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Effect of reaction temperature on conversion and thermal properties of polyamide hot-melt adhesives.

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ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING
Asia-Pac. J. Chem. Eng. 2007; 2: 599–608
Published online 6 August 2007 in Wiley InterScience
(www.interscience.wiley.com) DOI:10.1002/apj.061
Research Article
Effect of reaction temperature on conversion and thermal
properties of polyamide hot-melt adhesives
N. M. Ghasem,1 * J. Heiderian2 and W. W. Daud2
1
2
Department of Chemical and Petroleum Engineering, UAE University, Al-Ain 17555, UAE
Department of Chemical Engineering, University of Malaya, KL, Malaysia
Received 26 February 2007; Revised 13 June 2007; Accepted 21 June 2007
ABSTRACT: The work described in this paper aims at exploring the effect of reaction temperature, with and without a
catalyst on the conversion and thermal properties of polyamide hot-melt adhesives. The polyamides were synthesized
from C36 dimer acid and ethylenediamine; o-phosphoric acid was used as catalyst. The thermal properties investigated
were glass transition temperature, melting point, heat of fusion, and molecular weight of the final products. Glass
transition temperatures, heat of fusion, and melting point were found to increase with increasing molecular weight.
Glass transition temperature was found to be in the range of 62–66 ◦ C; however, for noncatalytic reaction at 130 ◦ C,
the final product was in liquid phase at room temperature and no glass transition temperature was detected. Results
show that as the polymerization reaction temperature increases, the number average molecular weight increases. In the
reaction, ethylenediamine and dimer acid should be taken in equivalent amounts to produce polyamides with high and
desirable molecular weights. Excess of ethylenediamine will lead to low molecular weight products with the free amine
group left unreacted. However, an extra amount of the ethylenediamine should be added initially to compensate for
the evaporated loss of ethylene diamines. The excess amount should be equivalent to the amount that would evaporate
during the preheating process. Parameters of the rate equations and the empirical parameters were determined with
nonlinear regression analysis. The kinetic model was used to simulate experiments that were not included in the
empirical parameter estimation. The comparison of the model predictions with the experimental data showed good
agreement.  2007 Curtin University of Technology and John Wiley & Sons, Ltd.
KEYWORDS: dimer acid; ethylenediamine; polyamide; adhesive
INTRODUCTION
Fatty polyamides are products of di- and polyfunctional
amines and di- and polybasic acids obtained by polymerization of unsaturated vegetable oil acids or their
esters. Dimer fatty acids have been traditionally used
to synthesize and formulate hot-melt adhesives, flexographic inks, functional coatings, and other engineering
materials (Xiao et al ., 1998). The use of polyamides as
hot-melt adhesives was found as early as 1959 (German and Degering, 1959). In comparison with ethylene
vinyl acetate (EVA), which has widely been used as a
hot-melt adhesive, it has a higher softening point and
higher adhesion strength, and therefore, its application
in hot-melt adhesives is becoming increasingly popular
(Li and Yu, 1991; Hu, 1989). Condensation of dimer
acids with diamines produces a polyamide through the
following reaction
*Correspondence to: N. M. Ghasem, Department of Chemical and
Petroleum Engineering, UAE University, Al-Ain 17555, UAE.
E-mail: nayef@uaeu.ac.ae
 2007 Curtin University of Technology and John Wiley & Sons, Ltd.
n HOOC–R–COOH + n H2 NR NH2 −−→
O
HO[– C –R–CONHR NH–]n H + (2n − 1)H2 O
Monomers that are joined by condensation polymerization have two functional groups: a carboxylic acid
and an amine group. Both reactants can form an amide
linkage. Since each monomer has two reactive sites,
they can form long-chain polymers by making many
amide links. Figure 1 shows monomers of dimer fatty
acids and ethylene diamines undergoing the condensation process to form polyamides as well as water.
To assist the condensation reaction, a catalyst, such as
phosphoric acid, may be added to the reaction mixture
in a catalytic proportion (David, 1995; Parker, 1995;
Heidarian et al ., 2006). The catalyst employed in the
condensation reaction may be either charged to the reaction mixture at the beginning of the reaction, or added
slowly just prior to the point at which the reaction rate
600
N. M. GHASEM, J. HEIDERIAN AND W. W. DAUD
Figure 1.
Scheme for the preparation of
polyamide hot-melt adhesive.
is slowing. The preferred concentration of the catalyst
is within the range of 0.001–3 wt%, and more preferably from about 0.01 to 1.0 wt% of the total materials
charged (Parker, 1995). Either the condensation polymerization reaction of fatty polyamides may be carried
out on a stepwise addition basis, or all reactants can
be mixed together at once. The former is preferable
because if all of the reactants are mixed together at
once, there will be a sudden and vigorous expansion of
the reaction mixture (foaming) because of the sudden
release of a substantial amount of water formed during
the reaction (David, 1995).
