Mechanical properties melt intercalation

This is a highly polar polymer and crystalline due to the presence of amide linkages. To achieve effective intercalation and exfoliation, the nanoclay has to be modified with some functional polar group. Most commonly, amino acid treatment is done for the nanoclays. Nanocomposites have been prepared using in situ polymerization [85] and melt-intercalation methods [113-117]. Crystallization behavior [118-122], mechanical [123,124], thermal, and barrier properties, and kinetic study [125,126] have been carried out. Nylon-based nanocomposites are now being produced commercially. 

Nylon-6-clay nanocomposites were also prepared by melt intercalation process [49]. Mechanical and thermal testing revealed that the properties of Nylon-6-clay nanocomposites are superior to Nylon. The tensile strength, flexural strength, and notched Izod impact strength are similar for both melt intercalation and in sim polymerization methods. However, the heat distortion temperature is low (112°C) for melt intercalated Nylon-6-nanocomposite, compared to 152°C for nanocomposite prepared via in situ polymerization [33]. 

Lepoittevin, B., Devalckenaere, M., Pantoustier, N., Alexandre, M., Kubies, D., Calberg, C., Jerome, R., and Dubois P. Poly (l-caprolactone)/clay nanocomposites prepared by melt intercalation Mechanical, thermal and rheological properties, Polymer (2002), 43,4017-4023. 

Intercalated and partially exfoliated PVC-clay nanocomposites were produced by melt blending in the presence and absence of DOP and characterised by X-ray diffraction and transmission electron microscopy. The effects of various factors, including volume fraction of clay, plasticiser content, melt compounding time and annealing, on nanocomposite structure and the thermal and mechanical properties of the nanocomposites were also examined. It was found that the best mechanical properties were achieved at 2% clay loading and 5 to 10% DOP loading. 18 refs. 

Examples of the synthesis of polysiloxane nanocomposites reported in the literature include Work by Ma et al (6) who modified montmorilIonite with short segments of PDMS and blended this into a polymer melt/solution to yield examples of fully exfoliated or intercalated PDMS/clay nanocomposites. Pan, Mark et al (7) synthesized well defined nano-fillers by reacting groups of four vinyl terminated POSS cages with a central siloxane core. These materials were subsequently chemically bonded into a PDMS network yielding a significant improvement in the mechanical properties of the polymer. 

Choi, M.H. In, J. Mechanical and thermal properties of phenolic resin-layered silicate nanocomposites synthesized by melt intercalation. J. Appl. Polym. Sci. 2003, 90 (9), 2316-2321. 

Botana et al. [50] have prepared polymer nanocomposites, based on a bacterial biodegradable thermoplastic polyester, PHB and two commercial montmorillonites [MMT], unmodified and modified by melt-blending technique at 165°C. PHB/Na and PHB/ C30B were characterized by differential scanning calorimetry [DSC], polarized optical microscopy [POM], X-ray diffraction [XRD], transmission electron microscopy [TEM], mechanical properties, and burning behavior. Intercalation/exfoliation observed by TEM and XRD was more pronounced for PHB30B than PHB/Na,... 

Variations in the preparation of nanocomposites have now been investigated extensively. Liu et al. [202] proposed the preparation of nylon-6/clay nanocomposites by a melt-intercalation process. They reported that the crystal structure and crystallization behaviors of the nanocomposites were different from those of nylon-6. The properties of the nanocomposites were superior to nylon-6 in terms of the heat-distortion temperature, strength, and modulus without sacrificing their impact strength. This is attributed to the nanoscale effects and the strong interaction between the nylon-6 matrix and the clay interface. More recently, nanocomposites of nylon-10,10 and clay were prepared by melt intercalation using a twin-screw extruder [203]. The mechanical properties of the nanocomposites were better than those of the pure nylon-10,10. 

Three main types of structures, which are shown in Fig. 5.3, can be obtained when a clay is dispersed in a polymer matrix (1) phase-separated structure, where the polymer chains did not intercalate the clay layers, leading to a structure similar to those of a conventional composite, (2) intercalated structure, where the polymer chains are intercalated between clay layers, forming a well ordered multilayer structure, which has superior properties to those of a conventional composite, and (3) structure exfoliated, where the clay is completely and uniformly dispersed in a polymeric matrix, maximizing the interactions polymer-clay and leading to significant improvements in physical and mechanical properties [2, 50-52]. Production of nanocomposites based on polymer/clay can be done basically in three ways (a) in situ polymerization, (b) prepared in solution and (c) preparation of the melt or melt blending [53]. 

