الفهرس 
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Abstract
The wood composites industry is one of the largest manufacturing sectors. Wood
adhesives are essential components in wood composites. Formaldehyde-based adhesives
such as phenol-formaldehyde, melamine-formaldehyde, and urea-formaldehyde are
derived from petrochemicals, which release formaldehyde during hot pressing and during
improper storage. Moreover, formaldehyde inhalation causes health problems and is
suspected to carcinogen. Therefore, the wood composites would be benefit greatly by
reducing the emission of free-formaldehyde. The present work aims to study the
possibility to minimize emission of free-formaldehyde via several trials.
The first trial for reducing emission of free-formaldehyde was incorporating of some inorganic ammonium salts to conventional UF-adhesive system. It is clear that, the incorporated ammonium salts such as ammonium chloride, monoammonium
phosphate, ammonium phosphate, ammonium sulfate and ammonium persulfate
achieved improvement in reduction of free HCHO. The reduction in free-Ht.Hr)
increases with increasing salt weight percent from 4 % to 20 % with respect to control
sample (Uf’-adhesive). As can be seen that, salt of phosphate anion showed higher
reduction percent in free-HCHO than salts of dihydrogen phosphate, sulfate,
persulfate, and chloride anions, respectively compared to control sample. This is
ascribed to the fact that, these salts reduced pH of the adhesive medium and caused
acceleration of crosslinking of formaldehyde-based adhesive. Inorganic salt of sulfate
anion resulted in high modulus of rupture (MOR) than other salts especially. at 4-8 %
incorporated weight percent. However, salt of persulfate anion only achieved higher
modulus of elasticity (MOE) value than UF-bagasse composite. The strong adhesion
of the UF-incorporated inorganic salt adhesive system may be due to the same reason
mentioned before. For the case of comparing the mechanical properties of UF-bagasse
composites produced from incorporating optimum percentages (20 % /UF) inorganic
salts for reducing free-HCHO adhesive system, OF-incorporated (NILt)3P04, OF, UFN&
CI adhesive systems had relatively high MOR, MOE and I.B were about 15 MPa
for MOR, and about 0.35 GPa for MOE and 0.43 MFa for internal bond strength (I.B)
is satisfied load boards requirements.
For water resistance, ammonium salts of persulfate and dihydrogen phosphate
anions showed best water resistance than other anions (chloride, phosphate, and
sulfate). The lower water absorption percentages were about 33 % and 42 % at 4 % incorporated ammonium persulfate and soaking time of 2 hours and 24 hours, compared to 48 % and 54 % respectively for control composite. While, the lower
thickness swelling percentages were 18 % and 26 % at 4 % incorporated
monoammonium phosphate and soaking time 2 hours and 24 hours comparing to 36
% and 40 % for control OF-bagasse composite. For thermal behavior, there was significant increase in total activation energy ( L E, = 350.5-426.1 kJ I mole) due to
incorporation of ammonium salts of sulfate, chloride, phosphate, and dihydrogen
phosphate anions to urea-formaldehyde compared to composite from using ureaformaldehyde
alone ( I Ea = 247.8 kJ I mole ). Salt of dihydrogen phosphate anion
incorporation showed relatively high thermal stability a: Ea = 426.1 kJ / mole) than salts of other anions.
The second trial was incorporation of some shelf (available) organic
compounds such as, starch, polyvinyl alcohol, polyacrylamide, urea, and melamine.
As the case of inorganic salts, the improvement in free-Hf’Hf) reduction percent of
adhesive systems increased gradually with increasing in weight percent of % reduction in free-HeHO). However, UF-PV A achieved lower reduction percent of
about 42 %. The observed reduction in free-HCHO content in adhesive system is
probably ascribed to the formation of strong hydrogen and covalent bonds between free-
HCHO and functional groups containing organic compounds, e.g. hydroxyl, amino, and
amide groups. As the amount of incorporated organic compounds increased from 4 % to
16 % weight amount (based on weight ofUF), the MOR increased then decreased by further incorporated amounts. The most common higher values were at 12 % weight percent. 16 % polyacrylamide gave higher MOR (- 18 MPa). However, MOE behaved
the reverse trend, where the MOE gradually decreased with increasing the amount of
incorporating organic compounds. Polyvinyl alcohol achieved relatively high MOE than
other compounds (- 2.4 MFa). The improvement in MaR is due to formation of strong
hydrogen as well as covalent bonds which plays an essential role in the strong adhesion.
