Surface molecular imprinting of nylon fibers for chiral recognition of d‐phenyllactic acid

In the current work, synthetic polyamide nylon fibers were modified via the strategy of surface molecular imprinting to develop enantio‐selective adsorbent fabrics for chiral recognition of d ‐phenyllactic acid (d‐ PhLA). The nylon fibers were first modified by grafting of polyacrylamide and then the incorporated amide groups were converted into functional amino groups via treatment with NaOCl (Hofmann degradation). The amino‐functionalized nylon fibers (Ny‐NH₂) were interacted with the targeted d‐ PhLA enantiomer before crosslinking the amino‐containing grafted chains with glutaraldehyde crosslinker followed by leashing the template d‐ PhLA out of the formed surface polymeric matrix by lowering the pH to 1 to finally produce the desired enantio‐selective adsorbent fibers DP‐Ny. Different instrumental methods such as elemental analysis, Fourier transform infrared spectroscopy, XRD and TGA were employed to examine all the synthetic procedures. SEM was also utilized to observe the morphological appearances of both native and modified nylon fibers. Moreover, the optimum extraction of d‐ PhLA was found to occur at pH 7. Isotherm studies of the prepared DP‐Ny fibers obeyed the common Langmuir linear equation with q_m values 130 ± 2 and 75 ± 1 mg g^?1 in the case of d‐ PhLA and l‐ PhLA, respectively. Furthermore, the enantiomeric resolution of (±)‐PhLA racemate was successfully carried out by a column technique with enantiomeric excess reaching approximately 78%. © 2019 Society of Chemical Industry     

Conductivity and structure of a polyamide/silver iodide nanocomposite

In this study, the structure and properties of an organic–inorganic composite material prepared from nylon 6 doped with fine particles of silver iodide (AgI) were examined. The preparation of the composite involved the complexation of nylon 6 with polyiodide ions such as I and I by immersion in an iodine/potassium iodide (I₂–KI) aqueous solution followed by reaction in a silver nitrate (AgNO₃) aqueous solution; this resulted in the in situ formation of β-AgI fine particles within the nylon 6 matrix. The AgI content formed in the composite was dependent on the immersion temperatures of the I₂–KI and AgNO₃ solutions. Lower solution temperatures resulted in larger amounts of AgI in the composite. This method readily provided a composite with a high content of AgI in nylon 6 and a conductivity of approximately 10⁻⁵ Ω⁻¹ cm⁻¹. In a uniaxially oriented nylon 6 matrix, AgI particles precipitated with anisotropic shape, which was caused by the orientation of the precursor polyiodide ions. The structure of the oriented composite provided the anisotropic conductivity. Additionally, the composite exhibited high antibacterial properties. The procedure used in this study is considered a unique method for the preparation of organic–inorganic composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Application of lipase immobilized on nylon‐6 for the synthesis of butyl acetate by transesterification reaction in n‐heptane

A purified alkaline thermotolerant bacterial lipase from Bacillus coagulans BTS‐3 was immobilized on nylon‐6 matrix activated by glutaraldehyde. The matrix showed ～ 70% binding efficiency for lipase. The bound lipase was used to perform transesterification in n‐heptane. The reaction studied was conversion of vinyl acetate and butanol to butyl acetate and vinyl alcohol. Synthesis of butyl acetate was used as a parameter to study the transesterification reaction. The immobilized enzyme achieved ～ 75% conversion of vinyl acetate and butanol (100 mmol/L each) into butyl acetate in n‐heptane at 55°C in 12 h. When alkane of C‐chain lower or higher than n‐heptane was used as an organic solvent, the conversion of vinyl acetate and butanol to butyl acetate decreased. During the repetitive transesterification under optimal conditions, the nylon bound lipase produced 77.6 mmol/L of butyl acetate after third cycle of reuse. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Phase behavior and reaction of nylon 6/6 in water at high temperatures and pressures

