Quantcast Uncured Elastomers

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loss of plasticizer.  Unreinforced, they have an extremely high
coefficient of thermal contraction-expansion.  However,
reinforcement (woven fiberglass mat or polyester reinforcement)
can vastly improve dimensional stability.
Uncured Elastomers.  Uncured elastomers are chemically
intermediate between the thermosetting (i.e., elastomeric) and
thermoplastic polymers.  The single-ply membranes containing
these intermediate polymers are CPE (chlorinated polyethylene),
CSPE (chlorosulfonated polyethylene, known commercially as
Hypalon), and PIB (polyisobutylene).
Relative to elastomeric and thermoplastic sheets,
advantages are:
lap seams can be heat-or adhesive-bonded.
easier field-forming of reliable lap seams;
c)  may cure or vulcanize over a period of time and
become thermosets.
A major disadvantage is that they lack the abrasion
resistance of vulcanized rubber.  Another disadvantage of CSPE is
that after it has cured, it is difficult to repair using heat-
bonding methods.
Modified Bitumens.  Modified bitumens are essentially
rubberized asphalts.  The addition of rubber to the asphalt
imparts elastomeric properties to the asphalt and increases the
membrane's breaking strain by a factor of 10 or more compared
with a conventional built-up bituminous membrane's breaking
strain.  The polymers used to make these physical improvements in
the modified-bitumen membranes include atactic polypropylene
(APP), styrene-butadiene rubber (SBR), and styrene-butadiene-
styrene block polymer (SBS).  Reinforcement is generally
polyester or glass fibers, sometimes in combination.
The Canadian General Standards Board (CGSB) divides
modified bitumen membranes into three categories:
a)  By exposure:  Type 1, exposed (always anchored);
Type 2, shielded (anchored or loose-laid);
b)  By surfacing:  Class A, granule-surfaced; Class B,
metallic-surfaced; Class C, plain-surfaced;


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