replace the reference liquid.

Electrical errors 

Condensation or sample contamination of the electrode connecting cable. This 
appears as an almost-constant measurement of about pH 7, even when the pH 
electrode is disconnected from the cable, or as a pH which changes less than 
it should, when tested with two standard solutions. If the cable is 
disconnected from the meter, the pH will start to drift.

There is a short circuit in the cable. The symptoms are similar to the above
case, except that bending the cable may create sharp, spurious readings. In 
most pH cables, between the two copper conductors there are two layers which 
appear to be insulators. The inner layer is an insulator, whereas the outer 
layer is a conductor to avoid trace electrical effects. If this outer layer 
does contact the inner conductor, there will be a short circuit. Replace 
suspect cables.

The input stage of the meter is contaminated with conducting liquid. The 
symptoms are the same as above, except that removing the cable has no
effect. Closely examine the input stage of the meter for liquid or deposits. 
If present, rinse with distilled water, then ethanol, and dry thoroughly.

The input stage of the meter is faulty. This gives random measurements.
Shorting both input wires does not make any difference. Repair the meter.

The input stage appears faulty. Shorting both input wires gives a stable
pH measurement of about 7. The meter may be faulty, but probably the problem 
is elsewhere in the electrical circuit.
 
Externally-generated Errors

If a significant flow of liquid passes the electrode, then there can
be a minor electrical effect. This generates a potential on the glass
membrane, which is superimposed on the actual pH measurement. This effect
becomes negligible for highly-conducting liquids. It is seldom observed.
If the trace electric effect does influence pH measurements, the addition 
of a little salt to increase the conductivity, or changing the flux of 
liquid around the electrode, should solve the problem.

Ground loops and spurious electrical currents may generate unexpected 
electrical signals. Such signals can strongly influence pH measurements. 
A pH reading in the range of -15 to +20 is possible, even if the pH is 7. 
Ground loops can be eliminated by grounding the system according to the
manufacturer's instructions, and ensuring insulation is in good condition. 
Often these problems can be extremely difficult to detect and remedy.

Low ionic strength samples can be affected by electrolyte from the electrode, 
and special electrodes are available.

26.3  What are ion-selective electrodes? 

Ion selective electrodes are electrochemical sensors whose potential varies
with the logarithm of the activity of an ion in solution. Available types:
1. The membrane is a single compound, or a homogeneous mixture of compounds.
2. The membrane is a thin glass whose chemical composition determines the 
   response to specific ions.
3. The support, containing an ionic species, or uncharged species, forms the
   membrane. The support can be solid or porous.  
Popular texts on applications of ion-selective electrodes include 
"Ion-Selective Electrodes in Analytical Chemistry" [3], and "Ion-selective
Electrode Methodology" [4].

26.4  Who supplies pH and ion-selective electrodes?

The best known manufacturer of ion-selective electrodes is Orion Research. 
There are several pH electrode manufacturers, including Radiometer and
Metrohm.

------------------------------

Subject: 27. Fuel Chemistry

27.1  Where does crude oil come from?.

The generally-accepted origin of crude oil is from plant life up to 3 
billion years ago, but predominantly from 100 to 600 million years ago [1]. 
"Dead vegetarian dino dinner" is more correct than "dead dinos".
The molecular structure of the hydrocarbons and other compounds present 
in fossil fuels can be linked to the leaf waxes and other plant molecules of 
marine and terrestrial plants believed to exist during that era. There are 
various biogenic marker chemicals such as isoprenoids from terpenes, 
porphyrins and aromatics from natural pigments, pristane and phytane from 
the hydrolysis of chlorophyll, and normal alkanes from waxes, whose size 
and shape can not be explained by known geological processes [2]. The 
presence of optical activity and the carbon isotopic ratios also indicate a 
biological origin [3]. There is another hypothesis that suggests crude oil 
is derived from methane from the earth's interior. The current main 
proponent of this abiotic theory is Thomas Gold, however abiotic and
extraterrestrial origins for fossil fuels were also considered at the turn 
of the century, and were discarded then. A large amount of additional
evidence for the biological origin of crude oil has accumulated, however
Professor Gold still actively promotes his theory worldwide, even though
it does not account for the location and composition of all crude oils.  