Polyamide resins, useful in the preparation of hotmelt inks for ink-jet printing, are prepared by the condensation polymerization reaction of a monoamine, a
diacid, and a third reactant selected from diamines,
where they are synthesized in the presence of a catalyst. The catalyst was added to assist the condensation
reaction; phosphoric acid (i.e. as catalyst) was added to
the reaction mixtures in catalytic proportions as reported
by David (1995). Foaming is considered as the distribution of a gas throughout a continuous liquid phase in
a finely divided form. Foam displays an exceptionally
large gas/liquid interface that separates one bubble from
its neighbor. The polyamides synthesized from dimer
acids and diamines has low crystallinity and a wide
range of melting temperatures, which make them particularly suitable to be used as hot-melt adhesives (Loeb,
1978; Campbell, 1981; Bonk, 1987; Harman, 1989).
The characteristics of polyamides synthesized from
dimer acid and single diamines were found to be brittle,
tending to crack at low temperatures (Li and Yu, 1991).
Polyamides synthesized from dimer acids and mixtures
 2007 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pacific Journal of Chemical Engineering
of ethylenediamine and hexamethylene diamines have
different results on different properties than those synthesized from single diamines (Peerman and Vertnik,
1968; Kale et al . 1994). Properties of polyamides,
such as Tg ; crystallinity, melting point, tensile properties, molecular weight, low-temperature properties, and
adhesive properties are affected by the type, contents,
and quantities of the diamine monomers and the dicarboxylic acids (Xuming et al ., 2002). The effect of the
content of sebacic acid, ethylenediamine, and piperazine
on the properties of resultant polyamide was experimentally investigated; the resultant polyamide properties
were of crucial importance for synthesizing polyamide
with excellent properties, especially low-temperature
properties (Xuming et al ., 2002). Therefore, acquiring
special properties of polyamides required a thorough
investigation of the relationship between the content of
these diamine monomers and the dicarboxylic acids.
In industry, the water produced during the reaction should be purged out to minimize reverse reaction. Evaporation of ethylenediamine during reaction
is another important factor that needs to be measured (Renfrew et al ., 1956), because if the evaporation
becomes high, the loss in ethylenediamine will cause
imbalance in acid and amine values, and this will affect
the final product.
In the present work, the polyamide hot-melt adhesive
is synthesized from C36 dimer fatty acids and ethylenediamine at different reaction temperatures, catalyst concentration, and fixed mixing rate: 75 rpm. The effect
of reaction temperatures on the thermal properties of
the synthesized polyamide, such as glass transition temperature, melting point, heat of fusion, and molecular
weight were experimentally explored. A kinetic model
was used to estimate the parameters of the rate equations using nonlinear regression. The model was used
to simulate experiments, which were not included in the
parameter estimation.
EXPERIMENTAL
Dimer acid, PRIPOL 1013 (0.1% monomer, 97% dimer,
3% trimer, and 195 acid value) from Uniqema, Gouda,
The Netherlands, and ethylenediamine of laboratory
reagent grade having a purity of 98% were used in
the reaction. o-Phosphoric acid of laboratory reagent
grade (85% purity) was used as catalyst. All other
materials used in the analysis were of reagent grade.
The experimental setup is shown in Fig. 2. In a typical
noncatalytic reaction experiment, 280 g (i.e. 0.5 mole)
of C36 dimer fatty acids was charged into the 600 ml
reactor and heated to 10 ◦ C below the desired reaction
temperature. An extra molar amount of ethylenediamine
(based on mole of dimer acid) is preheated to 116 ◦ C
and added to the reactor.
Asia-Pac. J. Chem. Eng. 2007; 2: 599–608
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
CONVERSION AND THERMAL PROPERTIES OF POLYAMIDE
Stirrer
To Cooling
Coil
Amine /
Inert Gas
Inlet/
Sampling
Point
Temperature
Detector
Controller
Cooling
Condenser
Heater
Distillate
Figure 2. Schematic diagram of the melt polymerization apparatus.
At reaction temperatures above the boiling point of
ethylenediamine, a portion of the ethylenediamine may
evaporate as it is added to the reactor. Because of the
imbalance in the reactant stoichiometric proportions,
high molecular weight polyamides will not be possible,
owing to the total consumption of the ethylenediamine.
The end groups of the polymer chains will be an acidic
group, and there will be no more amine to react to yield
high molecular weight polyamide. As a result, excess
ethylenediamines are recommended during the reaction
to compensate for the loss of ethylenediamine caused
by evaporation during the preheating stage.
