Topics


Polymer/layered silicate nanocomposite technology is not only suitable for the significant improvement of mechanical and various other materials properties of virgin polymers, it is also suitable to enhance the rate of biodegradation of biodegradable polymers such as polylactide. The biodegradability of polylactide in nanocomposites is completely depends upon both the nature of pristine layered silicates and surfactants used for the modification of layered silicate, and we can control the biodegradability of polylactide via judicious choice of organically modified layered silicate.

Macromole. Mater. Eng., 2003, 288, 203

The crystallization behavior of pure Nylon 6 and its nanocomposite with montmorillonite has been studied in detail. The crystallization rate of N6 is faster in thepresence of clay compared to pure Nylon 6, as revealed by light scattering experiments. Nylon 6 crystallizes exclusively in the g-form in the nanocomposite because of the epitaxial crystallization, which is also revealed from the transmission electron microscopic images (sandwiched structure) of the crystallized sample. The storage modulus of the nanocomposite is always higher than the pure Nylon 6, irrespective ofcrystallization temperatures. Much higher increment of storage modulus for pure Nylon 6 with increasing crystallization temperature is explained by the higher amount of the thermally stable a-form at higher temperature. A unique mechanism has been proposed to illustrate the crystallization behavior of Nylon 6 in the presence of the clay particles.

Macromole. Mater. Eng., 2003, 288, 440




Intercalated polycarbonate (PC)/clay nanocomposites (PCCN)s have been prepared successfully through melt intercalation method in presence of compatibilizer. The internal structure and morphology of the PCCNs has been established by using WAXD and TEM, respectively. The morphology of these nanocomposites and degradation of the PC-matrix after nanocomposites preparation can be controlled by varying surfactants used for the modification of clay and compatibilizers. The intercalated PCCNs exhibited remarkable improvements of mechanical properties when compared with PC without clay. We also discuss foam processing of PCCN by using supercritical CO2 at 10MPa in a batch process.

Macromole. Mater. Eng., 2003, 288, 543



Via a batch process in an autoclave, the foam processing of neat polylactide (PLA) and two different types of PLA/layered silicate nanocomposites has been conducted using supercritical carbon dioxide as a foaming agent. The morphological correlation between the dispersed silicate particles with nanometer dimensions in the bulk andthe obtained closed-cell structure of the foam is discussed. This is the first report that deals with the possibility of preparing biodegradable nanocellular polymeric foams via nanocomposite technology.

Macromol. Rapid Commun., 2003, 24, 457

This paper describes the preparation, characterization and materials properties of very new high performance biodegradable nanocomposite materials based on polylactide (PLA) and organically modified synthetic fluorine mica (OMSFM). The gas barrier properties of neat PLA significantly improved after nanocomposites preparation (see Figure) and are almost comparable to that of PET.

Chem. Mater., 2003, 15, 1456




The preparation, characterization, materials properties, biodegradability, crystallization, melt rheology, and foam processing of pure PLA and various kinds of PLA/organically modified layered silicate nanocomposites are discussed. These are new types of plant and natural materials. When disposed of in compost, these are safely decomposed into carbon dioxide, water, and humus through the activity of microorganisms. The carbon dioxide and water will become corn or sugarcane again through plant photosynthesis (see Figure). Thus, these materials hold future promise for potential applications as high-performance biodegradable materials and open a new dimension for plastics and composites.

Macromol. Rapid Commun., (Feature Articles) 2003, 24, 815-840

Intercalated polylactide/layered silicate nanocomposite was prepared by simple melt extrusion of PLA and organically modified montmorillonite. The detailed crystallization kinetics and morphology of neat PLA before and after nanocomposite preparation were studied by using polarized optical microscopy, light scattering, differential scanning calorimetric, wide angle X-ray diffraction analyses. The overall crystallization rate and spherulitic texture of pure PLA were strongly influenced in presence of clay particles.