On comparing the static bending and internal bond of UF-composites produced from
incorporating optimum percentages (20 %/UF) shelf organic compounds that gave
optimum reduction of free-HeHO in adhesive system, UF-PAM and UF-PVA had
higher MOR, MOE and I.B than those produced from UF-starch, Uf’-urea, and UFmelamine
adhesive systems. For’ water resistance, incorporation shelf organic
compounds to Uf’-adhesive reduced the water absorption and thickness swelling of composite produced. Increasing the percentage of PVA and PAM in adhesive system from 4 to 20 % led to gradually increasing the water resistance properties than using UF
alone. While, for incorporating starch, urea, and melamine maximum improvement in
water resistance was observed at 4 % weight percent. Incorporating 20 % of PAM to
UF-adhesive system was the best compound for producing high water resistance
composite. For thermal behavior, the incorporating organic compounds had the
following improving sequence: urea> PVA > PAM > melamine> starch where, the
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total activation energy <I E, ) due to incorporating shelf organic compounds in the
range of(265-395.83 kJ / mole); which <I Ea) ofUF-bagasse composite is 247.8 kJ /
mole. As well as the maximum peak temperature of DTG curve was shifted to high
temperature on incorporating organic compounds.
In third trial, the lab prepared nitrogen containing starch derivatives
(polyacrylamide-based starch and polacrylonitrile-based starch derivatives) were
- incorporated to UF-adhesive systems. The reduction in free-HCHO, mechanical, and
water resistance properties of the composites produced were found to be dependent on
both the nitrogen content and amount percent of incorporated nitrogen containing
organic polymer. Generally, increasing the nitrogen content and amount percent of
incorporated polymer resulted in an increase in the reduction offree-HCHO in adhesive
systems. The properties of the agro-based composites showed that, the prepared
composites from UF-incorporated polymer and bagasse had static bending and internal
bond significantly higher than EN and ANSI Standards requirements for conventional
particleboard and this may be due to formation of hydrogen and covalent bonds
between the incorporated nitrogen containing starch derivatives and excess HCHO. The
results were processed in a computer programmer to obtain regression equation, 30-
surface response and the predicted properties. Carbamoylethylated starch (CmE-starch)
and hydrolyzed Polyacrylonitrile-grafted starch (HP AN-g-starch) gave the higher
reduction in free-Hf.Ht) than other incorporated organic polymer. Carbamoylethylated
starch (CmE-starch) amount is greatly affected on increasing the reduction percent.
While, nitrogen content had no significant effect in the case of relatively high
incorporated amount (16-20 %). Higher reduction in free-HCHO (- 100 %) with
relatively low amount percent (12 %) is noticed at 2.5 % nitrogen content of CmEIV
starch. HPAN-g-starch, at nitrogen content 9.29 % and amount percent 16-20 %, higher
reduction in free-HCHO to about 100 % is observed, On isolation of homopolymer
from PAM-g-starch showed that PAM-g-starch has less effect on reducing the free-
HCHO of UF-adhesive than crude grafted starch. ArnO-starch behaved as HPAN-gstarch
gave the same reduction percent (-100 %) at higher weight amount (16-20 %).
PAM polymer gave (68.31 %) reduction in free-HCRO were at 20.98 % nitrogen
content and 20 % amount percent respectively. Cm-starch gave 26.338 % reduction in
HCRO were at 6.65 % and 16 % respectively.
