Hexamethylene Isophthalamide Research Articles

The effects of nanoclay and carbon nanotube co‐addition on properties of an amorphous polyamide/maleated styrene‐ethylene‐co‐butylene‐styrene blend

AbstractThis work studied the individual and combined addition of natural (MMT‐Na) and modified (MMT‐30B) nanoclays, and carbon nanotubes (CNTs) to a poly (hexamethylene isophthalamide co‐terephthalamide) (aPA)/styrene‐ethylene/butylene‐styrene (SEBS) blend grafted with maleic anhydride. Their effects on the blend's morphology, thermo‐mechanical properties, and flammability were evaluated. Morphological analysis showed that both clays were located in the aPA matrix, with the MMT‐Na as agglomerates and the MMT‐30B intercalated with exfoliated regions. The CNTs were dispersed and randomly oriented in the aPA matrix. Data obtained through dynamic‐mechanical analysis (DMA) showed that adding 1.0% MMT‐30B and 1.0% CNT increased the storage modulus (E') by 26% and 27%, respectively, while adding both 0.5% MMT‐30B and 0.5% CNT increased E' by 38%, suggesting synergy between the nanoparticles related to mechanical properties. Regarding flammability, since the first burn timing (t1) could not be obtained, none of the samples could be classified according to the UL94 standard. However, qualitatively, a better flammability performance was noticed for the nanocomposites than for the pure blend.

Interfacial In Situ Polymerization of Layered-Silicate/Poly (Hexamethylene Isophthalamide) Nanocomposites

In this work Poly (hexamethylene isophthalamide) (PA 6I) was synthesized via interface step polymerization at room temperature for the first time, here. Layered silicates were used in order to fabricate PA 6I nanocomposites by in-situ polymerization. Thermal, mechanical and morphological of obtained nanocomposites were examined. The dispersion effect of silicate layers in the matrix was studied by means of XRD and FE-SEM. The incorporation of layered silicates in PA 6I leads to a significant improvement in the mechanical properties of the resulting nanocomposites. The thermogravimetric analysis results showed that layered silicate incorporation enhances the thermal resistance of PA 6I nanocomposites. Improvements in thermal degradation properties, while Young’s moduli have also been modified.

Synthesis and Characterization of Novel Water-Soluble Polyamides with Enhanced Gas Barrier Properties

Poly(hexamethylene isophthalamide) (PA6I), an amorphous polymer characterized by high temperature resistance and significant oxygen barrier performances, has been chemically modified by using the 5-sulfoisophthalic acid sodium salt as a comonomer. Then, ionic groups have been randomly distributed along the polymeric chains. The new sulfonated PA6I samples were studied in order to understand structure–property relationships. It results that ionomeric PA6Is present an increment of Tg and, accordingly, a decrement of the oxygen transmission rate at 50% of relative humidity with the increment of the ionic content. Ionic groups, indeed, induce the formation of new interactions among the polymer chains, and then, a complex macromolecular network is realized. Interestingly, a molar amount of ionic groups equal to or higher than 10% makes sulfonated polyamides water-soluble. This characteristic, exploited to prepare new coatings on different polymers, opens a range of new applications for ionomeric PA6I.

Block and random copolyamides of poly(m‐xylylene adipamide) and poly(hexamethylene isophthalamide‐co‐terephthalamide): Methods of preparation and relationships between molecular structure and phase behavior

Copolymerization of poly(m‐xylylene adipamide) (MXD6) and poly(hexamethylene isophthalamide‐co‐terephthalamide) (PA6I‐6T) was used as an efficient strategy to prepare amorphous homogeneous systems with improved properties mainly for packaging applications. The preparation of block copolymers was first of all tried by co‐extrusion of the two polymers and then by thermal treatments at high temperatures in DSC or mixing in Brabender, also in the presence of a catalyst. The occurrence of transamidation reactions led to macromolecular structures with different randomness degrees. Further, random copolymers, with the full range of compositions, were synthetized from monomers, by a fast and simple two‐stage melt polycondensation. For all the copolymers, the sequence distribution was studied by using a 1H NMR method developed by the Authors. The effects of preparation procedures, of mixing temperature and time, of the presence of a catalyst on the chemical structure, and, then, on final properties were studied. Interesting correlations among block length, monomer distribution and phase behavior were discussed. POLYM. ENG. SCI., SCI., 55:1475–1484, 2015. © 2014 Society of Plastics Engineers

