Morphological and mechanical properties of extruded polypropylene/nylon-6 blends

Blends of polypropylene and nylon-6 extruded into ribbons at varying draw ratios generated laminar morphologies under our conditions. For the binary system, the size and distribution of the dispersed phase is coarse. The addition of an ionomer to the nylon prior to blending compatibilized the phases and produced much finer domains. The tensile properties of the virgin matrix material respond to the draw ratio in a parabolic manner attaining a maximum at intermediate values. Blending with nylon-6 attenuates the effect without improving the tensiles markedly. The compatibilized system however demonstrates greatly improved mechanical properties.     

Monomer casting nylon-6-b-polyether amine copolymers: Synthesis and properties

MC nylon-6-b-polyether amine copolymers were prepared with macro-initiator based on amino-terminated polyether amine functionalized with isocyanate via in-situ polymerization. It was found that the introduction of polyether amine delayed the polymerization process of caprolactam by increasing apparent activation energy and pre-exponential factor, resulting in the decrease of molecular weight of nylon-6. The motion of molecular chain of the copolymers was easy because of the decreased hydrogen bonds and weakened inter-molecular forces. The physical entanglement of molecular chains of the copolymers was significant and strong which increased the entanglement density. Only the nylon-6 phase crystallized in the copolymers and the crystal grain size, spherulite size and crystallinity of the copolymers decreased. A small amount of γ crystal formed at high polyether amine content. The copolymers presented obvious strain hardening behavior in stress-strain curves and the loss factor dramatically increased while the glass transition temperature and storage module decreased. The fracture surface of the copolymers became rough and presented hairy structure, indicating that the toughening mechanism of the copolymers corresponded to the multi-layer crack extension mechanism.     

Investigations of the properties of blockpolymerized and injection-moulded PLLA

The blockpolymerization and injection-moulding procedure are two main techniques used to produce PLLA for medical devices. Until now there has been no comparison of the well known data of blockpolymerized material and data of injection-moulded material. Test rods (2×3×25 mm) were made from block polymerized balls by the injection-moulding procedure. The rods were incubated in tris-buffer-saline for different periods (0, 2, 4, 6, and 8 weeks) at a pH of 7.4 and a temperature of 37°C. The test methods we used were the three-point-bending, the fatigue behaviour and the calculation of the decrease of molecular weight. Both materials under investigation are chemically similar but show very different mechanical properties, in particular the injection moulded material has a very decreased behaviour and a very low loss of molecular weight. Blockpolymerized PLLA rods show a very fast lost bending strength and after 6 weeks a low resistance against cyclic loads in the fatigue behaviour test. Injection moulded PLLA will be used in future for internal fixation of fractures.     

Microstructure and mechanical properties of low-pressure injection-moulded reaction-bonded alumina ceramics

Reaction-bonded alumina was fabricated using standard powder preparation methods and the low-pressure injection moulding (LPIM) forming technique, followed by reaction sintering. The feasibility of LPIM was investigated in terms of the compounding ability of a highly agglomerated mechanically alloyed powder in a non-polar organic vehicle, and the microstructural homogeneity and resulting reliability of sintered LPIM parts. The green density of LPIM parts after debinding, roughly corresponding to the solids loading in the LPIM feedstock, was in the range of fractional density achieved by dry pressing, although the powder packing and aluminium particle deformation during forming were not the same. LPIM forming and debinding induced microstructural inhomogeneities (i.e. larger voids due to trapped air and density fluctuations) which were reflected in a slightly lower Weibull modulus, while the average strength did not differ significantly from the values obtained with dry pressed samples. The microstructure and mechanical properties of sintered parts were also related to the purity of the starting powders. The presence of impurities in the starting aluminium powder resulted in a somewhat coarser microstructure, characterized by a broader Al2O3 grain-size distribution, as well as in the presence of a thin glassy phase on the grain boundaries and in partial destabilization of dispersed tetragonal (Y2O3-stabilized) ZrO2 particles. In spite of a less favourable microstructure, the room-temperature strength and Weibull modulus were still comparable to those obtained from high-purity starting powder. This revised version was published online in November 2006 with corrections to the Cover Date.     

