Journal of the Korea Furniture Society
Vol. 22, No. 3 July, 2011, 219-229
Green Adhesives Using Tannin and Cashew Nut Shell Liquid for
Environment-friendly Furniture Materials
Jeong-Hun Lee, Jisoo Jeon, Sumin Kim†
School of Architecture, Soongsil University, Seoul 156-743, Korea
Abstract: Sick building syndrome symptoms that are experienced by building occupants may be
caused by toxic substances such as formaldehyde and VOCs, which are known to be emitted
from building materials and wood composite products such as wood-based panel, furniture, engineered flooring and construction adhesive. In Korea, the use of wood composite products for
indoor environments has increased over the last decade. Recently, wood composite products
have been installed in approximately 95% of newly constructed residential buildings. The use of
these products has resulted in problems related to human health, and consequently a realization
about the importance of indoor air quality. In addition, consumer demand is increasing for natural materials because conventional building materials and wood composite products are made
by adding urea-formaldehyde resin or they contain formaldehyde-based resin. More recently,
many efforts have been made to reduce formaldehyde emission from building materials that laid
in the indoor environment. Especially, if conventional formaldehyde-based adhesives are replaced with green adhesives for residential spaces, it is possible to reduce most of the emission
amounts of formaldehyde in indoor environments. In line with this expectation, many researches are being conducted using natural materials such as tannin and cashew nut shell liquid
(CNSL). This study discussed the affects and possibilities of green adhesives to reduce formaldehyde emission in indoor environments.
Keywords: green adhesive, tannin, CNSL, VOCs, formaldehyde
1. Introduction
renovated housing. Sick building syndrome (SBS)
1)
is a serious problem of poor air quality caused by
Recently, residents have been spending almost
90% of their time indoors, which presents a high-
indoor contaminants in the home and work place
(Hodgson, M. 2002; Menzies, D. et al. 1997; Lee,
er risk from inhalation of pollutants than when
S.-w. et al. 2007).
they spend time outdoors. It has been reported in
recent years that many people complain of symp-
For all pollutants, building materials play a major role in determining the indoor air quality ow-
toms of illness such as headaches, irritation of the
ing to their larger surface area and permanent ex-
nose, nausea, skin disorders, and fatigue after
spending some time in new buildings or newly
posure to indoor air. Building materials can release a wide range of pollutants, particularly
VOCs, which can degrade the indoor air quality
making it worse than that of outdoor air. Recent
studies of VOC emissions in four newly built un-
Received for publication: June 28, 2011; Reviewed: July 6,
2011; Accepted: Received in revised form: July 14, 2011;
July 16, 2011
†
Corresponding author: Sumin Kim (skim@ssu.ac.kr)
occupied test houses showed that the building
219
220
Jeong-Hun Lee, Jisoo Jeon, Sumin Kim
(Pickrell et al. 1986).
The use of low emission materials or materials
with no-added formaldehyde is considered a fundamental method to reduce formaldehyde emission in indoor environments. The possibility of
using replacement materials for UF and PF adhesives has also been studied for some time. Among
alternative materials, tannin, soybean and CNSL
are considered appropriate natural materials to
replace formaldehyde-based resin (Bisanda and
Ansell 1992; Kim 2009, 2010; Emiliano et al.
2010).
Fig. 1. Chemical structure of some phenols synthesized
from HT (Bisanda et al. 2003).
materials are the main source of indoor air pollu-
In this study, we discussed the applications of
natural phenolic compounds for green adhesives
and the affects and possibilities of green adhesives to reduce formaldehyde emission in indoor
environments.
tion (Yu and Crump 1998). Polymeric materials
are used widely in buildings for the construction,
decoration, and furnishing of homes, offices and
2. Tannin Based-Adhesive
2.1. Tannin Based-Adhesive
schools, as well as other non-industrial work
places. Many of these materials are high VOC
emitters, such as solvent-borne paints and adhesives. Some constitute large surface areas within
buildings, such as coatings and coverings on
walls, ceilings, and floors (Schmidt-Etkin, D.
1992).
In addition, formaldehyde is a suspected human carcinogen that is released from wood-based
Recently, there has been growing interest in
tannin-based resins. Tannins are naturally occurring phenolic compounds that have been a subject of extensive research leading to the development of a wide range of industrial applications.
