A study on phase morphology and surface properties of polyurethane/organoclay nanocomposite

In this study, polyurethane/organically modified layered silicate (organoclay) nanocomposites were prepared through in situ polymerization in the presence of organoclay. Phase morphology of the polyurethane/organoclay nanocomposite was investigated by small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). The results suggest that the inter-domain repeat distance decreased with the introduction of organoclay. The organoclay has a more significant effect on the inter-domain repeat distance at a low hard segment content. Also with the increase of the hard segment, the inter-domain repeat distance and domain size increased markedly. The size of hard domain of the polyurethane was found to be in the range of 12-32 nm in this case, and it keeps nearly unchanged with the clay content. It is suggested by AFM phase imaging technique that the hard domain can self-organize further to form spherical aggregates. The introduction of clay into the polyurethane matrix resulted in the decrease in the size of the spherical aggregates from ∼800 nm to ∼500 nm, indicating clay has an important effect on the aggregation behavior of hard domains. The effect of clay on the surface energy was examined by means of AFM and goniometry techniques. The results obtained by two methods are consistent, i.e., with the increase of clay content, the surface energy decreased due to the effect of organic modifier.     

Atomic force microscopy study on blend morphology and clay dispersion in polyamide‐6/polypropylene/organoclay systems

The phase structure and clay dispersion in polyamide‐6(PA6)/polypropylene(PP)/organoclay (70/30/4) systems with and without an additional 5 parts of maleated polypropylene (MAH‐g‐PP) as a compatibilizer were studied with atomic force microscopy (AFM). AFM scans were taken from the polished surface of specimens that were chemically and physically etched with formic acid and argon ion bombardment, respectively. The latter technique proved to be very sensitive to the blend morphology, as PP was far more resistant to ion bombardment than PA6. In the absence of the MAH‐g‐PP compatibilizer, the organoclay is located in the PA6 phase; this finding is in line with transmission electron microscopic results. Further, the PP is coarsely dispersed in PA6 and the adhesion between PA6 and PP is poor. The addition of MAH‐g‐PP resulted in a markedly finer PP dispersion and good interfacial bonding between PA6 and PP. In this blend, the organoclay was likely dispersed in the PA6‐grafted PP phase. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43:1198–1204, 2005     

Studies on the conducting nanocomposite prepared by in situ polymerization of aniline monomers in a neat (aqueous) synthetic mica clay

The in situ polymerization of the anilinium‐intercalated synthetic mica clay can easily result in an intercalated polyaniline (PANI)/clay nanocomposite. The FT‐IR spectra demonstrated a significant shift for ν_{(C? N)} at 1292 cm^?1 of the templated polymerized and intercalated PANI molecules. A red shift of λ_max for PANI was found from UV–vis spectra. The intercalated PANI also expanded the clay basal spacing seen from WAXD patterns. The degradation rate and temperature of the nanocomposites were found to alleviate and increase compared to neat PANI, respectively. The microscopic examinations including TEM, SEM, and AFM pictures of the nanocomposite demonstrated an entirely different and more compatible morphology. Conductivity of nanocomposite gradually increased with PANI and apparent increase was found when intercalated PANI content reached 40.6 wt %, the possible percolation threshold. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1800–1809, 2008     

Amine‐cured epoxy/clay nanocomposites. II. The effect of the nanoclay aspect ratio

The thermophysical and mechanical properties of a nanocomposite material composed of amine‐cured diglycidyl ether of bisphenol A (DGEBA) reinforced with organomontmorillonite clay are reported. The storage modulus at 100 °C, which was above the glass‐transition temperature (T_g), increased approximately 350% with the addition of 10 wt % (6.0 vol %) of clay. Below the T_g, the storage modulus at 30 °C increased 50% relative to the value of unfilled epoxy. It was determined that the T_g linearly increased as a function of clay volume percent. The tensile modulus of epoxy at room temperature increased approximately 50% with the addition of 10 wt % of clay. The reinforcing effect of the organoclay nanoplatelets is discussed with respect to the Tandon–Weng and Halpin–Tsai models. A pseudoinclusion model is proposed to describe the behavior of randomly oriented, uniformly dispersed platelets in nanocomposite materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4391–4400, 2004     

