ANNUAL TRANSACTIONS OF THE NORDIC RHEOLOGY SOCIETY, VOL. 21, 2013
Rheological Behavior of an Environmentally Friendly Dry Blood Powder Based Adhesive for the Wood Industry
Alejandro Bacigalupe1, Daniela Belén Garcia1, and Omar Ferré1 1 Instituto Nacional de Tecnología Industrial, Buenos Aires, Argentina
ABSTRACT The aim of this paper is to study the
rheological behavior of an environmentally friendly adhesive based on a secondary product of food industry, dry blood powder (DBP), to replace formaldehyde-based adhesive such as urea-formaldehyde (UF) resins in the production of wood composites, increasing the added value of the raw material.
INTRODUCTION Petroleum-based adhesives like UF are
widely used in plywood, composite wood panels and furniture because of high adhesion strength and low cost. This adhesive has replaced historic based protein products such as casein or blood, which were displaced from the market.
However, highly toxic formaldehyde is emitted during the production and post production process. It is important to notice that formaldehyde was declared a carcinogen by the World Health Organization (WHO) in 2004.1 Besides, the future shortage of petrochemical-based products supposes a rise in relative price and lack of availability, leading on an increase in the development of “green” products from inexpensive and renewable resources. We decided to work with DBP, which is a secondary product of food industry and easy to get in our country.
Blood consist of plasma, cell fraction
and fibrillar fraction. Plasma contains
different substances like lipoprotein,
fatty acids,
sugars,
soluble
proteins (albumins and
globulins) and
mineral salts. The cell fraction (erythrocytes,
leukocytes and
platelets) is
rich
in hemoglobin. DBP is rich in proteins (see
Table 1), complex macromolecules and
contain a number of chemically linked
amino acid monomers, which form
polypeptide chains and constitute the
primary structure. These structural features
can be changed by physical, chemical or
enzymatic treatments. Such treatments alter
secondary, tertiary and quaternary structures
of the proteins without breaking the covalent
bonds and lead to protein denaturalization. It
is well known that the native structure of
protein can be modified to increase the
bonding strength of protein based adhesives.
Unfolded protein molecules have increased
surface area and hence afford improved
interaction with substrates.
Table 1. Chemical composition of DBP.
Chemical Percentage (%)
Constituent
Protein
80
Ash
10
Moisture
8
Fat Moisture
1
Others
1
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MATERIALS AND EQUIPMENT
Reactive DBP was provided by Willmor S.A. The Merck p.a. sodium hydroxide
(NaOH) was purchased. As antifoam the TEGO Foamex 1488
was used, provided by INTI-Procesos Superficiales.
For the UF adhesive the Coladur Plus by Jucarbe was used.
Instrumental Industrial stirrer DALV-50 with 0.5 HP. Anton Paar Rheometer Physica MCR
301 with Concentric Cone of 27 mm diameter geometry.
Hydraulic press Luis Santin model 100T with 7,5HP.
INSTRON 4467 Dynamometer, with 30 kN charge cell.
METHODOLOGY
Viscosity Determination
Skeist2 stated that all the protein based
adhesives present a non-Newtonian flow,
viscosity decreases with the increasing
sliding speed (Shear Thinning).
Therefore, the
mechanism for
the
measurement must cover all the ranges of
viscosities without any change in the slip
speed. The range of viscosity values have
been suggested for different applications by
Kumar et al.3 For absorbent adhesives the
viscosity is between 100 to 150 mPa.s (cP)
which is the value of a 50% UF adhesive
currently used by the local industry.
Adhesion depends on the ability of protein
to be dispersed in water and the interactions
with the substrate (wood). Stefani et al.4
indicates the dispersion is achieved through
the use of chemical agents that break the
secondary proteins structure (denature).
These include surfactants, urea and NaOH.
Different adhesives were prepared
varying DBP concentration from 20 to 40%
increasing in 5% at constant alkali concentration of 0.025% by weight, and compared to UF 50% adhesive.
All adhesives were analyzed in a Rheometer with a rotational viscosity curve at 25 ºC. The initial speed was 0,001 s-1 and it was gradually increased to 4000 s-1. A Concentric Cone of 27 mm diameter geometry (CC27) was used for the measurement. Results were shown in a viscosity versus share rate diagram.
Shear strength adhesion determination Five replications with pine wood were
prepared with the adhesives used for viscosity determination. The samples were applied in a hydraulic press, according to standard specifications5, at 70 ºC for 60 minutes and 3 MPa of pressure. Finally, samples were removed from press and stabilized for 2 days at 23 ºC ± 2 ºC and 50 ± 2% humidity. The adhesive weight applied was 400 g/m2. Adhesion was register as tension in MPa and plotted as tension versus DBP concentration.
