Morphological factors affecting the permeation resistance of nanocomposite blend films.
Two polymers having complementary properties can be combined to simultaneously effect improvements in performance and cost for commercial applications , Permeation resistance is a primary criterion in the selection of polymers for barrier film applications. Thus, different approaches, such as lamination , copolymerization , and blending/alloying  have been utilized to enhance permeation resistance in such barrier films. A variety of structures using single and multiple phases, from simple polymer fdms to coextruded laminates, two phase polymer systems and polymer composites comprising impermeable inorganic fillers, have been studied in-depth by Barrer ,
The technique of polymer blending was successfully investigated by Lohse and Datta  to produce single-layer rather than multilayer structures for packaging. Obviously, the high barrier component would be most effective if used either alone or as the major continuous phase of the blend. However, that scenario may not necessarily be desirable due to other considerations, such as cost, processability, or sealing.
The volume fraction and shape of the high barrier component as a dispersed minor phase are critical parameters for reducing diffusional transport through such a two-phase polymer system . A higher aspect ratio for the discontinuous barrier phase would decrease the permeation rate by lengthening the tortuous path for permeant molecules diffusing around it. Practical processing techniques for modifying the phase morphology in blends include the viscosity ratio for the two polymers in the blend , the presence of a compatibilizer  and both shear and extension rate levels during compounding .
The barrier resistance of polyethylene, a common polyolefinic packaging material, can be enhanced for nonpolar permeants by blending with a minor phase of nylon 6 (PA6). Compatibilization of any highly immiscible polymer pair like this is also required to reduce the size of the dispersed minor phase and enhance its aspect ratio by lowering interfacial tension  and to generate a strong interfacial region for mechanical coherence and effective property development. Because polyethylene-nylon blends find application in commercial packaging films, they represent a realistic system for studying of the effects of morphology on transport properties. A theoretical analysis of transport properties in such two-phase polymer blends was made by Garmabi and Kamal  using the Higuchi equation  that keys permeation rate to the volume fraction, shape and relative permeability of a well dispersed and oriented phase.
Likewise, nanoscale particles, especially layered silicates, can effectively augment the barrier property of a polymer by increasing path tortuosity when suitably dispersed in a polymer matrix [10-14], as their small platelike structure is of very high aspect ratio. Such a nanocomposite would represent a limiting case of the Higuchi equation for a completely impermeable dispersed phase. But the effects of volume fraction and filler aspect ratio of impervious particles on tortuosity could instead be modeled by the simpler equation due to Nielsen .
Layered silicate particles have thickness ranging from a few nanometers to hundreds of nanometers, depending upon their extent of disintegration due to polymer intercalation and any resulting exfoliation. Their easy availability and the existing depth of knowledge regarding their structure and surface chemistry (enhancing their affinity with many polymers) have fostered their widespread use. In addition, the layered silicates, due to their high aspect ratio, impart unique properties to the matrix polymer, such as enhanced modulus and strength , higher heat distortion temperature , low flammability , and increased solvent resistance , in addition to reduced gas permeability , all at significantly lower loadings (as little as 2 vol%) than commonly required for micro-scale reinforcements in conventional composites.
Merging the complementary technologies of micro-scale polymer-polymer blends and nanoscale composites to form a hierarchal nanocomposite blend provides additional system parameters whose manipulation then affords better opportunity to achieve broad synergistic permeation resistance. Thus, the incorporation of layered silicates in PA-6 would generate a well dispersed nanocomposite having very low oxygen with improved but still modest water vapor permeability, while subsequently blending polyethylene with this nanocomposite (including a compatibilizer) could impart further resistance to the transport of aqueous species while somewhat moderating the oxygen barrier.
This paper considers compositional and rheological effects in a multiphase system comprising a layered silicate, two major polymer phases and a compatibilizer on the type of phase morphology (comprising either a combination of continuous and dispersed phases or co-continuous phases) and the water vapor permeation properties of the resulting nanocomposite blend. The effects of the nanoclay presence on the crystallinity and thermal transition properties of the polymers are also addressed. The phase morphology in such a complex system is characterized using atomic force and transmission electron microscopy.
