CHARACTERIZATION OF ADHESIVES BASED ON AQUEOUS DISPERSION OF VINYL ACETATE
1,2
1
Catarina Santos , M. R. Ribeiro , M. C. Mouro
2
1 - Instituto Superior Técnico, 2 - Resiquímica, S.A.
ABSTRACT
The use of adhesives is very extensive and is present in our daily lives. The adhesives are substances
(usually polymers) that allow the union of different materials, introducing new functions and properties in
these materials after bonding.
The purpose of this study was the characterization of adhesives based on aqueous dispersion of vinyl
acetate used in wood and paper/board adhesives. This characterization related the adhesive performance in
application with the formulation of aqueous dispersion.
It has been concluded that structure of the particles, the stabilization system and formulation of polymers
used has great influence on the final application (adhesive).
Key-words: adhesives, vinyl polymers, stabilization system, adhesion, cohesion and tensile strength.
1 INTRODUCTION
Adhesive bonding is the process of joining two
The material of the adhesive layer is
or more solid parts with an adhesive substance.
commonly a polymer (natural or synthetic). In this
The advantages of adhesive bonding are the
study were characterized vinyl homopolymers with
ability of join dissimilar materials using fast and
application in wood and paper/board adhesives.
cheap
These polymers are aqueous dispersions of vinyl
joining
convenience
techniques,
and
flexibility.
providing
Adhesive
design
joint
acetate.
generally consists of two substrates surfaces with
An aqueous dispersion is a heterogeneous
the adhesive material filled gap between them.
system with a solid phase (polymer insoluble in
However the adhesive layer is not uniform.
water) that is dispersed in a liquid phase (water),
Besides the part of the adhesive layer, properties
remaining a pseudo-stable condition due to the
of which are not affected by the substrate, there
action of substances with special protective
are two boundary layers, witch have been
colloids and/or emulsifiers.
changed by impurities and products of reactions
Stabilization systems of vinyl polymers in study
at the substrate surfaces. The principle basis of
were protective colloids (polyvinyl alcohol and
adhesive
cellulose
bonding
is
a
phenomenon
called
derivatives)
and
emulsifiers.
The
adhesion. Adhesion is a complex physicochemical
protective colloids are water-soluble polymers with
process occurring at the interface of two materials
high molecular weight. The protective colloids
brought into an intimate contact, which result the
stabilize the emulsion during the polymerization
formation of an attractive force between two
and thus allow the stabilization of polymer
materials.
particles. Due to its high molecular weight and its
1
structure, the protective colloids are partially
two hours to determine the amount of
incorporated into particles of polymer ("grafting
polymer in dispersion.
polymerization"). For these reasons, the aqueous
dispersion
stabilized
with
protective
samples was measured with a Brookfield
colloids
DV-E Viscometer.
exhibit a high stability on the mechanical strength
when compared with the dispersion stabilized with
Brookfield
Model
DV-III
Programmable Rheometer in order to
water). In
determine the rheological behaviour.
aqueous solution, the emulsifiers form micelles in
which the hydrophobic part are in the contact with
Rheology – This test was determined
using
hydrophobic (affinity for monomers and polymer)
and other hydrophilic (affinity with
pH - This property was measured at 23ºC
with a Instruments pH Meter.
emulsifiers. The emulsifiers are low molecular
weight molecules consisting of two parts: a
Viscosity – The viscosity of the dispersion
Particle size – This test was determined
monomers and polymer and hydrophilic part is in
by Particle Size Analyzer 90 Plus (Brookhaven
contact with water. The polymerization occurs
Instruments Corporation).
inside the micelles. After polymerization, the
Minimum
(MFFT)
micelles with polymer are called to the particles of
film
–
formation
This
temperature
temperature
was
measured with a Rhopoint Bar 60.
polymer.
Vinyl homopolymers includes polymers of all
Surface tension was measured with a
molecular weights formed from the free radical
Dynometer Byk Labotron and contact angle
polymerization of vinyl acetate monomer. The
was determined by observation.
aqueous dispersions are, by far, the major form in
which vinyl acetate is used in the adhesive
Properties of applied product:
market. Aqueous dispersions of vinyl acetate
exhibit excellent compatibility with many modifying
resins, lending themselves to a broad range of
Open time – It was a manual finger test in
which the adhesive area applied in a
applications through formulation. In addition to
glass is touched with a finger tiop after
compatibility, molecular weight (or grade) and the
some time. This test measured the time of
amount and type of protective colloid used to
produce the emulsion affect adhesive properties.
