1. Polymorphic Behavior of Nylon G/Saponite
and Nylon G/Montmorillonite Nanocomposites
TZONG-MING WU* CUUI ERH-CHIANG CHEN
Department of MaterialScience and Engineering
I-Shou University
1,See. 1,Hsueh-Chew R d , Ta-HsuHsiang
Kaohsiung County, TQiwan84008
CHIEN-SHIUN LIAO
Department of Chemical Engineering
Y m - Z eUniversity
135 Yuan-lhrgRd., Nei-Li
Chung-Li, Taiwan 32026
X-ray diffractionmethods and DSC thermal analysishave been used to investigate
the structural change of nylon 6/clay nanocomposites. Nylon 6/clay has prepared
by the intercalation of s-caprolactam and then exfoliaton of the layered saponite or
montmorillonite by subsequent polymerization. Both X-ray diffraction data and
DSC results indicate the presence of polymorphism in nylon 6 and in nylon 6/clay
nanocomposites. This polymorphic behavior is dependent on the cooling rate of
nylon 6/clay nanocompositesfrom melt and the content of saponite or montmoril-
lonitein nylon 6/&y nanocompasites.The quenchingfrom the melt induces the crys-
tallization into the y crystallineform. The addition of clay increases the crystalliza-
tion rate of the Q crystalline form at lower saponite content and promotes the
heterophase nucleation of y crystalline form at higher saponite or montmorillonite
content. The effect of thermal treatment on the crystallinestructure of nylon 6/clay
nanocompositesin the range betweenTgand Tm is also discussed.
INTRODUCTION
olymer nanocomposites, defined by the particle
Psize of the dispersed phase containingat least one
dimension in the range of 1-100 nm, have received
increasinginterest because of their unusual combina-
tions of s W e s s and toughness,which are diacult to
attain from individualcomponents(1-3).For thisrea-
son, they can be widely used in the areas of trans-
portation, electronics and consumer products. Owing
to the nanoscale features, nanocomposites have rela-
tively high aspect ratios and display excellent physi-
cal,mechanical and thermal behaviors, much better
than their conventional microcomposite counterparts.
The preparation ofsynthesizingpolymer nanocompos-
ites is the intercalation of monomers or polymers into
swellable layer silicate hosts. The synthesis usually
*Compondenceto:T.-M. Wu. Currentaddnss: Deparbnentof Matuial Science
and Engineering. National Chung Hsing University. 250 Kuo Kuang Road,
Taichung,Taiwan402.Email:tmwu@dragon.nchu.edu.tw
involves either direct intercalation by polymer melts,
using a conventional extrusionprocess or intercalation
of a suitablemonomer and then exfoliatingthe layered
host into the nanoscale elements by subsequent poly-
merization (4-6). The high-aspect-ratiolayered silicate
would affect the physical, mechanical and thermal
properties of the synthesizingpolymer nanocomposites.
Nylon 6 is a highly crystalline polymer with two
crystallineforms, (Y and y (7-10). The (Y phase is com-
posed of a fully extended planar zigzagchain confor-
mation, in which adjacent anti-parallel chains are
joined to each other by hydrogen bonds. Therefore it
is the most thermodynamicallystable crystallineform,
and can be obtained by slowly cooling from the melt.
The y phase consists of pleated sheets of parallel
chains joined by hydrogen bonds. It is less stable and
can be obtained by fast cooling from the melt or fiber
spinning at a high speed (11, 12).The y form can be
converted into (Y by melting, followed by applyjngstress
at room temperature, by recrystalbition, and by an-
nealing at 16OOC in a saturated-steam atmosphere
without any signisCantlossof orientation(13-18).
POLYMER ENGINEERINGAND SCIENCE, JUNE 2002, Vol.42, No. 6 1141

2. Tzong-MingWu,Erh-Chiang Chen, Chien-ShimLiao
Murthy et d(19).using NMR and XRD measure-
ments on heated nylon 6,6 and nylon 6, indicated the
presence of a crystal-crystaltransition called the Brill
transition. In nylon 6.6, the room-temperature tri-
clinic structure transforms into a pseudohexagonal
structure at elevated temperatures (20-23). The Brill
transition can be clearly displayed in the X-ray dif-
fraction data of nylon 6,6, as two intense reflections
at 28 = 20.5" and 24" merge into a singlereflection at
28 = 21.5"during the transition. A similar crystalline
transformation has also been observed at elevated
temperatures in nylon 6. X-ray diffraction studies
show two intense reflections, (100)and (010)+ (110),
at 28 = 20.5" and 24" characteristicof the monoclinic
(Y phase, which shifted into 28 = 21.5" in the mono-
clinic y phase. The phenomenon is further confirmed
by infrared spectra duringtransition (24).
