Shish-kebab structures of nylon-6 obtained from quiescent solutions by application of self-seeding

A study has been made of the morphology and structure of nylon-6 crystals grown from diluted 1,4-butanediol solution. Isothermal crystallization from homogeneous solution resulted in smooth ribbons or lath-shaped crystals aggregated into sheaves. Shish-kebab structures of nylon-6 could be grown from the quiescent solution by self-seeding techniques. Electron microscopic investigations and small-angle x-ray measurements showed that the molecules in the lath-shaped backbones of the shish kebab are folded and oriented perpendicular to the long axis of the crystals. The polyamide laths have the α-monoclinic crystal structure with the hydrogen bonds parallel to the long axis. It is suggested that due to the anisotropic type of bonding in the crystal lattice the crystals fragment laterally during the heating stage in the self-seeding technique. Structural defects, e.g., twinning sites introduced during the dissolution and subsequent crystallization may cause the growth of shish-kebab structures from quiescent solution.     

Solvent-induced crystallization of nylon-6I

The ability of various hydrogen bond-forming solvents to induce crystallinity in nylon-6I was studied using DSC, FTIR spectroscopy, and x-ray diffraction. Comparison was made with predictions using the solubility parameter, which is related to possibilities of interaction formation. General predicted tendencies agreed with experimental results, in agreement with proposed influence of solvent-polymer interactions in the solvent-induced crystallization process. FTIR investigation of polymers treated with methanol and methanol-d shows that polymer segments forming hydrogen bonds with solvent molecules crystallize preferentially. It is therefore concluded that hydrogen bond exchanges with the solvent favor chain rearrangements leading to crystallization. © 1995 John Wiley & Sons, Inc.     

Molecular dynamics simulation study of the structural characteristics of water molecules confined in functionalized carbon nanotubes

Molecular dynamics (MD) simulations were performed to study the structural properties of water molecules confined in functionalized carbon nanotubes (CNTs). Four CNTs, two armchair-type (6, 6), (7, 7) and two zigzag-type (10, 0), (12, 0) CNTs, representing different helicities and different diameters, were chosen and functionalized at their open ends by the hydrophilic -COOH and the hydrophobic -CH3 groups. The structural properties of water molecules inside the functionalized CNTs, including the orientation distributions of dipole moment and O-H bonds, the length of the single-file water chain, and the average number of hydrogen bonds, were analyzed during a process of simulations. MD simulation results in this work showed that the -CH3 functional groups exert little special effects on the structural properties of water molecules. It is mainly due to the relatively small size of the -CH3 group and its hydrophobic nature, which is consistent with hydrophobic CNTs. For CNTs functionalized by -COOH groups, the configurations of -COOH groups, incurvature or excurvature, determine whether water molecules can enter the CNTs. The incurvature or excurvature configurations of -COOH groups are the results of synergy effects of the CNTs' helicity and diameter and control the flow direction of water molecules in CNTs.     

Thermal behavior and structure of clay/nylon-6 nanocomposite synthesized by in situ solution polymerization

This article discusses the effect of increasing mass percentage of nanoclay on the thermal, structural and morphological properties of nanoclay/nylon-6 nanocomposite. Polymerization of ε-caprolactam conducted in the presence of clay resulted in increased d-spacing and expansion of the clay galleries. A combination of differential scanning calorimetry, X-ray diffraction and electron microscopy was used to study the structure–property relationship. The effect of clay on the melting behavior of nylon-6 was studied by using quenched and normally cooled samples. The clay particles acted as external nucleating agents, and a dramatic effect on the crystallization behavior of nylon-6 was observed. The nylon-6 crystals formed are predominantly of the γ-type in the presence of clay. The presence of up to 1 % of clay lead to an increase in the heat of fusion. For nylon-6 samples containing greater than 1 % clay, the heat of fusion decreased significantly.     

Synergistic effect of carbon nanotubes and layered double hydroxides on the mechanical reinforcement of nylon-6 nanocomposites

Synergistic effect in network formation of nylon-6 （PA6） nanocomposites containing one dimensional （ID） multi-walled carbon nanotubes （CNTs） and two dimensional （2D） layered double hydroxide （LDH） platelets on improving the mechanical properties has been studied. Mechanical tests show that, with incorporation of 1 wt% LDHs and 0.5 wt% CNTs, the tensile modulus, the yield strength as well as the hardness of the ternary composite are greatly improved by about 230%, 128% and 110% respectively, as compared with neat PA6. This is mainly attributed to the unique, strong interactions between the CNTs and the LDHs as well as the jammed network-like structure thus formed between the nanofillers, as confirmed by the morphological observations. As compared with the binary nanocomposites, a much enhanced solid-like behavior in the terminal region of the rheological curves can clearly be observed for the ternary system, which also indicates the formation of a percolating filler network.     

