Polyamide 6 treated with pentabromobenzyl acrylate and layered silicates

A study of the simultaneous application of a brominated flame retardant and an organically layered silicate (OLS) for the flame retarding of polyamide 6 (PA6) is presented. Upon treating PA6 with at least 7 wt% monomeric pentabromobenzyl acrylate (PMA), a UL‐94 V‐0 rating and an oxygen index (OI) value of 29.7 were obtained. By adding 1 wt% organically layered montorillonite (OMMT) and 10 wt% PMA, the V‐0 rating remained, indicating cooperation between PMA and OMMT. Higher concentrations of OMMT result in a decreased UL‐94 rating showing an antagonism. The size and mass of drops formed in the UL‐94 test increased with increasing OMMT, suggesting an increase in the viscosity and density of the pyrolyzing matrix. The effect of the Br additive on the peak heat release rate (PHRR) measured in the cone calorimeter is similar, but smaller, than that of clay. A calculation of the synergistic effectivity related to PHRR enabling a numerical estimate of the extent of synergism or antagonism is presented. When the ill‐dispersed pristine clay (Na⁺MMT) is used, the viscosity does not increase, the PHRR decreases slightly, but the mass loss rate (MLR) is close to that of the matrix. The time of ignition (TOI) decreases upon the addition of PMA, similarly to the addition of OMMT. This is explained by migration of the Br additive to the surface barrier similar to that of clay so that the low thermal conductivity (TC) barrier is formed before the ignition. Accumulation of heat in the barrier decreases the TOI. Copyright © 2010 John Wiley & Sons, Ltd.     

Flame retarding polyamide 6 with melamine cyanurate and layered silicates

The flammability behavior of the system polyamide 6 (PA 6) + melamine cyanurate (MC) with or without organically modified layered montmorillonite (OMMT) or sodium montmorillonite (Na⁺MMT) was studied. The high degree of flame retardancy (FR) obtained with 13 wt% MC is maintained upon adding up to 0.2 wt% OMMT or Na⁺MMT. Increase mass % of OMMT is antagonistic to the MC effect. The rate of dripping decreases while the size and mass of drops in the UL‐94 tests increases with increasing wt% OMMT indicating increase in viscosity of the melt and decrease in the rate of sublimation of melamine. Addition of poly vinyl pyrrolidone (PVP) decreases the viscosity and partially restores the FR rating. Na⁺MMT does not increase the viscosity and the FR ratings are partially preserved. The peak of heat release rate (PHRR) in the cone calorimeter decreases with increased loading of OMMT. Addition of Na⁺MMT or PVP has little influence on the PHRR. The time of ignition decreases with increase in OMMT, but is not affected when Na⁺MMT is used. This is explained by the low thermal conductivity of the clay containing surface layer of samples during pyrolysis and combustion. Mechanistic considerations are presented. Copyright © 2008 John Wiley & Sons, Ltd.     

Nanocomposites of NLO chromophore‐modified layered silicates and polypropylene

Intercalation of guest species into layered inorganic solids is a method of producing ordered inorganic–organic assemblies with unique microstructures controlled by host–guest and guest–guest interactions. Smectite clay minerals, such as montmorillonite, having appropriate functional molecules in between the silicate layers are supposed to exhibit a wide range of novel characteristics. Nanocomposite material based on maleic anhydride‐grafted polypropylene and dye‐modified layered silicate was developed. Characteristics of organo‐modified montmorillonite particles and polymer/clay hybrids have been investigated through FTIR, SAXS, DSC, UV measurements, and transmission electron microscopy. The results of the intercalation process, structural characterization, and thermal properties will be discussed in comparison with the intercalation and nanocomposite preparation results. The intercalation was successfully conducted by the ion‐exchange method. It was shown that intercalated dibenzilidene acetone type chromophores exist in the clay galleries in an aggregated form, probably as J‐aggregates. This feature strongly effects on optical and nonlinear optical properties of nanocomposites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2493–2502, 2005     

Synthesis and physical properties of layered silicates/polyurethane nanocomposites

Samples of polyurethane nanocomposites were synthesized using diphenylmethane diisocyanate, poly(ε‐caprolactone) diol, di(ethylene glycol), and a clay functionalized by hydroxyl groups. The inorganic content in the hybrids was 2 wt %, 4 wt %, and 8 wt %. The X‐ray analysis showed that exfoliation occurred for clay content equal to 2% (w/w), whereas for higher contents, the inorganic phase rearranges in an intercalated structure. FTIR analysis suggested that the degree of hydrogen bonding in the hard segments was greatly reduced because of the amount of silicate layers and their dispersion. The dynamic‐mechanical analysis showed that the presence of clay lamellae extends very much the temperature range before the hard domain transition, causing the loss of mechanical consistency of the samples. It is less than 100 °C for the pure polymer, and increases up to 200 °C for the nanocomposites. The permeability of water vapor decreases linearly with inorganic content up to 4% of inorganic phase, and levels off at higher concentrations. The permeability behavior, at low activities, is largely dominated by the diffusion phenomenon. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2454–2467, 2005     