Choi and Chung [16] were the first to prepare phenolic resin/layered sihcate nanocomposites with intercalated or exfoliated nanostructures by melt interaction using linear novolac and examined their mechanical properties and thermal stability. Lee and Giannelis [10] reported a melt interaction method for phenolic resin/clay nanocomposites, too. Although PF resin is a widely used polymer, there are not many research reports on PF resin/montmorillonite nanocomposites, and most of the research investigations have concentrated on linear novolac resins. Up to now, only limited research studies on resole-type phenolic resin/layered silicate nanocomposites have been published [17-19] and there is still no report on the influence of nano-montmorillonite on phenolic resin as wood adhesive. Normally H-montmorillonite (HMMT) has been used as an acid catalyst for the preparation of novolac/layered silicate nanocomposites. Resole resins can be prepared by condensation reaction catalyzed by alkaline NaMMT, just as what HMMT has done for novolac resins. 

Kurokawa et al. [258-260] developed a novel but somewhat complex procedure for the preparation of PP/clay nanocomposites and studied some factors controlling mechanical properties of PP/clay mineral nanocomposites. This method consisted of the following three steps (1) a small amount of polymerizing polar monomer, diacetone acrylamide, was intercalated between clay mineral [hydrophobic hectorite (HC) and hydrophobic MMT clay] layers, surface of which was ion exchanged with quaternary ammonium cations, and then polymerized to expand the interlayer distance (2) polar maleic acid-grafted PP (m-PP), in addition was intercalated into the interlayer space to make a composite (master batch, MB) (3) the prepared MB was finally mixed with a conventional PP by melt twin-screw extrusion at 180°C and at a mixing rate of 160 rpm to prepare nanocomposite. Authors observed that the properties of the nanocomposite strongly dependent on the stiffness of clay mineral layer. Similar improvement of mechanical properties of the PP/clay/m-PP nanocomposites was observed by other researchers [50,261]. 

Recently, Ahmadi et al. [320] prepared EPDM/clay nanocomposites with organoclay that was intercalated with MA-grafted EPDM (MA-g-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. 

Sharif et reported that NR/OC nanocomposites were prepared by melt blending using electron beam irradiation as a substitute for sulfur. It was found that the physical and mechanical properties of radiation-induced crosslinking of NR composites with OC were improved due to the presence of nanosize intercalated silicate layers in the NR matrix. Replacing sulfur with radiation-induced crosslinking of NR/OC nanocomposites was not significantly affected by the amount of OC up to 10 phr. Meanwhile, the thermal stability of NR/OC nanocomposites improved with an increase in clay content up to 10 phr. 

Atomic force microscopy (AFM) is another technique used to characterize nanocomposites.AFM can provide information about the mechanical properties of a surface at a length scale that is limited only by the dimensions of the AFM tip. AFM tips with 10 nm radius of curvature are readily available from commercial suppliers. When probing mechanical properties, the attractive and repulsive force interactions between the tip and sample are monitored. Schematic depicting the intercalation process between a polymer melt and an organic-modified layered silicate is shown on Figure 6.8. 

Kong et al. [115] synthesized hy melt-intercalation silicone rubber (SR)/clay nanocomposites using synthetic Fe-montmoriUonite (Fe-MMT) and natural Na-MMT which were modified by cetyltrimethylammoniumbromide, surfactant. They obtained exfoliated and intercalated nanocomposites. With TGA and mechanical performance found that with the presence of iron significantiy increased the onset temperarnre of thermal degradation in SR/Fe-MMT nanocomposites. In addition, the thermal stability, gel fraction and mechanical property of SR/Fe-MMT were different from the SR/Na-MMT nanocomposites, so the iron not only in thermal degradation but also in the vulcanization process acted as an antioxidant and radicals trap. A new flame-retardant system, SR/Fe-OMT based on an EVA matrix, was examined Fang et al. [ 116]. The experimental analyses showed that the exfoliated Fe-OMT had better dispersion in the EVA matrix than Na-OMT, and it was more effective in improving... 

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