全 文 ：第 50 卷 第 1 期
2 0 1 4 年 1 月
林 业 科 学
SCIENTIA SILVAE SINICAE
Vol. 50，No. 1
Jan．，2 0 1 4
doi:10．11707 / j．1001-7488．20140121
Received date: 2013 － 02 － 21; Revised date: 2013 － 05 － 27．
* Lin Ruihang is corresponding author．
杉木液化液交联苯酚 －甲醛合成新型木材胶黏剂*
孙 瑾1 林锐航2 李晓增2 王晓波1 朱晓枫1 徐恩光1
(1．华南农业大学林学院木材科学与工程系 广州 510642; 2．广州市质量监督检测研究院 广州 510110)
摘 要: 探讨一种无污染、无废弃物排放的胶黏剂合成工艺———碱性的杉木液化物与少量的苯酚、甲醛合成一种
高性能的木材胶黏剂。检测胶黏剂的游离苯酚和游离甲醛、胶合板的胶合性能和甲醛释放量，并与工业用酚醛树
脂进行性能比对。结果表明: 杉木液化物 －苯酚甲醛胶黏剂具有较低的游离苯酚和游离甲醛，其制得的胶合板具
有更好的胶接性能和更低的甲醛释放量。红外分析结果表明: 杉木液化物与苯酚、甲醛发生了化学反应，并生成了
高聚物化学结构。DSC 结果显示: 杉木液化物 －苯酚甲醛胶黏剂需要更高的固化温度，但不影响其实用性。
关键词: 改性酚醛树脂; 液化; 胶接性能; 结构分析; 固化
中图分类号: TQ437 文献标识码: A 文章编号: 1001 － 7488(2014)01 － 0140 － 09
A Novel Plywood Adhesive Synthesized by Phenol-Formaldehyde
Crosslinking Alkaline Chinese Fir Liquid
Sun Jin1 Lin Ruihang2 Li Xiaozeng2 Wang Xiaobo1 Zhu Xiaofeng1 Xu Enguang1
(1 ． Department of Wood Science and Engineering，College of Forestry，South China Agricultural University
Guangzhou 510642; 2 ． Guangzhou Quality Supervision and Testing Institute Guangzhou 510110)
Abstract: A novel composite adhesive was synthesized in our experiment，which revealed the new zero-waste and zero-
pollution adhesive synthetic by blending of alkaline Chinese fir (Cunninghamia lanceolata) liquid with a small amount of
phenol-formaldehyde． The synthetic Chinese fir-based adhesive showed better physical properties of low free phenol as well
as free formaldehyde content compared with control PF resin． Plywood of three layers bonded with the synthesized
adhesives was made to determine bond strength and formaldehyde emission． The Chinese fir-based adhesive has been
proved to reduce the formaldehyde emission significantly without decreasing the bond strength at all． The FT-IR analysis
confirmed the polymer chemistry structure has been built by the Chinese fir liquid reacting with formaldehyde and phenol．
The DSC results indicated that although the Chinese fir-based adhesive’s curing need higher temperature than the PF
resin，the higher curing temperature hardly cripple the availability of Chinese fir-based adhesive．
Key words: modification of phenol-formaldehyde resin; liquefaction; bonding properties; structural analysis; curing
The petrochemical synthetic phenol-formaldehyde
resin adhesives， have commonly been used in the
production of wood-based panels ( He et al．，2012 ) ．
However，the declining fossil fuel reserves combined
with the increasing price of fossil fuel have become the
obstacles of the development of wood composite boards
( Schene et al．，2009 ) ． Therefore，more and more
exploitations aimed at adopting natural and economical
products as substitutes for conventional wood resin
adhesives have drawn many researchers’attention． In
recent years，there have been many attempts to replace
petrochemicals with renewable resources，such as lignin
(Alonso et al．，2011 )，cornstarch (Moubarik et al．，
2010)， tannin ( Jahanshaei et al．，2012 )， cellulose
(Qing et al．，2012)，cashew nut shell(Papadopoulou et
al．，2011)，wheat straw (Chen et al．，2012) for wood
resin adhesives． However，few of them can be further
applied for industrial process due to their inherent
disadvantages in compromised adhesive strength，low-
water resistance or high formaldehyde emission．
Wood，the most abundant biomass in nature，has
been regarded as the most promising renewable
第 1 期 孙 瑾等: 杉木液化液交联苯酚 －甲醛合成新型木材胶黏剂
resource． It is a complex bio-composite mainly
consisting of three structural components: cellulose，
hemicellulose and lignin(Binder et al．，2009) ． Lignin
is of particular interest because of its phenolic
formation from which a wide variety of phenols and
phenol derivatives and aromatic chemicals can be
derived． Cellulose and hemicellulose can be converted
into polyols， aldehydes and other small molecule
compounds under certain conditions ( Zhang et al．，
2012) ． Hence，considerable attention has been given
