Dynamic

Morphology and Dynamic Mechanical Properties of Nylon 66/Poly(Ether Imide) Blends KIL-YEONG CHOI, SUNG-GOO LEE, and JAE HEUNG LEE

Advanced Polymer Division Korea Research Institute of Chemical Technology Yusong. Taejon, 305-606,Korea and JINGJIANG LIU

C hangchun Ins tit Ute of App lied Chemistry ChineseAcademy of Sciences Changchun, 130022,P. R. China The morphology and dynamic mechanical properties of blends of poldether imide) (PEI) and nylon 66 over the full composition range have been investigated. Torque changes during mixing were also measured. Lower torque values than those calculated by the log-additivity rule were obtained, resulting from the slip at the interface due to low interaction between the components. The particle size of the dispersed phase and morphology of the blends were examined by scanning electron microscopy. The composition of each phase was calculated. The blends of PEI and nylon 66 showed phase-separated structures with small spherical dcmains of 0.3 0.7 Fm. The glass transition temperatures (T,s) of the blends were shifted inward, compared with those of the homopolymers, which implied that the blends were partially miscible over a range of compositions. T g l ,corresponding to PEI-rich phase, was less affected by composition than Tg2, corresponding to nylon 66-rich phase. This indicated that the fraction of PEI mixed into nylon 66-rich phase increased with decreasing PEI content and that nylon 66 was rarely mixed into the PEI-rich phase. The effect of composition on the secondary relaxations was examined. Both q,corresponding to the motion of amide groups in nylon 66, and T,., corresponding to that of ether groups in PEI, were shifted to higher temperature, probably because of the formation of intermolecular interactions between the components.

-

INTRODUCTION

ylon plastics are extensively used in the manufacture of automobile parts, engineering products, and textile fibers, because they have many advantages in properties such as high mechanical and impact strength and good processability. However, they reveal relatively low heat deflection temperature and absorb water easily, which limits uses in structural parts. Recently, blending nylon 66 with different polymers h a s generated considerable interest because this is a n easy and economical way of tailoring nylon 66 to suit specific end uses. Sometimes, blends of nylon 66 with novel mechanical performance and excellent processing properties were provided. Numerous studies have been carried out on the blends

N

of nylon 66 with polyethylene. polypropylene, poldethylene terephthalate), nylon 6, elastomers, and high performance engineering plastics (1-3). PEI, (poly(2,2’-bis(3,4-dicarboxyphenoxy) phenyl propane)-2-phenylene bisimide), belongs to a class of relatively new high performance materials. It is a thermally stable and soluble thermoplastic that has excellent high temperature resistance, toughness, good dielectric properties, low flammability, and high resistance to radiation and deformation under load a t elevated temperature. In particular, PEI combines a relatively low production cost with appreciable physical properties (4-6). However, it has some disadvantages, such as high melt viscosity and low resistance to chemicals, owing to its amorphous structure. Some basic research on the blends of PEI with thermotropic

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Kil-Yeong Choi, Sung-Goo Lee,Jae Heung Lee, and Jingjiang Liu liquid crystalline polymers, PEEK, poly(ether sulfone),and polybenzimidazole have been carried out (7- 10). The significant improvement in processing properties for PEI can be achieved without a consequent decrease in the mechanical properties by blending it with nylon 66, which is a semicrystalline material with relatively high mechanical properties, low cost, and low melt viscosity. Moreover, the strength and heat resistance of nylon 66 can be increased remarkably by adding PEI as a minor component. Blending the two polymers seems to be most attractive both in terms of processability and performance improvement. Blends of nylon 66 and PEI were studied over the whole range of composition. Morphology and rheological and dynamic mechanical properties were examined, and the miscibility between two components, transition, and relaxation behaviors were described. EXPERIMENTAL

Materials PEI is commercially available a s Ultem from General Electric Plastics. Ultem 1000 with a density of 1.27 g/cm3 was used in this study. Nylon 66, Toplamid 2021, was supplied by Tongyang Nylon Co. (Korea) in the form of pellets. The density and the melting point are reported a s 1.14 g/cm3 and 255°C respectively, by the manufacturer.

