Thermal stability and crystalline of electrospun polyamide 6/organo‐montmorillonite nanofibers

This research is mainly to investigate the thermal and crystalline differences between polyamide 6/montmorillonite (PA6/MMT) and polyamide 6/organo‐montmorillonite (PA6/O‐MMT) nanofibers, which were both prepared by electrospinning under the same process conditions. The structures of PA6/MMT and PA6/O‐MMT nanofibers were observed by scanning electrical microscope. It was identified that the interval between O‐MMT clays was increased in the PA6 matrix compared to that of MMT, which was detected by X‐ray diffraction (XRD). The thermal properties of PA6 nanofibers contained O‐MMT particles were more efficient than PA6/MMT nanofibers, that was verified using thermal gravimetric analysis. The crystalline properties of the electrospun nanofibers was investigated using differential scanning calorimeter and it was found that the degree of crystallinity in the PA6 nanofibers loaded with O‐MMT was much higher than PA6/MMT and PA6 nanofibers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation of porous nylon 6 fiber via electrospinning

Porous nylon‐6 fibers were obtained by electrospinning of ultra‐high molecular polyamide 6 (UHMW‐PA6). First, UHMW‐PA6/calcium formate composite nanofibers were prepared as precursors by electrospinning UHMW‐PA6 solutions containing different contents of calcium formate particles. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the surface morphology and inner structure of composite nanofibers. It was found that calcium formate particles were distributed both inside and on the surface of nanofibers. Fourier transform infrared (FTIR), differential scanning calorimetry, and thermal gravimetric analysis (TGA) were used to study the structure and properties of these nanofibers. Then, porous UHMW‐PA6 nanofibers were obtained by soaking the electrospun web in water for 24 h, to remove calcium formate particles. The removal of calcium formate particles was confirmed using FTIR and TGA tests. SEM and TEM observations revealed the formation of porous structure in these nanofibers. In addition, CaCl₂ was used instead of calcium formate to prepare the UHMW‐PA6 nanoporous fiber. POLYM. ENG. SCI., 55:1133–1141, 2015. © 2014 Society of Plastics Engineers     

Poly(amide‐imide)/organoclay nanocomposites using glycine as a natural amino acid: study on fire and thermal behavior

In the present study, new functional poly(amide‐imide)/organoclay nanocomposite films were successfully fabricated through the solution intercalation technique. New poly(amide‐imide) (PAI) containing glycine was synthesized via solution polycondensation of 1,1',3,3'‐tetraoxo(5,5'‐biisoindoline‐2,2'‐diyl)diacetic acid with 4,4′‐diaminodiphenylsulfone. The synthesized PAI was characterized by ¹H NMR, Fourier transform infrared (FTIR) spectroscopy, gel permeation chromatography, elemental analysis and inherent viscosity. Then, PAI/organoclay nanocomposite films containing 4 and 8 wt% of organoclay were prepared via solution intercalation through blending of organoclay 30B with the PAI solution. The nanostructures and properties of the PAI/organoclay were investigated using FTIR spectroscopy, XRD, transmission electron microscopy (TEM), TGA, DSC and microscale combustion calorimetry. XRD and TEM revealed the good dispersion of organoclay in the polymer matrix. TGA indicated that the addition of organoclay into the PAI matrix increases the thermal decomposition temperatures and char yields of the nanocomposites. Organoclay shows a positive effect in improving the flame retardancy of the PAI, reflecting the decrease in heat release rate, the total heat release and the heat release capacity of the PAI nanocomposites, while the thermal stability of the PAI nanocomposites only increased slightly compared with the neat polymer. © 2013 Society of Chemical Industry     

Influence of a synthetic ureido nucleating agent on crystallization behavior and mechanical properties of polyamide 6