In this report, we have used monomer of nylon 6 (E-
caprolactam)as the matrjx and two different types of
clays, montmorilloniteand saponite, as the dispersed
phase to prepare nylon 6/clay nanocomposites
through the intercalation of E-caprolactam and then
exfoliaton of the layered silicate by subsequent poly-
merization. The montmorilloniteis composed of dioc-
tahedral smectites with predominantly octahedral
substitution,while the saponite is composed of triocta-
hedral smectites with mainly isomorphous substitu-
tion of Si4+by A13+in the tetrahedral sheets. For this
reason, the structure of montmorilloniteis in the form
of hexagonal lamellae,while the saponite structure is
in the form of ribbons and laths (25).The mechanid
and thermal properties of nylon 6/clay nanocompos-
ites shown in Table 1 were superior to the nylon 6
matrix in terms of the heat-distortion temperature
and modulus without a signScant loss in the Charpy
impact. It is necessary to point out that the elongation
ratio for nylon G/saponite nanocomposites remained
above loo%, but it was dramatically decreased to
below 1OOhwhen montmorillonitewas used as a rein-
forcing filler. Meanwhile, the heat distortion tempera-
ture significantly increases by about 100°C for nylon
6/montmorillonite nanocomposites, but it is only
slightly improved for nylon 6/saponite nanocompos-
ites. This is probably due to the structural feature of
saponite and montmorillonite. which are, respectively,
classified in the form of laths/ribbons and hexagonal
lattice, or a relative better exfoliation in the nylon
6/montmorillonite nanocomposites. Therefore, differ-
ent types of clays containing their special structure
arrangement probably play significant roles affecting
their physical and thermal properties. Since the phys-
i d properties of nanocomposites are also directly re-
lated to the crystalline features and behaviors, it is
necessary to understand the effect of clays on the mi-
crostructure of nylon 6/clay nanocomposites during
formation.
Inthis study, we have focused on the possibility of
(Y and y polymorphism of nylon 6with the presence of
saponite and montmorillonite. X-ray diffraction and
DSC thermal analysis have been used to investigate
the crystallinestructure and behavior of nylon 6/clay
nanocomposites. The effect of cooling rate from the
melt on the (Y and y crystalline structures is dis-
cussed. Nylon 6/clay nanocompositesusually acquire
residual stress during processing, which can affect
the microstructure and properties of the composites.
Further thermal treatment in the range between Tg
and Tm can be used to remove residual stress during
preparation and has shown to change the crystalline
structure in polyimides, polyamides, and polyamide
nanocomposites (26-28). In this case, we will also
study the crystallinestructural change of nylon 6/clay
nanocomposites as a result of thermaltreatment.
EXPERIMENTAL
1. spscimens
Synthetic sodium saponite and natural sodium
montmorillonite (kindly provided by Kunimine Indus-
tries Co., Ltd.) with cation exchange capacities (CEC)
of 71.2 and 110 meq/lOO g, respectively, were used
as the dispersed phase to reinforce the nylon matrix.
The montmorilloniteis composed of &octahedralsmec-
titeswith predominantly octahedral substitution,while
the saponite is composed of trioctahedral smectites
with mainly isomorphous substitution of Si4+by A13+
in the tetrahedral sheets. Organically modified sapo-
nite and montmorillonite were prepared by a cation-
exchange reaction between sodium saponite or sodi-
um montmorilloniteand octadecylammoniumcations.
The nylon 6/clay nanocomposite was prepared by
using E-caprolactammixed with deionizedwater, phos-
phoric acid solutionand organicallymodified saponite
or montmorillonite at 80°C for 30 min. The polymer-
ization was carried out in a nitrogen atmosphere by
heating the mixtureto 27OoC,while stirring for 30 min
with the pressure elevated to 8 kg/cm2. The pressure
was then reduced to 1 kg/cm2 and the mixture was
Table 1. MechanicalandThermal Propertiesof Nylon6 and NylonWClay Nanocomposites.