尼龙-6 18的晶型转变研究

以偶偶尼龙-6 18为例, 通过示差扫描量热分析(DSC), 广角X射线衍射(WAXD)与傅里叶变换红外光谱(FTIR)等方法研究了其Brill转变的过程, 探索了脂肪族聚酰胺的晶型转变的本质. X射线衍射结果表明， 随着温度的升高, 尼龙-6 18由三斜晶系转变为假六方晶型, 同时其DSC曲线上出现一个较宽的吸热峰. 红外光谱结果表明, 在其晶型转变过程中, 晶体内氢键强度逐渐减弱, 与酰胺键相连的C—C和C—N键发生扭曲. 酰胺基团之间的亚甲基链段的振动逐渐增强, 部分亚甲基单元由反式构象变成旁式构象, 最后整齐排列的亚甲基链段逐渐变得无序化.     

尼龙66-盐与碳纤维复合-固态缩聚的研究

本工作借助偏光显微镜,扫描电子显微镜和热分析方法(DSC,TGA)研究了尼龙66盐与碳纤维复合-固态缩聚反应历程及纤维-树脂之间的界面效应。发现对尼龙66盐的“原位固态缩聚”存有如碳纤维表面的成核结晶和催化效应之类的界面效应。讨论了碳纤维的界面效应对尼龙66基体的外延结晶和熔融行为及其热氧化稳定作用的影响。     

尼龙1010／马来酸酐接枝聚丙烯共混体系的反应增容

利用Ｍｏｌａｕ实验、红外光谱、电子扫描显微镜等研究了尼龙１０１０与马来酸酐接技改性聚丙烯（ＰＰ－ｇ－ＭＡＨ）共混体系的结构，结果表明，尼龙１０１０分子链中胺基或亚胺基与Ｐｐ－ｇ－ＭＡＨ上的酸酐发生了化学反应，生成的接枝共聚物起到了共混体系增容剂的作用，改善了体系的亲合性。     

Crystal orientation in a semicrystalline polymer in relation to deformation of polymer spherulites. IV. Crystal orientation mechanism of nylon-6 under uniaxial stretching

A model relating crystal orientation to the deformation of nylon-6 spherulites under uniaxial stretching is discussed in terms of the orientation distribution functions of reciprocal lattice vectors of crystal planes, such as the (002) and (200) planes. The distribution functions calculated from the model are compared with those obtained from x-ray diffraction experiments. It is found that the crystal a axis and, consequently, the direction of hydrogen bonds within the crystal (α modification) orient parallel to the lamellar axis in the undeformed state, and that the crystal orientation behavior of nylon-6 is much different from that of low-density polyethylene, being characterized by much smaller values of the reorientation parameters of crystallites within orienting lamellae. Moreover, small-angle light scattering for H_v and V_v polarization is also calculated on the basis of the spherulite deformation model by taking the nylon-6 crystal as having orthogonal–biaxial symmetry in optical anisotropy. It is concluded that the H_v scattering can be realized in terms of the proposed model for spherulite deformation by taking into account a considerable contribution of hydrogen bonds to the molecular polarizability, so as to make the polarizability along the crystal a axis larger than that along the b axis. In other words, this conclusion suggests positively birefringent spherulites in the nylon-6 samples studied.     

Effect of the melt annealing time on the crystallization of nylon-6 with various molecular weights

The effect of melt annealing duration at 260 °C-high above melting temperature on the crystallization of nylon-6 with various molecular weights (between 5 800 and 255 500) using dilatometric and calorimetric (DSC) techniques has been studied. The samples were laboratory synthesized, purified and characterized by GPC. It was found that the crystallization behavior of nylon-6 depends strongly on the melt annealing duration as well as on the molecular weight. This effect is explained by the gradual destruction of the crystallization centers during annealing of the melt. The experimental data support the well known memory effect and the recently observed accumulative memory effect on the same polymer     

Effect of polymer molecular weight on the fiber morphology of electrospun mats

In this work, different fractions of solvent-induced polymer degraded solution were mixed with freshly prepared solution of same polymer, and its effect on fiber morphology of electrospun mats was investigated. Nylon-6 solution in formic acid was allowed to degrade for 3 weeks and different fractions of it were mixed with freshly prepared nylon-6 solution to get the electrospun mats. FE-SEM images of the mats indicated that the a large amount of sub-nanofibers (<50 nm in diameter) in the form of spider-net like structures were achieved by tailoring the amount of solvent degraded polymer solution in the freshly prepared nylon-6 solution. Large quantity of these ultrafine sub-nanofibers present in electrospun nylon-6 mats could increase its hydrophilicity and mechanical strength. The decreased average pore diameter and increased BET surface area of the mat, caused by spider-net like structure, can make it as a potential candidate for air/water filtration.     