Flexible polyurethane nanocomposite foam: Synthesis and properties

Flexible polyurethane (PU) nanocomposite foams were synthesized using organically modified montmorillonite clay (Cloisite 30B). The dispersion of organoclay was considered both in the isocyanate and polyol matrixes. Silicate layers of organoclay can be exfoliated in PU matrix by use of two steps mixing process. The presence of clay increased the cell density and reduced the cell size compared to the conventional PU foam. Clay dispersion was investigated by X-ray diffraction (XRD). The morphology and properties of PU nanocomposite foams were also studied. Generally, mechanical properties by addition of clay were improved. Foams in which clay was firstly dispersed in the isocyanate, showed better dispersion due to affinity of OH group on the clay surface to react with NCO groups. Better properties have been achieved with these nanofoams.     

Effects of spacing between the exfoliated clay platelets on the crystallization behavior of polyamide‐6 in polyamide‐6/clay nanocomposites

Exfoliated polyamide‐6 (PA6)/organoclay nanocomposite films with planar‐oriented clay platelets were prepared by the simple hot pressing of melt‐extruded nanocomposite pellets. The average distance between the neighboring clay platelets was controlled by changes in the clay loading content in the nanocomposites. The effects of the clay platelet spacing on the crystallization behavior of PA6 were investigated with transmission electron microscopy and wide‐angle X‐ray diffraction. The crystal lamellae were found to be mainly perpendicular to the clay surface for the nanocomposites with large spacing between the clay sheets at low clay loading contents. This perpendicular orientation morphology was attributed to the strong interactions between the PA6 molecular chain and the clay surface. In contrast, the crystal lamellae were found to be parallel to the clay surface when the spacing between the neighboring clay platelets was less than 30 nm. It was concluded that the confinement crystallization of PA6 within the nanoscale channels formed by clay sheets resulted in this parallel orientation texture. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 284–290, 2006     

Effect of Organoclays on Silicate Layer Structures and Thermal Stabilities of in-situ Polymerized Poly(D-lactide)/Clay Nanocomposites

Six kinds of organoclays were prepared through three kinds of polyols (PTMG, PEA and PCL) to investigate the effects of molecular weight and the chemical structure of organifiers. PTMG based organoclays showed higher ion-exchanged fraction than other organoclays and long chain organifier showed better efficiency in ion-exchanged fraction in the case of PTMG based organifiers. From WAXD and TEM analysis, it was confirmed that PTMG based organoclays formed partially exfoliated or fully exfoliated silicate layer structures. PDLA/clay nanocomposites were prepared by in-situ ring-opening polymerization of D-lactide with PTMG based organoclays as macro-initiators in the presence of equimolar Sn(Oct)₂/PPh₃ complex catalysts. The molecular weight of PDLA/clay nanocomposite decreased as increasing the feeding amount of organoclay because organoclay had hydroxyl terminal groups which can initiate the ring-opening polymerization of D-lactide. From TGA analysis, thermal stabilities of PDLA/clay nanocomposites improved with increasing organoclay content. From WAXD and TEM analysis, organoclay which was prepared by high molecular weight of PTMG based organifier was effective on the exfoliation of silicate layers in the in-situ polymerized PDLA/clay nanocomposite.     