Surface tension and contact angle –
dispersion drying.
Tensile strength and elongation – This
test is based on the European Standard
2 MATERIALS AND TEST METHODS
EN 1896: 2001 and determined tensile
strength and elongation of dry films when
The products in study were simultaneously
this are stretched to breakage at a
characterized by properties of product as such
constant pulling speed. This parameters
and applied product.
were determined by Hounsfield Equipment
Modelo H5K-S.
Properties of product as such:
by ASSTY.
Solids content – In this test the dispersion
samples were submitted to 105ºC during
Setting speed – This test was determined
Tensile shear strength of lap joints – This
test is based on the European Standards
2
EN 204: 2001 and EN 205: 2003. The test
3 RESULTS AND DISCUSSION
consisted in the determination of tensile
In
shear strength of lap joints at different
order
to
characterize
the
vinyl
conditioning sequences. In this test it was
homopolymers and classify them by application,
used the Monsanto P.L.C. Refª 20.
the obtained results of the tested aqueous
Heat resistance – This test is based on
dispersions were compared to each other.
the European Standard EN 14257: 2006.
Properties of product as such:
This Standard specifies a method for
testing the strength of adhesives at 80ºC.
Vinyl polymers presented solids content ≈ 50%
and low viscosity.
64000
56000
DHS
48000
DH
1080
τ (mPa)
40000
DLR
2003
32000
2004
2028
24000
D 01
D 50
16000
D 025
2040
8000
2042
DV
0
0,0
0,5
1,0
1,5
2,0
2,5
3,0
Taxa de Deformação D (rps)
Figure 1 – Results of rheological behaviour.
4,0
3,4
3,5
TMP (µ m)
3,0
2,6
Aumento da % PVOH
2,6
2,5
2,5
2,4
1,9
1,9
2,0
PVOH
2,4
1,5
1,7
1,3
1,5
Éter de Celulose
1,4
Emulsionante
1,0
0,3
0,5
0,0
D 50 D 025 D 01
DLR
1080
DH
2004 2028 2003
DHS 2040 2042
DV
Polidisp
Figure 2 – Results of particle size.
3
Properties of applied product:
Alongamento (mm)
300
261,9
250
212,9
200
150
109,9
100
70,4
50
3,6
2,2
1,2
0,8
4,5
0,7
0,4
1,0
2040
DV
13,0
0
D 50 1080
DH
2004 2028 DHS
D 025 D 01
DLR
2003 2042
Polidisp
2
Resistência à Tracção (N/mm )
Without Plasticizer
With Plasticizer
Figure 3 – Results of films elongation.
100
80
70,1
60
46,2
34,8
40
20,1
32,7
24,4
13,4
20
6,8
1,7
3,0
1,0
2,9
0,9
0
D 50
1080
DH
2004 2028
DHS
2040
DV
D 025 D 01
DLR
2003 2042
Polidisp
2
Resistência à tracção (N/mm )
Without Plasticizer
With Plasticizer
Figure 4 – Results of films tensile strength.
Aumento da % PVOH
14
11,9
11,6
12
10,1
9,9
10
8
8,7
8,6
7,9
D1, D2, D3, D4 ≥ 10 N/mm 2
8,7
7,5
PVOH
6,6
6,4
6
4,2
3,5
4
Éter de Celulose
Emulsionante
2
0
D 50 D 025
D 01
DLR
1080
DH
2004
2028
2003
DHS
2040
2042
DV
Polidisp
Figure 5 – Results of tensile shear strength of lap joints – Sequence 1 (7 days of drying at 23ºC).
4
2
Resistência à tracção (N/mm )
10
Aumento da % PVOH
9
7,8
8
D2 ≥ 8 N/mm2
7,8
7,0
7
6
5
5,1
4,9
5,5
4,7
4,5
4,3
PVOH
4,2
3,5
4
2,6
3
Éter de Celulose
2
Emulsionante
1
0,0
0
D 50 D 025
D 01
DLR
1080
DH
2004
2028
2003
DHS
2040
2042
DV
Polidisp
Figure 6 – Results of tensile shear strength of lap joints Sequence 2 (7 days of drying at 23ºC + 3h H2O immersion at
23ºC + 7 days of drying at 23ºC).
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4 CONCLUSION
After comparing the results, the aqueous
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DH
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1080
D1
DLR
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2003
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2004
D1
2028
D1
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--D 50
--D 025
--2040
--2042
--DV
---
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6