Effect of modified single‐wall carbon nanotubes on mechanical and morphological properties of thermoplastic elastomer nanocomposites based on (polyamide 6)/(acrylonitrile butadiene rubber)

Thermoplastic elastomer nanocomposites based on acrylonitrile butadiene rubber (NBR) and polyamide 6 (PA6), with acid functionalized single‐wall carbon nanotubes (SWNT), were prepared via a direct melt‐mixing process in an internal mixer. The influence of SWNT content (0, 0.5, 1, 1.5) on morphological properties of PA6/NBR with different ratios (80/20, 70/30, 60/40) were then investigated. Characterization of nanocomposites was conducted by using transmission electron microscopy, scanning electron microscopy, differential scanning calorimetry, and mechanical properties. Scanning electron microscopy micrographs proved the droplet‐matrix blend morphology in which the size of NBR droplets decreased as the SWNT loading increased, suggesting dispersion of SWNT in the PA6 phase. It was further proved by transmission electron microscopy images, showing homogenous dispersion of SWNT in the PA6 phase. Differential scanning calorimetry results showed a slightly reduced percentage of crystallinity in samples containing SWNT. The mechanical properties of nanocomposites indicated an enhancement in tensile strength, modulus, and hardness on increasing SWNT content. J. VINYL ADDIT. TECHNOL., 22:336–341, 2016. © 2014 Society of Plastics Engineers     

Improvement of polyamide 1010 with silica nanospheres via in situ melt polycondensation

Polyamide 1010 (PA1010) had been prepared by in situ melt polycondensation in presence of silica nanospheres with amine groups on the surfaces (SiO₂ NH₂). Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), and thermal gravimetric analysis (TGA) measurements demonstrated that the nanosphere surface was grafted with PA1010 chains. Wide angle X‐ray diffraction (WAXD) and differential scanning calorimetry (DSC) measurements showed that the PA1010/SiO₂ NH₂ nanocomposites had a lower degree of crystallinity (χ_c) in comparison with PA1010 and PA1010/SiO₂ nanocomposites. Dynamic mechanical analysis (DMA) indicated that SiO₂ NH₂ nanospheres improved glass transition temperature (T_g), tensile strength and storage modulus of PA1010 since SiO₂–NH₂ nanospheres limited the mobility of PA1010 chains. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Crystallization behavior of carbon nanotubes‐filled polyamide 1010

The nanocomposites of polyamide1010 (PA1010) filled with carbon nanotubes (CNTs) were prepared by melt mixing techniques. The isothermal melt‐crystallization kinetics and nonisothermal crystallization behavior of CNTs/PA1010 nanocomposites were investigated by differential scanning calorimetry. The peak temperature, melting point, half‐time of crystallization, enthalpy of crystallization, etc. were measured. Two stages of crystallization are observed, including primary crystallization and secondary crystallization. The isothermal crystallization was also described according to Avrami's approach. It has been shown that the addition of CNTs causes a remarkable increase in the overall crystallization rate of PA1010 and affects the mechanism of nucleation and growth of PA1010 crystals. The analysis of kinetic data according to nucleation theories shows that the increment in crystallization rate of CNTs/PA1010 composites results from the decrease in lateral surface free energy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3794–3800, 2006     

Crystallization and crosslinking of polyamide‐1010 under elevated pressure

The structure and thermal properties of polyamide‐1010 (PA1010), treated at 250°C for 30 min under pressures of 0.7–2.5 GPa, were studied with wide‐angle X‐ray diffraction (WAXD), infrared (IR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Crystals were formed when the pressures were less than 1.0 GPa or greater than 1.2 GPa. With increasing pressure, the intensity of the diffraction peak at approximately 24° was enhanced, whereas the peak at approximately 20° was depressed. The triclinic crystal structure of PA1010 was preserved. The highest melting temperature of the crystals obtained in this work was 208°C for PA1010 treated at 1.5 GPa. Crosslinking occurred under pressures of 1.0–1.2 GPa. Only a broad diffraction peak centered at approximately 20° was observed on WAXD patterns, and no melting and crystallization peaks were found on DSC curves. IR spectra of crosslinked PA1010 showed a remarkable absorption band at 1370 cm^?1. The N? H stretching vibration band at 3305 cm^?1 was weakened. Crystallized PA1010 had a higher thermal stability than crosslinked PA1010, as indicated on TGA curves by a higher onset temperature of decomposition. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2522–2527, 2002     

Crystallization studies on linear aliphatic polyamides derived from naturally occurring carbohydrates

