Studies on electrospun nylon-6/chitosan complex nanofiber interactions

Composite membranes of nylon-6/chitosan nanofibers with different weight ratio of nylon-6 to chitosan were fabricated successfully using electrospinning. Morphologies of the nanofibers were investigated by scanning electron microscopy (SEM) and the intermolecular interactions of the nylon-6/chitosan complex were evaluated by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), differential scanning calorimetry (DSC) as well as mechanical testing. We found that morphology and diameter of the nanofibers were influenced by the concentration of the solution and weight ratio of the blending component materials. Furthermore FT-IR analyses on interactions between components demonstrated an IR band frequency shift that appeared to be dependent on the amount of chitosan in the complex. Observations from XRD and DSC suggested that a new fraction of γ phase crystals appeared and increased with the increasing content of chitosan in blends, this indicated that intermolecular interactions occurred between nylon-6 and chitosan. Results from performance data in mechanical showed that intermolecular interactions varied with varying chitosan content in the fibers. It was concluded that a new composite product was created and the stability of this system was attributed to strong new interactions such as hydrogen bond formation between the nylon-6 polymers and chitosan structures.     

Crystallization of polyamides under elevated pressure: 3. The morphology and structure of pressure-crystallized nylon-6 (polycapramide)

The morphology and structure of nylon-6, crystallized from the melt under elevated pressure, has been investigated. Scanning and transmission electron microscopy on replicas of the fracture surfaces reveal that crystallization under pressures exceeding 4 kbar (1 kbar = 100 MN/m²) results in rough lamellar structures with some step heights corresponding to the contour lengths of the chains. Infra-red spectroscopy on the pressure-crystallized nylon-6 shows a considerable improvement of crystalline order, a closer packing of the polymer chains within the crystal, and the presence of a large proportion of free N-H groups. An absorption band at 1170 cm^?1 was assigned to the presence of folds in the nylon-6 crystals. Wide-angle X-ray measurements indicate that the crystal modification of the pressure-crystallized nylon-6 is predominantly the alpha phase. Pressure gives rise to an increase in crystallite dimensions as well as to a decrease of the distance between the crystal planes bonded by the hydrogen bonds and by the Van der Waals forces.     

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.     

尼龙6塑料的应用开发

论述了尼龙6塑料的研制、生产情况、新技术、新品种的开发动向。介绍了尼龙6树脂的聚合新工艺、成型加工方法和设备特性。探讨了尼龙6塑料品种改性和应用等的发展前景。     

Preparation of nylon-6/chitosan composites by nanospider technology and their use as candidate for antibacterial agents

Electrospun nylon-6/chitosan (nylon-6/Ch) nanofibers were prepared by nanospider technology. Quaternary ammonium salts as antibacterial agent were immobilized onto electrospun nylon-6/Ch nanofibers via surface modification by soaking the mat in aqueous solution of glycidyltrimethylammonium chloride (GTMAC) at room temperature overnight to give nylon-6/N-[(2-hydroxy-3-trimethylammonium)propyl] chitosan chloride (nylon-6/HTCC). The morphological, structural and thermal properties of the nylon-6/ch nanofibers were studied by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA). Biological screening has demonstrated the antibacterial activity of the electrospun nanofibers against Gram negative bacteria, Escherichia coli 35218, and Pseudomonas aeruginosa and Gram positive bacteria, Staphylococcus aureus 24213 among the tested microbes. Thus, the study ascertains the value of the use of electrospun nanofibers, which could be of considerable interest to the development of new antibacterial materials for biomedical applications.     

有机改性蒙脱土制备聚酰胺6/蒙脱土复合材料

采用有机复合改性的方法制备了改性蒙脱土,并采用原位聚合方法制备了尼龙-6/蒙脱土复合材料,利用FTIR、TG-DTA、XRD对有机蒙脱土进行了表征。结果表明,有机插层剂已进入蒙脱土的层间,使蒙脱土的层间距由原来的1.39 nm增大到2.32 nm,从而改善了它的分散性以及与尼龙-6之间的粘结作用,二者构成的纳米复合材料具有很好的力学性能。当加入2%的有机蒙脱土时,拉伸强度提高16%,冲击强度提高5%。     