Mixing Both nylon 66 and PEI are known to absorb moisture easily. Before use they were dried at 90°C for 24 hrs. A n internal mixer (Haake Rheocord 90) was employed to prepare the blends and determine their rheological properties during blending. Both shear rate and mixing temperature were controlled. Typically, a 50-g sample was mixed at 60 rpm for 10 min at 320°C. Torque and melt temperature with time were measured. The same processing prccedure was followed for the homopolymers. The hot blends were removed from the mixer, rapidly cooled to room temperature, and then stored in a desiccator until testing. The weight ratios of PEI and nylon 66 were as follows: 100/0, 90/10,85/15, 75/25, 50/50, 25/75, 15/85, 10/90, 5/95, and 0/100, which were coded as PEI100, PEI90, and so on.

-

Characterization The morphology of the blends of PEI and nylon 66 was investigated on compression molded samples. Transversal sections of the specimens were obtained by fracturing them in liquid nitrogen, and then the surface was coated with gold-palladium prior to viewing with a JEOL JSM-840A scanning electron micre scope operated at 20 KV. The apparent diameter of each particle in the field of view was measured. The 1644

volume fraction of the domains was calculated, with the assumption that the dispersed domain was of spherical shape and each particle had been cut at its equator. Dynamic mechanical measurements were performed in a Rheometrics Dynamic Spectrometer (RDS) in the shear mode operating at a frequency of 1 Hz and a constant strain of 0.1%. The dimension of the testing sample was 40(L) x 12(W)x 2(T) mm. Nitrogen gas was circulated in the environmental chamber to minimize degradation and chemical reaction during testing. The dynamic mechanical properties, shear storage modulus, G', shear loss modulus, G", and loss factor, tan 6 , were collected at a heating rate of 3"C/min over the temperature range of - 150 to 300°C. The temperature that corresponds to a maximum in the tan 6 vs. temperature curve was considered the glass transition temperature, Tg. for the homopolymers. For the blends, the higher Tq, represents the glass transition temperature of the PEI-rich phase i d the lower Tq2corresponds to that of nylon 66-rich phase. Each relaxation temperature denoted by the peak on tan 6 vs. temperature curves was reproduced exactly. The melting behavior of the blends was evaluated on the DuPont 990 Differential Scanning Calorimeter (DSC). The calibration in temperature and heat flow scales followed standard procedures. The 10 k 2 mg of sample was heated up to 300°C. held for 5 min to erase the effect of the previous thermal and mechanical history, and then cooled at 10"C/min to room temperature to obtain the crystallization exotherm. A dry -nitrogen atmosphere was used. The melting endotherms were obtained in the second heating cycle at 10"C/min. The melting point, Tm,and crystallization temperature, Tc,were given a s the maxima of the thermal transitions. The degree of crystallinity, Xc, for nylon 66 was calculated with equilibrium heat of fusion, A H ; , of 188.1 J / g for the 100% crystalline nylon 66 (1 1).

RESULTS AND DISCUSSION Rheological Behaviors Fzgure I shows the typical Haake Rheocord 90 data curves illustrating changes in torque during the mixing process at 320°C for the component PEI (PEI 1001, nylon 66 (PEIO), and the blends of PEIlO, PEI50 and PEI9O. The high loading peaks resulting from the melt fracture of cold samples were recorded prior to complete fusion of the materials. On the torque vs. time curves for the pure nylon 66 and specimen PEIlO in Fig. 1 , the second small peaks, resulting from the melting process of crystallites remained in the materials, were observed at around 1 min after the mixing was started. They were accompanied by the temperature decrease of the mixtures at the melting point of nylon 66, 250°C. After the mixing period exceeded 5 min, both the torque and temperature were leveled off, indicating that an equilibrium state was reached.

-

POLYMER ENGINEERING AND SCIENCE, OCTOBER 1995, Vol. 35, No. 20

Morphology a n d Properties of Nylon 6 6 / P E I Blends

- PEllOO

_ _ - P E I 90

_.- PEI 50 ..-__ 10

PEI PEI 0

-----_ 0

40

20

60

Time,rn I n

1. Changes in torque as a function of mixing time for PEI, nylon 66, and the PEI/ nylon 66 blends. Q.

The torque values at the equilibrium state are plotted as a function of composition in Fig. 2. The torque values can be easily converted to absolute viscosity via relationships reported elsewhere (12, 13).PEI revealed a much higher torque value than nylon 66, and a s the content of the nylon 66 was increased, the torque was greatly reduced, because the processability of the blend was improved with increasing content of nylon 66 with low melt viscosity. Many rheological empirical or semi-empirical equations have been reported and reviewed to describe the relationship between morphology, composition, rheology, and processing steps in the polymer blends (14- 16). Utracki suggested that the log-additivityrule might be used to classify the flow behaviors of the polymer blends ( 14): Log F =