The thermal behavior of three series of sugar‐derived polyamides (PA‐nSu) made from the arabinaric, mannaric and galactaric acids, respectively, and α,ω‐alkanediamines containing from 6 to 12 methylene units was investigated by DSC supported by polarizing optical microscopy. Crystallization from the melt under both isothermal and nonisothermal conditions was studied in detail. Melting temperatures of PA‐nSu were found to decay steadily with the length of the polymethylene segment. Data registered from isothermally crystallized samples were analyzed by the kinetics Avrami approach, which revealed that crystallization initiated by combination of instantaneous and sporadically nucleation. Crystallization half‐times indicated that “crystallizability” of PA‐nSu increases with the number of methylenes in the diamine unit and decreases with the length of the carbohydrate‐derived unit. Higher crystallinities were attained for polyamides made of shorter aldaric acids. The relation between thermal data and the configuration of the sugar moiety present in PA‐nSu was discussed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and properties of water soluble single‐walled carbon nanotube graft ionic polyacetylene nanocomposites

Water‐soluble single‐walled carbon nanotube‐polyacetylene [SWNT‐PA, SWNT‐P(2EPy‐MeTf)] nanocomposites have been synthesized by using the surface initiated “grafting‐from” method. The FT‐IR spectra confirmed the formation of an amide bond between the functionalized SWNTs and the initiator, 4‐(2‐Aminoethyl) pyridine, to polymerize N‐Methyl‐2‐ethynlypyridinium triflate (2EPy‐MeTf). UV‐vis spectroscopy indicated that the degree of polymerization of P(2EPy‐MeTf) in the SWNT‐polyacetylene composites is 15, based on the Lewis‐Calvin equation. The SWNT‐polyacetylene composites have been characterized by TGA, AFM, and TEM. From TGA analysis, the loading of SWNTs in the SWNT grafted ionic polyacetylenes is estimated to be 22%. AFM and TEM images clearly showed that the nanotube is wrapped with the PA. The SWNT‐polyacetylene composites displayed high water solubility (8 mg/ml). The room temperature electrical conductivity of the doped SWNT‐polyacetylene composites was found to be in the range of 10⁻³ to 10⁻⁴ S/cm, an order of magnitude of increase over neat P(2EPy‐MeTf) and a two order of magnitude increase over Dendrimer‐polyacetylen composites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Effect of crystallization conditions on spherulitic texture and tensile properties of sPS/PPO blends

In the second study on melt‐miscible syndiotactic polystyrene (sPS) and poly(phenylene oxide) (PPO) blends, the effect of processing conditions on morphology, ultimate tensile properties, and the mode of fracture is reported. Bulk samples of the blends were molded and then crystallized from melt as well as from the quenched state at different temperatures. The spherulitic morphology of the melt‐crystallized blends, observed by scanning electron microscopy, revealed formation of complete, well‐developed spherulites whose texture increased in coarseness with increasing crystallization temperatures. In all the cold‐crystallized blends lamellar bundles formed a meshlike structure whose texture did not vary significantly with crystallization temperature. Depending on the crystallization temperature, 50/50 melt‐crystallized blends showed varying tensile properties and different modes of failure. In the samples with the largest amorphous domain size of 0.6 μm, the amorphous ellipsoids were cold drawn into fibrils during tensile loading and very high tensile strengths were recorded. The tensile properties for the other melt‐crystallized and all cold‐crystallized blends did not vary substantially with the changing crystallization temperature. The micrographs of the fractured surfaces of the melt‐crystallized blends suggested that, although intraspherulitic fracture occurred at low crystallization temperatures, interspherulitic fracture took place at high crystallization temperatures. The correlation of the morphology and mechanical properties suggests that melt‐miscible blends have good interfacial adhesion between phases and that, by varying composition and processing conditions, it might be possible to control amorphous domain sizes, which is critical in achieving better mechanical properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1984–1994, 2003     

The use of master curves to describe the simultaneous effect of cooling rate and pressure on polymer crystallization

In a previous work a master‐curve approach was applied to experimental density data to explain isotactic polypropylene (iPP) behaviour under pressure and high cooling rates. Suitable samples were prepared by solidification from the melt under various cooling rate and pressure conditions with the help of a special apparatus based on a modified injection moulding machine. The approach here reported is more general than the case study previously shown, and is suitable to be applied to several materials and for different measures related to crystalline content. The proposed simple model is able to predict successfully the final polymer properties (density, micro‐hardness, crystallinity) by superposition of the effect of cooling rate and the effect of pressure in a wide range of experimental conditions. For this purpose three semi‐crystalline polymers were studied [iPP, polyamide‐6 (PA6) and poly(ethyleneterephthalate) (PET)], which exhibited remarkably different behaviour when crystallized under pressure and high cooling rates Copyright © 2003 Society of Chemical Industry     

