真空导入成型阴离子聚合尼龙6聚合体系及性能

通过测量不同聚合体系下的阴离子聚合尼龙6(APA-6)反应过程中转化率随时间的变化, 结合真空导入成型的特点, 研究了适合于真空导入成型的APA-6的聚合体系. 研究发现, 己内酰胺钠盐/双酰化内酰胺-1,6-己二胺(C10/C20)(100℃)和己内酰胺钠盐/甲苯二异氰酸酯(C10/TDI)体系反应初期均存在一个转化率线性缓慢增长期, 随后, 聚合体系开始快速反应, 转化率呈指数增长, 反应很快达到平衡. 初步判定这两种体系是适合真空导入成型APA-6复合材料的聚合体系. 在转化率测试的基础上, 利用DSC热分析从活性中心的形成机理进一步分析了C10/TDI体系更适合于较大、 较厚和结构复杂制品的整体成型的原因. 此外, 与普通PA6相比, 真空导入成型APA-6的结晶度、 模量和T_g显著提高, 并且在2种理想体系下聚合的APA-6的性能也有差别, 从活化剂的封端和解封端机理上进行了初步探讨.     

Study on the Effect of Uniaxial Elongational Flow on Polyamide Based Nanocomposites

This work focuses on the study of uniaxial elongational flow and its effects on morphology and stiffness of polyamide-6 based nanocomposites prepared by melt compounding. The elongational flow characterization was realized by converging flow method and fiber spinning technique. During the haul-off tests, fibers of the neat polyamide-6 and the hybrids (at 3 and 6 wt% of silicate) were collected at different draw ratios. Mechanical properties of the produced fibers were investigated and correlated to their nanostructure through analytical techniques sensitive to different aspects of morphology, such as DSC and TEM analysis. Rheological results, obtained with a capillary rheometer, indicate that the shear viscosity decreases with the silicate loading, while the extentional viscosity increases. Moreover, the presence of the silicate in polymer matrix leads to enhancements of draw-down force and reduction of the breaking draw ratio. In hybrid fibers an enhanced degree of exfoliation of the filler was observed upon drawing. Moreover, DSC analyses suggest that the crystalline structure of the fibers is the result of two opposite effects: the presence of the silicate which stabilizes the γ form and the drawing which promotes the α crystal phase. The degree of silicate exfoliation and the amount of the different crystal phases strongly affect the tensile properties of the fibers.     

Effect of moisture on the dynamic mechanical relaxation of polyamide-6/clay nanocomposites

This article investigates the effect of moisture on the dynamic mechanical behavior of polyamide-6 (PA6)/clay nanocomposites with dynamic mechanical analysis from −130 to 110 °C. The storage moduli increase with the clay loading for dried and moisture-absorbed samples because of the enhancing effect from the high-aspect-ratio nanoclay. Storage moduli for moisture-exposed samples are lower than those for dried samples; the longer the moisture absorption period is, the lower the moduli are for neat PA6 and PA6/clay nanocomposites. At temperatures below about 10 °C, however, samples exposed to moisture for longer periods tend to be stiffer than dried samples, probably because of the stiffening effect of ice. The peak temperature of the β relaxation shifts from −53 to −65 °C as the moisture content increases. The glass-transition temperature (T_g) or α relaxation dramatically shifts; its position is significantly lowered from 62 to 17 °C as the moisture content increases (longer moisture absorption period) and from 62 to 50 °C as the clay loading increases. The observed depression of the storage modulus and T_g may be attributed to the plasticization effect of moisture absorption. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1823–1830, 2004     

On the macro- and microphase separation of compatibilizers in immiscible polymer blends

Macro- and microphase separation of compatibilizing graft copolymers in melt-mixed polystyrene/polyamide-6 blends was studied by transmission electron microscopy and thermal analysis. Three different graft copolymers with main chains of polystyrene and side chains of poly(ethylene oxide) were used as additives at various concentrations. The polyamide-6 domain sizes decreased with increasing amounts of compatibilizing graft copolymers in the blends up to a saturation concentration, after which no further reduction was noted. Macrophase separation of the graft copolymers into discrete macrodomains 20–200 nm in size occurred at concentrations equal to or slightly lower than the saturation concentration. The macrodomains of the graft copolymers were microphase separated, and the sizes and shapes of the microdomains were found to largely depend on the graft copolymer structure and composition. As a consequence of microphase separation, poly(ethylene oxide) crystallinity was noted in blends with sufficiently high macrophase contents. Observations of a graft copolymer interphase between the polystyrene matrix and the polyamide-6 domains confirmed that the graft copolymer was present at the blend interfaces in some of the compatibilized blends. © 1996 John Wiley & Sons, Inc.     