Macromolecules 2003, 36 (19), 7126-7131


The measurement of rheological properties of any polymeric material under molten state is crucial to gain fundamental understanding of the processability of that material. In case ofpolymer/layered silicate nanocomposites, the measurements of rheological properties are not only important to understand the nature of processability of these materials but also important to find out the strength of polymer- layered silicate interactions and structure-property relationship in nanocomposites, because rheological behaviors are strongly influenced by their nanoscale structure and interfacial characteristics. In order to get these knowledge in case of polylactide (PLA) /montmorillonite (mmt) nanocomposites, we have studied rheological properties of these materials in detail. On the basis of rheological data, we have conducted foam processing of neat PLA and one representative nanocomposite via newly developed pressure cell technique using carbon dioxide as a physical blowing agent.

Macromol. Mater. Eng., 2003, 288, 936-944

Development of structures in new cycloolefin copolymers (COCs) of ethylene-norbornene (E-NB) and ethylene-tetracyclododecene (E-TD) of different NB/TD compositions were investigated under uniaxial elongational flow. For E-NB copolymer, which has multiblock sequences, a shoulder in WAXD at 0.76 nm was evident besides its amorphous halo, and the relative intensity of the peak increased with increasing comonomer content (NB). The appearance of a new peak for E-TD copolymer, and a relatively higher intense peak for E-NB copolymer at the same position of 0.76 nm, indicated that local ordering of the segments occurred when the COC was subjected to uniaxial flow. A lower comonomer composition of elongated COC, at a constant Hencky strain rate, exhibited two Tg values,whereas a higher composition showed a single Tg. Both local ordering and segmentization occurred in low comonomer content COCs but only local ordering occurred in highercomonomer content COCs. Both the shear viscosity and roll processing experiments exhibited similar phenomena of segregation. A model is proposed to illustrate the structure of COC after uniaxial elongation/deformation.

J Appl. Polym. Sci., 2004, 91, 3421-3427

The preparation and characterization of new type of nanocomposite materials that are based on biodegradable polylactide (PLA) and organically modified layered titanate. Layered titanate modified with N-(cocoalkyl)-N,N-[bis(2-hydroxyethyl)]-N-methylammonium cation was used as a new nanofiller (OHTO) for the nanocomposite preparation. Wide-angle X-ray diffraction and TEM analyses respectively confirmed that titanate layers were intercalated and nicely distributed in the PLA-matrix. The materials properties of neat PLA improved remarkably after nanocomposite preparation. The nanocomposites exhibited photodegradation behavior under sunshine weathermeter test owing to the photocatalystic nature of OHTO.

Macromol. Rapid Commun., 2004, 25, 1359


Polylactide (PLA)/N,N-ethylenebis(12-hydroxystearamide) mixture was prepared by using melt extrusion. The detailed crystallization kinetics and morphology of neat PLA and a mixture were studied by using polarized optical microscopy, light scattering, differential scanning calorimetry, and wide-angle X-ray diffraction analyses. The overall crystallization rate and spherulitic texture of PLA were strongly influenced in presence of the organic additive. The overall crystallization rate of matrix PLA increased with addition of WX1. These behaviors indicated that WX1 crystallites, which crystallized at the very early stage of PLA crystallization act as a nucleating agent for PLA crystallization.

Polymer, 2006, 47(4), 1340

For better understanding of the direct polymer intercalation into the nano-galleries, the interdigitated layer structure of the organically modified layered filler (OMLF) was proposed. For OMLFs with highly surface charge density, the intercalants can adopt a configuration with orientation, where the alkyl chains are tilted under the effect of the van der Waals forces. The smaller interlayer opening caused by the configuration with small tilt angle promotes the large amount of the intercalation of the polymer chains.

