High improvement in the properties of exfoliated PU/clay nanocomposites by the alternative swelling process

In this work, a stable de-aggregated solvent-swollen organic modified clay, ALA-MMT, suspension is prepared by an efficient solvent swelling process using a home-made shaking mixer. It is found that the estimated average size of the as-prepared organoclay particles in the suspension is reduced to about 155 nm, which has not been reported before. The X-ray diffraction (XRD) patterns confirm that the d-spacing of the silicate layers of the solvent-swollen ALA-MMT expands from 1.4 nm to about 2.1 nm. The de-aggregated solvent-swollen ALA-MMT suspension is then used with polyurethane (PU) to prepare a series of highly exfoliated and high-organoclay-loading nanocomposites, PU/ALA-MMT. Both the XRD patterns and the TEM photographs of the as-prepared PU/ALA-MMT nanocomposites indicate that the organoclay is uniformly dispersed in the PU matrix with a highly exfoliated morphology structure of up to 7 wt% loading. Meanwhile, the TEM photographs give the first report for PU/clay nanocomposites which are almost completely exfoliated, and ∼1-nm thin silicate nanolayers are homogeneously dispersed in the polymer matrix with a high aspect ratio of 30-100. The thermal, mechanical, and anti-corrosion properties are all tremendously enhanced for the as-prepared nanocomposites. The results obtained for the PU nanocomposite with 7 wt% ALA-MMT loading (PUC7) reveal a 19 °C increment in T_g, a 48 °C increment in T_5%, a 248% increase in the tensile strength, and a 123% increase in the elongation. The stainless steel disk (SSD) coated with PUC7 shows the lowest corrosion rate of 2.01 × 10⁻⁶ mm/year, which is 469% lower than that of the SSD coated with pure PU. The reinforcements are much greater than the previously reported PU/clay nanocomposites with comparable clay loadings ascribed to the exceptional homogeneity of as-prepared nanocomposites, which are accredited largely to the stable de-aggregated solvent-swollen organoclay suspension generated by the efficient solvent swelling process.     

Effect of organoclays on the properties of polyurethane/clay nanocomposite coatings

Linear, one‐binding‐site or two‐binding‐site (N⁺) organifiers with two hydroxyl end groups were synthesized, and novel organoclays were prepared through a cation‐exchange reaction between pristine sodium montmorillonite and the synthesized organifiers. After sonication of the as‐prepared organoclay in N,N′‐dimethylformamide for 10 min, the average size of the clay decreased to about 1 μm. The X‐ray diffraction patterns confirmed that the d‐spacing of the silicate layers of the organoclay expanded from 1.1 to about 1.9 nm and the peak intensity decreased with the molecular weight of the organifier increasing. Polyurethane/clay nanocomposites were synthesized by a one‐shot polymerization method. Both intercalated and exfoliated structures of the layered silicates in the polyurethane matrix were observed from transmission electron microscopy micrographs, and the d‐spacing ranged from 4 to 10 nm. The thermal and mechanical properties of the nanocomposite were enhanced by the introduction of the organoclay into the polyurethane matrix. An approximately 40–46°C increase in the onset decomposition temperature, a 200% increase in the tensile strength with a 0.5 wt % clay loading, and a 49% increase in Young's modulus with a 3 wt % clay loading were achieved. The effects of the molecular weight and the number of binding sites of the organifier on the properties of the nanocomposites were also evaluated. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of polyurethane–organoclay nanocomposites