The amount of ethylenediamine charged at each
temperature is given in Table 1. The stirring speed was
set at 75 rpm. Low mixing rate was used to prevent
foaming. The reaction was carried out at four different
temperatures in the range of 130–175 ◦ C. Within this
temperature range, the materials remained in molten
state. The water generated during the reaction and
evaporated diamines was purged out of the reactor using
nitrogen at a rate of 20 ml/min. These materials were
later condensed and collected in a prepared container
for analysis. The temperature of the cooling water for
condenser was kept at 4 ◦ C. The amount of distillate
collected with time was measured, and the sample
refractive index was analyzed using refractometry. The
samples were withdrawn from the reactor via a sampling
port at several time intervals for analysis of the acid and
the amine values.
The same procedures as that of the noncatalytic
reaction were followed, except that approximately 1
wt% by weight of o-phosphoric acid (85% pure) based
on total stoichiometric amount of monomers was added
to the reactor with C36 dimer acid. An extra molar
amount of ethylenediamine (based on mole of dimer
fatty acid) was preheated to 116 ◦ C and added to the
 2007 Curtin University of Technology and John Wiley & Sons, Ltd.
Table 1. Amount of ethylenediamine charged at each
temperature for catalytic reaction (initial weight of
dimer acid is 280 g).
Temperature
(◦ C)
130
145
160
175
Initial
ethylenediamine
(g)
o-Phosphoric acid
(g)
30.3
32.5
35.0
37.5
2.65
2.65
2.65
2.65
reactor. The amount of ethylenediamine charged at each
temperature along with the amount of o-phosphoric acid
is given in Table 1.
The materials that evaporated from the reactor were
condensed and collected in a prepared container for
analysis. The temperature of the cooling water for
the condenser was kept below 10 ◦ C. The amount
of distillate collected with time was measured and
the sample refractive index was measured using a
refractometer model NAR-1T. Before that, a calibration
curve was established by measuring several samples
of known weight fraction of ethylenediamine in water.
The weight fraction of ethylenediamine in the stream of
condensate was measured on the basis of the established
calibration curve. The polyamide samples were taken
out of the reactor via the sampling port at several time
intervals for analysis of acid and amine values.
The polymer samples withdrawn from the reactor
at certain time intervals via the sampling port were
analyzed for acid and amine values, and hence, conversion measurements. The acid value was determined
on the basis of ASTM D-1980-67 using a neutral solution (1 : 1 v/v) of n-butanol and xylene for dissolving
Asia-Pac. J. Chem. Eng. 2007; 2: 599–608
DOI: 10.1002/apj
601
602
N. M. GHASEM, J. HEIDERIAN AND W. W. DAUD
Asia-Pacific Journal of Chemical Engineering
the samples. The amine value was determined using
ASTM D-2074-62T with the same solvent as used for
determining acid value. The water generated during the
reaction and evaporated ethylenediamine were purged
out of the reactor using nitrogen.
For acid value, 5 g of the sample weighed to 0.1 mg
was transferred to a 500-ml Erlenmeyer flask, and
75–100 ml of hot ethyl alcohol was added to the flask.
Agitation and further heating may be necessary to bring
the fatty acid into complete solution. 0.5 ml of the
phenolphthalein indicator solution was added to the
solution. The solution was titrated immediately while
shaking with 0.5 N KOH to the first pink color that
persisted for 30 s. The acid value was calculated as
follows:
V × N × 56.1
(1)
Acid value =
S
where V is the volume in ml of KOH solution required
for the titration, N is the normality of the KOH solution,
and S is the specimen weight in grams. The value 56.1
is the molecular weight of KOH. For the amine values,
5 g of the polyamide sample weighed to 0.1 mg was
weighed and transferred into a 250-ml flask, 50 ml of
xylene and isopropanol (1/1 : v/v) was boiled for 1 min
to drive off any free ammonia that may be present, and
the boiled mixture was added to the 250 ml flask. The
solution was cooled to room temperature and five drops
of bromophenol blue indicator was added to the solution
and titrated while swirling with 0.2 N HCl to the yellow
ends. The total amine value was calculated as follows:
Amine value =
V × N × 56.1
S
(2)
where V is the volume of HCl solution required for the
titration in ml, N is the normality of the HCl solution,
and S is the specimen’s weight in grams. The number
average molecular weight, Mn, was calculated on the
basis of the following equation (Xiao et al ., 1998).
