Melt intercalation, silicate properties

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. 

Polypropylene (PP) is one of the most widely used plastics in large volume. To overcome the disadvantages of PP, such as low toughness and low service temperature, researchers have tried to improve the properties with the addition of nanoparticles that contains p>olar functional groups. An alkylammonium surfactant has been adequate to modify the clay surfaces and promote the formation of nanocomposite structure. Until now, two major methods, i.e., in-situ polymerization( Ma et al., 2001 Pirmavaia, 2000) and melt intercalation ( Manias et al.,2001) have been the techniques to prepare clay/PP nanocomposites. In the former method, the clay is used as a catalyst carrier, propylene monomer intercalates into the interlayer space of the clay and then polymerizes there. The macromolecule chains exfoliate the silicate layers and make them disperse in the polymer matrix evenly. In melt intercalation, PP and organoclay are compounded in the molten state to form nanocomposites. 

The synthesis of polymer nanocomposites is an integral aspect of polymer nanotechnology. By inserting the nanometric inorganic compounds, the properties of polymers improve and hence this has a lot of applications depending upon the inorganic material present in the polymers. The improvements obtained in day/PP nanocomposite structure can make this commercial thermoplastic polymer more suitable for automotive, construction and packaging applications. Different alkyl ammonium surfactants and compatibilizer was used to produce layered silicate/PP nanocomposites by the same melt intercalation technique. 

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. 

The PLA layered silicate nanocomposites were prepared by adding small amounts of the compatibilizer to form the randomly distributed intercalated silicate layers. Simple melt extmsion of PLA and organically modified montmorillonite lead to better parallel stacking of silicate layers and much stronger flocculation due to hydroxylated edge-edge interactions of silicate layers and consequently improved mechanical and barrier properties, which makes it suitable for food packaging applicatioa Fmther, Bondeson et al. used melt extmsion to fabricate a transparent bio-based nanocomposite of 5 wt% cellulose nanowhiskers (CNW) and cellulose acetate butyrate (CAB), plasticized by triethyl citrate (TEC) (2007). 

Lee, J. H., Jung, D., Hong, C. E., Rhee, K. Y, and Advani, S. G. Properties of polyethylenelayered silicate nanocomposites prepared by melt intercalation with a PP-g-MA compatibilizer. Composites Science and Technology, 65, 1996-2002 (2005). 

In other studies [307, 308], this same group produced bionanocomposites by melt intercalation of PCL and MMT modified by various alkylammonium cations. Depending on whether the ammonium cations contain nonfunctional alkyl chains or chains terminated by carboxylic acid or hydroxyl functions, microcomposites or nanocomposites were produced. The layered silicate PCL nanocomposites exhibited some improvement in mechanical properties and increased thermal stabihty as well as enhanced flame retardancy. The authors concluded that formation of PCL-based nanocomposites, not only depended on the nature of the ammonium cation and its functionaHty, but also on the selected synthetic route, that is, melt intercalation versus in situ intercalative polymerization. 

Nanometer-scale composites prepared from layered inorganic materials, especially clay, and polymers have also attracted much attention because of their unique optical, thermal, mechanical, gas barrier, and electrical properties. There are many reports describing polymer-clay nanocomposites. " The clay can be, for example, a sihca or silicate. In such a hybrid composite, weak dipolar and van der Waals forces provide the driving force for interactions between the layers, and they result in galleries being formed. There are three types of clay-polymer composites conventional, intercalated, and exfohated. Three mediods are widely used for the preparation of polymer-clay hybrid nanocomposites intercalation by in situ polymerization, direct intercalation, and polymer melt intercalation. Each of these methods has its advantages and disadvantages. For example, the in situ polymerization works only in tiie... 

Vaia R. A. and Giannelis E. P., Lattice model of polymer melt intercalation in organically-modified layered silicates , Macromolecules, 1997, 30, 7990-7999. Manias E., Touny A., Wu L., Lu B., Strawhecker K., Gilman J. W., and Chung T. C., Polypropylene/montmorillonite nanocomposites. Review of the synthetic routes and material properties , Chem Mater, 2001, 13, 3516-3523. 

---