Preparation,structure and thermomechanical properties of nylon-6 nanocomposites with lamella-type and fiber-type sepiolite

Nylon-6 nanocomposites filled with lamella-type and fiber-type sepiolite were prepared by the simple melt-compounding approach and compared with the common nylon-6/montmorillonite (MMT) nanocomposite. Morphology and dispersion state of fillers were observed by scanning and transmission electron microscopy. Wide-angle X-ray diffraction and differential scanning calorimetry analyses were carried out to investigate the crystallization behaviors of nanocomposites. The results suggested that sepiolite facilitates the formation of α-phase crystals of nylon-6, which is quite different from the case observed in MMT-filled nanocomposites. Thermomechanical tests showed that heat distortion temperature and Young’s modulus of sepiolite-filled nanocomposites are obviously improved compared with neat nylon-6. Interestingly, sepiolite-filled nanocomposites exhibited the highest level of reinforcement on the Young’s modulus, which may stem from the more efficient interfacial stress transfer. In addition, tensile fracture morphologies of nanocomposites filled with sepiolite and MMT are also compared.     

Tensile dilatometry of injection-moulded HDPE/PA6 blends

In order to understand the mechanism of deformation of injection-moulded HDPE/PA6 (25 vol% /75 vol%) blends both with and without compatibilizer, the volume change has been monitored using tensile dilatometry. Dog-bone specimens were either directly moulded or cut from rectangular plaques. Both neat materials and their blends were tested. For the directly moulded dog-bone specimen, a pure shear yielding mechanism was observed for all materials tested, i.e. PA6, HDPE, and their blends in the same proportion as above. In the case of a deformable minor phase (HDPE), the dispersed phase appeared to bear its share of stress and the flow-induced orientation mimics the effect of interfacial modification. This was not the case of a rigid minor phase (glass beads) at the same concentration; the effect of surface treatment changed the mechanism of deformation from mixed mode cavitation shear yielding (45%) to almost pure shear yielding (85%). Machined specimens made of neat PA6 and HDPE deformed through pure shear yielding. The addition of 25 vol% HDPE to PA6 resulted in a mixed mode cavitation (55%)/shear yielding mechanism of deformation in the transverse direction, while in the longitudinal case, the mechanism which prevailed was almost pure shear yielding (80%). This can be attributed to the flow-induced orientation as above. When adding 10% (based on the weight of the dispersed phase) of an ionomer as a compatibilizer, the blend deformed via shear yielding (85%) and in the longitudinal direction both compatibilized and non-compatibilized blends display similar behaviour. Varying the specimen thickness by changing the mould cavity, led to a significant variation in the dilatational behaviour. Dilatometric behaviour is shown to be closely related to the morphology generated as a result of flow-induced orientation. The skin/core ratio, which is an indication of the proportion of the oriented dispersed phase to the non-oriented one, plays a key role in influencing the mechanism of deformation involved.     

The structure and mechanical properties of an injection-moulded acetal copolymer

Processing conditions, microstructure and mechanical property correlations have been explored in injection-moulded plaques of an acetal copolymer. Barrel temperature was varied systematically between 453 and 503 K, with a constant mould temperature of 343 K. The microstructure and texture were determined by polarized light microscopy and X-ray pole-figure analysis, respectively. The overall structure of the mouldings was layered through the thickness and symetrical about the moulding centre line. At all barrel temperatures five layers were present: the outer three layers possessed significant preferred chain-axis orientation in the crystalline phase, while the two layers at the centre of the moulding were equiaxed. The texture and morphology of each layer is described and related to a model of mould filling. Increases in the barrel temperature reduced the extent of the outer oriented layers while increasing the extent of the equiaxed layers. Tensile tests were conducted on samples taken at 0° and 90° to the injection direction. Increases in barrel temperature had no influence on modulus but decreased both (=0 and 90°) engineering yield stresses. The yield stress could be correlated with the extent of the oriented layers within mouldings. At all barrel temperatures the yield stress was greater when =90°; this behaviour is explained in terms of a composite model.     

