PowerPoint Presentation
NATURAL RUBBERRubber is a natural polymer obtained from rubber
trees (Hevea brasiliensis).
Natural rubber or polyisoprene is made up of many isoprene units
as it monomers.
CHARACTERISTICS OF NATURAL RUBBER
1) Soft white solid2) Has elastic properties (returns to its
original shape and size after being stretched or compressed).
3) Becomes sticky upon heating
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4) Becomes hard upon cooling
5) Soluble in organic solvents
6) Insoluble in water7) Water resistant (forms an excellent
barrier to water).
8) Poor electrical conductor.RUBBER MOLECULES
Rubber molecules are enclosed by a layer of protein
membranes.The membrane are negatively charged, cause the rubber
molecules to repel (push) each other.This prevent coagulation
(change from liquid to solid state), so the latex remains in liquid
state.
Protein membraneRubber polymer REACTION OF LATEX WITH ACID AND
AMMONIA
Addition of acid can cause the coagulation of latex.1) REACTION
OF LATEX WITH ACID
Acid contains positively charged hydrogen ions.It will
neutralise the negatively charged protein membranes.Addition of
acidRubber polymer
This causes the membrane to break and let the rubber polymers
free.These rubber molecules then combine together and coagulate to
form solid.
Free rubber polymer
Coagulation of latex
The latex may coagulate without addition of acids.This happen
naturally due to activities of bacteria in the latex, which produce
acids.
Addition of ammonia solution (an alkali) can prevent the
coagulation of latex.Ammonia solution contains negatively charged
ions called hydroxide ions.The negative charged ions neutralise the
positive charged ions, which produced by bacteria in latex.Thus,
the coagulation of latex could not occur.
Negative charged hydroxide ion neutralises hydrogen ion from
acid