Tannins have traditionally been used for converting animal hides to leather, known as tanning,
due to their ability to interact with and precipitate
panels used in home construction such as prod-
proteins found in animal skin. The term tannin
ucts made with urea-formaldehyde (UF) resins
(e.g., particleboard, hardwood plywood, medium
originates from the ancient Celtic word for oak,
density fiberboard (MDF), and paneling) (Otson
in converting animal skin into leather (tanning).
Today, in addition to oak (Quercus sp.), there are
and Fellin 1992; Kelly et al. 1999). Many consumer products containing formaldehyde-based
resins release formaldehyde, leading to consumer
dissatisfaction and health-related complaints.
These emissions have resulted in a variety of
symptoms, the most common of which is irritation to the eyes and upper respiratory tract
which remains a popular source for tannins used
many other plant species that are being used to
produce commercial tannin. These include plants
such as Acacia sp. (wattle), Eucalyptus sp.,
Mirtus sp. (myrtle), Acer sp. (maple), Betula sp.
(birch), Salix Caprea (willow), Pinus sp. (pine),
etc. ( Bisanda et al. 2003).
Journal of the Korea Furniture Society Vol. 22, No. 3, 2011
Green Adhesives Using Tannin and Cashew Nut Shell Liquid for Environment-friendly Furniture Materials 221
R = H : procyanidin : R = OH : prodelphinidin
Fig. 2. Chemical structure of wattle tannin (Acacia
mearnsil) flavonoids (Bisanda et al. 2003).
Fig. 3. Chemical structure of proanthocyanidins and reaction with formaldehyde (Ping et al. 2011).
Chemically, tannins are made up of complex
name of Nox Primer for the treatment of rusted
steel surfaces prior to painting.
phenolic compounds of high molecular weight,
∙Rust converter to transform oxidized steel in-
ranging from 500 to 20,000. There are two main
to a smooth sealed surface.
categories of tannins: (a) hydrolysable tannins
(HT) and (b) condensed tannins (CT). Generally,
∙Wood adhesives for bonding wood chips in
producing particle board building materials.
tannins are soluble in water, with the exception
∙Rust inhibitor where tannin is added to min-
of some very high molecular weight compounds.
HTs are readily soluble in water, making it possible for them to react with other substances to
eral oil to protect cold rolled steel from corrosion
during transportation or storage.
yield a wide range of water-soluble chemicals
such as gallic acid (-gallotannins) or ellagic acid
2.2. Preparation of Tannin Based-adhesive
(-ellagitannins). Fig. 1 shows the chemical structures of simple phenols obtained in HT. CTs
(Proanthocyanidis) have a condensed chemical
nature, even though they are still capable of undergoing further condensation reactions. They
have complex chemical structures made of flavonoid units, with variations on the sites at which
the flavan bonds are created. In general, CTs
have rigid carbon–carbon bonds that cannot be
broken easily by hydrolysis. Fig. 2 shows the
Wood adhesive condensed tannins with forlaldehyde, have been used industrially since the
1970s for the interior and exterior wood bonding
of products such as particleboard and plywood.
They are obtained by the hardening of polymeric
flavonoids by polycondensation with formaldehyde, involving their more reactive A-ring
according to Fig. 3. Thus, it was demonstrated
that condensed tannins are both chemically and
economically interesting for the preparation of
adhesives and that they could be successfully
chemical structure of wattle tannin (Acacia
mearnsii) flavonoids according to Pizzi (Pizzi
used as substitutes for phenol in the production of
resins (Pinga et al. 2011).
Generally, most tannin-based adhesives are
1983, 2006).
A wide range of other industrial applications
have been found for tannins, in addition to their
fortified with a synthetic polymer system such as
commercial UF (Bisanda et al. 2003; Pizzi
2006), commercial PF (Vazquez et al. 2003), re-
widespread use in tanneries. These include an use
in the manufacture of inks for dyeing of textiles,
and as a corrosion inhibitor. In Chile and Brazil,
sorcinol-formaldehyde (Wen and Wei 2006) and
a variety of products have been developed from
isocyanates (Batubenga 1995).