Thermal and mechanical properties of syndiotactic polystyrene/organoclay nanocomposites with different microstructures

The fabrication of syndiotactic polystyrene (sPS)/organoclay nanocomposite was conducted via a stepwise mixing process with poly(styrene‐co‐vinyloxazolin) (OPS), that is, melt intercalation of OPS into organoclay followed by blending with sPS. The microstructure of nanocomposite mainly depended on the arrangement type of the organic modifier in clay gallery. When organoclays that have a lateral bilayer arrangement were used, an exfoliated structure was obtained, whereas an intercalated structure was obtained when organoclay with a paraffinic monolayer arrangement were used. The thermal and mechanical properties of sPS nanocomposites were investigated in relation to their microstructures. From the thermograms of nonisothermal crystallization and melting, nanocomposites exhibited an enhanced overall crystallization rate but had less reduced crystallinity than a matrix polymer. Clay layers dispersed in a matrix polymer may serve as a nucleating agent and hinder the crystal growth of polymer chains. As a comparison of the two nanocomposites with different microstructures, because of the high degree of dispersion of its clay layer the exfoliated nanocomposite exhibited a faster crystallization rate and a lower degree of crystallinity than the intercalated one. Nanocomposites exhibited higher mechanical properties, such as strength and stiffness, than the matrix polymer as observed in the dynamic mechanical analysis and tensile tests. Exfoliated nanocomposites showed more enhanced mechanical properties than intercalated ones because of the uniformly dispersed clay layers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1685–1693, 2004     

Nanocomposites of polyurethane with various organoclays: Thermomechanical properties,morphology, and gas permeability*

The properties of polyurethane (PU) nanocomposites with three different organoclays were compared in terms of their thermal stabilities, mechanical properties, morphologies, and gas permeabilities. Hexadecylamine–montmorillonite, dodecyltrimethyl ammonium–montmorillonite, and Cloisite 25A were used as organoclays for making PU hybrid films. The properties were examined as a function of the organoclay content in a matrix polymer. Transmission electron microscopy photographs showed that most clay layers were dispersed homogeneously into the matrix polymer on the nanoscale, although some particles of clay were agglomerated. Moreover, the addition of only a small amount of organoclay was enough to improve the thermal stabilities and mechanical properties of PU hybrid films, whereas gas permeability was reduced. Even polymers with low organoclay contents (3–4 wt %) showed much higher strength and modulus values than pure PU. Gas permeability was reduced linearly with an increasing amount of organoclay in the PU matrix. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 670–677, 2002; DOI 10.1002/polb.10124     

Surface modification of clay and its effect on the intercalation behavior of the polymer/clay nanocomposites

Melt intercalation of the methylsilylated organoclays with polar polymers such as SAN was examined to verify the adhesive role of guest polymeric chains between hydrophilic clay layers, so-called “glue effect” on intercalation behavior. Once methylsilylated organoclay was melt-blended with SAN, it was found that the mixture presented significant retardation of increase of interlayer spacing, d₀₀₁ with heating time, and a noticeable decrease of d₀₀₁ after the methylsilylation of organoclay, implying that the diffusion of SAN was highly suppressed by the decrease of polar interaction force caused by conversion of OH to methylsiloxyl groups. However, when applying shear force for the methylsilylated organoclay/SAN nanocomposites during melt intercalation, a noticeable increase of d₀₀₁ was observed, expressing that intercalation of clay by SAN occurred much more effectively because of the reduction of gluing force between host clay and guest polymers, which was well supported by dramatic improvements of mechanical properties after methylsilylation of organoclays. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2367–2372, 2004     

Synthesis of poly(2‐ethylhexyl acrylate)/clay nanocomposite by in situ living radical polymerization