Effects of Solution Concentration,Emitting Electrode Polarity,Solvent Type,and Salt Addition on Electrospun Polyamide-6 Fibers: A Preliminary Report

Electrospinning is a process by which ultrafine fibers which have diameters in the range of tens of nanometers to less than ten of micrometers can be produced. This process utilizes expulsion of charges as a means to very thin fiber formation. In this short report, the effects of some of the influencing solution and process parameters (i.e. solution concentration, emitting electrode polarity, solvent type, and salt addition) on morphological appearance of electrospun polyamide-6 fibers were investigated based on visual observation of a series of scanning electron micrographs. It was found that all of the parameters studied played important roles in determining morphology and sizes of the fibers obtained.     

Morphology and mechanical properties of extruded ribbons of LDPE/PA6 blends compatibilized with an ethylene-acrylic acid copolymer

Two grades of low density polyethylene (LDPE) were blended with polyamide-6 (PA) in the 75/25 and 25/75 wt/wt ratios and shaped into ribbons with a Brabender single screw extruder. An ethylene-acrylic acid copolymer (EAA) was used in the 2 phr concentration as a compatibilizer precursor (CP). The morphology of the ribbons and its evolution during high temperature annealing were investigated by scanning electron microscopy (SEM). The results confirmed that EAA does actually behave as a reactive compatibilizer for the LDPE/PA blends. In fact, in the presence of EAA, the interfacial adhesion is improved, the dispersion of the minor phase particles is enhanced and their tendency toward fibrillation is increased, especially for the blends with the higher molar mass LDPE grade. The mechanical properties of the latter blends were found to be considerably enhanced by the addition of EAA, whereas the improvement was relatively modest for the blends with the lower molar mass LDPE. The fracture properties of double end notched samples of the ribbons prepared with the blends containing the lower molar mass LDPE grade were also studied. It was shown that, despite of the increased interfacial adhesion caused by the presence of EAA, the latter plays a measurable positive effect on the fracture properties only for the blends with LDPE as the matrix.     

Crystal structure,morphology, and mechanical properties of biaxially oriented polyamide-6 films toughened with poly(ether block amide)

Biaxially oriented polyamide-6 (BOPA) film has been widely used in many packaging applications. However, the BOPA film with excellent toughness is still required when utilizing in the field of soft-packaged lithium - ion batteries, pharmaceutical blister packaging, or frozen food packaging especially for vacuum packaging of irregular-shaped food products. The purpose of this study was to improve the toughness of BOPA films by toughening with poly(ether block amide) (PEBA) (BOPA/PEBA films) based on the simultaneous biaxial stretching technology. The crystal structure, morphology, optical properties, barrier, and mechanical properties of BOPA/PEBA films were investigated. The results showed that the incorporation of PEBA into BOPA films slightly decreased the melting temperature and crystallinity of PA6, and the BOPA/PEBA films exhibited only α-form crystals and no preferential orientation in the machine direction (MD) and transition direction (TD). The morphological observation showed that higher addition of PEBA led to the formation of microvoids due to the poor compatibility between PA6 and PEBA. As a result, the transmittance and oxygen barrier properties of the BOPA/PEBA films decreased. In addition, mechanical analysis suggested that the addition of PEBA could effectively improve the toughness of BOPA film.     

Small-angle neutron scattering study on the transamidition of polyamide-4.6

The interchange or so-called transamidation process in polyamide-4.6 was investigated by means of small-angle neutron scattering (SANS). For this purpose, a 50/50 blend of partially deuterated and fully hydrogenous polyamide-4.6 was processed at 300°C for variable times (1–20 min). The obtained results are in line with the theory as described by Benoit to quantify the transesterfication process in homopolyesters. An exponential relaxation time τ of approximately 1500 s was obtained. On the basis of this relaxation time τ, it can be calculated that approximately four interchange reactions per chain occur in polyamide-4.6 during a typical processing time of 3 min at 300°C. The data interpretation is not complicated by the presence of some crystallinity in polyamide-4.6. © 1996 John Wiley & Sons, Inc.     

Preparation of polyamide-6/chitosan composite nanofibers by a single solvent system via electrospinning for biomedical applications

This work was focused on preparation and characterizations of chitosan blended polyamide-6 nanofibers by a new single solvent system via electrospinning process for human osteoblastic (HOB) cell culture applications. The morphological, structural and thermal properties of the polyamide-6/chitosan nanofibers were analyzed by using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, Raman spectroscopy, differential scanning calorimetry (DSC) and thermogravimetry (TGA). SEM images revealed that the nanofibers were well-oriented and had good incorporation of chitosan. FT-IR results indicated that the amino groups of chitosan existed in the blended nanofibers. TGA analysis revealed that the onset degradation temperature was decreased with increasing chitosan content in the blended nanofibers. The morphological features of the cells attached on nanofibers were confirmed by SEM. The adhesion, viability and proliferation properties of osteoblast cells on the polyamide-6/chitosan blended nanofibers were analyzed by in vitro cell compatibility test.     