Nanocomposite polyurethane (PU)–organoclay materials have been synthesized via in‐situ polymerization. The organoclay is first prepared by intercalation of tyramine into montmorillonite (MMT)‐clay through ion exchange process. The syntheses of polyurethane–organoclay hybrid films containing different ratios of clay were carried out by swelling the organoclay into diol and diamine followed by addition of diisocyanate and then cured. The nanocomposites with dispersed and exfoliated structure of MMT were obtained as evidenced by X‐ray diffraction and scanning electron microscope. X‐ray diffraction showed that there is no peak corresponding to d₀₀₁ spacing in organoclay with the ratios up to 20 wt%. SEM images confirmed the dispersion of nanometer silicate layers in the polyurethane matrix. Also, it was found that the presence of organoclay leads to improvement in the mechanical properties. The tensile strength was increased with increasing the organoclay contents to 20 wt% by 221% in comparision to the PU with 0% organoclay. POLYM. COMPOS. 28:108–115, 2007. © 2007 Society of Plastics Engineers     

Synthesis and properties of polybenzoxazole-clay nanocomposites

A novel polybenzoxazole (PBO)/clay nanocomposite has been prepared from a PBO precursor, polyhydroxyamide (PHA) and an organoclay. The PBO precursor was made by the low temperature polycondensation reaction between isophthaloyl chloride (IC) and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane with an inherent viscosity of 0.5 dl/g. The organoclay was formed by a cation exchange reaction between a Na⁺-montorillonite (Na⁺-Mont) clay and an ammonium salt of dodecylamine. The PHA/clay was subsequently thermal cured to PBO/clay. Both X-ray diffraction and transmission electron microscope analyzes showed that the organoclay was dispersed in the PBO matrix in a nanometer scale. The in-plane coefficient of thermal expansion (CTE) of PBO/clay film decreased with increasing amounts of organoclay. The CTE of PBO/clay film containing 7 wt% clay was decreased by 21% compared to the pure PBO film. Both of the glass transition temperature (T_g) and the thermal decomposition temperature of PBO/clay increased with increasing amounts of organoclay. The thermal decomposition temperature and the T_g of PBO/clay containing 7 wt% clay increased to 12 and 16 °C, respectively.     

Poly(lactic acid) nanocomposites: comparison of their properties with montmorillonite and synthetic mica (II)

Our study was to clarify the intercalation of polymer chains to organoclays and to improve the thermo-mechanical properties. Two organoclays were synthesized. One was a montmorillonite modified with hexadecylamine (C₁₆-MMT); the other was a fluorinated-mica modified with hexadecylamine (C₁₆-Mica). Dispersions of organoclays with poly(lactic acid) (PLA) were by using the solution intercalation method at different organoclay contents to produce nano-scale composites. The maximum ultimate tensile strength was observed for blends containing 4 wt% of either of the two organoclays and decreased with further increases in the organoclay content. The initial modulus increased with increasing organoclay content up to 4 wt% for C₁₆-MMT. When the C₁₆-MMT content was greater than this critical wt%, the modulus of the hybrids started to decrease. In contrast, the initial modulus of the hybrids using C₁₆-Mica increased continually with increasing clay content from 2 to 8 wt%. The tensile properties of the C₁₆-Mica hybrids were higher than those of the hybrids containing C₁₆-MMT. The optical translucency was not affected by the organoclay content up to 6 wt%; however, the films containing 8 wt% organoclays were slightly more cloudy.     

Polyimide nanocomposites prepared from high-temperature, reduced charge organoclays

Montmorillonite clays modified with the dihydrochloride salt of 1,3-bis(3-aminophenoxy)benzene (APB) were used in the preparation of polyimide/organoclay hybrid films. Organoclays with varying surface charge based upon APB were prepared and examined for their dispersion behavior in the polymer matrix. High molecular weight poly(amide acid) solutions were prepared in the presence of the organoclays. Films were cast and subsequently heated to 300 °C to cause imidization. The resulting nanocomposite films, containing 3 wt% of organoclay, were characterized by transmission electron microscopy and X-ray diffraction. The clay's cation exchange capacity (CEC) played a key role in determining the extent of dispersion in the polyimide matrix. Considerable dispersion was observed in some of the nanocomposite films. The most effective organoclay was found to have a CEC of 0.70 meq/g. Nanocomposite films prepared with 3-8 wt% of this organoclay were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and thin-film tensile testing. High levels of clay dispersion could be achieved even at the higher clay loadings. Results from mechanical testing revealed that while the moduli of the nanocomposites increased with increasing clay loadings, both strength and elongation decreased.     