This investigation reports the preparation of tailor‐made poly(2‐ethylhexyl acrylate) (PEHA) prepared via in situ living radical polymerization in the presence of layered silicates and characterization of this polymer/clay nanocomposite. Being a low T_g (?65 °C) material, PEHA has very good film formation property for which it is used in paints, adhesives, and coating applications. 2‐Ethylhexyl acrylate was polymerized at 90 °C using CuBr and Cu(0) as catalyst in combination with N,N,N′,N″,N″‐pentamethyl diethylenetriamine (PMDETA) as ligand. A tremendous enhancement in reaction rate and polymerization data was achieved when acetone was added as additive to increase the efficiency of the catalyst system. PEHA/clay nanocomposite was prepared at 90 °C using CuBr as catalyst in combination with PMDETA as ligand. Different types of clay with same loading were also used to study the effect on reaction rate. The molecular weight (M_n) and polydispersity index of the prepared nanocomposites were characterized by size exclusion chromatography. The active end group of the polymer chain was analyzed by ¹H NMR analysis and by chain extension experiment. Polymer/clay interaction was studied by Fourier Transform Infrared spectrometry and wide‐angle X‐ray diffraction analyses. Distribution of clay in the polymer matrix was studied by the transmission electron microscopy. Thermogravimetric analysis showed that thermal stability of PEHA/clay nanocomposite increases on addition of nanoclay. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Preparation, characterization and electrochemical corrosion studies on environmentally friendly waterborne polyurethane/Na-MMT clay nanocomposite coatings

In this study, we present the first practical evaluation for the corrosion protection effect of waterborne polyurethane (WPU)/Na⁺-montmorillonite (Na⁺-MMT) clay nanocomposite coating. Typically, a series of waterborne polyurethane (WPU)/Na⁺-montmorillonite (Na⁺-MMT) clay nanocomposite materials have been successfully prepared by effectively dispersing the inorganic nanolayers of commercially purified Na⁺-MMT clay in WPU matrix through direct aqueous solution dispersion technique. First of all, WPU was prepared by polymerizing PCL, DMPA and H₁₂MDI, followed by characterized by nuclear magnetic resonance (¹H NMR), Fourier transform infrared (FTIR) and gel permeation chromatography (GPC). Subsequently, the as-prepared PU/Na⁺-MMT clay nanocomposite (Na⁺-PCN) materials were subsequently characterized by FTIR, X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM).PCN materials in the form of coating at low Na⁺-MMT clay loading up to 3 wt% coated on the cold-rolled steel (CRS) coupons were found to exhibit superior corrosion protection effect over those of neat WPU based on a series of electrochemical measurements of corrosion potential, polarization resistance, corrosion current and impedance in 5 wt% aqueous NaCl electrolyte. Effects of the material composition on the gas permeability, thermal stability and optical clarity of neat WPU along with a series of Na⁺-PCN materials, in the form of coating and free-standing film, were also studies by gas permeability analyzer (GPA), thermogravimetric (TGA), differential scanning calorimetry (DSC) and ultraviolet UV-visible transmission spectroscopy, respectively. As control experiments, a series of PU/organo-MMT nanocomposite (denoted by organo-PCN) materials were also prepared for comparative studies.     

Waterborne trifunctionalsilane‐terminated polyurethane nanocomposite with silane‐modified clay

Trifunctional organosilane‐modified clay was synthesized and used to prepare waterborne trifunctionalsilane‐terminated polyurethane (WSPU)/clay nanocomposite dispersions in this study. Qualitative evidence of the presence of chemically attached silane molecules on clay were confirmed by Fourier transform infrared spectroscopy. The grafted amount and the grafting yield were determined by thermogravimetric analysis and the obtained results were in good agreement with the cation exchange capacity of pristine clay. X‐ray diffraction and transmission electron microscopy examinations indicated that the clay platelets are mostly intercalated or partially exfoliated in the SPU matrix with a d‐spacing of ～2.50 nm. Clay does not influence the location and peak broadness of the glass transition temperature of soft segment as well as hard segment domains in the WSPU/clay films. WSPU/clay dispersion with higher clay content exhibits a marginal increase in the average particle size, but silane modified clay has a pronounced effect compared with Cloisite 20A‐based nanocomposites. In addition, the incorporation of organophilic clay can also enhance the thermal resistance and tensile properties of WSPUs dramatically through the reinforcing effect. The improvement in water and xylene resistance of the silane modified clay nanocomposites proved that trifunctional organosilane can be used as effective modifiers for clays. Storage stability results confirmed that the prepared nanocomposite dispersions were stable. This method provides an efficient way to incorporate silane modified clay in SPU matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2747–2761, 2007     