Pot Life Determination The optimal DBP adhesive, obtained
with the Viscosity Determination was prepared and analyzed as same conditions. Viscosity was measured in the Rheometer over 0, 7 and 14 days (DBP D0, DBP D7, and DBP D14) and compared with UF 50%. Results were presented as viscosity versus shear rate.
Five replications with pine wood for the three samples were applied and measured at same conditions that the Shear strength adhesion determination. Results were presented as tension versus time.
RESULTS
Viscosity Determination Although viscosity at a low shear rate
(steady behaviour) is very different between UF and DBP adhesives, at high shear rate
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(application condition) the adhesives have similar behaviour. DBP 35% present similar viscosity than UF 50% and therefore, same properties during application conditions with spray (see Fig. 1).
It was shown by Lin and Gunasekaran6 that at low shear rate, high molecular weight protein chains experience Brownian motion. As the shear rate sufficiently increases to overcome the Brownian motion, the proteins chains become more ordered along the flow field and offer less resistance to flow and lower viscosity.
1.E+08
DBP 20%
V 1.E+07
i
s 1.E+06
c
o s
1.E+05
i
t 1.E+04
y
1.E+03
DBP 25% DBP 30% DBP 35% DBP 40% UF 50%
m
P 1.E+02
a
. 1.E+01
s
1.E+00 1.0E‐05
1.0E‐04
1.0E‐03
1.0E‐02 1.0E‐01 Shear Rate [1/s]
1.0E+00
1.0E+01
1.0E+02
[
]
Figure 1. Viscosity curve for UF 50% and DBP adhesives.
Shear strength adhesion determination All Samples present useful adhesion
values although with high dispersion; this is an expected behavior when we used natural raw materials (see Fig. 2). Considering adhesion values and that all the samples presented cohesive failure it was decided to work with the adhesive chosen by Viscosity determination.
Tension (Mpa)
5.000
4.500 4.000 3.500 3.000
4.055 3.253 3.420 2.894 3.066
2.500
2.000
15
25
35
45
% DBP
Figure 2. Adhesion of DBP adhesives.
Pot Life Determination The DBP 35% adhesive was used for
this determination (see Table 2) and measured as DBP D0.
All three samples show acceptable adhesion values and wood cohesive failure (see Fig. 3). DBP D7 presents very low viscosity variation and still is an adhesive with desirable rheological behaviour. DBP D14 shows a significant decrease of the viscosity due to alkali reactions which leads to shorter protein chains, leading to an excessive and undesirable water absorption which would make difficult the application process (see Fig. 4).
Table 2. Adhesive formulation with 35%
DBP.
Chemical
Percentage (%)
Constituent
DBP
35.0
NaOH 0,5%
5.0
Antifoam
0.3
Water
59.7
47
Tension (Mpa)
5.000 4.000 3.000 2.000 1.000 0.000
3.420 0
3.947
7 Time (days)
4.172 14
Figure 3. Adhesion versus time for 35% DBP adhesive.
1.E+08
1.E+07
V i sm cP oa s. is t y
]
[
1.E+06 1.E+05 1.E+04 1.E+03 1.E+02
1.E+01
UF 50% DBP D0 DBP D7 DBP D14
1.E+00 1.0E‐03 1.0E‐02 1.0E‐01 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04
Shear Rate [1/s]
Figure 4. Viscosity curve of DBP at 0, 7 and 14 days.
CONCLUSION Trough this work, we optimize the DBP
percentage in the adhesive formulation, based on their viscosity compared with UF adhesives at application conditions.
The adhesion test allows us to conclude that all the percentages studied present cohesive failure of wood specimens; giving a high performance adhesive for wood industry.
Finally, the pot life determination shows a slight increase in shear strength adhesion within the desired values, but with significant decrease in viscosity, making difficult the application process. Based on the properties analyzed, it was concluded that the useful life of the adhesive is less than 7 days of formulated process.
The viscosity, shear strength adhesion and pot life determination allows us to obtain a zero-emission formaldehyde adhesive as a renewable and environmentally friendly alternative for wood industry.
REFERENCES 1. International Agency for Research on Cancer (2004). Press release # 153. 2. Skeist, I. (1989), “Handbook of Adhesives”, Springer, pp. 163-173. 3. Kumar, R. Choudhary, V. Mishra, S. Varma, I.K. Mattiason, B. (2002), “Adhesives and plastics based on soy protein products” Ind. Crops Prod., 18, 155172. 4. Stefani, P.M. Leiva, P. Ciannamea, E. Ruseckaite, R. (2006) “Aplicación de Adhesivos de Soja para Aglomerados” http://www.acsoja.org.ar/images/cms/conten idos/614\_b.pdf 5. IRAM 45054, Adhesivos para estructuras de madera bajo carga. 6. Lin, H. and Gunasekaran, S. (2010), “Cow blood adhesive: Characterization of physicochemical and adhesion properties” International Journal of Adhesion & Adhesives, 30, 139-144.
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