Phase separation and mechanical responses of polyurethane nanocomposites

Nanocomposites of a diamine-cured polyurethane with nanofillers of different kinds, sizes, and surfaces were studied. Atomic force microscopy, scanning electron microscopy, X-ray diffraction, tensile tests, and dynamic mechanical thermal analysis were employed in the experiments. Experimental results suggest that mechanical properties are strongly correlated to polymer phase separation, which depends on the nature of the interface between the polymer and the nanoparticles. Two stages of phase separation were observed: the first stage involves the self-assembly of the hard segments into small hard phases of about 10 nm in width; the second stage involves the assembly of the 10 nm wide hard phases into larger domains of about 40-100 nm in width. In the case of polyurethane/ZnO nanocomposites with 5 wt% (less than 1 vol%) 33 nm ZnO nanoparticles, the covalent bonds that were formed between the polymer and ZnO surface hydroxyl groups constrain both stages of phase separation in polyurethane, resulting in approximately 40% decrease in the Young's modulus, 80% decrease in the strain at fracture, and 11 °C increase in the glass transition temperature of the soft segments. In the case of polyurethane/Al₂O₃ nanocomposites with 5 wt% 15 nm Al₂O₃ nanoparticles, hydrogen bonds between the particles and the polymer mainly constrain the second step of the phase separation, resulting in about 30% decrease in the Young's modulus and 12 °C increase in the glass transition temperature, but only a moderate decrease in the strain at fracture. The most striking results come from polyurethane/clay composites, where only van der Waals type interactions exist between polyurethane and the organically modified clay (Cloisite 20A). With the addition of 5 wt% surface modified clay (Cloisite 20A), both the Young's modulus and the strain at fracture decrease more than 80%, but the glass transition temperature increases by about 13 °C. Adding 10 wt% Cloisite 20A into polyurethane almost totally disrupts the phase separation, resulting in a very soft composite that resembles a “viscous liquid” rather than a solid.     

Fracture behavior of nanocomposites based on poly(ethylene-co-methacrylic acid) ionomers

The fracture behavior of nanocomposites formed from an organoclay, based on montmorillonite (MMT), and a poly(ethylene-co-methacrylic acid) ionomer prepared by melt compounding was investigated using an instrumented impact test. The data were analyzed using the essential work of fracture (EWF) methodology. Transmission electron microscopy revealed that the clay platelets were well-exfoliated in this matrix. The fracture energy of these nanocomposites increased with organoclay addition at low concentrations but decreased with further increase in organoclay concentration with a maximum between 2 and 3 wt% MMT. The initial increase in fracture energy is a result of the higher forces during loading caused by the increase in modulus and yield stress upon addition of clay; however, the fracture energy eventually decreases with further addition of clay owing to the continuous decrease in ductility or deflection during testing. The EWF of fracture analysis showed that the energy per unit area of crack surface formed exhibits a maximum at 2-3 wt% MMT while the energy dissipated per unit volume in the surrounding process zone decreases monotonically for all clay loadings with a transition from ductile to brittle behavior occurring at 7-8 wt% MMT.     