A synthetic ureido mixture prepared from the reaction of 4,4′‐diphenylmethane disocynanate (MDI) and cyclohexylamine without using any harmful organic solvents, has been used as a nucleating agent (PNA) for polyamide 6 (PA6). The effect of PNA on the crystallization and mechanical properties of PA6 has been studied by means of differential scanning calorimetry (DSC), polarized optical microscopy (POM), tensile test, melt flow index (MFI), and X‐ray diffraction (XRD). The results show that PNA is an effective nucleation agent for PA6. PNA affects the nucleation mechanism of PA6, and substantially accelerates the crystallization rate of PA6 and gives rise to smaller crystal size. In comparison with PA6, the crystallization temperature (T_c) of PA6/PNA (100/0.5) increases 21.3°C and the degree of sub‐cooling (ΔT_c) decreases 23.7°C. Furthermore, because of the heterogeneous nucleation induced by PNA, the spherulites of PA6 become even and tiny based on POM observation. Polymorph transform has been obtained from XRD analysis. The virgin PA6 is free of γ‐phase crystals, presented as α‐phase crystals in this study, but γ‐phase crystal appears after the introduction of PNA. The mechanical and thermal properties of PA6 are obviously improved by the addition of PNA. POLYM. ENG. SCI., 55:2011–2017, 2015. © 2015 Society of Plastics Engineers     

Structure evolution of polyamide (11)’s crystalline phase under uniaxial stretching and increasing temperature

Thermal processing of polyamide influences the internal crystalline structure and thereafter the post product mechanical performance. In this article, the crystalline transition of polyamide-11 (PA11) plate under uniaxial stretching and increasing temperature was investigated systematically using in-situ synchrotron X-ray technique. It was discovered that the lamellar slippage, fragmentation and recrystallization occurred in sequence under increasing temperature. In detail, the crystal of PA11 plate was stretched with a transition from triclinic α-form to mesomorphic phase at 25 °C. For the thermally activated γ-form crystals, crystal transition was inhibited when temperature was increased up to 160 °C. The melt-recrystallization was inclined to take place at large tensile strains. This work enhances the research significance of the thermal processing of polyamide and provides a theoretical method to improve the high performance of polyamide products.     

Influence of thermal processing on the perfection of crystals in polyamide 66 and polyamide 66/clay nanocomposites

A study of the changes in crystal perfection of polyamide 66 (PA66) and polyamide 66/clay nanocomposites (PA66CN) due to different thermal processing was carried out. We designed three series of thermal processing including melt-quench (MQ), post-annealing MQ sample (MQA), and melt–slow cooling–annealing (MSA). The annealing temperature was set as 180 or 210 °C, which is within Brill temperature range of PA66. Fourier transform infrared (FT-IR) spectroscopy and wide angle X-ray diffraction (WAXD) were employed to characterize the perfection in short-range order and long-range order structures, respectively. The results showed that the crystal perfection of PA66 and PA66CN with different thermal processing is quite different, and the changing fashions with thermal processing for different ordered structures are not similar. In this work, MSA is optimal thermal processing for high crystallinity and crystal perfection. Exfoliated nanoclay layers exert considerable impact on the perfection of long-range ordered structures, but little on that of short-range ordered ones.     

Comparative study of the tribological properties of polyamide 6 filled with molybdenum disulfide and liquid crystalline additives

The effect of adding a 1 wt % proportion of thermotropic liquid crystals 4,4′‐dibutylazobenzene (LC1) and 4‐octyl, 4′‐cyanobiphenyl (LC2) on the tribological properties of polyamide 6 (PA 6) is compared with that of the addition of MoS₂ in different concentrations (1 and 5 wt %). Friction and wear are determined in a pin‐on‐disk tribometer by using injection‐molded additivated nylon disks against steel or aluminum pins, below (25°C) and above (80°C) glass transition temperature. Polymeric blends are characterized by differential scanning calorimetry and by optical and scanning electron microscopy and microanalysis. Concentration of liquid crystalline additives is higher at the surface than in the bulk of PA 6 disks. Crystallinity degree of PA‐6 is not significantly changed by the presence of additives. Addition of 1 wt % LC1 improves processibility of PA 6 by increasing its melt flow rate. Cyanoderivative liquid crystal (LC2) shows the best wear‐reducing ability for PA 6/steel contacts at all temperatures. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2426–2432, 2001     

