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Crystal modulus of a new semiaromatic polyamide 9-T.


Polyamide 9-T (PA9-T) is a new semiaromatic polyamide recently industrialized as a high-performance engineering plastic in the name of Genestar (TM) by Kuraray Co. (1). In PA9-T, a long, flexible aliphatic linkage consisting of nine methylene groups in a sequence is incorporated in the main chain of aromatic polymer to lower the melting point, i.e., make it to melt processable. This polymer has received wide attention, as it appears to have a good balance of properties and manufacturing cost. PA9-T offers several unique advantages, such as good heat stability ([T.sub.g] is more than 100 [degrees]C), low water absorption, high heat-moisture resistance, and a considerable resistance to hot water, acid, alkali, and organic solvents. Owing to its outstanding properties, PA9-T heat-resistant resin has been commercially marketed in making several electric/electronic and automobile parts. Later on, the applications of this useful polymer were widened by producing its fiber to make high-quality fishing nets and other textile and industrial materials (2). The successful preparation of PA9-T fiber by melt spinning and drawing together with the structure and properties of as-spun and drawn fibers were reported in our previous articles (1-4).

The crystal modulus of a polymer provides an important information on the molecular conformation and intermolecular forces in the crystal lattice (5). Moreover, the value of crystal modulus is a significant parameter as it represents the maximum attainable initial modulus of a polymer when attempting to fabricate a high modulus material. The crystal modulus [E.sub.1] was measured by X-ray diffraction technique for a large number of polymers (5-11). Experimental data accumulated to date made it possible to establish a relationship between the [E.sub.1] values of these polymers and their molecular conformation and mechanical properties (5). For instance, polymers having a fully extended planer zigzag conformation such as polyethylene (PE) and polyvinyl alcohol (PVA) exhibit high [E.sub.1], values (PE: 235 GPa, PVA: 250 GPa). In these polymers, the deformation modes of a molecular chain are both bond stretching and bond angle bending which have high force constants. In contrast, polymers with helical or contracted conformation such as isotactic polypropylene (PP) and polyoxymethyelne (POM) possess relatively lower [E.sub.1] (PP: 42 GPa, and POM: 54 GPa). The deformation of these polymers is greatly predominated by internal rotation whose force constant is much smaller than those of bond stretching and bond angle bending.

As a pari of the siruciure and property analyses of PA9-T polymer, this article reports the crystal modulus [E.sub.1] of PA9-T in the direction parallel to the chain axis measured by X-ray diffraction. The relation of crystal modulus with its molecular conformation and mechanical properties is discussed.



PA9-T used in this study prepared by the condensation polymerization of terephthalic acid and normal aliphatic diamine. The chemical structure of PA9-T is shown in Fig. 1. Two kinds of PA9-T polymers with different intrinsic viscosities (IV), 0.72 dl [g.sup.-1] and 0.93 dl [g.sup.-1], respectively, were used for the measurement of [E.sub.1]. Melt-spun PA9-T fibers were drawn to their maximum draw ratio by a C[0.sub.2] laser-heated-drawing system (1), (12). The drawn libers were then annealed in a vacuum oven at 180 [degrees] C for 24 h at a constant length.


Wide-angle X-ray Diffraction (WAXD) was performed with a Rigaku RU-200B X-ray generator operating at 40 kV and 150 mA using a Ni-filtered Cu-[K.sub.[alpha] line (the wave-length: 0.15418 nm) m an X-ray source. The lattice spacings were calibrated with silicon and hexamethylenetetramine powders as an internal reference.

Density of the fibers was determined by the flotation method using a mixture of carbon tetrachloride and w-heptane at 25 [degrees] C.

Differential scanning ealorimetry (DSC) analyses were performed on a Perkin-EImer Pyris-1 analyzer. Both temperature and heat flow were calibrated with a standard indium reference. Fiber weights were maintained within the range of 4-5 mg. Ail thermal analyses were performed under a dry nitrogen atmosphere.

Tensile properties of the specimens were measured with an Orientec Tensilon RTC-1250A tensile tester. The measurements were performed at a gauge length of 50 mm and a crosshead speed of 50 mm [min.sup.-1]. The experimental results represent the average of 10 individual measurements. The macroscopic specimen modulus [Y.sub.1] was determined from the initial slope of the stress-strain curves.

The crystallite size D was determined from the reflection at ca. 28 [degrees] in WAXD meridional profiles followed by correction for both the instrumental and Cu[K.sub.alpha] broadening. D was then calculated using Scherer's equation:

D = [lambda] / [beta] cos [theta] (1)

where [beta] is the integral width of the reflection, [theta] is the Bragg's angle, and [lambda] is the X-ray wavelength.