Fibrillation of thermotropic liquid crystalline polymer enhanced by nano-clay in nylon-6 matrix

The influence of well-dispersed nano-clay filler on the morphology of thermotropic liquid crystalline polymer (TLCP) in nylon-6 matrix was investigated by melt extrusion process. The good dispersion of clay in the hybrid blends was confirmed by X-ray diffraction, transmission electron microscopy and rheological measurement. Morphological observation showed that the clay platelets had dramatic influences on the dispersion and deformation of TLCP phase. The TLCP droplets got smaller at the clay content ≤3 wt%, and deformed into fibrils at the clay content up to 5 and 7 wt%. The morphology evolution of TLCP in the hybrid blends, especially at 7 wt% of clay loading, was consistent well with the prediction based on the micro-rheology parameters such as the viscosity ratio of the dispersed phase to the matrix (η_d/η_m) and the ratio of capillary number to the critical capillary number (Ca/Ca_crit). This enhanced fibrillation of TLCP droplets was attributed to the role of nano-clay particles as a compatibilizer to improve the interfacial adhesion and to suppress the interfacial slip between TLCP and nylon phases in the melt, so that the shear stress was effectively transferred to the dispersed TLCP phase.     

Preparation of clay/epoxy nanocomposites by layered-double-hydroxide initiated self-polymerization

An anionic clay, magnesium-aluminum layered double hydroxide (Mg₂Al-NO₃-LDH), was prepared by a co-precipitation method and intercalated with poly(oxypropylene)-amindocarboxylic acid (POP-amido acid). Depending on the POP-intercalating agents with molecular weight at 2000 or 400 g/mol, the intercalated LDHs were analyzed to have d spacing of 6.8 or 2.7 nm and organic incorporation of 80 and 55 wt%, respectively. Two comparative POP/LDH hybrids were allowed to initiate the self-polymerization of the epoxy resin, diglycidyl ether of bisphenol-A (DGEBA). The curing rate was significantly increased by using the hybrids as initiators for epoxy curing, demonstrated by DSC thermal analysis that the exothermic peak shifted from 182 to 152 °C by increasing organoclay addition. The resultant nanocomposites prepared from the anionic LDH initiated epoxy self-polymerization have the improved thermal and physical properties, evidenced by TGA, XRD, TEM, and SEM analyses.     

Polystyrenes with macro-intercalated organoclay. Part II. Rheology and mechanical performance

Polymeric nanocomposites (PNC) of polstyrene (PS) with organoclay were studied for their rheological and mechanical behavior. The organoclay (COPS) is a product of clay quaternization with a copolymer of styrene with vinyl benzyl tri-methyl ammonium chloride. PNC preparation and characterization was described in Part I of this paper. The clay platelets in COPS and its PNC's are well dispersed, i.e. with the interlayer spacings of d₀₀₁=7-8 nm. By contrast, d₀₀₁=3-4 nm for PNC with Cloisite^® 10A. However, the COPS in PS formed large, deformable domains. At concentration exceeding 5.8-wt% of COPS, the domains started to form a three-dimensional network with enhanced elasticity and progressive viscoelastic non-linearity. At temperatures of 160-180 °C the neat COPS did not flow; its behavior resembled that of a crosslinked elastomer. Application of the time-temperature superposition led to master curves of bending moduli vs. 19 decades of reduced frequency. The curves indicated a transition at ca. 180 °C, most likely associated with the disintegration of ammonium ion clusters. With the same amount of clay the mechanical properties of PNC with COPS were slightly worse than those with Cloisite^® 10A—the immiscibility of COPS, and the presence of extractable (by the matrix) low molecular weight compounds explain the behavior.     

Vegetable oil based highly branched polyester/clay silver nanocomposites as antimicrobial surface coating materials