Water vapor transmission rate (WVTR) was selected for studying the permeation behavior of nanocomposite blends because of the simplicity of the test apparatus and the ease of analysis of the permeation rate. Yet it readily allows barrier evaluation and performance comparisons among the various polymer and nanocomposite components of the blends along with morphological effects. While oxygen transmission rate is perhaps of higher commercial importance in preservative film applications for the food industry, it requires more specialized test apparatus and analysis instrumentation. Thus, these water vapor permeation data represent a model study that can form the base for developing generalized mathematical models and selecting optimal blend system morphologies appropriate to barrier performance of any permeation situation in multiphase systems.
Two different types of nylon nanocomposite were used: PA-6 (grade-Capron B73ZP, Honeywell Plastics) melt mixed with nanoclay (grat/e-Cloisite 30B, Southern Clay Products) and PA-6 NCH (Ube Industries, Japan) prepolymerized with 1.9 wt% organoclay in-situ. High-density polyethylene (HDPE, grade-M6210) obtained from Equistar Chemicals and low-density polyethylene (LDPE, gracfc-PE4517) obtained from Chevron Phillips Chemical Company were melt blended with nylon or the nylon nanocomposites. Maleic anhydride-grafted HDPE (MPE) obtained from DuPont Industrial Polymers (grade-Fusabond MB 100D) served as a compatibilizer for the nylon-polyethylene blends. An inherent gas barrier nylon, Poly(m-xylylene adipamide), (PA-MXD6, g/We-S6007) produced by Mitsubishi Gas Chemical Company, was used in neat form as well as in combination with HDPE and nanoclay as a benchmark.
Compounded PA-6 nanocomposites containing 2 vol%, 4 vol%, and 8 vol% clay silicate or PA-6 NCH were blended with HDPE or LDPE, as reported in Tables 1-4 on a weight percentage basis. These were compounded in a Brabender internal mixer at 80 rpm rotor speed and a temperature of 250[degrees]C for the PA-6 compositions or 270[degrees]C for those containing PA-MXD6. The notations (C), (D), and (C-C) shown in those tables refer to continuous, dispersed and co-continuous phase morphology, respectively. All nylon constituents were dried under vacuum for 12 hr at 80[degrees]C prior to compounding.
Molding of Films for Measuring WVTR
A Carver compression press was used to mold polymer films averaging about 3 mil (76 pm) thickness with a variation of [+ or -] 5 [micro]m
for all of the compositions. The molding temperature was 250[degrees]C or 270[degrees]C for PA-6 or PA-MXD6 blends, respectively. Compression molded sheets of 2 mm thickness were also prepared utilizing similar molding parameters for morphological characterization of the blend compositions.
Differential Scanning Calorimetry (DSC) Measurements
A Thermal Advantage Universal Q 1000 differential scanning calorimetry (DSC) analyzer was used to measure crystallization behavior of the individual components, nanocomposites and blend formulations. Two heating/ cooling scans were run for each material specimen at 10[degrees]C/min between 30[degrees]C and 300[degrees]C. The second scan provided means to obliterate processing heat history effects on the reported melting and crystallization phenomena.
Ultra-thin sections (40-70 nm.) were cut from 2 mm thick compression moldings prepared as above for characterization of the phase structure and clay partitioning in the blends using a Reichert Ultracut S ultramicrotome at -120[degrees]C and analyzed with a Phillips Tecnai 12 transmission electron microscope at a 120-kV accelerating voltage. The remaining sample stubs, from which the ultrathin sections were cut, were then utilized for atomic force microscopy.
Atomic force micrographs were obtained both with a Digital Instruments Nanoscope III and a Quesant Instrument Corporation Q-scope 350 operated in the tapping mode.
