Received Date: July 13, 2017 Accepted Date: July 20, 2017 Published Date: September 13, 2017
Citation: Mostafa AD, Zakir MOR, Erdoğan A (2017) Preparation and Characterization of Thermoplastic Elastomers/Plasticizer - Compatibilizer/ Organoclay Nanocomposites by Reactive Extrusion System. Chem Sci J 8: 166. doi: 10.4172/2150-3494.1000166
Copyright: © 2017 Mostafa AD, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Polymer layered silicate nano-composites were prepared in melt by reactive extrusion (25:1 21 mm Rondol twinscrew compounding line) using poly(ethylene-co-propylene- co-ethylidenenorbornene) terpolymer (EPDM) as a matrx polymer, PP-g-MA and poly[(maleic anhydride-alt-1-octadecene)-g-PEO (poly(MA-alt-OD)-g-PEO) as functionalized polymer compatibilizer-internal plasticizer, octadecyl amine-montmorillonite (ODA-MMT) and dimethyldidodecyl ammonium -MMT (DMDA-MMT) as reactive and non-reactive nano-fillers, respectively. The formation of nano structural fragments, polymer blend composition-properties (thermal behavior and morphology) was studied using FTIR, XRD, TGA-DTG and DSC analysis methods. It was found that intercalation/exfoliation degree of EPDM macromolecules significantly depends on the origin and content of organoclays. Better results were obtained for nanocomposites prepared in the presence of reactive organo-filler (ODA-MMT) and PEO grafted alternating copolymer. The results of FTIR (chemical structure) and XRD (physical structure and exfoliation degree) analyses indicate that amidization of anhydride copolymer with alkyl amine groups of organo-filler and esterification of alternating copolymer with α -hydroxy- ω -methoxy- PEO occur in melt compounding in situ processing in the chosen extrusion conditions (barrel temperature: 120, 130, 140 and 145°C, twin-screw speed around 30-40 mrp). The glass-transition (Tg), melting (Tm) and recrystallization (Tc) temperatures strongly depend on the origin and content of organoclay and PEO-grafted copolymer-compatibilizer, respectively. Thermal behavior, crystallinity and thermostability of nanocomposites were significantly improved as compared with pristine EPDM terpolymer.
EPDM rubber; PP-g-MA; Alternating copolymer; PEO; Organoclays; Reactive extrusion; Nanocomposites
In the last decade, an increasing number of research groups in academia and industry focused their research efforts on thermoplastic and thermoset polymer, synthetic and natural rubber silicate layered (PLS), polymer/silica hybrid (PSH) and polymer/carbon nanotube (PCNT) nanocomposites. This considerable scientific and engineering interest has been stimulated by the possibility of the significant improvements in physical, mechanical, thermal and other important specific properties of PLS materials. The results of these studies, especially on PLS were summarized and discussed in several reviews [1-4] and books [5-8].
PLSs are a class of organic-inorganic hydride, composed of organic polymer matrix in which layered silicate particles of nanoscale dimension are embedded because these nanocomposites show enhanced mechanical properties [9-12], fıne dispersed morphology , thermal stability [5,14], gas barrier properties [15-18], and improved chemical resistance  low flammability [3,20-22] and protection effects from corrosion [18,23]. Many industrial applications have emerged since the discovery of organo-silicates. Particularly, the ability of organo- clays to swell and delaminate in organic solvents has led to their widespread use as rheological control agents, as additives in paints, greases, inks, and oil-well drilling fluids, as reinforcement/ filler in plastics and rubber, and as additives to enhance flammability of plastics .
Now organoclays, especially organo-montmorillonite (MMT) are the most widely utilizated silicates in polymer nanotechnology. MMT is a layered silicate, crystal lattice which consists of two silica tetrahedral and one aluminum octahedral sheets with a plate-like structure of 1-nm thickness and 100-nm length . Isomorphous substitution of central metal ion Al3+ by lower-valent metal ions, i.e., Mg2+, Mn2+, results in a charge imbalance of the surface of each platelet. The negative charge imbalance is neutralized by the absorption of hydratable cations, i.e., Na+, Ca2+, being responsible for the hydrophilic nature of MMT  MMT has hydrophilic surface with exchangeable metal ions and does not disperse very well in organic polymers, especially in hydrophobic polymers such as polyolefins, polystyrene, halogen-containing polymers, etc.