Cellulose-Reinforced nylon-reaction injection molded composites

The properties of cellulose-reinforced nylon-6 block copolymers were studied. Composites were prepared by Reaction Injection Molding (RIM) of a nylon system in which one of the reactants contained cellulose fibers. Incorporation of cellulose fibers into the liquid reactant of the nylon-RIM system resulted in increased viscosity, depending on the amount and the aspect ratio of cellulose fibers. After proper drying, cellulose did not disturb the polymerization of the nylon-RIM system. The cellulose fibers increased the stiffness of the nylon-6 block copolymer. The stiffening effect depended on the aspect ratio and surface treatment. The tensile strength of cellulose-nylon composites was slightly decreased. Elongation at break and impact strength were reduced compared to glass fiber-reinforced nylon. Dynamic mechanical measurements (DMA) showed that the cellulose improved the elastic modulus of the nylon, especially at elevated temperatures. Scanning Electron Microscopy (SEM) on fractured surfaces showed improved adhesion between fiber and matrix when a surface treated cellulose was used.     

Interfacial Contact and Bonding in Autohesion II-Intermolecular Forces

The second stage of autohesion involves bond formation after contact is established by elastic, viscous, or viscoelastic deformation of the surfaces. The interfacial bonding for polystyrene is mainly through van der Waals intermolecular forces. Molecular repeat units across the interface interact to yield an attractive force. The intermolecular forces are derived from a 6-12 Lennard-Jones potential. The two unknown constants for this potential are determined from the equilibrium distance and comparison of the computed lattice energy with the cohesive energy.     

Relation between ductility and segmental mobility of nylon-6

High-resolution solid-state ¹⁵N and ¹³C NMR and dynamic mechanical measurements were carried out for solution grown crystals of the α- and γ-forms of nylon-6 to understand the relation between segmental mobility including interchain interactions and ductility of polyamides. The ductility, in the temperature range of 100-180 °C, was lower for the α-crystals than for γ-crystals. ¹⁵N chemical shift revealed that the hydrogen bonding was stronger for the γ-crystals than for α-crystals. In addition, lower mobility of NH group in the γ-crystals than in α-crystals was shown by results. The results suggest that the ductility of nylon-6 could not be simply related to the strength of hydrogen bonding. Highly crystalline films of aggregates of solution grown α-crystals and γ-crystals showed no crystalline relaxation in the temperature dependence of dynamic mechanical loss factor, suggesting an existence of strong intermolecular interactions in the crystalline regions although data indicated that the mobility of methylene units was higher in the γ-crystals than in α-crystals. Information on the large-scale chain dynamics in the crystalline regions might be necessary to understand the low ductility of polyamides.     

Interfacial Contact and Bonding in Autohesion II-Intermolecular Forces

The second stage of autohesion involves bond formation after contact is established by elastic, viscous, or viscoelastic deformation of the surfaces. The interfacial bonding for polystyrene is mainly through van der Waals intermolecular forces. Molecular repeat units across the interface interact to yield an attractive force. The intermolecular forces are derived from a 6–12 Lennard-Jones potential. The two unknown constants for this potential are determined from the equilibrium distance and comparison of the computed lattice energy with the cohesive energy.     

Time-dependent behavior of nylon-6 under uniaxial and biaxial loadings at constant rate

The large deformation behavior of nylon-6 when subjected to constant loading rate tests has been investigated experimentally. Three types of loadings—tension, torsion, and combined tension-torsion—have been used and the strain histories for each type analyzed. It is shown that a piecewise power law in time can adequately describe the strain histories up to equivalent strains as high as 30 percent for all cases. This piecewise power law shows well-defined transitions from one mode to the other while each mode is characterized by a power law exponent valid for all types of loading. On the basis of experimental results, it is also possible to establish the functional form of various kernels involved in the Green-Rivlin representation of the non-linear viscoelastic behavior of nylon-6. This method of finding kernels is much simpler than the conventional method of carrying out a large number of multi-step creep tests. A comparison is also made between the results of the present work and the well-known Findley equation, particularly with respect to the instantaneous strain response of materials.     

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.     

Crystallization behavior of nylon-6 confined among ultra-fine full-vulcanized rubber particles

The crystallization behavior of nylon-6 confined in a hybrid of nylon-6 and ultra-fine full-vulcanized powdered rubber was studied. It is found that carboxylic styrene-butadiene ultra-fine full-vulcanized powdered rubber (CSB-UFPR) could behave as a nucleating agent for nylon-6 crystallization, which can increase the crystallization temperature, the onset temperature of crystallization as well as the glass transition temperature of nylon-6 confined in the hybrid of nylon-6 and ultra-fine full-vulcanized powdered rubber. It is also found that nylon-6 molecules confined among CSB-UFPR particles favor the crystalline form of γ than that of α. The crystallization process of γ phase of nylon-6 in nylon-6/CSB-UFPR hybrid is a diffusion-controlled process, and thus it can be accelerated by raising the crystallization temperature or by extending oil into CSB-UFPR. It is expected that these results will benefit the research on crystallization behavior of other constrained geometry polymer, such as ultra-thin film and polymer/clay hybrid, and etc.     