The phase behavior and reaction of nylon 6/6 in water were studied with a diamond anvil cell (DAC) technique and visual microscopy. Nylon 6/6 concentrations in water and cell temperatures were varied from 11 to 46% and from 264 to 425°C, respectively. The pressures studied ranged from 30 to 900 MPa. When an aqueous solution of 27% nylon 6/6 was rapidly heated (2.6°C/s) to 372°C at 30 MPa, the solution became homogeneous at 331°C. Upon cooling, the final pressure was 30 MPa and both particles and gas were observed. Analysis of the particles by Raman indicated decomposed nylon 6/6 solid. When an aqueous solution of 31% nylon 6/6 was rapidly heated (2.9°C/s) to 425°C at 58 MPa, the solution became homogeneous at 323°C. Upon cooling, the final pressure was 143 MPa, and, remarkably, only a second liquid precipitated and no gas or solids were observed. From the experiments, we concluded that the reaction pathways are completely different between the subcritical and supercritical water conditions. For the case of subcritical conditions, the final products were solid particles having a nylon character along with a considerable amount of gas. At supercritical water conditions, the final products were liquids having little nylon character and no gas. Experiments were performed at a constant temperature of 272°C at initial pressures ranging from 87 to 400 MPa. As the reaction proceeded, the pressure was measured at 30‐s intervals. At average pressures less than 300 MPa, the nylon 6/6 samples melted and appeared to become homogeneous. At average pressures higher than 520 MPa, the nylon 6/6 samples remained heterogeneous. From these results, the rate of hydrolysis was concluded to increase with pressure. The reaction volume was found to be −21.1 cm³/mol, which can be explained by the overall formation of water‐soluble products. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1062–1073, 2000     

Structure and thermal behaviour of nylon 6 nanocomposites

In this article, nylon 6/clay nanocomposites with 5 wt % clay (NCN5) were prepared by a twin screw extruder. The effects of annealing including solid‐state annealing (170 and 190°C) and melt‐state annealing (240°C) on the polymorphic behavior and thermal property of NCN5 and nylon 6 have been comparatively studied as a function of annealing time using modified differential scanning calorimetry (MDSC) and wide‐angle X‐ray diffraction. It was demonstrated that NCN5 and nylon 6 exhibit a similar polymorphic behavior when they were annealed at 190°C for different time durations. As the annealing temperature was elevated to 240°C, significant differences in thermal behavior and polymorphism between NCN5 and nylon 6 could be found. For example, the α crystal became the absolutely dominating crystalline phase for NCN5 sample independent on the annealing durations, whereas the formation of γ crystal is greatly enhanced in neat nylon 6 with increasing annealing time. Moreover, a small endothermic peak is observed around 180°C in both nylon 6 and NCN5 samples annealed at 170 and 190°C, which might be related to the melting of microcrystals formed in the amorphous regions during annealing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3116–3122, 2006     

Biodegradation of nylon4 and its blend with nylon6

The nylon4 portion in the blend films composed of nylon4 and nylon6 was degraded and completely disappeared within 4 months in two kinds of composted soils gathered from different university farms as well as pure nylon4 film reported previously, while the nylon6 portion remained even after the burial test for 15 months. Nylon4 powder was also degraded to carbon dioxide in the degradation test in an activated sludge obtained from a sewage disposal institution in Kogakuin University. Three species of microoganisms (i.e., ascomytous fungi) were isolated through the inoculation from the nylon4 film partially degraded in the soil on a medium containing nylon4 powder as a carbon source. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2307–2311, 2002     

Dyeing mechanism and model of nylon 6 fiber dyeing in low‐temperature hydrogen peroxide–glyoxal redox system