Type nylon 6 nylon6lmontmorillonitenanocomposites nylonWsaponite nanocomposites
~~ ~ ~~
Clay content (wt%) 0 2.5. 5 2.5 5
Tensilestrength (MPa) 69 a7 82 75 65
Tensilemodulus(GPa) 1.1 4.48 5.85 3.38 3.80
Flexuremodulus(GPa) 2.90 4.20 5.25 3.27 3.60
Charpy impact strength (kJ/m) 6.2 6.2 5.9 6.1 5.9
Heatdistortiontemperature(264 psi) 65 152 169 65 77
Elongation(%) > 100 < 10 < 5 >loo >loo
1142 POLYMERENGINEERINGAND SCIENCE, JUNE 2002, Vol. 42, No.6

3. PolymorphicBehavior
polymerized at 260°Cfor 6 h. Upon completion of the
polymerization, the reinforced nylon 6/clay nanocom-
posite was removed from the reactor and cut into pel-
lets. The pellets thus obtained were washed with hot
water at 80°Cfor 8 h and dried at 100°Cfor 12 h in
Samples of pure nylon and nylon 6/clay nanwom-
posites were hot pressed into thin film at 240°C and
then cooled kom the melt to room temperature at a
rate of 1O-5O0C/min in either liquid nitrogen or ice
water.
2. Wide w e X-Ray Difllraction
X-ray 8/28 diffraction scans of these specimens
were obtained using a 3kW Rigaku 111 diikictometer
equipped with Ni-filtered CuKa radiation. These data
were recorded in the reflection mode. From the X-ray
data, quantitative evaluations of the contents of the
two crystallineformswere obtained by the curve fitting
to calculate the area of each peak. A linear back-
ground correction was applied separately to the ob-
servedpeaks to obtain the area of each peak,for which
we assumed Gaussian profiles.
5. Thermal Analysis
vacuum.
Thennal analysis of nylon 6/clay nanocomposites
was preformed using a Perkin-Elmer DSC7 differential
scanningcalorimeter calibrated using indium, and all
experiments were carried out under a nitrogen at-
mosphere. All specimens were weighted in the range
of 4 to 6 mg. The glass transition temperature (Tg),
crystallizationtemperature (Tc)and melting tempera-
ture were obtained by the following procedures:
these specimens were heated to 250°C at a rate of
100°C/minand held for 10 min to remove the resid-
ual crystals, which may be seeds for the following
crystalkation. The samples were then cooled to 20°C
at a rate of l-5OoC/min and heated to 250°C at a
rate of 10°C/min.
4. T h e Treatment
For the thermal treatment experiment, samples of
pure nylon and nylon 6/clay nanocomposites were
hot pressed into thin films at 240°C and then trans-
ferred quickly from the hot stage to a silicon oil bath
kept between 140°Cand 210°Cfor various lengths of
time.
RESULTSAND DISCUSSION
Figure 1 shows the X-ray difhction scans of nylon
6 and nylon 6/clay nanocomposites after being hot
pressed into thin films at 240°C and then cooled to
room temperature at a rate of 10°C/min. Nylon 6 con-
tains multi-crystalline forms and usually exhibits a
more stable a crystalline form rather than the y crys-
talline form. The polymer matrix shows two a crys-
talline peaks at 28 = 20.5"and 24".Beside these two
peaks,the polymer contains an additionaldistinct dif-
fraction peak at 28 = 21.5",corresponding to the y
form.Afteraddition of 2.5wt?! syntheticsaponite into
the nylon 6 matrix, the X-ray diffraction data showed
only the presence of two a crystalline peaks at 28 =
20.5"and 24",with no indication of a y crystalline
peak at 28 G 21.5".With addition of more saponite
into nylon 6 up to 5 wt??, the X-ray diffraction data
exhibited a sharp y crystallinepeak at 28 = 21.5"and
small traces of two a crystalline peaks at 28 = 20.5"
and 24".X-ray data of nylon 6/montmorillonitenano-
composites are also shown in Fig. 1, but they are
quite different from those of nylon 6/saponite nano-
composites. X-ray diffraction data of 2.5 wt??nylon
6/montmorillonite nanocomposite exhibit only a
sharp a crystallinepeak at 28 = 24"and traces of an-
other a crystalline peak at 28 = 20.5".The intensity of
the a crystalline peak at 28 = 20.5"decreases with
the presence of montmorillonite and is probably due
to the structural feature of hexagonal lattice, in which
the surface of the (110)layer of montmorillonitecould
prefer the crystal arrangement along the (110)planes
of nylon 6 (28 = 24")during the crystal formation.