The unison of nanotechnology and polymer science enables the development of novel silver-based polyester nanocomposite as an antimicrobial coating material. Highly branched polyester/clay silver nanocomposites based on vegetable oil with different loadings of silver were prepared via reduction of silver salt by employing dimethylformamide as solvent as well as reducing agent at room temperature. Organically modified montmorillonite clay of 2.5 wt% was used as the nanofiller for the property improvement of the pristine polymer. The highly branched polyester resin was synthesized by condensation of 2,2-bis(hydroxymethyl) propionic acid with Mesua ferrea L. seed oil based carboxyl terminated pre-polymer, as reported earlier. FTIR, UV–vis, XRD, SEM and TEM studies substantiate the formation of well-dispersed silver nanoparticles within the clay gallery with an average size of 15 nm. The thermostability of the silver nanocomposites obtained by thermogravimetric analysis was enhanced by 20 °C. The mechanical properties such as tensile strength and scratch hardness were improved 4.5 and 2.6 units respectively and impact resistance improved a little by nanocomposites formation. The antimicrobial efficacy of the as-prepared silver nanocomposites was also premeditated and highly antibacterial activity against Gram negative bacteria (Escherichia coli and Psuedomonas aeruginosa) was observed. Excellent chemical resistance in various chemical media except in alkali has also been noticed. The study reveals that the polyester/clay silver nanocomposites based on vegetable oil show the potential to be applicable as antibacterial surface coating materials.     

Preparation and characterization of nylon 11/organoclay nanocomposites

Nylon 11/organoclay nanocomposites have been successfully prepared by melt-compounding. X-ray diffraction and transmission electron microscopy indicate the formation of the exfoliated nanocomposites at low clay concentrations (less than 4 wt%) and a mixture of exfoliated and intercalated nanocomposites at higher clay contents. Thermogravimetric and dynamic mechanical analyses as well as tensile tests show that the degree of dispersion of nanoclay within polymer matrix plays a vital role in property improvement. The thermal stability and mechanical properties of the exfoliated nylon 11/clay nanocomposites (containing lower clay concentrations) are superior to those of the intercalated ones (with higher clay contents), due to the finer dispersion of organoclay among the matrix.     

Morphology, thermal, and viscoelastic properties of poly(glycidyl methacrylate-co-methyl methacrylate)-based nanocomposites with various organo-modified clays

New nanocomposites of poly(glycidyl methacrylate-co-methyl methacrylate) (PGM) cured with cyclohexanedicarboxylic anhydride (CDCA) and layered silicates of inorganic content 3 and 5 wt% were prepared by casting the solution of the mixture and subsequent cross-linking at finally 200 °C. Non-modified montmorillonite (MMT) and organo-MMTs (ODA-M, ALA-M, LEA-M, and HBP-M) modified with octadecylamine, 12-aminolauric acid, N-lauryldiethanolamine, and hexadecyltributylphosphonium bromide, respectively, were used as layered silicates. X-ray diffraction and morphological studies using transmission electron microscopy revealed that the highly intercalated nanocomposites with the interlayer spacing more than 5.5 nm are formed for the PGM-CDCA/ODA-M, LEA-M, and HBP-M composites with inorganic content 3 wt%. When the inorganic content was increased from 3 to 5 wt%, the degree of intercalation of all the PGM-CDCA/organoclay composites was lowered. Dynamic viscoelastic measurement revealed that the organoclay nanocomposites have significantly higher storage modulus than the PGM-CDCA neat resin. The thermogravimetric analysis revealed that the HBP-M composite with inorganic content 5 wt% has the highest thermal decomposition temperature.     

Poly(butylene terephthalate)/organoclay nanocomposites prepared by in situ interlayer polymerization and its fiber (II)

Intercalated nanocomposites with poly(butylene terephthalate) (PBT) incorporated between the montmorillonite layers were synthesized from dimethyl terephthalate and 1,4-butane diol by using an in situ interlayer polymerization. The PBT nanocomposites were melt-spun at different organoclay contents to produce monofilaments. The samples were characterized by using wide angle X-ray diffraction, electron microscopy, thermal analysis, and tensile testing. The extent of the clay layer in the PBT was confirmed by using X-ray diffraction and electron microscopy, and the clay layer was found to be highly dispersed on a nanometer scale. The addition of only a small amount of organoclay was enough to improve the thermo-mechanical properties of the PBT hybrid fibers. The hybrids were extruded with various draw ratios (DRs) to examine the tensile mechanical property of the fibers. At DR=1, the ultimate tensile strength of the hybrid fibers increased with the addition of clay up to a critical content and then decreased. However, the initial modulus monotonically increased with increasing amount of organoclay in the PBT matrix. When the DR was increased from 1 to 6, for example, the strength and the initial modulus values of the hybrids containing 3 wt% organoclay decreased linearly.     