Nanocomposites of poly(ethylene terephthalate‐co‐ethylene naphthalate) with organoclay

Poly(ethylene terephthalate‐co‐ethylene naphthalate) (PETN)/organoclay was synthesized with the solution intercalation method. Hexadecylamine was used as an organophilic alkylamine in organoclay. Our aim was to clarify the intercalation of PETN chains to hexadecylamine–montmorillonite (C₁₆–MMT) and to improve both the thermal stability and tensile property. We found that the addition of only a small amount of organoclay was enough to improve the thermal stabilities and mechanical properties of PETN/C₁₆–MMT hybrid films. Maximum enhancement in both the ultimate tensile strength and initial modulus for the hybrids was observed in blends containing 4 wt % C₁₆–MMT. Below a 4 wt % clay loading, the clay particles could be highly dispersed in the polymer matrix without a large agglomeration of particles. However, an agglomerated structure did form in the polymer matrix at a 6 wt % clay content. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2581–2588, 2001     

Polyurethane‐nanocomposite materials via in situ polymerization into organoclay interlayers

New nanocomposite materials based on polyurethane intercalated into organoclay layers have been synthesized via in situ polymerization. The syntheses of polyurethane–organoclay hybrid films were carried out by swelling the organoclay [12‐aminododecanoic acid montmorillonite] into different kinds of diols followed by addition of diisocyanate then casting in a film. The homogeneous dispersion of MMT in the polymer matrix is evidenced by scanning electron microscope and x‐ray diffraction, which showed the disappearance of the peak characteristic to d₀₀₁ spacing. It was found that the presence of organoclay has improved the thermal, solvent resistance and mechanical properties. Also, the tensile strength is increased with increasing the organoclay contents to 20% by the ratio 182% related to the PU with 0% organoclay. On the contrary, the elongation has decreased with increasing the organoclay contents. Copyright © 2007 John Wiley & Sons, Ltd.     

Chiral poly(amide-imide)/organoclay nanocomposites derived from pyromellitoyl-bis-l-isoleucine and benzimidazole containing diamine: synthesis, nanostructure, and properties

In this study, a series of polymer–clay nanocomposite materials, consisting of organosoluble poly(amide-imide) (PAI) matrix and dispersed nanolayers of inorganic montmorillonite clay, were successfully prepared by solution dispersion technique. At first, the reactive organoclay was prepared by using protonated l-isoleucine amino acid as a swelling agent for silicate layers of Cloisite Na⁺. Then, organosoluble PAI containing isoleucine amino acid was synthesized through step-growth polymerization reaction of N,N′-(pyromellitoyl)-bis-isoleucine diacid and 2-(3,5-diaminophenyl)-benzimidazole under green condition using molten tetrabutylammonium bromide. This polymer was end-capped with amine end groups near the completion of the reaction to interact chemically with acidic group of organoclay. Finally, PAI/organoclay nanocomposite films containing 2%, 5%, 10%, and 15% of organoclay were prepared via solution intercalation method through blending of organoclay with the PAI solution. Dispersion of the modified clay in the PAI matrix resulted in a nanostructured material containing intercalated polymer between the silicate layers. Structures of exfoliation were confirmed by X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. Thermogravimetric analysis data indicated that the addition of organoclay into the PAI matrix increased the thermal decomposition temperatures of the obtained nanocomposites compared to the pure PAI.     

Synthesis of self‐healing polyurethane urea‐based supramolecular materials

Supramolecular polyurethane ureas are expected to have superior mechanical properties primarily due to the reversible, noncovalent interactions such as hydrogen bonding interactions. We synthesized polyurethane prepolymers from small molecular weight of poly(tetramethylene ether)glycol and isophorone diisocyanates, which were end capped with propylamine to synthesize polyurethane ureas with high contents of urea and urethane groups for hydrogen‐bonding formations to facilitate self‐healing. The effects of polyurethane urea molecular weight (3000 ≤ M_n ≤ 9000), crosslinking, and cutting direction were studied in terms of thermal, mechanical, and morphological properties with an emphasis on the self‐healing efficiency. It was found that the thermal self‐healability was more pronounced as the molecular weight of polyurethane urea decreased, showing a maximum of more than 96% with 3000 M_n when the sample was cut along the stretch direction. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 468–474     