Nevertheless, there is no indication of a y crystalline
peak at 28 = 21.5"with the presence of 2.5 wtYo
montmorillonite.By adding more montmorilloniteinto
nylon 6 up to 5 wt%, the X-ray Waction data shows
a result similarto that of 2.5wt?? nylon 6/montmoril-
lonite nanocomposite except for the presence of small
traces of y crystalline peaks at 28 = 21.5".These data
indicate that the saponiteor montmoflonite probably
plays an important role in increasing the crystalliza-
tion rate of the a form at a lower content of clay and
the heterophase nucleation of the y form at a higher
content of clay.
Figure 2 shows X-ray diffraction scans of nylon 6
and nylon 6/clay nanocomposites after being hot
pressed into thinfilms at 240°Cand then immediately
cooled to room temperature at a rate of 50"C/min.
The X-ray diffraction data of nylon 6 shows a sharp y
crystalline peak at 28 = 21.5"and traces of two a
crystallinepeaks at around 28 = 20.5"and 24".This
result is significantlydifferent from the X-ray data of
nylon 6 by slow cooling, which contains mainly a
crystalline peaks and a relatively weak y crystalline
peak. This result indicates that the fast cooling from
the melt preferably forms less stable y crystalline in
nylon 6.
By adding 2.5 wt?hsynthetic saponite into nylon 6
matrix, the X-ray diffmction data shows the presence
of twoa crystallinepeaks at 28 = 20.5"and 24"and a
small trace of y crystalline peak at 28 = 21.5".This
result is similar to that of the 2.5 wt?! slowly cooled
nylon 6/saponite sample, except for the presence of a
small y crystallinepeak. Therefore,the addition of 2.5
wt% synthetic saponite promotes the crystallization
rate of the a form, which is even faster than the for-
mation of y crystalline induced by fast cooling from
the melt. By addmg more synthetic saponite into the
nylon 6 matrix up to 5 wt%, the X-ray diffraction
data show a result similar to that of the sloWiy cooled
POLYMER ENGINEERINGAND SCIENCE, JUNE 2002, Vol. 42, No. 6 1143

4. Bong-Ming Wu, Erh-Chiang Chen, Chien-ShiunLiao
r- -7
t I I 1 I I I I I I I
12 14 16 18 20 22 24 26 28 30 32
2 8 (degrees)
FTg. 1. X-ray difiactometer scansfor (a) nylon 6, (b) 2.5 wt%saponite in nylon 6/clay nanocomposites, (c)5 wt% saponite in nylon
6/clay nanooomposites,(d) 2.5 wt%montmorillonitein nylon 6/clay nanocomposites and (el 5 wt%montmofinite in nylon 6/clay
nanocompositesafterbeing hotpressed intojZms andslowlycooledto room temperature.
A e
C
12 14 16 18 20 22 24 26 28 30 32
2 8 (degrees)
FTg. 2. X-ray diiactomek scansfor (a) nylon 6, (b) 2.5 wt%saponitein nylon 6/clay nanooomposites, (c)5 wt%saponite in nylon
6/clay namxomposiiks, (d)2.5 wt%montnwdbnitein nylon 6/clay nanocompositesand (el 5 wWo montmonllonite in nylon 6/clay
nanocompositesafterbeing hotpressed intofilmsand rapidly cooled to room temperature.
1144 POLYMER ENGINEERINGAND SCIENCE, JUNE 2002, Vol. 42, No. 6

5. PolymorphicBehavior
sample containing a distinct y crystalline peak and
traces of two a crystallinepeaks. This is probably due
to the presence of a highcontent of syntheticsaponite
in the form of ribbons and laths, induced by the
strong heterophase nucleation of the y form from the
surfaceof the structure.