Morphology and properties of injection-moulded carbon-nanofibre poly(etheretherketone) foams

Poly(ether ether ketone) (PEEK) is a high performance polymer that cannot usually be foamed reliably using conventional injection-moulding processes. Here, vapour-grown carbon nanofibres (CNFs) are introduced to stabilise the foaming process, and the resulting morphology of injection-moulded integral foams is investigated in detail. Different image analysis techniques revealed the positive effect of the nanofiller on the cellular structure. Electron microscopy confirmed a homogeneous dispersion of the nanofibres in the cellular PEEK cores. The mechanical properties of the foam injection-moulded samples, in bending, showed an increase in yield strength and elastic modulus with nanofibre loading fractions up to 15 wt%. Although the compressive properties of the foams were reduced as compared to the solid-polymer, the CNFs clearly offset this reduction in properties. Detailed differential scanning calorimetry (DSC) and dynamic mechanical analysis provide further evidence of an interaction between the matrix and the nanoscale filler.     

Mechanical properties of nylon-6/SiO2 nanofibers prepared by electrospinning

SiO₂ nanoparticles reinforced nylon-6 nanofibers were prepared by electrospinning of nylon-6/SiO₂ solution in formic acid. The effect of concentration and applied voltage on the diameter of the fibers was investigated. A nanoscale three-point bending test was used to evaluate the mechanical property of a single nylon-6/SiO₂ nanofiber. It was found that the elastic modulus of the nanofibers decreased with the increase in fiber diameter. This elastic modulus was in the range of 3.1-6.9GPa as the diameter ranged from 600 to 100nm.     

Photocatalytic and antibacterial properties of a TiO2/nylon-6 electrospun nanocomposite mat containing silver nanoparticles

Silver-impregnated TiO(2)/nylon-6 nanocomposite mats exhibit excellent characteristics as a filter media with good photocatalytic and antibacterial properties and durability for repeated use. Silver nanoparticles (NPs) were successfully embedded in electrospun TiO(2)/nylon-6 composite nanofibers through the photocatalytic reduction of silver nitrate solution under UV-light irradiation. TiO(2) NPs present in nylon-6 solution were able to cause the formation of a high aspect ratio spider-wave-like structure during electrospinning and facilitated the UV photoreduction of AgNO(3) to Ag. TEM images, UV-visible and XRD spectra confirmed that monodisperse Ag NPs (approximately 4 nm in size) were deposited selectively upon the TiO(2) NPs of the prepared nanocomposite mat. The antibacterial property of a TiO(2)/nylon-6 composite mat loaded with Ag NPs was tested against Escherichia coli, and the photoactive property was tested against methylene blue. All of the results showed that TiO(2)/nylon-6 nanocomposite mats loaded with Ag NPs are more effective than composite mats without Ag NPs. The prepared material has potential as an economically friendly photocatalyst and water filter media because it allows the NPs to be reused.     

Influence of microstructure on the dynamic fatigue properties of injection-moulded polypropylene

A polypropylene copolymer was injection-moulded using several processing conditions and with different gating systems to produce a range of typical spherulitic microstructures. In addition to internal weld lines, some specimens were joined to form external mirrorplate butt-welds. The effect of the different microstructures on the fatigue and impact properties as a function at two test temperatures of 23 and – 10° C are reported. The influence of the different microstructures resulted in significant differences in load-bearing ability.     

Modification of nylon-6 with semi-rigid and wholly-rigid aromatic polyamides

Nylon-6 was reinforced by two semi-rigid aromatic polyamides, poly(p-diphenylmethyl terephthalamide) (PMA), and poly(p-diphenyloxide terephthalamide) (POA), and also one wholly-rigid aromatic polyamide, poly(m-phenylene isophthalamide) (PmlA) by physical blending and chemical copolymerization usingp-amino phenyl acetic acid (P-APA) as a coupling agent. From the results of differential scanning-calorimetry, it was shown that both the polyblends with semi-rigid and wholly-rigid polyamides exhibited a glass transition temperature,Tg, higher than that of nylon-6 homopolymer. It also showed that theT _gs of wholly-rigid polyblends were higher than those of semi-rigid polyblends. Nevertheless, the multiblock copolyamides appeared to have even higherT _g andT _m, and better thermal stability. Morphological observations revealed that all the polymer alloys (polyblends and copolymers) were a dispersed phase structure, although the multiblock copolyamides were more homogeneous and compatible. Based on wide-angle X-ray diffraction, it was found that the polyblends had two diffraction peaks, i.e. 2 = 20.5 ° and 24 °. However, the multiblock copolyamides had only one peak at 2 = 20 °, evidently indicating a new crystal structure of the multiblock copolyamides formed. For the mechanical properties, it was found that the multiblock copolyamides had a more significant reinforcing effect than those of polyblends, especially those copolymerizing with wholly aromatic polyamides.     

