Polymer/layered silicate nanocomposites: a review from preparation to processing

A review is given of the academic and industrial aspects of the preparation, characterization, materials properties, crystallization behavior, melt rheology, and processing of polymer/layered silicate nanocomposites. These materials are attracting considerable interest in polymer science research. Hectorite and montmorillonite are among the most commonly used smectite-type layered silicates for the preparation of nanocomposites. Smectites are a valuable mineral class for industrial applications because of their high cation exchange capacities, surface area, surface reactivity, adsorptive properties, and, in the case of hectorite, high viscosity and transparency in solution. In their pristine form they are hydrophilic in nature, and this property makes them very difficult to disperse into a polymer matrix. The most common way to remove this difficulty is to replace interlayer cations with quarternized ammonium or phosphonium cations, preferably with long alkyl chains. 0079-6700/03/$ see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.progpolymsci.2003.08.002 Prog. Polym. Sci. 28 (2003) 1539–1641 www.elsevier.com/locate/ppolysci * Corresponding author. Tel.: þ81-52-809-1863; fax: þ81-52-809-1864. E-mail addresses: [email protected] (S. Sinha Ray); [email protected] (M. Okamoto). Abbreviations: AA, acrylamide; AEA, N,N-dimethylaminoethyl acrylate; AFM, atomic force microscopy; AIBN, N-N0-azobis (isobutyronitrile); AN, acrylonitrile; ANI, aniline; APES, aliphatic polyester; ATRP, atom transfer radical polymerization; BDMA, benzyldimethylamine; BPO, dibenzoyl peroxide; CEC, cation exchange capacity; CL, 1-caprolactone; CSA, camphorsulphonic acid; DBSA, docecylbenzenesulfhonic acid; DETDA, diethyltoluene diamine; DGEBA, diglycidylether of bisphenol A; DMA, dynamic mechanical analysis; DMF, dimethylformamide; DSC, differential scanning calorimetry; EG, ethylene glycol; EPDM, ethylene propylene diene methylene linkage rubber; EPR, epoxy polymer resin; EVA, poly(ethylene-co-vinyl acetate); FTIR, Fourier transformed infrared; HBP, hyperbranched polymer; HDPE, high-density polyethylene; [(HE)2M1R1], bis(hydroxyethyl)(methyl)-rapeseedquaternary ammonium; HHMPA, hexahydro-4methylphthalic anhydride; IC, isophthaloyl chloride; MAO, methylaluminoxane; MMA, methyl methacrylate; M-MDI, 4,40-di-phenymethylate diisocyanate; MMT, montmorillonite; MPP, modified polyether polyol; N6, nylon-6; NMR, nuclear magnetic resonance; NVC, Nvinylcarbazole; OMLS, organically modified layered silicate; PAA, N,N-dimethylaminopropyl acrylamide; PANI, polyaniline; PBO, polybenzoxazole; PBS, poly(butylene succinate); PBT, poly(butylene terephthalate); PC, polycarbonate; PCL, poly(1-caprolactone); PDS, poly (dimethyl siloxane); PDT, polymer delamination temperature; PE, polyethylene; PEG, poly(ethylene glycol); PEI, poly(etherimide); PEO, polyethylene oxide; P2Epy, poly(2-ethanylpyridin); PET, poly(ethylene terephthalate); PEVA, poly(ethylene vinyl alcohol); PHA, polyhydroxyamide; PHB, polyhydroxy butyrate; PI, polyimide; PLA, polylactide; PLS, polymer/layered silicate; PMMA, poly(methyl methacrylate); PMT, poly(trimethylene terephthalate); PNVC, poly(N-vinyl carbazole); PP, polypropylene; PP-MA, maleic anhydride grafted polypropylene; PPV, poly( p-phenylene vinylene); PPY, polypyrrole; PSF, polysulfone; PSPI, polystyrene–polyisoprene; PS, polystyrene; PVA, poly(vinyl alcohol); PVP, poly(N-vinyl pyrrolidone); PU, polyurethane; PUU, polyurethane urea; QAþ, quaternaryammonium cation; S, styrene; SAN, poly(styrene-co-acrylonitrile); sap, saponite; SAXS, small angle X-ray scattering; SFM, synthetic fluorine mica; SPN, diethylmethylammonium modified smectite; sPP, syndiotactic polypropylene; STN, methyltrioctilammonium modified smectite; TEM, transmission electron microscopy; TGA, thermogravimetric analysis; TGAP, trifunctional triglycidyl p-amino phenol; TGDDM, tetrafunctional tetraglycidyldiamino diphenylmethane; THF, tertrahydrofuran; WAXD, wide angle X-ray diffraction. A wide range of polymer matrices is covered in this review, with special emphasis on biodegradable polymers. In general, polymer/layered silicate nanocomposites are of three different types, namely (1) intercalated nanocomposites, for which insertion of polymer chains into a layered silicate structure occurs in a crystallographically regular fashion, with a repeat distance of few nanometers, regardless of polymer to clay ratio, (2) flocculated nanocomposites, for which intercalated and stacked silicate layers flocculated to some extent due to the hydroxylated edge–edge interactions of the silicate layers, and (3) exfoliated nanocomposites, for which the individual silicate layers are separated in the polymer matrix by average distances that depend only on the clay loading. This new family of composite materials frequently exhibits remarkable improvements of material properties when compared with the matrix polymers alone or conventional microand macro-composite materials. Improvements can include a high storage modulus, both in solid and melt states, increased tensile and flexural properties, a decrease in gas permeability and flammability, increased heat distortion temperature, an increase in the biodegradability rate of biodegradable polymers, and so forth. q 2003 Elsevier Ltd. All rights reserved.