Characterization of layered silicate dispersion in polymer nanocomposites using Fourier transform infrared spectroscopy

AbstractFourier transform infrared (FTIR) spectroscopy was used to characterize the state of dispersion of layered silicate in polymer nanocomposites. The nanocomposite samples were based on poly(hexamethylene isophthalamide) and montmorillonite nanoclay prepared by melt intercalation. The infrared spectra of SiO stretching bands between 1150 and 960 cm−1 are found to be very sensitive to the extent of nanoclay dispersion at the molecular level. Increased level of nanoclay delamination resulted in significant changes to the out‐of‐plane a mode at 1082 cm−1 and the two in‐plane modes b and b at 1050 and 1030 cm−1, respectively. The a mode shows a substantial increase in intensity and shifts toward lower wave numbers. The bandwidths of the b and b modes are reduced significantly. The b mode also shifts toward higher wave numbers in exfoliated nanoclay. Hence, FTIR can complement other methods to characterize the morphology of polymer nanocomposites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Study of Glass Transition and Reinforcement Mechanism in Polymer/Layered Silicate Nanocomposites

The structure−property relationship of polymer/layered silicate nanocomposites was investigated in this study. Polymer nanocomposites based on completely amorphous poly(hexamethylene isophthalamide) with exfoliated, intercalated, or agglomerated nanoclay morphology were produced and analyzed by X-ray diffraction and transmission electron microscopy. Differential scanning calorimetry measurements were used to characterize the glass-transition behavior. Dynamic mechanical analysis was performed to investigate the nature of the constrained region as the reinforcement mechanism. The modulus enhancement of the organoclay nanocomposites was found to have good linear correlation with the volume of the constrained region. The type of polymer−nanofiller interaction strongly influences the amount and modulus of the constrained region, and both of the latter contribute to the enhancement in the storage modulus of the polymer nanocomposite. The mechanical properties of the constrained region are temperature-dependent...

Synthesis and thermal oxidative degradation of a novel amorphous polyamide/nanoclay nanocomposite

A novel amorphous polyamide/montmorillonite nanocomposite based on poly(hexamethylene isophthalamide) was successfully prepared by melt intercalation. Wide angle X-ray diffraction and transmission electron microscopy showed that organoclay containing quaternary amine surfactant with phenyl groups was delaminated in the polymer matrix, resulting in well-dispersed morphologies even at high montmorillonite content. Thermal oxidation behavior of the polymer nanocomposites was studied by thermogravimetric analysis (TGA), and the chemical evolution in the solid residue was monitored by elemental analysis and Fourier transform infrared spectroscopy (FTIR). TGA results showed that the addition of well-dispersed organoclay resulted in a substantial increase (30 °C) in the onset degradation temperature of the nanocomposites as compared to the homopolymer. Elemental analysis on the solid residue indicated that the presence of nanoclay resulted in char formation with greater thermal stability. FTIR spectra showed that thermal degradation in air occurred via both oxidative and non-oxidative mechanisms simultaneously. In the homopolymer, the oxidative mechanism was more dominant. However, with the addition of well-dispersed organoclay, the non-oxidative pathway became more significant. Hence the presence of delaminated nanoclay layers could effectively retard thermo-oxidative degradation of the amorphous polymer by constraining the polymer chains and slowing down the rate of oxygen diffusion through the nanocomposites, but it was not as effective in hindering the non-oxidative degradation reaction pathway.

Morphology and mechanical properties of a novel amorphous polyamide/nanoclay nanocomposite

AbstractA novel amorphous polyamide/montmorillonite nanocomposite based on poly(hexamethylene isophthalamide) was successfully prepared by melt intercalation. Wide angle X‐ray diffraction and transmission electron microscopy showed that organoclay containing quaternary amine surfactants with phenyl and hydroxyl groups was delaminated in the polymer matrix resulting in well‐exfoliated morphologies even at high montmorillonite content. Differential scanning calorimetry results indicated that clay platelets did not induce the formation of a crystalline phase in this amorphous polymer. Tensile tests demonstrated that the addition of nanoclay caused a dramatic increase in Young's modulus (almost twofold) and yield strength of the nanocomposites compared with the homopolymer. The nanocomposites exhibited ductile behavior up to 5 wt % of nanoclay. The improvement in Young's modulus is comparable with semicrystalline aliphatic nylon 6 nanocomposites. Both the main chain amide groups and the amorphous nature of the polyamide are responsible for enhancing the dispersion of the nanofillers, thereby, leading to improved properties of the nanocomposites. The structure‐property relationship for these nanocomposites was also explored. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2605–2617, 2008

