Bitumen adhesive
Bitumen, bituminis is a very ancient product. The Egyptians, the Greek and the Romans were
already acquainted with it. The Romans called it earthpitch. Its natural source was Ragusa on
Sicily, where it was found in rock-formations, which contained about 14% of bituminis. They
were using it as an adhesive for wood and glass, as well as a caulk sealant to make their boats
watertight. There were other places in Europe where people discovered this sticky, dark-
brown, tough and very useful product, as Val de Traver, Neuchâtel and Bentheim. In Europe
bitumen is a common term. When we are talking about asphalt, we actually mean bitumen
mixed with fillers, pebbles and flintstones to pave roads. While in the U.S. bitumen is called
asphalt. A very famous natural source is the Asphalt Lake in Trinidad. The product found
there contains about 39% of bitumen.
While the request for bitumen was continuously increasing, the industry developed a synthetic
alternative. Nowadays bitumen is made from crude oil. In a few words: separation sand and
water and distilling off all the low molecular products of crude oil gives a residue which is
also called bitumen. It is a mixture of heavy carbonhydrogens with molecular weight of 1000
to 10.000. Bitumen consists of an oily phase, the maltenes, and a dispersed phase of
asphaltenes. These phases can be separated by extraction with selected solvents. The
consistency may vary from syrup-viscous to a hard brittle product. This product becomes low
viscous at higher temperatures. Bitumen is thermoplastic by nature. It has a darkbrown colour.
It is poisonless, tasteless and it has a very soft non-disagreeable smell. It is very resistant to
inorganic bases and acids. The Water Vapour Transmission Rate (WVTR) and the Water
Transmission Rate are very low.
Because of its viscosity elastic properties bitumen happens to flow under certain conditions.
The amount of flow depends of the type of bitumen, of the temperature, the time, the layer
thickness and of the force being applied. There are very many types of bitumen: like
penetration bitumen, hard and blown bitumen and modified bitumen. The latter are mixtures
of thermoplastics with penetration bitumen.
Bitumen is applied in various ways as in:
· paving
· hydraulic engineering, for example in dike and sea-bottom coverings and its
reinforcement
· adhesives in building and roof covering materials
· sealants
· covering for pipelines and storage tanks
· protective coatings for steel and concrete against seawater
· impregnating ropes, non-wovens and wood
· it has found its way in electrical industry and it is used for many other applications
As already mentioned before, bitumen has some disadvantages:
· it is black, which makes it unsuitable for many applications
· it is high viscous or hard, so it needs energy before being applied
· it has cold flow properties, so modifications are necessary when a constant load is present
· it is brittle at low temperatures (hard-bitumen)
· it is fluid or soft at higher temperatures (penetration bitumen)
· it is not resistant to solvents, oils and greases
1
But bitumen has so many advantageous properties, which is in the favour of this product.
Therefore, it is a very attractive base material for industrial applications.
· it is low cost, that makes it an economically interesting base material
· is has bonding properties, so it is an interesting product for adhesives
· it is very resistant to water and organic chemicals it is attractive for coatings and adhesives
· while its WVTR is low, it prevents steel from corrosion and concrete from degradation
The cold flow, the flow and brittleness at low temperature are the most unpleasant
performance properties of bitumen. For modern adhesive applications, where more and more
low temperature flexibility and high temperature resistance are required, bitumen is
unsuitable. The need for high performance adhesives depends of the application. We all know
that the aircraft industry has higher requirements than the building industry. It is clear that this
building industry needs a lot of adhesives. The adhesives to be used should have the following
properties:
List of demands for building industry adhesives :
a. low cost
b. easy-to-handle
c. independence of weather during application
d. colour: preferably black for roofing and cellars
e. temperature resistant from 20 up to at least 80ºC
f. for moving connections flexibility is required
g. impermeable and resistant to water and water vapour
h. long lasting: at least 30 years
i. resistant to acidic rain and basic leakwater
j. it should not affect the environment
Now, it is so, that bitumen matches all these properties except e. and f. So if these two
parameters can be achieved by modification of bitumen, the result will be a good adhesive for
building application.
There are three ways to improve the cohesive properties of bitumen:
1. combination with thermosetting like PUR
2. incorporation of a thermoplastic material like APP, EVA, SBR, nitril or butyl rubber or
combinations here of
3. incorporation of a low molecular weight substance, which is subsequently reacted, so a
matrix of branched polymers with bitumen is achieved.
Sub 1 Although very strong adhesives can be obtained, non is useful as a hotmelt. Because
these are thermosetting, we leave this subject.
Sub 2 In this way pure thermoplastic compounds are obtained. High shear rates are necessary
to get constant quality products. These products are very suitable as compounds to
make pressure sensitive tape for the automotive and the building industry. As hotmelts
they are only applicable by extruders.
Sub 3 Hardcast worked out recipies in which low molecular weight thermoplastic materials
are mixed with bitumen. The next step is slightly crosslinking the thermoplastic
material whereas some of the bitumen is reacted with. The product obtained is called
Hardcast Bitumentape.
Since 1982 Hardcast produces Bitumentapes. The adhesive is the base material for all related
2
products. Originally Hardcast started with Bitumentape as a hotmelt in tapeform.
Projects accomplished more than 10 years ago are still watertight.
Bitumentape is used now as a water barrier and overlap tape-sealant in ponds, basins, car
grave yards, bathrooms, building industry etc. The adhesion increase over time and the
elasticity of the adhesive is more than 200%.
Other results of our testing :
(Bitumentape double sided, 1,4mm thickness)
Water Vapour Transmission Rate ASTM E 96-53T
0.29grs/m²/24 hrs
Water Transmission Rate NEN 1013
no water transmitted
Temperature-resistance
-20
to
70°C
Resistance to acidic and basic influences
after 1 year immersion no change
Resistance
to
manure
after 1 year immersion no change
Comparison of resistance of Hardcast bitumentape vs other types of sealants :
Bitumen
adhesive
PUR
Polysulphides
Silicones
UV
radiation
+
+
+
++
Water
++
+
++
++
Acids
++
- +
++
Bases
++
0
+
+
Solvents
-
0
+
-
Manure
++
-
-
-
On the long term it was the Bitumentape that showed out to be the only material resistant to
manure. So it is an excellent product for agricultural applications such as dungpits and
manure containers.
Hardcast produces several types of Bitumentape all with different backings. Most of
them are used in building industry for sealing, reparation and renovation.
Several types Bitumentape :
Type
Thickness
in
mm
Backing
carrier
DSF7910
1.0
*
glassfiber
AAA7910
1.0
* aluminium
foil
VPB7914
1.2
laminated
PE-foil
PWA7908
0.8
PP
non
woven
ALP7910
1.0
* Alu-PE
laminate
· also available in 1.4mm
Safety aspects
Bitumen and bitumen compounds are generally speaking: Non toxic, non carcinogeneous and
they do not affect the environment. However, one should take care, not to allow more than 5
mg of an aerosol of bituminous products per m³ of air, especially when one is spraying.
So finally it will be clear that bitumen, already used for over ages, has very good properties
for applications in building industry. Modification of bitumen with reacted thermoplastics
results in products suitable as pressure sensitive adhesives.
Written by E Overtoom
3