27.2  What are CNG/LPG/gasoline/kerosine/diesel?. 

Crude oil consists mainly of hydrocarbons with carbon numbers between one and
forty. The petroleum refinery takes this product and refines it into several
fuel fractions that are optimised for their intended application. For spark
ignition engines, the very volatile and branched chain alkane hydrocarbons
have desirable combustion properties, and several fractions are produced.
          
CNG ( Compressed Natural Gas ) is usually around 70-90% methane with 10-20% 
ethane, 2-8% propanes, and decreasing quantities of the higher HCs up to 
pentane.  The major disadvantage of compressed gaseous fuels is the reduced 
range. Vehicles may have between one to three cylinders ( 25 MPa, 90-120 
litre capacity), and they usually provide about 50% of the gasoline range. 

LPG ( Liquefied Petroleum Gas ) is predominantly propane with iso-butane
and n-butane. It has one major advantage over CNG, the tanks do not have
to be high pressure, and the fuel is stored as a liquid. The fuel offers   
most of the environmental benefits of CNG, including high octane - which
means higher compression, more efficient, engines can be used. Approximately 
20-25% more fuel than gasoline is required, unless the engine is optimised 
( CR 12:1 ) for LPG, in which case there is no decrease in power or any 
significant increase in fuel consumption [4,5].

Gasoline contains over 500 hydrocarbons that may have between 3 to 12 
carbons, and gasoline used to have a boiling range from 30C to 220C at 
atmospheric pressure. The boiling range is narrowing as the initial boiling 
point is increasing, and the final boiling point is decreasing, both 
changes are for environmental reasons. A detailed description of the 
composition of gasoline, along with the properties and compositions of CNG, 
LPG, and oxygenates can be found in the Gasoline FAQ, which is posted monthly 
to rec.autos.tech.

Kerosine is a hydrocarbon fraction that typically distils between 170-270C
(narrow cut kerosine, or Jet A1) or 100-250C ( wide cut kerosine, or JP-4 ). 
It contains around 20% of aromatics, however the aromatic content will be 
reduced for high quality lighting kerosines, as the aromatics reduce the 
smoke point. The major use for kerosines today is as aviation turbine (jet) 
fuels. Special properties are required for that application, including high 
flash point for safe refuelling ( 38C for Jet A1 ), low freezing point for
high altitude flying ( -47C for Jet A1 ), and good water separation 
characteristics.  Details can be found in any petroleum refining text and
Kirk Othmer.

Diesel is used in compression ignition engines, and is a hydrocarbon fraction 
that typically distils between 250-380C. Diesel engines use the Cetane 
(n-hexadecane) rating to assess ignition delay. Normal alkanes have a high 
cetane rating, ( nC16=100 ) whereas aromatics ( alpha methylnaphthalene = 0 ) 
and iso-alkanes ( 2,2,4,4,6,8,8-hexamethylnonane = 15 ) have low ratings, 
which represent long ignition delays. Because of the size of the hydrocarbons,
the low temperature flow properties control the composition of diesel, and
additives are used to prevent filter blocking in cooler temperatures. There
are usually summer and winter grades. Environmental legislation is reducing
the amount of aromatics and sulfur permitted in diesel, and the emission of
small particulates ( diameters of <10um ) that are considered possibly
carcinogenic, and are known to cause other adverse health effects. Details 
can be found in any petroleum refining text and Kirk Othmer.