Macromol. Rapid Commun., 2006, 27, 751-757


Via a batch process in an autoclave, the foam processing of intercalated polycarbonate (PC)/clay nanocomposites (PCCNs), having different amount of clay, has been conducted using supercritical carbon dioxide (CO2) as a foaming agent. The cellular structures obtained from various foaming temperature-CO2 pressure ranges were investigated by using scanning electron microscopy (SEM). The incorporation with nano-clay induced heterogeneous nucleation because of a lower activation energy barrier compared with homogeneous nucleation as revealed by the characterization of the interfacial tension between bubble and matrix. The controlled structure of the PCCN foams became from microcellular (d~20 mm and Nc~1.0 × 109 cell/cm3) to nanocellular (d~600 nm and Nc ~3.0 ×1013 cell/cm3). The mechanical properties of PCCN foams under compression test were discussed.

Macromol. Mater. Eng., 2006, 291, 773-783


Polymer/layered silicate nanocomposites (PLSNCs) offer remarkably improved mechanical and other properties with low inorganic filler loading. The major development in this field has been carried out over last one and a half decades. However the authors are far from the goal in terms of understanding the mechanisms of the enhancement effect in the nanocomposites. Continued progress in nanoscale controlling and an improved understanding of the physicochemical phenomena at the nanometer scale have contributed to the rapid development of novel PLSNCs. The present paper discribes recent advances in PLSNCs with the primary focus on these advances from basic science to technology.

Mater. Sci. & Tech., 2006, 22(7), 756-779



Solid-state processing for the preparation of poly(p-phenylenesulfide) (PPS)-based nano-composites having finely dispersed layered fillers was conducted. The mixture of PPS and organically modified layered filler (OMLF) (95/5 wt) was subjected to the processing using thermostatted hot-press at 150 °C, below Tm of PPS (i.e., PPS is still at the solid-state), and applying pressures of 33MPa for 300s. The mixture exhibited disorder and delaminated layer structure with the thickness of 10-20 nm into PPS matrix. On the contrary, nano-composite prepared by melt compounding at 300 °C for 3 min showed the large stacked silicate layers in the PPS matrix. The processing led to delaminate of the silicate layers and attained the discrete dispersion.

Macromol. Rapid. Commun., 2006, 27, 1472-1475


For the reference system of poly(p-phenylenesulfide) (PPS)-based nano-composites, we investigated the intercalation behavior of diphenyl sulfide (DFS) molecules into nano-galleries based on organically modified layered fillers (OMLFs) consisting of different types of intercalants and nano-fillers with different surface charge density. The smaller initial interlayer opening led to the larger interlayer expansion, regardless of the miscibility between intercalant and DFS. We examined the preparation of PPS-based nano-composites with and/or without shear processing at 300 °C. The finer dispersion of OMLFs in the nano-composite was observed when using OMLF having small initial interlayer opening. The delamination of the stacked nano-fillers was governed by the initial interlayer opening, whereas the uniform dispersion of the nano-fillers was affected by the shear.

Macromol. Mater. Eng., 2006, 291, 1367-1374


To understand the effect of the foam structure on the enzymatic degradation and porous structure development, we have examined the enzymatic degradation of a poly(L-lactide) (PLLA)-based nano-composite foam having different cell density (microcellular and nanocellular), using proteinase-K as a degrading agent at 37 °C. The surface and cross sectional morphologies of the foam recovered after enzymatic hydrolysis for different intervals were investigated by using scanning electron microscopic and mercury porosimetric analyses. The fabrication of porous three-dimensional structure for tissue engineering scaffolds and the degradation performance in nano-composite foams were discussed.

Polym. Degrad. Stab., 2008, 93, 1081-1087


Via time-resolved Fourier transform infrared spectroscopy (FTIR), we examined the real-time investigation of the conformational changes of poly(vinylidene fluoride) (PVDF) chain segment during crystallization of neat PVDF and the corresponding nano-composites. It was shown that on the following crystallization processes the chain folding mechanisms of the crystal growth were virtually the same in both nano-composites and neat PVDF. We have examined an annealing at an infinitely long time at 200 °C (~20 min) to erase the thermal history in the nano-composites. The dispersed titanate nano-filler particles exhibited strong contribution to enhance the heterogeneous nucleation for the formation of both gamma- and beta-phase crystals.