to the preparation of environmentally friendly polymeric
products from liquefied woods and their derivatives．
Until now，there were two main methods of wood
liquefaction． The first liquefaction method is called
phenolysis，involving phenol with acids as catalysts，
which resulted in liquefaction products rich in
combined phenolic compounds． Further application in
the preparation of phenolic adhesives is similar to the
conventional phenol resins (Mohamad Ibrahim et al．，
2011)，mouldings (Lee et al．，2011) and others． The
second method was achieved in existence of alcohols，
especially polyhydric alcohols，and the gained products
can be used as polyols for the preparation of
polyurethane and epoxy products(Pan et al．，2012; Wu
et al．，2010) ． But only little information can be found
in the literature concerning controlled liquefaction of
wood in alkaline medium． However，alkaline treatment
at elevated temperature is often used to enhance the
reactivity of the crystalline cellulose through decreasing
DP ( degrees of polymerization ) and increasing
accessibility of cellulose． Meanwhile， the lignin
components depolymerize to form monomeric and
oligomeric phenolic compounds． In view of the above，
liquefaction of wood combining alkaline catalysts under
high temperature appears to be an attractive way to
obtain low molarcular weight compounds in the
further use．
In this study，we evaluated the huge potential of
waste Chinese fir as a biomass resource for the
production of adhesives． In order to obtain a Chinese
fir-based adhesive of desirable properties for bonding
plywood in exterior use，the Chinese fir was liquefied
in alkaline medium at 200 ℃ for pretreatment，then
co-polymerized with phenol-formaldehyde to synthesize
biomass adhesive． The Chinese fir-based adhesives
were formulated with high percentages of Chinese fir
liquefied resultant in the adhesive formulations to
reduce the petrochemical dependency of conventional
wood adhesives．
1 Experimental
1. 1 Materials
Chinese fir ( collected in Guangdong Province，
China ) was ground into flour in a rotating
disintegrator． The wood flour with a dimension passing
100 meshes was dehydrated in an oven at 105 ℃ until
oven-dried． Reagent grade phenol and formaldehyde
( formalin， at concentration of 37% ) solution were
purchased from Guangdong Guanghua Chemical
Factory Co． Ltd，China． Other analytical chemicals
such as sodium hydroxide，hydrochloric acid，sodium
thiosulfate pentahydrate， absolute ethyl alcohol，
potassium iodide， iodine， hydrochloric acid，
ammonium acetate，acetylacetone were obtained from
Guangzhou chemical reagent factory，China．
1. 2 Liquefaction of Chinese fir flour
The Chinese fir flour was liquefied in sealed
reactor using the stainless steel instrument under the
following conditions: column，12 cm × 12 cm × 1. 5 cm
(diameter × height × thickness); limit temperature，
500 ℃ ; limit pressure，12 MPa． About 75 g Chinese
fir flour was loaded into the reactor． A concentration of
25% sodium hydroxide solution (300 g in total) was
gradually charged into the reactor with stirring． After
all of the sodium hydroxide solution had been loaded，
the reactor was sealed，and the mixture was kept in oil
bath at ( 200 ± 2 ) ℃ for 15 min． The liquefied
resultant was then cooled and preserved for synthesis．
1. 3 Preparation of Chinese fir-based adhesives
For preparing Chinese fir-based adhesives， the
Chinese fir liquid was used to prepare resins in the
reaction flask． The three weight ratios of Chinese fir
(CF) liquid to phenol-formaldehyde ( PF) ( 60 /40，
55 /45 and 50 /50)，three molar ratio of formaldehyde
to phenol ( the values are 2 ∶ 1，2. 5 ∶ 1 and 3 ∶ 1) were
chosen respectively as the analyzing variable factors．
The typical synthesis procedure was described as below
in which the PF /CF was 60 /40 with molar ratio of
2∶ 1． The preparation conditions of all adhesives are