Wi log F,

(1)

where F and F, are the melt rheological functions, e.g., shear viscosities of the blends and the component, and Wi is a measure of composition, usually expressed as weight or volume fraction of the compe nent. The use of Eq 1 makes it possible to distinguish a positive deviating blend (PDB), a negative deviating blend (NDB), and a positive-negative deviating blend (PNDB) with a sigmoidal dependence. Comparison between the variations in torque of the blends as a function of the composition measured experimentally and those calculated readily from Eq 1 can provide us with very interesting information about the morphology of blend melts during mixing. As shown in Fig. 2, all the polymer blends of PEI and nylon 66 revealed NDB behaviors. The largest NBD behavior was shown in PEI50, in which the amounts of the two polymers were comparable. When the weight fraction of nylon 66, Wn, was less than 0.25 or more than 0.8, many fewer NBDs were observed, meaning that the miscibility was improved for the blends with low content of one component. Lower melt viscosities than the calculated values

PEI,w t Yo 2. Comparison of experimental equilibrium torques for the blends of PEI and nylon 66 with the calculated ualues with Equation 1.

Q.

by the log additivity rule for the polymer blends have been observed elsewhere (17-20). Reasons for the phenomena have been discussed. It is well known that a n incompatible blend, characterized by a sharp interface and essentially no interaction between the two phases, frequently exhibits a n interlayer slip, which gives rise to a reduction in viscosity of the blend, and hence the negative deviations of the viscosities from the additivity values have been observed. Figure 2 reveals that the interface slip predominates the melt viscosity reduction for the blends in the middle of the composition range. The dependence of miscibility on the composition of the blends has been observed in PEEK and PEK-C blends (2 1). At low blend compositions, miscible blends of PEEK/PEK-C were achieved. However, the analysis of the rheological properties of polymer blends is very complicated. Besides experimental difficulties in measuring a n average rheological response of a blend, there are limitations in interpreting the results owing to concentration and stress field dependent morphology, as well a s inherent difficulties in stress orientational effects. Certain imposed morphologies and the viscoelasticity of both components by the stress field frequently allow the structures to exist long enough to be retained in the cooled specimens. Sometimes, the rheological properties of the blends during mixing could not be in agreement with those determined at solid states. Morphology The morphology of the blends in a mixing chamber can be related to their memory of the rheological history in addition to the miscibility between the components. To evaluate the miscibility of the blends in detail, it seems to be suitable to carry out the morphological investigation on the compression molded samples for convenience. The scanning electron micrographs (SEMs) of the fractured surfaces of

POLYMER ENGiNEERiNG AND SCIENCE, OCTOBER 1995, Voi. 35, No. 20

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Kil-Yeong Choi,Sung-Goo Lee, J a e Heung Lee,and Jingjiang Liu

Fig. 3. Scanning electron micrographs or the blends of PEI and nylon 66.

the blends are shown in Fig. 3 and the information listed in Table 1 is a summary of the composition and size of the domains obtained from the SEMs. It is seen in the SEMs that the blends of PEI and nylon 66 have phase-separated structures with small spherical domains, less than 1 p m in size, mainly ranging from 0.3 to 0.7 p m which means the blend systems are partially miscible, probably because of the h y d r e gen-carbonyl interactions between the polymer chains. The nylon 66 with lower melt viscosity formed the continuous phase with spherical PEI domains for the blends with PEI composition u p to 50%. and above that composition, the discrete nylon 66 phase was segregated in the PEI matrix as spherical d e Table 1. Morphological Parameters Obtained From the Scanning Electron Micrographs. Particle Code

+J+,,*

D, wn

Volume Fraction of Domains,+,

PEI 5

0,04510.955 0.09010.910 0.2310.77 0.4710.53 0.8910.11

0.38 0.44 0.58 0.64 0.49

0.0048 0.025 0.15 0.32 0.14

Composition

PEI 10 PEI 25 PEI 50 PEI 90

Size

@d/+i

+d/+n

0.11 0.28 0.65 0.68

4PrE

1.27

* $ i and 6" correspond to the volume fractions of PEI and nylon 66 in the blends, respectively.