Glass transition temperature in nylons

The determination of the glass transition temperature of semi-crystalline polymers is a controversial problem in the literature, because of the complexity of the phenomenon and of the different methods used for its measurement. In this work the glass transition temperatures of five commercial nylons (nylon-6, nylon-6,6, nylon-6,10, nylon-11, nylon-12) have been measured by both thermal and mechanical methods. The behaviour observed during thermal measurements is analogous to that observed by Gordon, who found that the transition detected in the heating cycle disappeared in the subsequent cooling cycle and appeared again only after a sufficient rest period of the samples, and at a temperature different from the initially measured one. He attributed this behaviour to the structure of the amorphous regions of the material, where the hydrogen bonding groups form an irregular network. The delay in reforming the above mentioned network is the main cause of the dependency of the observed transition on the thermal history imposed on the samples. Mechanical measurements give results that are quite insensitive to the thermal treatment of the materials, and thus provide very reproducible values of the transition. This feature allows the possibility of attributing to the transition obtained the character of a true glass transition where the main cause of the phenomenon is the increased mobility of the chain backbone in the amorphous regions of the materials with increasing temperature. This character was also confirmed by dilatometry, with results in agreement with Boyer's criteria for a true glass transition temperature.     

Crystallization of polyamides under elevated pressure: 4. Annealing of nylon-6 (polycapramide) under pressure

A study has been made on the annealing of nylon-6 under elevated pressure. Heat treatment of meltcrystallized nylon-6 at 6.5 kbar and 20°C below the beginning of melting for a period of 120 h yielded an increase in the heat of fusion from 14.2 to 41.2 cal/g and an increase in atmospheric melting temperature from 222° to 256°C (1 kbar = 100 MN/m²; 1 cal/g = 4.187 kJ/kg). Stepwise annealing by exposing nylon-6 to progressively higher temperatures at 6.5 kbar led to a heat fusion of 40.8 cal/g and a melting temperature of 269°C. Annealing was found to be particularly effective in improving the crystalline structure at pressures exceeding 4 kbar. The rate of annealing at 6.5 kbar increased with temperature in the range between 260° and 280°C. Electron microscopy of fracture surfaces disclosed that annealing could give rise to a marked increase in lamellar thickness. Wide-angle X-ray diffraction showed that crystal growth also occurred in the lateral direction and that the alpha-crystalline modification was preserved during annealing. From a comparison between the melting characteristics of nylon-6 obtained by pressure-induced crystallization from the melt and by annealing under pressure of folded-chain material, it is inferred that the folded-chain lamellar state may be an essential intermediate stage of the chain extension in polyamides under pressure.     

Cure Characteristics and Mechanical Properties of HRH Bonded Nylon-6 Short Fiber-Nanosilica-Acrylonitrile Butadiene Rubber Hybrid Composite

Nano silica was synthesized by acid hydrolysis of sodium silicate using diluted hydrochloric acid. This synthetic nanosilica was used in place of hydrated silica in a HRH (hexamethylenetetramine, resorcinol and silica) bonding system for acrylonitrile butadiene rubber–nylon-6 short fiber composite. Nanosilica was also used as a reinforcing filler in acrylonitrile butadiene rubber–nylon-6 short fiber hybrid composite. Cure characteristic and mechanical properties of the hybrid composites were evaluated. Minimum torque, maximum torque, and cure time of the hybrid composites increased with silica loading. Cure rate increased with fiber loading and decreased with silica content. Scorch time also decreased with fiber loading and silica content. Volume fraction of rubber in a solvent-swollen sample increased with nanosilica. The efficiency of the HRH dry bonding system was improved in the presence of nanosilica. Nanosilica in the rubber composites also improved the tensile strength, modulus, and tear strength better than the conventional silica composites. Abrasion loss, hardness, resilience, and compression set properties were also better for the nano silica composites. The composites showed anisotropy in mechanical properties.     

