Structure and property study of nylon‐6/clay nanocomposite fiber

The crystal structures of nylon‐6 and nylon‐6/clay fibers were investigated on annealing and drawing. Annealing increased the γ‐crystalline form of both fibers, as indicated by the DSC curves, and its effect was dominant in nylon‐6/clay fiber. On drawing, the γ‐crystalline form was easily converted into the α form in nylon‐6, whereas it was still observed at a relatively high spin‐draw ratio in nylon‐6/clay fiber. However, although the α‐crystal form was dominant in nylon‐6, the γ‐crystal form was dominant in nylon‐6/clay with annealing and drawing, on the basis of the XRD data. The fast crystallization rate of nylon‐6/clay compared with pure nylon‐6 was confirmed, on the basis of the Avrami exponent. The initial modulus of nylon‐6/clay fiber was 30 % higher than the neat nylon‐6 fiber. The reinforcing effect of clay on the dynamic storage modulus was observed. Copyright © 2004 Society of Chemical Industry     

γ‐Crystalline form of nylon‐10,10 in nylon‐10,10–montmorillonite nanocomposite

Wide‐angle X‐ray diffraction (WAXD) and variable temperature WAXD spectroscopy and Fourier‐transform infrared (FTIR) spectrometry were used to identify the γ‐crystalline form of nylon‐10,10 in the nanocomposite of nylon‐10,10 and montmorillonite. A new diffraction peak at 2θ = 22° was observed in the WAXD pattern of the nanocomposite as compared with nylon‐10,10, and the data of variable temperature WAXD indicated that it was the characteristic peak of γ‐crystalline form of nylon‐10,10. The amide VI band at 624 cm^?1 was also observed in the FTIR spectrum of the nanocomposite, which is characteristic of γ‐crystalline nylon. In addition, the shoulder peak at 1553 cm^?1 can be assigned to the amide II band of γ‐crystalline form of nylon‐10,10. Copyright © 2003 Society of Chemical Industry     

Morphology and crystallization behavior of nylon 6‐clay/neat nylon 6 bicomponent nanocomposite fibers

Nylon 6‐clay hybrid/neat nylon 6, sheath/core bicomponent nanocomposite fibers containing 4 wt % of clay in sheath section, were melt spun at different take‐up speeds. Their molecular orientation and crystalline structure were compared to those of neat nylon 6 fibers. Moreover, the morphology of the bicomponent fibers and dispersion of clay within the fibers were analyzed using scanning electron microscopy and transmission electron microscopy (TEM), respectively. Birefringence measurements showed that the orientation development in sheath part was reasonably high while core part showed negligibly low birefringence. Results of differential scanning calorimetry showed that crystallinity of bicomponent fibers was lower than that of neat nylon 6 fibers. The peaks of γ‐crystalline form were observed in the wide‐angle X‐ray diffraction of bicomponent and neat nylon 6 fibers in the whole take‐up speed, while α‐crystalline form started to appear at high speeds in bicomponent fibers. TEM micrographs revealed that the clay platelets were individually and evenly dispersed in the nylon 6 matrix. The neat nylon 6 fibers had a smooth surface while striped pattern was observed on the surface of bicomponent fibers containing clay. This was speculated to be due to thermal shrinkage of the core part after solidification of the sheath part in the spin‐line. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39996.     

Effect of nanoclay on the thermal,mechanical, and crystallization behavior of nanofiber webs of nylon‐6

Nylon‐6 and nanoclay/nylon‐6 composite nanofibers were prepared by electrospinning technique, in which formic acid was used as a solvent for good solubility of nylon‐6. The diameter of nylon‐6 and nanoclay/nylon‐6 nanofibers was below 350 nm and had smooth surfaces. The DSC heating curves of nylon‐6 and composites nanofibers show two endotherm behaviors, T_m1 (about 214°C) and T_m2 (about 220°C), corresponding to the melting events of γ‐form and α‐form crystals, respectively. The WAXs study showed that the γ‐crystalline phase predominantly present in both nylon‐6 and nanoclay/nylon‐6 nanofibers. The mechanical properties of the nanoclay/nylon‐6 composite nanofibers were higher than neat nylon‐6 electrospun nanofibers, which was decreased as the quantity of the clay increased. It might be due to the aggregation of nanoclay at high concentration. The thermal properties of the composite nanofibers were higher than neat nylon‐6 nanofibers. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Phase stability and melting behavior of the α and γ phases of nylon 6