T. Tabarsa et al. studied four types of resins:
tannin (Bisanda et al. 1992):
∙Anti-corrosive primer, sold under the brand
PF, T10%PF, T20%PF, and T30%PF, which
Journal of the Korea Furniture Society Vol. 22, No. 3, 2011
222
Jeong-Hun Lee, Jisoo Jeon, Sumin Kim
were tannin-modified PF resins containing 0, 10,
2.3. Discussion of Tannin Based Adhesive
20%, and 30% tannin content, respectively. The
The objective of T. Tabarsa’s work is to eval-
PF resin was supplied in liquid form, and before
uate the mechanical and physical properties of
an use, a 2% by weight hardener zink acetate [Zn
three-layer boards made with wheat straw and
(CH3COO)2] was added and the mixture was
bonded with a tannin-based adhesive. The me-
thoroughly stirred. The tannin was extracted
chanical properties of panels were evaluated by
from oak (Quercus castaneifolia) trees. The mod-
static bending, modulus of rupture (MOR) and
ification of the PF resin was made through the
modulus of elasticity (MOE), the internal bond
substitution of 10, 20% and 30% of a solution of
(IB) tests. Physical properties such as water ab-
40% tannin extract (Tabarsa et al. 2011).
sorption (WA) and thickness swelling (TS) in wa-
A. Moubaric et al. studied cornstarch-que-
ter were determined. In general, all types of straw
bracho tannin-based resins designed as adhesive
panels produced in this work met the MOR,
in plywood production. The resol type of phenol
formaldehyde with a solids content of 46% and a
MOE, IB and TS requirements for general uses
according to European standards. Although the
viscosity of about 450 cp was prepared using a
wheat straw boards made with tannin-modified
2.2 : 1 formaldehyde: phenol ratio and 7.3%
(w/w) of NaOH. The resols were prepared in a
PF resins had slightly poorer mechanical properties compared to the boards made with pure PF,
two liter glass reactor with mechanical stirring
the T10% PF resin showed higher bond ability
and temperature control. The necessary amount
of reactive according to the established for-
than other modified PF resins. The highest
MOR, MOE, IB and the lowest WA and TS were
mulation was fed into the reactor, and when the
achieved at a 12 min press time and by using
operating temperature was reached 90°C, the extension of reaction was monitored, measuring the
Type 10% PF resin. An increase in the press time
positively affected the physical and mechanical
resol viscosity at 25°C. The adhesives were pre-
properties of the panels produced. With respect
pared by copolymerisation at the room temperature of cornstarch and quebracho bark tannins
to the findings of the study, it may be stated that
wheat straw can be used as a promising raw ma-
in variable quantities with the previously pre-
terial for panel production with the use of a tan-
pared resols (Moubarika et al. 2009).
S. Kim studied PVAc/Tannin hybrid adhesives
nin-modified PF adhesive.
The aim of Amine A. Moubarik’s work was to
in accordance with the wt% of tannin. The pre-
demonstrate the performances of cornstarch–
pared adhesives were used on the face of the decorative veneer bonding of engineered flooring
quebracho tannin-based resins designed as adhesives in plywood production. The cornstarch and
and the formaldehyde emission level and surface
quebracho tannin was introduced in the classic
bond strength were evaluated. PVAc was added
to the natural tannin adhesive to increase the vis-
adhesive formulation in order to supply part of
the phenol–formaldehyde (PF). The physical
cosity of tannin adhesive for surface bonding. For
properties of rheological characterization, ther-
tannin/PVAc hybrid adhesives, 5, 10, 20% and
30% of PVAc were added to the natural tannin
mogravimetric analysis and solid phase 13C
NMR analysis of the formulated resins were
adhesives (Kim 2009).
measured. In order to evaluate the mechanical
performances of optimal cornstarch–quebracho
Journal of the Korea Furniture Society Vol. 22, No. 3, 2011
Green Adhesives Using Tannin and Cashew Nut Shell Liquid for Environment-friendly Furniture Materials 223
Fig. 5. VOC emission concentrations (toluene, ethylbenzene, xylene and styrene) from engineered flooring
bonded with natural adhesive and tannin/PVAc hybridadhesives as determined by the VOC analyzer (Kim
2009).
Fig. 4. Initial adhesion strength of natural tannin adhesive and tannin/PVAc hybridadhesives (Kim 2009).
tannin-based resins, plywood panels were produced and mechanical properties were investigated. These mechanical properties included
then decreased. The initial adhesion strength was
tensile strength, wood failure and 3-point bending strength. The performance of these panels is
sufficient to be maintained within the optimum
initial tack range.
comparable to that of plywood panels commer-
In addition, the standard formaldehyde emis-
cially made with PF resin. The results showed
that plywood panels bonded with cornstarch -
sion test (desiccator method), field and laboratory
emission cell (FLEC) and VOC analyzer were
quebracho tannin - PF resins (15 : 5 : 80, w/w/w)
used to determine the formaldehyde and VOC
exhibited better mechanical properties than plywood panels commercially made with PF resin.