Polymer Nanocomposites Containing Fullerene C60 Nanofillers

Summary: The effect of fulleroids (fullerene C₆₀, mixture of C₆₀/C₇₀ and fulleroids soot which used for fullerenes production) and carbon fillers (carbon black, graphite) on mechanical properties of polymer nanocomposites based on reactoplasts (epoxy resins) and thermoplasts (polyamide-12) was investigated. The nanocomposites were prepared by in situ polymerization. It was found that additives of these fillers did not influenced on the properties of reactoplasts. Therefore, the tensile modulus and tensile strength of thermoplast based polymer nanocomposites are improved by about 30-40% with loading of 0.02-0.08 fulleroids materials. Best results were obtained for a mixture of C₆₀/C₇₀.     

Isothermal-crystallization kinetics and spherulite growth of aliphatic polyketone/polyamide-6 blends

In this research,the morphologies,isothermal-crystallization kinetics,and spherulite growth of aliphatic polyketone/polyamide-6 blends were studied.A single glass-transition temperature (Tg) was determined,and the composition dependence of Tg for these blends was well described by the Kwei equation.The strong intermolecular interaction between the two polymer components was confirmed by melting-point depression.The isothermal-crystallization kinetics were analyzed on the basis of the Avrami approach.A linear increase in the radii of the spherulites with time was observed for all compositions.All the spherulites continued to grow at nearly identical growth rates.With increasing polyamide-6 content,the size of the spherulites in the polyketone/polyamide-6 blends gradually decreased,and the number of spherulites in the blends increased.     

MORPHOLOGY AND MECHANICAL PROPERTIES OF POLYPROPYLENE WITH in situ FORMED POLYAMIDE-6 FIBRILS

in situ Fibril formation of polyamide-6(PA6)in isotropic polypropylene(iPP)was first fabricated using a slit die extrusion and hot stretching process.Then the prepared materials were subjected to injection molding in the temperature range higher than the melting temperature of iPP but lower than that of PA6.The obtained injection-molded samples were characterized via scanning electron microscopy(SEM),differential scanning calorimetry(DSC)and two-dimensional wide- angle X-ray scattering(2D-WAXS).Mechanical properties were also investigated.The SEM result shows that the optimum fibril formation could be only achieved in the range of 20 wt% to 30 wt% of PA6 content for the studied system.The fibril morphology changes along the sample thickness in the injection-molded bars.The fibril morphology in the skin layer was better than that in the core layer.2D-WAXS results showed that the orientation of PP decreased with the increase of PA6 content,which indicated that the orientation of PP was confined by PA6 fibrils.Combined consideration of mechanical properties and morphology indicates that only PP/PA6 composites with 20 wt% of PA6 content show better properties because of the better fibril morphology and PP chain orientation.     

Comparative Study of Efficiency of Nucleating Agents in PA-6

The isothermal and anisothermal crystallization of nucleated polyamide-6 (PA-6) was investigated by DSC. A comparative study was made of twelve potential nucleating agents, including some commercial products for PA-6 and polypropylene. The amide wax processing aid lubricant originally introduced into the polymer was found to exhibit a marked nucleation ability. This revised version was published online in July 2006 with corrections to the Cover Date.     

ORIENTATION OF MOLECULAR GROUPS IN CROSS SECTION OF POLYAMIDE-6 FIBER BY INFRARED ATTENUATED TOTAL REFLECTION DICHROISM STUDIES

The polymer fiber usually possess typical uniaxial orientation. The molecular chains are symmetrically distributed around fiber axis. In this work, the orientation of molecular groups in the cross section of polyamide-6 fiber has been measured by using IR ATR method. The results indicated that the polyamide-6 fiber mainly contains α-crystalline form. The direction of hydrogen bonds of amide groups is predominately parallel with the surface in the cross section of the fiber.     

Study on the radiation degradation of polyether-polyurethane induced by electron beam

Polyether-urethane samples were irradiated at the dose range from 10 to 2000 kGy by 2 MeV electron beams. Volatile species from the polymer degradation were analyzed quantitatively and qualitatively with GC/MS. Thermal properties and micro-phase separation of the samples were examined by TG and the morphology was studied by TEM and SEM. The results show that the irradiated polyether-polyurethane evolves CO₂, H₂, CH₄ and C₂H₆, etc. The thermal stabilities between the hard and soft segments in the irradiated samples are different. At high doses, the phase separation in the sample is predominant and the hard segment of sample is more stable. The dose rate affects the soft segment of the irradiated sample much more.     