A Rheometrics Scientific Advanced Rheometrics Expansion System dynamic viscometer was used in its parallel plate configuration with disk-shaped samples for the measurement of dynamic rheological properties. All component polymers and nanocomposites were tested for frequency dependence of the complex modulus and viscosity. The disks were molded to 25 mm. diameter and about 2 mm thickness, while the gap between the discs was set at 1.5-1.7 mm for all the samples. The strain was 1% and frequency was swept from 0.5 rad/sec to 100 rad/sec. The temperatures used were 250[degrees]C for PA-6 and 260-280[degrees]C for PA-MXD6.
Measurement of WVTR
Bottles filled with water and sealed with film pressed from the compounded samples were introduced into a dry atmosphere in a desiccator loaded with Dryrite desiccant to induce a water vapor gradient across the film, as shown in Fig. 1. High-vacuum grease was applied to produce an effective seal between the bottle and the film that was held in place by a ring cap, ensuring that the loss of water vapor was only by diffusion through the film. The rate of water vapor loss from the bottle through the polymer film was determined by weighings made at regular time intervals according to ASTM E 96-00. The measurements were continued until a steady rate of weight loss could be reported. WVTR measurements were corrected for film thickness variation by multiplying the value by the thickness of the film and reporting normalized WVTR as g.mil/hr.[m.sup.2].
RESULTS AND DISCUSSIONS
Figure 2 shows the variation in heats of transition (fusion and crystallization) with varying clay concentration. The heat of fusion obtained from DSC analysis is considered an indicator of the crystallinity developed in the system. Change in crystallization temperature upon addition of nanoclay suggests nucleation that could affect the permeation resistance of the system by alteration of the microstructure of the PA-6 crystallite through its association with the clay. Increased crystallization temperature would benefit nanoclay-filled systems over unfilled PA-6 in allowing shorter cooling cycle in injection molding process and increased production rate (pull rate) in film or sheet extrusion through quicker setting of the product dimensions. The effect of nanoclay addition on nanocomposite heat of fusion can also be attributed to changes in the nylon's crystal structure. There is also evidence in Fig. 2 for cold crystallization of the PA-6 in nanocomposites as seen by a higher heat of fusion vs. primary crystallization at the levels of maximum clay affect around 2 vol% silicate. Figure 3 shows primary crystallization temperature to increase upon addition of nanoclay up to a maximum at 2 vol% silicate concentration, followed by reduction to a plateau level at higher loadings. Thus, the clay is more effective in nucleating crystallization when present at lower concentration. In contrast, melting point (fusion temperature) decreases monatonically over the range of clay concentrations studied.
Rheological and Morphological Characterization
Rheological data for all nanocomposites as well as individual polymer components of the blend formulations identified in Tables (1-4) are shown in Figs. 4-6. Morphological characterization by transmission electron microscopy is presented in Figs. 7-10. As seen in rheological analysis, unfilled nylons (PA-6 and PA-MXD6) display a Newtonian flow behavior with minimal change in viscosity at increased frequency. At higher frequency, the break-up of network structure in the clay-filled nylon nanocomposites generates shear thinning behavior. This behavior becomes more pronounced at higher loadings of clay, as seen for the PA-6 filled with 2 and 4 vol% silicate in Fig. 4. While both unfdled LDPE and HDPE display a non-Newtonian behavior, their disparate viscosity levels (substantially higher in the case of the HDPE) produce different blend morphologies.
A co-continuous morphology was observed (Fig. 7) for the blend system involving PA-6 and HDPE, which can be attributed not only to the equal amounts of blend components present but also to the similar viscosities of these two polymers in the higher frequency region characteristic of compounding processes (as highlighted within the dotted line ellipse in Fig. 5). The generation of a co-continuous morphology would render the penneation characteristics of a polymer phase otherwise discretely dispersed more pronounced, while reducing the effective permeation through the previously sole continuous phase, at the same blend composition. In general, the permeation properties of a blend are governed by the proportion, continuity, directionality, size, and shape (aspect ratio) of the constituent phases. Recourse may be taken to geometrical models, such as series/parallel arrays and discontinuous inclusions for predictions of the permeability of any particular phase arrangement. In practice, permeation will be lower when the least permeable phase is more prominent or continuous. Thus, blend morphology becomes a tool for controlling permeation through optimal arrangement of the two polymer phases given their relative barrier resistance to any permeant, as for example in the polyethylene/nylon system under consideration here in regard to water vapor permeation.