emissions. Using the desiccator method and
FLEC, the formaldehyde emission level of each
The introduction of small proportions of corn-
adhesive showed a similar tendency to that of the
starch and quebracho tannin in PF resins contributes to the improvement of the boiling water per-
natural tannin adhesive. PVAc did not cause increasing formaldehyde emission. All adhesives
formance of these adhesives. The formaldehyde
satisfied the E1 grade (below 1.5 mg/L) and E0
emission levels obtained from panels bonded
with cornstarch - quebracho tannin - PF were
grade (below 0.5 mg/L) with UV coating, as
shown in Table 1. VOC emission results obtained
lower than those obtained from panels bonded
by the FLEC and VOC analyzer differed from the
with control PF (Moubarika et al. 2009).
In S. Kim’s study, tannin/PVAc hybrid adhe-
formaldehyde emission results. Fig. 5 presents
the concentrations of the four indicated VOCS
sives showed better bonding than the commercial
from engineered flooring bonded with each adhe-
natural tannin adhesive with a higher level of
wood penetration. Fig. 4 shows the probe tack re-
sive system, as determined by the VOC analyzer.
Xylene was the highest detected compound in all
sults for maple decorative veneer. With the in-
samples, followed by ethylbenzene and toluene
crease of open assembly time, the probe tack of
the natural tannin adhesive and tannin/PVAc
consecutively. Styrene, however, was not detected in any of the systems. However, the TVOC
hybrid adhesives increased for a certain time and
emission of the PVAc added tannin adhesive sys-
Journal of the Korea Furniture Society Vol. 22, No. 3, 2011
224
Jeong-Hun Lee, Jisoo Jeon, Sumin Kim
Table 1. Formaldehyde and TVOC emission of engineered flooring bonded with naturaladhesive and tannin/PVAc
hybrid adhesives by desiccator and FLEC methods (Kim 2009)
Equipment
FLEC (mg/m h)
Formaldehyde
Air pollutant
a
2
Dessicator (mg/L)
Formaldehyde
TVOC
0.34
0.2
0.32
0.44
0.21
0.39
0.47
0.21
0.4
a
Non-coated
Coated
Natural tannin adhesive
1.19
Tannin90/PVAc10
1.32
Tannin80/PVAc20
1.33
UV curable urethane acrylate coating.
polymer scientists throughout the world because
of its potential attribute as substitute petrochemical derivatives. With petroleum production in-
(a) Anacardic acid
(b) Cardanol
creasingly facing exhaustion, scientists and technologists focus their attention towards renewable
resources because these materials may act as potential raw materials for the manufacture of polymers in the 21st century (Bhunia et al. 1999).
CNSL, an agricultural by-product of the cashew
(c) Cardol
(d) 2-methyl cardol
nut processing industry and a renewable resource, is a source of a long chain, m-substituted
Fig. 6. Components of CNSL (Park et al. 2005).
phenol which promises to be an excellent mono-
tem was slightly increased compared to the natu-
mer for polymer production. CNSL occurs as a
reddish brown, viscous fluid in the soft honey-
ral tannin adhesive. This tendency of form-
comb structure of the shell of cashew nuts. Many
aldehyde and TVOC emission from the natural
tannin adhesive and tannin/PVAc hybrid adhe-
researchers have investigated on the chemistry
and composition its extraction. CNSL contains
sives was confirmed by the FLEC test as shown
four major components: 3-pentadecenyl phenol
in Table 1. The difference between each system
of formaldehyde emission was not shown in the
(cardanol), 5-pentadecenyl resorcinol (cardol),
6-pentadecenyl salicylic acid (anacardic acid) and
FLEC data, while the TVOC of tannin/PVAc
2-methyl 5-pentadecenyl resorcinol (2-methyl
hybrid adhesives was slightly increased by adding
PVAc compared to the natural tannin adhesive
cardol). Fig. 6 gives the chemical structure of
these components.
The application of CNSL as a full replacement
(Kim 2009).