Recently, attention of many researchers has been focused on natural and synthetic rubber/organoclayclay nanocomposites due to their high mechanical and gas barrier properties and flame resistance. Many important properties of rubber/clay nanocomposites strongly depend on the dispersion state of organoclay in the rubber matrix. The interlayer spacing and dispersion of the organo-MMT are greatly affected by polar forces between the organoclay and the polymeric matrix material. The layered silicates dispersed at the nanosized level are reported to provide an effective reinforcement to synthetic and natural rubber materials [25-27]. There are very important studies on the preparation and properties of rubber/clay nanocomposites, especially by means of a conventional rubber compounding process. EPDM and its MA grafted derivative were often utilized in preparation of nanocomposites by a melt compounding process. To control the dispersion of the organoclay in polymer blends different reactive copolymers- compatibilizers can be utilized in the blending process, which can significantly influenced the in situ exfoliation and dispersion processing, and therefore, the morphology and mechanical properties of nanocomposites. However, utilization in rubber/organoclay system functional copolymers as reactive compatibilizers is limited with functionalized graft copolymers, predominantly maleic anhydride grafted polyolefins or rubbers.
Recent progress in rubber-organoclay nanocomposites
The layered silicates dispersed at the nanosized level are reported to provide an effective reinforcement to synthetic and natural rubber materials [28-31]. There are very important studies on the preparation and properties of rubber/clay nanocomposites, especially by means of a conventional rubber compounding process. Wang et al.  prepared three kinds of rubber/clay nanocomposites by latex and solution methods. They showed that clay could be dispersed in the rubber matrix as one or several layers, while polymer molecules intercalated to the clay galleries; compared with other methods, the latex method was more convenient and could be widely used to prepare polymerclay nanocomposites. The authors reinforced the nanocomposites and other rubbers with carbon black and then processed with conventional technology, vulcanized, and tested. Rubber-clay nanocomposites were characterized with TEM and XRD. The TEM showed clay had been dispersed to one or several layers. The XRD showed that the basal spacing in the clay was increased. The clay layer could be uniformly dispersed in the rubber matrix on the nanometer level. The mechanical tests showed that the nanocomposites had good mechanical properties. Authors also reported the synthesis and properties of silicone rubber/ organo- montmorillonite hybrid nanocomposites prepared via a melt-intercalation process . The resulting hybrid nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The results proved that the organo-montmorillonite could be exfoliated into ca. 50-nm thickness and uniformly dispersed in the silicone rubber matrix during the melt-intercalation process. Furthermore, the mechanical properties and thermal stability of the hybrids were very close to those of aerosilica-filled silicone rubber. According to the authors, polyurethane nanocomposites form by adding a methylenebis-pphenylene diisocyanate prepolymer to a mixture of organoclay and glycerol propoxylate, stirring at 50°C for 12 h. The mixture was cured at 95°C for 10 h under N2 atmosphere; the alkylammonium exchange ions of the organoclay are assumed to couple to isocyanate groups. Gallery expansion beyond polyol solvation was evidenced by the authors using a broad X- ray diffraction peak at low angle, signifying that intragallery polymerization contributes to the dispersion of nanolayers. They found that the clay nanolayers, even when aggregated in the form of intercalated tactoids, strengthen, stiffen, and toughen the matrix; at a loading of only 10% organoclay whereas the strength, modulus, and strain -at- break increased by more than 100%. According to the authors, the polyurethane-silicate intercalate nanolayer composites have good transparency, reduced water permeability, solvent resistance, making them suitable as packaging materials, protective films, and high barrier sealants.
E-P rubber-clay nanocomposites were prepared by meltcompounding poly[(E-P)-g-MA] with organophilic clay, and their properties were examined by Nasegawa et al. . They found that silicate layers of the used clay exfoliated and homogeneously dispersed in the nanocomposites, which was confirmed by transmission electron microscopy observation. It is thought that MA units (or maleic acid groups generated by hydrolysis) grafted to the E-P polymer chains selectively absorb to the dispersed silicate layers and form strong ionic interaction, because MA units have good affinity to ionic surfaces of silicate layers. According to the authors, the silicate layers, dispersing at the nanometer level, play a role of large pseudo-crosslink points and improve creep resistance of nanocomposites. Nonocomposite technology using small amounts of silicate layers can lead to improved properties of thermoplastic elastomers with or without conventional fillers such as carbon black, talc, etc.
