Kinetic aspects of the silver ion release from antimicrobial polyamide/silver nanocomposites

Spherical silver nanoparticles were grown in situ in different polyamides by a thermal reduction of silver acetate during melt processing of the polymers. Most of the particles have a diameter of about 20 nm. The absolute amount as well as the kinetics of the silver ion release from the various polyamide/silver nanocomposites differ strongly, although the filler content in all materials is the same (1.5 wt. %) and the morphologies of the silver particles are not very different. One result of the investigations was that the absolute amount of the long-term silver ion release increases exponentially with the maximum water absorption of the polymers used as matrix materials, because silver ions are formed from elemental silver particles in the presence of water, only. Moreover, it was also found that the long-term silver ion release increases with a growing diffusion coefficient of water in the polymer. The water absorption properties of the polymers govern the kinetics of the silver ion release, too: for strong hydrophilic polyamides like PA6 or PA6.6, which are plasticized by water, the silver ion release is a zero-order process. For nanocomposites with less hydrophilic polyamides like a cycloaliphatic polyamide or a P12 modified with polytetrahydrofurane (PA12-poly-THF), the silver ion release is governed by diffusion. As expected from the efficacy of the silver ion release, PA6, PA6.6, PA12 and PA12 modified with polytetrahydrofurane and a cycloaliphatic polyamide filled with 1.5 wt. % of silver nanoparticles are active against Escherichia coli. But, only nanocomposites with PA6, PA6.6 and P12-poly-THF as matrix materials are suitable as long-term biocidal materials. PACS 68.35.bm; 68.35.Fx; 68.37.Lp     

Effects of Carbon Nanotubes on the Morphology and Properties of Uncompatibilized and Maleic Anhydride-grafted Polypropylene-compatibilized Polyamide 6/Polypropylene Blends

The effects of carbon nanotubes (CNTs) on the morphology of uncompatibilized and maleic anhydride-grafted polypropylene (MAPP)-compatibilized polyamide 6 (PA6)/polypropylene (PP) (70/30 w/w) blends prepared using a torque rheometer were investigated. TEM observations showed that the CNTs were selectively located in the major PA6 phase and at the interface. Such localization of nanofillers in the literature usually leads to a refinement in a sea-island morphology. Unexpectedly, our results show that increasing amounts of CNTs in the samples prepared using a torque rheometer led to a transformation from typical sea-island morphology to co-continuous morphology for uncompatibilized PA6/PP blends and to partial fibrillization of the PP domains for MAPP-compatibilized PA6/PP blends. These unusual morphological changes are attributed to a retarded morphology evolution process caused by the CNTs. According to rheological measurements and theoretical analysis, this was achieved through the role of CNTs in enhancing the viscoelasticity of the PA6 phase and promoting interfacial slip. The electrical resistivites, crystallization, and melting behavior of all samples were also studied.     

Ultrasound-assisted synthesis of nanocomposites based on aromatic polyamide and modified ZnO nanoparticle for removal of toxic Cr(VI) from water

In this study, novel nanocomposites (NCs) of aromatic polyamide (PA) and surface modified ZnO nanoparticle with s-triazine heterocyclic ring was introduced for efficient removal of toxic hexavalent chromium (VI) from aqueous solution. The surface of ZnO nanoparticle was modified by s-triazine core silane coupling agent (ZnO-TSC) and PA/ZnO-TSC NCs with different amount of ZnO-TSC nanoparticles (0, 5, 10 and 15 wt%) were prepared by ultrasonic irradiation. The synthesized PA/ZnO-TSC NCs were characterized by FT-IR, XRD, FE-SEM, TEM and TGA methods. TEM images showed that ZnO nanoparticles were dispersed homogeneously in the polymer matrix. The adsorption experiments were carried out in batch mode to optimize various parameters like contact time, pH and concentration of metal ion that influence the adsorption rate. The maximum uptakes of Cr(VI) at pH 4.0 was 72%, 81%, 89% and 91% for pure PA, NC5%, NC10% and NC15%, respectively. The kinetic of adsorption was investigated and the pseudo second-order model is an appropriate model for interpretation of adsorption mechanism of Cr(VI) ions.     