The phase stability and melting behavior of nylon 6 were studied by high‐temperature wide‐angle X‐ray diffraction and differential scanning calorimetry (DSC). The results show that most of the α phase obtained by a solution‐precipitation process [nylon 6 powder (Sol‐Ny6)] was thermodynamically stable and mainly melted at 221°C; the double melting peaks were related to the melt of α crystals with different degrees of perfection. The γ phase formed by liquid nitrogen quenching (sample LN‐Ny6) melted within the range 193–225°C. The amorphous phase converted into the γ phase below 180°C but into the high‐temperature α phase at 180–200°C. Both were stable over 220°C. α‐ and γ*‐crystalline structures were formed by annealing but were not so stable upon heating. Typical double melting peaks were shown on the DSC curve; melt recrystallization happened within the range 100–200°C. The peak at 210°C was mainly due to the melting of the less perfect crystalline structure of the γ phase and a fraction of the α phase; the one at 219°C was due to the high‐temperature α‐ and γ‐phase crystals. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Crystal transition behavior of odd–odd nylon 11,11 under annealing and stretching

Nylon 11,11 is a new odd–odd polyamide with multiple crystalline structures. The wide‐angle X‐ray scattering indicated that the structure of quenched sample was not amorphous but a γ‐form crystal with a relatively low crystallinity. The α‐form and the γ‐form crystal of nylon 11, 11 could be obtained by annealing the quenched samples at high and low temperature, respectively. No crystal transition happened for the α‐form sample when annealed at any temperature before melting. However, the γ‐form would quickly transform into the α‐form when annealed above 145°C. Under the stretching conditions, the α‐form rapidly transformed into the γ‐form at low temperature, while the γ‐form changed into the α‐form only at high temperature. These results indicated that the stretching inducement was beneficial to produce the γ‐form, and the thermal inducement was favorable to forming the α‐form. POLYM. ENG. SCI., 54:2785–2790, 2014. © 2013 Society of Plastics Engineers     

Clay induced thermoplastic crystals in thermoset matrix: Thermal,Dynamic mechanical,and morphological analysis of clay/nylon‐6‐epoxy nanocomposites

A novel procedure to synthesize in situ clay/nylon‐6 composite suspension was explored via anionic solution polymerization. The suspension was efficiently blended with water‐based epoxy resin using mechanical stirrer at room temperature. Hence, a 3‐component coating system was obtained consisting of nano‐clay, nylon‐6 and epoxy resin. Large number of coatings and films were prepared with variation in clay and nylon‐6 loading. Concentration of clay was found to have profound effect on crystallinity of nylon‐6, thereby affecting the overall properties of clay/nylon/epoxy composite. All the films were characterized for thermal and dynamic mechanical behavior using differential scanning calorimeter (DSC) and dynamic mechanical analysis (DMA). Lower amount of clay was found to increase the crystallinity of nylon‐6 which in turn increased the plasticization of epoxy resin indicated by reduction in T_g. A multiphase morphology with distinct amorphous and crystalline zones was observed under scanning electron microscopy (SEM). A remarkable symmetrical morphology with branched dendritic crystal structure was observed for few of the clay/nylon/epoxy system. POLYM. COMPOS., 37:2206–2217, 2016. © 2015 Society of Plastics Engineers     

Effects of γ‐aminopropyltriethoxylsilane on morphological characteristics of hybrid nylon‐66‐based membranes before electron beam irradiation