Ethylene -propylene- diene terpolymer (EPDM) is an unsaturated polyolefin rubber with wide applications. However, up to now, there have been very few investigations on grafting of MA onto EPDM in the molten phase and its further utilization in thermoplastics [33-37], as well as on formation of EPDM/organoclay nanocomposites [38-41]. Uzuki et al.  prepared the hybrid nanocomposites based on organophilic montmorillonite (MMT) and ethylene-propylene -diene rubber (EPDM) by a melt compounding process. From the analysis by X-ray diffraction and transmission electron microscopy, authors found that the rubber molecules are intercalated into the galleries of organoMMT and the silicate layers of organoMMT are uniformly dispersed as platelets of 50-80 nm thickness in the EPDM matrix. Dynamic mechanical studies of authors indicate a strong rubber-filler interaction in the hybrid nanocomposite which is manifested in the lowering of tan δ at the glass transition temperature. They demonstrated that the hybrid nanocomposites exhibit great improvement in tensile and tear strength, and modulus and elongationat- break as well as in barrier properties. According to Chang et al. , EPDM/organophilic montmorillonite hybrid nanocomposites could successfully be prepared by a simple melt compounding process. The organoclay prepared by treating sodium montmorillonite with the octadecylammonium ion and subsequently with a low molecular weight EPDM oligomer. X-ray diffraction analysis indicates that matrix rubber molecules could be intercalated into the gallery of the organoclay effectively. Moreover TEM images confirmed that silicate layers of the organoclay are uniformly dispersed on the nanometer scale in the EPDM rubber matrix. The uniform dispersal of the clay nanolayers in the rubber matrix is considered to form a physical barrier against a growing crack, which leads to the increase in the resistance to tearing. These observations of authors indicated that the intercalation of rubber macromolecules into the galleries of organo- MMT can offer the hybrid nanocomposite effective enhancement in toughness, strength and stiffness. In the EPDM hybrid filled with 10 phr of organo-MMT [dodecylammonium cation (C18H37NH3+) modified montmorillonite], the oxygen permeability was decreased to 60% relative to unifilled EPDM. This unique barrier property was explained by the authors in forming dispersion of the impermeable clay with planar orientation in the rubber matrix, as observed by TEM micrographs.
Lee and Goettler  prepared the polymer blend nanocomposites, comprising nanoscale platelets derived from layered silicates treated with an organic modifier in thermoplastic vulcanizates (TPV) and polypropylene/EPDM blend, by direct melt intercalation. Authors showed that the interlayer spacing and dispersion of the organo- MMT are greatly affected by polar forces between the nanoclay and the polymeric matrix material. The structure- property relationship studies of authors in this class of nanocomposites indicate that with the increase of organoclay loading, the tensile modulus of TPV/clay nanocomposites increases by up to 170% at 8 wt% organoclay loading, while tensile strength gradually decreases with increase of organoclay loading. According to the authors, it is possible to control the dispersion of the nanoclay in physical polymer blends using different addition sequences in the blending process, which can significantly affect the phase partitioning and mechanical properties.
Recently, Ahmadi et al.  pepared EPDM/clay nanocomposites with organoclay that was intercalated with MA grafted EPDM (MAg- EPDM) and EPDM-clay composites with pristine clay via indirect melt intercalation method. Authors characterized the dispersion of the silicate layers in the EPDM matrix by XRD and TEM analysis methods. They showed that the particles of organoclay were completely exfoliated in EPDM matrix, and the mechanical, thermal and chemical properties of nanocomposites were significantly improved compared with conventional composites. Yang et al.  reported two processing methods for one-step processing method, in which the elastomer and the filler directly melt blended with PP matrix, and the preparation of PP/EPDM)SiO2 ternary composites:
• One-step processing method, in which the elastomer and the filler directly melt blended with PP matrix, and
• Two-step processing method, in which the elastomer and the filler were mixed first, and then melt, was blended with pure PP. To control the interfacial interaction among the components, authors used two kinds of PP (virgin PP and grafted with MA, PP-g-MA) and SiO2 (treated with or without coupling agent). They found that the formation of filler-network structure could be a key for a simultaneous enhancement of toughness and modulus of PP and its formation seemed to be dependent on the work of adhesion and processing method. It was observed that the formation of filler-network structure was favorable in the two-step processing. According to the authors, in this case, a super toughened PP ternary composite with the Izod impact strength 2-3 times higher than PP/EPDM binary blend and 15-20 times higher than pure PP could be achieved.