1646

mains, as shown in PE190 of Fg. 3. From close observation of the domain boundaries, it can be noticed that the adhesion a t the interface region became poorer as the PEI content was increased. The weight fraction of PEI in the blends has been converted into volume fraction, 4,, as shown in Table 1. The average diameter of the domains, D, depended significantly on the composition in the blends, as shown in Fig. 3 and Table 1. The particle size distribution of the dispersed phase appeared to be polydisperse, but became narrow as the particle size decreased. The largest domain size and the widest distribution of the particle diameter were observed in PEI50. Morphology generation during mixing of polymer components involves a balance between the competing processes of fluid drop breakup and coalescence. Taylor studied the deformation and disintegration of Newtonian fluids (22, 23). Tokita h a s derived a n expression for describing the particle size of a dispersed phase in polymer blends (19, 24). At equilibrium, where breakup and coalescence are balanced, the equilibrium particle size, D, may be expressed as: (2)

POLYMER ENGINEERING AND SCIENCE, OCTOBER 1995, Vol. 35, No. 20

Morphology a n d Properties of Nylon 66/ PEI Blends where v12,v , E. and P, refer to stress field, interfacial tension, bulk breaking energy. and probability that a collision will result in coalescence, respectively. Equation 2 predicts that the equilibrium particle size decreases when the stress field becomes larger, the interfacial tension becomes smaller, and the volume fraction of the dispersed phase is smaller (23). A s represented inTable 1 and Fig. 3, the average domain size increased from about 0.38 p m to 0.64 p m with a n increase in the PEI weight fraction in these blends u p to 50%. which was in agreement with the trends predicted in Eq. 2. For the blends with higher PEI content, PEI was found to form the continuous phase with domains of nylon 66, as revealed in PEISO blend. A domain size of 0.49 p m was observed in the SEM for PEISO, while particles about 0.44 p m in diameter were distinguishable for PEI 10. Moreover, much wider particle size distributions of the dispersed phase were revealed in PEISO than in PEI10, even though the volume fractions of the minor component were approxt mate amounts in the two blends. PEISO represented a significant departure from PEI 10 series of blends, because the matrix viscosity, qm, and hence at the same strain rate, the shear stress, (r12,were much higher for PEISO than those for PEI10. In addition, the interaction between the components in PEIlO seems to be different from the case of PEISO. As shown in Fig. 3, the sharp interface was observed in PEISO, whereas a n improved adhesion between the dispersed phase and the continuous phase was recognizable in PEI10. The interactions between the component polymers serve to diminish the interfacial tension, and hence the motion of dispersed particle within the matrix phase. As pointed out in the literature (19). the differences of the particle size between the various polymer blends at constant composition are due primarily to changes in the interfacial tension and viscosity ratio. The morphology of immiscible or partially miscible blends appears to be controlled by a hierarchy of effects, such as : interfacial tension > viscosity ratio > shear stress (23). The former predominated the morphological difference between PEI 10 and PEISO. The volume fractions of the PEI component, 4,, and of the nylon 66 component, 4". are related to the actual composition of the blends because they are converted from the density and weight fraction, as shown in Table 1. On the other hand, the volume fraction of the dispersed domains, I $ ~ can , be obtained from the SEM. Provided the domains consist of pure PEI in PEI5, PEI10, PEI25, and PEI50, the ratios of the volume fraction of dispersed phase, 4d, to 4, represent the relative contents of PEI composing the domains. For example, 11% of PEI forms the dispersed phase and 89% of PEI is mixed with the matrix, nylon 66, to form a homogeneous continuous phase in the case of PEI5, as shown in Table 1. The information presented in Table 1 documents the trend of a decrease in the relative amount of PEI in the continuous phase with an increase in the weight