Selection of the optimal phase continuity may be driven by economics as well as physics. Addition of a cheaper though more permeable discontinuous phase may be desirable to reduce the overall cost of the system without compromising too much of the barrier property. On the other hand, if a larger portion of a permeable phase were required, due perhaps to cost or processing considerations, it would tend to become continuous by virtue of its larger presence, which would be undesirable. Then, according to the tortuous path models, the required level of permeation resistance could be regained, at least to some extent, by introducing a discontinuous minor phase of a less permeable component such as another polymer or a solid, preferably a platy mineral.
Path tortuosity for permeant water molecules at the nanoscale can be increased by addition of nanoclay to the PA-6 phase, which has an affinity for water due to the formation of hydrogen bonds. The incorporation of nanoclay in the PA-6 phase of the blend raises its melt viscosity, as shown in the non-Newtonian rheological data presented in Fig. 5. This increase in viscosity of the PA-6 phase induces a consequent change in the phase morphology of the nanocomposite blend previously pictured in Fig. 7 from co-continuous to having the nylon dispersed in HDPE, as shown in Fig. 8. Having the HDPE be continuous will improve the blend's resistance to water permeation in addition to the reduced nylon permeability afforded by its nanoclay content. In regard to oxygen barrier requirements, though, the less permeable PA-6 phase would preferably be continuous, but the lower cost of the HDPE continuous phase could compensate for the more expensive nanoclay inclusion in the PA-6 that again also renders it even more impermeable, thus maintaining the cost-effectiveness of the nanocomposite blend.
Rheological data from Fig. 5 (taken from the higher shear rate region) show that the melt viscosity of LDPE is the lowest among all blend components, including the PA-6 phase. Therefore, instead of forming a nylon nanocomposite component to render the nylon phase discontinuous, substitution of LDPE having a lower melt viscosity in the important higher frequency region for the HDPE can also generate the necessary enhanced nylon-to-PE phase viscosity ratio to produce a dispersed nylon phase at the same component ratio in the blend, as shown in Fig. 9. Thus, rheological analysis can prove to be an important tool in predicting and controlling the morphology of inhomogeneous blend systems.
Similar rheological data for PA-MXD6 blends are given in Fig. 6. Figure 10 shows the morphology of such a blend comprising 80% polyethylene to feature a dispersed nylon nanocomposite phase despite its lower viscosity, due to the preponderance of polyethylene in the blend composition.
WVTR for Individual Polymers and Nanocomposites
Table 5 provides water vapor permeation data for all of the component polymers and nanocomposites used in the blends. The WVTR of the subsequent blend compositions reflect a dependence upon these characteristics of the constituent materials in addition to phase continuity/ morphology. As shown in Table 5, HDPE and LDPE have lower WVTR values of than nylon due to their inherent nonpolar chemical nature and the affinity of nylon's polar amide functional group for water molecules.
The atomic force micrograph shown in Fig. 11 depicts the morphology of a compression molded PA-6 NCH nanocomposite in a plane normal to the surface of the compression press platens. The highly ordered texture comprising ridges at about a 30 nm spacing oriented by the squeezing flow during molding suggests a laminated structure comprising silicate platelets that would produce an effective permeation barrier by generating a tortuous diffusion path. In both, PA-6 NCH (PA-6 in-situ polymerized with organoclay) and PA-6 compounded with 2 vol% silicate, WVTR was reduced by nearly 60% as compared with unfilled PA-6. However, according to the permeation data of Table 5, PA-6 NCH (with 1.9 wt% in-situ polymerized organoclay) offers a slightly reduced permeability as compared to PA-6 compounded with 2 vol% clay at almost half the clay loading level. (Note that a concentration of 2 vol% in compounded PA-6 is equivalent to 3.5 wt% of clay.) This exceptional performance is derived from a tethering effect during in-situ polymerization of caprolactam molecules in the clay galleries, leading to further expansion of clay galleries and exfoliation into individual layers of clay silicates upon polymerization to PA-6 .