summarized in Tab． 1．
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林 业 科 学 50 卷
Tab． 1 Preparation conditions of Chinese fir-based adhesives and PF adhesives
Adhesive ID Chinese fir liquid / g Phenol / g 37% Formaldehyde / g 50% NaOH solution / g CF /PF F /P
60 /40 － 2∶ 1 160. 5 47 60 / 60 /40 2∶ 1
55 /45 － 2∶ 1 130. 78 47 60 / 55 /45 2∶ 1
50 /50 － 2∶ 1 107 47 60 / 50 /50 2∶ 1
60 /40 － 2. 5∶ 1 183 47 75 / 60 /40 2. 5∶ 1
55 /45 － 2. 5∶ 1 149. 11 47 75 / 55 /45 2. 5∶ 1
50 /50 － 2. 5∶ 1 122 47 75 / 50 /50 2. 5∶ 1
60 /40 － 3∶ 1 205. 5 47 90 / 60 /40 3∶ 1
55 /45 － 3∶ 1 167. 44 47 90 / 55 /45 3∶ 1
50 /50 － 3∶ 1 137 47 90 / 50 /50 3∶ 1
2∶ 1 / 47 60 21. 4 / 2∶ 1
2. 5∶ 1 / 47 75 24. 4 / 2. 5∶ 1
3∶ 1 / 47 90 27. 4 / 3∶ 1
47 g of phenol and 60 g of formalin ( the F /P
molar ratio was 2) were charged into a three-necked，
500mL flask equipped with a condenser， a
thermometer， a teflon stirrer and the reaction
temperature was maintained at 45 － 50 ℃ for 30 min．
Then the temperature was gradually raised to around
80 ℃，and 160. 5 g of Chinese fir liquid was then
added during a period of 50 min． After all of the
Chinese fir liquid had been infused， the reaction
temperature was set at (92 ± 2 )℃ immediately and
maintained until the Gardner-Holdt viscosity reached
(3 000 ± 200 ) mPa·s ( 20 ± 2 )℃ ． The viscosity
measurements were carried out at 10 － min intervals．
The finished adhesive was cooled to room temperature
and kept in the refrigerator for use． About 250 g of
each adhesive sample was prepared． The PF resin was
prepared as control sample． The solid content， free
formaldehyde content and free phenol content of
prepared adhesives were determined according to the
China Industry Standard (GB /T 14074—2006) ．
1. 4 Resin solid content
The percent of resin solid content is calculated by
the following equation．
S (% ) = S1 / S0 × 100 ．
where“S”was the percent of resin solid content and
“S0”and“S1”were the weight of the resin before and
after the test，respectively．
1. 5 Free formaldehyde content
The free formaldehyde content of the prepared
resins was determined by the hydroxylamine
hydrochloride method． Accurately weighed about 3 or
5 gm of resin sample was transferred into 250 mL
beaker and dissolved in 50 mL methyl alcohol or 50 mL
75% isopropyl alcohol． Simultaneously，the pH value
of the solution was adjusted to 3. 5 by 1 N hydrochloric
acid solution． 25 mL of 10% hydroxylamine
hydrochloride solution was added and stirred for 10
min． Finally， the mixture solution was titrated with
0. 1 N or 1 N sodium hydroxide solution． Free
formaldehyde content was calculated by using following
formula．
Free formaldehyde content(% ) =
3c(V1 － V0)
m
．
where “V1”and “V0” are volumes of sodium
hydroxide solution required in the titration for sample
and blank，respectively． “c”is the exact normality of
sodium hydroxide solution． “m”is weight of sample in
gm．
1. 6 Free phenol content
The percentage of free phenol was evaluated
according to bromometry method． Accurately weighed
about 2 gm of resin sample was taken in 1 000 mL
round-bottomed flask． To that 100 mL distilled water
was added and the pH value of the solution was
adjusted to 4. 0 by 20% hydrochloric acid solution．
Then steam distilled until the negative test for phenol
with bromine water． The distillate was diluted to 1 000
mL with double distilled water． An aliquot of 50 mL
was taken in Erlenmeyer flask and 25 mL of 0. 1 N
bromate-bromide solution and 5 mL concentrated HCl
was added． The flask was then closed and kept in dark
for 15 min． After that，1. 8 gm potassium iodide was
added and kept in dark for another 10 min． Finally，
the mixed solution was titrated with 0. 1 N sodium
thiosulphate solution using starch as indicator． The free
phenol was calculated by following formula
Phenol content(by weight) =
241
第 1 期 孙 瑾等: 杉木液化液交联苯酚 －甲醛合成新型木材胶黏剂
(V1 － V2) × c × 0. 015 68 × 1 000
m × 50