X-ray diffraction data of nylon 6/montmorillonite
nanocompositesalso shownin Rg. 2 contains a sharp
y crystallinepeak at 28 = 21.5" and smalltraces of a
crystalline peaks 28 -= 20.5" and 24". These results
are similar to those of nylon 6 and nylon 6/saponite
nanocomposites, except for the 2.5 wt% nylon
6/saponite nanocomposite. The X-ray data of 2.5 wt??
nylon 6/saponite nanocomposite contains mainly a
crystalline peaks and a relatively weak y crystalline
peak. This result indicates that the structural
changes of nylon 6/montmorillonite nanocomposites
are strongly dominanted by the cooling rate rather
than the presence of montmorillonite. Therefore, we
can surmise that the fast cooling from the melt can
induce the unstable y crystalline formation, and
meanwhile, the addition of synthetic saponite could
increase the crystallization rate of the a form at a
lower saponitecontent and gradually promote the het-
erophase nucleation of the y form at a higher contents
saponiteor montmorillonite.
In order to obtain more information related to the
crystal transition in nylon 6/clay nanocomposites,
non-isothermal thermal analysis was operated by
using DSC coolug scans of nylon 6 and nylon 6/clay
nanocompositesat coohngrates in the range between
1 and 50"C/min and then heated to 300°C at a rate of
10°C/min. All the coolingscans of nylon 6/clay nano-
composites have only one exothermic peak, but the
peak forms and peak temperatures of the nanocom-
posites differ from those of the polymer matrix. The
peaks and onset temperatures of nylon 6 and nylon
6/clay nanocompositesare listed in Table2.The pres-
ence of saponite or montmorillonitein the nanocom-
posites increases the crystallization temperature of
nylon and narrows the width of the crystalline peak.
These results indicate that the saponiteor montmoril-
lonite increases the crystallization rate or promotes
heterophasenucleationin nylon 6.
Figure 3a shows the DSC heating scans of slowly
cooled nylon 6 and nylon 6/clay nanocomposites.It is
clearly seen that the nylon 6 matrix has two melting
peaks, in which the high-temperature peak corre-
sponds to the a form and the low-temperature peak
corresponds to the y form. Upon addition of 2.5 W?
saponite or montmorillonite in nylon 6, both DSC
heating scans show only one melting peak corre-
sponding to the (Y form. This result indicates that the
addition of saponite or montmorillonitehas increased
the a crystalline formation. By adding more saponite
or montmorillonite into nylon 6 up to 5wt??,the DSC
data shows two melting peaks correspondingto the a
and y form for nylon 6/saponite nanocompositesbut
only one high melting peak corresponding to the a
form for nylon 6/montmorillonite nanocomposites.
The endothermic peak of the y form at high saponite
content becomes more clear. This is probably due to
the presence of a high content of synthetic saponite,
inducing the strong heterophase nucleation of the y
form.
Figure 3b shows the DSC heating scansof quenched
nylon 6 and nylon 6/clay nanocomposites. All DSC
heating scans exhibit two melting peaks correspond-
ing to the presence of both the a form and y form, ex-
cept that 2.5 wt?? nylon 6/saponite nanocomposites
showonly one meltingpeak correspondingto the lower
temperature y form. Therefore, these DSC results are
qualitatively consistent with those data from X-ray
difhction except for the ratio of the a form to the y
form. Differences are probably due to the melting of
the lower-temperatureunstable y crystallineform and
recrystallization of the more stable a form during the
DSC heating scans.
Figure 4 showsX-ray dithction scans of a quenched
nylon 6 sample after it was thermally annealed at var-
ious temperatures and then rapidly cooled to room
temperature. These results show that the y form dif-
fkaction peak at 28 = 21.5" gradually disappears, and
the a form diihction peaks at around 28 = 20.5" and
24" become sharper as the annealing temperatures
increase. Sincethe structure of nylon 6 showsthe Brill
transition over a broad range of temperature from
160°Cto 200"C, it is possible to induce a crystal-crys-
tal transition during the annealing process at this
range. These thermal treatments favor the formation
of the a form rather thanthe y form in nylon 6, as the
a form is the thermodynamically more stable crys-
talline form. Therefore,the effect of thermal annealing
at various temperatures on the crystallinestructure of
Table 2. Peak and Onset Temperature of DSC Cooling Scans of Nylon 6 and Nylon WClay
Nanocompositesat the Cooling Rate inthe Range Between1 and 50 Chin.