Synthesis and characterization of novel segmented polyurethane/clay nanocomposite via poly(ε-caprolactone)/clay

A novel segmented polyurethane/clay (PU/clay) nanocomposite based on poly(caprolactone), diphenylmethane diisocyanate, butanediol, and poly(caprolactone)/clay prepolymer was synthesized as evidenced by FTIR and X-ray diffraction studies. Poly(caprolactone)/clay (PCL/clay) prepolymer was first synthesized in a nanocomposite form as confirmed by X-ray diffraction. X-ray diffraction study showed that PU/clay contained crystalline structure due to the presence of PCL/clay. In mechanical properties, about 1.4% PCL/clay in PU/clay resulted in a large increase in the elongation of PU/clay. However, when the amount of PCL/clay was 4.2%, the elongation of PU/clay was reduced drastically. This behavior indicated that PU/clay can be transformed from an elastomer to a thermoplastic material as the amount of PCL/clay in PU/clay increased. Additionally, the lap shear stress of PU/clay was at least three times that of neat PU as a result of the PCL/clay component. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2225–2233, 1999     

Poly(lactic acid)/organoclay nanocomposites: Thermal,rheological properties and foam processing

In this study, polymer nanocomposites based on poly(lactic acid) (PLA) and organically modified layered silicates (organoclay) were prepared by melt mixing in an internal mixer. The exfoliation of organoclay could be attributed to the interaction between the organoclay and PLA molecules and shearing force during mixing. The exfoliated organoclay layers acted as nucleating agents at low content and as the organoclay content increased they became physical hindrance to the chain mobility of PLA. The thermal dynamic mechanical moduli of nanocomposites were also improved by the exfoliation of organoclay; however, the improvement was reduced at high organoclay content. The dynamic rheological studies show that the nanocomposites have higher viscosity and more pronounced elastic properties than pure PLA. Both storage and loss moduli increased with silicate loading at all frequencies and showed nonterminal behavior at low frequencies. The nanocomposites and PLA were then foamed by using the mixture of CO₂ and N₂ as blowing agent in a batch foaming process. Compared with PLA foam, the nanocomposite foams exhibited reduced cell size and increased cell density at very low organoclay content. With the increase of organoclay content, the cell size was decreased and both cell density and foam density were increased. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 689–698, 2005     

Effect of surface modification of montmorillonite on the properties of aromatic polyamide/clay nanocomposites

The surface modification of montmorillonite clay was carried out through ion‐ exchange reaction using p‐phenylenediamine as a modifier. This modified clay was employed to prepare aromatic polyamide/organoclay nanocomposite materials. The dispersion behavior of clay was examined in the polyamide matrix. Polyamide chains were synthesized from 4‐aminophenyl sulfone and isophthaloyl chloride (IPC) in dimethylacetamide. These amide chains were suitably end‐capped with carbonyl chloride end groups to interact chemically with modified montmorillonite clay. The resulting nanocomposite films containing 2–20 wt% of organoclay were characterized by TEM, X‐ray diffraction (XRD), thin‐film tensile testing; thermogravimetric analysis (TGA), differential scanning calorimetric (DSC) and water absorption measurements. Mechanical testing revealed that modulus and strength improved up to 6 wt% organoclay loading while elongation and toughness of nanocomposites decreased with the addition of clay content in the matrix. Thermal decomposition temperatures of the nanocomposites were in the range 225–450 °C. These nanocomposites expressed increase in the glass‐transition temperature values relative to pure polyamide describing interfacial interactions among the phases. The percent water uptake of these composites reduced upon the addition of modified layered silicate depicting improved barrier properties. Copyright © 2008 John Wiley & Sons, Ltd.