× 100% ．
where“V1” and “V2” are the volumes of 0. 1 N
sodium thiosulphate solution required for blank and
sample，respectively． “m”is the weight of sample in
gm and “ c” is the exact normality of sodium
thiosulphate solution．
1. 7 Evaluation of plywood
Eucalyptus veneers with dimensions of 320 mm ×
320 mm × 2. 1 mm were used to prepare 3-layer
plywood panels． Chinese fir-based adhesive was
applied to double sides of a veneer at a spread rate of
350 g·m － 2 ( for double gluelines ) ． The adhesive-
coated veneer was then stacked between two uncoated
veneers with the grain directions of two adjacent
veneers perpendicular to each other． Thereafter，the
assembled veneers were pre-pressed(pressure，1 MPa)
at room temperature for 1 h． After that， the pre-
pressed veneers were hot-pressed at 160 ℃ for 15 min
at the same pressure of 1 MPa． The specimens were
maintained at room temperature，for 24 h，sawn to get
samples for the test of bonding strength and
formaldehyde emission． A total of 48 specimens of 100
mm × 25 mm ( 4 cycles’ test，12 specimens were
prepared for each cycle) were cut from each panel for
bond strength tests， according to JIS K6806—2004
standard． Ten specimens of 150 mm × 50 mm were cut
from panel to determine the formaldehyde emission
according to JIS A1460—2003 standard．
1. 8 Fourier transform infrared ( FT-IR )
spectroscopy test
The adhesive sample was placed in an oven at
(160 ± 2)℃ until a constant weight was obtained． FT-
IR spectra of both samples were performed in a Perkin
Elmer model Spectrum V10 instrument． Each spectrum
was recorded in a frequency range of 400 － 4 000 cm － 1
using potassium bromide ( KBr) disc． The KBr was
previously oven-dried at 300 ℃ to reduce the
interference of water．
1. 9 Differential scanning calorimetry (DSC) test
DSC measurements were conducted on a
NETZSCH 204 F1 differential scanning calorimeter．
Dynamic scans were conducted in a temperature range
of 30 － 250 ℃， at constant heating rate of 10
℃·min － 1，under nitrogen atmosphere at a flux rate of
50 mL·min － 1 ． For sample preparation， the sample
was placed in an oven at (40 ± 2)℃ until a constant
weight was obtained． About 6 mg of the resin was used
in an aluminum crucible of 40 μL with a
perforated lid．
2 Results and discussion
2. 1 Physical properties analysis
All of the Chinese fir-based adhesives had the
dark color with the specific odor． The resin solid
content， free formaldehyde content and free phenol
content were measured and the results are presented in
Tab． 2．
Tab． 2 Resin solid content，free formaldehyde
content and free phenol content
Adhesive ID
Solid
content (% )
Free formaldehyde
content (% )
Free phenol
content (% )
60 /40 － 2∶ 1 46. 16 ± 0. 06 0. 185 ± 0. 007 0. 048 ± 0. 001 3
55 /45 － 2∶ 1 47. 08 ± 0. 03 0. 258 ± 0. 003 0. 066 ± 0. 001 9
50 /50 － 2∶ 1 48. 71 ± 0. 11 0. 276 ± 0. 002 0. 081 ± 0. 000 7
60 /40 － 2. 5∶ 1 42. 27 ± 0. 11 0. 368 ± 0. 002 0. 031 ± 0. 001 1
55 /45 － 2. 5∶ 1 44. 17 ± 0. 03 0. 498 ± 0. 002 0. 062 ± 0. 000 7
50 /50 － 2. 5∶ 1 46. 74 ± 0. 07 0. 693 ± 0. 003 0. 085 ± 0. 001 0
60 /40 － 3∶ 1 40. 78 ± 0. 16 1. 021 ± 0. 003 0. 018 ± 0. 000 2
55 /45 － 3∶ 1 42. 89 ± 0. 17 1. 724 ± 0. 001 0. 056 ± 0. 000 5
50 /50 － 3∶ 1 45. 41 ± 0. 03 1. 921 ± 0. 003 0. 070 ± 0. 000 6
2 /1 54. 99 ± 0. 16 0. 355 ± 0. 002 0. 126 ± 0. 000 6
2. 5∶ 1 49. 48 ± 0. 12 1. 284 ± 0. 019 0. 098 ± 0. 000 3
3∶ 1 47. 93 ± 0. 03 4. 241 ± 0. 015 0. 074 ± 0. 000 6
Resin solid content is an important property for
phenolic resin． Low solid content adhesive will eject
out more water during the hot pressing，which could
reduce the bonding strength of the plywood． As
expected，the control PF resin adhesives have higher
solid content than the Chinese fir-based adhesives at
the same F /P molar ratio． The solid content of Chinese
fir-based adhesives ranges from 40. 78% to 48. 71%，
which exceeded the minimum requirements of 35% in