The WVTR for gas barrier PA-MXD6 and its nanocomposite are lower than the corresponding figures pertaining to PA-6. The presence of aromatic rings in the PA-MXD6 causes a reduction in free volume by hindering the motion of the methylene segments, resulting in a higher density of 1.22 g/[cm.sup.3] vs. 1.13 g/[cm.sup.3] for PA-6 and higher glass transition temperature . Table 6 shows water absorption as a function of relative humidity (RH) to be significantly reduced in the PA-MXD6, which may account in part for its reduced water permeability. However, the incorporation of 2 vol% nanoclay in the PA-MXD6 matrix further reduced the WVTR by 38% to 0.85 g.mil/hr.[m.sup.2] as shown in Table 5. Even though this research work is focused on water permeation resistance, it should be noted that PA-MXD6 is widely utilized as a gas barrier due to its superior permeation resistance to oxygen compared with PA-6 and poly ethylene terephthalate (PET) as well as its reduced water uptake vs. ethylene vinyl alcohol (EVA) at higher RH levels.
WVTR for Polymer/Nanocomposite Blends
Table 1 shows PA-6 NCH to be the continuous phase for the composition of 80 wt% PA-6 NCH and 20 wt% polyethylene phase (comprising 16 wt% HDPE and 4 wt% MPE), while it formed the dispersed phase when present at only 20% by weight of the composition. The WVTR in this latter blend was 87% below that for the composition containing 80 wt% PA-6 NCH. Thus, when polyethylene predominated as the continuous phase with nylon nanocomposite as the dispersed phase, the rate of movement of water vapor through the blend was retarded by the chemical dissimilarity between the continuous non-polar matrix and the polar water molecules. It might be noted that the WVTR through neat PA-6 NCH reported in Table 5 is actually lower than that of the blend of this same PA-6 NCH with 20 wt% of HDPE in Table 1, even though chemical considerations would suggest that the HDPE blend should be less compatible with and hence less permeable to water molecules. This unexpected result indicates the complexity of the polymer blend, comprising interfacial regions in addition to the primary phase components.
The compositions and their corresponding changes in WVTR reported in Table 2 show the effect of change in phase continuity from a co-continuous morphology to continuous-dispersed phase morphology upon clay addition to the nylon blend component. For equal amounts of PA-6 and HDPE in the blend without nanoclay, a co-continuous morphology comprising the two polymer phases was observed, as discussed earlier and shown in Fig. 7. Inclusion of nanoclay (2 vol%) in the PA-6 phase increased the viscosity of the phase, as evident in Fig. 5, thus resulting in the PA-6 nanocomposite phase becoming dispersed in a continuous polyethylene matrix, as shown in the micrograph of Fig. 8. These changes in the system were manifested in the corresponding drop in the WVTR shown by the first two compositions in Table 2.
The effect of phase morphology on the permeation resistance of nonclay blends comprising equal amounts of PA-6 and polyethylene was studied by replacing the HDPE with a lower viscosity grade of LDPE (as depicted by Compositions 1 and 3 in Table 2). As shown in the rheological characterizations of Fig. 5 and the morphology observed in Fig. 9, the lower viscosity LDPE component (as compared to HDPE) still formed a continuous phase but PA-6 became a dispersed phase, as a result of change in the flow characteristics of the polyethylene component. The WVTR for this blend composition was observed to be lower than that for the one comprising HDPE and PA-6 components in a co-continuous morphology even though the inherent WVTR of the LDPE is higher than the HDPE (see Table 5).
