Epoxy resins, layered silicate

In this article, recent developments in the formation and properties of epoxy layered silicate nanocomposites are reviewed. The effect of processing conditions on cure chemistry and morphology is examined, and their relationship to a broad range of material properties elucidated. An understanding of the intercalation mechanism and subsequent influences on nanocomposite formation is emphasized. Recent work involving the structure and properties of ternary, thermosetting nanocomposite systems which incorporate resin, layered silicates and an additional phase (fibre, thermoplastic or rubber) are also discussed, and future research directions in this highly active area are canvassed. 

Composites containing both nano- and microparticles possess an even higher wear performance for both types of epoxy matrices. To understand the beneficial effect of calcium silicate (CaSiOj) and its role as internal lubricant, one has to consider the structure of the particles, characterized by silicate layers. Once in contact with the counterpart, the layers may detach and adhere on the metal surface and on the epoxy resin surface. Silicate layers provide protection and may prevent the polymer matrix from severe wear. The microparticles can also protrude out of the matrix and shield it. The steel ring then slides partially on the particle material that is harder than the matrix itself. 

In a study of dental silicate cements, Kent, Fletcher Wilson (1970) used electron probe analysis to study the fully set material. Their method of sample preparation varied slightly from the general one described above, in that they embedded their set cement in epoxy resin, polished the surface to flatness, and then coated it with a 2-nm carbon layer to provide electrical conductivity. They analysed the various areas of the cement for calcium, silicon, aluminium and phosphorus, and found that the cement comprised a matrix containing phosphorus, aluminium and calcium, but not silicon. The aluminosilicate glass was assumed to develop into a gel which was relatively depleted in calcium. 

To take advantage of both modified layered silicate and the substantial presence of phosphorus, the combined use of phosphorus-modified silicates and phosphorus compounds may represent an innovative solution to achieve high levels of flame retardancy. Phosphonium-modified layered silicates in epoxy resins were associated with organo-phosphorus FRs by Schartel et al.59 Ion exchange of Na-montmorillonite was carried out using tetraphenyl phosphonium bromide. Triphenyl phosphate and a reactive phosphorus compound were used as FR incorporated in the epoxy resin. 

B. Schartel, U. Knoll, A. Hartwig, and D. Ptttz, Phosphonium-modified layered silicate epoxy resins nanocomposites and their combinations with ATH and organo-phosphorus fire retardants, Polym. Adv. Technol., 2006, 17 281-293. 

Schartel B, WeiB A, Mohr F, Kleemeier M, Hartwig A, Braun U. Flame retarded epoxy resins by adding layered silicate in combination with the conventional protection layer building flame retardants melamine borate and ammonium polyphosphate. J. Appl. Polym. Sci., 2009, submitted. 

Gilman, J.W., Kashiwagi, T., Nyden, M., Brown, J.E.T., Jackson, C.L., Lomakin, S., Giannelis, E.P., and Manias, E., Flammability studies of polymer layered silicate nanocomposites Polyolefin, epoxy, and vinyl ester resins, in Chemistry cmd Technology of Polymer Additives, Al-Malaika, S., Golovoy, A., and Wilkie, C.A., (Eds.), Blackwell Science, Oxford, U.K., 1999, Chapter 14, pp. 249-265. 

Becker, O., Cheng, Y.-B., Varley, R. J., and Simon, G. R, Layered silicate nanocomposites based on various high functionality epoxy resins the influence of cure temperature on morphology, mechanical properties and free volume, Macmmolecules, 36,1616-1625 (2003). 

As most work reported to date on thermosetting layered silicate nanocomposites involves epoxy resins, this review will focus on this class of thermosetting materials. However, some work pubUshed on other thermosets such as vinyl ester resins and imsaturated polyesters will be included where appropriate. 

Fig. 6 Small-angle x-ray characterization of epoxy layered silicate nanocomposites synthesized using n-CioH2iNH3-montmorillonite (SCIO), Shell Epi-Cure curing agent (W) and Shell Epon 862 resin where q is the scattering vector [47]...

Fig. 18 Glass transition temperature, Tg, of highly crosslinked epoxy nanocomposite systems. The resin systems are diethyltoluene diamine cured octadecylammonium modified layered silicate DGEBA, TGAP and TGDDM [63]...

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