Creep behavior of nylon-6 thermoplastic composites

A systematic investigation of the creep behavior of nylon-6 thermoplastic composites reinforced with continuous carbon fibers was conducted by a strain gauge method. The creep strains of carbon fiber/nylon-6 composites were measured at various stress conditions and temperatures. The relationship between the creep strain, strain rate, creep compliance and stress condition, time, and temperature were established. The experimental creep strain data were shifted to a reference temperature to form a master curve by using the time-temperature superposition principle. The master curve can be used to predict the creep behavior of the carbon fiber/nylon-6 composites over long times. The effect of fiber orientation on the creep behavior was also measured and reported.     

改性尼龙6复合材料力学性能的研究

通过熔融共混制备了PA6/OMMT、PA6/Zn-EAA、PA6/OMMT/Zn-EAA三种复合材料,研究了OMMT、Zn-EAA(Zn-中和乙烯-丙烯酸)含量对复合材料力学性能的影响。结果表明:OMMT的加入提高了复合材料的拉伸强度,但冲击强度有所下降;Zn-EAA的加入可以提高复合材料的冲击强度,改善其韧性。     

Synthesis of highly conducting nylon-6 composites and their electrical properties

Highly conducting nylon-6 composites are synthesized by exposing nylon-6 films or fabrics impregnated with an oxidizing agent, cupric chloride, simultaneously to aniline and hydrochloric acid vapors. The conductivity of composite films reaches up to 10^?2 S/cm and can be controlled by varying the experimental conditions for the composite synthesis. The effects of the concentration of cupric chloride, exposure time to aniline and hydrochloric acid vapors, and concentration of hydrochloric acid to the polyaniline content and the conductivity of nylon-6/polyaniline composites are analyzed by means of statistical F test. The morphology change of composite films resulting from the synthesis conditions, conductivity in relation to the morphology, and stability of conductivity to ambient air exposure have been investigated.     

Thermal expansivity of oriented nylon-6 and nylon-6,6

Measurements on the thermal expansivities along (α_∥) and normal (α⊥) to the draw direction have been carried out from 120 to 380K for nylon-6 and nylon-6,6 with draw ratio λ between 1 and 3.6. The sharp drop in α∥ and the slight increase in α⊥ with increasing λ can be attributed to the gradual alignment of chain segments in both the crystalline and amorphous regions. Using the presently available expansivity data on nylon-6 crystals it is found that the observed orientation dependence below the glass transition can be quantitatively described by a two-phase aggregate model. Water acts as a plasticizer and so its absorption leads to a drop of about 80K in the glass transition temperature. At low temperature, however, water appears to form bridges between molecular chains. This gives rise to a stronger interchain interaction and hence a lowering of the thermal expansivity.     

Thermal properties and transition studies of multi-wall carbon nanotube/nylon-6 composites

Transition behavior and thermal properties of a multi-wall carbon nanotube (MWCNT)/nylon-6 composite (P-composite) made by in situ polymerization and subsequently structurally modified by high-pressure–high-temperature treatment have been established. The thermal conductivity (κ) of nylon-6 improved ∼27% by the addition of 2.1 wt.% MWCNT filler simultaneously as the heat capacity per unit volume decreased ∼22% compared with that of nylon-6 at 1 atm and 298 K. Moreover, the MWCNT filler raises the glass transition temperature (T_g) of nylon-6, but the pressure dependence of T_g remains unchanged. A model for κ indicates that the interfacial thermal resistance between the MWCNT filler and the nylon-6 matrix decreases 20% up to 1 GPa and most significantly above 0.8 GPa. P-composite was structurally modified by a sluggish cold-crystallization transition at 1.0 GPa, 530 K, which further increased κ by as much as ∼37% as the crystallinity of nylon-6 improved from 31% to 58% with a preferred crystal orientation and increased crystal size.     

Formation and properties of nylon-6 and nylon-6/montmorillonite composite nanofibers

Nanocomposite fibers of nylon-6 and an organically modified montmorillonite (O-MMT), Cloisite-30B, were prepared by electrospinning. Dispersion and exfoliation of O-MMT in nylon-6 were achieved by melt-extrusion in a twin-screw extruder prior to dissolving in aqueous formic acid for electrospinning. The effects of O-MMT layers on the properties of the nylon-6 solution and electrospun nanocomposite fibers were investigated. Homogeneous, cylindrical nanocomposite fibers with diameters ranging from 70 to 140 nm could be prepared from the 15% composite solution. The O-MMT layers were well exfoliated inside the nanocomposite fibers and were oriented along the fiber direction. Both the degree of nylon-6 crystallinity and the crystallite sizes increased for the nanocomposite fibrous mats, most significantly for those composed of the smallest fibers electrospun from 15% solution. The mechanical properties of the electrospun fibrous mats and single fibers depended not only on the addition of O-MMT layers but also on the sizes of the fibers. Smaller fibers exhibited higher Young's modulus.     