Poly(ethylene-co-octene) (PEO) as a relatively new PO elastomer was manufactured by Dow Chemical Co. using a metallocene catalyst. It is known that PEO and PEO-g-MA form homogenous and fine dispersion blend with PP [41-45] and PA/thermoplastic polyurethane (TPU), respectively . Chiu and Chuang reported that the 80PA/20TPU/20POE-g-MA blend prepared by twin screw extrusion has better tensile stress and elongation than non-modified 80PA/20TPU blend, and furthermore, PEO-g-MA significantly improves the impact strength of PA, even to super-toughness grade . Wahit et al. used PEO as an effective toughening agent for preparation of rubber-toughened PP/PA6 nanocomposites [48-51]. They showed that the addition of PEO to the PA6/PP (PA6 (30/70) nanocomposites increased the toughness of the nanocomposites but with limited success due to its immiscibility with PA6. Recenty, these authors prepared PEO elastomer and PEO grafted MA (POE-g-MA) toughened nanocomposites of PP/PA6 containing 4 wt% organophilic modified MMT clay by melt compounding followed by injection moulding. PP-g-MA was used by authors to compatibilize the blend system . According to the authors, elastomer domains of PEO-g- MA show a finer and more uniform dispersion than that of PEO in the PP/PA6/organoclay matrix. They proposed that reduction in dispersed particle size and an increase in adhesion between the phases due to the reaction between the amino group of PA6 and the anhydride group of PEO-g-MA during melt compounding and formation of PEO-g-PA6 copolymer are important factors for the toughness and morphology improvement of these blends.
Natural rubber (NR) is widely used in various applications particularly for tires because of its excellent elastic properties over other synthetic counterparts. However, its non-polar character limits its application due to poor oil resistance and high air permeability . Grafting of MA or other polar monomers onto NR backbone improves the compatibility between NR and other polar elastomers and some engineering plastics such as polyamide. According to several authors [53-59], the grafting process of MA onto polydienes, such as NR, styrene-isoprene, and styrene- butadiene-styrene block copolymer, involves two different mechanisms, i.e., radical-induced grafting and thermal grafting via an ene mechanism. For the ene mechanism, high temperature (160-240°C) is required for the fixation of MA to polydiene backbone. In the case of radical mechanism, the reaction usually occurs quickly and at a lower temperature than the ene reaction . The MA modification of different kinds of rubbers is a useful way of compatibilizing immiscible polymer blends as well as improving interfacial adhesion in polymeric composites. Thus, the modification of EPDM rubber with MA in a twin screw extrusion process has been described by Oostenbrink and Gaymans . They proposed that the knowledge of MA content in the rubber by covalent linking is important not only to evaluate its application but also to choose the best manner of grafting. Couitinho et al. . Chemically modified the EPDM elastomer (1.7% of norbornene unit) with MA in chlorobenzene solution with benzoyl peroxide as an initiator. The presence of MA grafting on elastomer was determined by MR-FTIR analysis using 1856 and 1780 cm-1 band of anhydride carbonyl groups. The above mentioned, developed rubber functionalization methods via introducing polar units, especially MA will also definitely help in the utilization of these graft copolymers for the preparation of various polymer silicate layered nanocomposites with fine dispersion mineral clay, organoclay and silica particles [62-66] 1-origin,13,17,18,23]. Hakim and Ismail  prepared natural rubber (NR)/organoclay nanocom- posites by using maleated NR. They investigated the effect of organoclay content on the curing characteristics, mechanical and thermal properties and morphology of NR based nanocomposites. It was shown that organoclay filled NR nanocomposites with maleated NR exhibit shorter processing time, higher tensile properties and homogeneous dispersed morphology.
