IDENTIFICATION OF RUBBER

          IDENTIFICATION OF RUBBERS

 

S.No.	Identification process	Description	Remarks
PRELIMINARY  EXAMINATION
1	Appearance	Raw polymer	Physical form may be lumps, sheet, granules
		Compounded stock	Powder, Paste, Milled sheet
		A finished article	Any finished product like Gasket
2	Method of Fabrication	Moulded, Extrusion, Calendered, Casting	To examine the flash, flash line, other process marks

3	Rigidity	Flexibility	To identify for thermo plastics, rubbers both can be usually cut cleanly with a sharp knife
4	Effect of heat
	A small piece (of about 0.1 gm) of the material is placed on a spatula and warmed very gently over a small Bunsen flame so that decomposition does not occur and the effects on the sample is noted
		Appreciably softens	Unvulcanised rubber of themoplastic
		Little effect	Vulcanized rubber or thermosetting plastics
		Initially softens & then hardens	Uncured compounded polymer which cross- links during the heating process

IDENTIFICATION OF RUBBERS

Sl. No.	Identification process	Description	Remarks
INITIAL TESTS: (To be done before the heat test analysis)
1	Beilstein Test
	A bright Copper Wire (about 5 cm long with one end embedded in a cork, which serves as a handle) is cleaned by heating to redness in a colourless Bunsen flame & the material under test is touched by the hot wire which is then returned to the flame

		Green Flame	Presence of Halogen or  Halogen containing ingredients in the sample (Fluorine seldom gives a positive result)
2	Specific gravity by floation method
	The sample of about 0.02 gm is put into the water and pushed below the surface of the water in a test-tube with a glass rod
		Floats	If raw sample may be Butyl, EPDM, NR, IR, BR, Silicone, SBR, Vinylpyridine Rubber
		Submerged	On the raw sample – CR, FKM,  CSM, NBR-PVC
3	Bounce
		No Bounce	Butyl rubber
		Bounce	Other than Butyl, if too high is the bounce, then BR
4	Odour	Pronounced Odour	Polysulphides, NR, Acrylic standard odours has to be compared
5	Feel	Waxy	PTFE
6	Colour		Particularly for Raw Polymer Phenol Formaldehyde will be darker
HEATING TESTS
A small piece (about 0.1 gm) of the material is placed on a clean spatula, previously heated to remove any traces of combustible material. It is then gently warmed without ignition over a small colourless Bunsen flame until it begins to fume. The sample is then removed from the flame and the odour of the fumes and whether they are acid, alkaline, or neutral (using damp litmus paper) is ascertained. The odour, fumes type is to be observed. Now the sample is moved to the hottest zone of the small Bunsen flame and “the observations on the burning behaviour, nature & colour of the flame, continuity of the burning behaviour after the removal from the flame, & the nature of any residue” to be observed

	Observations:
	i) Material burns but extinguishes itself on removal from the flame
		Bright yellow flame with grey fumes & acrid odour	May be CHLOROSULPHONATED POLYETHYLENE Rubber (CSM)
		Yellow, smoky flame with acidic fumes & acrid odour	May be Polychloroprene – CR
		Yellow flame with acidic fumes & slight sickly odour	May be fluorinated rubbers (Vinylidene Fluoride co- polymers) FKM
		Yellow flame with acidic fumes & slight acrid odour	May be Polychlorotrifluoroethylene Polymer
		Yellow flame burns with extreme difficulty, chars very slowly with acidic fumes & no  odour	May be Poly Tetrafluoroethylene polymer
		Yellow flame with green base with acidic fumes & acrid odour	May be Polyvinyl Chloride Polymer
		Pale yellow flame with acidic fumes, sparks on ignition & acrid odour	May be Polyvinylfluoride Polymer
		Yellow with green base, spurts green flame with acidic fumes & acrid odour	May be Polyvinylidene Chloride Polymer
		Yellow with green base smoky flame with acidic fumes & pungent  odour	May be Rubber Hydrochloride

		Pale yellow with light blue-green smoky flame which is very difficult to ignite, alkaline fumes & fish-like odour (formaldehyde)	May be urea-formaldehyde polymer
	ii) Material burns and continues to burn on removal from the flame
		Yellow smoky flame & fruity odour	May be acrylic rubber
		Yellow smoky flame & light sweet odour	May be butyl rubber
		Yellow flame with blue base & resembles burning candle wax	May be EPDM Rubber
		Yellow smoky flame & sickly sweet odour	May be Nitrile rubber
		Yellow flame with blue base, smoky & sickly sweet	May be Polybutadiene rubber
		Yellow smoky flame & pungent odour	May be Polyisoprene (Natural rubber and Synthetic IR)
		Blue flame with acidic fumes & Sulfurous odour	May be Polysulphide rubber
		Yellow with blue base & acrid odour	May be Polyurethane Rubber
		Bright yellow-white flame with white fumes & white residue & no  odour	May be Silicone Rubber
		Yellow flame with very smoky & Styrene odour	May be Styrene-butadiene polymer (SBR), Vinylpyridine Polymer.

