Uses and Performance of Rubber Sealants

Abstract

A pertinent aspect in the preparation of sealants is testing 1,3 , which is important to confirm the effectiveness of a bonding process and also to investigate parameters or process variables in the performance of the bonds. There are two general test categories for sealants which comprise of fundamental property test and end-use test. The most common fundamental property tests for sealants are the measurement of viscosity, shelf life, service life, cure rate, hardness and percentage of solids. On the other hand, the end-use tests for sealants are movement capability test, peel adhesion, tear strength, compression set resistance and environmental tests.

Full text

UV absorbers and ozone inhibitors. These additives are
added to improve adhesion properties and provide special
performance with regards to applications and storage
properties.
A pertinent aspect in the preparation of sealants is
testing1,3, which is important to conrm the effectiveness
of a bonding process and also to investigate parameters
or process variables in the performance of the bonds.
There are two general test categories for sealants which
comprise of fundamental property test and end-use test.
The most common fundamental property tests for sealants
are the measurement of viscosity, shelf life, service life,
cure rate, hardness and percentage of solids. On the
other hand, the end-use tests for sealants are movement
capability test, peel adhesion, tear strength, compression
set resistance and environmental tests.
Uses of Sealants
Sealants are often classied according to their end-
use or function. The end-use classications include
construction sealers, automobile sealers, insulated
glass sealers as well as highway, walkway and airport
runway sealers. Typical application areas for sealants are
presented in Table 1.
Although sealant volume is mostly used in construction
and automotive applications, there are other end uses for
sealants as niche application in the agricultural sector. For
instance, a sealant is used in G-Flex, a latex stimulation
technique as well as in the rainguard apparatus, which is
as an apparatus to protect latex collection from rain. In the
la te 1980s6, Rubber Research Institute of Malaysia (RRIM)
developed ‘YUSIL’, a type of sealant that can be used with
INTRODUCTION
Sealant is a material capable of attaching at least two
surfaces together by lling the space between them to
eliminate dirt, moisture and chemicals1. Sealants have low
strength due to large amounts of inert ller material, mainly
for cost reduction and gap lling purposes.
Generally, sealants contain a base polymer, ller,
plasticisers and additives to improve adhesion1–2. The
base polymer is usually supplied in the form of solid
rubber, liquid polymer or latex emulsion. Solid rubber is
liqueed with a solvent. Liquid polymers with low viscosity
such as polysulphide, silicone and polyisobutylene can
be used to make sealants with little or no solvent, whilst
latex emulsions including acrylic, polyvinylchloride,
polyvinylacetate and their blends are easy to formulate
since the base material is in a uid form. Solvents are also
required in large amounts to liquefy the base polymer
in order to lower its viscosity, facilitate application and
help homogenise the various ingredients in sealant
formulation. Fillers are added into sealant formulations
to increase viscosity and total solid content, resulting in
faster drying in the case of water-based sealants. Fillers
also provide better gap lling properties while lowering the
cost of sealants. In general, a ller does not give much
added strength but may affect other performances such
as hardness and water resistance. Examples of suitable
llers are calcium carbonate, silica, titanium dioxide and
carbon black. Plasticisers may also be added as one of the
ingredients in a sealant’s composition. It is used to reduce
elastic modulus, attain desirable degree of softness and
enhance stress relaxation ability of the sealant composite.
Other type of additives may also be included, for
instance, coupling agents, primers, antibacterial agents,
Rohani Abu Bakar
37
Volume 13(2) 2013
Uses and Performance of
Rubber Sealants
Uses and Performance of
Rubber Sealants

38 MRB Rubber Technology Developments
Malaysian Rubber Board (MRB) in particular has
developed a butyl rubber sealant to be used in G-Flex
gas stimulation technique. The sealant, made from a
compound of butyl rubber, ller and plasticiser, was mixed
using an internal mixer followed by the extrusion process.
This butyl rubber sealant was further tested according to
the American Society for Testing and Materials (ASTM)
standard test method. Presently, there are two ASTM
test methods adopted in MRB. These methods are Effect
of Heat Aging on Weight Loss, Cracking and Chalking of
Elastomeric Sealant (ASTM C 792)7 and Adhesion in Peel
of Elastomeric Joint Sealants (ASTM C 794)8.
The test method for Effect of Heat Aging on Weight
Loss, Cracking and Chalking of Elastomeric Sealant
(ASTM C 792) is suitable for elastomeric solvent release-
corrugated aluminium foil as an apparatus to protect latex
collection from rain, commonly termed as a rainguard
abbreviated as RRIMGUD.
Performance of Butyl Rubber Sealants
Butyl rubber is a copolymer of isobutylene with about
2% of isoprene. It has a relatively long and straight
carbon-hydrogen backbone and this regular structure
provides butyl low permeability to air, gases and moisture.
Approximately 86%5 of worldwide usage of butyl rubbers
is found in tyres or inner tubes. In addition to tyre
applications, butyl low air impermeability, weathering and
ozone resistances, good ex properties as well as stability
make them good material for hoses, mechanical goods
and construction sealants.
TABLE 1. TYPICAL APPLICATION AREAS FOR SEALANTS1,2,4
Type of Sealant Typical Application
Silicone solar panel, construction, insulating glass, automotive
Polyurethane automotive glass bonding/sealing, high performance building joints, insulating glass,
waterproong
Plastisol body-sealing/automotive
Emulsion exterior joints and interior use joints on plywood
Butyl caulking expansion and contraction joints, home sealants, construction, repair of gaskets,
tapes, with resin for hot melts on insulating glass
Polysulphide aircraft fuel tanks, boating, building joints, sealing between dissimilar metals
Silyl Modied Construction
Rainguard application G-Flex
1.2
1.0
0.8
0.6
0.4
0.2
0
7 days
A+B A B
Weight loss (%)
28 days 7 days
Curing period and types of butyl rubber sealant
23ºC 50ºC 70ºC
28 days 7 days 28 days
Rainguard application G-Flex
1.2
1.0
0.8
0.6
0.4
0.2
0
7 days
A+B A B
Weight loss (%)
28 days 7 days
Curing period and types of butyl rubber sealant
23ºC 50ºC 70ºC
28 days 7 days 28 days
Figure 1. Application of Sealants