CRYSTALLIZATION IN PARTIALLY MOLTEN ORIENTED BLENDS OF POLYCONDENSATES AS REVEALED BY X-RAY STUDIES*

Oriented fibers or films of binary polymer blends from polycondensates were investigated by two-dimensional (2D) wide-angle X-ray scattering (WAXS) during the finishing process of microfibrillar reinforced composite (MFC) preparation, that is, heating to a temperature between the melting temperatures of the two components, isothermal annealing, and subsequent cooling. It is shown that the crystallization behavior in such MFC from polycondensates depends not only on the blend composition, but also on thermal treatment conditions. Poly(ethylene terephthalate)/polyamide 12 (PET/PA12), poly(butylene terephthalate)/poly(ether ester) (PBT/PEE), and PET/PA6 (polyamide 6) composites were prepared in various compositions from the components. Materials were investigated using rotating anode and synchrotron X-ray source facilities. The effect of the annealing time on the expected isotropization of the lower melting component was studied in the PET/PA6 blend. It was found that PA6 isotropization took place after 2 h; shorter (up to 30 min) and longer (up to 8 h) melt annealing results in oriented crystallization due to different reasons. In PET/PA12 composites, the effect of PA12 transcrystallization with reorientation was confirmed for various blend compositions. The relative strength of the effect decreases with progressing bulk crystallization. Earlier presumed coexistence of isotropic and highly oriented crystallites of the same kind with drawn PBT/PEE blend was confirmed by WAXS from a synchrotron source.

     

Chemical bond strain in molecules of polyamide 6 coatings on the steel surface

The structure and stresses of chemical bonds in a 20 μm thick polyamide 6 (PA 6) coating on the steel surface are studied by IR spectroscopy. It is found that PA 6 molecules in the coating are oriented parallel to the metal surface and the content of metastable crystalline (γ) and mesomorphic (β) phases in it is twice as low as in PA 6 films. In the crystalline α phase, the molecular skeleton is compressed and “lateral” (respective to the skeleton) chemical bonds are extended. In the mesomorphic β phase, the concentration of overstressed (extended to a prerupture state) parts in the molecular skeleton is higher than in the film. These effects are explained by a change in the PA 6 low-frequency vibration spectrum at the PA 6-metal interface.     

Ultrasound Assisted Development of Structure and Properties of Polyamide 6/Montmorillonite Nanocomposites

In this paper, polyamide 6/montmorillonite nanocomposites (PA6CNs) were prepared via conventional and an ultrasonic extrusion technology developed in our laboratory. The structure and morphology of montmorillonite dispersed in conventional and ultrasonicated PA6CNs were studied by x‐ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The experimental results gained by XRD, differential scanning calorimetry (DSC), and polarizing optical microscopy (POM) showed that the dispersed morphology of montmorillonite plays an important role in the crystalline form, nucleation rate, crystallization temperature, crystallinity, and spherulite size of PA6 crystals. The ductility of conventional PA6CNs decreases with the addition of montmorillonite because of the presence of large, stacked montmorillonite particles. Compared with the conventional PA6CNs, the elongation at break and impact strength of the ultrasonicated PA6CN increase greatly due to the improved dispersion of montmorillonite and decreased size of spherulites, while also showing the higher yield strength. Thermogravimetric analysis (TGA) revealed a decrease in thermal stability of conventional PA6CNs, with the introduction of ultrasound further accelerating thermal decomposition. A possible explanation for the observed decrease in polymer thermal stability on ultrasonic treatment is provided.     

Influences of Carbon Nanotube Networking on the Conductive,Crystallization, and Thermal Expansion Behaviors of PA610-Based Nanocomposites

The electrical, crystallization and thermal expansion behaviors of polyamide 610 (PA610)/multi-walled carbon nanotube (CNT) nanocomposites prepared by melt mixing were investigated. Electron microscopy (Scanning Electron Microscopy and Transmission Electron Microscopy) revealed that a good dispersion of CNT and CNT network was obtained in the PA610 matrix. Addition of CNT to PA610 matrix led to polymer nanocomposites exhibiting higher electrical conductivity and lower thermal expansion. The network of CNT in the PA610 matrix, which can be tuned by the loading of CNT and the melt isothermal treatment, was found to play an important role in reducing thermal expansion and achieving higher conductivity. Furthermore, it was shown that significant reduction in thermal expansion in PA610/CNT nanocomposites was due to both thermally insensitive CNT and formation of CNT network.     

Formation of silver nanoparticles during deposition onto viscous-fluid epoxy resin

A new method is proposed for synthesizing metallic nanoparticles in a polymer matrix. These nanoparticles are synthesized during thermal vacuum evaporation of a metal (4.8 × 10⁻⁶ g/cm²) onto the surface of viscousfluid epoxy resin (at a viscosity of 20–120 Pa s) having room temperature, which is well below the glass transition temperature of the polymer. As a result, epoxy resin layers containing silver nanoparticles in their volume form; these nanoparticles are studied by transmission electron microscopy and optical absorption spectroscopy. Various types of disperse structures formed by metallic nanoparticles in the polymer are detected. The morphology of the composite material is found to be controlled by the polymer viscosity and the metal deposition time.     