Nylon‐66 is a typical semicrystalline polymer that can be crosslinked using crosslinking agents and electron beam irradiation. Hybrid nylon‐66‐based membranes are more porous but denser compared to the pure nylon‐66 membrane. Besides that, hybrid nylon‐66 membranes exhibit higher water uptake and severe swelling in water. Si/nylon‐66 membranes were prepared by adding γ‐aminopropyltriethoxylsilane (APTEOS). Crosslinked silica in nylon‐66 membranes is confirmed with high gel content and Fourier transform infrared peaks, but XRD results showed that there is a low crystalline degree in these membranes. The thermal stability of hybrid nylon‐66 membranes is also less affected by APTEOS. The crosslinking agent only improves storage modulus in hybrid nylon‐66 membranes. After irradiation, it is learned that APTEOS improves separation performance of nylon‐66 membranes. However, excessive APTEOS causes the ratio of effective thickness over porosity (Δx/A_k) reduces significantly resulting a lower permeability membrane. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Crystallization Controlled by Silicate Surfaces in Nylon 6‐Clay Nanocomposites

The crystallization behavior of pure nylon 6 (N6) and its nanocomposite with montmorillonite has been studied in detail. The crystallization rate of N6 is faster in the presence of clay compared to pure N6, as revealed by light scattering experiments. Nylon 6 crystallizes exclusively in the γ‐form in the nanocomposite because of the epitaxial crystallization, which is also revealed from the transmission electron microscopic images (sandwiched structure) of the crystallized sample. The storage modulus of the nanocomposite is always higher than the pure nylon 6, irrespective of crystallization temperatures. Much higher increment of storage modulus for pure nylon 6 with increasing crystallization temperature is explained by the higher amount of the thermally stable α‐form at higher temperature. A unique mechanism has been proposed to illustrate the crystallization behavior of nylon 6 in the presence of the clay particles.

Transmission electron micrograph of N6C3.7 crystallized at 210 °C, showing the typical shish‐kebab type of structure.     

High‐performance filaments by melt spinning low viscosity nylon 6 using horizontal isothermal bath process

Several techniques and treatments have been developed for the production of high‐performance nylon‐6 fibers. The inherent problems of low productivity, high production cost, and high energy consumption, complexity of chemical reaction, mass transfer, and waste recovery systems make most of them inappropriate for industrial application. Horizontal isothermal bath (hIB) is an alternative ecofriendly simple treatment that can be used during melt spinning process for production of technical textile fibers. The efficacy of hIB in improving the mechanical properties of multifilament nylon‐6 yarn is studied in this research. The results showed that such treatment can increase the molecular orientation of the amorphous and crystalline functions up to 0.54 and 0.983, respectively, and raised both the amorphous isotropy and fiber birefringence by 67 and 45%, respectively. Hot drawing of the yarn at a very low draw ratio of 1.38, increased the tenacity and modulus up to 10 and 43.9 g/den, respectively, and decreased the elongation to 27%. POLYM. ENG. SCI., 55:2457–2464, 2015. © 2015 Society of Plastics Engineers     

Structure development in the melt spinning of nylon 66 fibers and comparison to nylon 6

The development of crystallinity and orientation during the melt spinning of nylon 66 was investigated. Nylon 66 was found to crystallize in the spinline to form the Bunn-Garner α-triclinic structure. This behavior differs from that of nylon 6. Nylon 66 was found to develop lower crystalline orientation than nylon 6 under comparable spinning conditions.     

Enhanced crystallization of the γ‐form of propylene–ethylene copolymer in its miscible blends with propylene homopolymer

BACKGROUND: How to promote the formation of the γ‐form in a certain propylene‐ethylene copolymer (PPR) under atmospheric conditions is significant for theoretical considerations and practical applications. Taking the epitaxial relationship between the α‐form and γ‐form into account, it is expected that incorporation of some extrinsic α‐crystals, developed by propylene homopolymer (PPH), can enhance the crystallization of the γ‐form of the PPR component in PPR/PPH blends. RESULTS: The PPH component in the blends first crystallizes from the melt, and its melting point and crystal growth rate decrease with increasing PPR fraction. On the other hand, first‐formed α‐crystals of the PPH component can induce the lateral growth of PPR chains on themselves, indicated by sheaf‐like crystal morphology and positive birefringence, which is in turn responsible for enhanced crystallization of the γ‐form of the PPR component. CONCLUSION: Crystalline/crystalline PPH/PPR blends are miscible and the crystallization of the γ‐form of the PPR component is largely enhanced due to the heterogeneous nucleation from the α‐crystals first developed by the PPH component. Our findings could provide an effective way in practice to obtain isotactic polypropylene copolymers rich in γ‐form. Copyright © 2009 Society of Chemical Industry     

