Effect of lactic acid on polymer crystallization chain conformation and fiber morphology in an electrospun nylon-6 mat

The role of lactic acid (LA) on the polymer crystallization chain conformation and the surface modification of the electrospun nylon-6 fibers were examined. The effect of different amounts of LA on the polymer crystallization chain conformation of nylon-6 mat was evaluated using XRD, FT-IR and Raman spectroscopy whereas the surface modification of the electrospun mats was examined by FE-SEM, contact angle and mechanical properties measurement. It was found that the transition of meta-stable γ-form into the thermodynamically stable α-form was achieved by increasing the amounts of LA in the blend mixture. The adhesive property of LA was found to be responsible for the transformation from non-bonded to the point-bonded structure of nanofibers in the electrospun nylon-6 mat. The resultant LA/nylon-6 hybrid mat with improved hydrophilicity and mechanical properties may be a potential candidate for tissue scaffold.     

Studies of electrospun regenerated SF/TSF nanofibers

The Bombyx mori silk fibroin/Tussah silk fibroin (SF/TSF) nanofibers with diameters between 300 and 3500 nm were prepared by electrospinning with the solvent HFIP. The average diameters of SF/TSF blend fibers increased from 404 to 1977 nm, with the increase of SF content in blend solutions, and the relationship between the average diameters of SF/TSF and SF content was proved to be linear correlation. Results from FTIR, TG-DTA and X-ray diffraction showed that the electrospun fibers were mainly β-sheet structure and, heterogeneous micro-structures. In particular, the presence of two different endothermic peaks at 300 and 360 °C in the TG-DTA curves may be ascribed to the thermal decomposition of SF and TSF. These results suggested that SF and TSF were still immiscible even dissolved in hexafluoroisopropanol (HFIP) after electrospinning and ethanol treatment. Moreover, the thermal decomposition temperature and enthalpy were improved with the blend of SF and TSF, else the SF/TSF nanofibers' moisture absorption was higher than the pure SF or TSF nanofibers. To study the cytocompatibility and cell behavior on the SF/TSF nanofibers, MSCs, VECs, and Neurons were seeded onto the nanofibers. Results indicated that the SF/TSF nanofibers promote cell attachment and spreading, suggesting that these nanofibers could be a candidate scaffold for blood vessel and nerve injury recovery.     

Preparation, characterization, and encapsulation/release studies of a composite nanofiber mat electrospun from an emulsion containing poly(lactic-co-glycolic acid)

The aim of this study was to investigate the preparation, characterization, and encapsulation/release performance of an electrospun composite nanofiber mat. The hypothesis was that the composite nanofiber mat with nano-scaled drug particles impregnated in biocompatible and biodegradable polymer nanofibers can serve as an innovative type of tissue engineering scaffold with desired and controllable drug encapsulation/release properties. To test the hypothesis, the composite nanofiber mat electrospun from an emulsion consisting of poly(lactic-co-glycolic acid) (PLGA) Rhodamine B (a model compound to simulate drugs), sorbitan monooleate (Span-80, a non-ionic emulsifier/surfactant that is presumably non-toxic/safe for cell-growth), chloroform, DMF, and distilled water was prepared and characterized; and the Rhodamine B encapsulation/release profile in phosphate buffered saline (pH = 7.4) was recorded and analyzed. For comparison purposes, two additional nanofiber mats electrospun from (1) a solution containing PLGA and Rhodamine B, and (2) a solution containing PLGA, Rhodamine B, and Span-80 were also prepared and assessed as the control samples. The results indicated that the composite nanofiber mat electrospun from the emulsion had the most desired and controllable Rhodamine B encapsulation/release profile and the excellent morphological sustainability; thus, it could be utilized as both a drug encapsulation/release vehicle and a tissue engineering scaffold.     