A study on blends of nylon-6 and nylon-66

Blending of nylon-6 and nylon-66 was carried out by coextrusion in the whole range of compositions with particular emphasis on small amounts of one polymer in the other. Most significant improvement in properties is achieved at low blend compositions in which the minor component remains amorphous while severely affecting the crystallization behavior of the major component. The nylon-6-rich blends crystallize predominantly in the γ-crystalline form, whereas the nylon-66-rich blends exhibit low crystallinity. Because of this property, the blends are more easily drawable, giving rise to a more highly oriented structure with improved tensile properties and uniformity. High tenacity and modulus are observed in drawn blends containing 70% nylon 6 and 30% nylon-66.     

Fiber reinforced nylon-6 composites produced by the reaction injection pultrusion process

Reaction injection pultrusion (RIP) combines the injection pultrusion process with reaction injection molding (RIM) techniques to yield one of the more novel methods of thermoplastic matrix pultrusion. An experimental set-up was designed and built to pultrude nylon-6 RIM material and continuous E-glassfiber. Well-impregnated nylon-6 composites with 66.5, 68.8, 71.1, and 73.3 vol% fiber were produced. Internal temperature profile within the die was recorded during the process, and physical properties of resulting composites were measured. This paper presents results of the effect of fiber content, die temperature profile and pulling speed variations on internal temperature profile, monomer conversion, and physical properties. The study showed that increasing pulling speed lowered both peak temperature and monomer conversion. Higher die temperatures accelerated the reaction, resulting in a higher exotherm, a higher peak temperature, and a higher monomer conversion within the range investigated. Shear strength, flexual strength, flexual modulus, and transverse tensile strength were proportional to monomer conversion. Flexual modulus increased with higher fiber content within the range observed. Data allow the proper combination of die temperature profile and pulling speed to be selected to achieve a desired level of monomer conversion and physical properties. Results of this study provide basic information required for product design with nylon-6 composites as well as tool design, selection of processing conditions, and quality control for the process.     

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.     

Effect of water absorption on the behavior of E-glass fiber/nylon-6 composites

The effect of water absorption on the stress transferability across E-glass fiber/nylon 6 interface has been studied using the embedded single fiber composite technique. The behavior of silane coated fiber and untreated fiber composites after periods of water immersion were compared. The silane coating provided both higher interfacial shear stress transferability and protection from permanent water damage in the interphase region. It was found that water absorption in the nylon matrix reduced the shear stress transferability through plasticization of the matrix, weakening of the interface, and the development of tensile swelling stresses at the phase boundaries. In untreated materials the shear stress transferability was limited by decoupling of the matrix from the broken fiber ends by either interface slippage or local plane strain fracture in the interphase region near the fiber end. In the silane treated materials the shear stress transferability was limited by constrained yielding of the polysiloxane/nylon interphase at the fiber end, thus indicating plasticization of the matrix was the primary factor. After 20 days of water immersion, there was permanent deterioration of stress transferability in the untreated samples, but very little permanent damage in the treated samples.     

原位聚合制备尼龙-6/多壁碳纳米管复合材料及其结晶行为

采用酰氯化处理的多壁碳纳米管(MWNT)同氨基封端的尼龙-6(PA6)原位聚合的方法制备了PA6/MWNT复合材料.红外光谱说明了MWNT与PA6化学的键合作用.DSC测试表明MWNT对PA6的分子链段运动有较大的阻碍作用.动力学分析表明MWNT具有成核作用,提高了PA6的结晶温度;共价键连接使MWNT对PA6的分子链段运动有强烈的阻碍作用,造成复合材料(含MWNT质量分数2%)的总结晶速率降低.     