Nm
Nd
Nt −1
W
+
+
(3)
Mn =
(CA VA + CB VB ) 1
2
3
AV = CA × VA × MWKOH /W
(4)
AmV = CB × VB × MWKOH /W
(5)
where W is the weight of solid sample titrated;
CA , CB , VA , and VB are the concentrations and actual
volumes used from the standard solutions of the
sodium hydroxide and the hydrochloric acid, respectively. Nm , Nd and Nt are the percentage concentrations
of the monomers with one, two, and three functional
groups (acid and amide) in the products. AV is the
acid value, and AmV is the amine value, MWKOH is
the molecular weight of potassium hydroxide (MW =
56.1 g/mol)
 2007 Curtin University of Technology and John Wiley & Sons, Ltd.
Substituting Eqns (2) and (3) in (1), yields
Mn = 2 × MWKOH /(AV + AmV )
(6)
Glass transition temperature, melting points, and heat
of fusion were measured using differential scanning
calorimetry (DSC) with heating rate of 20 ◦ C/min and
under nitrogen atmosphere from room temperature to
200 ◦ C. Less than 1 g of the produced polymer is melted
on a glass slide as a film under vacuum for half an
hour. The sample was kept at 120 ◦ C in an oven for
the removal of water. The sample was then cooled. The
melting point of the prepared sample was obtained using
DSC. The DSC curves of the samples are presented in
Figs 9 and 10 for noncatalytic and catalytic reaction,
respectively.
KINETIC MODEL
In the derivation of the reactor model, some fundamental assumptions were introduced (Elias, 1977). The
liquid phase in the reactor was presumed to be in batch;
however, some volatilization of the compounds, particularly water and diamines, were assumed to take place.
The reaction rates were described with respect to the
mass of the liquid (i.e. r is in units of mol/kg min).
The analytical concentrations of carboxylic groups, and
amount of distillate were measured during the reaction.
On the basis of these assumptions, the mass balance
of component i in the liquid phase can be written as
follows (Juha et al ., 1996):
ri m = Fi +
dni
dt
(7)
where m is the mass of the liquid phase, Fi is the
amount of substance leaving the reactor in the gas phase
condensed and collected as the distillate. The amount
of substance in the reactor is expressed with the mass
of liquid and the concentration,
ni = ci m
(8)
dm
i
Differentiation of ni with time (i.e. dn
dt = ci dt +
i
m dc
dt ) and substituting in Eqn (7), the resultant mass
balance equation is transformed to:
Fi
ci dm
dci
= ri −
−
dt
m dt
m
(9)
The flow leaving the reactor is expressed as the
concentration in the distillate (cdi ) and the distillate
mass flow (ṁd ):
(10)
Fi = cdi ṁd
For the instant mass in the reactor (m), the mass in
the distillate (md ), the mass withdrawn from the liquid
Asia-Pac. J. Chem. Eng. 2007; 2: 599–608
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
phase as samples ( ms ), the total mass balance is
applied:
mo = m + md +
ms
(11)
where mo is the total mass initially present in the
reactor. The total mass balance of the collected distillate
is:
dmd
.
(12)
ṁd =
dt
Since the total mass (m0 ) is constant, using the discrete sampling method and differentiation of Eqn (11)
gives the simple relation
dmd
dm
+
=0
dt
dt
(13)
Relation (13) is emphasized in the definition of Fi
Fi = cdi
dmd
dt
(14)
Substituting Eqns (14) in (9) and rearranging leads to
Eqn (15)
ci − cdi dmd
dci
= ri +
(15)
dt
m
dt
Dividing Eqn (11) by m0
md
m
=1−
−
m0
m0
ms
mo
(16)
Introducing the following dimensionless quantities:
ms
md
,ψ =
(17)
ξ=
m0
mo
and inserting Eqns (17) in (16) and then to Eqn (15)
lead to the following equation:
ci − cdi dξ
dci
= ri +
dt
1 − ξ − ψ dt
(18)
This approach would be, in principle, applicable also
for the cumulative mass of distillate (ξ ). However, an
efficient way to describe the time evaluation of the
distillate is to fit an empirical model to the experimental
data. The empirical dimensionless cumulative mass of
distillate is:
(19)
ξ = A(1 − e −Bt )
The distillate was analyzed, i.e. the weight fractions (xi ) of water and diamines in the distillate were
obtained. The experimentally observed weight fractions
(xi ) and the molar masses (Mi ) were used to calculate
the concentration of distillate (cdi )
cdi =
xi
Mi
(20)