Synthesis and properties of hydroxyapatite nanorod‐reinforced polyamide 6 nanocomposites

BACKGROUND: Polyamide 6 (PA6)/hydroxyapatite (HA) nanocomposites, which combine the bioactivity and biocompatibility of HA and the excellent mechanical performance of PA6, have emerged as new biomaterials with potential applications in the clinical setting. It has been shown that these nanocomposites show good similarity to natural bone in terms of chemistry and mechanical properties. RESULTS: In this study, highly crystallized hydroxyapatite nanorods (HANR) were used to fabricate PA6/HA nanocomposites via in situ hydrolytic ring‐opening polymerization of ε‐caprolactam. The effect of the HANR on the thermal stability, crystallization behavior and hydrogen bonding of PA6 was investigated using thermogravimetric analysis, differential scanning calorimetry and Fourier transform infrared (FTIR) spectroscopy, respectively. It was found that HANR can obviously increase the crystallization temperature and decrease the degree of supercooling. In addition, the thermal degeneration temperature of PA6 is also increased by the incorporation of HANR. FTIR analysis of the hydrogen bonded N? H stretching vibration revealed that, with increasing HANR loading, the hydrogen bonded N? H stretching band shifts to higher frequency and decreases in intensity. CONCLUSION: The thermal stability and crystallization ability of PA6 are improved considerably by the incorporation of HANR. However, the hydrogen bonding strength is weakened and the degree of ordering of hydrogen bonding is reduced by the incorporation of HANR, which can be explained by the formation of hydrogen bonds at the interface between ? OH groups of HANR and the ? N? H or ? C?O groups of PA6. Copyright © 2009 Society of Chemical Industry     

Free‐volume hole properties of two kinds thermoplastic nanocomposites based on polymer blends probed by positron annihilation lifetime spectroscopy

Two type of nanocomposites—an immiscible blend, high density polyethylene/polyamide 6 (HDPE/PA‐6) with organomodified clay, and a compatibilized blend, high density polyethylene grafted with acrylic acid/PA‐6 (PEAA/PA‐6) with organomodified clay—were prepared via melt compounding. X‐ray diffraction and transmission electron microscopy results revealed that the clay was intercalated and partially exfoliated. Positron annihilation lifetime spectroscopy has been utilized to investigate the free‐volume hole properties of two type of nanocomposites. The results show a negative deviation of free‐volume size in PEAA/PA‐6 blend, and a positive deviation in HDPE/PA‐6 blend, and I₃ has a greater negative deviation in compatibilized blend than in immiscible blend due to interaction between dissimilar chains. For nanocomposites based on polymer blends, in immiscible HDPE/PA‐6/organomodified clay system, the variation of free‐volume size with clay content is not obvious and the free‐volume concentration and fraction decreased. While in the case of compatibilized PEAA/PA‐6/organomodified clay nanocomposites, complicated variation of free‐volume properties due to interactions between two phases and organomodified clay was observed. And the interaction parameter β shows the interactions between polymers and organomodified clay. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2463–2469, 2006     

Crystallization and melting behavior of amorphous poly(iminosebacoyl iminodecamethylene)

Multiple melting behavior was observed in the differential scanning calorimetry (DSC) scans for the isothermally crystallized poly(iminosebacoyl iminodecamethylene) (PA1010) samples. Coexistence of crystal populations with different lamellar thickness in PA1010 was discussed by means of DSC, wide‐angle X‐ray diffraction (WAXD), and small‐angle X‐ray scattering techniques. During crystallization of the polymer, a major lamellar crystal population developed first, which possessed a higher melting temperature. However, a small fraction of the polymer formed minor crystal population with thinner lamellae, which was metastable and, upon post‐annealing, could grow into more stable and thicker lamellae through melting and recrystallization process. Lamellae insertion or stacks would develop during the post‐annealing at a lower temperature for the isothermally crystallized samples; thus, multiple crystal populations with different thickness could be produced. It is the multiple distribution of lamella thickness that gives rise to multiple melting behavior of crystalline polymers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 993–1002, 2000     

The structure and properties of PA6/MMT nanocomposites prepared by melt compounding

Polyamide 6 (PA6)/organo‐montmorillonite nanocomposites prepared by melt compounding using a co‐rotating twin‐screw extruder were intercalated nanocomposites. The modulus, bending strength and heat distortion temperature of these nanocomposites increased with increasing clay content, and tensile strength increased up to 4.3 wt% and then decreased with further increases in montmorillonite content. The notched Izod impact strength decreased slightly with montmorillonite content. Nanocomposites based on the higher‐molecular‐weight PA6 yielded higher moduli, tensile strengths, and heat distortion temperatures at the same montmorillonite content. Polym. Eng. Sci. 44:2070–2074, 2004. © 2004 Society of Plastics Engineers.     