尼龙-6纳米纤维膜老化性能的研究

分别将w(尼龙-6)=10%、12%和14%的甲酸溶液经静电纺丝后得到具有不同纤维直径的纳米纤维膜,模拟自然环境,将其与普通薄膜进行老化性能对比.研究结果表明在相同薄膜厚度的情况下,纳米纤维膜比普通薄膜具有更好的耐老化性能,并且随纳米纤维直径的减小,相应纳米纤维膜的耐老化性能增强.     

阴离子聚合尼龙6的改性研究进展

介绍了阴离子聚合尼龙改性的研究发展,重点介绍了阴离子聚合尼龙6的填充和共聚改性研究,并规纳最新动向及发展趋势。     

Adhesion of nylon-6 on surface treated aluminium substrates

The adhesion between nylon-6/aluminium is discussed in terms of mechanical interlocking mechanism on a microscopic scale. A new shaft-loaded blister test was adopted to measure simultaneously the adhesive properties of thin nylon-6 films. Fracture toughness is also measured by a double cantilever beam geometry. Variables including polymer film thickness, hot-press conditions and durability are also investigated.     

Effect of short nylon-6 fibres on natural rubber-toughened polystyrene

Composites based on polystyrene and natural rubber at a ratio of 85/15 were prepared by melt mixing with nylon-6 fibres using an internal mixer. The loading of short nylon-6 fibre, untreated and resorcinol formaldehyde latex (RFL)-treated, was varied from 0 to 3 wt.%. Tensile and flexural test samples were punched out from sheets and tested to study the variation of mechanical and dynamic mechanical properties. The tensile behaviour of the composite has been determined at three different strain rates (4.1 × 10⁻⁴ s⁻¹, 2 × 10⁻³ s⁻¹ and 2 × 10⁻² s⁻¹). Both the tensile strength and Young’s modulus of the composite increased with strain rate. The tensile strength, tensile modulus, flexural strength and flexural modulus increased with the increase in fibre content up to 1 wt.%, above which there was a significant deterioration in the properties. The RFL-treated fibre composites showed improved mechanical properties compared to the untreated one. Dynamic mechanical analysis (DMA) showed that the storage modulus of the composite with RFL-treated fibre was better compared to the untreated one. The fibre–matrix morphology of the tensile fractured specimens was studied by scanning electron microscopy (SEM). The results suggested that the RFL treatment of nylon fibre promoted adhesion to the natural rubber phase of the blend, thereby improving the mechanical properties of the composite.     

Effect of nano sized silver on electrospun nylon-6 fiber

We incorporated silver nanoparticles into a nylon solution, fabricated electrospun nanofibers, and studied various parameters of the electrospun fibers. We found that the addition of silver nanoparticles introduces antibacterial effects into nylon composite fibers. The average fiber diameter and fiber morphology was greatly affected when parameters such as solution concentration and the amount of silver nanoparticles were changed. The composite fibers that we prepared have the potential to be used as filtration membranes.     

The effect of weathering on residual stresses and mechanical properties in injection-moulded semi-crystalline polymers

Injection-moulded bars made from polypropylene (PP), polyacetal (POM) and nylon 6,6 (N6, 6), have been weathered outdoors in Jeddah, Saudi Arabia, for varying periods. In POM and N6, 6 the residual stresses became tensile near the surface, though this happened even with unexposed bars. Prolonged ageing or weathering of PP caused the residual stresses to fall to very low values. With POM and N6, 6 significant surface damage developed on weathering, and multiple surface cracks opened up during uniaxial tensile testing. With N6,6 these developed into the form of diamond-shaped ductile fracture cavities, and the failure mechanism appeared quite different to that obtained with unexposed mouldings. With weathered PP no significant surface damage was visible even in the scanning electron microscope, but prolonged weathering caused a change in the failure mechanism, with fracture usually occurring without necking and drawing with specimens weathered for two years or more.