 2007 Curtin University of Technology and John Wiley & Sons, Ltd.
CONVERSION AND THERMAL PROPERTIES OF POLYAMIDE
The only components of significant importance in
the distillate were water and diamines. The empirical
formula for the weight fraction of diamines is:
xNH2 = Ce −Dt + E
(21)
The water weight fraction:
xH2 O = 1 − xNH2
(22)
The parameters included in Eqns (19) and (21) were
determined simultaneously from the experimental data
using nonlinear regression analysis. Minimizing the
objective function using Excel software (2003) and the
solver option that is based on reduced gradient method
the Generalized Reduced Gradient (GRG) algorithm for
optimizing nonlinear problems. The equation for rate of
reaction for amine and acid is as follows:
ri = kf CCOOH CNH2 − kr CCONH CH2 O
(23)
Equation (23) is applied on the basis of secondorder reaction. CCOOH , CNH 2 , CCONH , and CH2 O are the
concentrations of acid, amine, linkage (reacted acid and
amine), and water, respectively.
The estimation of the rate parameters was performed
stagewise. The mass balances were solved numerically
during the objective function minimization with the
Runge Kutta method available in MATLAB software.
The objective function is the minimization of the error
(e1 ):
(COOHj ,cal − COOHj ,exp )2
(24)
e1 =
where COOHj ,cal is the calculated acid concentration
from the kinetic model and COOHj ,exp is the experimental concentration of acid. Tables 2 and 3 show
the empirical constants (A–E) and the reaction rate
constants, respectively. The kinetic model was used
to simulate experiments, which were not included in
the parameter estimation. Two verification experiments
were made at isothermal conditions (175 ◦ C) for both
noncatalytic and catalytic reactions, which are shown
in Figs 6 and 7, respectively. The kinetic model predicts the experimental data in an acceptable way. The
minor differences between the model predictions and
the experimental data are simply due to experimental
scattering.
RESULTS AND DISCUSSION
The acid concentration vs time at various reaction
temperatures (without catalyst) is presented in Fig. 3.
The diagram shows that the acid concentration is
strongly influenced by the reaction temperature. At
a specific reaction time, as the reaction temperature
Asia-Pac. J. Chem. Eng. 2007; 2: 599–608
DOI: 10.1002/apj
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N. M. GHASEM, J. HEIDERIAN AND W. W. DAUD
Asia-Pacific Journal of Chemical Engineering
Table 2. Empirical parameters used in the model.
T(◦ C)
175
175
Percent
catalyst
concentration
A
B
C
D
E
0
1
0.0686
0.0761
0.0782
0.1816
0.7279
0.6065
0.3895
0.9999
0.2721
0.3930
Table 3. The kinetic values of the rate constants for catalytic and noncatalytic
reactions.
Noncatalytic
T ( C)
130
145
160
175
Catalytic reaction
k1 (kg/mol min)
k2 (kg/mol min)
0.0063
0.0178
0.0212
0.0498
0.0019
0.0028
0.0038
0.0157
increases, acid concentration decreases, and hence, the
reaction conversion increases. Figure 3 reveals that after
100 min of reaction time there is a slight drop in acid
concentration. The acid and amine values are nearly
the same at the later stage of the reaction as seen in
Fig. 4, and this indicates that the correct amounts of
the extra ethylenediamine were added at the beginning
of the reaction to compensate for the evaporation loss.
For the noncatalytic reaction, Fig. 5 shows the variation in the water concentration inside the reactor vs
time for the non-catalytic reaction. The diagram shows
that the amount of water increased sharply at the very
beginning of the reaction because of the high reaction
rate and the high rate of water produced. After about
5 min of operation, water concentration drops sharply
for 10 min due to the increase in the rate of water
k1
(kg/mol min)
0.0043
0.0272
0.0444
0.0629
k2 (kg/mol min)
0.0012
0.0046
0.00767
0.0035
6
Amine concentration (mol kg-1)
◦
5
4
3
2
1
0
0
10
20
30
Time (min)
40
50
Figure 4. Concentrations of the amine groups vs reaction
time at 160 ◦ C (with no catalyst reaction); experimental ()
and predicted (solid line).
3.5
Acid concentration (mol kg-1)
604
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
50
100
150
200
Time (min)
250
300
350
Figure 3. Concentration of carboxylic acid vs time with no
catalyst. The continuous lines represent the complete kinetic
model (before 90% conversion); 130 ◦ C (), 145 ◦ C (),
160 ◦ C (), 175 ◦ C (), solid lines are the predicted results.
 2007 Curtin University of Technology and John Wiley & Sons, Ltd.
evaporation and the decrease in the rate of water production. After 20 min of operation, water concentration
inside the reactor remains almost constant, because of
the decrease in the rate of reaction, and the evaporation
reaches constant value. This phenomenon is attributed
to the low rate of production of water due to the low
concentration of reactants at the end part of the reaction.
