A)
BURNING TEST
Cut about 2 cm long strip and burn the
strip on burner flame. Apply flame corner (edges) to strip and observe :
(a) SBR - Burns with smoky flame and
unpleasant smell Burnt residue is non-tacky.
(b) NR - Burns comparatively with less
smoke than SBR and distinctive odour. Burnt residue tacky.
(c) CR - (Polychloroprene Neoprene) Strip
will extinguish on removal of flame and gives smell of Hydrochloric acid. Also
on rubbing the vulcanized piece against rough surface typical polychloroprene
odour.
(d) NBR - Burns with smoke with unpleasant
smell. Formation of bubbles at the burnt end.
(e) Silicon - Burns with white ash which is
Silica.
(f) Hypalon - Will extinguish as CR but on
rubbing no typical smell.
(g) Butyl - Burns with clear flame and If
loaded with Carbon black would give smoke. Hydrocarbon type odour while burning.
Formation of bubbles at burnt end.
B)
ACID TESTS
1) Conc H2SO4 - Place about 10mg piece
in test tube containing 1 cc. Conc. H2SO4 and wait for few minutes. Except Butyl
rubber, all others get decomposed.
2) Conc HNO3 - Stability of rubber
polymers against HN03 is in the following decreasing order.
Hypalon, Butyl, Polychloroprene, Nitirle, SBR, NR. The stability will
also depend on other compounding ingredients.
C) COPPER WIRE TEST
Heat a piece of copper wire to
red heat on burner till no green flame is visible. Touch this red hot wire to
rubber sample for few seconds and hold over the burner flame. If the flame
becomes greenish presebce of halogens is indicated i.e presence of CR, Hypalon,
etc. (Halogen containing polymers).