Measurement of Crystal Modulus

Figure 2 shows the meridional diffraction profiles of the PA9-T (low-and high IV) fibers. Many diffraction peaks were observed and the values determined at approximately 2 [theta] = 28 [degrees], 43[degrees], and 78[degrees] were used for the measurement of [E.sub.1]. These peaks are not assigned in this study because the decisive crystal structure of PA9-T has not been reported yet.

The lattice extension under a constant load was measured using an X-ray diffractometer equipped with a stretching device and a load cell (5). The strain [epsilon] in the crystalline regions was estimated using the relationship:

[epsilon] = [DELTA]d/[d.sub.o] (2)

where [d.sub.o] denotes the initial lattice spacing, and [DELTA]d is the change in lattice spacing induced by a constant stress. The experimental error in measuring the peak shift was found to be generally less than [+ or -] 1/100 [degrees] for each 2 [theta] angle.

The stress [sigma] in the crystalline regions was assumed to be equal to the stress applied to the sample. This assumption of a homogeneous stress distribution has been experimentally proven for various polymers such as cellulose (13), PE (14), PVA (15), and poly (p-phenylene terephthalamide) (PPTA) (16).

The elastic modulus [E.sub.1] was calculated as:

[E.sub.1] = [sigma]/[epsilon] (3)

More detailed descriptions of these measurements have been reported in earlier publications [5-10].


Characterization of PA9-T Samples

The characteristics of the PA9-T libers are summarized in Table 1. Both low-and high IV PA9-T samples show the high glass transition, [T.sub.g] (115[degrees]C) and melting temperatures, [T.sub.m] (305[degrees]C). The molecular weight of each sample does not influence [T.sub.g] and [T.sub.m]. On the other hand, the mechanical properties depend on the molecular weight. The tensile strength and initial modulus for high IV PA9-T are higher than those of low IV sample.

TABLE 1. Basic characteristic of PA9-T fibers.

Parameters                                        Low IV  High IV

Intrinsic viscosity, IV (dl [g.sup.-1])             0.72     0.93

Draw ratio                                             5      5.5

Density (g c [m.sup.-3]                            1.151    1.157

[T.sub.g] of as-spun fiber [([degrees] C).sup.a]     115      115

[T.sub.m]of as-spun fiber [([degrees] C).sup.a]      305      305

Tensile strength (MPa)                               585      867

Specimen modulus (GPa)                               5.8      6.0

(a) [T.sup.g] and [T.sup.m] were determined from DSC measurement.

Figure 3 shows the WAXD photographs of the low-and high IV PA9-T fibers. A cursory review of these images suggest that both the PA9-T fibers possess high crystallinity and a high degree of crystallite orientation.

Crystal Modulus of PA9-T

Figure 4 illustrates the stress-strain curves of the three meridional reflections at approximately 2 [theta] = 28 [degrees], 42 [degrees], and 78 [degrees] for the PA9-T libers at ambient temperature (ca., 20 [degrees] C). The curves of all meridional reflections could be expressed with straight lines. The line slopes in each plot differ, implying widely changing [E.sub.1] values with the order of reflection. Moreover, the slope of the stress-strain curves increases with decrease of reflection angle. The [degrees] values were obtained from the inclination of the each curve at three different diffraction angles. The results for both low-and hieh IV PA9-Ts are shown in Table 2. The [E.sup1] values for both low-and high IV PA9-Ts are coincident at 40 GPa for only at 78 [degrees].

TABLE 2. Crystal modulus [pounds sterling], of PA9-T
measured at different meridional diffraction angles.

                       [E.sub.1] (GPa)
Diffraction angle, 20  Low IV  High IV

29 [degrees]              17        24

42 [degrees]              24        30

78 [degrees]              40        40

The [E.sub.1] value of a polymer should be an inherent and independent value irrespective of the order of reflection as observed for most of the polymers. For the case of nylon 6 [alpha]-form, in exception, the [E.sup1] value depends on the order of reflection (53 GPa for the 040 plane and 183 GPa for the 0140 plane where the fiber axis is b-axis) 117]. For nylon 6, the crystallite size along the chain direction is small and changes with applied stress. The diffraction peak shifts not only due to the lattice extension but also by the change in the Laue lattice factor. The same phenomena were also observed for polyether ether ketone (PEEK), polyether ketone (PEK), and poly(p-phenylene sulfide) (PPS) (18).

The Laue lattice factor cannot be neglected when (i) the number of subperiods in a unit cell (in the case of nylon 6 [alpha]-form, this value corresponds to the number of methylene groups) is larger than the number of stacked unit cells in the crystallites, and (ii) the crystallite size is very small [19]. In these cases, higher-order reflections give higher [E.sub.1] values and longer fiber identity periods. In this study, the higher-order reflections of PA9-T also give higher [E.sub.1] values. This tendency resembles with the results of nylon 6 [alpha] form (18), PEEK, PEK, and PPS (18). The fiber identity period of the PA9-T crystal has been reported as 3.86 nm (20). This value is comparable with the crystallite sizes along the chain direction, which were determined as 3-3.5 nm for each sample, indicating the possible influence by the Laue lattice factor.