By comparing simulated water concentration inside the
reactor at different temperatures, it was observed that as
the reaction temperature increases, the concentration of
water inside the reactor decreases, since at high polymerization reaction the amount of water produced as
a result of the polymerization reaction is higher than
those attained for polymerization reaction at lower temperatures and similar reaction time period. By contrast,
the rate of water evaporated at high polymerization
Asia-Pac. J. Chem. Eng. 2007; 2: 599–608
DOI: 10.1002/apj
CONVERSION AND THERMAL PROPERTIES OF POLYAMIDE
temperatures is higher than that at lower reaction temperatures; consequently, the amount of water held inside
the reactor at high temperatures is lower than that held
at elevated polymerization temperatures.
The change in the acid concentration in the presence
of a catalyst with time is presented in Fig. 6. The
diagram shows that the rate of reaction is strongly
influenced by the reaction temperature. The acid and
amine values are nearly the same at the later stages of
the reaction and this indicates the correct amount of
extra ethylenediamine that was added at the beginning
of the reaction to compensate for the evaporation
loss (Fig. 7). At 175 ◦ C, the amine was almost totally
consumed in less than 10 min, thus almost terminating
the reaction.
Figure 8 shows the variation in the concentration of
water that remains inside the reactor vs reaction time
at 175 ◦ C, and the results reveal that the concentration
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
10
20
30
Time (min)
40
50
Figure 5. Simulated liquid phase concentration of water at
200 ◦ C (noncatalytic reaction).
Acid concentration (mol kg-1)
3.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
20
40
60
80
Time (min)
100
120
140
Figure 7. Concentrations of the amine groups vs time at
175 ◦ C in the presence of a catalyst, Experimental () and
predicted (solid line).
reaches a constant value after sometime and that is
accredited to the low rate of water produced due to the
lower concentration of reactants at the end part of the
reaction. For catalytic reaction, A and B are both higher
than for the noncatalytic reaction, C and D increase and
E decreases (Table 2). The amount of water produced
in the presence of a catalyst is higher than that of the
noncatalytic reaction as shown in Table 4. Comparison
between acid concentration for catalytic and catalytic
condensation polymerization is shown in Fig. 9. The
diagram shows that at fixed mixing rate and reaction
temperature the concentration drops sharply for catalytic
reaction, and consequently conversion is higher than
noncatalytic reaction.
The thermal properties such as melting point, heat
of fusion, glass transition temperatures and the number
average molecular weight at different reaction temperatures and 75 rpm are experimentally investigated and
are shown in Table 5. The results were obtained using
DSC (Mettler DSC 820). The melting points of the
3.0
1.6
2.5
2.0
1.5
1.0
0.5
0.0
0
50
100
150
Time (min)
200
250
Water concentration (mol kg-1)
Water concentration (mol kg-1)
1.8
4.5
Amine concentration (mol kg-1)
Asia-Pacific Journal of Chemical Engineering
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
Figure 6. Concentration of the carboxylic acid with time in
the presence of a catalyst. The continuous lines represent
the complete kinetic model; 130 ◦ C (), 145 ◦ C (), 160 ◦ C
(), 175 ◦ C ().
 2007 Curtin University of Technology and John Wiley & Sons, Ltd.
50
100
Time (min)
150
200
Figure 8. Simulated liquid phase concentration of water at
160 ◦ C in the presence of catalyst reaction.
Asia-Pac. J. Chem. Eng. 2007; 2: 599–608
DOI: 10.1002/apj
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N. M. GHASEM, J. HEIDERIAN AND W. W. DAUD
Asia-Pacific Journal of Chemical Engineering
Table 4. Amount of produced water at different
catalyst concentrations.
3.5
catalytic reaction
non catalytic reaction
Acid concentration (mol/kg)
3
Catalyst (wt%)
0%
2.5
Time
(min)
2
1
0
0
10
20
30
40
50
60
Time (min )
70
80
90
0
200 οC, 75 rpm
105
-10
160 οC, 75 rpm
94
-15
130 οC, 75 rpm
-20
67
-30
30
50
70
90
110
130
0
3.86
5.91
5.92
5.92
5.92
0.0
4.12
5.94
6.15
6.23
6.23
100
Figure 9. Acid concentration for catalytic and noncatalytic
reaction.
-5
1.0%
Water (g)
0
10
20
25
60
90
1.5
0.5
Heat flow (mW)
606
150
Temperature (οC)
Figure 10. The DSC diagram for fatty polyamides in the
absence of catalyst (20 ◦ C min−1 ).
final products were measured using DSC with the intention of making sure that those high molecular weight
polyamides were achieved.