27.3  What are oxygenates?.

Oxygenates are just pre-used hydrocarbons :-). They contain oxygen, which can 
not provide energy, but their structure provides a reasonable anti-knock 
value, thus they are good substitutes for aromatics, and they may also reduce
the smog-forming tendencies of the exhaust gases [6]. Most oxygenates used 
in gasolines are either alcohols ( Cx-O-H ) or ethers (Cx-O-Cy), and contain 
1 to 6 carbons. Alcohols have been used in gasolines since the 1930s, and
MTBE was first used in commercial gasolines in Italy in 1973, and was first
used in the US by ARCO in 1979. The relative advantages of aromatics and 
oxygenates as environmentally-friendly and low toxicity octane-enhancers are 
still being researched.

    Ethanol                                  C-C-O-H      C2H5OH
  
                                               C
                                               |
    Methyl tertiary butyl ether              C-C-O-C      C4H9OCH3
    (aka tertiary butyl methyl ether )         |
                                               C

They can be produced from fossil fuels eg methanol (MeOH), methyl tertiary 
butyl ether (MTBE), tertiary amyl methyl ether (TAME), or from biomass, eg 
ethanol(EtOH), ethyl tertiary butyl ether (ETBE)). MTBE is produced by 
reacting methanol ( from natural gas ) with isobutylene in the liquid phase 
over an acidic ion-exchange resin catalyst at 100C. The isobutylene was 
initially from refinery catalytic crackers or petrochemical olefin plants, 
but these days larger plants produce it from butanes.

Oxygenates have significantly different physical properties to hydrocarbons,
and the levels that can be added to gasolines are controlled by the EPA in
the US, with waivers being granted for some combinations. Initially the
oxygenates were added to hydrocarbon fractions that were slightly-modified
unleaded gasoline fractions, and these were commonly known as "oxygenated"
gasolines. In 1995, the hydrocarbon fraction was significantly modified, and
these gasolines are called "reformulated gasolines" ( RFGs ). The change to
reformulated gasoline requires oxygenates to provide octane, but also that 
the hydrocarbon composition of RFG must be significantly more modified than 
the existing oxygenated gasolines to reduce unsaturates, volatility, benzene,
and the reactivity of emissions. 

Oxygenates that are added to gasoline function in two ways. Firstly they
have high blending octane, and so can replace high octane aromatics
in the fuel. These aromatics are responsible for disproportionate amounts
of CO and HC exhaust emissions. This is called the "aromatic substitution 
effect". Oxygenates also cause engines without sophisticated engine 
management systems to move to the lean side of stoichiometry, thus reducing 
emissions of CO ( 2% oxygen can reduce CO by 16% ) and HC ( 2% oxygen can 
reduce HC by 10%)[7]. However, on vehicles with engine management systems,
the fuel volume will be increased to bring the stoichiometry back to
the preferred optimum setting. Oxygen in the fuel can not contribute 
energy, consequently the fuel has less energy content. For the same
efficiency and power output, more fuel has to be burnt, and the slight
improvements in combustion efficiency that oxygenates provide on some 
engines usually do not completely compensate for the oxygen.
 
There are huge number of chemical mechanisms involved in the pre-flame 
reactions of gasoline combustion. Although both alkyl leads and oxygenates 
are effective at suppressing knock, the chemical modes through which they 
act are entirely different. MTBE works by retarding the progress of the low 
temperature or cool-flame reactions, consuming radical species, particularly 
OH radicals and producing isobutene. The isobutene in turn consumes 
additional OH radicals and produces unreactive, resonantly stabilised 
radicals such as allyl and methyl allyl, as well as stable species such as 
allene, which resist further oxidation [8,9]. 

The major concern with oxygenates is no longer that they may not be 
effective at reducing atmospheric pollution, but that their greater water 
solubility, and very slow biodegradability, can result in groundwater
pollution that may be difficult to remove. Their toxicological and
environmental effects are also still being researched. 