Adsorption of organic anions from aqueous solutions by layered silicates modified with cationic surfactant

The interaction of anionic organic dyes with layered silicates (kaolinite and hydromica) both natural and modified with a cationic surfactant (cetylpyridinium bromide) is studied by adsorption and spectral methods. The adsorption of organic anions by modified silicates is proved to proceed via the formation of ionic associates of these adsorbates with the modifier. It is found that the interaction of large organic anions with the modifier results in the desorption of the latter, followed by its secondary adsorption in the form of ionic associates with the adsorbates. The selectivity of layered silicates modified with the cationic surfactant to organic anionic dyes is determined by the stability of the formed dye/modifier ionic associates and their affinity to the surface. These factors depend on the sizes of the hydrocarbon moieties of both components of the associates. Therefore, the selection of a suitable modifier allows one to control the selectivity of modified minerals to different organic anions. Using long-chain organic cations as modifiers, organic anions of any sizes can be extracted from aqueous solutions.     

Thermally stable organically modified layered silicates based on alkyl imidazolium salts

A series of imidazolium salts having various substituents and functional groups were synthesized and characterized by FTIR and NMR spectroscopy. Organic modification of natural and synthetic layered silicates involving montmorillonite (MMT), laponite (lap), and synthetic mica (mica) was carried out by ion-exchange reaction. The obtained organo-clays were characterized by FTIR and powder X-ray diffraction techniques. Results indicate that these organically modified clays have much higher thermal stabilities compared to their corresponding imidazolium halides. It was also observed from TGA analysis that thermal stability does not depend on the functional group present at the 3-position of the imidazolium salts. These studies strongly supports premise that the removal of halide is necessary to improve the thermal stability of the organo-clay produced.     

Structure-property relationships of copolyamides. I. Thermal properties and crystallization

Six nylon salts [hexamethylenediammonium adipate (6.6), hexamethylenediammonium terephthalate (6.T), hexamethylenediammonium isophthalate (6.I), p-xylylenediammonium adipate (PXD.6), m-xylylenediammonium adipate (MXD.6), and m-xylylenediammonium isophthalate (MXD.I)] were copolymerized with ε-caprolactam. The resulting random copolyamides showed different modes of crystallization as confirmed by the melting temperature depression and the decrease in the isothermal crystallization rate. By selective hydrolysis it was found that the differences in T_m depression and isothermal crystallization rate were due to partial inclusion of comonomers in the crystal lattice. The effect of comonomer structure on the crystallization rate is also discussed.     

Organic/inorganic hybrid materials and nanocomposites based upon layered silicates modified with cyclic amidines

Various cyclic amidinium cations were used to exchange intergallery sodium cations of water‐swellable fluorohectorite in order to produce novel families of organic/inorganic hybrid materials. Oligomeric cyclic amidinium cations, such as mono(imidazolinium)‐terminated oligostyrene, oligostyrene‐co‐oligo(acrylonitrile), and oligo(methyl methacrylate) with number‐average molecular masses around 3 000 g/mol afforded effective exfoliation during melt processing. Morphology and dynamic mechanical properties were measured as a function of silicate content and silicate modification.     

Thermal properties of poly-ε-caprolactam and copolyamides based on ε-caprolactam

The copolyamides consisting of ε-caprolactam and 6.1–24.5 wt.% of nylon salt prepared from adipic acid and 1-(2-aminoethyl) piperazine were synthesized. Physical and thermal characteristics of polyamide 6 and the copolyamides were compared. Nylon salt does not influence the polyreaction equilibrium so it is possible to prepare the copolyamides with high molecular weight and with the content of low-molecular compounds comparable with that of pure PA 6. Melting temperatures of the copolyamides are lower in comparison with PA 6 and decrease proportionally to the amount of the nylon salt. The thermal stability of the copolyamides is good and equal to that of PA 6. The melting enthalpies indicate that the process of crystallization of the copolyamides is influenced by the time of crystallization and the amount of comonomer present. Longer time of the crystallization assures higher degree of crystallization. The kinetics and the level of crystallization are positively influenced by the mobility of copolyamide segments mainly up to 10 wt.% of comonomer.     

Effect of organomodified layered silicates on the properties and structure of polytetrafluoroethylene

The physicomechanical and triboengineering properties and the structures of polymer composite materials based on polytetrafluoroethylene and layered silicates are studied. The triboengineering characteristics are substantially improved by the introduction of a small amount of layered silicates (2–5 wt %). It is found that the introduction of organomodified layered silicates leads to a considerable reduction in the friction coefficient, by an order of magnitude, and causes an increase in wear resistance (2000-fold). With the use of X-ray structural analysis and scanning electron microscopy, it is shown that, during friction loading, filler particles are localized on the friction surface, thereby hampering wear of the material.     