39
Volume 13(2) 2013
and joints. In general, for every 1% weight loss, there is
about 2% volume shrinkage. However, a low weight loss
and absence of chalking or cracking does not necessarily
assure good durability.
The Adhesion in Peel of Elastomeric Joint Sealant
(ASTM C 794) test method provides a good indication of
how sealants might perform under severe peel conditions.
It gives a valuable measurement of the ability of cured
sealants to maintain a bond to the substrate. This is
the most common method for determining the relative
adhesion of sealant joints. Figure 4 shows that peel
strength of butyl rubber sealant B is higher compared to
that of butyl rubber sealant A and butyl rubber sealant
A+B.
SUMMARY
Current demand in construction, transportation, industrial,
aerospace, appliances and many other industries could
not be met without advances in sealants. Construction
and automotive industries represent a very large market
for sealants. The basic function of sealants include
lling the gap between two or more substrates while
maintaining sealing property for the expected lifetime,
type sealants. The signicance of this method is due to
weight loss through volatilisation of sealant composition
that may affect appearance of the sealant due to shrinkage
and sealant performance due to loss of functional sealant
compositions. Excessive shrinkage can cause voids in
sealant joint and uneven stress distribution. Substantial
losses of weight may help predict early failures in durability
of sealants.
Three types of butyl rubber sealants were developed.
The percentages of weight loss of the three sealants
were measured and determined according to ASTM
C 792. The three sealants were designated as butyl
rubber sealant A, butyl rubber sealant B and butyl rubber
sealant A+B. Instead of exposing the sealants at 70ºC
based on ASTM C 792, the sealants were exposed to
50ºC in an oven to observe temperature dependence.
From Figure 3, the percentage of weight loss for butyl
rubber sealant B is lower than butyl rubber sealant A
and butyl rubber sealant A+B. This indicates that as
temperature and time of curing increases, weight loss
increased. It can be observed that all sealants lost not
more than the minimum requirement of 7% of their original
weight or show any cracking and chalking when tested.
Low shrinkage is often required after application of sealant
since the main objective of sealants is to seal assemblies
Rainguard application G-Flex
1.2
1.0
0.8
0.6
0.4
0.2
0
7 days
A+B A B
Weight loss (%)
28 days 7 days
Curing period and types of butyl rubber sealant
23ºC 50ºC 70ºC
28 days 7 days 28 days
Figure 3. Weight loss percentages at several curing period of butyl rubber sealants.

40 MRB Rubber Technology Developments
REFERENCES
1. EDWARD E. PETRIE (2000) Handbook of Adhesives and
Sealants. McGraw-Hill Publications, 451–474.
2. ADOLFAS DAMUSIS (1967) Sealants. Reinhold Publishing
Corporation.
3. PHILIPPE COGNARD (2005) Adhesives and Sealants:
Basic Concepts and High Tech Bonding. Elsevier.
4. MICHAEL GROWNEY (2013) The Global Sealants Market.
www.pcimag.com April 2013, 30–32.
5. Paintindia (2013) April 2013, 165–166.
6. M.H. SAKHIBUN, A.A. YUSOF, P.D. ABRAHAM, M.D.
MOHD SIDEK, H. ISMAIL, M.T. AHMAD ZARIN, H.G.
CHUA (1988) Promising RRIM Rainguard with New Sealant
(RRIMGUD), Planters’ Bulletin, 194, 18–23.
7. ASTM C 792 (1993) Standard Test Method for Effects of
Heat Ageing on Weight Loss, Cracking and Chalking of
Elastomeric Sealants.
8. ASTM C 794 (2001) Standard Test Method for Adhesion-in-
Peel of Elastomeric Joint-Sealants.
operating conditions and environment. To determine
sealant performance, testing is an extremely important
aspect which should not be neglected. There are many
parameters that can affect performance of sealants.
Many of the useful and common tests for sealants are
dened in terms of American Society for Testing and
Materials (ASTM) specications and also International
Organisation for Standardisation (ISO). They are very
useful for comparing and determining the consistency of
materials and processes. However, they are less valuable
in predicting the actual strength of specic joints under
actual operating conditions.
The test methods adopted in MRB are selected ASTM
standards for sealants. The data obtained from the
test methods adopted does not intend to simulate the
conditions encountered by a sealant in actual operating
condition or eld exposure. However, it provides a
quantitative approximation in sealant performance.
ACKNOWLEDGEMENT
Assistance rendered by En. Meor Syuhaidy Meor Shapiei
is gratefully acknowledged. Acknowledgement is also
extended to En Asrul Mustafa, Dr Fauzi Mohd Som, Dr
Mazlina Mustafa Kamal, Pn Siti Salina Sarkawi and En
Muhammad Akbar Abdul Ghaffar for their support.
6
5
4
3
1
2
0
A+B A B
Peel strength (N)
Types of butyl rubber sealant
Figure 4. Peel strength of butyl rubber sealants.