Photosensitive poly(amic acid)/organoclay nanocomposites

A project was carried out aimed at reducing the coefficient of thermal expansion (CTE) of photosensitive polyimide formulations (photoresists) through the incorporation of small amounts of an organoclay. The organoclay was formed by a cation exchange reaction between a NA⁺-montmorillonite clay and an ammonium salt of dodecylamine. Two polyimide precursors, a poly(amic ester) (PAE) and a poly(amic acid) (PAA), were used in this study. The PAE was prepared by direct polymerization of 2,2′-bis-(3-amino-4-hydroxyphenyl)hexafluoropropane and bis(n-butyl)ester of pyromellitic acid in the presence of phenylphosphonic dichloride as an activator. The polymer had an inherent viscosity of 0.23 dL/g. The PAA copolymer was prepared by polymerization of pyromellitic dianhydride, oxydiphthalic anhydride and oxydianiline. The polymer had an inherent viscosity of 1.00 dL/g. Two photosensitive resin/clay formulations were prepared from these two PI precursors using 2,3,4-tris(1-oxo-2-diazonaphthoquinone-5-sulfonyloxy)-benzophenone as the photosensitizer and 3 wt% organoclay. The films obtained from the PAA formulation were transparent and tough, while the films prepared from the PAE formulation were opaque and brittle. Both X-ray diffraction and transmission electron microscope analyses showed that, although the organoclay was not dispersed well in the PAE matrix, it was dispersed in the PAA matrix on a nanometer scale. The clay particles remained well dispersed after the PAA film was thermally imidized. The CTE of the polyimide film obtained was 23% lower than that of a similar film that did not contain the organoclay. The temperature at which the polyimide underwent a 5% weight loss when subjected to TGA in nitrogen was also increased by 13%. The photosensitive PAA/clay nanocomposite showed a sensitivity of 301 mJ/cm² and a contrast of 1.66 when a 0.2 wt% tetramethylammonium hydroxide developer was used. A line/space pattern with a resolution of 10 μm was obtained from this formulation.     

Development of stiff, strong, yet tough composites by the addition of solvent exfoliated graphene to polyurethane

We have prepared graphene dispersions, stabilised by polyurethane in tetrahydrofuran and dimethylformamide. These dispersions can be drop-cast to produce free-standing composite films. The graphene mass fraction is determined by the concentration of dispersed graphene and can be controllably varied from 0% to 90%. Raman spectroscopy and helium ion microscopy show the graphene to be well-dispersed and well-exfoliated in the composites, even at mass fractions of 55%. On addition of graphene, the Young’s modulus and stress at 3% strain increase by ×100, saturating at 1 GPa and 25 MPa, respectively, for mass fractions above 50 wt%. While the ultimate tensile strength does not vary significantly with graphene content, the strain at break and toughness degrade heavily on graphene addition. Both these properties fall by ×1000 as the graphene content is increased to 90 wt%. However, the rate of increase of Young’s modulus and stress at 3% strain with mass fraction is greater than the rate of decrease of ductility and toughness. This makes it possible to prepare composites with high modulus, stress at low strain and ultimate tensile strength as well as relatively high toughness and ductility. This could lead to new materials that are stiff, strong and tough.     