Polymer, 2008, 49, 5186-5190
The highly neutralized ionomer-based nano-composite materials were prepared via direct melt processing using zinc oxide (as a neutralizating agent) and organically modified clay. The nano-structure was characterized using wide-angle X-ray diffraction analyses, transmission electron microscopy observations and rheometry. The dispersed organo-clay acted as catalytic sites for the neutralization. From TEM analyses, the nano-sized ionic aggregates with a domain size of approximately 2 nm were randomly arranged in the ionomer matrix. The calculated aggregates density for the nano-composite was 0.08-0.15 nm-2. The temperature-dependent relaxation process observed in the viscoelastic measurements was somehow affected by the presence of the silicate layers, whereas it was strongly affected by the specific interaction via ionic aggregated domains.

Composite Part A, 2008, 39, 1924-1929
To understand the effect of the montmorillonite (MMT) particles on the crystallization kinetics and crystalline morphology of nylon 6 upon nano-composite formation, we have characterized the crystallization behaviors by using light scattering, wide-angle X-ray diffraction (WAXD), transmission electron microscope (TEM) and rheological measurement. The correlation between the nucleating effect and the growth mechanism of the different polymorphism (g-phase) of nylon 6 in the nano-composite (N6C3.7) was probed. N6C3.7 exhibited g-phase crystal due to the nucleating effect of the dispersed MMT particles into the nylon 6 matrix throughout the whole Tc range (= 150-215 °C). The lamellar growth of the g-phase crystal took place on both sides of the dispersed MMT particles. In comparison between the temperature dependence of the characteristic relaxation time and the crystallization time, the lamellar growth of the g-phase crystal has been discussed. The stable growth of the g-phase was strongly disturbed at at low Tc range (= 160-190 °C) due to the lack of time for crystallization.

Polymer,2009, 50, 4718-4726


Via a batch process, the foam processing of polyethylene-based ionomers having two different degree of the neutralization has been conducted using supercritical CO2. The cellular structures obtained from various ranges of foaming temperature-CO2 pressure were investigated by using field emission scanning electron microscopy. For comparison, the corresponding nano-composite also has been examined. The ionic cross-linked structure in the ionomer exhibited significant contribution to retard the cell growth and coalescence of cell, especially in ionomer having higher degree of the neutralization. For nano-composite foaming, experimentally, nano-clay particles led to an increase in cell density after foaming. However, the dispersed nano-clay particles did not act as nucleating sites for cell formation. The competitive phenomenon between the cell nucleation and the cell growth including the coalescence of cell was discussed in the light of the interfacial energy and the relaxation rate as revealed by the modified classical nucleation theory and rheological measurement, respectively.

Composites: Part A, 2009, 40, 1708-1716

To understand the correlation between foamability and melt rheology of polyethylene-based ionomers having different degree of the neutralization and corresponding nano-composites, we have conducted the foam processing via a batch process in an autoclave and microcellular foam injection molding (FIM) process using the MuCell(R) technology. We have discussed the obtainable morphological properties in both foaming processes. All cellular structures were investigated by using field emission scanning electron microscopy. The competitive phenomenon between the cell nucleation and the cell growth including the coalescence of cell was discussed in the light of the interfacial energy and the relaxation rate as revealed by the modified classical nucleation theory and rheological measurement, respectively. The FIM process led to the opposite behavior in the cell growth and coalescence of cell as compared with that of the batch process, where the ionic cross-linked structure has significant contribution to retard the cell growth and coalescence of cell. The mechanical properties of the structural foams obtained by FIM process were discussed.