The results show that the melting points are quiet high
except for those obtained at low reaction temperatures,
and thus, high molecular weight polyamide is produced
at all reaction temperatures. At low temperatures, the
melting point is low because the final products’ number
average molecular weight is low due to the low rate
of reaction. The same phenomena were reported for
aromatic fatty polyamides Eqn (14). The results indicate
that the melting point increases because of the increase
in the number average molecular weight which was
calculated on the basis of Eqn (6) (Xiao et al ., 1998).
As the reaction proceeds, acid and amine values
decrease. The decrease in the acid value is an indication
of the increase in both molecular weight and conversion.
From Eqn (25) it can be deduced that as the acid and
amine values decrease the number average molecular
weight increases. Heat of fusion, which is a function
of the crystalline phenomena, increases with increasing
conversion, because high conversions leads to longchain polymer and hence high molecular weight. Large
molecular weight polymers have better crystalline characteristics than low molecular weight polyamides. Glass
transition temperature (Tg ) is found to be in the range of
62–66 ◦ C except for the noncatalytic reaction at 130 ◦ C,
where the final product is in liquid form at room temperature, and hence does not have a glass transition
temperature in the range of 20 ◦ C–100 ◦ C. By contrast,
for catalytic reaction at the same polymerization temperature (i.e. 130 ◦ C), glass transition temperature was
detected, that is, accredited to the high conversion of
the polyamides produced, and hence higher molecular weights. The polymer produced being linear and
Table 5. Results of melting point, heat of fusion, glass transition
temperatures, and number average molecular weight at different
temperatures and mixing rates for the noncatalytic reaction.
Temp.
(◦ C)
Conversion
(%)
Melting
point
(◦ C)
Tg , Glass
transition
(◦ C)
Heat of
Fusion
(J/g)
Molecular
weight
(g/mol)
130
145
160
175
54.16
86.57
95.15
92.69
65.64
87.78
100.33
102.97
–
65.69
62.38
62.67
−4.22
−3.06
−10.20
−11.00
1063
2006
5648
4482
 2007 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pac. J. Chem. Eng. 2007; 2: 599–608
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
CONVERSION AND THERMAL PROPERTIES OF POLYAMIDE
Table 6. Thermal analysis of final products as a function of temperature at
75 rpm in the presence of a catalyst.
130
145
160
175
Conversion
(%)
Melting
point
(◦ C)
Tg , Glass
transition
(◦ C)
Heat
of fusion
(J/g)
Molecular
weight
(g/mol)
59.18
88.49
92.49
95.27
82.3
88
102.2
105
54.2
65.6
69.8
68.6
−2.27
−1.91
−3.58
−8.92
1205
2819
4453
5604
not cross-linked is another reason for the production
of a low melting point polymer. The glass transition
temperature increases with increasing molecular weight.
The glass transition temperature reflects the Brownian
motion of amorphous chains. The melting temperature represents the chain motion in crystals. The higher
the glass transition temperature and melting point the
stronger the restrained amorphous segments and the
higher ordered crystals due to the increased molecular
weight of the samples (Wang and Lin, 1991).
Figure 10 is the DSC diagram for fatty polyamides
obtained at different reaction temperatures (i.e. 130,
145, and 175 ◦ C) and a fixed mixing rate of 75 rpm.
The DSC heats a sample (a small piece of material
contained in a pan) and a reference (an identical
empty pan, thus negating the thermal effect of the
pan) at a fixed rate, (usually ∼10 ◦ C per minute) and
measures thermal differences between the two. The
DSC uses a sample and reference heated by different
resistive heaters and monitored separately. The sample
and reference are heated at the same rate and the
power difference needed to keep them at the same
temperature is recorded. This difference is reported as
‘Heat Flow’, which is the output data of the DSC. This
device has the advantage that changes in heat capacity
can be directly measured. The diagram shows that the
sample produced at a reaction temperature of 130 ◦ C
has a lower melting point (i.e. ∼67 ◦ C), and no glass
transition temperature is detected since the sample was
in liquid phase at room temperature. For polymers at
a reaction temperature of 160 ◦ C, both glass transition
temperature and melting temperature were witnessed
since at higher reaction temperature, the molecular
weight was higher than that at 130 ◦ C, and the sample
was in solid phase at room temperature. For samples
produced at a reaction temperature of 200 ◦ C, the glass
transition temperature and melting point were spotted at
lower heat flow. After a temperature of 100 ◦ C there is
a peak, and it is associated the to occurrence of reaction
and evaporation of produced the water because at this
temperature, usually, conversion is low, and there is
unreacted functional group for more reaction. In some
cases, and in the DSC thermogram, there is a small
peak after 110 ◦ C, and it is related to the production of
a small amount of higher molecular weight polyamides.