Mie散射研究聚合物合金相结构的形成及相尺寸分布

本文应用Mie散射理论研究了聚丙烯 /尼龙 1 0 1 0合金的相结构与形态 ,计算了相尺寸分布。其结果与电子显微镜及Rayleigh散射结果进行了比较。     

The influence of moisture on atmospheric pressure plasma etching of PA6 films

The moisture in the substrate material may have a potential influence on atmospheric pressure plasma treatment. In order to investigate how the existence of moisture affects atmospheric pressure plasma treatment, polyamide 6 (PA6) films were treated by helium, helium/oxygen (O₂) plasmas using atmospheric pressure plasma jet (APPJ) at different moisture regain. The film surfaces were investigated using contact-angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) to characterize the surfaces. The exposure of PA6 film surfaces to the plasmas led to the etching process on the surfaces and changes in the topography of the surfaces. It was shown that the etching rate and the surface roughness were higher for the 9.33% moisture regain (relative humidity 100%) group than that of the 1.61% moisture regain (relative humidity 10%) group with the same plasma gas and power.     

Comparison of the Morphological,Mechanical, and UV Protection Properties of TiO2/Polyamide 6 (PA6), and ZnO/PA6 Nanocomposite Multifilament Yarns

The properties of TiO₂/polyamide 6 (PA6) and ZnO/PA6 nanocomposite filament yarns produced on a pilot-plant melt spinning machine were compared. Concentrated masterbatches were prepared using a twin screw extruder. Then continuous multifilament yarns were produced by blending nylon 6 chips and various amounts of the prepared masterbatches. Melt spinning was carried out at the spinning temperature of 265°C and take-up speed of 4000 m/min. As-spun multifilament yarns were then drawn and textured. Morphological properties of the produced yarns were studied. Thermal behavior and physical properties, including shrinkage and tensile properties, were measured. Weft-knitted fabrics were evaluated for their ultraviolet protection properties. Although both kinds of the nanoparticles had a positive effect on the ultraviolet protection properties of their nanocomposite fabrics as compared to pure PA6 fabric, the efficiency of the TiO₂ nanoparticles was more than that of the ZnO ones for the same concentrations. The differences between the different properties of the two kinds of nanocomposites are discussed based on their interaction with the polymeric matrix, specific surface area, steric hindrance effect, and band gap energies.     

Phase Structure of Polyamide 6/Poly(styrene-co-acrylonitrile) and Poly(styrene-b-(ethylene-co-butylene)-b-styrene) or Poly(maleated Styrene/Ethylene-co-Butylene/Styrene) Ternary Blends

Two sets of ternary blends; polyamide 6/poly(styrene-co-acrylonitrile)/poly(styrene-b-(ethylene-co-butylene)-b-styrene) (PA6/SAN/SEBS) and polyamide 6/poly(styrene-co-acrylonitrile)/poly(maleated styrene/ethylene-co-butylene/styrene) (PA6/SAN/SEBS-g-MA), based on 70 wt% of matrix and 30 wt% of the dispersed phases at various concentrations of the minor components, were prepared via melt blending. Morphologies of the ternary systems were studied using scanning electron microscopy (SEM) and compared with the predictions of the spreading coefficient (SC), minimum relative interfacial energy (RIE), and dynamic interfacial energy (DIE) phenomenological models. The effects of different reported surface tensions of the used polymers and different protocols of the core-shell ratio calculation on the prediction of the models were investigated. The core-shell structure for PA6/SAN/SEBS system and two separate minor phases for PA6/SAN/SEBS-g-MA were observed at all of the compositions. The results indicated that the most important parameter for the accurate prediction of the models is the accurate calculation of the interfacial tension of the used polymers, in both the static and dynamic conditions.     