Long term ageing of polyamide 6 and polyamide 6 reinforced with 30% of glass fibers: temperature effect

Because the prediction of the durability of polyamide materials is a very important issue for designers and users, the effect of environment conditions on their mechanical properties is an active field of research. For this reason this experimental investigation was conducted in order to study the effect of temperature on long term ageing of polyamide 6 (PA6) and polyamide 6 reinforced with 30 wt% of glass fibers (PA6GF30). Ageing was realized in distilled water (pH?≈?6; 100% RH) at 30 °C, 50 °C, 70 °C and 90 °C for up to 80 days. Results highlighted the impact of ageing temperature on both conditioned materials. Thus, several surface damages such as crazing and yellowness were recorded especially at high temperatures indicating the materials degradation. These structure changes were induced by the combined effects of water and temperature. As the water diffuses within the polymer, the glass transition temperature T_g drops progressively with ageing temperature to reach the lowest value for samples aged at 90 °C for both tested materials. This tendency was also observed for Young’s modulus, tensile strength and the elongation at break. Thus, a significant loss in stiffness and strength of both materials was recorded as a function of conditioning temperature. This loss of mechanical properties is mainly caused by hydrolysis process and/or interfacial debonding. The appearance of this irreversible phenomenon rises with ageing temperature. Moreover, contrarily to PA6GF30, the temperature effect was also pointed out on SEM observations of PA6 samples. Thus, the hygrothermal ageing induces a change in the mode of fracture from ductile to moderate brittle one according to the ageing temperature. Accordingly, it seems that the ageing temperature has a great effect on the severity of damage of tested materials after long term immersion.     

Blends of polyamide 6, polycarbonate,and poly(propylene oxide). II. Reactive compatibilization–thermal degradation relationships

The thermal degradation of some blends of polyamide 6/polycarbonate (PA6/PC) and polyamide 6/polycarbonate/poly(propylene oxide) (PA6/PC/PPO) were investigated. The copolymer formed during the mixing of polyamide 6 and polycarbonate, at 240°C, for 30 min, increases the thermal stability of PA6/PC and of PA6/PC/PPO blends. This increase in the thermal stability occurs due to the plasticizing effect of PPO, which increases the mobility of the molecules of PA6 and PC, and consequently increases the probability of the reaction between the —NH₂ and —O—CO—O groups of polyamide 6 and polycarbonate, respectively. The ternary blends with PPO (5–10% w/w) have lower thermal stability than PA6/PC blends. This is due to the decrease of miscibility between these polymers and the rise of the diluting effect. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2556–2562, 2001     

Preparation and Properties of Nanocomposites Derived from Aromatic Polyamide and Surface Functionalized Nanoclay

Nanocomposites were synthesized from polyamide and aminosilane functionalized montmorillonite through solution intercalation method. Polyamide resin was prepared by reacting a mixture of p-phenylenediamine and 4,4′-oxydianiline with isophthaloyl chloride (IPC) in N,N′-dimethyl acetamide (DMAc) under anhydrous conditions. The resulting chains were end capped with carbonyl chloride using slight excess of IPC near the end of reaction. 3-Aminopropyltriethoxysilane (APTS) was used for the surface modification of clay. Triethoxysilane groups of APTS promoted the reaction between silane and hydroxyl groups on the surface of clay. The compatibility between the two disparate phases was achieved through interaction of free amine groups of modified clay with carbonyl chloride of the matrix. Thin films obtained by evaporating the solvent were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), Thermogravimetric analysis (TGA), Differential scanning calorimetry (DSC), and tensile measurements. XRD and TEM results revealed the formation of partially delaminated and intercalated clay platelets in the matrix. Mechanical data showed improvement in the tensile strength and moduli of the nanocomposites with clay loading up to 6 wt.%. The glass transition temperature increased up to 134°C for the nanocomposites containing 6 wt.% clay content and also the thermal stability augmented with increasing clay loading.     