fraction of PEI in the blends when PEI forms the dispersed phase, which implies that the miscibility between PEI and nylon 66 increases with a decrease in content of PEI in the blends when PEI was the minor component. These results are associated with the dynamic mechanical properties of the blends, which is discussed in the next part in this paper. For PEISO, the ratio of the volume fraction of the dispersed nylon phase, qbd, to the volume fraction of the nylon component, $,,. is 127%. It can be concluded that the dispersed domains consist of the homogeneous mixture of PEI and nylon 66 with a PEI content of a t least 27%. Dynamic Mechanical and Transitional Behaviors Figure 4 shows the temperature dependence of the loss factor (tan 6 ) for the blends. Clearly, three welldefined relaxation peaks were observed for pure PEI and nylon 66, respectively. The mechanism of the relaxations resulting from the molecular motion has been investigated by a number of workers. For pure nylon 66, three mechanical loss peaks, denoted as a , p , and y , are shown in Fig. 4. The maximum in tan 6, a relaxation, associated with Tg occurs a t -80°C. while the p and y relaxations are found near -50 and - 120"C, respectively, which are related to the mobility of the polar groups (-CONH-) and the excitation of cooperative motions in the methylene groups (-CH,-) in the main chain, respectively (2, 25). For pure PEI, three dynamic damping peaks are assigned as a ' , p ' , and 7'. The sharp a' peak at about 230°C is due to the glass transition of the PEI. The broad 0' peak near 80°C may correspond to a local motion of the main chain, which h a s been o b served around 127°C in polyimides based on benzophenone tetracarboxylic acid (26). The y ' peak near - 100°C appears in all polyimides in which the rigid phenyl groups consist of rigid backbone molecules spaced with flexible groups such as methylene, and ether (26). The dynamic mechanical spectrum h a s become a classic method of determining miscibility because the height and position of the mechanical damping peaks are affected remarkably by miscibility, intermolecular interaction, interface feature, and morphology. The dynamic mechanical properties of the blends are also affected by the composition, with particular emphasis on the amount of the minor component. In the blends of PEI containing a small amount of nylon 66, i.e., PEISO, the absence of a n u peak is noteworthy. On the other hand, when PEI is the minor component and its content is more than 10 wt%, double Tgs, a and a ' , are clearly visible in the blends. The phase structure of a blend is inferred from the number of glass transition temperatures observed in the thermograms; that is, the appearance of two glass transitions is a clear indication of phase separation; that of a single glass transition at a temperature intermediate between those of the pure components indicates miscibility.

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Kil-Yeong Choi, Sung-Goo Lee, Jae Heung Lee, and Jingjiang Liu 1-

- PEIIOO

_ _ PEI 90

PEI 50

0-

- - _ _ _PEI I 0 0

-

4:-1- Y

-3

I

-150

I

-60

I

I

I

I

1

I

I

21 0

120

30

0

Tempera ture,'C

Fig. 4. Tan6 us. temperature curvesfor PEI, nylon 66, and the PEI/ nylon 66 blends.

While the miscibility of the blends can be speculated from the number of Tgs, the composition of the phases can be calculated adequately according to the Fox equation, with the Tg shift values for the partially miscible blends, which is:

The subscripts 1 and 2 refer to the pure components, and W refers to the weight fraction. According to the Tgcriterion for miscibility, the polymer blends of PEI and nylon 66 appeared to be partially miscible because two Tgs, which were shifted inwardly compared with Tgs of their respective pure component polymers, were detected in the composition range of nylon from 0.15 to 0.90. For the polymer blends with extremely high or low nylon compositions, the detection of the single Tg might result from the small amount of the minor component. Assuming that the Fox relation holds for the Tg dependence on composition in the blends and that the system has attained thermodynamic equilibrium unaffected by both the fast cooling to room temperature and the mixing dynamics, that is, the quenched two phases are at equilibrium: the PEI-rich phase with higher Tg that corresponds to the nylon 66-plas ticized PEI phase and the nylon 66-rich phase with lower Tg that corresponds to the PEI-reinforced nylon 66 phase, the composition of each phase can be calculated by the Fox equation. A summary of the experimental investigation on the Tg shift and calculated phase composition is represented in Fig. 5 and Table 2. A slight decrease in the Tg of the PEI-rich phase was recognizable, showing that a plasticizing role of nylon 66 took place for the PEI, and the content of nylon 66 mixed into the PEI phase was very low. The PEI-rich phases consisted of 99% PEI and 1% nylon 66 over a wide composition range of the blends investigated. On the other hand, the amounts of PEI contained in nylon 66-rich phases 1648

340' 0

I

I

I

I

I

20

40

60

80

100

PE I , w t % Fig. 5. Changes in glass transition temperature as a-function of PEI content for the PEI/ nylon 66 blends. ( 0 ) Tg : ( - ) T y 2 : (--I Fox equation.