27.4  What is petroleum ether?.

Petroleum ether ( aka petroleum spirits ) is a narrow alkane hydrocarbon
distillate fraction from crude oil. The names "ether" and "spirit" refer
to the very volatile nature of the solvent, and petroleum ether does not
have the ether ( Cx-O-Cy ) linkage, but solely consists of hydrocarbons. 
Petroleum ethers are defined by their boiling range, and that is typically 
20C. Typical fractions are 20-40C, 40-60C, 60-80C, 80-100C, 100-120C etc. 
up to 200C. There are specially refined grades that have any aromatic 
hydrocarbons removed, and there are specially named grades, eg pentane
fraction (30-40C), hexane fraction (60-80C, 67-70C). It is important to
note that most "hexane" fractions are mixtures of hydrocarbons, and pure
normal hexane is usually described as "n-hexane".  

27.5  What is naphtha?.

Naphtha is a refined light distillate fraction, usually boiling below 250C,
but often with a fairly wide boiling range. Gasoline and kerosine are the 
most well-known, but there are a whole range of special-purpose hydrocarbon 
fractions that can be described as naphtha. The petroleum refining industry
calls the 0-100C fraction from the distillation of crude oil "light virgin
naphtha" and the 100-200C fraction " heavy virgin naphtha". The product
stream from the fluid catalytic cracker is often split into three fractions,
<105C = "light FCC naphtha", 105-160C = "intermediate FCC naphtha" and 
160-200C "heavy FCC naphtha".  

27.6  What are white spirits?.

White spirits are petroleum fractions that boil between 150-220C. They can 
have aromatics contents between 0-100%, and Shell lists eight grades with 
aromatics contents below 50%, and six grades with aromatics contents above
50%. The two common "white spirits" are defined by British Standard 245, 
which states Type A should have aromatics content of less that 25% v/v and 
Type B should have an aromatics content of 25-50% v/v. The most common 
" white spirit" is type A, and it typically has an aromatics content of
20%, boils between 150-200C, and has an aniline point of 58C, and is 
sometimes known as Low Aromatic White Spirits. The next most common is 
Mineral Turpentine (aka High Aromatic White Spirits ), which typically has
an aromatics content of 50%, boils between 150-200C and has an aniline
point of 25C. For safety reasons, most White Spirits have Flash Points
above ambient, and usually above 35C. Note that "white gas" is not white 
spirits, but is a volatile gasoline fraction that has a flash point below 
0C, which is also known by several other names. Do not confuse the two 
when purchasing fuel for camping stoves and lamps, ensure you purchase the
correct fuel.   

27.7  What are biofuels?.

Biofuels are produced from biomass ( land and aquatic vegetation, animal
wastes, and photosynthetic organisms ), and are thus considered renewable
within relatively short time-frames. Examples of biofuels include wood,
dried animal dung, methyl esters from triglyceride oils, and methane from
land-fills. The renewable aspect of most biofuels is essentially the use
of solar energy to grow crops that can be converted to energy. There is
a large monograph "Fuels from Biomass" in Kirk Othmer, and the subject
is frequently discussed in alt.energy.renewable, sci.energy, and 
sci.energy.hydrogen.  

27.8  How can I convert cooking oil into diesel fuel?. 

Diesel engines can run on plant and animal triglycerides such as tallow
and seed oils, however most trials have resulted in reduced engine life, or
increased service costs. The solution is to transesterify the triglycerides
into esters, taking care to avoid the formation of monoacylglycerides
that will precipitate out at low temperatures or when diesel is encountered.
There are several plants in Austria that produce Rapeseed Oil Methyl Esters
as fuels for diesel engines. The economics of the process are very 
dependant on the price of diesel and the market for the glycerol byproduct.

The common catalysts used to transesterify triglycerides are sodium 
hydroxide, sodium methoxide and potassium carbonate. If the esters are to 
be blended with diesel fuel, then a two stage reaction is usually required 
to ensure that monoacylglycerides are kept below 0.05%. Usually this 
involves using 22g of methanol ( containing 0.6g of sodium hydroxide ) and 
100g of tallow refluxed for 30 minutes. The mixture is cooled, the glycerol 
layer removed, and a further 0.2g of sodium hydroxide is reacted for 5 
minutes at 35C in a stirred reactor. The glycerol phase is allowed to 
separate, and the ester phase is washed with water to remove residual 
catalyst, glycerol and methanol. Note that sodium hydroxide is the most 
cost-effective catalyst, but also has the worst tendency to form soaps. 
The catalyst and methanol can be of industrial grade without further 
purification required, however care should be taken to prevent additional 
water entering the reaction [10]. 