Improved thermal conductivity of ceramic filler‐filled polyamide composites by using PA6/PA66 1:1 blend as matrix

Polyamide‐type composites with improved thermal conductivity are prepared by using polyamide 6(PA6)/polyamide 6,6 (PA66) 1:1 blend as the matrix and aluminum nitride (AlN) as the filler through melt compounding. Field emission scanning electron microscopy coupled with energy dispersive spectrometry (EDS) mapping of Al is used to investigate distribution of AlN. Differential scanning calorimeter is used to investigate the crystallization behavior of the composites. The thermal conductivity of PA6/PA66/AlN composite with 50 wt % AlN is 1.5 W m^?1 K^?1, 88% enhancement compared to those of single polymer based PA6/AlN or PA66/AlN composites. The reason for the improved thermal conductivity is the increased effective volume concentration of AlN in one (probably PA66) phase. The experimental data are fitted into Bruggeman and Agari–Uno model. Composites with similar thermal conductivity are also prepared using silicon carbide as the filler instead of AlN, showing that using PA6/PA66 1:1 blend as the matrix is a universal method to prepare thermally conductive composites with less filler loading. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45371.     

A new semicrystalline reinforced polyamide engineering thermoplastic

A new rapidly crystallizing aromatic-aliphatic polyamide has been developed by reacting 4,4′-methylene bis(phenylisocyanate) (MDI) with aliphatic dicarboxylic acids. The polymer has a T_g of 130°C and T_m, of 290°C. Glass reinforced resin shows better flexural creep resistance at high stress levels (3000 psi) at elevated temperatures (75°C) than most reinforced semicrystalline commercial polymers i.e., nylons, thermoplastic polyesters and acetal because of its high T_g. Glass reinforced polyamide can be injection molded on conventional equipment to afford flexural moduli in excess of 1,000,000 psi and HDT's as high as 250°C at 264 psi. Because of the high level of crystallinity these parts will not dissolve or swell in most organic solvents and this aromatic aliphatic polyamide is also far less sensitive to moisture than commercial nylons.     

Melting behavior and nonisothermal crystallization kinetics of polyamide 6/polyamide 66 molecular composites via in situ polymerization

The melting behavior and nonisothermal crystallization kinetics of pure polyamide 6 (PA 6) and its molecular composites with polyamide 66 (PA 66) were investigated with differential scanning calorimetry. The PA 6/PA 66 composites had one melting peak, whereas the coextruded PA 6/PA 66 blends had two melting peaks. With the addition of PA 66 to PA 6 via in situ anionic polymerization, the melting temperature, crystallization temperature, and crystallinity of PA 6 in the composites decreased. The half‐time of nonisothermal crystallization increased for a PA 6/PA 66 molecular composite containing 12 wt % PA 66, in comparison with that of pure PA 6. The commonly used Ozawa equation was used to fit the nonisothermal crystallization of pure PA 6 and its composites. The Ozawa exponent values in the primary stage were equal to 1.28–3.03 and 1.28–2.97 for PA 6 and its composite with 12 wt % PA 66, respectively, and this revealed that the mechanism of primary crystallization of PA 6 and PA 6/PA 66 was mainly heterogeneous nucleation and growth. All the results indicated that the incorporation of PA 66 into PA 6 at the molecular level retarded the crystallization of PA 6. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2172–2177, 2005     

One-step synthesized azo-dye modified Mg-Al LDH reinforced biobased semi-aromatic polyamide containing naphthalene ring; study on thermal stability and optical properties

A new series of polyamide Mg-Al layered double hydroxide (LDH) nanocomposites (PANC) were prepared using solution intercalation method. The biobased polyamide (PA) was synthesized using direct polycondensation reaction. Organo azo-dye modified Mg-Al LDH (OLDH) was prepared by one-step method and its effect on the thermal and optical properties of PA was investigated. The X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) results showed the uniform distribution of LDH sheets in the PA matrix. The UV-Vis spectra of PANC showed a blue shift as well as reduction in absorbance intensities and the photoluminescence studies revealed the higher emission intensities for PANC as compared to the neat PA. The results of thermogravimetric analysis (TGA) in both nitrogen and air atmospheres showed that the addition of OLDH up to 5 mass% was slightly improved thermal properties of PA.     