,

were much higher, -4-9 wt%, depending on the composition in the blends. In addition to the above, there were a few other differences worthy of note on the storage shear modulus, G', vs. temperature plots, as shown in Fig. 6. G' decreased with increasing content of nylon 66 in the blends at the temperature range from about 50°C to 230°C, i.e., from Tg2 to Tyl,owing to the low modulus of the rubbery amorphous phase of nylon 66. In contrast to the temperature region between the T,s of the component polymers, G' increased with increasing content of nylon 66 and in addition exhibited rubber-like plateau behaviors in the temperature range from 230°C to 255°C. probably because of the physical crosslinks resulting from the crystallites in nylon 66. The crosslinks enable the plateau region to

POLYMER ENGINEERING AND SCIENCE, OCTOBER 1995, Yo/. 35, No. 20

Morphology and Properties of Nylon 66/ PEI Blends Table 2. Phase Compositions of the Blends of PEI and Nylon 66. -

Nylon 66-rich phase

Code

W"

w,

WilW,

1 .o 0.96 0.94 0.93 0.91 0.91

0 0.04

-

-

PEl-rich phase

Code

T,,,'C

TmPloC

T,,C

AH,J/g

X,

262.1 262.8 263.6 262.7 259.5 257.7

234.4 233.7 232.8 232.0

69.9 59.5 47.3 33.4 16.2 5.33

0.37 0.35 0.34 0.36 0.34 0.28

~~

PEI 0 PEI 5 PEI 10 PEI 15 PEI 25 PEI 50 PEI 85 PEI 90 PEI 100

~

Table 3. Thermal Transition Parameters of the Blends of PEI and Nylon 66.

0.06 0.07 0.09 0.09

w,

W"

-

~

0.80 0.60 0.47 0.36 0.18

-

-

0.99 0.99 0.99 0.99 0.99 0.99 1.o

-

-

0.01 0.01 0.01 0.01 0.01 0.01

-

-

-

-

~

PEI 0 PEI 10 PEI 25 PEI 50 PEI 75 PEI 90

252.5 252.0 252.6 252.0 ~

-

order to understand how the PEI component with high viscosity influences the crystallization behaviors of the blends, a detailed investigation on isothermal crystallization from the melt is being performed, and the results will be reported elsewhere. Difficulties in detection of crystalline melting behaviors in the G' vs. temperature curves for PEISO, as shown in Fig. 6, might result from both the low crystallinity in nylon 66, due to the restriction of crystal formation of nylon 66 by the PEI component with high viscosity, and the low sensitivity of RDS for detecting the crystalline melting process for blends of low degrees of crystallinity. DSC is more frequently used to investigate the thermal transition properties for the polymer materials. The DSC thermograms of the blends are shown in Fig. 7 and the transition parameters are summarized inTable 3. Double melting endotherms of nylon 66 (Tml,Tm2)due to the transformation of crystalline structures were observed. The degree of crystallinity for nylon 66 was calculated with the heat of fusion 188.1 J / g for 100% crystalline nylon 66. The crystallinity was decreased with a n increase in PEI content from 0.37 for pure nylon 66 to 0.28 for the PEISO

* W,

and W, are PEI wt% and nylon 66 wt% in the phase, respectively. W , is PEI wtQ in the blends.

extend the higher temperatures ( T > Tql) until the crystallites in nylon 66 are melted at about 255°C. In the crystallizable blends, there are many small crystallites that act a s crosslinks, and hence the viscoelastic properties of the blends are related strongly to the content of crystallites. In PEI/nylon 66 blends, the degree of crystallinity of nylon 66 is believed to affect strongly the dynamic mechanical properties in the temperature region from the glass temperature of PEI to the nylon melting temperature. From the results mentioned above, it has been implicitly concluded that nylon 66 should improve the rigidity of PEI at temperatures > 230°C. The degree of crystallinity of nylon 66 is strongly dependent on the mobility of the polymer chains determined mainly by the temperature. The crystallization temperatures (T,) of nylon 66 were observed near the T,s of PEI where the mobility of the polymer chains changes abruptly, as shown in Table 3. In

-.

.-

I

61

Q.