Long-Term Hydrothermal Aging Behavior and Life-Time Prediction of Polyamide 6

The long-term hydrothermal aging behavior of polyamide 6 (PA6), with and without stabilizers at 100% relative humidity/90ºC was studied. It was found that the first stage of aging was the Fickian process and corresponded to the physical absorption of water until equilibrium, resulting in slight change of reduced viscosity and chemical structure of the sample of PA6. The second stage of aging was the initiation process of hydrolytic degradation of PA6, which resulted in a decrease of reduced viscosity and increase of end group content. In the final stage of aging, the relative weight gain (W_r) dropped, the reduced viscosity decreased monotonically, and end groups increased continuously, resulting from the hydrolysis of amido links and molecular degradation of PA6. The presence of four types of stabilizers effectively weakened the oxidation reaction and resulting molecular degradation of PA6 during aging. The lifetime of PA6 in a hydrothermal environment was predicted through a method based on the Arrhenius model by considering both temperature and humidity as environmental factors, and, furthermore, was predicted through the time–temperature superposition method.     

光散射在聚合物共混过程中形态发展研究的应用

本文应用光散射法和电子显微镜对聚丙烯/尼龙1010(PP/PA1010=90/10,体积比)共混体系的微观形态发展进行了研究。利用激光背散射在线系统采集了散射图象,由散射光斑的积分强度和Debye Bueche理论计算的相关距离讨论了共混物形态演化过程。结果表明,这一体系在共混初期(即1分钟以前)形态有较大变化,这一阶段是聚合物在密炼机中软化、变形和熔融混合的过程。由不同时刻采样并进行电镜观察发现,在共混1分钟以后,共混物的形态确实变化不大,这说明光散射法用于研究聚合物共混过程中的形态发展是可行的。     

Chain Extension of Polyamide 6 Using Bisoxazoline Coupling Agents

The chain extension behaviors of 2,2′-(1,3-phenylene)bis(2-oxazoline) (MPBO) and 2,2′-bis(2-oxazoline) (BOZ) were studied to evaluate the coupling effect on polyamide 6 (PA6) in a Haake Rheocord mixer and an extruder. The coupling results showed that there existed an optimal dosage of chain extender, lack of which caused deficiency of chain extension and excess of which led to more blocking reaction. The effect of chain extension with MPBO was shown to be inferior to BOZ. When the optimum amount of chain extenders was added in PA6, the intrinsic viscosity of the polyamide 6 increased from 1.632dl/g to 1.787dl/g(MPBO) and 2.031dl/g(BOZ), respectively. The reaction time decreased very fast with an increase in the temperature. The chain-extended products dissociated at high temperature; the degradation is suggested to proceed from the onset of the chain extension reaction, as do the coupling and blocking reactions. Furthermore, the effects of MPBO and BOZ on the thermal and mechanical properties of chain-extended PA6 were also investigated.     

Effect of viscosity ratio of the components of thermoplastic and liquid-crystalline polymer blends on the properties

The effects of viscosity ratio on the rheological and mechanical properties of the blends of four thermoplastics of low viscosity and a liquid crystalline polymer (LCP) were studied. A polyamide of reduced crystallinity (amorphous PA), a polycarbonate (PC), a polyethylene-terephthalate (PET), and a cyclic polyolefin (COC) were investigated with the copolymer of 2-hydroxy-6-naphthoic acid (HNA) and 4-hydroxybenzoic acid (HBA) (Vectra A type LCP). The LCP content changed in the range of 0–50 w/w%. The mechanical properties were determined by tensile tests on injection molded test bars in parallel and perpendicular directions to the flow. Except for the PC/LCP blends, the viscosity decreased with increasing LCP content, the tensile strength increased significantly in the parallel and decreased in the perpendicular direction indicating formation of fibrillar phase morphology. In the case of PC/LCP blends, a reinforcing effect was observed at low LCP contents, but above 20 w/w% the viscosity increased and the parallel tensile strength dropped to the value measured in the perpendicular direction. The loss of the reinforcing effect might originate from chemical reactions of the two polymers.     

Effect of Added Monosodium Glutamate on Characteristics of Polyamide Dope Solutions

Formic acid (FA) solutions prepared with various concentrations of polyamide 66 (PA 66) and monosodium glutamate (MSG) were evaluated in terms of properties, such as density, viscosity, and cloud point. The influence on density was insignificant, whereas the viscosity was strongly affected by the amount of PA 66 and MSG additive. The solutions were further evaluated by casting them in a flat film form and determining the demixing time in a humid atmosphere. The considered cases at lower polymer concentrations at various MSG amounts, indicated that the demixing time increased with increase in polymer concentration. The time for demixing, however, decreased for a given higher amount of polymer when the amount of additive was increased in the dope solution. Membranes were prepared at various coagulant bath temperatures. The tensile strength and degree of adsorption (DOA) of these membranes were found. The tensile strength was higher when the membranes were prepared at higher temperature. The DOA, on the other hand, was higher for the membranes formed at lower temperature.     