Thermo‐mechanical behavior of polyamide 12—polyamide 66 recycled fiber composites

Postconsumed polyamide 66 (PA66) short fibers derived from carpets were utilized as reinforcement in a commercial polyamide (PA12) matrix at different concentrations, ranging from 10 wt% to 30 wt%, in order to evaluate the effect of PA66 content on the mechanical and dynamic behavior of the resulting materials. DSC tests revealed that both melting and crystallization behavior of PA12 matrix was slightly affected by the presence of the fibers, showing a somewhat nucleation effect of PA66. Quasi‐static tensile tests evidenced that the introduction of PA66 fibers provided a slight stiffening effect on the resulting composites, increasing the elastic modulus with the filler content, especially at testing temperatures above T_g. On the other hand, the presence of agglomerated fibers led to an embrittlement of polyamide composites, showing a significant reduction of the tensile properties at break increasing the PA66 fibers content. Tensile dynamic tests confirmed the stiffening effect provided by the recycled fibers, increasing both dynamic moduli (E′ and E″) with PA66 content over the whole range of considered temperatures. Glass transition temperature of PA12 was substantially increased by the presence of the fibers, while the coefficient of linear thermal expansion above T_g was progressively reduced with the filler content. Interestingly, isothermal creep compliance of the material above T_g was substantially reduced by the presence of PA66 fibers. Morphological analysis on the cryofractured surfaces revealed a quite good fiber‐matrix interfacial adhesion, with the presence of some nucleating phenomena on the pulled out surfaces. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Enhancement of physical and mechanical properties of polyamide 66 fibers using polysiloxane-functionalized multi-walled carbon nanotubes

A polyamide 66/3-aminopropyl-terminated poly(dimethylsiloxane) (PA66/APDMS)-carboxylate multiwalled carbon nanotubes (CMWNTs) nanocomposite (PA66/APDMS-CMWNTs) was synthesized using a one-pot method, and the product was melt-spun into fibers. The glass transition temperature (T_g) of the PA66/APDMS-CMWNTs nanocomposite fiber is 68.0°C, which is 22% higher than that of the pure PA66 fiber. This result indicates that there is a strong interfacial interaction between APDMS-CMWNTs and the PA66. Furthermore, the crystallinity of PA66/APDMS-CMWNTs nanocomposite fiber reaches a maximum due to the addition of APDMS-CMWNTs. Additionally, the tensile strength and Young's modulus of PA66/APDMS-CMWNTs nanocomposite fiber are 167% and 631% higher, respectively, than that of the pure PA66 fiber. The strengthening mechanism was discussed using force balance-based expression, which demonstrates that the stress on the PA66 is more efficiently transferred to the APDMS-CMWNTs. These results argue that using APDMS-CMWNTs as a filler can enhance the physical-mechanical properties of PA66 with an elevated degree never being reported.     

Grafting polyamide 6 onto multi‐walled carbon nanotubes using microwave irradiation

Chemical reactions under microwave irradiation can be very efficient, with a significant shortening of reaction time. Few studies have reported the use of microwaves to functionalize carbon nanotubes. In the work reported, a new method of formulating functionalized multi‐walled carbon nanotubes (MWNTs) was developed by covalent grafting of polyamide 6 (PA6) chains onto the carbon nanotubes assisted by microwave irradiation. PA6 chains were grafted onto acidified MWNTs through condensation reaction between the carboxylic groups of the MWNTs and the terminal amine groups of PA6 using microwave radiation heating. The functionalized carbon nanotubes (MWNT‐g‐PA6) were characterized systematically using infrared and Raman spectroscopy, transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). TEM showed that the surface of the MWNTs was covered with a layer of PA6. TGA results indicated that the MWNT‐g‐PA6 contained about 47 wt% of polymer. A novel, convenient and efficient functionalization approach is reported, involving covalently grafting PA6 chains onto MWNTs assisted by microwave irradiation. Copyright © 2010 Society of Chemical Industry     