3. Green Adhesive Using Cashew
Nut Shell Liquid (CNSL)
for synthetic resins is of immense interest in the
current climate of diminishing petroleum reserves. About 90% of CNSL consists of anacardic
3.1. CNSL
acid, cardanol and cardol (Mwaikambo and
Ansell 2003). Cardanol, which can be obtained
The synthesis of polymers from renewable re-
by thermal treatment of CNSL, is a phenol de-
sources has attracted considerable attention from
rivative mainly composed of the meta substitute
Journal of the Korea Furniture Society Vol. 22, No. 3, 2011
Green Adhesives Using Tannin and Cashew Nut Shell Liquid for Environment-friendly Furniture Materials 225
phenol-HCHO resin. In this study, the effect of
CNSL-based phenolic resin in an adhesive formulation for aluminium-aluminium bonding
(Al-Al) was studied. The effect of fillers and adhesion promoters in the adhesive formulation
Fig. 7. Possible CNSL-formaldehyde structure (Lubi
and Thachil 2006).
were also studied (Lubi and Thachil 2006).
3.2. Preparation of CNSL Based-adhesive
of a C15 unsaturated hydrocarbon chain with one
Biswas et al. describe the preparation and char-
to three double bonds (Kim et al. 2007; Bhunia et
acterization of a CNSL modified phenol - form-
al. 1998). Double vacuum distillation of CNSL
aldehyde resin. The optimum settings disclosed
yields pure cardanol at 50% yield (Ikeda et al.
are CNSL: phenol weight ratio of 2 : 1 and their
2000). CNSL constitutes nearly one-third of the
total nut weight. Thus, a large amount of CNSL
reaction with formaldehyde at a temperature of
is formed as a by-product of the mechanical processes used to render the cashew kernel edible and
its total production approaches one million tons
annually (Park et al. 2005).
CNSL has potential industrial applications
such as for resins, friction lining materials, and
surface coatings. Especially in the field of polymers, CNSL has mostly been studied as a modifier of phenol–formaldehyde resins due to its
structural similarity with phenol. CNSL reacts
30∼40°C (Biswas et al. 2009). Mwaikambo and
Ansell describe the synthesis of a resin with
CNSL and formaldehyde using NaOH as catalyst
and hexamethylenetetramine (HMTA) as hardener (Mwaikambo and Ansell 2003). Bisanda et
al. have synthesized a resin consisting of CNSL,
hydrolyzed tannin and urea - formaldehyde resin.
This resin was tested in particleboard production. Although the CNSL modified phenolic
resins are suitable for many applications and perform improved corrosion and insulation resistance, they have the disadvantage of requiring a
with formaldehyde under a variety of conditions,
yielding both resol and novolak resins depending
longer time to be totally cross-linked (set) compared to their petrochemical counterparts. This
on the catalyst used. Fig. 7 shows the possible
structure of cross-linked CNSL-formaldehyde
resin where R represents the side chain. The phenolic nature of the constituents of CNSL along
consideration has thus far constrained their broad
utilization by the wood-based panels industry,
since the manufacturers are reluctant to use a resin that is regarded as needing longer pressing.
with varying degrees of unsaturation in the side
chain makes it a highly polymerizable substance
This would affect a manufacturer’s profits as it
would mean an increase in the production costs
amenable to a variety of polymerization reactions. The most obvious and common method
of obtaining polymeric materials from CNSL is
and lowering of the economic benefits (Bisanda
et al. 2003).
the condensation reaction with formaldehyde.
The reaction of CNSL with formaldehyde is slow
compared to that of phenol with formaldehyde.
3.3. Discussion of CNSL
Pure CNSL-HCHO resin is a rubbery substance
CNSL is a natural product, and because of its
phenolic nature it undergoes reactions similar to
with inferior mechanical properties compared to
those of phenol. The cost of CNSL is consid-
Journal of the Korea Furniture Society Vol. 22, No. 3, 2011
226
Jeong-Hun Lee, Jisoo Jeon, Sumin Kim
Fig. 8. Bonding strength between the face of the decorative veneer and plywood substratein engineered flooring: CNSL-formaldehyde (CF) resin and CF/PVAc
green adhesives (Kim 2010).