		Yellow smoky flame with black residue & vinyl acetate odour	May be Polyvinyl acetate
ELEMENTAL   ANALYSIS
	Elemental analysis indicate the nature of the unknown polymer by analyzing elements Nitrogen, Sulfur,  Halogens
	For Raw Polymer / Rubber solvent extractions is not required
For unvulcanised & vulcanized rubber the solvent extraction is essential as other compounding ingredients will also contain Nitrogen, Halogens & Sulphur. The following method can be used for solvent extraction.
About 2 gm of sample is finely cut with the scissors/knife and has to be divided into two portions of 50 ml each of Methyl Ethyl Ketone for 15 min. each in a beaker, covered with a watch-glass, on a steam bath. The extracted sample is dried with filter paper or if sticky, in an oven @ 100oC. This procedure which is unsuitable for quantitative work, removes organic compounding ingredients (& their residues) which may contain nitrogen, Sulphur (if the sample is vulcanized the extracted material will still contain small amounts of sulphur) and halogens.
The Lassaigne procedure is used for analysing the elements: The procedure of sodium fusion forms the basis of the examination for elements. A small piece of clean sodium (about 0.02 gm) is placed in an ignition tube and a small quantity (about 0.1 gm) of the substance to be tested is added. The tube is gently heated until reaction subsides and then strongly until the glass is red-hot. The tube is then plunged into distilled water (10ml) contained in a boiling tube. This operation can be dangerous and the mouth of the boiling tube should be covered. The resulting mixture is heated to boiling and filtered from carbon and fragments of glass. The filtrate is divided into four equal portions which are used for the following tests:

	a) NITROGEN TEST:
	The test portion is boiled with 3 drops of freshly prepared aqueous ferrous sulphate (approx. 5%) and then cooled. After acidification with 5N sulphuric acid, a  drop of 0.5N aqueous ferric chloride is added.
		- A substantial blue precipitate of ferric ferrocyanide (Prussian Blue)	* Presence of Nitrogen
		- The precipitate is slight	* Nitrogen is not a constitutent of the  polymer
	b) SULPHUR TEST:
	Three drops of freshly prepared aqueous sodium nitroprusside (approx. 5%) are added to the test portion.
		- A violet colouration	* Presence of Sulphur
		- A transient colouration	* Small amounts of Sulphur
	c) CHLORINE & BROMINE TEST:
	The test portion is acidified with 5N nitric acid and if nitrogen or sulphur has been found, the solution is boiled for 2 min. 0.1N aqueous silver nitrate is then added.
		- A white precipitate, soluble in ammonia	* Presence of chlorine
		- A yellow precipitate insoluble in ammonia	* Presence of Bromine

		No precipitate	* May be the presence of Fluorine also
	d) FLUORINE TEST
	An aqueous solution of zirconium nitrate (0.1%) and alizarin red S(0.1%) is prepared. Filter paper is immersed in the solution and then allowed to dry. When required, a small piece of the paper is moistened with aqueous acetic acid (50%). The solution to be tested is neutralized with 5N hydrochloric acid and a drop placed on the moistened test paper
		- The red spot turns yellow	* Presence of Fluorine
	If all the above elemental analysis gives the negative test results then the polymer / rubber will contains only carbon & hydrogen or only carbon, hydrogen & oxygen or is a silicone
	Polymer / Rubber classification based on the above test procedures to following  groups:
		i) Containing Nitrogen	* May be Nitrile Rubber, Polyurethane Rubber, Vinylpyridine
		ii) Containing Sulphur	* May be Chlorosulphonated Polyethylene (CSM) (small amount with Chlorine, Polysulphide (Large amount)
		iii) Containing Chlorine	* May be Chlorinated Butyl, Chlorosulphonated Polyethylene, Polychloroprene (also with small amount of Sulphur for G Type), Chlorinated Polyethylene

		iv) Containing Bromine	* May be Bromo Butyl
		v) Containing Fluorine	* May be Fluorinated Rubbers, Fluoro-silicones
		vi) Not containing Nitrogen, Sulphur, or halogens	* Acrylic Rubber / Polymer, Butyl, EPDM, Natural Rubber (possibly with small amount of Nitrogen), Polybutadiene Rubber (BR), Polyisoprene Rubber (IR) silicone & SBR