Synthesis and investigation of oligosiloxanes containing γ‐trimethylsiloxy‐propyl or γ‐hydroxy‐propyl groups

Oligosiloxanes having different distributions of Si? H groups were prepared, and the addition of Si? H bonds to C?C double bounds of trimethyl(2‐propenyloxy)silane was utilized to obtain oligosiloxanes having different distributions of γ‐trimethylsiloxy‐propyl or γ‐hydroxy‐propyl groups as substituents. The oligosiloxanes were characterized by IR and ¹H‐NMR spectroscopy. Viscosity was studied to investigate the effects of the substituents. Differential scanning calorimetry (DSC) was used to investigate the thermal behaviour of these oligosiloxanes. It was found that they are completely amorphous materials and, hence, show only a glass transition. We found that the viscosities and glass transition temperatures of these materials increased with the increasing of the number of substituents. Hydrogen bonds have a considerable influence on the increase of the viscosities and glass transition temperatures of oligosiloxanes. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2431–2435, 2002     

Preparation and characterization of polyamide‐6 with three‐branched chains

With trimesinic acid as a molecular weight regulator, the hydrolytic polymerization of ?‐caprolactam was carried out, and nylon‐6 or polyamide‐6 with three‐branched chains was obtained. Through a systematic study of the effects of conditions such as the reaction time and concentration of trimesinic acid on the polymerization, we found that the conversion of caprolactam was almost insensitive to the initial concentrations of the regulators, but the relative viscosity of the polymer decreased with increasing trimesinic acid. Characterization investigations showed that differential scanning calorimetry curves changed from a single peak for normal nylon‐6 to one main peak and one shoulder or one small peak for the branched polymer; the melting point of the star‐shaped nylon‐6 decreased with an increasing amount of trimesinic acid, whereas its crystallization temperature was higher than that of linear‐chain nylon‐6. A wide‐angle X‐ray diffraction study indicated that the crystal structure of the star‐shaped nylon‐6 still belonged to the α form, and the crystallizability of the branched polymer with an elevated amount of trimesinic acid during polymerization did not seem to be weakened; the characteristic absorption of infrared spectra provided indirect evidence for the existence of branched chains in the polymer. Moreover, the mechanical properties of star‐shaped nylon‐6 and linear‐chain nylon‐6 were compared. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3184–3193, 2001     

Studies on the kinetics of orientation and crystallization of nylon‐66 during high‐speed melt spinning

A new way of applying on‐line experimental data and basic theory to study the mechanism of orientation of a high‐speed melt spinning process is described. The relationship of birefringence and stress for Nylon‐66 was developed to understand the phenomena in the spinning line. The value of birefringence along the spinning line was calculated by various models to predict the orientation change. By comparison of the model prediction and on‐line experimental birefringence, a suitable mechanical model to simulate the change of the profiles along the spinning line was chosen, and the structural development mechanism is discussed. The results show that the orientation mechanism of high‐speed melt spinning of Nylon‐66 is determined by deformation and deformation rate along the spinning line. For Nylon‐66, molecular and crystal orientations develop independently and are controlled by the rotation of crystals and chain segments in the deformation field. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3157–3163, 2001     

Identification and Characterization of a Methionine γ‐Lyase in the Calicheamicin Biosynthetic Cluster of Micromonospora echinospora

CalE6 is a previously uncharacterized protein involved in the biosynthesis of calicheamicins in Micromonospora echinospora. It is a pyridoxal‐5′‐phosphate‐dependent enzyme and exhibits high sequence homology to cystathionine γ‐lyases and cystathionine γ‐synthases. However, it was found to be active towards methionine and to convert this amino acid into α‐ketobutyrate, ammonium, and methanethiol. The crystal structure of the cofactor‐bound holoenzyme was resolved at 2.0 Å; it contains two active site residues, Gly105 and Val322, specific for methionine γ‐lyases. Modeling of methionine into the active site allows identification of the active site residues responsible for substrate recognition and catalysis. These findings support that CalE6 is a putative methionine γ‐lyase producing methanethiol as a building block in biosynthesis of calicheamicins.     