In this work, we firstly used dual compatibilizers such as poly(MA-alt-OD)/PP-g-MA and poly(MA-alt-OD)-g- PEO/PP-g- MA in the EPDM/organoclays (reactive and non-reactive) systems. General schemes of proposed in situ physical and chemical interfacial interaction during the melt compounding processes can be represented as follows (Figures 1-3).
The rubber/clay nanocomposite quality depends on the nature of organoclay particles and their contact area and force of interfacial interaction with polymer chains during melt compounding, the matrix polymer flow properties, the geometry of the mixer in the reactive extruder and the operating conditions such as temperature, mixing time and rotor speed. All these factors provide the effective in situ intercalation and exfoliation processing, which are responsive to the formation of nanostructures in rubber/organoclay nanocomposite. Taking into consideration this principle, we have utilized the following row materials-additives and nano processing methods to design and prepare a new generation of rubber/clay nanocomposites .
EPDM rubber was utilized as a matrix polymer in the preparation of silicate layered nanocomposites with different compositions. Some important properties of this rubber are presented in Tables 1 and 2. Well known physical and chemical structures of montmorillonite (MMT) mineral clay, organicderivatives of which are important components of the studying rubber/clay nanocomposites, were presented in Figure 4.
|Specific density (g/cm)||0.91|
|Melt Flow Index (MFI, 190°C/2.16Kg) (g/10 min)||1|
|Mooney Viscosity (at 125°C, MU)||20|
|Glass-transition temperature (T,°C)||1.53|
|Melting point (°C)||94.3|
|Degradation temperature (T (max),°C)||474|
|Content of ethylene unit (%)||85|
|Coontent of propylene unit (%)||10.1|
|Content of Ethylidenenorbornene monomer (ENB) unit (%)||4.9|
Table 1: Main properties of poly(e-co-p-co-dm) terpolymer rubber (dow chem. Co., hydrocarbon rubber nordal ip 4820) as a matrix polymer.
|Poly(EPDM) rubber||matrix polymer||85|
|NC-1||PP-g-MA (2%) ODA-MMT||reactive ONF-1||5|
|Poly(EPDM) rubber||matrix polymer||85|
|NC-2||PP-g-MA (2%) DMDA-MMT||non-reactive ONF-2||5|
|Poly(EPDM) rubber||matrix polymer||84.5|
|Poly(EPDM) rubber||matrix polymer||84.5|
|Poly(EPDM) rubber||matrix polymer||83.5|
Table 2: Components and composition of rubber/organoclay blends.
Chemical structures of the bases additives and their nanocomposites
Chemical structure of individual components and matrix polymer and their nanocomposites were studied by FTIR (Figures 5-7) and H (13C) NMR (Figures 8 and 9) spectroscopy. The formation of amide and H-bonded carboxyl fragments in the structures of nanocomposites were confirmed by FTIR analysis (Figure 7). Appearance of new absorption bands in the carbonyl region such as 1700, 1640 and 1575 cm-1 were observed. These bands are associated with C=O stretching in the –COO–, carboxylic (H-bonding) and amide groups, respectively. Presence of the characteristic chemical shits in NMR (1H and 13C) spectra (Figure 8) from anhydride and octadecyl units with fixed areas (or integral curves) and intensities confirmed alternating structure of copolymer.
Structure of α-hydroxy-ω-methoxy-PEO was confirmed with presence of characteristic chemical shifts in the NMR (1H and 13C) spectra (Figure 9) from protons of the side-chain (CH2-O)n group and terminated end CH2-OH and OCH3 groups at 3.24, 3.42 and 3.13 ppm, and from carbon atoms of these groups at 70.2, 72.8 and 62.6 ppm, respectively.
Interpretation of XRD powder diffraction analysis (physical structure)
To evaluate the effects of organoclay nanofillers (reactive ONF-1 and non-reactive ONF-2) and dual copolymer-compatibilizers (PP-g- MA and alternating anhydride-1-octadecene copolymer) natures on the in situ interfacial interactions and intercalating/exfoliating processes during melt compounding of the various PEPDM/compatibilizers/ organoclay nanofiller reactive blends, we have performed XRD patterns for the utilized individual components and their nano-composites. The results of these analyses were illustrated in Figures 10-14, and summarized in Table 3. Addition of novel functional copolymerpoly( MA-alt-1-octadecene)-compatibilizer increases the exfoliation degree and crystallinity of nanocomposites (Figure 13, NC-1 and NC-2).