碳纤维-尼龙1010界面形态的研究

通过偏光显微镜,研究了碳纤维-尼龙1010的界面形态,发现石墨、高模量碳纤维(M40)诱发尼龙1010形成横晶的能力大于高强度、中强度碳纤维;界面横晶形态强烈地依赖于结晶温度。     

离子聚合物在Nylon－1010／PP共混物中的增容作用

离子聚合物在Ｎｙｌｏｎ－１０１０／ＰＰ共混物中的增容作用曲桂杰，刘景江（中国科学院长春应用化学研究所长春１３００２２）关键词聚丙烯，Ｎｙｌｏｎ－１０１０，离子聚合物，增容选择离子聚合物作为高聚物共混的增容剂，通过离子间的相互作用可达到增容效果［１］。...     

碳纳米管表面修饰程度对碳纳米管载Pt电催化性能的影响

比较了用不同温度的浓HNO₃处理的碳纳米管(CNTs)作载体的Pt(Pt/CNTs)对甲醇氧化的电催化活性. 结果表明浓HNO₃处理使CNTs表面修饰上的含氧基团对CNTs上沉积Pt粒子的平均粒径有较大影响. 表面修饰程度适当时, 制得的Pt/CNTs中Pt粒子较小, 因此, 对甲醇氧化的电催化活性较高. 而表面修饰程度过大, 易使Pt粒子团聚, 从而降低Pt/CNTs催化剂对甲醇氧化的电化学活性.     

Bulk properties of synthetic polymer-inorganic salt systems. V. Mechanical properties of oriented poly(caproamide)

Single filaments of nylon-6 and of its mixtures with KCl, LiCl, and LiBr (salt content up to 5% w/w) were prepared by extrusion at 265°C. As-spun filaments with a varying degree of orientation were obtained by altering the take-up velocity a t constant outflow velocity. These as-spun filaments were further subjected to controlled thermal and mechanical treatments. Determinations of the elastic modulus, of birefringence, of wide-angle x-ray scattering, and of shrinkage were carried out for the as-spun and for the treated filaments. While KCl caused no detectable alteration of the properties of nylon-6, lithium halides caused a considerable increase of the elastic modulus of the polymer. Under the conditions adopted, moduli up to 14 GPa were obtained. The birefringence of as-spun fibers was, however, lower when lithium salt was present. Greater shrinkage a t 170°C was exhibited by the salted than by the pure polymer. The body of results has been interpreted in terms of a more efficient orientation of the extruded polymer when lithium salt is present. The latter effect is associated with the role of these salts in reducing the crystallization rate and in increasing the melt viscosity of the polyamide as characterized in preceding papers of this series. Lithium salts also favor the α → γ transformation between the two crystalline forms of nylon-6. The transformation was, however, reversed under sufficiently high applied stress.     

Synthesis of well-aligned carbon nanotubes on the NH3 pretreatment Ni catalyst films

Well aligned multi-walled carbon nanotubes (CNTs) have been synthesized on large area Nideposited SiO₂/Si substrates via the pyrolysis of C₂H₂ using thermal chemical vapor deposition technique at 900°C. We concluded that NH₃ pretreatment was very crucial to control the surface morphology of catalytic metals and thus to achieve the vertical alignment of CNTs. With higher density of the Ni particles, better alignment of the CNTs can be obtained due to steric hindrance effect between neighboring CNTs. The degree of crystallization of the CNTs enhanced with the increase of the NH₃ pretreatment time was investigated by X-ray diffraction and transmission electron microscope studies. Energy dispersive X-ray spectrum analysis revealed that CNTs grew by a tip growth mechanism.     

Matrix-assisted laser desorption/ionization collision-induced dissociation of linear single oligomers of nylon-6.