Spectral properties of TMPyP intercalated in thin films of layered silicates

The objective of this study was to investigate the spectral characteristics of tetracationic porphyrin dye (TMPyP), intercalated into films of three smectites. The smectites represented the specimens of high (Fluorohectorite; FHT), medium (Kunipia F montmorillonite; KF), and low layer charge (Laponite; LAP). Intercalation of TMPyP molecules was proven by XRD measurements. The molecular orientations of the dye cations were studied by means of linearly polarized ultraviolet-visible (UV-vis) and infrared (IR) spectroscopies. Both the UV-vis and the IR spectroscopy proved the anisotropic character of the films. The spectral analysis of the polarized UV-vis spectra and consequent calculations of tilting angles of the transition moments in the region of Soret band transitions were in the range of 25-35 degrees . The determined angles indicated that the molecular orientation of the dye cations was almost parallel to the surface of the silicates. Slightly higher values, determined for a FHT film, indicated either a slightly more tilted orientation of the dye cations or the change of molecular conformation after the intercalation of the dye. Quenching of TMPyP fluorescence was observed, resulting from the formation of bimolecular layer arrangements with sandwich-type assemblies of the dye molecules.     

Solution properties of copolyamides

Mark-Houwink-Sakurada relations for random copolymers from para-aminobenzoic acid and 6-aminohexanoic acid were determined in N,N-dimethylacetamide, dichloroacetic acid and trifluoroacetic acid. Unperturbed chain dimensions, solvent-polymer interaction parameters and conformational parameter, δ, were obtained by using the Stockmayer-Fixman equation. The unperturbed dimensions were also calculated by using a semi-empirical relation of Krigbaum; they compare favourably with values calculated through the use of (S-F) equation. The results show that the unperturbed dimensions are dependent on the solvent nature.     

Synthesis of copolyamides based on PA 66 bearing lithium sulfonate groups and having unique thermal properties

Copolyamides of PA 66/6 lithium 5‐sulfoisophthalic acid (LiSIPA) containing up to 40 mol % of LiSIPA were prepared in a 1L‐pilot reactor operating at high pressures and high temperatures. Interestingly, the presence of lithium sulfonate moieties highly impacted the glass transition temperature of the polyamide. The T_g increased from 59 °C for PA 66 to 155 °C for a copolymer containing about 40 mol % of LiSIPA. 1,3‐Dihexylbenzenedicarboxamide and lithium p‐toluenesulfonate were synthesized as model compounds to investigate the interaction of lithium sulfonate moieties and amide functions. Infrared spectroscopy using ATR technology performed on mixture of both compounds showed that the carbonyl group of amide functions interacts with the lithium cation of lithium sulfonate moieties. Similar S? O and C? O adsorption bands were observed in copolyamides PA 66/6LiSIPA and in mixture of model compounds, which strongly suggest the formation in the copolyamides of physical cross‐linking points centered on lithium cations coordinated by carbonyl groups of amide functions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of intrinsically flame‐retardant copolyamides and their employment in PA6‐fibers

Flame‐retarded polyamide 6.6 (FR‐PA6.6) was prepared by the cocondensation of hexamethylene diammonium adipate (AH‐salt) with the corresponding salts of hexamethylene diamine and two different organophosphorus compounds, namely, 3‐hydroxyphenylphosphinylpropanoic acid (3‐HPP, 1) and 9,10‐dihydro‐10‐[2,3‐di (hydroxycarbonylpropyl]‐10‐phosphaphenanthrene‐10‐oxide (DDP, 2). The incorporation of the phosphorus comonomers and the thermal and physical properties of the resulting copolyamides have been studied. The phosphorus‐modified FR‐PA6.6 possesses high relative viscosities of 2.0 to 2.4, good thermal stability, and was used for the production of polyamide blends by merging FR‐PA6.6 with commercial PA6. This offered access to flame‐retarded PA6 multifilaments, which possess tensile strengths up to 0.7 GPa and elastic moduli up to 6.2 GPa. Knitted fabrics of FR‐PA6 exhibit high limiting oxygen index (LOI) values between 36 and 38 and executed burning tests demonstrate that the incorporation of phosphorus‐based comonomers improve flame retardancy significantly. The approach presented here offers a straightforward access to effective flame retardancy in nylon 6.     