This article reports the results of a study of nylon 6 fiber dyed in a low‐temperature hydrogen peroxide–glyoxal redox system. It was expected that the dyed fiber would have better dye fastness and higher economic value than would conventional fiber. In addition, this article presents the proposed mechanism for and model of a free‐radical dyeing system as well as a derived theoretical equation. From the experimental results, it was found that formation of covalent bonds by the coupling of the dye and the fiber radical in free‐radical dyeing was only 25%–40%, whereas with the conventional type of ionic dyeing, it was almost 60%–75%. Because the initiation efficiency of free‐radical formation is affected by many factors, such as the pH of the dye bath and the concentrations of the oxidant and reductant, the aims of this study were to investigate the formation of free radicals and the effects on dye uptake of the concentrations of dye, oxidant, and reductant and of the fiber amine end group. In addition, the dyeing properties of dyed fiber were investigated, and the dyeing order and rate constant of the rate equation were evaluated from the experimental data. From the experimental results, the following conclusions were drawn. (1) The hydrogen peroxide–glyoxal redox system produced many free radicals in the dye bath as temperature reached 70°C. (2) The amine end group in the nylon fiber was the main site of ionic and covalent bonding between nylon 6 fiber and dye. (3) The proposed model of free‐radical dyeing showed, from the fit of the experimental data into the equation and the evaluation of the equation parameters, that the order fit the theoretical value well, with the rate constant dependent on the dyeing conditions; at pH = 3, it could match the equation's best (rate equation of the proposed model: d[D]_R/dt = k_A[GO]¹[H₂O]^m[D]^1/2[F]^1/2). (4) The optimum dyeing conditions in the hydrogen peroxide–glyoxal redox system were: [H₂O₂] = 0.15–0.20M, [glyoxal] = 0.07–0.10M, pH = 3, dyeing temperature = 70°C, and dyeing time = 45–50 min. (5) The redox dyeing system had better dye fastness than did the conventional system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4197–4207, 2006     

Preparation and characterization of polyimide‐g‐nylon 6 copolymers from nonfunctionalized polyimides

In this research, the anionic polymerization of ?‐caprolactam was carried out in the presence of small amounts of several different polyimides to generate polyimide‐g‐nylon 6 copolymers. The polyimides, which were prepared from 2,2′‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]propane dianhydride and commercially available diamines with a one‐step method, were first dissolved in molten ?‐caprolactam. Phenylmagnesium bromide was then added at 120°C. Under these conditions, caprolactam anions were formed that attacked the five‐membered imide rings to form N‐acyllactam moieties, which activated the anionic polymerization of caprolactam. In essence, nylon 6 chains grew from the polyimide backbones. Probably because of a high activation energy, the process was relatively slow, requiring 1 h at 120°C. The introduction of 5 wt % polyimide into the graft copolymers produced significant increases in the tensile modulus and tensile strength in comparison with those of low‐ and high‐molecular‐weight nylon 6. The elongation to break, however, was reduced. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 292–299, 2006     

Structure and properties of polyimide‐g‐nylon 6 and nylon 6‐b‐polyimide‐b‐nylon 6 copolymers

Polyimide‐g‐nylon 6 copolymers were prepared by the polymerization of phenyl 3,5‐diaminobenzoate with several diamines and dianhydrides with a one‐step method. The polyimides containing pendant ester moieties were then used as activators for the anionic polymerization of molten ε‐caprolactam. Nylon 6‐b‐polyimide‐b‐nylon 6 copolymers were prepared by the use of phenyl 4‐aminobenzoate as an end‐capping agent in the preparation of a series of imide oligomers. The oligomers were then used to activate the anionic polymerization of ε‐caprolactam. In both the graft and copolymer syntheses, the phenyl ester groups reacted quickly with caprolactam anions at 120°C to generate N‐acyllactam moieties, which activated the anionic polymerization. All the block copolymers had higher moduli and tensile strengths than those of nylon 6. However, their elongations at break were much lower. The graft copolymers based on 2,2′‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]propane dianhydride and 2,2′‐bis[4‐(4‐aminophenoxy)phenyl]propane displayed elongations comparable to that of nylon 6 and the highest moduli and tensile strengths of all the copolymers. The thermal stability, moisture resistance, and impact strength were dramatically increased by the incorporation of only 5 wt % polyimide into both the graft and block copolymers. The graft and block copolymers also exhibited improved melt processability. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 300–308, 2006     

