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IDENTIFICATION OF PLASTICS
IDENTIFICATION OF PLASTICS
VISHAL VERMA
Technical Officer
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IDENTIFICATION OF PLASTICS
IDENTIFICATION
When working with plastics there is often a need to identify
which particular plastic material has been used for a given
product. This is essential to get an idea of the cost and likely
properties of the product. The identification of plastics is
generally very difficult due to:
 The wide range of basic polymers that is available for
use.
 The wide range of additives that can be used to modify
the properties of the basic polymer.
 The wide range of mixtures or compounds of polymers
that can be manufactured to get the required
properties.
Despite this there are some simple tests that can be carried
out to get a basic idea of the possible base polymer used for
the manufacture of any given product.
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IDENTIFICATION OF PLASTICS
CONTENTS
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Introduction
Simple method
 cutting test
 hot wire penetration test
 flotation test
 bending test
 dropping test
Burning test
Pyrolysis test
Specific gravity test
Solubility test
Softening and Melting point
Elemental Analysis
Confirmation test
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IDENTIFICATION OF PLASTICS
IDENTIFICATION BY SIMPLE METHOD

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
Stage 1: Look at the sample
This will give you a lot of information. The colour of the plastic will give
you some information. Some polymers have restricted colour ranges,
particularly the thermosetting types. Others tend to be glossier in colour
(polypropylene), whereas some are both glossy and glassy (the acrylics).
Stage 2: Feel the sample
After you have carried out the tests in the is series a few times you will
start to get the feel for various plastics. The polyolefins have a very
distinctive feel and you can generally tell if it is one of them. The presence of
glass fibre or other reinforcement materials can alter the feel and stiffness of
the sample but you can sometimes tell by the feel if there is reinforcement
present.
Stage 3: Cut a thin sliver from the edge of the sample
Cut a small sliver off the sample. This tells you a lot about the type of
plastic you are trying to identify
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IDENTIFICATION OF PLASTICS
CUTTING TESTS
 If a shaving can be pared off with knife, it may be a
thermoplastic.
Note: PMMA and Polystyrene are brittle and difficult to
pare
 If the material is rigid and will not pare off instead flakes of
powders, it may probably a thermoset plastic.
 Scuff the sample with your fingernail.
Results
 Scuffs with fingernail - Urea formaldehyde resin.
 Does not scuff with fingernail - Melamine formaldehyde
resin.
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IDENTIFICATION OF PLASTICS
HOT ROD PENETRATION TEST

Heat an electronic soldering iron to red hot and press
against the unknown sample.

If the plastic material softens, and the rod penetrates the
sample is thermoplastic.

If the plastic material does not soften and the rod does
not penetrate, the sample is thermoset plastic.
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IDENTIFICATION OF PLASTICS
FLOTATION TEST
This test will give the idea to distinguish the material
according to their density.
Floats on type
of plastics
Alcohol
Vegetable oil water
glycerin
PET
No
No
No
No
HDPE
No
No
Yes
Yes
PVC
No
No
No
No
LDPE
Yes
No
Yes
Yes
PP
Yes
Yes
Yes
Yes
PS
No
No
No
Yes
Note:Filled polyolefin’s and cellular foams are exceptional
for this test.
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IDENTIFICATION OF PLASTICS
BENDING TESTS
Some plastics will exhibit particular characteristics in the manner
in which they respond to bending. The bending behaviour of some
plastics are given in Table
PLASTICS
BENDING BEHAVIOUR
1.
Polyethylene
Bends, tends to remain
2.
Polypropylene
Unbends most of the way
3.
Polystyrene
Cracks but retains bend
4.
ABS
Bend tends to remain
5.
PVC (Rigid)
Bends easily and springs back quickly
6.
Cellulose acetate
Bend tends to remain
7.
PMMA
Cracks and splinters
8.
Nylon
Difficult to bend, springs back
9.