Syntheses and properties of phosphorus-containing copolyamides

Caprolactam was copolymerized with 1,5-dioxo-1-methyl-4-azaphosphepane or methylphosphacaprolactam. The molecular weight of the resulting copolymers decreased with increasing concentration of the thermally labile phosphorus moieties. Copolymers based on ≥40% caprolactam were shown to be crystalline by differential scanning calorimetry and x-ray techniques. As the concentration of the phosphorus structures in the copolymers increased, the glass transition and crystallization temperatures increased while the melting temperatures, crystallinities, and thermal stabilities decreased. Melt blends of nylon 6 and polymethylphosphacaprolactam were shown by differential scanning calorimetry, a selective extraction technique, and elemental analysis to contain appreciable amounts of block copolyamides, and no crystalline random structures were detected. The thermal stabilities of the melt blends were similar to those of random copolymers having comparable concentrations of the phosphorus-containing sequences.     

New poly(butylene succinate)/layered silicate nanocomposites. II. Effect of organically modified layered silicates on structure,properties, melt rheology,and biodegradability

A series of new poly(butylene succinate) (PBS)/layered silicate nanocomposites were prepared successfully by simple melt extrusion of PBS and organically modified layered silicates (OMLS). Three different types of OMLS were used for the preparation of nanocomposites: two functionalized ammonium salts modified montmorillonite and a phosphonium salt modified saponite. The structure of the nanocomposites in the nanometer scale was characterized with wide-angle X-ray diffraction and transmission electron microscopic observations. With three different types of layered silicates modified with three different types of surfactants, the effect of OMLS in nanocomposites was investigated by focusing on four major aspects: structural analysis, materials properties, melt rheological behavior, and biodegradability. Interestingly, all these nanocomposites exhibited concurrent improvements of material properties when compared with pure PBS. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3160–3172, 2003     

Preparation and some properties of organically modified layered alkali titanates with alkylmethoxysilanes

The silylation of K2Ti4O9 x nH2O with organosilanes (methyl, n-butyl, n-octyl, n-dodecyl, n-octadecyltrimethoxysilanes and n-octadecyldimethylmethoxysilane) was conducted using the octylammonium-exchanged form as the intermediate. The surface coverage of the octadecylsilylated derivative was controlled by changing the employing amounts of octadecyltrimethoxysilane. The swelling behaviors of the octyl, dodecyl, and octadecylsilylated derivatives in organic solvents were investigated to show that the degree of the swelling varies depending on the kind of solvents, the alkyl chain length of the attached alkylsilyl groups, and the surface coverage. The octadecylsilylated derivative with the largest surface coverage was converted to film with a thickness of ca. 500 nm by casting the chloroform suspension on a substrate. The octadecylsilylated derivative showed a reversible thermoresponsive change of the basal spacing by ca. 0.5 nm in the temperature range between 15 and 60 degrees C.     

Melt intercalation of polystyrene in layered silicates

We have studied the melt intercalation of polystyrene into organically modified sodium bentonite, a layered, mica-type silicate, using a variety of techniques. Wide-angle X-ray scattering experiments on polymer/silicate hybrid samples demonstrate that intercalation of polymer chains leads to an ∼25% increase in the spacing between silicate layers. The magnitude of this increase, compared with the radius of gyration of the melt polymer, implies a flattened conformation of chains in the galleries. Low voltage scanning electron microscopy reveals voids in the intercalated hybrid matrix that correspond to regions where pristine polymer was present in the physical mixture of polymer and silicate before intercalation. Differential scanning calorimetry shows that only unintercalated polymer contributes to the measured glass transition trace, so that the magnitude of the trace is diminished upon intercalation. © 1996 John Wiley & Sons, Inc.     

Preparation and properties of silicon containing copolyamides

Copolyamides containing siloxane moieties in main chain were prepared by a melt polycondensation with 1,3-bis(3-aminopropyl)tetramethyldisiloxane (E), hexamethylenediamine (N6), and adipic acid (6). Glass transition temperature (T_g), cold crystallization temperature (T_cc), and melting temperature (T_m) were measured by differential thermal analysis (DTA). The depression of T_m for copolyamide was fitted by the Flory curve. Melting peak remarkably broadens with increasing E6 component in copolyamide. The change of T_g was fitted by the Gibbs and Dimarzio's equation in which the number of flexible bond is considered. The difference between T_g and T_cc increased with increasing E6 component. These DTA studies suggest that the crystallization of N66 component in copolyamide is hindered by the bulky siloxane moiety, while the micro-Brownian motion of amorphous segment is promoted by the flexible siloxane bond. Tensile strength and Young's modulus decreased with increasing E6 component. The solubility in various solvents increased with increasing E6 component. Permeability of oxygen and nitrogen increased with an increase of temperature and E6 component. The separation coefficient of oxygen to nitrogen rapidly increased near 50 mol% of E6 concentration and then leveled out above 70 mol%. The contact angle with water and methylene iodide increased with an introduction of the siloxane moiety into polymer chain.