Crystallization behavior of polypropylene in polypropylene/nylon 6 blend

This article describes the crystallization behavior of polypropylene (PP) in the presence of a crystallizable polymer, namely, nylon 6, in the binary blend of PP/nylon 6 in the composition range from 0 to 30 wt % of nylon 6 content in the blend. The crystallization behavior was studied through variation of the crystallinity with the blend composition and changes in the crystallization exotherms were recorded by differential scanning calorimetry (DSC) and the spherulite morphology was observed via polarized light microscopy (PLM). Comparison of the crystallization exotherms and melting endotherms revealed some differences which are attributed to the role of a sufficiently high thermal energy of the nylon 6 crystals on the melting of PP. The crystallinity of PP decreased in the presence of nylon 6, whereas the crystallinity of nylon 6 increased considerably in the presence of PP. The rate of nucleation of PP on addition of nylon 6 decreased rapidly in the region 0–10 wt % nylon 6 content, and, thereafter, at a higher nylon 6 content, decrease of the nucleation rate was relatively slow. PLM observation revealed the presence of composite spherulites with PP spherulites grown on the surface of the already‐formed nylon 6 spherulites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1153–1161, 1999     

Structure and thermal behavior of nylon‐6/polytetrahydrofuran triblock copolymers obtained via anionic polymerization

The structure, crystallization, and phase behavior of nylon6‐b‐polytetrahydrofuran‐b‐nylon6 triblock copolymers synthesized via activated anionic polymerization have been studied. The composition, molecular weight of polytetrahydrofuran (PTHF) soft block, and type of polymeric activators (PACs) have been varied. Differential Scanning Calorimetry (DSC), Wide‐Angle X‐ray Diffraction (WAXD), Transmission Electron Microscopy (TEM), and Polarized Light Microscopy (PLM) experiments have revealed that in triblock copolymers only the nylon‐6 component crystallizes while PTHF segments are amorphous. The soft blocks do not alter the spherulitic crystalline structure of nylon‐6 and hard blocks crystallize in the α‐modification. The degree of crystallinity decreases with increasing PTHF concentration. The phase behavior has been investigated by Dynamic Mechanical Thermal Analysis (DMTA). Two different glass transition temperatures (T_g) for all samples have been observed. This indicates that nylon‐6 and PTHF segments are not molecularly miscible and the copolymers are microphase separated. The mechanical properties of the copolymers synthesized have been evaluated. Nylon‐6 copolymers with soft block concentrations up to 10 w/w %, exhibit improved notched impact strength in comparison to the nylon‐6 homopolymer, retaining relatively high hardness and tensile strength. All copolymers possess low water absorption and good thermal stability. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1448–1456, 2002; DOI 10.1002/app.10448     

Graphenes for low percolation threshold in electroconductive nylon 6 composites

Moderately functionalized graphenes, prepared by the thermal reduction of graphite oxide, were utilized to prepare electroconductive graphene/nylon 6 composites which exhibited a highest conductivity value of 6.84 × 10^?4 S cm^?1 for a low carbon incorporation of 0.54 wt% and a lowest percolation threshold of 0.39 wt%, the lowest values reported so far for graphene/nylon 6 composites. The functionality of the graphenes was modulated by the thermal reduction time. The graphitic structure of graphene was strengthened by extended thermal treatment. The main strengthening mechanism in the first 5 min was the generation of new sp² domains followed by the growth of the domains during the next 5 min. This extended thermal treatment improved the conductivity of the graphene itself as well as the composite loaded with graphene. However, it led to poor dispersion of the graphene in the composites, reduced crystallization of nylon 6 and reduced reinforcement of nylon 6 by graphene. © 2013 Society of Chemical Industry     

Flow stress of high density polyethylene and nylon 66 at high rates of strain

Measurement of the flow stress of high density polyethylene (HDPE) and nylon 66 at strain rates of 10³ s^?1 using a split Hopkinson pressure bar technique is discussed. The flow stress at a strain of 10% has been determined for both polymers at 20°C. The intrinsic errors involved in this technique are briefly reviewed. The results indicate that the flow stress of HDPE and nylon 66 were 50MPa and 150MPa, respectively, at strain rates of about 10³s^?1.     