Thermal properties and phase morphology of melt‐mixed poly(trimethylene terephthalate)/poly(hexamethylene isophthalamide) blends

AbstractThis work examines the thermal properties and phase morphology of melt‐mixed poly(trimethylene terephthalate) (PTT)/poly(hexamethylene isophthalamide) (PA 6I) blends. Two temperatures, i.e., 250 and 260°C, are used to prepare the blends, respectively. Differential scanning calorimetry results indicate the immiscible feature of the blends. It is thus concluded that the ester‐amide interchange reaction hardly occurred in the PTT/PA 6I blends. Depending on the composition and mixing temperature, the crystallization ability of PTT in the blends is either enhanced or hindered. Basically, a lower PA 6I content shifts the PTT melt crystallization to a higher temperature, whereas a higher PA 6I content causes an opposing outcome. The original complex melting behavior of neat PTT becomes more regular after the incorporation of 60 wt % or 80 wt % of PA 6I. Thermogravimetry analyses (TGA) show that the thermal stability of the blends improves as the PA 6I content increases. The two‐phased morphology of the blends is examined by scanning electron microscopy (SEM). Polarized light microscopy (PLM) results reveal that the PTT spherulites become coarser with the inclusion of PA 6I; only smaller/dispersed crystallites are observed in the blend with 20 wt % of PTT. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effect of water sorption on oxygen‐barrier properties of aromatic polyamides

AbstractAromatic polyamides based on poly(m‐xylylene adipamide) (MXD‐based polyamides) and poly(hexamethylene isophthalamide) (HMD‐based polyamides) were examined. Insight into the excellent gas‐barrier properties was obtained by the characterization of the effect of water sorption on the thermal transitions, density, refractive index, free‐volume hole size, and oxygen‐transport properties. Reversing the carbonyl position with respect to the amide nitrogen substantially lowered the oxygen permeability of MXD‐based polyamides in comparison with that of HMD‐based polyamides by facilitating hydrogen‐bond formation. The resulting restriction of conformational changes and segmental motions reduced diffusivity. The primary effect of water sorption was a decrease in the glass‐transition temperature (Tg) attributed to plasticization by bound water. No evidence was found to support the idea that sorbed water filled holes of free volume. When the polymer was in the glassy state, the drop in Tg accounted for hydration‐dependent changes in the density, refractive index, and free‐volume hole size. The correlation of the oxygen solubility with Tg and density confirmed the concept of oxygen sorption as filling holes of excess free volume. In some cases, water sorption produced a glass‐to‐rubber transition. The onset of rubbery behavior was associated with a minimum in the oxygen permeability. The glass‐to‐rubber transition also facilitated the crystallization of MXD‐based polymers, which complicated the interpretation of oxygen‐transport behavior at higher relative humidity. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1365–1381, 2005

Isothermal crystallization kinetics of nylon 6, blends and copolymers using simultaneous small and wide-angle X-ray measurements

Crystallization behavior in a number of blends and copolymers of nylons (polyamides) was investigated using time-resolved X-ray scattering data obtained simultaneously in the small- and wide-angle regimes. The following samples studied were: nylon 6 homopolymers (N6) of different molecular weights, copolymers of N6 and nylon 6,6 (N6/66), and blends of these with an amorphous nylon (N6I/T), which is a 70:30 random copolymer of poly(hexamethylene isophthalamide) and poly(hexamethylene terephthalamide). Addition of comonomers and blending with the N6I/T reduces the crystallinity of N6. Isothermal crystallization data obtained at several temperatures showed the expected faster crystallization kinetics at higher degrees of supercooling. Comonomer units in the N6 backbone reduce the rate of crystallization. N6I/T affects the crystallization (lamellar growth) behavior of N6/N66: the rate is higher at temperatures above the T g of N6I/T (120 °C) where the crystallization is nucleation-driven, and lower below the T g of N6I/T where it is growth-driven. Lamellar spacing decreases with an increase in the degree of supercooling, and this decrease is smaller in the blends than in the homopolymer. Larger lamellar spacing in N6I/T blends is due not to the insertion of N6I/T segments into the interlamellar regions but to an increase in the lamellar thickness. Blending seems to change the morphology by affecting the crystallization behavior rather than by thermodynamic phase separation. Residual monomers, which act as plasticizers, dramatically reduce the crystallization rate, whereas shear or similar mechanical history of the resin considerably accelerate the crystallization rate.