Trifluoroethanol/chloroalkane mixtures: Excellent novel solvents for aliphatic polyamides

Certain mixtures of TFE/CHCl₃ were found to be excellent solvents for aliphatic polyamides such as nylon-6, nylon-66, nylon-11, nylon-12, nylon-69, nylon-610, and nylon-612. Intrinsic viscosities were measured and Mark–Houwink coefficients determined for nylon-6/TFE/CHCl₃, indicating TFE-rich mixtures to be better solvents than TFE alone. Similar results were obtained for TFE/CH₂Cl₂. Four ternary phase diagrams were constructed for nylon-6/TFE/chloroalkanes, of which the ones with CHCl₃ and CH₂Cl₂ are the most interesting. In the nylon-6/TFE/CHCl₃ diagram higher nylon-6 solubility in TFE-rich mixtures and a biphasic region in the CHCl₃-rich compositions are evident. In the TFE/CH₂Cl₂ system, the higher dissolution of nylon-6 is observed, but no biphasic regions are detected. In certain solvent compositions and/or polymer concentrations the polymer is incompletely soluble, making the phase diagrams rather complicated. Observed thermodynamic excess properties appear to relate to the quality of TFE/chloroalkanes as solvents for nylon-6. Studies on swelling of nylon-6 networks immersed in TFE/CHCl₃ show a behaviour previously described by Krigbaum and Carpenter for a general case where the formation of contracts between molecules of the two solvents is discouraged and their preferential solvation of the polymer is, therefore, encouraged. The phenomena observed in this work can be qualitatively explained as arising from antagonistic interaction of TFE molecules with chloroalkane ones. The presence of the polyamides in solution reduces such contacts, enchancing the dissolution of the polymer in the (TFE-rich) solvent mixtures.     

尼龙6/纳米钛合金复合材料的制备及结构

将经过有机化处理的纳米钛合金粉体与尼龙6通过熔融共混制备成了尼龙6/纳米钛合金复合材料。X-射线衍射和透射电镜显示,在钛合金粉体含量低时,钛合金粉体在尼龙6基体中实现了纳米尺度的分散,但随钛合金粉体含量增加,团聚现象明显增加;红外光谱(IR)分析和Molau试验表明,复合材料中钛合金粉体与周围尼龙6分子间存在某种键合;实验结果还表明,钛合金粉体对尼龙6基体的化学结构和结晶形态没有产生明显的影响。     

Terminal functionalized hydroxyl‐terminated polybutadiene: An energetic binder for propellant

We report the functionalization of hydroxyl terminated polybutadiene (HTPB) backbone by covalently attaching 1‐chloro‐2, 4‐dinitrobenzene (DNCB) at the terminal carbon atoms of the HTPB. The modification of the HTPB by the DNCB does not alter the unique physico–chemical properties and the microstructure of the parent HTPB. IR, ¹H‐NMR, ¹³C‐NMR, size exclusion chromatography (SEC) and absorption spectroscopy studies prove that the DNCB molecules are covalently attached to the terminal carbon atoms of the HTPB. The π electron delocalization owing to long polymer chain, strong electron withdrawing effect of the DNCB molecule are the major driving forces for the covalent attachment of the DNCB at the terminal carbon atom of the HTPB. We are the first to observe the existence of intermolecular hydrogen bonding between the terminal hydroxyl groups of the HTPB. IR study shows that the attached DNCB molecules at the terminal carbon atoms of the HTPB breaks the intermolecular hydrogen bonding between the HTPB chains and forms a hydrogen bonding between the NO₂ groups of the DNCB and the OH groups of the HTPB. Absorption spectral study of the modified HTPB indicates the better delocalization of π electron of butadiene due to the strong electron withdrawing effect of the DNCB molecules. Theoretical calculation also supports the existence of hydrogen bonding between the OH and NO₂ groups. Theoretical calculation shows that the detonation performance of both the DNCB and the HTPB‐DNCB are promising. HTPB‐DNCB is the new generation energetic binder which has potential to replace the use of HTPB as binder for propellant.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

基布对聚氨酯合成革性能影响的研究

以涤纶非织造布，锦纶非织造布作基布，制作了聚氨酯浸渍试样，研究了其拉伸，弯曲性能，认为由于锦纶与聚氨酯的结合较强，影响了锦纶基布柔软性的发挥。当上浆率超过一临界值时，锦纶基布聚氨酯合成革已不如涤纵横在布聚氨酯合成革柔软。