TGA analysis of γ‐irradiated linear low‐density polyethylene

Linear low‐density polyethylene (LLDPE), based on butene‐1 or hexene‐1, was irradiated with γ‐rays under vacuum or in the presence of air. The study focused on the influence of the dose rate and the γ‐dose on the thermal properties of LLDPE. Differential scanning calorimetry, thermogravimetric analysis (TGA), and TGA/FTIR techniques were used to address the thermal behavior as a result of γ‐irradiation. During this irradiation, competition between crosslinking and scission reactions, subsequent to oxidation reactions, occurred in the polymeric material, which strongly depends on the experimental conditions. A decrease of the crystallinity for γ‐irradiated samples was observed in particular for samples irradiated under vacuum. This observation may be explained by increased hindrance of segment mobility due to crosslinking reactions that prevent crystal growth. TGA investigations revealed an enhancement of the thermal stability for samples irradiated under vacuum but not for those irradiated in air. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2790–2795, 2006     

Melt spinning and drawing of 2‐methyl‐1,3‐propanediol‐substituted poly(ethylene terephthalate)

The structure and properties of fibers prepared from copolymers of poly(ethylene terephthalate) (PET) in which 2‐methyl‐1,3‐propanediol (MPDiol® Glycol is a registered trademark of Lyondell Chemical Company) at 4, 7, 10, and 25 mol% was substituted for ethylene glycol were studied and compared with those of PET homopolymer. Filaments were melt spun over a range of spinning conditions, and some filaments that were spun at relatively low spinning speeds were subjected to hot drawing. The filaments were characterized by measurements of birefringence, differential scanning calorimetry (DSC) crystallinity, melting point, glass transition temperature, wide‐angle X‐ray diffraction patterns, boiling water shrinkage, tenacity, and elongation to break. Filaments containing 25 mol% MPDiol did not crystallize in the spinline at any spinning speed investigated, whereas the other resins did crystallize in the spinline at high spinning speeds. However, compared with PET homopolymer, increasing substitution of MPDiol reduced the rate at which the crystallinity of the melt spun filaments increased with spinning speed and reduced the ultimate crystallinity that could be achieved by high‐speed spinning. The rate of development of molecular orientation, as measured by birefringence, also decreased somewhat with increasing MPDiol content. Shrinkage in boiling water decreased at high spinning speeds as the amount of crystallinity increased; however, the shrinkage decreased more slowly with increase in spinning speed as MPDiol content increased. Tenacity also decreased slightly at any given spinning speed as MPDiol content increased, but there was no significant effect on elongation to break. The addition of MPDiol in amounts up to 7 mol% increased the maximum take‐up velocity that could be achieved at a given mass throughput. This result indicates that the use of higher spinning speeds could potentially increase the productivity of melt spun yarns. Copolymer filaments spun at low speeds were readily drawn to produce highly oriented fibers with slightly less birefringence, crystallinity, and tenacity than similarly processed PET homopolymer. Preliminary dyeing experiments showed that the incorporation of MPDiol improved the dyeability of the filaments. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2598–2606, 2003     

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     

胺类改性剂对尼龙6树脂可纺性能的影响

在己内酰胺水解聚合时加入一定量的可反应型复合胺类改性剂,合成出含有胺类改性剂的尼龙6树脂。研究了该改性剂对改善尼龙6树脂可纺性的作用。结果表明:在实验的添加量范围内,改性尼龙6树脂熔体黏度对切变速率的依赖敏感性下降,纺丝过程可以处于相对稳定的状态;与空白试样相比,当改性剂用量为0.1份时,尼龙6树脂中的低聚物含量明显减少,相对分子质量分布由1.7677降低到1.6093,表明在尼龙6熔体的纺丝成形过程中,胺类改性剂可以有效地改善其可纺性。