phenolic resin adhesive ( Jin et al．，2010 ) ． With
increasing the CF /PF mass ratio and F /P molar ratio，
a decreasing solid content in Chinese fir-based
adhesives was observed．
Free formaldehyde and free phenol are the
archcriminal of toxicity in phenols or aldehydes
synthetic resin． In general，low toxic PF resin follows
with poor bond strength，while great bonding strength
341
林 业 科 学 50 卷
is often accompanied with high toxicity． Results in
Tab． 2 showed that the free formaldehyde and free
phenol of the synthetic Chinese fir-based adhesives
would decrease along with the increasing addition of
Chinese fir liquid． As the CF /PF rising from 50 /50 to
60 /40，the free formaldehyde content and free phenol
content of the Chinese fir-based adhesives ( F /P =
2∶ 1 ) decreased from 0. 276% to 0. 185% and
0. 081% to 0. 048%， respectively，which were far
less than those of control PF resin． The free
formaldehyde and free phenol were similar to those of
the Chinese fir-based adhesives with higher F /P molar
ratios (El Barbary Hassan，et al． ) ． As known，the
alkaline liquefaction of Chinese fir breaks down
lignin，cellulose and hemicellulose． The lignin was
further hydrolyzed to three main structural units of
benzyl propane: Guaiacyl ( G )， Hydroxyl Phenyl
(H) and Syringyl ( S) (Yang et al．，2012) ． G-type
units have a free C5 position ( ortho to the phenolic
hydroxyl) in the ring， susceptible of reacting with
formaldehyde，while in S-type units both C3 and C5
positions are linked to a methoxy group，resulting in
low reactivity with formaldehyde． From this point of
view，lignin with G groups as the principal structural
units must be a priori more suitable for PF
formulations， and the H groups take the second
place． The units of H and G react with formaldehyde
in alkaline medium producing H-hydroxymethyl and
G-hydroxymethyl． Then the H-hydroxymethyl and G-
hydroxymethyl happen dehydrolytic condensation and
form the cross-linked structure． When exposed at high
temperature ( 200 － 220 ℃ )， cellulose and
hemicellulose were firstly degraded through hydrolysis
path to oligosaccharide and then converted in alkaline
pathway to glucose ( Yin et al．，2011 ) ． Through
diverse elimination reactions，glucose transformed to
5-hydroxymethyl furfural(5-HMF) ． Due to the similar
chemical property to formaldehyde， the phenol was
consumed by the condensation reaction of the 5-HMF，
which occurred at three reactive sites． Hence，the use
of an optimum amount of formaldehyde and phenol can
form and improve the chance of Chinese fir liquid’s
incorporation into the PF resin structures． As
discussed above，the adhesive made from CF /PF =
60 /40 with F /P = 2 ∶ 1 got the best physical
properties．
2. 2 Bonding properties analysis
In order to enhance the bonding strength and
boiling water resistance，formaldehyde and phenol were
used to co-polymerize with alkaline Chinese fir liquid．
The boiling bonding strength and wood failure were
evaluated for plywood panels bonded with various
Chinese fir-based adhesives and control PF resin
adhesives． The test results are presented in Tab． 3． To
verify the boiling water resistance and durability，the
test specimens were measured on more rigor conditions
after the plywood specimens had been subjected to a
54-h，76-h and 100-h cycle． The results showed that
all the 28-h boiling-drying-boiling tests for panels
prepared with Chinese fir-based adhesives with F /P = 2
exceeded 1. 1 MPa without evaluating the wood failure．
This means that the Chinese fir-based adhesives
formulation with F /P = 2 outdistanced the requirement
set by JIS K6806—2004 for application in exterior
use． The results in the 52-h boiling cycle test were also
outstanding because the values were greater than
1. 0MPa as before． Moreover，the 76-h boiling tests for
panels prepared with the formulation of 50 /50 － 2 ∶ 1
and the 55 /45 － 2 ∶ 1 were (1. 23 ± 0. 05 ) MPa and