Mater. Sci. Eng. C, 2010, 30, 62-70

To understand the effect of confined space (interlayer space in montmorillonite (MMT)) on the nonisothermal ordering transition (chain packing) kinetics and disorder transition (chain melting) behavior including the conformational changes of the chain segment of the cationic surfactants, we have characterized MMT modified with dioctadecyl dimethylammonium (DC18DM) ions (MMT-DC18DM) using temperature-modulated differential scanning calorimeter (TMDSC), wide-angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FTIR) technique. For MMT-DC18DM, the chain conformational disorder-order phase transition took place during the cooling process. The transition peak was much broader and it appeared at lower temperature (Tc) when compared to the crystallized dioctadecyl dimethylammonium bromide (DC18DM-Br), as a reference
In MMT-DC18DM, the formation of gauche conformers was enhanced and the chains were not as densely packed as in crystalline DC18DM-Br. The normal crystallization took place in the bulk during the nonisothermal crystallization of DC18DM-Br. The confined ions (DC18DMs) in one or two dimensional order contributed to the nonisothermal chain packing for a higher cooling rate of 5.0-20.0 °C/min. The observed chain packing in confined space at different Tc ranges (cooling rate > 5.0 °C/min) could be explained by much lower energy barrier.

Appl. Clay Sci., 2010, 48, 73-80

Solid-state processing for the preparation of polypropylene (PP)-based nano-composites having finely dispersed layered fillers was conducted. The mixture of PP and organically modified layered filler (OMLF) (95:5 wt./wt.) was subjected to the processing using alumina mortar heated 65 °C, below Tm of PP (i.e., PP is still at the solid-state), and ground for 8 h before melt compounding. On X-ray diffraction, the d(001) peak of OMLF was broaden and peak position shifted slightly. The mixture prepared by solid-state processing exhibited disorder and delaminated layer structure with the thickness of 3-7 nm into PP matrix through TEM observations. On the contrary, nano-composite prepared by melt compounding at 180 °C for 3 min (without solid-state processing) showed the large stacked silicate layers in the PP matrix. Furthermore, instead of using alumina mortar, we carried out solid-state processing using internal mixer. X-ray diffraction pattern and TEM observation exhibited similar results. The solid-state processing led to delaminate of the silicate layers and attained the discrete dispersion.

Polymer, 2010, 51,4238-4242
Via time-resolved FTIR, we examined the real-time investigation of the structural change in molecular chain of nylon 6 during crystallization of neat nylon 6 and the corresponding nano-composite (N6C3.7) having fully exfoliated structure. The neat nylon 6 predominantly formed alpha-phase in the crystallization temperature (Tc) range of 155-195 °C. For N6C3.7 crystallization at low Tc range of 150-168 °C, where the network structure formed by the dispersed clay particles still affected chain folding of nylon 6, the formation of the gamma-phase was dominant. The crystallization took place so rapidly (less than 1s) without induction time of crystallization. At high Tc range (=177-191 °C), the stable growth of the alpha-phase crystal coexisting with gamma-phase occurred in N6C3.7 crystallization. The growth mechanism in the subsequent crystallization processes (amides III alpha and III gamma) were virtually the same in both N6C3.7 and neat nylon 6.

Polymer, 2010, 51,5585-5591

We synthesized three allophanes from precursors by a hydrothermal reaction at 100°C for 48h. The precursors were formed from the solutions of Na4SiO4 and AlCl3?6H2O at different Si/Al molar ratios (0.5, 0.75, 1.0). The nanostructure of the synthetic allophanes was compared with that of a natural allophane from New Zealand by using X-ray diffractometry, energy dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, thermogravimetry/ differential thermal analysis, 29Si and 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR), field emission electron microscopy, and pore-size distribution based on the Cranston-Inkley method. The propensity of the allophanes to adsorb adenine and adenosine-5’-monophosphate (5’-AMP) was assessed by batch experiments. The adsorption data were fitted by the Freundlich equation and the adsorption parameters were discussed in relation to the properties of the natural and synthetic allophanes. The adsorption capacity (Kf) of the natural allophane for 5’-AMP was three times that for adenine. The average Kf value of the three synthetic allophanes for 5’-AMP was more than twice that of the natural allophane, possibly due to the higher purity of the synthetic allophanes.
Key words: allophanes, nanoparticles, adenine, 5’-AMP, adsorption.

Appl. Clay Sci., in press, 2011