 2007 Curtin University of Technology and John Wiley & Sons, Ltd.
The thermal analysis of final products in the presence
of a catalyst is shown in Table 6. The results obtained
experimentally are at different reaction temperatures
and fixed mixing rate (i.e. 75 rpm). The amount of
catalyst was 1.0 (wt%) of the total mass of reactants.
The thermal properties of the polyamide under catalytic
reaction were of the same trend as that obtained for
the noncatalytic reaction. Glass transition temperature
(Tg ), melting temperature (T m), and enthalpy of fusion
(H ) gradually increase with increase in molecular
weight as reported in the literature (Xuming et al .,
2002).
Molecular weight increases with increasing conversion are shown in Table 5 for noncatalytic reaction
and Table 6 for catalytic reaction. At 145 and 175 ◦ C,
although the conversions are the same, the molecular
weight of the product produced at 175 ◦ C is more, and it
is due to less amine concentration in the final product at
this temperature. Molecular weight is inversely related
to amine and acid concentrations, so although the final
acid concentration is the same, the amine concentration
is less, and so the molecular weight is higher. The reason is that at high reaction temperatures, the reaction
will progress until the amine is totally consumed, and
there will be no more amine for reaction. Figure 10
is the DSC diagram for fatty polyamides obtained at
175 ◦ C and 75 rpm. The trend of the curves in Fig. 11
is the same as that in Fig. 10.
0
-2
Heat flow (mW)
Temp.
(◦ C)
-4
175 οC, 75 rpm
-6
-8
-10
-12
100οC
-14
20
40
60
80
100
120
140
160
Temperature (οC)
Figure 11. The DSC diagram for fatty polyamides obtained
at 175 ◦ C and 75 rpm in the presence of a catalyst.
Asia-Pac. J. Chem. Eng. 2007; 2: 599–608
DOI: 10.1002/apj
607
608
N. M. GHASEM, J. HEIDERIAN AND W. W. DAUD
CONCLUSIONS
The effect of reaction temperature on the thermal properties of the polyamide hot-melt adhesives produced
from C36 dimer acid and ethylenediamine were experimentally investigated, with and without the presence
of a catalyst. The results show that as the reaction
temperature increases, conversion increases, and a high
molecular weight polyamide is produced. Melting point
is influenced by the polymer molecular weight, and
as the molecular weight increases the melting point
increases. Heat of fusion, which is a function of degree
of crystallinity, increases with increasing conversion
and molecular weight. The glass transition temperature
was found to be in the range of 62–66 ◦ C for such linear
polymers; however, with increasing molecular weight
the melting point increases while Tg increases slightly.
These results agree with those previously reported in literature for polyamides synthesized for dimer acids and
different amine mixtures (Xuming et al ., 2002). The
effect of the catalyst was mainly to accelerate the reaction rate. At a fixed reaction temperature and time, the
conversion achieved under catalytic reaction is higher
than that of noncatalytic reaction. A kinetic model was
employed to estimate parameters of the rate equations
and the empirical parameters of the model using the
nonlinear regression. The model was used to simulate
experiments that were not included in the parameter
estimation. The comparison of the model predictions
with the experimental data were in good agreement with
minor differences between the model predictions and
the experimental data, the differences are merely due to
experimental scattering.
Acknowledgements
The authors would like to thank Uniqema, Gouda, The
Netherlands, for their help in providing the samples of
the C36 dimer acid.
NOMENCLATURE
A, B , C , D, E
Av
Amv
c
cdi
DSC
e
k1 , k2 , k1 , k2
Empirical constants
Acid value (mg KOH/g solution)
Amine value (mg KOH/g solution)
Concentration (mol/kg)
Concentration of component i in distillate
Differential scanning calorimetry
Error
Reaction rate constant for noncatalytic
and catalytic reactions (kg/mol min)
 2007 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pacific Journal of Chemical Engineering
m
md
ṁd
MwKOH
n
F
N
Nd
Nm
Nt
r
t
V
x
ξ
ψ
Mass of the liquid phase (kg)
Mass of distillate (kg)
Distillate mass flow rate (kg/min)
Molecular weight of KOH (56.1 g/mol)
Amount of substance (mol)
Molar flow of evaporated samples
(mol/min)
Normality
Percent dimer
Percent monomer
Percent trimer
Generation rate of a functional group
(mol/kg min)
time (min)
Volume of titrated solution (ml)
Weight
fraction
(dimensionless)
Greek Letters
Dimensionless mass of distillate
Dimensionless mass of samples
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Asia-Pac. J. Chem. Eng. 2007; 2: 599–608
DOI: 10.1002/apj
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