The fuel can be converted into other esters, such as ethyl and butyl, but
it really depends on the availability of cheap alcohol along with the
desired properties of the fuels. The effect of catalysts, reagent ratio, 
temperature, and moisture on the production of methyl, ethyl, and butyl
esters from some common oils has been investigated [11]. The New Zealand 
government investigated a wide range of techniques for turning various 
vegetable and animal triglycerides into esters for diesel, and the reports 
cover many aspects of the kinetics and efficiencies [12]. There is a general 
overview of the current processes and technology available in Inform [13]. 
A specific technique for analysing the monoglycerides has been published 
[14], however I have found that acetylation followed by narrow bore 
( 0.1mm ID ) capillary chromatography is faster and cheaper.  

------------------------------

Subject: 28. Pharmaceutical Chemistry

28.1  Does Thalidomide racemise in humans?.

Thalidomide ( N-phthaloyl-alpha-aminoglutarimide ) is well known as an 
enantiomeric sedative-hypnotic drug that caused tragic birth defects in 
the early 1960s. It has often been claimed that the defects were caused by 
the presence of the other isomer in the production batches, and if the pure 
enantiomer had been sold, then the tragic defects would have been avoided. 

Unfortunately, thalidomide is optically unstable in solution; the pure 
isomers of thalidomide racemise by the opening of the phthalimide ring, with 
half-lives of 4-5 hours in buffer at pH 7.4, and less than 10 minutes in the 
blood. Thus shortly after administration of either enantiomer, the other 
enantiomer will be present in significant quantities [1].

Some recent work has revealed that thalidomide inhibits the production of
tumour necrosis factor alpha. Elevated levels of TNF-alpha are associated
with several inflammatory conditions. This has led to the development of
analogues that are chirally stable in reconstituted human plasma, and which
are undergoing development as anti-inflammatory drugs [2].   

------------------------------

Subject: 29. Adhesive Chemistry 
   
------------------------------

Subject: 30. Polymer Chemistry 
     
30.1  How can I simply identify common plastics?. 

Read the recycle code :-). Alternatively, give it to the nearest IR 
spectroscopist who has a polymer library. But if you want some fun, try the
following.
 
There are several simple tests that can be performed in the home that can
assist in separating common plastics, however it is important to realise that
formulated products contain large quantities of pigments, plasticisers, and
fillers that can dramatically alter the following properties. If possible
repeat the tests on a reference sample of the plastic.

a. Visually examine the sample, looking for recycle codes :-)
   While you are at it, you can check for indications of how the plastic
   was made - moulded, injected, rolled, machined etc. 
b. Try assessing the flexibility by bending, and look at the bending zone
   - does the material stretch or is it brittle? 
c. Test the hardness, try scratching it with pencils of differing hardness 
   ( B,HB,1-6H ) to ascertain which causes a scratch in the plastic. 
   Alternatively, attempt to scuff the sample with a fingernail. 
d. Cut a small slither with a sharp knife. Does the sample cut cleanly
   ( thermoplastic )?, or does it crumble ( thermosetting )?.
e. Hold sample in small flame, note whether it burns, self-extinguishes on
   removal from the flame, colour of the flame, and smell/acrid nature of 
   fumes when flame is blown out ( Caution - the fumes are likely to be 
   toxic ). Also attempt to press melted sample against a cold surface, and 
   pull away - does sample easily form long threads.    
f. Drop onto a hard surface, does the sample "ring" or "thud"?
g. Place it in water. Does it float, sink slowly, or sink rapidly?
   If it sinks rapidly, it is likely to be halogenated ( PVC, Viton, PTFE ) 

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