Polycarbonate
Tough to bend
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IDENTIFICATION OF PLASTICS
DROPPING TEST
When a polymer moulded component is dropped on hard
surface, it creates sound, which shall be either metallic
sound or dull sound. On the basis of sound polymer is
distinguished in two categories, which is tabulated in
Table
Metallic sound
dull sound
PS, HIPS
Cellulosics
SAN, ABS
Polyamides
PC, PPS
PTFE, PMMA
PPO
Polyacetal
Polysulphone
PVC , Polyolefins
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IDENTIFICATION OF PLASTICS
BURNING TEST
A small sample is held in flame. If it ignites withdraw it
from the flame a distance of flame. Make observations
as listed below and record the observations, for
example:
Degree of flammability burns
Self extinguishing
does not burn
Colour of flame
yellow and orange; Blue; blue with yellow edges; clear,
Type of flame
steady; tall; short; sputtering
Smoke
none, black, thin and thick black with sooty streamers
Melt behaviour
softens remains hard; flows; bubbles; swells; does not
char but melts; melts and chars
Odour
Burning rubber; sweet – fruity; marigolds; burning
paper; acid; rancid butter
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IDENTIFICATION OF PLASTICS
Typical results of burning tests of polymers (thermoplastics)
Thermoplastics
Melting Behaviour
Colour of Flame/ kind
of smoke
Odour / smell
PE
Melt and bubbles fiercely
around the edge, Drips
Blue base
with yellow tip
Waxy (Burning Candle)
PP
Becomes soft, tends to
form a ball, Drips
Blue base
with yellow tip
PTFE
Does not melt, self –
Extinguishing
Will not burn
Orange – Yellow, Heavy,
Black, Sooty Smoke
PS / SAN
Melts and bubbles around
the edge, spurting, burns
readily
High Impact poly
styrene
Melts and bubbles around
the edge, spurting, burns
readily
Orange – Yellow, Heavy,
Black, Sooty Smoke
ABS
Becomes soft but not fluid
Orange – Yellow, Heavy,
Black, Sooty
PVC
Soften and forms a ball,
chars at bottom, self –
Extinguishing
Yellow with green bottom
edge, Some White Smoke
Lubricating oil smell
None
Mari gold, Strong smell
of Styrene and Burning
rubber
Slight burning rubber
smell
Slight burning rubber
smell
Chlorine smell, pungent
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IDENTIFICATION OF PLASTICS
Typical results of burning tests of polymers (thermoplastics)
cont.
Thermo
plastics
Melting Behaviour
Colour of Flame/ kind
of smoke
Odour / smell
CA
Melts and emits white smoke boils
and chars
Yellow, burns brown at
base, Some light Smoke
Smell of Vinegar (Acetic
acid)
CN
Melts and emits white smoke –
Burn Furiously, dangerous
Hot, White
CAB
Melts and Char at the edge, drips
PMMA
Boils and Bubbles
PC
Dark yellow with light blue
base, Some light black
Smoke
Camphor (Mothball)
Rancid butter (an Odour
of butyric acid)
Blue and Yellow Flame,
Some light black Smoke
Fruity, Floral smell
Melt but chars, Bubbles develops a
cellular structure before
decomposing, self – Extinguishing
Orange yellow flame with
black smoke
Phenolic smell ( ink
smell)
PPO
Melt but chars, self – Extinguishing
Orange yellow flame with
black smoke
Nylon
Melts round edges and chars,
Froth formation and drips
Blue with Yellow tip
Phenolic smell ( ink
smell)
Burning hair / wool /
vegetarian
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IDENTIFICATION OF PLASTICS
Typical results of burning tests of polymers (thermoplastics)
Thermo
plastics
Melting Behaviour
Colour of Flame/ kind of
smoke
Odour / smell
Acetal
Melts, forms drops, Burns
readily
Pale blue
Pungent smell of
Formaldehyde
PET/ PBT
Melts, opacifies, blackens,
Molten Material drips
Yellow, Slightly smoky
Polyvinyl
Acetate
Softens
Dark Yellow, Spurts with black
smoke
Casein
Swells and chars on
ignition, Self –
Extenguishing,
Yellow, Grey smoke
Poly
phenylene
sulphide
Melt and char, self
extinguish
Orange yellow flame with black
smoke
PU
Drip like oil
Blue base yellow tip burns
continuously, no smokeYellow
flame, black smoke
cont.