We constructed a schematic model of the PA9-T skeletal conformation as shown in Fig. 5. For simplicity, the confirmation of this model was assumed to have a fully extended planar zigzag structure (20) with the liber identity period of 4.1 nm that can be calculated from bond length and bond angle for each component. The meridional WAXD intensity profile was calculated (Fig. 6) for the proposed structure according to the method of Kaji and Sakurada (21) using the following equations:

[|F(00 [zeta])|.sup.2] = [|[SIGMA] [f.sub.j] cos(2 [pi] [zeta] [z.sub.j])|.sup.2] + [|[SIGMA] [f.sub.i] sin(2 [pi] [zeta] [z.sub.j])|.sup.2] (4)

[|G(00 [zeta])|.sup.2] = [N.sup.2.sub.1] [N.sup.2.sub.2] (sin 2 [pi] [N.sub.3] [zeta]) / (sin 2 [pi] [zeta]) (5)

where F and G are the structure factor and Laue lattice factor, respectively; [zeta] is a reciprocal space coordinate in the meridional direction; [f.sub.j] is the atomic scattering factor of the jth atom; [y.sub.j] is the atomic coordinate of the jth atom in the unit cell; and [N.sub.1], [N.sub.2], and [N.sub.3] are the number of unit cells along the three crystal axes a, b, and c when the crystallite is assumed to be a parallelepiped. In Fig. 6 that the calculated reflections roughly agree with those measured for PA9-T (Fig. 2). Therefore, the model in Fig. 5 basically reflects an actual PA9-T conformation.

Next, we investigated the influence of the Lauc lattice factor for the meridional reflections at 28[degrees] and 78[degrees]. The fiber identity period of actual PA9-T is 3.86 nm [20], which is comparable with the measured crystallite size along the chain direction, that is, the number of [N.sub.3] is near 1. Moreover, the number of subperiods in a unit cell (9 methylene groups in PA9-T) is much larger than the number of unit cells in a crystallite. Figure 7 shows the dependence of the peak maximum position of the calculated meridional reflections at 28[degrees] and 78 [degrees] on [N.sub.3]. In this case, [N.sub.1] and [N.sub.2] are assumed to have a value of 8 based on the determination of crystallite size in the equatorial direction. For reflections at 28[degrees], the peaks shift to a higher diffraction angle when [N.sub.1] is 1 or 2, indicating that the Laue lattice factor influences the peak position. On the other hand, the peak does not shift for reflections at 78[degrees] regardless of the [N.sub.1] value and thus there is no influence of the Laue lattice factor for this reflection at higher angles. Therefore, the [E.sub.1] of PA9-T derived at the highest diffraction peak can be considered as the most reliable value, and it is appropriate to use the diffraction at 78[degrees] to obtain an accurate [E.sub.1] for PA9-T.

Relationship of [E.sub.1] with Molecular Conformation

The [E.sub.1] values for both low-and high IV PA9-Ts measured at the highest reflection angle are identical at 40 GPa, which is lower than those of PE (235 GPa), PVA (250 GPa), PPTA (156 GPa), and nylon 6 [alpha]-form (183 GPa).

Table 3 shows the E; value, the cross-sectional area (S) of one molecule in the crystal lattice and the f-value (the force required to stretch a molecule by 1% calculated from Ef and S) of PA9-T together with some other commonly used polymers. The [E.sub.1] for PA9-T is smaller than that for PE and PVA, which have a fully extended planner zigzag conformation. The S value of PA9-T for a molecule in the crystalline region is relatively large, indicating that an applied load cannot be transmitted to many molecules packed in a unit area, unlike polymers having small cross-sectional areas. The low-value of PA9-T reflects the low rigidity, i.e., high deformability of PA9-T molecules.

TABLE 3. The [E.sub.1] cross-sectional area (S) and
f-values or PA9-T and some other polymers.

Polymer       [E.sub.1]    S (n       f-value
                (GPa)    [m.sup.2)  ([10.sup.-5

PA9-T                40      0.227         0.91

PE (14)             235      0.182         4.28

PVA (15)            250      0.216         5.40

Nylon 6             183      0.182         3.34

PPTA (16)           156      0.202         12.9

As can be seen in the proposed structural model of PA9-T shown in Fig. 5, the phenyl rings are incorporated as the skeletal amis in the zigzag conformation. The small [E.sub.1] value of PA9-T can be attributed to these longer crankshaft arms (0.57 nm), where the moment of force acts during deformation. For PEEK, PEK, and PPS, the long force moment arm length of phenyl rings also lead to smaller [E.sub.1] values of 71, 57, and 28 GPa, respectively 119]. In the case of PE, which has an [E.sub.1] of 235 GPa, the arm length in the zig-zag structure is as short as ca. 0.1 nm [14].