The fracture behavior of rubber-toughened,short-fiber composites of nylon 6,6

This study critiques the use of both rubber particles and short-glass fibers for the improvement of polymer fracture toughness (K_c). Although dry neat nylon is brittle with only a moderate K_c value (4.2 Mpa√m), additions of either second phase produce rising K_R-curves and associated high K_c values (8.1 Mpa√m for rubber-toughened nylon, and 10.0Mpa√m for 17 vol% Glass-fiber neat nylon). In the rubber -modified resin, the high K_c value is associated with extensive plastic blunting at the crack tip. In the fiber-reinforced neat resin, K_c is improved due to a combination of fiber-bridging and increased strength, the latter being associated with additional load carrying capacity of the fibers. When both rubber and fibers are added, however, no further increase in K_c is noted (K_c = 9.3 Mpa√m for 17 vol% glass-fiber rubber-modified nylon). The extent of ductile blunting in the rubber + fiber resin is not as great as in the rubber-only resin. Furthermore, the fracure strength of the rubber + fiber resin is not as high as the fiber-only resin. The net result is a balance of properties for the rubber-toughened composite.     

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.     

Degradation of nylon-6 in ethylene glycol

Glycolysis of nylon-6 in boiling ethylene glycol was studied. Oligoamides with amino- and hydroxylend-groups were obtained. The following catalysts were examined: zinc acetate, sodium glycolate and poly(phosphoric acid). The reaction rate constants found for first order reaction proved that the amino-groups formed during the degradation take part in acceleration or slowing of the reaction velocity. The reaction rate constants did not change in the polymerization degree range of $\text{P}\text{?}\text{= 150?20}$. Beginning from the polymerization degree $\text{P}\text{?}\text{= 20}$ in case of zinc acetate, sodium glycolate and without the catalyst the reaction rate constants increased, the reverse effect was observed when poly(phosphoric acid) was used.     

Melt-crystallized nylon-6 nucleated by the constrained chains of its non-stoichiometric cyclodextrin inclusion compounds and the nylon-6 coalesced from them

Non-covalently bonded crystalline inclusion compounds (ICs) have been formed by threading host cyclic starches, cyclodextrins (CDs), onto guest nylon-6 (N-6) chains. When excess N-6 is employed, non-stoichiometric (n-s)-N-6-CD-ICs, with partially uncovered and “dangling” N-6 chains, result. While the host crystalline CD lattice is stable to ∼300 °C, the uncovered, yet constrained, portions of the N-6 chains emanating from the CD-IC surfaces may crystallize below, or be molten above ∼225 °C, and confer upon them shape-memory. When heated between the T_m of N-6 and the decomposition temperature of the (n-s)-N-6-CD-IC, they may be deformed into a new shape, which is retained following a rapid quench below T_m. When this newly-shaped sample is heated above the T_m of the un-included and crystalline portions of N-6, it reverts back to its original shape in response to the constraining CD-IC crystals.When added at low concentrations, the non-toxic (n-s)-N-6-CD-ICs serve as effective nucleating agents for the bulk crystallization of N-6 from the melt. This is a consequence of the ability of the N-6 chains protruding from their (n-s)-CD-ICs to crystallize more rapidly and at higher temperatures than bulk N-6 chains when their molten mixture is cooled, thereby providing finely dispersed crystalline nuclei for the subsequent crystallization of the bulk N-6 chains. Melt-crystallized N-6 nucleated with (n-s)-N-6-CD-ICs have finer grained more homogeneous morphologies than un-nucleated N-6 samples. Furthermore, N-6s coalesced from their CD-ICs by appropriate removal of the host CD are also found to effectively nucleate the melt-crystallization of bulk N-6, even after long periods of annealing above the T_m of N-6. N-6 coalesced from stoichiometric CD-ICs, with full N-6 coverage, and from (n-s)-N-6-CD-ICs, with only partial N-6 coverage, show very similar crystallization behaviors and both are effective as nucleants, and this is reflected by their higher densities and improved mechanical properties.     

Dye-uptake behaviour of nylon-6 filaments and its structural dependence

This article presents results of a study made in two parts on the dye-uptake behaviour of nylon-6 filaments. In the first part, nylon-6 monofilaments were dry heat-set at temperatures between 80 and 200°C and dyed under similar conditions with two dyes, viz. an acid and a disperse dye. In the second part, dry-set and steam-set nylon-6 multifilament yarns were dyed with an acid dye. The roles played by the physical structure of the fibre and chemical affinity between the dye and the fibre have been examined in an effort to explain the differences in the dye uptake results for the two dyes. It was found that the physical structure has a predominant effect in both cases; however, in the case of the acid dye, chemical affinity also plays an important role. On the basis of structural studies, some comments are made on how structural reorganisation proceeds in nylon-6 fibre on heat-setting.