Nanoindentation and morphological studies on injection-molded nylon-6 nanocomposites

The nanoindentation behavior and morphology of the injection-molded specimens of nylon-6 (PA6)/clay nanocomposites prepared by melt-compounding have been studied in present study. The elastic and plastic properties as well as creep behavior of PA6 and its nanocomposites are comparatively evaluated as the function of clay loading by using nanoindentation technique. The anisotropic characteristics in mechanical properties are studied by indenting the injection-molded specimens in two different directions (i.e. parallel and perpendicular to the injection direction). The uneven distribution of both the clay nanofiller and the crystallinity of the polymeric matrix induced by melt-processing leads to the variation of the mechanical property of the nanocomposites in certain directions and locations within the molded specimens. The microstructural and morphological changes of PA6 upon incorporating with clay nanofiller are evidenced by transmission electron microscopy and small-angle X-ray scattering, which are closely correlated with the anisotropy of the mechanical properties observed by nanoindentation.     

Morphological changes in nylon-6/acrylonitrile-butadiene-styrene reactive blend

The morphological changes of blends of nylon-6 and acrylonitrile-butadiene-styrene (ABS) with reactive compatibilizer [poly(N-phenylmaleimide-styrene-maleic anhydride)] as a function of viscosity ratio of the components, concentration of compatibilizer, and the feed rate have been studied using an intermeshing corotating twin screw extruder. The occurrence of reaction between the amine end group of nylon-6 and maleic anhydride of compatibilizer during melt blending was identified by the solvent extraction and infrared spectroscopy study. It was found that the minimum dispersed phase size occurred at the viscosity ratio (p) = 0.75. Dispersed phase size was decreased significantly by the addition of compatibilizer and tended to equilibrate at about 15 wt % compatibilizer based on the amount of nylon-6. It was observed that the morphology was strongly dependent on the feed rate. The presence of maximum dispersed phase size was observed as a function of feed rate. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1595–1604, 1997     

Effects of processing history and annealing on polymorphic structure of nylon-6/montmorillonite nanocomposites

The effects of processing history and annealing treatment on the thermal property and polymorphic structure of nylon-6/clay nanocomposites (NCNs) have been investigated. The nanocomposites, including intercalated and exfoliated ones, were prepared by extruding nylon-6 (N6) with sodium montmorillonite (Na-MMT) or organo-montmorillonite (OMMT), respectively. DSC analysis revealed multiple melting endotherms in either the extruded or the injection-molded N6 and NCNs samples. It has been observed that a small exothermic peak around 195 °C just before the lower melting peak in the skin regions. We demonstrated that this sub-T_m transition was directly related to the processing-induced shear stresses. WAXD analysis was further performed to characterize the polymorphic structure of injection-molded N6 and NCNs before and after annealing. Annealing at a temperature (80 °C) above the T_g of N6 resulted in increase of the absolute content of γ-form in the skin regions and of the relative content of γ-form in the core regions of NCNs. In particular, annealing only leaded to increase the fraction of γ-form in the exfoliated N6/OMMT nanocomposites, which might be related to a confining effect of MMT platelet on the polymer chains mobility.     

Effects of clay orientation and aspect ratio on mechanical behavior of nylon-6 nanocomposite

The mechanical properties of nylon-6/clay nanocomposites with variations in clay aspect ratio and orientation were studied. A large-scale simple shear process was utilized to alter the clay aspect ratio and orientation within the reference nanocomposite. It was found that the modulus, strength, and heat distortion temperature of the nanocomposites decreased as the clay aspect ratio and degree of orientation were reduced. Furthermore, the reduction of clay aspect ratio and orientation led to an increase in fracture toughness and ductility. The Halpin-Tsai and Mori-Tanaka micromechanics-based models were implemented to gain a better understanding with regard to the dependence of clay structural parameters, i.e. aspect ratio and orientation, on the reinforcement effect of the nanofillers. The micromechanical models can accurately describe the relationship between clay structural parameters and the corresponding moduli for exfoliated nanocomposites.     