Preparation of the HIPS/MA graft copolymer and its compatibilization in HIPS/PA1010 blends

The graft copolymer of high‐impact polystyrene (HIPS) grafted with maleic anhydride (MA) (HIPS‐g‐MA) was prepared with melt mixing in the presence of a free‐radical initiator. The grafting reaction was confirmed by infrared analyses, and the amount of MA grafted on HIPS was evaluated by a titration method. 1–5% of MA can be grafted on HIPS. HIPS‐g‐MA is miscible with HIPS. Its anhydride group can react with polyamide 1010 (PA1010) during melt mixing of the two components. The compatibility of HIPS‐g‐MA in the HIPS/PA1010 blends was evident. Evidence of reactions in the blends was confirmed in the morphology and mechanical behavior of the blends. A significant reduction in domain size was observed because of the compatibilization of HIPS‐g‐MA in the blends of HIPS and PA1010. The tensile mechanical properties of the prepared blends were investigated, and the fracture surfaces of the blends were examined by means of the scanning electron microscope. The improved adhesion in a 15% HIPS/75% PA1010 blend with 10% HIPS‐g‐MA copolymer was detected. The morphology of fibrillar ligaments formed by PA1010 connecting HIPS particles was observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2017–2025, 1999     

Melt processing of polyamide 12 and cellulose nanocrystals nanocomposites

The fabrication of nanocomposites of polyamide 12 (PA12) and cellulose nanocrystals (CNCs) isolated from cotton and tunicates is reported. Through a comparative study that involved solution‐cast (SC) and melt‐processed materials, it was shown that PA12/CNC nanocomposites can be prepared in a process that appears to be readily scalable to an industrial level. The results demonstrate that CNCs isolated from the biomass by phosphoric acid hydrolysis display both a sufficiently high thermal stability to permit melt processing with PA12, and a high compatibility with this polymer to allow the formation of nanocomposites in which the CNCs are well dispersed. Thus, PA12/CNC nanocomposites prepared by melt‐mixing the two components in a co‐rotating roller blade mixer and subsequent compression molding display mechanical properties that are comparable to those of SC reference materials. Young's modulus and maximum stress could be doubled in comparison to the neat PA12 by introduction of 10% (CNCs from tunicates) or 15% w/w (CNCs from cotton) CNCs. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42752.     

Crystallization,melting, and rheology of reactive polyamide blends

The crystallization and melting characteristics of a series of polyamide blends based on PA 4,6 and PA 6I were investigated by calorimetric methods; preparation of the samples was conducted so as to control the extent of transamidation occurring in the melt before crystallization. Blend samples with minimal prior thermal history displayed a modest degree of melting point depression compared to the equilibrium melting temperature of PA 4,6 (T = 309.5°C). Application of the Nishi–Wang equation indicated a value of χ = ?0.25 for the blends. PA 4,6 and the blends followed Avrami crystallization kinetics with exponents in the range 2.0 to 2.5; no systematic variation of n with blend composition was observed. The influence of transamidation was investigated for samples exposed to varying melt temperatures and melt times with the extent of transreaction quantified using ¹³C‐NMR. Increasing extents of transreaction led to a decrease in both the rate of crystallization and the overall bulk crystallinity of the blends owing to a reduction in the length and number of crystallizable blocks present along the polymer chains. Capillary rheometry studies indicated a strong sensitivity to time in the melt for the PA 4,6 homopolymer, and the mechanism responsible for the observed decrease in apparent viscosity was also operative in the blend samples. As such, it was not possible to independently assess the influence of transreaction on the rheology of the blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1245–1252, 2004     