Matrix-assisted laser desorption/ionization, collision induced-dissociation (MALDI-CID) has been used to obtain structural information for linear single oligomers of nylon-6. The effects of matrix and cationization agent in MALDI-CID analysis have been investigated. Fragmentation mechanisms are proposed for the series of ions that are observed in the MALDI-CID spectra of the hexamer, octamer and dodecamer. Fragmentation processes observed in the MALDI-CID spectra include cleavage of the end groups followed by dissociation of the m/z 113 unit. Cleavage of the oligamide chain occurs at the amide linkage, as well as at adjacent bonds. For the four matrices and three cationization agents investigated, 2,5-dihydroxybenzoic acid and sodium chloride showed the best performance for MALDI-CID analysis of the dodecamer. In addition, yields of the fragment ions in MALDI-CID spectra were found to be dependent on the chain length distribution.     

Effect of rubber on properties of nylon-6/unmodified clay/rubber nanocomposites

Three nylon-6/unmodified clay/rubber nanocomposites with high toughness, high stiffness, high heat resistance and reduced flammability were studied in this paper, on basis of three compound powders of ultra-fine full-vulcanized powdered rubber (UFPR)/montmorillonite (UFPRM). It was found that all of the three UFPRs used in the study can help the silicate layers without organic treatment to be exfoliated in the nylon-6 matrix, despite some differences in compatibilities between them and nylon-6. Accordingly, the clay in different UFPRMs at the same loading content can lead to a similar improvement in stiffness and heat resistance of nanocomposites. In other words, UFPRs having different compatibilities with nylon-6 do not affect the stiffness and heat resistance of nanocomposites largely. However, the nylon-6 nanocomposites, modified with different UFPRMs, show different superior properties. Butadiene styrene vinyl-pyridine UFPRM (VP-UFPRM) is more effective in improving toughness of nylon-6. Nylon-6/silicone UFPRM (nylon-6/S-UFPRM) nanocomposite exhibits more reduced flammability, good flowability and high thermal stability. As for nylon-6/acrylate UFPRM (nylon-6/A-UFPRM) nanocomposite, it shows high toughness and thermal stability. Furthermore, the mechanism of unmodified clay exfoliation during the melt compounding and the effect of different UFPRs on the properties of the nylon-6/UFPRM nanocomposites are also discussed.     

Non-isothermal crystallization of ethylene-vinyl acetate copolymer containing a high weight fraction of graphene nanosheets and carbon nanotubes

The effect of the different geometrical dimensionality of two dimensional graphene nanosheets(2D GNSs) and one dimensional carbon nanotubes(1D CNTs) on the non-isothermal crystallization of an ethylene-vinyl acetate(EVA) copolymer at high loading(5 wt%) was studied.Transmission electron microscopy indicated a homogeneous dispersion of GNSs and CNTs in EVA obtained by a solution dispersion process.Fourier-transform infrared spectroscopy and differential scanning calorimetry measurements showed that 1D CNTs and 2D GNSs acted as effective nucleating agents,with a noticeably increased onset crystallization temperature of EVA.A high weight fraction of nano-fillers slowed the overall crystallization rate of composites.At the same crystallization temperature,the crystallization behavior of GNS/EVA composites was slowed compared to that of the CNT/EVA ones owing to larger nucleus barrier and activation energy of diffusion.Dynamic mechanical relaxation and rheology behavior of CNT/EVA and GNS/EVA composites demonstrated that the planar structure of the GNSs had an intensively negative effect on EVA chain mobility due to interactions between nanofillers and polymer chains,as well as spatial restriction.     

Polyamide synthesis from 6-aminocapronitrile, part 2: heterogeneously catalyzed nitrile hydrolysis with consecutive amine amidation

To test the potential of heterogeneous catalysts for the nylon-6 synthesis from 6-aminocapronitrile, a number of zeolites, aluminum silicate, and metal oxides were tested as catalysts for the model reaction of pentanenitrile with water and hexylamine to N-hexylpentanamide. All zeolitic and aluminum silicate systems showed an insufficient performance, while the metal oxides (TiO(2), ZrO(2), Nb(2)O(5)) showed very promising results. The kinetic behavior of the metal oxides was further investigated. First the nitrile was catalytically hydrolyzed to the terminal amide and subsequently the amidation of the hexylamine occurred. To polymerize 6-aminocapronitrile into nylon-6, more than 99 % nitrile conversion was required to obtain a high-molecular-weight polymer. Pentanenitrile conversions larger than 99 % can be obtained within six hours, at 230 degrees C, by using ZrO(2) as the catalyst. A kinetic study (by using IR spectroscopy) on the behavior of the metal oxides demonstrated that the adsorbed nitrile was catalytically hydrolyzed at the surface, but remained tightly bound to the surface. Zirconia-catalyzed polymerizations of 6-amino-capronitrile demonstrated that high-molecular-weight nylon-6 is feasible by using this route.