1

I

1

100

I

150 200 Tempera ture,"C 6. Shear storage modulus (GI) curuesJor PEI, nylon 66, a n d the PEI/ nylon 66 blends. 50

POLYMER ENGlNEERlNG AND SCIENCE, OCTOBER 1995, Vol. 35, No. 20

1 I

250

1649

Kil-Yeong Choi, Sung-Goo Lee, J a e Heung Lee, a n d Jingjiang Liu

Secondary Relaxations and Intermolecular Interactions Four secondary relaxations, denoted as p , y . p ' and y ' , were measured on the dynamic mechanical spectra for the blends. The mechanical loss peaks for PEI, nylon 66, and PEI/nylon 66 blends are shown in Fig. 8, and the relaxation temperatures defined by the loss peaks are summarized in Table 4. The y ' relaxations for the PEI phase were shifted to higher temperatures and the height of the loss peak was reduced as the content of nylon 66 was increased in the blends. The increase in T,. and a decrease in tan 6 might result from the interaction between the polar groups of amide and ether, and hence the hindrance of the rotation along the PEI main chain. The intermolecular interactions for the blends in which nylon 66 forms the continuous phase may be further verified by the results shown in Table 4 . The %is shifted to higher temperatures with increasing PEI content in the blends. It is possible that some portion of PEI migrates from the dispersed phase into the matrix nylon 66 and mixed with nylon 66, thereby hindering the motion of amide groups. However, even if all the PEI in the nylon 66-rich phase does so, the total amount is relatively small (for example, 9 wt% of PEI in the nylon 66-rich phase for PEI50, as shown in Table Z ) , and thus the changes in PEI composition due to the migration would not seem enough to explain the Tp increases observed. Further evidence for the interaction between nylon 66 and PEI might be the observed T, relaxations that appeared as a shoulder overlapped on the a ' dispersion, as shown in Fig. 8 and Table 4. T, is located about 213°C regardless of PEI content in the blends. It is inferred from the relaxation of polymer chains at the interface re-

-PEI100 I

I

150

I

250 Ternperature,"C

200

300

3 I

Fig. 7. DSC heating thermograms for PEl, nylon 66, a n d the PEI/ nylon 66 blends.

blend, probably because of the dilution effect of PEL These results are intuitively confirmed by the morphology in PEISO, in which a dispersed phase of nylon 66 is visible. A detailed study on the thermodynamics and the reorganization on heating in the blends will be published elsewhere.

---:PEI

__

I

-1 50

I

-60

100 _ - - - PEI 10 PEI 90 ----.PEI 0

1

I

I

120

30

I

210

L

300

Temperature P C Fig. 8. Shear Zoss modulus ( G I curves for PEL nylon 66, and the PEI/ nylon 66 blends. T,is indicated a t right. 1650

POLYMER ENGlNEERlNG AND SCIENCE, OCTOBER 1995, Vol. 35, No. 20

Morphology and Properties of Nylon 6 6 / P E I Blends Table 4. Secondary RelaxationTemperatures of the Blends and Homopolymersof PEI and Nylon 66. Code

rp,"c

PEI 0 PEI 5 PEI 10 PEI 15 PEI 25 PEI 50 PEI 85 PEI 90 PEI 100

-62 -56 -54 -53 -52 -51

T,,

"c

-136 -130 -130 -133 -132 -134

ri,"c

r,;,"c

T;, "c

213 213 213 213 76 79 81

- 75 - 78 -101

gion (27). However, conclusive evidence for the intermolecular interactions in the PEI-nylon 66 blend systems will be sought by using Fourier-transform infrared (FTIR) and ultraviolet (W)spectroscopies in a future communication. ACKNOWLEDGMENT

We would like to thank the Ministry of Sciences and Technology of Korea for supporting this research under Grant No. of KRICT JG-2043. REFERENCES 1. T. S. Ellis, J . Polym Sci., Polym Phys.. 31, 1109 (1993). 2. J. P. Bell and T. Murayama, J . Polym Sci.. Part A-2. 7. 1059 (1969). 3. A. Verma. B. 1., Deopura. and A. K. Sengupta, J . Appl Polym Sci., 31,747 (1986). 4. R. T. Woodhams, Polym Eng. Sci., 25,446 (1985). 5. R. 0. Johnson and E. 0. Teutsrh, Polym Compos.. 4, 162 ( 1983). 6. R. J. Karcha and R. S. Porter. J . Polym Sci.. Polym Phys., 31,821 (1993). 7. M. K. Nobile. D. Acierno, L. Incarnato, E. Amendole, L. Nicolais, and C. Carfagna. J . Appl Polym Sci., 41,2723 ( 1990).

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