Annals of Warsaw University of Life Sciences - SGGW

interesting is the research on the proteins that have a role in underwater adhesion produced by
marine mussels. Research efforts have focused on identifying the genes responsible for the
adhesive proteins and strategies for producing natural adhesives similar to the native mussel
adhesive proteins (SILVERMAN 2007). The adhesives are known for their superior strength
and durability compared with man–made materials. They are ecological and can bind various
materials.
In our experiments, we researched influence of chosen modifying agents (hydrolysed
collagen (HC) in combination with activator AG based on glutaraldehyde) on network
formation and the structure of cured UF adhesive. We expect modified adhesives to be
stronger and more reactive due to large number of –NH 2 groups involved into reactive
mixture by HC. Glutaraldehyde can strengthen the cured adhesive structure, mechanical
strength, elasticity, water resistance and chemical stability.
RESULTS AND DISCUSSION
In experimental work we tested UF and MUF adhesives and hardener R-60. Natural
polymers were added into adhesives in form of skin collagen hydrolysate. The hydrolysate
was a liquid: collagen content 26 %, solid content 43 %, and pH = 5.2. Hardener was
modified with activator (AG) based on glutaraldehyde (VIPO a.s.). AG was added into
hardener R-60 in amount 1 % (Hr1), 3 % (Hr3), or 5 % (Hr5).
Plywood was prepared from beech or birch veneers; adhesive spread 160 g.m -2 ,
temperature 105 °C (UF), 130 °C (MUF), specific pressure 1.8 MPa, pressing time 5 minutes.
Shear strength was measured according to EN 314-1,2 standard. Measured values of shear
strength were evaluated by one-factor statistical analysis ANOVA on the level α = 0.05.
UF adhesive with activator AG
Firstly, we evaluated influence of added hardener on strength and stability of glued
joints. Results of shear strength for plywood specimens conditioned for adhesive class Nr.1
are given in table 1.
Tab. 1 Shear strength according to EN 314-1,2 standard for adhesive class Nr.1
Adhesive
mixture
Average
Shear
strength
[MPa]
Standard
deviation
[MPa]
Coefficient
of
variation
[%]
Measured
value min.
[MPa]
Measured
value max.
[MPa]
number
[pcs]
UF+HrR 1.78 0.39 22.08 1.01 2.87 18
UF+Hr1 1.93 0.42 21.71 1.12 2.62 20
UF+Hr3 1.93 0.29 15.05 1.42 2.40 20
UF+Hr5 2.05 0.45 21.78 1.17 2.70 19
Shear strength of all tested specimens in adhesive class Nr.1 reached required shear
strength 1.0 MPa. Shear strength of joints glued with UF adhesive with modified hardener
was a little higher in comparison with shear strength of joint glued with standard adhesive.
AG in adhesive mixture positively influenced shear strength – shear strength of joints glued
with mixture with the highest content of AG was the highest. Based on one-factor analysis,
we can say that factor “adhesive mixture”, does not influence plywood shear strength statistic
significantly. Adding AG into adhesive mixture shear strength was raised, but not statistic
significantly (fig. 1).
Specimens conditioned for adhesive class Nr.2 collapsed when boiled. UF adhesive
joints with AG stay being classified in adhesive class Nr.1. Expected possibility to classify
modified adhesive joints in adhesive class Nr.2 was not confirmed.
39