Synergistic effects of novolac-based char former with magnesium hydroxide in flame retardant polyamide-6

In this paper, a novel synergistic flame retardant system containing magnesium hydroxide (MH) and methyl-blocked novolac (MBN) synthesized by Williamson ether route, were used for the flame retardance of polyamide-6 (PA6). The investigations showed that the thermal oxidative stability of MBN was obviously enhanced in the presence of MH compared with virgin novolac due to the decrease of phenol hydroxide groups subjected to be oxidized. It proved that MBN plays double roles: on the one hand, it remarkably promotes char formation and effectively eliminates the melt drips of PA6, therefore endows the materials with good flame retardancy; on the other hand, it also serves as an efficient lubricant and compatibilizer between MH and PA6, leading to the great improvement of the processability, as well as finer dispersion of MH in matrix, thus the flame retardant PA6 with good comprehensive performance can be obtained.     

Study of bulk chain coupling reactions. I. Reaction between bisoxazolones and amine-terminated polyamide 12

2,2′-Bis(4,4-dimethyl-5(4H)-oxazolone) ( B3 ) and 2,2′-(1,2-ethylene)-bis(4,4-dimethyl-5(4H)oxazolone) ( B4 ) have been reacted in the bulk with α, ω-diamino polyamide-12 ( PA12 ) of M?_n = 1000. The reactions have been studied by SEC, and ¹H- and ¹³C-NMR and resulting polymers characterized by DSC and TGA. The chain coupling reaction is fast and gives high molar mass polymers within 10 min at 200°C with B4 while some side reactions occur with B3 leading to polymers of lower molar mass. The crystallinity of resulting polymers is lower than that of starting oligomer. However, the thermal stability is higher. Model reactions using B3 or B4 and hexamethylene diamine or 1-dodecanamine have been carried out and studied. An intramolecular cyclodehydration giving 2-imidazolin-5-ones takes place during the reactions. Higher cyclization extent is found in the presence of amino group excess. 2-Imidazolin-5-one heterocyclic structures are also observed in the chains of the polymers obtained from PA12 and B3 or B4 . © 1993 John Wiley & Sons, Inc.     

Post-irradiation stability of polyvinyl chloride at sterilizing doses

Post-irradiation stability of plasticized PVC irradiated by ⁶⁰Co gamma ray at sterilizing doses has been studied. Effects of irradiation upon chemical structure, mechanical properties and rheological behaviour of samples contained different amounts of Di(2-ethylhexyl)phthalate as plasticizer have been investigated. Formation of conjugated double bonds, carbonyl and hydroxyl groups have been followed by UV and FTIR spectrometers up to 6 months after irradiation. FTIR spectra of irradiated samples showed no significant changes in carbonyl and hydroxyl groups even 6 months after irradiation. However, changes in UV-visible spectra was observed for the irradiated samples up to 6 months post-irradiation. This has been attributed to the formation of polyenes which leads to the discoloration of this polymer. Despite a certain degree of discoloration, it appears that the mechanical properties of PVC are not affected by irradiation at sterilizing doses. No change in the melt viscosity of the irradiated PVC samples with post-irradiation was observed, which is in consistent with the IR results.     

Study on the radiation effect of polyether-urethane in the gamma-radiation field

The radiation effect of γ-ray on polyether-urethane foam was studied. The gas products from irradiated samples were analyzed quantitatively and qualitatively by gas chromatography, the thermal property and radical intensity were determined by differential thermal gravimetry and electron spin resonance. The dynamic mechanical property, compression and tensile properties were analyzed. Positron annihilation lifetime of irradiated samples was also measured at room temperature in vacuum. The results show that the general mechanical properties of ETPU sample irradiated by γ-rays at a dose of 8.0·10⁵ Gy is excellent, but there are considerable gas products and a great deal of radicals created, which indicates that the sample has been damaged by radiation. Relatively, the thermal stability of the sample remained fine.     

Thermal Stability Evaluation of PA6/LLDPE/SEBS-g-DEM Blends

Summary: The thermal stability of a polyamide-6/low linear density polyethylene blend (PA6/LLDPE) was studied using thermal analysis techniques. The thermogravimetric studies carried out showed that when a diethyl maleate grafted styrene- ethylene/butadiene-styrene terpolymer (SEBS-g-DEM) is added to the PA6/LLDPE blend there is an actual enhancement of the thermal stability due to the increase in the interfacial area within the blend. The Invariant Kinetic Parameter method (IKP) proved to be a qualitative technique unfolding the type of degradation mechanisms taking place in the material vicinity. Nucleation and phase boundary reactions are the kinetic models of thermal decomposition with the most significant probability of occurring.