Abstract. The results of this chapter has been submitted for publication in Soft Matter.

Transcription

1 Chapter 7 Influence of Filler Loading, Blend Composition and Organic Modification on the Gas Barrier Properties of NR/NBR Blend Nanocomposites - Permeation of O2 and CO2 Abstract In this chapter the gas permeability studies done on NR/NBR/O1Mt nanocomposites are given. The studies have been done by referring mainly to the blend composition, filler loading, preparation method etc. The barrier properties have been studied using two different gases O2 and CO2 and it was found that the permeation of CO2 was higher. The permeability of gas transport was affected profoundly by blend composition and it was found that an increase in NBR component decreased the permeability to an appreciable level. The permeability was also found to decrease with the filler loading. The preparation method also influenced the gas transport behaviour. The modelling of the gas transport behaviour of the blend composites was also done using parallel mode, series model, Maxwell model and Brugmann model to permeability properties of gases on the basis of blend morphology. While Nielson model and Baradwaj model was applied to compare the experimental value based on the dispersion of the nanoclay. 1 1 The results of this chapter has been submitted for publication in Soft Matter.

2 222 Chapter Introduction Combining an elastomer of poor barrier properties with a highly impermeable elastomer, which can be produced by an industrially viable method has significant applications in packaging industries or coating industries. Improvement in barrier properties of polymer blends will be beneficial for applications in pharmaceuticals, packaging of electronic items and particularly packaging of food products, which are sensitive to gaseous molecules. On blending together incompatible polymers results in poor dispersion, in which the dispersed phase is very large and there is a weak adhesion between the two polymers. The morphological development of the blend nanocomposites influences the transport properties of polymer blends to a great extent. Zemboua et al. 1 studied the barrier properties of poly(3-hydroxybutyrate-co- 3-hydroxyvalerate)/polylactide blends prepared by melt mixing. They reported that PHBV imparted better water and oxygen barrier properties to PHBV/PLA blends by acting as an efficient barrier promoter for PLA, even at quite low ratio. Lafitte et al. 2 have studied the influence of the blend composition and morphology on the barrier properties of polyamide 11/ poly (hydroxy amino ether) blend and found that the improvement of hydrogen barrier properties was mainly related to the blend composition whereas a significant effect of the blend morphology was observed on mechanical properties in the rubbery state. Subramanian et al. 3,4 have studied the barrier properties of polymer blends and reported on the influence of morphology of the blend on the barrier property. However, in many cases the required property cannot be reached due toweak adhesion and presence of voids or free volume. This adversity of the incompatible polymers can be reduced to a great extent by incorporating a compatibilizer which can improve the interface and modify the dispersion.

3 Gas barrier properties of In immiscible polymer blends, these compatibilizers can reduce the interfacial tension or influence other parameters like viscosity ratio which influence the homogenous dispersion of the dispersed domains. Thus carefully controlling the morphology, the gas transport through polymer blends can be modified. This is mainly influenced by blend composition, nature of blends, preparation of the blends and the presence of other materials in the blend. The introduction of nanoparticles can impart some significant effect in tuning up the blend morphology. Recently, a lot of work have been reported 5-8 which have made use of nanoparticles as property enhancer or compatibilizer in immiscible polymer blends. Frounchi et al. 9, have studied the gas barrier properties of PP/EPDM blend nanocomposites and found that the oxygen and carbon dioxide permeability of the nanocomposite reduced twice by adding only 1.5 vol% of nanoclay. Yeh et al. 10 have investigated the oxygen barrier properties of clay mineral nanocomposites prepared from modified polyamide (MPA) and nylon-6 clay (NYC) blends and found that at 20 wt.% optimum content of NYC, the oxygen barrier improvement of nanocomposites reached the maximum. 11 All films have been shown to possess superior oxygen barrier properties compared to the plain PE films. Ghanbari et al 12. studied the O2 barrier properties of polymer/organoclay nanocomposites based on poly(ethylene terephthalate) and sulfo polyester blendsand reported that for all the nanocomposite films, the permeability is decreased in comparison to neat PET due to both the presence of clay particles and a higher crystallinity. This proved the strong influence of the nanoclay distribution on the barrier properties. Bitinis 13 et al. have studied the barrier properties of organoclay filled polylactic acid/natural rubber blend bionanocomposites and observed that organoclays were preferentially located at the interface and acted as