Morphology,thermal, and mechanical properties of polyamide 66/clay nanocomposites with epoxy‐modified organoclay

A new kind of organophilic clay, cotreated by methyl tallow bis‐2‐hydroxyethyl quaternary ammonium and epoxy resin into sodium montmorillonite (to form a strong interaction with polyamide 66 matrix), was prepared and used in preparing PA66/clay nanocomposites (PA66CN) via melt‐compounding method. Three different types of organic clays, CL30B–E00, CL30B–E12, and CL30B–E23, were used to study the effect of epoxy resin in PA66CN. The morphological, mechanical, and thermal properties have been studied using X‐ray diffraction, transmission electron microscopy (TEM), mechanical, and thermal analysis, respectively. TEM analysis of the nanocomposites shows that most of the silicate layers were exfoliated to individual layers and to some thin stacks containing a few layers. PA66CX–E00 and PA66CX–E12 had nearly exfoliated structures in agreement with the SAXS results, while PA66CX–E23 shows a coexistence of intercalated and exfoliated structures. The storage modulus of PA66 nanocomposites was higher than that of the neat PA66 in the whole range of tested temperature. On the other hand, the magnitude of the loss tangent peak in α‐ or β‐transition region decreased gradually with the increase in the clay loading. Multiple melting behavior in PA66 was also observed. Thermal stability more or less decreased with an increasing inorganic content. Young's modulus and tensile strength were enhanced by introducing organoclay. Among the three types of nanocomposites prepared, PA66CX–E12 showed the highest improvement in properties, while PA66CX–E23 showed properties inferior to that of PA66CX–E00 without epoxy resin. In conclusion, an optimum amount of epoxy resin is required to form the strong interaction with the amide group of PA66. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1711–1722, 2006     

Nonisothermal crystallization and morphology of crystallites of polyamide 66 and copolyamide 66 containing 2‐carboxyethyl phenyl phosphinic acid

Flame‐retardant polyamide 66 with a 10% mass fraction of 2‐carboxyethyl phenyl phosphinic acid (CEPPA) hexamethylene diamine salt (PA66‐10) was fabricated in our previous study. In this study, the nonisothermal crystallization kinetics of pure polyamide 66 (PA66‐0) and PA66‐10 were measured by differential scanning calorimetry, and the data obtained were analyzed, and we calculated the average Avrami exponent (n) and used the Jeziorny, Mo, and Kissinger methods. The results from all of these methods show that the crystallization mechanism of PA66‐0 mainly consisted of three stages, whereas PA66‐10 mainly consisted of two stages. At the prime stage, both PA66‐0 and PA66‐10 may have had the same crystallization mechanism. When the cooling rates were 15 and 20°C/min, the approximate n suggested that the growth form of the spherulite mode in PA66‐0 may have been complicated, whereas PA66‐10 may have had a one‐dimensional, two‐dimensional space‐extension, circular, diffusion controlled growth. The crystallization activation energies were determined to be 183.2 and 301 kJ/mol for PA66‐0 and PA66‐10, respectively, by the Kissinger method. To further study the influence of the addition of CEPPA on the crystallization behaviors of PA66‐0, the spherulitic morphologies were examined by polarized light microscopy. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41790.     

Hydrogen bonding in polyamide toughened novolac type phenolic resin

The hydrogen bonding, miscibility, and thermal stability of polyamide toughened novolac type phenolic resin were investigated. The intermolecular force of the resin increased with the content of the soft segments of polyamides (nylon 6, nylon 66) that absorb the loads in the network of brittle phenolic resin. IR (IR region) spectra and differential scanning calorimetry results confirmed that the phenolic/polyamide blend was completely miscible. Its thermal degradation temperature was higher than 400°C and increased with the increasing of polyamide content. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2283–2289, 1999