The role of organically modified layered silicate in the breakup and coalescence of droplets in PBT/PE blends

In this study, we investigated the effect of organically modified nanoclay (organoclay) on the morphology of immiscible polymer blends (PBT/PE) with various compositions of PBT ranging from 1 to 90 wt%. When a small amount of organoclay between 1 and 3 phr is added to the blend, the thin clay tactoids of the thickness of the order of 10 nm are located at the interface between PBT and PE phase. As its content is increased, the additional organoclay positions in a specific component depending on its affinity with the component. The addition of a small amount of organoclay results in the effective size reduction for PBT/PE blend. The organoclay located at the interface forms the interfacial phase with a non-homogeneous distribution of clay along the interface and changes the interfacial tension, which result in the coalescence suppression of the droplets. Rigid organoclay with a high aspect ratio allows the blend morphology with long-term thermal stability by suppressing the Brownian motion. This ability of the organoclay to suppress the coalescence of the droplets effectively reduces the droplet size. On the other hand, additional organoclay results in the rheological properties of particular component being increased, which means the change in the viscosity ratio. The change in the viscosity ratio, together with the coalescence suppression effect, affects the determination of the droplet size, depending on the location of the organoclay. Therefore, the organoclay suppresses the coalescence of the droplets at the interface, while simultaneously influencing the breakup of the droplets due to the change of viscosity ratio.     

Nanostructure and dynamic mechanical properties of silane-functionalized montmorillonite/epoxy nanocomposites

In this work sodium montmorillonite (Na-MMT) was functionalized with N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane and the corresponding silylated clay was used to modify epoxy matrix cured with triethylenetetramine. The grafting/intercalation of the aminosilane inside the clay galleries were followed by infrared spectroscopy, X-ray diffraction, thermogravimetric analysis and ²⁹Si cross-polarization magic-angle-spinning nuclear magnetic-resonance (CP/MAS NMR) spectroscopy. Epoxy-based nanocomposites were prepared with different amounts of silylated clay or commercial organoclay, Cloisite 30B, whose intercalating agent consists of a methyl, tallow, bis-2-hydroxyethyl quaternary ammonium salt. The degree of intercalation/exfoliation was estimated by X-ray diffraction experiments and confirmed by small angle X-ray scattering. Nanocomposites prepared with silylated clay displayed no peak in both XRD and SAXS curves whereas those prepared with Cloisite 30B exhibited a clear interference peak corresponding to an interlayer spacing d₀₀₁ of 4.1 nm. The former also presented a better dispersion, with a high proportion of tactoids smaller than 2 nm, as estimated by SAXS. From the results of dynamic mechanical analysis it was observed that most of the nanocomposites display higher storage modulus mainly at temperatures above the glass transition temperature. The glass transition temperature is similar or higher than the neat epoxy network for nanocomposites containing 1 wt.% of silylated clay or higher.     

Characteristics of polyurethanes incorporating starch granules

Polyurethanes containing different starch contents were synthesized in a one-step reaction by suspending starch granules in polycaprolactone diol, MDI and 1,4 butane diol in a bulk phase at 175 °C. The products were characterized by FTIR spectroscopy, SEM, DSC, and swelling behavior. Their mechanical properties, e.g. tensile strength and elongation, were measured for different starch contents. The starch dispersed well as a grafted state in the polyurethane phase. The grafted percentage of polyurethane to starch granules increased with the starch content to a maximum point (about 20 wt%) and then decreased due to gapping between the two phases and probably the homo-polymerization tendency of the polyurethane. The DSC indicated that T_g increased with the starch content due to the decreased average molecular weight of the homo-polyurethane. Three endothermic transitions at 60-70 °C (I), ∼150 °C (II), 190-210 °C (III) were observed. Transition I was not changed by the starch content, whereas transition II appeared only for the psb2m3 series (32-48 wt% hard segment) at the lower range of 26 wt% of starch content. The temperature of transition III, which is related to the melting point of the hard segments, increased with the starch content despite a decrease in the molecular weight of the homo-polyurethane. The tensile strength and the elongation of the polymers slightly increased or were constant up to about 20 wt% of starch, and then decreased rapidly because of phase separation (gapping) between the starch granules and the polyurethane phase and division of the starch granules.