Microstructure, nucleation and thermal properties of high-pressure crystallized MWCNT/nylon-6 composites

Multi-wall carbon nanotube (MWCNT)/nylon-6 composites made by in-situ polymerization and subsequently modified by treatment at 1.0 GPa (or 1.7 GPa) and 530 K have been studied by WAXD, DSC and NMR. The pressure treatment gives an amorphous to crystalline transformation where the crystallinity increases from ∼31% to as much as ∼58% concurrently as the nylon-6 crystals increase in size and attain a preferred orientation relative to the applied pressure. A composite of 2.1 wt% purified MWCNT in nylon-6 shows significantly higher melting temperature than neat nylon-6 after identical pressure treatments. The improved thermal stability of the composite is attributed to crystal growth in the presence of reinforcing MWCNTs. The NMR spectrum of a pressure treated composite is similar to that of nylon-6 single crystals, which suggests a reduction of crystal boundaries after treatment, but there is no indication of covalent bonds between the nylon-6 chains and the MWCNTs.     

Studies on the electrospun Nylon 6 nanofibers from polyelectrolyte solutions: 1. Effects of solution concentration and temperature

Polyelectrolyte solutions of Nylon 6 in 99 vol% formic acid were electrospun, and the effect of polymer concentration was studied. Using a laser device to locally heat the needle spinneret, the solution temperature was feasibly elevated up to 66 °C, and its effect on electrospinning was investigated as well. The microstructure of the as-spun products was characterized by several analytical techniques, including electron diffraction, differential scanning calorimetry (DSC) and wide-angle X-ray diffraction. Based on the solution rheology, the entanglement concentration (c_e) was determined to be 1 wt%. To prepare bead-free fibers, the minimum polymer concentration was 8 c_e, which was much higher than that (1.75-2.0 c_e) required for conventional neutral solutions. Increasing the polymer concentration and/or solution temperature led to a gradual change of electrospun products from round fibers with major γ form crystals to ribbon-like fibers in possession of exclusive α form ones. For intermediate concentrations, nanowebs made of nanofibrils with diameters of 20-40 nm were seen. Thin ribbon-like fibers (ca. 40 nm thick) with nanowebs became the dominant products obtained from the 15 wt% solutions at high temperatures. The dramatic variations in morphological features and crystal modification could be thoroughly explained on the basis of the interplay between solvent evaporation at the jet surface and solvent diffusion in the liquid jet. DSC heating traces on the ribbon-like fibers exhibited an unusually high melting temperature of ∼235 °C, which is higher than the equilibrium melting temperature of Nylon 6 crystals of 232 °C.     

Influence of nonsolvents on dissolution characteristics of nylon-6

The dissolution of nylon-6 has been made effective by adding a nonsolvent to the primary solvents that in turn created potential combined contact sites and enhanced the process of dissolution. It is found that 50% of a primary solvent like m-cresol or phenol could be replaced by solvents that are relatively economical and safe to handle. Nylon-6 is found to get dissolved at a faster rate and with ease in a blend of 45 : 55 phenol-toluene compared to other solvent blends. The dependence of limiting viscosity on solute-binary solvent interactions is used as a measure of the solvency power of solvent blends for nylon. The lowering of temperature is found to favour the dissolution of nylon-6 in m-cresol. Its dissolution is found to be optimum in phenol at 55°C and further increase in temperature has adverse effects on it.     

A numerical study on the effects of acidic catalyst on the polymerization of nylon-6

The effects of acetic acid on the polymerization characteristics of nylon-6 are investigated in a reactor model that consists of a continuous flow stirred tank reactor (CSTR) and a tubular reactor connected in series. Mathematical models for the CSTR and the tubular reactor have been established and solved by numerical methods. In the CSTR, the monomer conversion and the molecular weights are increased as the feed acetic acid concentration is increased. In the tubular reactor, the acid acts as both a catalyst and a modifier for the polymerization reaction. The effects of the feed acetic acid content on the zeroth, first and second moments and the polydispersity index of the polymer have been discussed.     