Study on the structure of nylon 6 films iodinated before forming. II. Investigation of the crystallization behavior through thermal analysis

Two kinds of amorphous nylon 6 films iodinated before forming from the powders iodinated with 0.2N and 1.0N I₂/KI aqueous solutions were prepared by a melt‐press, and isothermally treated at 20 to 80°C for 1 day to 20 days. Thermal analyses were performed to investigate mainly the crystallization behavior on the treatment. The DSC thermograms for the treated films exhibit three temperature‐groups of endothermic peaks at 60 ～ 70°C, 105 ～ 120°C, and higher than 150°C, which may be associated with the melting of the complex crystal, the relaxed γ‐crystal, and the relaxed α‐crystal, respectively. The film containing less I₂/KI and treated at the higher temperature exhibits the peaks associated with the more stable type of crystal. The peak temperature generally increases with the treating temperature and time. On the occasion of there being two peaks associated with the γ‐crystal and the α‐crystals, ΔH for the α‐crystal increases while that for the γ‐crystal decreases with increasing the treating time. The TG curves indicate two temperature‐zones of weight loss by the volatilization of I₂ from I₅^? and the decompositions of I₃^? and nylon 6. With increasing treating temperature, the % weight loss by the volatilization of I₂ decreases, and consequently the temperature of the weight loss by the decomposition of nylon 6 increases. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1062–1069, 2004     

Studies on 3D Printability of Novel Impact Modified Nylon 6: Experimental Investigations and Performance Evaluation

The development of functional polymer parts with complex geometrical shape has been possible through additive manufacturing. In this research work, the issues such as warping, filament clogging, and layer delamination related to fused deposition modeling-based 3D printing of nylon 6 are focused and its poor printability is improved. Nylon 6 is toughened by blending with an impact modifier, ethylene terpolymer. Complex viscosity, storage, and loss moduli of modified nylon increase significantly, which help to improve 3D printability of nylon 6. 3D printing of modified nylon is performed at optimized conditions, such as printing temperature, print speed, bed temperature, and cooling speed. Izod impact strength of 3D printed nylon 6-based blend is observed ≈543 J m⁻¹, which is significantly higher than the value (48 J m⁻¹) available in literature for injection molded pristine nylon 6. Thermomechanical analysis of modified nylon shows higher coefficient of linear thermal expansion in normal direction as compared to that in flow direction, which is due to the orientation of polymer crystals during processing. The voids are observed on the cross-sectional surface of impact fractured sample, which are responsible to produce light-weight 3D printed specimens.     

Interior synthesizing of ZnO nanoflakes inside nylon‐6 electrospun nanofibers

Doping of the polymeric electrospun nanofibers by metal oxides nanoparticles is usually performed by electrospinning of a colloidal solution containing the metal oxide nanoparticles. Besides the economical aspects, electrospinning of colloids is not efficient compared with spinning of sol–gels, moreover well attachment of the solid nanoparticles is not guaranteed. In this study, reduction of zinc acetate could be performed inside the nylon‐6 electrospun nanofibers; so polymeric nanofibers embedding ZnO nanoflakes were obtained. Typically, zinc acetate/nylon‐6 electrospun nanofibers were treated hydrothermally at 150°C for 1 h. Besides the utilized characterization techniques, PL study affirmed formation of ZnO. The produced nanofibers showed a good antibacterial activity which improves with increasing ZnO content. Overall, the present study opens new avenue to synthesize hybrid nanofibers by a facile procedure. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Identification of caprolactam oligomers and related compounds in aqueous extracts of nylon‐6

Cyclic oligomers of caprolactam were isolated from a multilayered polyolefin plastic film containing a nylon‐6 layer and subsequently characterized. Nylon‐6 was extracted with aqueous solutions and the levels of the oligomers were measured in the resulting extracts. Oligomers up to n = 5 were present at high and comparable levels in all the nylon‐6 extracts. The levels of the oligomers dropped off rapidly with increased compound size after n = 5, with the heptamer being barely observable in the extract chromatograms. The effect of extracting solution pH on the compound's concentration in the extract was small, except for the monomer, whose accumulation was significantly decreased at low pH. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1262–1274, 2005     