The data of free-HCRO content in mg /100 g board showed that, HPAN-gstarch
reduces free-HCRO content to give (- 4.2), ArnO- starch gave (- 8.1), CmEstarch
gave (~16), HCE-starch gave (- 18.5), and CE-starch gave (~ 18.8) compared to
control, UF-adhesive (21.8 mg /1 00 g board).
Greater improvement in static bending is achieved on incorporating CrnE-starch,
MOR was at 2.5 % nitrogen content and 16 % weight amount to give value - 37 MPa,
while optimum nitrogen content and amount percent that achieved the higher MOE
were at 1.8 % and 16 % respectively to give value of about 4.2 GPa.16 %. On studying
the effect of purification of the prepared crude starch from homopolymer showed that,
incorporating PAM-g-starch to UF-adhesive produced bagasse composites with
relatively low static bending strength than those produced from incorporating crude
PAM-g-starch to UF-adhesive.
For the water resistance property, where, the relatively low amount percent of
incorporated grafted starch (4 % / UF) achieved best water resistance properties than
higher amount (8-20 %). lncreasing the nitrogen content of the grafted starch
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accompanied by increase in water resistance of composite produced ..pAM composite
showed the better water resistance than other incorporated organic polymer composites
especially water absorption giving 23.4 % water absorption and 12.4 % thickness
swelling at 21 % nitrogen content and 4 % weight amount while PAM-g-starch
composite gave better thickness swelling 25 % water absorption and 8 % thickness
swelling at 9.5 % nitrogen content and 4 % weight amount. Thermogravimetric
measurements of investigated composites on using organic coi.ipounds showed that,
incorporating HPAN-g-starch achieved relatively high improvement in thermal stability
than urea and conventional hardener bagasse composite was 483.25 kJ / mole while <L
Ea) ofUF-bagasse composite was 247.8 kJ / mole.
In fourth trial, bagasse composites were surface-treated by using aqueous
solution contains 20 % of PAM, PAM-g-starch, and carbamoylethylated starch based on
the dry weight of UP-adhesive. It was found that, this surface treatment showed
improvements in both mechanical and water resistance. However, incorporation
treatment with the same compounds gave better results than surface one.
Finally, the resistance of the prepared composites to aging conditions was
studied. The boards were treated with HPAN-g-starch and CmE-starch were exposed to
93 %, 65 % relative humidities respectively compared with conventional UP-hardener
composites for different periods from one day to seven days at 26°C. It was noticed
that, increasing exposure to relative high humidity with time produced a progressive
increase in emission of HCHO of board. When boards were exposed to 93 % relative
humidity (RH) showed higher increase of emission percent in free HCHO than when
exposed to 65 % RH. The conventional hardened particleboard was the most influenced
than Cmfi-starch and HPAN-g-starch treated particleboards respectively. This may be
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discussed based on moisture caused hydrolysis of the resin decreasing its molecular
weight. It was noticed that, 93 % RH showed higher loss in mechanical properties than
65 % RH. The greater resistance in mechanical strength to aging conditions (MOR,
MOE, and I.B) in both relative humidities order was as following: in case of MOR
MOE, and ill: HPAN-g starch treated board> CE-starch treated board> conventional
UF-hardener composite.
-Results of the Uf-agro-composites from different raw materials such as, rice
straw, reed, and cotton stalks in addition to sugar-cane bagasse as lignocellulosic fibers
were treated with highly effective organic polymer (lIPAN-g-starch) and casein either
by incorporation or by surface treatment. Generally, incorporation treatment gave less
free HCHO content percent than surface one compared with control (OF -bonded
hardened lignocellulosic composites from different raw materials). HPAN-g-starch
showed less free HCHO percent than casein did compared with conventional hardener
UF-bagasse composite. In case of mechanical properties, incorporation of HPAN-gstarch
and casein to UF gave better results than surface treatment compared with
control. HP AN-g-starch gave better results than casein did. Rice straw, reed, and cotton
stalks gave fewer improvements than bagasse composite owing to their differences in
chemical composition of raw material and presence of highly waxy layer that prevents
penetration of resin into fibers, and consequently decreased mechanical strength
increased water absorption and thickness swelling.