Hydrolysis of ricebran oil in a fluidised-bed recycle reactor using immobilised lipase on nylon-6

A recycling fluidises-bed Immobilised enzyme reactor for the hydrolysis of ricebran oil employing an inexpensive Nylon-6 matrix as the immobilisation carrier is described. The catalyst has high initial activity and excellent long term stability. The tractor design exploits the fact that fluidisation permits the use of small catalyst particles, so overcoming the yield-limiting diffusion-associated problems encountered in the case of conventional fixed-bed reactors. The conventional fluidised-bed reactor did not plugging and high pressure drop problems typical of fixed-bed reactors. Conversion yields of 72% were achieved in the reactor, which generally showed superior performance to that of a fixed-bed design.     

静电纺丝PBT/PVA复合膜的制备及性能研究

以三氟乙酸和二氯甲烷为混合溶剂,采用静电纺丝法制备聚对苯二甲酸丁二酯(PBT)/聚乙烯醇(PVA)复合膜。用旋转粘度计和电导率仪测定溶液的黏度和电导率,用扫描电子显微镜、拉伸和水接触角测试PBT/PVA不同比例对纤维膜的形貌、力学和亲水性能的影响。结果表明,随着PVA比例的增加,混合溶液的黏度逐渐增大,而电导率先增大后减小;当PBT/PVA的比例为90/10时,纳米纤维的平均直径最小,为323 nm,而其纳米纤维膜的力学性能与纯PBT纤维膜相比显著提高,拉伸强度、弹性模量和断裂伸长率分别增加了213%,260%和57%;PVA的加入改善PBT纤维的亲水性,制备出力学性能优异且亲水的PBT/PVA纤维膜。     

Studies of chitosan. I. Preparation and characterization of chitosan/poly(vinyl alcohol) blend films

Various blending ratios of chitosan/poly (vinyl alcohol) (CS/PVA) blend films were prepared by solution blend method in this study. The thermal properties and chemical structure characterization of the CS/PVA blend films were examined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and Fourier transform infrared (FTIR). Based upon the observation on the DSC thermal analysis, the melting point of PVA is decreased when the amount of CS in the blend film is increased. The FTIR absorption characteristic is changed when the amount of CS in the blend film is varied. Results of X‐ray diffraction (XRD) analysis indicate that the intensity of diffraction peak at 19° of PVA becomes lower and broader with increasing the amount of CS in the CS/PVA blend film. This trend illustrates that the existence of CS decreases the crystallinity of PVA. Although both PVA and CS are hydrophilic biodegradable polymers, the results of water contact angle measurement are still shown as high as 68° and 83° for PVA and for CS films, respectively. A minimum water contact angle (56°) was observed when the blend film contains 50 wt % CS. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Blend membranes from carboxymethylated chitosan/alginate in aqueous solution

The blend membranes were satisfactorily prepared by coagulating a mixture of O‐carboxymethylated chitosan (CM‐chitosan) and alginate in aqueous solution with 5 wt % CaCl₂, and then by treating with 1 wt % HCl aqueous solution. Their structure and miscibility were characterized by scanning electron micrograph, X‐ray diffraction, infrared spectra, differential thermal analysis, and atomic absorption spectrophotometer. The results indicated that the blends were miscible, when the weight ratio of CM‐chitosan to alginate was in the range from 1 : 1 to 1 : 5. The polymers interpenetration including a Ca²⁺ crosslinked bridge occurred in the blend membrane, and leads to high separation factor for pervaporation separation of alcohol/water and low permeation. The tensile strength in the wet state (σ_b = 192 kg cm⁻² for CM‐chitosan/alginate 1 : 1) and thermostability of the blend membranes were significantly superior to that of alginic acid membrane, and cellulose/alginate blend membranes, owing to a strong electrostatic interaction caused by —NH₂ groups of CM‐chitosan with —COOH groups of algic acid. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 610–616, 2000     

尼龙6/PEO聚电解质抗静电复合材料的结构与性能研究

通过碱金属离子与聚氧化乙烯（PEO）的络合配位制备了不同比例的PEO聚电解质,将PEO聚电解质与尼龙6熔融共混挤出,制备抗静电尼龙6复合材料;测试了复合材料的力学性能和电性能;分析了影响机理,并借助傅立叶转换红外光谱和扫描电镜表征了复合材料的结构.结果表明,碱金属离子与PEO结构单元的物质的量比为1/6时,复合材料体积电阻率下降幅度达到了5个数量级,同时冲击强度明显提高,拉伸强度有所下降.红外谱图显示,尼龙6基体与聚电解质发生了相互作用.     