4 224 Chapter 7 compatibiliser between both polymer phases and resulted in a marked improvement of the physical and mechanical properties of the system. Here, this chapter reports the analysis of gas transport behaviour through NR/NBR blend nanocomposites with reference to the blend composition, filler loading, nature of permeant and preparation type. The purpose of the study in discussed in this chapter is to know the effect of nanoclay in enhancing the gas barrier properties of immiscible and incompatible NR/NBR blends. The study also aimed in knowing the relationship between barrier properties and morphological development of the blend nanocomposite system. 7.2 Results and discussion Effect of blend composition Barrier properties of oxygen through NR/NBR blends show improvement on increasing the NBR content. The gas permeability values shown in Fig.7.1 shows the extent of improvement compared to gum NR. It can be noted that for 30/70 composition 94% of improvement in gas permeability was observed (improved about 16-fold) by adding only 30 parts, while for 70/30 and 50/50, an 84% and 82% of reduced permeability was observed. This can be attributed to the homogenous dispersion of NR domains in the NBR matrix for 30/70 composition although the NBR content is increased which should have contributed to the reduction in permeation for 50/50. The SEM micrographs show that the blends are heterogeneous in nature and that NR exists as domains in the continuous NBR matrix. The dispersed/matrix morphology of blend offers a more tortuous path for the penetrant 14, thereby reducing the diffusivity through the membrane, which in turn results in the reduction in permeability. For pure NR the chain flexibility is very high due to the low glass transition temperature of NR. So NR becomes the continuous phase for 50/50 and 70/30 composition and offers a comparatively better permeation of O2 thereby increasing the permeability value. The

5 Gas barrier properties of continuous morphology of 50/50 blend composites (Fig.7.2) also contributes to the higher permeability 15. Also the permeability of a gas molecule through a polymeric membrane can be determined from the relationship between cohesive energy density and activation energy given by the equation developed by Meares (Eq.7.1) 16 =/( ( (7.1) Where is the cross section of the penetrant molecule, the jump length and NA is the Avogadro s number and CED the cohesive enrgy density. The polarity of NBR makes the cohesive energy density of NBR high and hence results in low permeability. The reason for the decrease in permeability on adding NBR can thus be clearly explained Permeability g/cm /0 70/30 50/50 30/70 0/100 Blend composition (NR/NBR) Figure 7.1: Oxygen permeability of different NR/ NBR nanocomposites with varying blend composition

6 226 Chapter 7 Figure 7.2: SEM of 50/50 NR/NBR blend Effect of filler loading Incorporating nanoclay into the NR/NBR polymer blend system has reduced the gas permeability of the elastomer films (Fig 7.3 to Fig. 7.5, & Fig.7.7). The inorganic nature of nanoclay makes it impermeable to gases. The large aspect ratio and nano scale dimensions either in exfoliated stage or intercalated stage present large surface area even at low concentration of nanoclay, and there by reduces the area of cross section available for permeation. The tortuosity also is increased in the blend and hence increases the path length of diffusing molecules. This can be observed from the morphological data of TEM given in Fig.7.3 and Fig. 7.4 (inset), Fig.7.6, & Fig.7.8 where the images for different filler loading is given. The decrease in the free volume due to the densely packed polymer chains 17 as a result of interaction between nanoclay with NR and NBR can also be the contributing factor in decreasing the permeability.

7 Gas barrier properties of Permeability (g/cm 2 ) phr 1phr 2phr 5phr 10phr Filler loading (phr) Figure 7.3 Oxygen permeability of NBR nanocomposites with varying filler loading. (inset)the TEM image of NBR nanomposite at 5 phr loading Permeability (gm/cm 2 ) phr 1phr 2phr 5phr 10phr Filler loading (phr) Figure 7.4 Oxygen permeability of NR nanocomposites with varying filler loading (inset) the TEM image of NR nancomposite at 5 phr loading.

8 228 Chapter Permeability (g/cm 2 ) phr 1phr 2phr 5phr 10phr Filler loading (phr) Figure 7.5 Oxygen permeability of 50/50 NR/NBR blend with varying filler loading. Figure 7.6 TEM images showing of 50/50 NR/NBR blend with 2,5 and 10phr nanoclay.