Pleasant elusive odour
Vinyl acetate smell (Sweet
odour)
Burning milk
H2S smell or rotten egg
smell
Faint apple smell or castor
oil smellFiant apple smell
or castor oil smell
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IDENTIFICATION OF PLASTICS
Typical results of burning tests of polymers (thermoset)
Thermoset
Colour of Flame/ kind of smoke
Odour/ smell
Phenol Resin
Yellow flame, self extinguishing,
Some sparks
Charcoal smell
Urea Resin
Yellow with light blue edge, self
extinguishing
Fishy smell
Melamine Resin
Yellow with light blue edge, self
extinguishing
Fishy smell
Polyester Resin
(Unsaturated)
Burn with orange yellow flame, Black
smoke
Ester smell
Epoxy
Yellow flame, Black smoke
Charred flour
smell
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IDENTIFICATION OF PLASTICS
Typical results of burning tests of polymers (Elastomer)
Elastomer
Colour of flame/ smoke
Flame
& kind of smoke
Odour/ smell
Other notable
characteristics
Poly butylene
Yellow, blue base Smoky
Disagreeable, Sweet
Chars readily
Styrene - butadiene
Burns continuously
Yellow sooty
Pungent smell of styrene
Chars readily, dry
powdery
Ethylene propylene
dienemer (EPDM)
Burns continuously no
smoke, blue base yellow tip
Waxy smell
Dry powdery
NBR
Yellow sooty
Unpleasant
Tacky
Butile rubber (IIR)
Smoke free, candle like
Hydrocarbon smell
Melt does not char
readily, tacky
Polyisoprene (NR)
Yellow sooty
Pungent like burn rubber
Chars & crack
Polychloroprene (CR)
Self extinguishing
Yellow & smoky
Pungent smell
of chlorine
Strongly acidic fumes,
black residue dry
powdery
Silicone rubber
Burns continuously, glow
with white smoke powdery
No odour
Dry white powdery
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IDENTIFICATION OF PLASTICS
PYROLYSIS TESTS

In this testing, heat few milligrams of the sample in an ignition tube and
test the pyrolytic vapour with a moistened indicator paper. The behaviour
of vapour to indicator paper is given as follows:

ACID:
turns blue litmus to red

BASIC:
turns red litmus to blue.



ACID VAPOURS: may come from carbohydrate polymers & their
derivatives. [e.g., cellulose acetate]
HIGH ACID VAPOURS: often indicates the presence of chlorine. e.g.,
PVC or rubber neutral vapors] evolved from hydro carbon
polymers, silicones and some polyesters hydrochloride.
ALKALINE VAPOURS: indicate the presence of N2. e.g. polyamide,
proteins & amino formaldehyde resins.
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IDENTIFICATION OF PLASTICS
SPECIFIC GRAVITY TEST
A simple test for differentiating
between different types of
plastics can be carried out by
placing specimens in water.
Some will sink and some will
float depending on their specific
gravity as shown in Table .
Those with the higher specific
gravities will sink as shown in
the Table. Accurate specific
gravity results can be obtained
by the standard method of
relating weight of the material to
weight of water displaced.
Floats in water (S.G. 1)
Specific Gravity ≤ 1
PP
0.90
LDPE
0.92
HDPE
0.96
Sink in Water floats in
Hypo
1 ≤ Specific Gravity
≤ 1.1
PS
1.07
SAN
1.1
ABS
1.1
NYLON
1.1
Sinks in Hypo
Specific Gravity ≥
1.1
PMMA
1.2
PMMA
1.2
CA
1.3
PVC
1.4
ACETAL RESIN
1.4
UREA RESIN
1.5
PTFE
2.75
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IDENTIFICATION OF PLASTICS
SOLUBILITY TESTS
Solubility tests form a basis of some older identification schemes for
main types of plastic materials. However, in many cases solubility
varies considerably for different samples of the same resin and it is
difficult to interpret the results Solubility of plastics may vary
according to the grade or to the whether or not other constituents
are present in the sample. The data in Table refer in principle to pure
polymers, although even those polymers may exhibit differences in
solubility. The solubility test should be carried out directly in a test
tube. To about 100 mg of a powdered sample add 10ml of solvent,
mix occasionally shake the contents of the test tube and observe for
a few hours swelling may occur before complete dissolution of the
polymer.