THERMAL BEHAVIOR OF PP/PA6 BLENDS UNDER DYNAMIC CONDITIONS. THE EFFECT OF DIFFERENT INTERFACIAL AGENTS BASED ON CHEMICALLY MODIFIED ATACTIC POLYPROPYLENE

The thermal behavior in dynamic conditions of polypropylene/polyamide 6 (PP/PA6) blends with a modified interphase is discussed in terms of the crystallinities of the polypropylene and polyamide components imposed by the processing step conditions and after removal of those constraints by holding the blends 5 min in the molten state in the calorimeter. As interfacial agents, two based on succinic anhydride or succinil-fluoresceine grafted atactic polypropylenes were used. The experimental program was run following the Box-Wilson experimental design methodology. Thermal scans were made using round samples (5 mm diameter and 100 μm thick) cut from compression-molded sheets with morphologies and macroscopic behavior studied previously. Changes of the amount of crystallinity of each polymer in the modified blends are contrasted with the tensile strength values of the heterogeneous materials as a whole; evidence of the different roles played by each interfacial agent acting at the interface among blend components is shown.     

Preparation and Properties of Polyamide/Polyethylene/Near Infrared Reflective Pigment Composites

The effect of the addition of NIR (near infrared reflective pigment filler, nickel antimony titanium yellow rutile) into the polyamide/metallocene-based polyethylene elastomer (mPE) blends on increasing the infrared reflection of PA6 (Polyamide 6) and limiting the thermal heat accumulation in light of environmental and energy conservation concerns was examined. The NIR was included in mPE or mPE-g-MA (maleic anhydride) to form NmPE or NmPE-g-MA masterbatches, respectively, which were used in combination with polyamide 6 (PA6) to prepare PA6/NmPE or PA6/NmPE-g-MA composites. The dispersed domains of mPE modifier were larger in dimension in comparison with those of the corresponding counterparts using mPE-g-MA as the NIR carrier due to the increased interfacial interactions of the anhydride groups of the MA and the amine groups in PA6. NIR tended to increase the crystallization temperature of PA6 of up to 3°C through the nucleation role of the NIR for the NmPE-filled samples. However, this increment was diminished at higher mPE-g-MA content for the NmPE-g-MA-filled samples, suggested to be due to the interaction of mPE-g-MA and PA6 impeding the chain mobility for crystallization growth, offsetting the nucleation role of NIR. The NmPE-g-MA modified samples resulted in the highest improvement in Young’s modulus compared with the NmPE modified samples. An increase of 2 times in the impact strength occurred for PA6/NmPE(60 phr) sample, which increased to a value of 80?±?5 (J/m). However, a non-break behavior was observed for the PA6/NmPE-g-MA samples at higher modifier contents. The values of infrared reflection increased significantly, indicating the effectiveness of NIR to improve the reflection properties of the prepared composite systems.     

Long-Term Hydrothermal Aging Behavior and Aging Mechanism of Glass Fibre Reinforced Polyamide 6 Composites

Long-term hydrothermal aging of polyamide 6 (PA6)/glass fibre (GF) composites was conducted and the effects of the GF on variations of structure and properties of the composites with aging time were investigated. It was found that the first stage of aging was a Fickian process and corresponded to the physical absorption of water until equilibrium, resulting in a slight change of reduced viscosity and chemical structure of the PA6. The water diffusing process was slowed down slightly by addition of the GF. The second stage of aging was the initiation process of hydrolytic degradation of PA6, resulting in a rapid decrease of reduced viscosity and an increase of end group content. In the final stage of aging, the relative weight gain (W_r) dropped, the reduced viscosity decreased and the end groups increased slowly. The degradation rate and carbonyl index of PA6 increased with increasing GF content, and the increasing rate of end groups concentration of the composites was higher than that of pure PA6 during the aging process, indicating addition of GF accelerated the hydrolysis degradation and oxidative aging of PA6. In mechanical property tests, compared with unaged samples of the composites which underwent matrix rupture around the matrix-fiber interfacial layer, for aged samples several smooth fibres without coatings were pulled out and the interfacial debonding was the main failure mode, causing severe deterioration in mechanical properties. The hydrolytic degradation activation energy (E_a) was calculated through a method based on the Arrhenius model by considering both temperature and humidity as environment factors; with increasing GF content, E_a decreased, indicating that the addition of GF made PA6 easier to degrade.