9 Gas barrier properties of Permeability (g/cm 2 ) phr 1phr 2phr 5phr 10phr Filler Loading (phr) Figure 7.7 Oxygen permeability of 30/70 NR/NBR blend with varying filler loading. Figure 7.8 TEM images showing of 30/70 NR/NBR blend with 2,5 and 10phr nanoclay Increasing the clay content to 10% reduced the permeability for all the blend composite although the extent of decrease is different for different blend composite. While for NR nanocomposite a 8 fold improvement in barrier properties was shown the barrier property improvement was only 4 fold for the NBR nanocomposite. While the extent of barrier property improvement was 2 fold, for 50/50 blend nancomposites (Fig 7.7), For 30/70 (Fig 7.7) and 70/30 (Fig 7.8) blend nanocomposites showed a 2.8 fold and 1.5 fold increase

10 230 Chapter 7 at higher clay loading (Fig. 7.9). This shows the difference in dispersion of the nanoclay in these blends which influence the barrier properties. It was interesting to note that all the composites showed a levelling off at higher concentration. It can be considered to be due to the multilayer localization or interfacial saturation as explained in chapter 6. The stacks of nanoclay at the interface or the NBR domains doesn t contribute further in increasing the barrier properties. The low degree of dispersion of clay platelets which gets stacked together can also be another reason and can be further observed from the TEM images. (Fig 7.10) Permeability (g/cm 2 ) phr 1phr 2phr 5phr 10phr Filler loading (phr) Figure 7.9 Oxygen permeability of 70/30 NR/NBR blend with varying filler loading.

11 Gas barrier properties of Figure 7.10 TEM images showing 70/30 NR/NBR blend with a)2 b)5 and c)10phr nanoclay Effect of gas type The effect of size of gas molecules on the permeability property of NR/NBR blend were also observed and is given in Fig The influence of penetrant size clearly contributes to the diffusion of gas molecules. It can be observed that for all the composition the permeability of O2 is very low compared to CO2. It is interesting to find that the CO2 which posses a higher molecular weight is showing higher permeability. One reason for this behaviour is the higher solubility of C02 with rubber. Yet another reason can be explained using Stokes Einstein equation which explains that, diffusion of gas molecules is inversely related to the friction exerted. The eq. (7.2) is given by D=K.T/f..(7.2) Where KB is the Boltzmann constant, T is the absolute temperature, and f is the friction factor which is given by eq (7.3). f=6πμr..(7.3) The increase in radius of the gas molecule the friction factor also increases by the relation and there is a corresponding decrease of permeability. Also on considering the kinetic diameter of the two gas molecules also explains this

12 232 Chapter 7 reduction of permeability for O2. It is reported that among the various descriptions of the sizes of molecules, that most applicable to transport phenomena is called the "kinetic diameter" of molecules. The kinetic diameter is a reflection of the smallest effective dimension of a given molecule. It is given that for O2 the kinetic diameter is 3.4X 10-10m while for CO2 it is 3.3 x10-10 m.this shows that C02 is having lower kinetic diameter than O2 and therefore C02 shows higher permeability than C02. This point is included in the revised thesis Oxygen Carbon dioxide 8000 Permeability (g/cm 2 ) /50(1) 50/50(2) 50/50(5) 50/50(10) Blend composition (NR/NBR/01Mt) Figure 7.11 Comparison of oxygen permeability and carbon dioxide permeability of 50/50 NR/NBR blend with varying filler loading 7.3 Models for permeation Theoretical prediction of polymer blends Models such as Parallel model, Series model, Maxwell model and Brugmann model have been applied to the blend system to predict the permeability properties of gases in homogeneous and heterogeneous blends, on the basis of

13 Gas barrier properties of blend morphology. Equation 7.4 represents the series model where the components are considered to be arranged series to each other and equation (7.5) represents the parallel model =! "! + "..(7.4) 1 " % =! % + " %.(7.5..(7.5)!. where P is the permeability of the blend, P1 and P2 are the permeabilities of components 1 and 2, and φ1 and φ2 are the volume fractions of components 1 and 2, respectively. Two theoretically based models, the Maxwell model and Bruggeman model that were developed to describe transport properties in micro particulate dispersion of one component in a continuous matrix of a second component are also applied to fit the permeation data. The Maxwell model and Bruggeman model given in equation (7.6) and (7.7) respectively corresponds to a morphology with continuous and dispersed phase structure. ) *+,-. =) / ) 8 6) / ). 7 ) 93 / > :;. < = ==..(7.6) ) *+,-. =) /? ). % )/ ; ) 4 *+,-.% )/ ) B.% )/ ;3 A.. (7.7) where Pblend is the blend permeability, Pc, is the permeability of the continuous phase, Pd is the permeability of the dispersed phase, and φd is the volume