Table 3: XRD Parameters of Poly(Epdm)/Poly(Ma-Alt-Od) Or Poly(Ma-Alt-Od)-G-Peo/Pp-G-Ma/Organo-Mmt Nanocomposites.
The comparative analysis of XRD spectra of matrix (a) polymer (Figure 11) and conventional graft copolymer- compatibilizer (Figure 12) with those for NC-1 prepared in the presence of alternating copolymercompatibilizer and reactive organoclay (ODA-MMT) indicates a dramatic change of main crystallographic peaks in the matrix polymer pattern which transferred from multi-peak image to one relative broad peak at 2θ=21.5° (d-spacing=5.273 Å). This fact can be explained by the formation of compact crystalline structure with high exfoliation degree of the matrix polymer chains between silicate galleries. Similar effect with appearance of a main broad peak (d- spacing=4.19 Å (Figure 14a, NC-3) was observed by an addition of lower amount of end hydroxylfunctionalized PEO (Mn=2000 g/mol). It can be proposed that added PEO undergoes a chemical reaction, i.e., esterification of anhydride units from dual compatibilizers, especially from alternating copolymer, and insisted on a role of internal plasticizer via formed flexibile long ester-ether side-chain branches in the melt extrusion conditions.
However, in the presence of alternating copolymer-compatibilizer and non-reactive DMDA-MMT clay (Figure 13b-NC-2) and reactive ODAMMT clay position of all peaks is not changed but their intensities significantly increase, especially an intensity of main peak (NC-4) increases more than 6 times after addition of PEO (1.5 wt%).
It was observed that the almost disappearance of characteristic peaks with d-spacing 10.96 (1:2 silicate layers) in XRD patterns of NC-1 and NC-3 and their shift. To a lower region due to the d001 basal reflections in all samples of the nanocomposites. These observed changes clearly indicate the significant increase of interlamellar distance (Δd=dnc-dº) (Table 3) due to in situ processing through complex formation and amidization reactions between anhydride and surface alkyl amine groups, as well as increasing in crystallinity of nanocomposites as compared with pristine PEPDM matrix polymer. This can also produce a driving force necessary for the effective intercalation and exfoliation of matrix polymer chains between delaminated silicate layers. The results of comparative XRD analysis of pristine EPDM matrix polymer and its nanocomposites prepared in melt by reactive extrusion in the presence of two types of organoclays and dual polymeric compatibilizers such as conversional PP-g-MA, specific poly(MA-alt-OD) and poly(MA-alt- OD)-g-PEO indicate the structural changes and improvement of the important properties of nanocomposites. The rubber macro-molecules are intercalated/exfoliated into the silicate layers of organo- MMT clays with higher values of d -spacing for the EPDM/organoclay systems due to the chemical (amidization and esterification in situ reactions) and physical (strong H-bonding) interactions between reactive polymer compatibilizers and alkyl amine (or ammonium cation).
Nanocomposite structure-composition-thermal behavior relationships
In this part, we have investigated the effects of structure and composition of the PEPDM matrix polymer, individual componentsadditives and their nanocomposites on the thermal parameters such as glass- transition (Tg), melting (Tm), crystallization (Tc) and enthalpy of phase transitions (ΔH), thermal degradation and stability (Td), etc. These parameters were determined by thermo graphical (TGA), differential thermo graphical (DTG), differential thermal (DTA) and differential scanning calorimetric (DSC) analysis methods. Obtained results were illustrated in Figures 15-19 and summarized in Table 4.
|NCs and their Individual components||Tm-1 (°C)||?Hm-1 (J/g)||Tm-2 (°C)||?Hm-2 (J/g)||Td (°C)|
Table 4: Thermal Parameters [Melting Point (Tm), Glass-Transition (Tg) and Degradation (Td(Max))] of Epdm Layered Silicate Nanocomposites (Nc) and their Individual Components.