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IDENTIFICATION OF PLASTICS
PLASTIC MATERIAL
SOLVENTS
Cellulose esters
Ketones, esters
Poly (vinyl chloride)
Dimethylformemide, tetrahydrofuran, cyclohexenone
ABS
Methylene chloride
Vinyl chloride / Vinyl acetate
Methylene chloride, cyclohexanone, tetrahydrofuran
Polytetrafluoroethylene
Fluorocarbon oil e.g. C21 F44 {hot)
Polyacrylonitrile
Dimethylformamide,
butyrolactone,
nitrohenel,
mineral
dimethylsulphoxide, aqueous solutions of some inorganic salts.
Poly (Methacrylic acidesters)
Arimatic hydrocarbons dioxen, chlorinated hydracarbons, esters, ketones.
Polyamides
Phenols, formic acid, tetrafluoropropanel, conc. Mineral acids.
Poly (vinyl acetal)
Esters, Retones, tetrahydro – furan
Poly (vinyl alcohol)
Formamide water
Polycarbonates
Chlorinated hydrocarbons, dioxan, cyclohexanene.
Polyesters, unsaturated
Ketenes, styrene, acrylic esters.
Polyethylene
Dichloroethylens, tetralin, hot hydrocarbons
Polyformaldehyde
Hot selvantas phenels, benzyl alcohol, dimethylformide.
Polypropylene
At elavator temp, aromatic and chlorinated hydrocarbons, tetralin
Polystyrene
acids,
Aromatic and chlorinated hydrocarbons, pyridinc, ethylacetate, methylethyl
ketone, diovan totralin.
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IDENTIFICATION OF PLASTICS
SOFTENING AND MELTING POINTS
The temperature range of softening and melting – point can be used to
characterize/ identify the material.
Procedure: Place the 2 to 3 mg portion on a clean glass slide and cover
with No 1 cover glass. Heat the slide, sample and cover on a hot plate
to slightly above the softening point of the polymer so that a thin film
can be formed. By slightly pressure on the cover glass form a thin film
0.01 to 0.04 mm, and allow it to cool slowly by turning of the hot plate
power to promote crystallization. Keep the slide on hot plate melting
point apparatus. Adjust the hot plate temperature about 10 deg C below
the melting point of sample. Then adjust the temperature ramp at 0.5
deg C/ min. observe the sample through microscope and note down the
temperature where the material starts melting.
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IDENTIFICATION OF PLASTICS
Melting and softening point of polymer materials
S. No.
Polymer material
Softening Point
140
Melting Point
260
1.
PET
2.
HDPE
120
130
3.
Poly Urethane Linear
125
150 – 185
4.
PP
110
165 – 170
5.
6, 10 Polyamide
180
210 – 215
6.
6, Polyamide
120
215 – 220
7.
6,6 Nylon
140
255
8.
PC
200
220 – 360
9.
PTFE
277
325 – 360
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IDENTIFICATION OF PLASTICS
CONFIRMATION TEST - Thermoplastics
Tests for Polyolefins
A piece of dry sample is pyrolysed in a tube closed with a
filter paper which is drenched with a solution of 0.5 g
yellow mercury (II) oxide in sulphuric acid (1.5 ml conc.
Sulphuric acid added to 8 ml. Water). If the vapour gives a
golden yellow spot, indicates polyisobutylene, butyl
rubber and polypropylene (the latter only after a few
minutes). Polyethylene does not react. Natural and nitrile
rubber, as well as polybutadiene yield a brown spot.
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IDENTIFICATION OF PLASTICS
CONFIRMATION TEST - Thermoplastics
Cont.
Test for Chlorine containing polymers
Copper wire test
 Take the piece of copper wire about 5 mm long. Push on end
of the wire in to a small cork.
 Place one pellet or plastics sample near your Bunsen burner.
This is the sample you will be testing.
 Hold the free end of the copper wire in the burner flame until
it is red-hot and the flame no longer has a green colour.
 Remove the wire from the flame and torch the hot wire to the
plastics pellet or sample you will be testing. A small amount
of the plastics should melt onto the wire.
 Place the end of the wire, with small amount of plastic on it,
into the flame. You should see a slight flash of a luminous
flame (a yellow- orange colour). If the flame turns green in
colour, then the sample contains chlorine.
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IDENTIFICATION OF PLASTICS
Cont.
CONFIRMATION TEST - Thermoplastics
Test for Caprolactum in Nylon 6
About 0.5 gm of sample is heated in 5.0 ml of distilled
water and allowed to boil for 10 to 15 min. After cooling,
2-3 drops of con. H2SO4 is added to 0.5 ml of the above
solution followed by addition of 2 ml. of potassium iodo
bismuthate ( a solution of 5 gm. of basic bismuth nitrate
and 25 gm. of potassium iodide in 10 ml. of 2% H2SO4).