(1. 02 ± 0. 03)MPa，which still met the JIS K6806—
2004 standard 0. 98MPa． In the 100-h boiling cycle
procedure， nothing but the evaluated value of the
Adhesive 50 /50 － 2 ∶ 1 exceeded the minimum
requirement of JIS K6806—2004 standard． All the
results above indicated that the Chinese fir-based
adhesive had wonderful water resistance and durability，
especially the Adhesive 50 /50 － 2∶ 1．
The boiling bonding strength and wood failure of
Adhesive 50 /50 － 2 ∶ 1 for the 52-h cycle test，76-h
cycle test，and 100-h cycle test were (1. 35 ± 0. 03)
MPa ( 70% )，( 1. 23 ± 0. 05 ) MPa ( 60% )， and
(1. 08 ± 0. 03 ) MPa ( 50% ) apparently，while the
results for the control PF were ( 1. 28 ± 0. 05 ) MPa
(65% )，(1. 12 ± 0. 05)MPa (50% )，and (0. 91 ±
0. 05)MPa (40% ) under the same test conditions． It
indicated that the Adhesive 50 /50 － 2 ∶ 1 had better
boiling water resistance and durability than the control
PF resin． And it is important that the Chinese fir liquid
is not used as filler but raw material reacted with
formaldehyde and phenol．
441
第 1 期 孙 瑾等: 杉木液化液交联苯酚 －甲醛合成新型木材胶黏剂
Tab． 3 Boiling bond strength of plywood on different test conditions
Adhesive ID 28-h
① boiling test
(wood failure)
52-h② boiling test
(wood failure)
76-h③ boiling test
(wood failure)
100-h④ boiling test
(wood failure)
60 /40 － 2∶ 1 1. 14 ± 0. 03⑤ (60⑥ ) 1. 01 ± 0. 03(50) 0. 89 ± 0. 05(30) 0. 41 ± 0. 05(10)
55 /45 － 2∶ 1 1. 32 ± 0. 08(80) 1. 22 ± 0. 08(75) 1. 02 ± 0. 03(55) 0. 85 ± 0. 04(25)
50 /50 － 2∶ 1 1. 51 ± 0. 06(90) 1. 35 ± 0. 03(70) 1. 23 ± 0. 05(60) 1. 08 ± 0. 03(50)
60 /40 － 2. 5∶ 1 0. 96 ± 0. 06(60) 0. 72 ± 0. 03(20) 0. 33 ± 0. 04(0) Failure
55 /45 － 2. 5∶ 1 1. 42 ± 0. 04(90) 1. 11 ± 0. 05(60) 0. 93 ± 0. 04(45) 0. 71 ± 0. 03(30)
50 /50 － 2. 5∶ 1 1. 38 ± 0. 05(85) 1. 14 ± 0. 05(70) 0. 95 ± 0. 04(50) 0. 77 ± 0. 05(30)
60 /40 － 3∶ 1 0. 56 ± 0. 04(30) Failure Failure Failure
55 /45 － 3∶ 1 0. 84 ± 0. 04(50) 0. 46 ± 0. 04(10) Failure Failure
50 /50 － 3∶ 1 1. 00 ± 0. 07(60) 0. 82 ± 0. 04(50) 0. 71 ± 0. 03(30) Failure
2∶ 1 1. 54 ± 0. 05(90) 1. 28 ± 0. 05(75) 1. 12 ± 0. 05(70) 0. 91 ± 0. 05(60)
2. 5∶ 1 1. 48 ± 0. 05(90) 1. 11 ± 0. 04(80) 0. 98 ± 0. 05(60) 0. 78 ± 0. 05(40)
3∶ 1 1. 34 ± 0. 05(80) 1. 01 ± 0. 06(60) 0. 89 ± 0. 04(30) Failure
①4 h in boiling water，20 h in (63 ± 3)℃ oven，4 h in boiling water; ②a procedure plus 20 h in (63 ± 3)℃ oven，4 h in boiling water; ③b
procedure plus 20 h in (63 ± 3)℃ oven，4 h in boiling water;④c procedure plus 20 h in (63 ± 3)℃ oven，4 h in boiling water; ⑤unit: MPa; ⑥unit:
% ．
2. 3 Formaldehyde emission
Formaldehyde emission of specimens was
measured by 24-h desiccator method． Fig． 1 shows the
formaldehyde emission results for the various
specimens． Each specimen was tested twice and good
repeatability of results was obtained with a maximum
relative standard deviation of less than 2% ． The
formaldehyde emission of all the panels approached to
the value of E0 specified in the JIS A1460—2003
standard( the value is less than 0. 5 mg·L － 1 ) except
the panel bonded with the control PF resin with the F /
P ratio of 3 ∶ 1． The quantity of formaldehyde emission
of plywood bonded with Chinese fir-based adhesives
decreased with the increasing CF /PF ratio as shown in
Fig． 1． It can be seen that the sample in the group of
F /P = 3 ∶ 1，with a CF /PF ratio of 60 /40，achieving
the lowest formaldehyde emission value of 0. 102 mg·
L － 1，which was only 1 /5 of the E0 specified value．
Panels bonded with the Chinese fir-based adhesives
emitted less formaldehyde than panels bonded with the
control PF resin adhesive by 50% － 80% ． This may be
due to the depolymerization products of lignin
maintaining their aromatic character and high
reactivity，which act as radical scavengers and can
therefore readily react with free formaldehyde in the
mixture，during crosslinking process ( Kunaver et al．，
2010) ． It is significant that formaldehyde emission