For comparison purposes, the [E.sub.1] of PA9-T was also calculated by the Treloar's method using the relevant bond length, bond angles, and force constants (listed in the appendix) [22, 23]. For the calculation of the [E.sub.1] value. the molecular chain was assumed to have a planar zigzag structure with no chain contraction or torsional conformation. The calculated value was 58 GPa, which is higher than the measured one.

Thus, another factor, the high chain contraction, is considered to be related with the lower [E.sub.1] value of PA9-T. Chain contraction was calculated by the following formula:

Chain contraction = (C - M)/C (6)

where C is the calculated chain length as shown in Fig. 5 and M is the chain length measured by X-ray diffraction. For PA9-T, C--4.1 nm and M = 3.86 nm, with chain contraction thus calculated to be 5.9%. A key point to note here is that the chain contraction of PA9-T is quite high. The reason for its high chain contraction can be considered to be due to the existence of torsional and contraction conformations that were shown in nylon 6 a-form [17] and PPTA [24]. The presence of torsional and contraction conformations are generally accompanied by internal rotation of the polymer chain under extension, which reduces [E.sub.1] value. The contraction of PA9-T chain originates from the amide-melhylene bonds that are twisted and trans form [20]. They predicted that ara-mid pails were packed with intermolecular hydrogen bonds in a similar way to the packing of PPTA [24|. Therefore, the internal rotational twist of amide-methylene bonds is considered to lead to the lower [E.sub.1] value of PA9-T.

Relationship of E/ with Mechanical Properties

We previously mentioned that the [E.sub.1] value of a polymer is the maximum attainable value of initial modulus. In this study. [E.sub.1] for PA9-T is 40 GPa that is relatively low and is assumed to limit the specimen modulus ([Y.sub.1],) of this polymer. As shown in Table 1, the [Y.sub.1] values of the PA9-T samples are relatively small (around 6 GPa), corresponds to 16.5% of [E.sub.1]. This implies that noncrystalline regions of PA9-T predominate the tensile properties of the PA9-T fiber.


The crystal modulus [E.sub.1] of PA9-T in the direction parallel to the chain axis was measured by the X-ray diffraction. It was found that the lower-order reflections of PA9-T gave lower [E.sub.1] values resulted from the apparently higher peak shifts with load than actual, influenced by the Laue lattice factor. When corrected this fact, the [E.sub.1] of PA9-T derived at the highest diffraction angle was considered to be the most reliable value and it was 40 GPa. The lower [E.sub.1] value of PA9-T, than other polyamides such as nylon 6 and PPTA, is due to the presence of the long crankshaft arms and chain contraction of its molecular conformation.


Stretching                                         Bending

                          Force                             Force
                Bond      constant.   Angle       Bond      constant.
                distance  [k.sub.1]               angle     [k.sub.p]
                          [10.sup.2]              (degree)  [10.sup.2]
Bond            (A)       (Nm)                              N[m.sub.-1]

[H.sub.2] C-C       1.54       3.948  C-C-C          111.5          0.3


OC-NH               1.40       6.118  C-C-N(H)       111.5          0.3

[H.sub.2] C-NH      1.47        5.74  C-N-C(O)       123.0         0.68

OC-[C.sub.aro]      1.48        4.36  N-C(O)-C       116.0         0.38

[C.sub.aro]-        1.39       6.433  [C.sub.arom]-     --         0.66
[C.sub.aro]                           [C.sub.arom]-

                                      C-C               --         1.06


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Ahmed Jalal Uddin, (1) Yasuo Gotoh, (1) Yutaka Ohkoshi, (1) Takashi Nishino, (2) Ryokei Endo (3)

(1.) Division of Chemistry and Materials, Faculty of Textile Science and Technology, Shinshu University, Ueda, Nagano 386-8567, Japan

(2.) Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Rokko, Nada, Kobe 657-8501, Japan

(3.) Kuraray Co. Ltd., 7471 Tamashimaotoshima, Kurashiki, Okayama 713-8550, Japan

Correspondence to: Y. Gotoh; e-mail:

Contract grant sponsor: Global COE program, Ministry of Education, Culture, Sports, Science and Technology of Japan.

DOI 10.1002/pcn.22086

Published online in Wiley Online Library

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Author:Uddin, Ahmed Jalal; Gotoh, Yasuo; Ohkoshi, Yutaka; Nishino, Takashi; Endo, Ryokei
Publication:Polymer Engineering and Science
Article Type:Report
Geographic Code:9JAPA
Date:Feb 1, 2012
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