Cooling rate nylon6 nylonWmontmorillonitenanocomposites nylon Wsaponite nanocomposites
("amin) 2.5 wt% 5 wt% 2.5 W h 5 wt%
peak(%) onset(%) peak(%) onset('C) peak(%) onset(%) peak(%) onset("C) peakPC)onset ("C)
1 194.4 203.1 197.7 202.0 196.1 202.9 194.1 198.5 193.6 199.3
5 185.9 196.9 190.0 196.4 188.6 195.2 186.4 191.4 186.2 192.1
10 179.4 194.1 185.0 193.0 182.8 193.5 184.8 191.0 181.6 188.8
20 172.1 189.0 179.5 189.0 177.8 189.0 179.6 187.0 175.2 184.8
30 166.6 187.9 174.9 186.2 172.1 182.8 175.6 185.2 171.2 181.1
50 155.6 183.4 167.0 179.4 166.1 178.9 170.0 180.3 163.2 176.0
POLYMER ENGINEERINGAND SCIENCE, JUNE 2002, Vol.42, No. 6 1145

6. Bong-Ming Wu, Erh-Chiang C k n , Chien-ShimLiao
5E
3
W
0
Lrr
-+
8
e
d
C
b
a
I I I
150 175 200 225 250
e
d
C
b
a
I I I I I I I I I
150 160 170 180 190 200 210 220 230 240 250
Temperature (OC)
Ffg. 3b.DSC second heating scansfor (a)nylon 6, (b) 2.5 wi96 sapon& in nylon 6/clay nanocomposites,(c) 5 wt96 sapnite in nylon
6/clay naruxomposites,(42.5 wt96 montmDriuDnitein nylon 6/clay nanocomposites and (el5 wt96 monbnorillonite in nylon 6/clay
nanocomposites after mlingfrom 300°Ctoroomtempetatueat5OoC/min
nylon 6 would favor the formation of the (Y form dur-
ing the process. After annealing at a temperature
close to the higher temperature of the Brill transition
in nylon 6, there is only the presence of relative sharp
(Y form crystalline peaks.
Figures 5 and 6 shows X-ray diffi-action scans of
quenched nylon 6/saponite and nylon G/montmoril-
lonite specimens after thermally annealingat various
temperatures and then rapid cooling to room temper-
ature. These results also show a similar crystalline
transition at the range of the temperature of the Brill
transition. Therefore we can conclude that the addi-
tion of saponite and montmorillonite does not change
the thermodynamics of the system at a temperature
below the temperature of Brill transition even though
the nanometer distances from the surface of the
1146 POLYMER ENGINEERINGAND SCIENCE, JUNE 2002, Vol. 42, No. 6

7. Fig. 4. X-ray dipactometerscans
for nylon 6 after thermaLly anneal-
ing at (a) 160°C, &) 18OoC,(c)
200°C and (d)210°C.
Fig. 5a. X-ray diffractorneter
scans for 2.5 wt% saponite in
nylon 6/clay nanocompositesa@
thermally annealing at [a) 160°C.
[b) 180°C (c) 2OO0C, and (dl
210°C.
Fig. 5b. X-ray diffractorneter
scansfor 5 wi% saponite in nylon
6/clay nanocomposites after the^
maUy annealing at [al 160"C, @I
180°C, (c)200°C and (dl 210°C.
PolymorphicBehavior
1
I I I I I I I I I I
12 14 16 18 20 22 24 26 28 30 32
29 (degrees)
I
I I I 1 I I I I I I
12 14 16 18 20 22 24 26 28 30 32
2 8 (degrees)
I I t I I
12 14 16 i a 20 22 24 26 20 30 32
2 8 (degrees)
I I I I I
POLYMER ENGINEERINGAND SCIENCE, JUNE 2002, Vol.42, No. 6 1147

8. Tzong-MingWu, Erh-Chmq Chen,Chien-ShimLiaO
Fig. 6a. X-ray diffractorneter
scans for 2.5 wt% nwntnudbdte
in nylon 6/clay nanocomposites
after thermally annealing at [a)
160°C.b) 180°C,(c) 200°C.and
(4210°C.