14 234 Chapter 7 fraction of the dispersed phase. Using pure component permeability values for each penetrant in NR and NBR, the Maxwell and Bruggeman models predict the dependence of permeability on blend composition. A comparison of blend permeability for O2 values predicted by these models and experimental data is shown in Fig Maxwell Model is valid when the dispersion of dispersed phase are uniformly maximised. The Bruggeman model corresponds to a random packing of dispersed phases. The Maxwell model fits quite well with the experimental value when both the phases are continuous. For 50/50 and 30/70 blends the Maxwell model deviates from the experimental data while the Bruggeman model fits well with the experimental value at all other blend composition, predicting the random arrangement of dispersed phase. Permeability (g/cm 2 /day) Experimental Series Parallel Maxwell Brugmann 100/0 70/30 50/50 30/70 0/100 Blend composition (NR/NBR) Figure 7.12 Theoretical fiittng of the permeability values for different blends

15 Gas barrier properties of Theoretical prediction of permeation for polymer blend nanocomposites Now, to account for the polymer nanocomposite properties, there are several models reported for predicting the properties of composite materials based on the properties of the pure components and the morphology of the composite. They all describe the decrease in permeability in polymer composite, based on different aspects like tortuosity, orientation etc. Although several factors like component properties, such as matrix type, volume fraction, filler aspect ratio, filler orientation, and filler distribution determines the impermeability in the case of filled system, it is the dispersion 18 and distribution of nanoparticles in the polymer matrix that influences the most in barrier properties. However, the main factors behind the improvement in gas barrier properties are not yet fully understood. The reason for the decrease in permeability is affected by different factors. The factors which have decreased the permeablitiy can be found out based on the theoretical equations predicted, based on different factors. One model for polymer filled system which describes the maximum decrease in permeability is Nielsen model 19. According to this theory, if the fillers are impenetrable to a diffusing gas or liquid molecule, then the diffusing molecule should follow a tortuous path, which is the ratio of the actual distance that a penetrant must travel to the shortest distance that it would have travelled in the absence of the layered silicate. It was predicted by Nielson that fillers with large aspect ratio plate - like filler can dramatically reduce the permeability. If the filler particles are substantially impenetrable to a diffusing gas or liquid molecule, then the diffusing molecules must go around the filler particles. As clays are crystalline materials, they are believed to increase the barrier properties by creating a maze or tortuous path that restricts the progress of

16 236 Chapter 7 the gas molecules to pass through the polymer matrices 19. According to this theory, the addition of fillers reduce the gas permeability of polymers as per eq. (7.8)...(7.8) Where "s is the volume fraction of filler and L/2W is the aspect ratio of filler particles, Ps and Pp represent the permeabilities of the nanocomposite and neat polymer respectively. Later Bharadwaj 20 modified the model by correlating the sheet length, concentration, relative orientation, and state of aggregation of the filler in the polymer matrix. This model could thus give further direction in the design of better barrier materials for nanocomposites. Bharadwaj predicted, using equation 7.9 that the relative permeability (Ps/Pp) is a function of the silicate sheet length. Bharadwaj modified the tortuosity factor to include the orientational order (S), writing the relative permeability using equation (7.9)..(7.9) According to Gulsev and Lusti 21 the permeablility levels that can be obtained with nanocomposites are dependent on two factors viz. a geometric factor that reduces the permeability by increasing the diffusion pathways around the platelets and changes in the local permeability due to molecular-level transformations in the polymer matrix. Bhatia et al. 22 have reported the increase of oxygen barrier properties of styrene-butadiene co-polymer montmorillonite based nanocomposites, and attributed it to the increase of the nanoclay/polymer interactions. These interactions would lead to a decrease of

