Intercalation polymer melt

Vaia, R.A., Ishii, H. and Giannelis, E.P. 1993. Synthesis and properties of two dimensional nanostructures by direct intercalation of polymer melts in layered silicates. Chemistry of Material 5 1694-1696. 

XRD was used to investigate the spacings of silicate layers of montmorillonite (from 1.9 to 4nm) in PP/montmorillonite (MMT) nanocomposites prepared by in situ graft-intercalation in the presence of acrylamide [331]. Similarly, XRD and TEM were used to study the dispersibility of PP/MMT nanocomposites prepared by melt intercalation using organo-montmorillonite and conventional twin screw extrusion [332]. Various delaminated and intercalated polymer (PA6, PA 12, PS,... 

Since the possibility of direct melt intercalation was first demonstrated [11], melt intercalation has become a method of preparation of the intercalated polymer/ layered silicate nanocomposites (PLSNCs). This process involves annealing, statically or under shear, a mixture of the polymer and organically modified layered fillers (OMLFs) above the softening point of the polymer. During annealing, the polymer chains diffused from the bulk polymer melt into the nano-galleries between the layered fillers. 

In order to understand the thermodynamic issues associated with the nanocomposite formation, Vaia et al. have applied the mean-field statistical lattice model and found that conclusions based on the mean field theory agreed nicely with the experimental results [12,13]. The entropy loss associated with confinement of a polymer melt is not prohibited to nanocomposite formation because an entropy gain associated with the layer separation balances the entropy loss of polymer intercalation, resulting in a net entropy change near to zero. Thus, from the theoretical model, the outcome of nanocomposite formation via polymer melt intercalation depends on energetic factors, which may be determined from the surface energies of the polymer and OMLF. 

R. A. Vaia, E. P. Giannelis, Polymer melt intercalation in organically-modified layered silicates Model predictions and experiment, Macromolecules, vol. 30, pp. 8000-8009, 1997. 

Choudhury et al. [36] in their work on hydrogenated nitrile butadiene rubber (HNBR)-nanoclay systems showed the thermodynamic aspects of nanocomposite formation using the mean-field-lattice-based description of polymer melt intercalation, which was first proposed by Vaia and Giannelis [37]. Briefly, the free... 

As outlined in the introduction, polymer melts can intercalate layered inorganic compounds unassisted by shear or solvents. This is a rather surprising result as it implies that polymer chains can undergo large center of mass displacement in almost two dimensional interstices as the distances between the confining sur-... 

On a global scale, the linear viscoelastic behavior of the polymer chains in the nanocomposites, as detected by conventional rheometry, is dramatically altered when the chains are tethered to the surface of the silicate or are in close proximity to the silicate layers as in intercalated nanocomposites. Some of these systems show close analogies to other intrinsically anisotropic materials such as block copolymers and smectic liquid crystalline polymers and provide model systems to understand the dynamics of polymer brushes. Finally, the polymer melt-brushes exhibit intriguing non-linear viscoelastic behavior, which shows strainhardening with a characteric critical strain amplitude that is only a function of the interlayer distance. These results provide complementary information to that obtained for solution brushes using the SFA, and are attributed to chain stretching associated with the space-filling requirements of a melt brush. 

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. 

Vaia, R.A. Jandt, K.D. Kramer, E.J. Giannelis, E.P. Microstructural evolution of melt intercalated polymer-organically modified layered silicates nanocomposites. Chem. Mater. 1996, 8, 2628-2635. 

V aia, R. A. Giannelis, E.P. Lattice model of polymer melt intercalation in organically-modified layered silicates. Macromolecules 1997,30, 7990-7999. 

Nanocomposites of MMT polymer can be obtained by direct polymer melt intercalation where the polymer chains diffuse into the space between the clay galleries. This process can be carried out through a conventional meltcompounding process [6, 4]. 

FIGURE 5.90 Schematic presentation of two extremes of composite structures that can be obtained by polymer melt intercalation of layered silicates. The rectangular bars represent individual silicate layers (1 nm thick), (a) Single polymer layers intercalated in the silicate galleries, (b) Delamination (exfoliation) of layered silicates and dispersion in a continuous polymer matrix. (After Giannelis, E. R 1996. Adv. Mater., 8(1), 29. With permission.)... 

The manufacturing methods for PLA nanocomposites include intercalation of polymer from solution, polymer melt intercalation and intercalation of a suitable monomer and subsequent in situ polymerization. 

Another route is polymer melt intercalation. This method, an environmentally benign one, uses all types of polymers as well as being compatible with practicing polymer industrial processes such as injection molding, being the most popular procedure to prepare nanocomposites for industrial applications. In this method, polymers, and layered hosts are annealed above the softening point of the polymer [73]. 

Vaia RA, Jant KD, Kramer EJ, Giaimelis EP.(1996). Microstructural evaluation of melt-intercalated polymer-organically modified layered silicate nanocomposites. Chem Mater. 8 2628-35. 

---