Effect of Dye‐Bath pH on Photostability of Dyed Nylon 66

Nylon 66 films were dyed in aqueous dye‐bath with C. I. Acid Blue 25 (1‐amino‐4‐(aminophenyl)‐2‐anthraquinone sodium sulfonate) at various pH values ranging from 2.0 to 7.0. Films were exposed to polychromatic irradiation (λ ⪈ 290 nm) at 60°C in air. The extent of photo‐oxidation was monitored by FT‐IR spectroscopy. Fading of dye with polychromatic irradiation was monitored by UV spectroscopy. We observed a peculiar effect of dye‐bath pH on the photostability of dyed nylon 66. Samples were more stable when dyed at pH 3 and above that (up to pH 7), whereas the samples dyed at pH < 3.0 showed sensitized photo‐oxidative degradation in nylon 66. Formation of quaternary ammonium salt on dye‐chromophore was considered responsible for the pH‐controlled behavior of anthraquinone acid dyes. The dyeing pH significantly effects the photofading behavior of dyed samples. The effect of dye‐bath pH on photofading of the dyed samples was more pronounced at lower dyeing pH and prevailed up to pH 4. The hydronium ion concentration was considered to be responsible for the enhanced fading of dye for the samples dyed at the lower pH.     

High‐flow nylon 6 by in situ polymerization: Synthesis and characterization

A new synthetic strategy for high‐flow nylon 6 was developed in this article. Generation 1, 2, 3 (G1, G2, G3) polyamidoamine (PAMAM) dendrimers reacted with p‐phthalic acid by equimolar terminal groups in water solution, respectively, and mother salt solution was then prepared. The high‐flow nylon 6 was prepared with suitable quantity of mother salt solution, end‐capping agent, and ?‐caprolactam by in situ polymerization. Blue shifts are found for the peaks of NH (γN? H and 2δN? H) of the high‐flow nylon 6 compared with pure nylon 6 in the IR spectra. Comparing with the pure nylon 6, the high‐flow nylon 6 containing low content of PAMAM units, has high‐flow property and almost the same mechanical property. The high‐flow nylon 6 with low content of PAMAM units has greater melt‐flow index (MFI) (the value of MFI increased by 70–90%). Hardly any decrease in the tensile strength is observed with the elongation at break decreasing by 20–35%. But the izod impact strength of the high‐flow nylon 6 increases. The SEM images show that the high‐flow nylon 6 presents brittle fracture with conglomeration‐like structure, while pure nylon 6 exhibits plastic fracture with island‐like structure. DSC thermograms of nonisothermal crystallization exhibit that the peak of high‐flow nylon 6 broadens compared with pure nylon 6, and the broader peak means the wider processing temperature. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nonisothermal decomposition kinetics of nylon 1010/POSS composites

The thermal stability of nylon 1010/polyhedral oligomeric silsesquioxane (POSS) composites prepared by melt blending was investigated with thermogravimetric analysis. The octavinyl POSS (vPOSS) and epoxycyclohexyl POSS (ePOSS) were used, and it was found that nylon/vPOSS composites have higher integral procedure decomposition temperature and char yield at 800°C than nylon/ePOSS composites. The Doyle–Ozawa (model‐free) and Friedman (model‐fitting) methods were used to characterize the nonisothermal decomposition kinetics of nylon 1010 and its composites. The activation energy (E_a), reaction order (n), and the natural logarithm of frequency factor of nylon 1010 were 267 kJ/mol, 1.0, and 47 min^?1, respectively, in nitrogen. After the addition of POSS, the E_a of nylon 1010 considerably increased, whereas n had less change. The E_a steadily increased with increasing conversion and with increasing heating rate. The lifetime of nylon 1010 and its composites decreased with increasing temperature. At a given temperature, POSS significantly prolonged the lifetime of nylon 1010. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009