Monodisperse polyamide oligomers: a facile synthesis of small polyamide oligomers on a solid polymer support

Monodisperse oligomers of poly(hexamethylene isophthalamide) (nylon-6I) with degrees of polymerization of one and two were prepared by solid-state synthesis on a Merrifield-type hydroxymethyl polystyrene resin using symmetrical diamines and diacid chlorides as starting materials.

A new thermally-processable aramid/amorphous nylon blend with high heat resistance and high stiffness

Polymer blends based on a rigid-rod aramid poly (2-chloro-1,4-phenylene terephthalamide) (CIPPTA) and an amorphous nylon poly(hexamethylene isophthalamide) (nylon 6I) were prepared by coprecipitation, and pressed into films by hot-compression. By differential scanning calorimetry (d.s.c.), optical microscopy and dynamic mechanical thermal analysis (d.m.t.a.), formation of a co-continuous superstructure in the blend films was suggested. The blend films exhibited high heat resistance and high stiffness, which are ascribable to the continuous aramid phase characteristic of the co-continuous structure.

On the Miscibility of Blends of Nylon 66 and Poly(hexamethylene isophthalamide), Nylon 6I

On the Miscibility of Blends of Nylon 66 and Poly(hexamethylene isophthalamide), Nylon 6I

Miscibility of polyamide blends: effects of configuration

The influence of the configuration of elementary chemical species, such as methylene, amide and phenyl groups, upon the phase behaviour of polyamide blends has been examined with reference to poly(hexamethylene isophthalamide), (nylon-6I) and poly( m-xylene adipamide) (MXD6), respectively, in aliphatic polyamides. The observable differences have been correlated with a binary interaction model to illustrate how the segmental interaction parameters are affected. It is proposed that the small differences detected may be attributed to the influence of neighbouring species on the interactions and that segments should be considered in terms of their triad groups. This is analogous to the approach already applied to blends of random addition copolymers. Additional experimental investigations, accompanied by predictive calculations, are also presented for blends of MXD6 with various aromatic polyamides, including the aramid poly( m-phenylene isophthalamide), and various aliphatic copoly(ester-amides).

Miscibility of Polyamide Blends. 2. Thermal Study of Poly(hexamethylene isophthalamide)/Nylon-n,m Blends

Miscibility of a series of nylons-6,m with poly(hexamethylene isophthalamide), abbreviated 6I nylon, was investigated. Four polyamides (nylon-6,5, nylon-6,7, nylon-6,8, and nylon-6,9) were found miscible, on a DSC scale, with 6I nylon. A series of nylon-n,m which had the same number of CH 2 groups as nylon-6,7 was also studied; no miscible blend with 6I nylon was found. This was taken as direct evidence of the importance of average interamide distances for miscibility. Negative deviations from linearity in T g -composition behavior of the blend are proposed to stem from conformational changes leading to weaker van der Waals interactions. These weak interactions are counterbalanced, in terms of energy, either by more ordered hydrogen bond networks or by entropy effects

The effect of absorbed water on the dynamic mechanical properties of some polyamides

The dynamic mechanical properties of poly(hexamethylene isophthalamide) and poly(dodecamethylene terephthalamide) have been determined over a wide range of temperature at low frequencies (∼ 1 c/s) by torsion pendulum measurements and at high frequencies (∼ 500 c/s) by a vibrating reed technique. It has been shown that absorbed moisture leads to the appearance of an intermediate loss peak at temperatures in the range −20°C to −70°C, between the main glass/rubber transition at 120°C and a low temperature process with a peak near −150°C. Unlike other polyamides such as nylon 6-6, the main glass/rubber transition is unaffected by moisture.

Adhesive properties of polyisophthalamides

Poly(hexamethylene isophthalamide) was shown to possess good adhesive properties at temperatures up to 100°C. and under wet conditions. Poly(hexamethylene isophthalamide) was blended with both epoxy resins and plasticizers to give adhesive joints with strengths greater than that of the unmodified polymer. The adhesive bond strengths of the aromatic polyamides to aluminum in homologous series of poly(alkylene isophthalamide) increased with increasing diamine chain length.