The relative contributions of composition, morphology and clay content on the reduction of permeation can be estimated as follows: a simple blend having 45 wt% LDPE and 5 wt% MPE as the continuous phase with 50 wt% unfilled PA-6 as a dispersed phase produces a WVTR of 0.90 g.mil/hr.[m.sup.2] (see Table 2). This reduction of the WVTR value is down from 8.51 g.mil/hr.[m.sup.2] for unfilled PA-6 (compositional effect) or 4.23 g.mil/hr.[m.sup.2] on a 50 wt% basis according to the rule of mixtures (morphological effect in forming a co-continuous network). Thus, the level of improvement obtained due only to morphological changes is 79% (from 4.23 g.mil/hr.[m.sup.2] to 0.90 g.mil/hr.[m.sup.2]). Upon addition of clay to PA-6 and maintaining polyethylene as the continuous phase with PA-6 nanocomposite (2 vol% silicate) as a dispersed phase (see Table 2), WVTR dropped further to 0.62 g.mil/hr.[m.sup.2]. This additional 32% improvement due to the addition of clay (as compared with 0.90 g.mil/hr.[m.sup.2]) can be considered a nanocomposite effect upon the observation that the morphology does not further change. Were the small difference in WVTR between the HDPE and LDPE, per Table 2, to be taken into account, the improvement in the nanocomposite WVTR would still be on the order of a significant 22%. These comparisons thus highlight the effects of polymer phase properties and phase continuity that depend on relative viscosities, which can be changed either by incorporating a filler such as nanoclay or through polymer selection.
The effect of clay addition to the dispersed nylon phase of a blend without changing the phase continuity is furthermore explored through the formulations given in Table 3. Inclusion of 2 vol% nanoclay silicate in the PA-MXD6 lowers the WVTR 57% below that of the composition devoid of nanoclay, as shown. The blend with nylon nanocomposite shows a lower water vapor permeation rate than even the HDPE phase alone (see Table 5). This result does not imply that a PA-MXD6 nanocomposite has lower water permeability than neat HDPE (note the data of Table 5 showing a permeation rate for HDPE of 0.30 g.mil/hr.[m.sup.2] and for PA-MXD6 with 2 vol% nanoclay of 0.85 g.mil/hr.[m.sup.2]), but rather some further refinements to the nanocomposite blend morphology perhaps involving clay migration and/or compatibilization, as suggested by the mixed phase morphology pictured in Fig. 10. The use of PA-MXD6 with its higher oxygen barrier resistance in place of PA-6 in this PE blend system opens up the possibility to simultaneously maximize both water vapor and oxygen permeation resistance by optimizing the selection of components, including the incorporation of nanoclay, along with the morphology of the blend.
Table 4 shows the compositions and corresponding changes in WVTR of blends used for studying the effect on permeation rate of nanoclay addition to the compatibilizer component, which might be expected to improve the overall barrier resistance of a nanocomposite blend system even more than its inclusion in the nylon phase due to the resulting higher clay concentration and its effective placement at the interface between the two major polymer components. This approach would be particularly effective when the more permeable phase is dispersed, by isolating it from the permeant. With equal amounts of PA-MXD6 and HDPE phase, the polymer blend as expected formed a co-continuous morphology. The permeation of this blend dropped by 51% (from 0.56 g.mil/hr.[m.sup.2] to 0.27 g.mil/hr.[m.sup.2]) upon addition of nanoclay to the MPE compatibilizer, as shown in Table 4. This percentage reduction is about equal to that reported in Table 2 for PA-6 nanocomposite/HDPE while requiring significantly less total clay (0.16 vol% vs. 1.0 vol%) than that to render the nylon phase discontinuous by addition to the bulk nylon. The preferential location of nanoclay inclusions thus provides opportunities for synergistic permeation reduction.
SUMMARY AND CONCLUSIONS
The meshing of polymer blend and nanocomposite concepts can produce multiphase systems with enhanced barrier properties. Permeation through a nanocomposite blend system depends not only on the polymer properties and phase morphologies but also on the effects of the additional nanoclay inclusions. There are performance attributes which each component of a blend imparts to the overall functioning of the multicomponent system. The polar PA-6 has high affinity for permeant water molecules, while the nonpolar polyethylene phase and the nanoclay present in the systems studied can act as physical barriers for water vapor permeation. Partially aromatic PA-MXD6 nylon can contribute additional permeation resistance by reduced hydrogen bonding due to the presence of aromatic structure, which both reduces availability of the amide functionality for bonding with water molecules and compacts the molecular structure to reduce diffusivity.