Precipitation of an orange red complex indicates the
presence of caprolactum.
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IDENTIFICATION OF PLASTICS
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CONFIRMATION TEST - Thermoplastics
Test for Adipic acid in Nylon 6,6
About 0.2 gm of sample is heated in low flame in a test
tube and the vapour coming out of the tube is passed over
a filter paper moistened with a saturated solution of Onitrobenzaldehyde in 2N aqueous NaOH. A deep violet
colour confirms the presence of adipic acid.
A yellowish green colour develops in the case of
polyethylene-terephthalate and polybutylene-terephthalate
confirming the presence of terephthalic acid.
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IDENTIFICATION OF PLASTICS
CONFIRMATION TEST - Thermoplastics
Cont.
Test for Polycarbonate
About 1.0 gm of sample is pyrolysed in an ignition tube,
which is plugged with cotton. The cotton is removed and
immersed in 1% methanolic solution of p-dimethylamino
benzaldehyde and then one drop of 5 N-Hydrochloric acid
is added.
A dark blue colour appears in the case of
polycarbonates.
A red colour that does not change to blue is observed in
the case of polyamides.
The cotton floak in which the prolysed vapours of the
sample absorbed is treated with dilute (1:1) HCI. An
intense red colour which is unaffected by methanol,
indicates the presence of polycarbonate.
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IDENTIFICATION OF PLASTICS
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CONFIRMATION TEST - Thermoplastics
Test for PMMA
About 1 gm of sample is heated in an ignition tube and the
pyrolysate is collected in a test tube wrapped with a wet
filter paper. To the distillate, 1 ml. of conc. HNO3 is added
and heated just to boiling. After cooling, 5 ml. of water is
added an then sodium nitrite (0.1 gm) is added. A blueish
green
colour
confirms
the
presence
of
polymethylmethacrylate.
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IDENTIFICATION OF PLASTICS
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CONFIRMATION TEST - Thermoplastics
Test for Polyacetals
Polyacetals produce formaldehyde on heating.
A small
amount of sample is heated with 2 ml. conc. Sulphuric acid
and a few crystals of chromotropic acid for about 10 min
at
60
-70C.
A
strong violet colour indicates
formaldehyde.
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IDENTIFICATION OF PLASTICS
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CONFIRMATION TEST - Thermoplastics
Tests for PET and PBT
PET and PBT are soluble in nitrobenzene.
A small sample
is pyrolysed in a glass tube covered with filter paper. The
filter paper is drenched with a saturated solution of Onitrobenzaldehyde in dilute sodium hydroxide.
A blue-
green colour, which is stable against dilute hydrochloric
acid, indicates terephthalic acid.
Then PET and PBT are
differentiated based on melting points.
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IDENTIFICATION OF PLASTICS
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CONFIRMATION TEST - Thermoplastics
Test for polyurethane
About 0.5 gm of sample is dissolved in 10 ml of glacial
acetic acid and 0.1 gm of p-dimethylamino benzaldehyde is
added. The solution turning yellow after several minutes
shows the presence of polyurethane.
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IDENTIFICATION OF PLASTICS
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CONFIRMATION TEST - Thermoplastics
Test for Cellulose Ethers:
The important cellulose ethers are Methyl cellulose, Ethyl.
Cellulose and Benzyl cellulose.
Reaction to Heating and Burning:
Cellulose ethers melt and char after heating and
continuously burn after ignition. Nature of flame and smell
of the cellulose ethers are as follows:
Methyl cellulose
Brilliant yellow flame
Ethyl cellulose
less brilliant flame accompanied by dripping
Benzyl cellulose
Brilliant sooty flame smells like bitter almonds
Odour of
burnt
paper
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IDENTIFICATION OF PLASTICS
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CONFIRMATION TEST - Thermoplastics
Polyvinyl Alcohol
A Sample (about 0.02g) is dissolved in water 5ml and
iodine reagent described above (5 drops) added. The
formation of Blue colour confirms the presence of
Polyvinyl alcohol.