As seen from Figure 15a, alternating copolymer only exhibits glasstransition at 133°C and multi-steps of degradation which accompanied decarboxylation of anhydride units around 200-250°C. While PEO (Mn=2000 g/mol) shows Figure 15b) melting transition is observed at 62.8C and relative narrow peak of chain degradation at 390°C. Thus copolymer has a rigid- amorphous structure but PEO is a flexible crystalline polymer. Both polymers contain reactive OH and anhydride groups, respectively.
It was observed that in the DSC curves of both the organically modified (intercalated) MMT clays (Figure 16a and 16b) Tg-transitions appear which can be related to the transition of surface organic linkages of these clays. Broad endo-peaks are associated with the melting of various crystalline structures (around 150-310°C) of mineral clays. Pristine Na+-MMT clay does not exhibit any glass-transition, but shows very broad melting endo-peak at higher temperature region. All the MMT clays demonstrated higher thermal stability. TGA and DCS curves of PEPDM matrix polymer (Figure 17) show the Tg (1.53°C) and Tm (94.3°C) transitions in the lower temperature regions similar to the other polymer elastomers. This polymer can be related to a class of synthetic rubber with semi-crystalline structure.
The results of TGA and DCS analyses of the PEPDM based nanocomposites prepared in the presence of dual compatibilizers and two types of organoclays are illustrated in Figure 18. It was found that new endo-peaks (Tm2) appear in the DSC curves (Figures 18b and 18c) of both the nanocomposites, and characteristic Tm1 transition valuefor matrix polymer chains visibly decreases. New melting peaks at 163.9°C for ODA-MMT based nanocomposites and at 169.8°C for DMDAMMT based nanocomposites, which are associated with melting of exfoliated crystalline nanostructures, show different areas (ΔH), i.e., different degree of crystallinity.
This fact can be explained by the different mechanisms of nanostructure formation in both nanocomposites.
In the presence of reactive ONF-1 in situ interfacial interactions occur via chemical reactions but for nanocomposites prepared with non-reactive ONF-2 these interactions occur only via physical reactions (strong H- bonding).
Above mentioned proposal is confirmed by the comparative analysis of crystallization process of the pristine matrix polymer and its nanocomposites in the cooling conditions (Figure 18).
It was observed that re-crystallization of PEPDM matrix polymer proceeds rapidly (Δ=Tm-Tc=7.8°C) as compared with nanocomposites (Δ=Tm-Tc=51.8°C for ONF-1 and Δ=Tm-Tc=65.2°C for NCF-2) due to higher flexibility of the rubber chains and compact crystalline structure of nanocomposites, respectively. However, crystallization temperature of PEPDM chains in both nanocomposites is almost constant.
Addition of small amount (0.5 wt%) of end OH- functionalized PEO in polymer blends containing reactive dual compatibilizers and ONF-1 and ONF-2 significantly changes thermal behavior, especially melting and crystallization temperatures (Figure 19 and Table 4). It was observed as a decrease in Tm1 (matrix polymer), Tm2 (nanocomposites) values in these systems. This is a reasonable agreement which confirm the effect of PEO as internal plasticizing agent in melt reactive compounding processes via in situ chemical and physical interactions with anhydride units of used copolymer- compatibilizers.
In summary, this work presents a new approach in the preparation of EPDM/organoclay nanocomposites which are synthesized by reactive extrusion compounding in the presence of alternating copolymer and its PEO branched derivative as novel effective compatibilizerinternal plasticizers and organoclays as reactive and non-reactive nano -fillers which are able to interact with anhydride units of functional copolymers in situ processing via amidization and strong complex formation (H-bonding) reactions. in situ processing and properties of nano- composites strongly depend on the origin of organoclays and content of compatibilizer-internal plasticizer (especially content of branched PEO linkages); rubber nanocomposites prepared in the presence of reactive ODA-MMT clay and poly(MA-alt-OD)-g-PEO exhibit relatively high performance properties. New Tm endo-peak which can be related to nanostructure and significant increase of crystallinity and thermal parameters were observed. The vulcanization of these novel nanocomposite systems by means of a conventional rubber compounding process will be a subject our future investigations in collaboration with Standard Profile Automotive Ind. & Com. Inc. (Düzce-Turkey).