reduction appears to a large extent， while sizable
amounts of free formaldehyde present in the synthesized
resins can be ignored before use in plywood
manufacturing．
Fig． 1 Formaldehyde emission of plywood
2. 4 FT-IR analysis
As shown in Fig． 2， the Chinese fir-based
adhesive showed a similar FT-IR absorbance to that of
the control PF resin adhesive． The band at 3 420 cm － 1
in Chinese fir-based adhesive and the band at 3 416
cm － 1 in control PF resin are assigned to aromatic and
aliphatic OH groups while the bands at 2 948，2 850
and 1 460 cm － 1 in Chinese fir-based adhesive and the
bands at 2 946，2 845 and 1 458 cm － 1 in control PF
resin are related to the C—H vibration of CH2 and CH3
groups． They are typical vibrations of methoxyl groups．
However，with the incorporation of wood components，
the FT-IR spectra of the Chinese fir-based adhesive
contained some different bands compared with that of
the control PF resin． The major difference in the
spectra between the Chinese fir-based adhesive and
control resin adhesive is the absorbance in the carbonyl
region． As shown in Fig． 3 the peaks at 1 733，1 698，
and 1 652 cm － 1 in Chinese fir-based adhesive are
ascribed to the ester carbonyl stretch，aryl ketone or
aldehyde carbonyl stretch， and the di-substituted
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林 业 科 学 50 卷
alkene C CH2，respectively． However，the control
PF resin showed no absorbance in this region as
expected． Furthermore，the spectra of the Chinese fir-
based adhesive also showed two weak bands at 1 473
and 879 cm － 1 caused by tetra substituted (1，2，4，
and 6 ) ring which did not occur in the spectra of
control resin． It implies that the existence of some
lignin fragments，most of which are tetra substituted
aromatic rings in the Chinese fir-based adhesive． The
other difference in the spectra between the Chinese fir-
based adhesive and control resin occurred at 1 077
cm － 1( shown in Fig． 4)，where the band attributed to
the ether linkage on the furan ring and the band at
1 048 cm － 1 attributed to the single bond C—O—C
stretch with —CH2OH vibrations． Based on the above
discussion， the bands at 1 077， 1 048 cm － 1 are
associated with the 5 － HMF that reacted with phenol
during the polycondensation reaction．
Fig． 2 FT-IR spectra of adhesive 50 /50 － 2∶ 1 and adhesive 2∶ 1
Fig． 3 FT-IR spectra of adhesive 50 /50 － 2∶ 1 and adhesive 2∶ 1
2. 5 DSC analysis
The isothermal DSC curves at a heating rate of
10 ℃·min － 1 of Chinese fir-based adhesives and
control PF resin adhesives are shown in Fig． 5 and
Fig． 6． The results obtained are summarized in Tab． 4
containing onset temperature， peak temperature
Fig． 4 FT-IR spectra of adhesive 50 /50 － 2∶ 1 and adhesive 2∶ 1
and ΔH．
Fig． 5 and Fig． 6 show that the resin samples
gave a single or two exothermic peaks in the range of
141. 4 － 157. 5 ℃ ． Both of the exotherms obtained in
the resin systems were attributable to the curing
reaction． According to the previous researchs(Perez et
al．，2011) the lower exothermic peak in the range of
141. 4 － 144. 8 ℃ has been attributed to the addition
reaction of free formaldehyde to phenolic ring，and the
upper exothermic peak in the range of 143. 8 －
157. 5 ℃ was associated with the chain-building
condensation reactions，involving hydroxymethyl groups
attached to various phenolic species． The appearance
of single exothermic peak is mainly due to the F /P
molar ratio below 2. 3 that resulted in the overlapping
of exothermic signals， two well-separated exothermic
peaks are revealed when the F /P molar ratio was larger
than 2. 3(Holopainen et al．，1997) ．
Fig． 5 hows the DSC curves of the Chinese fir-
based adhesives (F /P = 2) with a CF /PF ratio of 50 /
50，55 /45 and 60 /40，respectively． As the data listed
in Tab． 4，the extrapolated onset temperatures for the
Chinese fir-based adhesives at F /P = 2 were found to