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IDENTIFICATION OF PLASTICS
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CONFIRMATION TEST - Thermoplastics
Casein
A sample about (0.02g) is dissolved in concentrated HNO3
(2ml) by boiling for about 5mn. The solution is cooled and
excess 5N ammonium hydroxide added. The formation of
orange colour confirms the presence of casein.
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IDENTIFICATION OF PLASTICS
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CONFIRMATION TEST - Thermoplastics
Shellac
A sample (0.05g) is dissolved in ethanol (1ml) with
warming. To the cooled solution is added water (about 1ml)
to give an emulsion like precipitate. 5N aqueous NaOH 2
drops is added to the mixture. The colour change is
reversed on acidification with 5N HCL. The formation of
Violet - red colour confirms the presence of Shellac.
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IDENTIFICATION OF PLASTICS
CONFIRMATION TEST - THERMOSET PLASTICS
Test for formaldehyde
A small amount of sample is boiled in water in presence of
H2SO4 and filtered. Few drops of 5% aqueous chromotropic
acid solution (1,8-dihydroxynaphthalene-3, 6-disulphonic
acid) and excess of cone. H2SO4 are added to the filterate
and heated at 1000 C for few minutes. In the presence of
formaldehyde, the solution turns violet/dark violet. Poly
(vinyl formal), polyoxymethylenes, PF, UF and MF resins
contain formaldehyde.
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IDENTIFICATION OF PLASTICS
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CONFIRMATION TEST - THERMOSET PLASTICS
Test for Phenol in PF
Million's Reagent: About 10 gm of Hg is dissolved in 10 ml.
of HNO3 by gentle heating and then diluted with 15 ml. of
distilled water.
The sample is heated to boiling for two minutes with 1 ml.
of clear million's reagent. Red colour indicates the
presence of phenol in the sample.
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IDENTIFICATION OF PLASTICS
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CONFIRMATION TEST - THERMOSET PLASTICS
Test for Urea in UF
About 0.5 gm. of sample is refluxed for 30 min. with 20%
acetic acid (50 mI.). The mixture is cooled and filtered. To
the filterate added a solution of (2 ml.) xanthydrol in
methanol (1% solution) and boiled for 1-2 minutes. White
bulky precipitate confirms the presence of urea.
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IDENTIFICATION OF PLASTICS
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CONFIRMATION TEST - THERMOSET PLASTICS
Test for Melamine in MF
About 0.5 gm of sample is refluxed with 80% acetic acid
(25 ml.) for 30 min., cooled and filtered. Then the filterate
is evaporated to dryness and added 2 ml. of water, cooled
and filtered. To the filtrate one drop of saturated aqueous
picric acid is added. Yellow precipitate indicates the
presence of melamine.
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IDENTIFICATION OF PLASTICS
Cont.
CONFIRMATION TEST - THERMOSET PLASTICS
Tests for Epoxy Resin
Foucry Test:
About 0.25 gm. of sample is dissolved in 98% H2SO4 by
slight warming. After cooling 1 ml. of 63% HNO3 is added.
After shaking, the mixture is poured into 100 ml. of 5%
aqueous NaOH. A bright red or orange red colour
indicates the presence of epoxy resin.
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IDENTIFICATION OF PLASTICS
Rubber Testing: For identification of CR, NBR, SBR, NR / IR, IIR type of
rubbers
Test Procedure: Heat strongly 0.5gm of sample in a test tube until sample begins
to decompose and pass the fume in solution II and I and observe change in
colour initially and after heating. (Refer the following table)

Solution - I : Dissolve one gram of p - dimethyl amino benzaldehyde in
5ml of HCl and add 10ml of ethylene glycol. Adjust the density to 0.851
gm /cc. by addition of methanol.

Solution - II : Dissolve 2gm sodium citrate , 200mg of citric acid , 300mg
of bromo cresol green and 300mg of metanil yellow in 500ml of water.
RUBBER
Solution - I
Solution II
Initial
After Heating
Blank Solution
Pale Yellow
Pale Yellow
Green
CR
Yellow
Pale Yellow Green
Red
NBR
Orange Red
Red
Green
SBR
Yellow Green
Green
Green
NR / IR
Brown
Violet Blue
Green
IIR
Yellow Droplet Floats
Pale Blue Green
Green
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IDENTIFICATION OF PLASTICS
Identification code of plastics
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IDENTIFICATION OF PLASTICS
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