Fig. 9. Formaldehyde emission from engineered flooring bonded with CNSL-formaldehyde (CF) resin and
CF/PVAc green adhesives as determined by thedesiccator method (Kim 2010).
erably less than phenol. P. A. Mahanwar experimentally investigated the effect of replacing
resin based on CNSL can be employed in adhesive formulations. It improves the bonding
phenol with CNSL on the properties of novolak
strength of Al-Al significantly. The addition of
and resole resins. The addition of CNSL into
phenol seems to increase reaction times for the
3-aminopropyl triethoxy silane improves the
shear strength and peel strength of adhesives used
preparation of novolak as well as resole type
in metal-to-metal bonding considerably. Although
resins. When CNSL with an acid value of more
than 10 was used, no satisfactory resin could be
the copolymerization of crude CNSL and phenol
has generally led to some deterioration of shear
formed. The resulting mass was only a viscous
and peel performance compared to the case of
fluid with very low resin content. This suggests
that only CNSL with an acid value less than 10
pure phenol- based resins, considering the low
cost of CNSL and its renewable nature, the parti-
was suitable for resin preparation. In conclusion,
al use of CNSL for this adhesive application is an
the addition of CNSL leads to a decrease in tensile strength but an improvement in the impact
attractive proposal (Lubi and Thachil 2006).
S. Kim carried out the reduction of form-
strength and electrical properties of the resole
aldehyde and VOCs emission from wood-based
resins. CNSL with an acid value above 10 is unsuitable for making resins (Mahanwar and Kale
flooring by green adhesive CNSL. In this study,
to discuss the reduction of formaldehyde and
1996).
VOC emissions from engineered flooring, CNSL-
CNSL is a desirable starting material for adhesive formulations due to its renewable nature,
formaldehyde (CF) resin and CF/PVAc resin
were applied for the maple face of the veneer
high polarity, inherent tackiness of phenolic ma-
bonding on plywood. The bonding strengths of
terials, and ease with which liquid-to-solid conversions can be accomplished. M. Lubi C. and
the engineered flooring samples bonded with CF
resin and PVAc are shown in Fig. 8. The bonding
Eby Thomas Thachils’study aims to investigate
strengths of the non-treated (before boiling), en-
the effect of the incorporation of CNSL-based
resin in neoprene adhesive formulations. Phenolic
gineered flooring samples made using CF/PVAc
hybrid adhesives were considerably higher than
Journal of the Korea Furniture Society Vol. 22, No. 3, 2011
Green Adhesives Using Tannin and Cashew Nut Shell Liquid for Environment-friendly Furniture Materials 227
those of the CF resin. With increasing PVAc con-
to the overall properties of the resin (Papadopou-
tent, the bonding strength was increased until a
lou and Chrissafis 2011).
PVAc content of 20% was obtained. Fig. 9
The understanding of the thermal character-
shows that the CF resin and CF/PVAc resin sys-
istics of the CNSL resin curing is essential for the
tems with UV coating satisfied the E1 and E0
materials selection, design and manufacture of
grades of the Korean Standard. Before surface
natural fiber reinforced composite material.
coating, the formaldehyde emissions from the
Therefore, there is intense interest in under-
products glued with CF resin were already less
standing the curing characteristics and properties
than the E1 grade of the formaldehyde emission
of CNSL-based resins. In L. Y. Mwaikambo
level in the Korean Standard, even though the CF
resin contained formaldehyde. Renewable phe-
and M. P. Ansells’s work the DSC technique has
been applied to study the change in the glass tran-
nolic compounds from trees and plants such as
sition temperature of the oven-cured resin with
tannin, lignin and CNSL were successfully applied as a thermosetting wood adhesive for wood
and without HMTA in order to monitor the extent of the cure. The glass transition temperature
panels to reduce formaldehyde emission. These
was found to rise when the alkaline catalysed res-
renewable phenolic compounds give excellent
adhesive performance, good moisture resistance,
in was subjected to higher curing temperatures regardless of the concentration of formaldehyde
and tend to give a lower formaldehyde emission
used. The mode of cure of the NaOH-catalysed
than UF resin (Kim 2010).
In E. Papadopoulou and K. Chrissafisbs’ study,
CNSL-formaldehyde resin has been found to be
more regular with HMTA hardener. FT-IR spec-
an experimental phenol–formaldehyde resin
troscopy has been used to study the neat CNSL
with 20% phenol replacement by CNSL was
studied and compared with a conventional phe-
and polymerised CNSL-formaldehyde resin with
and without HMTA. The use of the DSC and
nol–formaldehyde resin synthesized totally from
FT-IR techniques to elucidate the extent of cure
petrochemical raw materials. The adhesion strength
of these resins was investigated by their applica-
of CNSL resins is a valuable step towards the production of commercially successful CNSL-natu-
tion in plywood production. The plywood panels
ral fiber composites.
were tested for their shear strength and wood failure performance while their free formaldehyde
4. Summary
emissions were determined with the desiccator
method. It was proved that although the neat
CNSL modified PF resin (PCF) cures at a longer
time and higher temperature than a conventional
PF resin, wood affects it more significantly, resulting in curing on the evening of their curing
Tannin is a renewable resource obtained from
plants such as Acacia sp., Eucalyptus sp., Mirtus
sp., Acer sp., Betula sp., Salix Caprea, Pinus sp.