17 Gas barrier properties of the free volume and of the chain segment mobility. This decreases the mobility of each polymer, forming a more compact structure with a smaller free volume than normal polymeric membranes. Yang, et. al 17 in their studies on super gas barrier of all-polymer multilayer thin films, further reports that the interaction between polymers will decrease the mobility of each polymer 23, forming a more compact structure with a smaller free volume, than normal polymeric membranes. In these models, different parameters are considered viz. the aspect ratio, the volume fraction of the impermeable phases, and the orientation of the nanoclay platelets. In the present study, of NR/NBR nanocomposites, the Bhardwaj model and Nielsen model are considered to be more appropriate as it includes the influence of parameters like aspect ratio, the volume fraction of the impermeable phases and the orientation of the nanoclay platelets, according to the equation (7.8) and (7.9) respectively. The fitting of the experimental permeation data for both, the Neilson model and Bhardwaj model is presented in Figure 7.13 and 7.14 respectively. The two equations differ as explained earlier. For Bharadwaj the orientation of the clay layers also is included in the tortuosity factor. Here, the orientation represented as S reduces to Neilson equation when the value of S= 1 i.e. when there is a planar arrangement. An orthogonal arrangement is expected when the value of S = -1/2 i.e. when there is negligible increase in the tortuosity, the permeability will be almost similar to that of neat polymer 24. According to equation (7.9), the tortuosity factor (P1m=P1c) can be as high as 3 29-fold for impermeable platelets with fully dispersed aspect ratios of , at low mineral loadings 25. While Bharadwaj concluded that if the length (L) of the sheet like filler is >500 nm it will be orientated randomly inside the matrix, it was more beneficial for the barrier properties than the case

18 238 Chapter 7 where the sheets were aligned perpendicular to the diffusing path. The two models and their theoretical assumption are given in table 7.1. Table 7.1:- The theoretical assumption of two models used. The experimental data fitted to Nielson model is shown in Fig. 7.13(inset). The fitted aspect ratio is found to be 138nm, which is appreciable compared to the aspect ratio of montmorillonite clay which is reported as approx. 200nm 26. Also it is reported that, for cloiste 10A, aspect ratio is nm, when a high degree of clay dispersion occurs and of approximately 300nm when the clay is exfoliated in the polymer nanocomposite Comparing this with the obtained value, it is suggested that the clay layers have dispersed to a good extent, and have a high intercalation rate although it is not completely exfoliated. Other parameters such as the interactions between polymer and nanoclays and the stiffness of the polymer chain at the vicinity of the nanoclays also should have influenced this factor. Based on the Bhardwaj model (equation 7.9), it is observed that the aspect ratio is found to be 189nm and the calculated order parameter is approximately equal to 0.5 (Fig. 7.14) (Inset). The obtained value of S suggests that the orientation of clay platelets should have existed in between parallel and orthogonal arrangement as it lies in between the two values viz 1 and Both the data fit reasonably well with the experimental results which proves that both

19 Gas barrier properties of tortuosity and orientation of the clay platelets have influenced the permeability of gas molecules through the NR/NBR clay nanocomposites. The TEM images given in Fig. (7.15) also shows aspect ratio to be near to the calculated value based on the Bharadwaj model. Relative permeability of O Model: Neilson Chi^2/DoF = R^2 = L/2W = ± Volume fraction of nanoclay (φ) Figure 7.13 The experimental data fitted to Nielson model for 50/50 NR/NBR/O1Mt naocomposites with different clay loading

20 240 Chapter Model: Bharadwaj Relative permeability of O Chi^2/DoF = R^2 = L/2W = 63.12±13.9 S = 0.47 ± Volume raction of nanoclay (φ) Figure 7.14 The experimental data fitted to Bharadwaj model for 50/50 NR/NBR/O1Mt naocomposiutes with different clay loading Figure 7.15 TEM micrograph of 50/50(5) NR/NBR/O1Mt nanocomposites Fig shows the aspect ratio of the nanoclay found from the TEM micrographs using image j software. Both models could not be validated well as there were changes in aspect ratio compared to theoretical prediction although the experimental value could follow the same trend.

21 Gas barrier properties of Conclusion NR/NBR/cloisite 10A nanocomposite with 2,5, and 10 wt% of nanoclay were prepared for different blend composition. Using TEM and SEM their morphology was examined. Improvement in oxygen permeability was significantly noticed for NR/NBR/Cloisite 10A nano composites with the addition of O1Mt. However, the permeability was found to depend on the blend composition, and permeation rate showed varied improvement with different NR/NBR composition. Although, the stacks of clay and nonuniform dispersion of clay particle was shown in the TEM micrographs, the tortuosity path for the gas molecules was increased sufficiently to make a significant improvement in gas barrier properties. The models for blends like Maxwell model and Bruggemann model l were found to fit well with the experimental values.of NR/NBR/cloisite 10A nanocomposites, and could validate the Bharadwaj model and Nielson's model up to 5wt% of clay content. For higher nanoclay loading, deviation from both was observed due to the presence of clusters and agglomerates.