Rheological,thermal, and morphological properties of ABS–PA1010 blends

Noncompatibilized and compatibilized ABS–nylon1010 blends were prepared by melt mixing. Polystyrene and glycidyl methacrylate (SG) copolymer was used as a compatibilizer to enhance the interfacial adhesion and to control the morphology. This SG copolymer contains reactive glycidyl groups that are able to react with PA1010 end groups ( NH₂ or  COOH) under melt conditions to form SG‐g‐Nylon copolymer. Effects of the compatibilizer SG on the rheological, thermal, and morphological properties were investigated by capillary rheometer, DSC, and SEM techniques. The compatibilized ABS–PA1010 blend has higher viscosity, lower crystallinity, and smaller phase domain compared to the corresponding noncompatibilized blend. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 683–688, 1999     

Structure,mechanical, and fracture properties of nanoreinforced and HNBR‐toughened polyamide‐6

Hydrogenated nitrile rubber (HNBR) and synthetic nanofillers, viz. water‐swellable sodium fluorohectorite (FH) and water dispersible boehmite alumina (BA), were used to toughen and reinforce polyamide‐6 (PA‐6). FH and BA were introduced in HNBR latex that was dried prior to melt mixing with PA‐6. Binary blend (PA‐6/HNBR) and ternary nanocomposites (PA‐6/HNBR/nanofiller) were produced and their structure–property relationships studied. HNBR was coarsely and microscale dispersed in PA‐6. FH, slightly intercalated, was present in PA‐6 and in the PA‐6/HNBR interphase, whereas BA was mostly located in the HNBR droplets. HNBR improved the ductility of the PA‐6/HNBR blend at cost of stiffness and strength. The fracture toughness and energy, determined on notched Charpy specimens at different temperatures (T = ?30°C, room temperature, and T = 80°C) were improved by blending with HNBR at 9 wt %. Additional incorporation of the nanofillers in 2.5 wt % enhanced the stiffness and strength of the PA‐6/HNBR blend but reduced its ductility. The fracture toughness of the ternary nanocomposites was between those of PA‐6 and PA‐6/HNBR, whereas their fracture energy fairly agreed with that of the parent PA‐6. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Morphology of polyethylene spherulite crystallized from melt

The morphology of melt‐crystallized polyethylene is reported. The samples were crystallized for different times at high temperature to produce early stages of spherulitic growth. Morphology studies using transmission electron microscopy showed that the largest proportion of the early objects was monolayers associated with a giant screw dislocation, and the remaining objects were multilayers. At the basal surfaces of these objects, the traces of the {1 0 0} planes were identified, and the angle between the different planes was found to be 67°30′. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1125–1129, 1999     

Preparations and properties of a high performance semicrystalline copolyimide and composites reinforced with glass fiber

A semicrystalline copolyimide derived from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (s‐BPDA), 1,3‐bis‐(4‐aminophenoxy)benzene (TPER), and 4,4′‐oxydianiline (4,4′‐ODA), end capped with phthalic anhydride (PA), was synthesized. Glass fiber reinforced composite was also prepared by impregnating powdery glass fiber with poly(amic acid) followed by solution imidization techniques. This copolyimide displayed a glass transition temperature of 202°C and a melting temperature of 373°C by differential scanning colorimeter (DSC). Crystallization and melting behaviors were investigated under nonisothermal and isothermal crystallization conditions. Double exothermic peaks were found by DSC when the copolyimide was cooled from the melt and multiple melting behaviors can be observed after the coployimide had been isothermally crystallized at different temperatures. Mechanical properties were investigated by dynamical mechanical analysis (DMA) and tensile experiments. The samples were cured at different temperatures and then tested at different temperatures. Results indicated that the copolyimide and the composite showed excellent mechanical properties. Additionally, this copolyimide also showed lower melt viscosity by rheological analysis. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40345.     

Chain extension of PA1010 by reactive extrusion by diepoxide 711 and diepoxide TDE85 as chain extenders

The chain extension behaviors of two diepoxides, epoxide TDE85 and 711, were studied to evaluate their coupling effects on polyamide 1010 (PA1010). The former gave better coupling effects and a faster reaction rate. The torque of PA1010 melt increased dramatically with reaction time. The effect of the diepoxy chain extender on the flowability, thermal properties, and mechanical properties of chain‐extended PA1010 was investigated. The melt flow index (MFI) dramatically decreased as the diepoxide was added to PA1010, and the notched Izod impact strength of the chain‐extended products also increased. Furthermore, study on the usage of chain extender showed that there exists an approximate platform on the curve of melt torque versus content of chain extender, beyond which crosslinking may occur. Theoretical analysis of the occurrence of crosslinking was carried out by Flory criterion, which demonstrated that the average amount of functional groups in the chain extension system played a significant role in avoiding crosslinking. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2347–2355, 2004