(pine), etc. Also, CNSLs are a by-product of the
agriculture industry. They are naturally occuring
phenolic substances. Being an agricultural by-
performance. This is a novel finding that manifests the possibility of replacing a conventional
PF resin by a CNSL modified resin in the ply-
product, they have the advantages of low cost
wood production, without changing any of the
and renewable supply. They can replace phenol
in many applications. Tannins and CNSL are
production conditions and with an improvement
groups of natural resins that are receiving wide
Journal of the Korea Furniture Society Vol. 22, No. 3, 2011
228
Jeong-Hun Lee, Jisoo Jeon, Sumin Kim
attention as alternative materials to synthetic
binders in the production of biocomposites.
UF is the commercial resin popularly used for
wood-based panel production. The most significant problem is the emission of formaldehyde
and TVOC from wood-based panel. To improve
indoor air quality, the reduction of using UF resin is considered to be the most effective solution.
In previous works, many authors suggested that
tannin and CNSL are appropriate resources as
resins for wood-based panel production and
proved the reduction of toxic substances by using
tannin and CNSL.
However, there are a number of problems using
tannin and CNSL, such as decreasing in bonding
strength, MOE and MOR. Thus, in previous
works, many efforts had been made to improve
mechanical properties by seek of an optimal ratio
with a synthetic polymer system such as commercial UF, PF, resorcinol–formaldehyde, or adding PVAc, etc. As a result, the mechanical properties of green adhesives exhibited the performance that met the minimum performance requirement.
Acknowledgments
This research was supported by the Converging
Research Center funded by the Ministry of
Education, Science and Technology (2010K001141).
Batubenga, D. B., A. Pizzi, A. Stephanou, R. Krause,
and P. Cheesman. 1995. Isocyanate/phenolics wood
adhesives by catalytic acceleration of copolymerization. Holzforchung 49: 84-86.
Bisanda E. T. N. and M. P. Ansell. 1992. Properties of
sisal-CNSL composites. J Mater Sci., 27: 1690-700.
Papadopoulou, E. and K. Chrissafis. 2011. Thermal
study of phenol - formaldehyde resin modified with
cashew nut shell liquid, Thermochimica Acta 512:
105-109.
Bisanda, E. T. N., W. O. Ogola, and J. V. Tesha. 2003.
Characterisation of tannin resin blends for particle
board applications, Cement & Concrete Composites
25: 593-598.
Ciannamea, E. M., P. M. Stefani, and R. A. Ruseckaite. 2010. Medium-density particleboards from
modified rice husks and soybean protein concentrate-based adhesives. Bioresource Tech- nology
101: 818-825.
Bhunia, H. P., G. B. Nando, T. K. Chaki, A. Basak, S.
Lenka, and P. L. Nayak. 1999. Synthesis and characterization of polymers from cashewnut shell liquid
(CNSL), European Polymer Journal 35: 1381-1391.
Bhunia, H. P., R. N. Jana, A. Basak, S. Lenka, and G.
B. Nando. 1998. Synthesis of polyurethane from
cashew nut shell liquid (CNSL), a renewable resource, J. Polym. Sci. Polym. Chem. 36: 391-400.
Hodgson, M. 2002. Indoor environmental exposures
and symptoms. Environ. Health Perspect. 110:
663-667.
Kelly, T. J., D. L. Smith, and J. Satola. 1999. Emission
rates of formaldehyde from materials and consumer
products found in California homes. Environmental
Science & Technology 33: 81-88.
Mwaikambo, L. Y. and M. P. Ansell. 2003. Hemp fi-
References
bre reinforced cashew nut shell liquid composites,
Composites Science and Technology 63: 1297-1305.
Moubarika, A, A. Pizzi, A. Allal, F. Charrier, and B.
Charrier. 2009. Cornstarch and tannin in phenol–
formaldehyde resins for plywood production.
Industrial Crops and Products. 30: 188-193.
Biswas, B. K., S. Biswas, M. Khan, and B. Chandra
Ray. 2009. Preparation and characterization of
CNSL modified phenol formaldehyde resin, J.
Polym. Mater. 28: 7-15.