22 242 Chapter 7 References 1 Zembouai, I., Kaci, M., Bruzaud, S., Benhamida, A., Corre, Y. M., & Grohens, Y. Polymer Testing,2013, 32(5), Lafitte G, Espuche E, Gérard JF, European Polymer Journal 2011, 47, Subramanian, P. M. and Mehra, V. Polymer Engineering Science, 1987, 27: doi: /pen Subramanian, P.M, Koros W.J. (Eds), Polymer Blends: Morphology and Solvent Barriers, Ch. 13 in Barrier Properties of Polymers, American Chemical Society , DOI: /bk Boonprasith, P., Wootthikanokkhan, J., & Nimitsiriwat, N. (2013). Journal of Applied Polymer Science, 130(2), Martinez-Sanz, M., Abdelwahab, M. A., Lopez-Rubio, A., Lagaron, J. M., Chiellini, E., Williams, T. G.,... & Imam, S. H. European Polymer Journal,2013, 49(8), Risse, S., Tighzert, L., Berzin, F., & Vergnes, B. (2014). Journal of Applied Polymer Science. 8 Kang, H., Zuo, K., Wang, Z., Zhang, L., Liu, L., & Guo, B. Composites Science and Technology, 2014,92, Fr Frounchi, M., Dadbin, S., Salehpour, Z., & Noferesti, M.Journal of Membrane Science, (1), Yeh, J. T., Fan Chiang, C. C., & Yang, S. S. Journal of Applied Polymer Science 1997; 64(8): Yeh, J. T., Chang, C. J., Tsai, F. C., Chen, K. N., & Huang, K. S. Applied Clay Science, (1), 1-7.

23 Gas barrier properties of Ghanbari, A., Heuzey, M. C., Carreau, P. J., & Ton-That, M. T. Rheologica Acta, 2013,52(1), Bitinis, N., Verdejo, R., Maya, E. M., Espuche, E., Cassagnau, P., & Lopez-Manchado, M. A.Composites Science and Technology, 2012, 72(2), Pucci Mark S, Blends of immiscible polymers having novel phase morphologies. EPO Patent A1, Johnson, T. "Transport of small molechules trough Natural rubber, epoxidised natural rubber and natural rubberepoxidised natural rubber blends." Ph.D Thesis, Mahatma Gandhi University Meares, P. Journal of American Chemical Society. 1954, 76, Yang, Y. H., Haile, M., Park, Y. T., Malek, F. A., & Grunlan, J. C. Macromolecules, 2011, 44 (6), Takahashi, S., Goldberg, H. A., Feeney, C. A., Karim, D. P., Farrell, M., O'leary, K., & Paul, D. R. Polymer, (9), Nielsen, L. E. Models for the permeability of filled polymer systems. Journal of Macromolecular Science-Chemistry, 1967,1(5), Bharadwaj, R. K. Macromolecules. (2001). 34(26), Gusev, A. A., & Lusti, H. R. Advanced Materials,2001, 13(21), Bhatia, A., Gupta, R. K., Bhattacharya, S. N., & Choi, H. J. Journal of Applied Polymer Science, 2009,114(5), Leväsalmi, J.-M.; McCarthy, TJ Macromolecules 1997, 30, Meera A. P., Effect of spherical and layered type fillers on the morphology and physico mechanical properties of natural rubber

24 244 Chapter 7 nanocomposites. Ph.D Thesis Mahatma Gandhi University, Kottayam, Kerala India Azlina, HN.; Sahrim, HA.; Rozaidi, R.; Bahri, ARS.; Yamamoto, Y.; Kawahara, S. Polymer-Plastics Technology and Engineering 2011,50 (15), Govindjee, S., & Sackman, J. L.,Solid State Communications, (4), Sinha Ray, S., & Okamoto, M. Progress in Polymer Science, (11), Pinnavaia T. and Beall G., Polymer-Clay Nanocomposites, John Wiley & Sons, Ltd., New York (2000) 29 Sontikaew, S. PET/Organoclay nanocomposites. Ph.D. Thesis, Brunel University, School of Engineering and Design.2008.