be 114. 6，115. 6 and 116. 4 ℃，respectively． It was
close to the control PF resin adhesive of the same molar
ratio，but slightly higher than the Chinese fir-based
adhesive with larger F /P molar ratio． This indicated
that with larger F /P molar ratio Chinese fir-based
adhesives were more reactive at the low temperatures．
As far as the effect of CF-to-PF ratio is concerned，it
can be seen from Fig． 5 that the onset temperature and
peak temperature of the Chinese fir-based adhesives
shifted to higher temperatures with an increase of CF /
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第 1 期 孙 瑾等: 杉木液化液交联苯酚 －甲醛合成新型木材胶黏剂
PF mass ratio． However， the ΔH of cure were
significantly reduced． Compared with the control PF
resin at the same molar ratio，the Chinese fir-based
adhesives had higher peak temperature and lower ΔH．
This is probably because lignin has less free ring
positions than phenol and more steric impediments what
delays the hardening of Chinese fir-based adhesives．
Furthermore， lignin introduces an extra amount of
methylol groups similar to those produced by
formaldehyde during curing， what will act in the
opposite way．
Tab． 4 The onset temperature，peak temperature and ΔH of the adhesives
Adhesive ID Onset temperature /℃ Peak 1 temperature /℃ Peak 2 temperature /℃ ΔH /(mJ·mg － 1 )
1∶ 2 114. 7 / 141. 8 96. 4
(70 /30) － 1∶ 2 116. 4 / 149. 3 68. 7
(60 /40) － 1∶ 2 115. 6 / 147. 5 72. 9
(50 /50) － 1∶ 2 114. 6 / 146. 1 78. 3
(50 /50) － 1∶ 2. 5 112. 5 142. 1 155. 0 89. 2
(50 /50) － 1∶ 3 111. 4 144. 8 159. 5 101. 5
Fig． 5 DSC curves of adhesive at F /P = 2
Fig． 6 DSC curves of Chinese fir-based adhesive
with CF /PF = 50 /50
Fig． 6 shows the DSC curves of the Chinese fir-
based adhesives (CF /PF = 50) with F /P molar ratios
of 2∶ 1，2. 5 ∶ 1 and 3 ∶ 1． Due to the F /P molar ratio
lower than 2. 3，the DSC curve of the Chinese fir-based
adhesive (F /P = 2∶ 1) reveals only a single exothermic
at the peak temperature of 146. 1 ℃ ． The DSC curves
of the Chinese fir-based adhesives(CF /PF = 50) with
a F /P molar ratio of 2. 5∶ 1 and 3∶ 1 manifested that the
curing behavior is completed in two steps which are
signified by two exothermic curves． The peak
temperature for the Chinese fir-based adhesive with a
molar ratio of 2. 5 ∶ 1 was 142. 1 ℃ and 155. 0 ℃，
respectively． And they were 144. 8 ℃ and 157. 2 ℃
for the Chinese fir-based adhesive with a molar ratio of
3∶ 1． It implied that the Chinese fir-based resins with
larger F /P molar ratio needed a higher temperature for
completely curing． The ΔH in Tab． 4 suggested that the
Chinese fir-based adhesive ( CF /PF = 50 /50 and
F /P = 3∶ 1) reacted more strongly than the other resins
due to the larger ΔH released during curing．
3 Conclusions
The alkaline Chinese fir liquid is proved a
wonderful raw material for plywood adhesives． The
process of liquefaction is easy to prepare which make it
possible for industrial production． The synthetic
Chinese fir-based adhesives exhibit excellent
improvements for free formaldehyde content and free
phenol content． More important， the properties of
plywood glued with the the Chinese fir-based adhesives
(CF /PF = 50 /50，F /P = 2 ∶ 1 ) after 100-h boiling
drying cycle still meet the requirement of the JIS
K6806—2004 standard in exterior application and the
formaldehyde emission is only 0. 074 mg·L － 1 which is
much less than that of the E0 specified in the JIS
A1460—2003 standard ( the value is less than 0. 5
mg·L － 1) ． In addition， the cost of this adhesive
appears much lower than that of the synthetic phenolic
resins traditional used for wood adhesives． Hence，we
can predicate that the Chinese fir-based adhesive will
not only help reduce the polymer industry ’ s
dependence on petro-chemical industry but also be
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林 业 科 学 50 卷
applied for industrial production．
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