Ping, L., A. Pizzi, Z. D. Guo, and N. Brosse. 2011.
Condensed tannins extraction from grape pomace:
Characterization and utilization as wood adhesives
for wood particleboard. Industrial Crops and
Products. 34: 907-914.
Lee, S.-W., Y.-S. Yang, T.-H. Ahn, C.-S. Bae, C.-J.
Journal of the Korea Furniture Society Vol. 22, No. 3, 2011
Moon, S.-H. Kim, S.-Y. Song, H.-Z. Hwang, and
J.-C. Kim. 2007. Subacute toxicity evaluation in rats
Green Adhesives Using Tannin and Cashew Nut Shell Liquid for Environment-friendly Furniture Materials 229
exposed to concrete and hwangto building environments. Environ. Toxicol. 22: 264-274.
Lubi, C. and E. T. Thachil. 2006. Studies on Metalto-Metal Adhesives Based on CNSL Resins, PolymerPlastics Technology and Engineering, 45.
Menzies, D. and J. Bourbeau. 1997. Building related
illnesses. New Eng. J. Med. 337: 1524-1531.
Otson, R. and P. Fellin. 1992. Characterization and
cycling. In: Nriagu JO, editor. Gaseous pollutants.
New York: John Wiley and Sons. 335-421.
Mahanwar, P. A. and D. D. Kale. 1996. Effect of cashew nut shell liquid (CNSL) on properties of phenolic
resins, Journal of Applied Polymer Science 61:
2107-2111.
Pickrell, J. A., L. C. Griffis, B. V. Mokler, C. H.
Hobbs, G. M. Kanapilly, and A. Bathija. 1986.
Formaldehyde release rate coefficients from selected
consumer products. Washington, DC. In: Meyer B,
Andrews B, Reinhardt RM, editors. Symposium series, formaldehyde release from wood products.
American Chemical Society Symposium Series,
385: 40-51.
Pizzi, A., editor. 1983. Wood adhesives-chemistry and
technology. Marcel Dekker Inc.
Pizzi, A. 2006. Recent developments in eco-efficient
bio-based adhesives for wood bonding: opportunities and issues. J. Adhesion Sci. Technol. 20:
829-846.
Ikeda, R., H. Tanaka, H. Uyama, and S. Kobayashi.
2000. A new crosslinkable polyphenol from a renewable resource, Macromol. Rapid Commun. 21:
496-499.
Park, S. Y., Y. H. Kim, and B. K. Song. 2005. Polymer
synthesis by enzyme catalysis, Polym. Sci. Technol.
16: 342-353.
Schmidt-Etkin, D. 1992. Office furnishings/equipment
& IAQ health impacts, prevention & mitigation.
Indoor Air Quality Update. Arlington, MA, USA:
Cutter Information Corporation.
Kim, S. 2009. Environment-friendly adhesives for surface bonding of wood-based flooring using natural
tannin to reduce formaldehyde and TVOC emission, Bioresource Technology 100: 744-748.
Kim, S. 2010. The reduction of formaldehyde and
VOCs emission from wood-based flooring by green
adhesive using cashew nut shell liquid (CNSL),
Journal of Hazardous Materials 182: 919-922.
Tabarsa, T., S. Jahanshahi, and A. Ashori. 2011.
Mechanical and physical properties of wheat straw
boards bonded with a tannin modified phenol–
formaldehyde adhesive. Composites: Part B. 42:
176-180.
Vazquez, G., J. Gonzalez-Alvarez, F. Lopez-Suevos,
and G. Antorrena. 2003. Effect of veneer side wettability on bonding quality of Eucalyptus globules
plywoods prepared using a tannin - phenol - formaldehyde adhesive. Bioresour. Technol. 87: 349-353.
Wen, J. L. and C. L. Wei. 2006. Properties of resorcinol - tannin - formaldehyde copolymer resins
prepared from the bark extracts of Taiwan acacia
and china fir. Biores. Technol. 97: 257-264.
Kim, Y. H., E. S. An, S. Y. Park, and B. K. Song.
2007. Enzymatic epoxidation and polymerization of
cardanol obtained from a renewable resource and
curing of epoxide-containing polycardanol, J. Mol.
Catal. B: Enzym. 45: 39-44.
Yu, C. and D. R. Crump. 1998. A review of the emission of VOCs from polymeric materials used in
buildings, Building and Environment 33: 357-374.
Journal of the Korea Furniture Society Vol. 22, No. 3, 2011