Fig. 6b. X-ray dvfractometer
scansfor 5 wt% montmorillonite in
nylon 6/clay nanocompositesa@
themtally m a l i n g at (4160°C,
(b) 180°C. (c) 200°C, and (d)
210°C.
I I I I 1 I I I I 1
12 14 16 18 20 22 24 26 28 30 32
28 (degrees)
I I I I I I I I I
montmorillonite become small in the y form. The pos-
sible explanation for this behavior is the structure of
the y form generated as the amine end groups in
nylon 6 are tightly bound to the surface of saponite
and montmorillonite, but not arrayed on the surface
at the interchain distance that allows formation of
the layered hydrogen-bonded sheets of the a form.
But there is a controversial result for 5 wtYo nylon
6/montmorillonite nanocomposite: At an annealing
temperature close to the higher temperature of the
Brill transition of nylon 6, the X-ray data shows the
presence of a more unstable y crystalline form. The
phenomenon is probably due to the presence of mont-
morillonite induced strong heterophase nucleation of
14 16 18 20 22 24 26 28 30 32
28 (degrees)
the y form. w e 7shows the change of a crystalline
form asthermallytreated temperatureincxeased.It can
be seen that the y crystalline form increases as the
treated temperature in the range of the temperatureof
brill transition increases. The a crystal lamella are fa-
vored to grow more readily in nylon 6 rather than in
nylon 6/clay nanocomposites.As the treated tempera-
ture close the temperature of brill transition, it is pos-
sibleto provide the energyto overcomethe barrier from
the anti-parallelchain conformation of y form to par-
allel chain conformationof y form. Therefore,the pres-
ence of hgh content of montmorillonite could induce
more heterophasenucleation of y form and could grow
faster in the rapidly cooling process. For this reason,
1148 POLYMER ENGINEERING AND SCIENCE, JUNE 2002, Vol.42, No. 6

9. PolymorphicBehavior
n
zW
lo10 1 I I I I I I I
150 160 170 180 190 200 210 220
Treated Temperature (OC)
Fig. 7.Plots of hfiaction of01 crysMline form at the thermally treated temperatures of (a) nylon 6, @I 2.5 wt% sqwniie in nylon
6/c@ nanocomposiies,{c)5 wWo sqponite in nylon 6fclay nanocomposites,(c42.5 wt96 monbnorillonite in nylon 6/clq nanocom-
posites and (e)5 WWOmnbnorillonitein nylon 6/c@ nanocomposites. Thefraction of a crystallineform before treatmentis 25.1,40,
10,26.0 and 20.8for nylon 6, 2.5 wt% and 5 wt% nylon 6/saponite nanocompositesand 2.5 wt% and 5 wt% nylon G/mntmod-
lonitenanocomposiies,respectively.
thermal annealing close to the temperature of brill
transition of nylon 6/montmorillonitenanocomposites
could contain more y crystallineform of nylon 6/mont-
morillonitenanocompositesduring the crystallinefor-
mation.
CONCLUSIONS
X-ray diffraction and DSC thermal analysis show
the presence of polymorphism in nylon 6/clay nano-
composites. This polymorphic behavior is clearly de-
pendent on the content of saponite or montmorillonite
in nanocomposites and the cooling rate of nanocom-
posites from melt. The hgh coolingrate from the melt
can induce the formation of less stable y crystalline,
the addition of clay could increase the crystallization
rate of a form at lower content of saponite and pro-
mote the heterophasenucleation and growth of y form
at higher content of saponite or montmorillonite.
Thermal treatment of nylon 6 and nylon 6/clay nano-
composites at various temperatures promotes mostly
the a form crystalline formation during the process.
But the 5 W ! o nylon 6/montmorillonitemocompos-
ites shows the presence of more unstable y crystalline
form after the annealing temperature close to the
higher temperature of The brill transition in nylon 6.
That is probably due to the presence of montmoril-
lonite induced the heterophase nucleation of y form,
the fast cooling from the melt preferred forming less
stable y form, and the high treated temperature elimi-
nated the structural memory of a form.
ACKNOWLEDGMENTS
The financial support provided by NSC through the
project NSC89-2216-E-214-031 is greatly appreci-
ated.
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