The different concentrations of the polymer components along with their respective viscosities and flow field definition determine the phase morphologies, which can be a deciding factor for tailoring penneation properties. The preferential phase partitioning of the nanoclay is dictated by the nature of the permeation barrier required (such as for water, gas, or fuel) and also by the phase morphology and the properties and economics of the blend components. This work has shown the nanoclay partitioning into either the more permeable PA-6 phase or the interphase region between the two incompatible polymer phases to strongly affect the WVTR of the blend.
Controlling the morphology of the blend along with the proper selection of polymer components and nanoclay could lead to optimized water vapor and oxygen permeation resistance. Ultimately, the application requirements define the decision points regarding component selection, blend composition and morphology to optimize utilization of the property attributes of each blend constituent.
Applications of nanocomposite blend systems can be multifold, going beyond penneation resistance to encompass other perfonnance attributes in automotive and industrial applications utilizing a variety of polymer types as blend components. Reduced weight or part density is an important advantage for automotive companies to gain improved fuel economy. Incorporation of a small amount of nanoclay, replacing larger amounts of other fillers and reinforcements in polymer blends, can achieve some of the performance attributes of highly filled systems while providing additional advantages such as better surface appearance, reduced weight, improved flame retardancy, and reduced stress-whitening.
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Nihir A. Bhuva, (1) Lloyd A. Goettler (2)
(1) Daruma Polymer Solutions, Mumbai, India
(2) Department of Polymer Engineering (retired), The University of Akron, Akron, Ohio
Correspondence to: Nihir A. Bhuva; e-mail: email@example.com
This research work was performed at Institute of Polymer Engineering, The University of Akron, Akron, Ohio 44325-0301.
Published online in Wiley Online Library (wileyonlinelibrary.com).
TABLE 1. Blends addressing effect of phase inversion on WVTR. WVTR Compositions PA-6 NCH HDPE MPE (g.mil/hr.[m.sup.2]) 1 80(C) 16(D) 4 3.91 2 20(D) 64(C) 16 0.48 TABLE 2. Blends showing phase inversion attributed to viscosity changes upon addition of nanoclay or PE substitution and effect on WVTR. Vol% silicate Compositions PA-6 in PA-6 HDPE LDPE 1 50(C-C) -- 45(C-C) -- 2 50(D) 2 45(C) -- 3 50(D) -- -- 45(C) WVTR Compositions MPE (g.mil/hr.[m.sup.2]) 1 5 1.20 2 5 0.62 3 5 0.90 TABLE 3. Blends of similar phase morphology showing effect of nanoclay addition on WVTR. WVTR Vol% silicate (g.mil/ Compositions PA-MXD6 in PA-MXD6 HDPE MPE hr.[m.sup.2]) 1 20(D) -- 76(C) 4 0.38 2 20(D) 2 76(C) 4 0.16 TABLE 4. Blends addressing effects of nanoclay addition to the compatibilizer on WVTR. MPE-NC (4 vol% WVTR nanoclay (g.mil/ Compositions PA-MXD6 HDPE MPE in MPE) hr.[m.sup.2]) 1 48(C-C) 48(C-C) 4 -- 0.56 2 48(C-C) 48(C-C) -- 4 0.27 TABLE 5. Measured WVTR of component materials. Materials WVTR (g.mil/hr.[m.sup.2]) HDPE 0.30 LDPE 0.48 PA-6 8.51 PA-6 NCH 3.29 PA-6 with 2 vol% silicate 3.94 PA-MXD6 1.37 PA-MXD6 with 2 vol% silicate 0.85 TABLE 6. Nylon water absorption reported by Williams et al. . % Water absorbed PA type at 23[degrees]C 50% RH 100% RH PA-6 2.8 9.5 MXD-6 1.9 5.8
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|Author:||Bhuva, Nihir A.; Goettler, Lloyd A.|
|Publication:||Polymer Engineering and Science|
|Date:||Jun 1, 2014|
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