Effect of solvent evaporation rate on the crystalline state of electrospun Nylon 6

The role of solvent evaporation on the crystalline state of electrospun Nylon 6 fibers was examined by electrospinning into a closed chamber filled with different concentrations of solvent vapor. It was found that the thermodynamically stable α form became increasingly dominant in Nylon 6 fibers electrospun out of both 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and formic acid as the vapor phase solvent concentration increased. It is believed that the formation of the metastable γ form is due in part to the fast solvent evaporation kinetics associated with the electrospinning process. By varying the vapor phase concentration and thus the rate of solvent evaporation during electrospinning, we were able to vary the resulting crystal structure of the electrospun Nylon 6, as shown by XRD, Raman and FTIR.     

Effect of polyurethane structure on mechanical properties of nylon-66/polyurethane blends

A polyamide (nylon-66, N66) was blended with a series of polyurethanes (PU) based on different polyols or chain extenders. The effects of PU structure and content on the mechanical properties of the blends were investigated. The morphology of the polyblends was examined by scanning electron microscopy. The Izod impact strength of the blends increased with increasing PU content and showed a maximum value at the composition of 15 wt % PU. The effects of moisture content on the mechanical properties of the blends were also investigated. It was found that the water-toughened N66 could be further toughened by the addition of PU. Polyester-type PU rather than polyether type PU was recommended for the toughening of N66 because the blends containing the former showed higher tensile strength and Izod impact strength except at very low moisture (0.3 wt %) content. Carboxyl groups was introduced into the molecular chains of PU by using dimethylol propionic acid as chain extender replacing part of 1,4-butanediol. The blends containing PU with carboxyl groups showed a lower Izod impact strength than those without carboxyl groups in the structure of PU.     

丝素/羧甲基壳聚糖共混膜的结构性能探讨

将含有甘油和戊二醛的丝素与羧甲基壳聚糖按一定比例混合,制得丝素/羧甲基壳聚糖共混膜,对共混膜的结构与性能进行了探讨。结果表明:随着羧甲基壳聚糖含量的增加,共混膜的透气率增大,加入交联剂戊二醛有效地改善了共混膜的力学性能,但其透气率有所降低;当丝素与羧甲基壳聚糖的质量比为4/1时,共混膜的断裂强度最大,力学性能较好,共混膜相容性较好,其断面光滑、致密。制备丝素/羧甲基壳聚糖共混膜的较佳条件为:丝素中的甘油质量分数为15%,戊二醛质量分数为0.075%,丝素与羧甲基壳聚糖质量比为4/1。     

Crystallization,morphology, structure and thermal behaviour of nylon-6/rubber blends

An experimental study was carried out in order to investigate the morphological, kinetic, structural and thermodynamic properties of nylon-6/rubber (namely ethylene-propylene copolymer (EPM) and ethylene-propylene copolymer functionalized by inserting along its backbone succinic anhydride groups (EPM-g-SA)) blends. The morphology and the overall kinetics of crystallization of the blends strongly depend on the type of copolymer added to nylon and on the blend composition. The EPM-g-SA acts as a nucleating agent for the Ny spherulites and at the same time causes a drastic depression of the overall kinetic rate constant. This decrease is related to the increase of the melt viscosity observed in Ny/EPM-g-SA blends. The crystalline lamella thickness of the Ny phase in the blends is lower than that of pure Ny crystallized at the same T_c suggesting that the presence in the melt of an elastomeric phase disturbs the growth of the Ny crystals. The rubber does not influence the thermal behaviour of the nylon. The results found lead to the conclusion that in the melt nylon-6 is incompatible with both EPM and EPM-g-SA copolymers.