Fabrication and characterisation of polypropylene nanofibres by meltblowing process using different fluids

In nonwoven industry, meltblowing has been widely used as an important technique for the production of nonwoven webs consisting of microfibres, suitable for various applications. Recently, great attention is being paid to fabricate nonwoven webs consisting of nanofibres, commonly known as nanowebs. In this paper, polypropylene has been successfully used for the fabrication of nanowebs by meltblowing process with the injection of different fluids (such as air and water) at the vent port of commercial meltblowing equipment. The lowest average fibre diameters achieved were 755 and 438 nm by the use of air and water, respectively. Differential scanning calorimetry results showed the presence of single melting peaks in the first heating cycle and double melting peaks in the second, due to the re-crystallisation and re-organisation by heating during the experiments. The results obtained from thermo gravimetric analysis and intrinsic viscosity studies showed thermal degradation of the nanofibres during meltblowing. X-ray diffraction studies showed that all the meltblown polypropylene fibres produced with the injection of the fluids contained low degrees of crystallinity and monoclinic α-form crystals. The crystallinity was increased with annealing. Similar Fourier transform infrared spectra of the polymer and the fibres indicated no change to the chemical functionality of the nanofibres by the application of the fluids and high temperature during meltblowing.     

Functional polyaniline nanofibre mats for human adipose-derived stem cell proliferation and adhesion

Conductive polymer poly(aniline-co-m-aminobenzoic acid) (P(ANI-co-m-ABA)) and polyaniline (PANI) were blended with a biodegradable, biocompatible polymer, poly(l-lactic acid) and were electrospun into nanofibres to investigate their potential application as a scaffold for human adipose-derived stem cells (hASCs). These polymers, in both conductive and non-conductive form, were electrospun with average fibre diameters of less than 400 nm. Novel nanoindentation results obtained on the individual nanofibres revealed that the elastic moduli of the nanofibres are much higher at the surface (4–10 GPa, h_max <75 nm) than in the inner fibre core (2–4 GPa, h_max >75 nm). The composite nanofibres showed great promise as a scaffold for hASCs as they supported the cell adhesion and proliferation. After 1 week of cell culture hASCs were well spread on the substrates with abundant focal adhesions. The electrospun mats provide the cells with comparably stiff, sub-micron sized fibres as anchoring points on a substrate of high porosity. The conductive nature of these composite nanofibres offers exciting opportunities for electrical stimulation of the cells.     

Evaluation of the structural behaviour of annealed nylon 6 fibres from density measurements

Nylon 6 fibres were annealed in the temperatures range 80–185 °C for times from 1–10 h, and the density of the annealed fibres was measured by a system based on the theory of vibrating strings. The fibre diameter was also determined, using the laser forward diffraction technique. Differential thermal analysis (DTA) measurements were used to determine the glass transition temperature and the melting point of nylon 6. Some annealed samples were subjected to X-ray diffraction to clarify the variation of crystallinity with the annealing conditions. The mechanism of structural variations for nylon 6 fibres due to the annealing process is discussed, and structural details for crystalline and non-crystalline phases of a polymer are suggested. The behaviour of the number of oriented chains, number of crystallized nuclei, relative amount of recrystallized material and the shrinkage ratio with annealing time is proposed to explain the thermal structural variations.     

金属纤维／聚合物导电复合材料的性能研究

以铜纤维和不锈钢纤维为导电填料，分别填充了ＡＢＳ、ＨＩＰＳ和ＰＰＳ对脂基体，制得导电复合材料。研究了金属纤维含量及工艺条件对复合材料的导电性能和力学性能的影响。结果表明，选择合适的工艺条件以保证金属纤维有较大的长径比并在树脂中有良好的分散状态，是制造性能优良的导电复合材料的关键。     

Effect of glass-fibre reinforcement and annealing on microstructure and mechanical behaviour of nylon 6,6

The effects of glass fibres and annealing on the microstructures and spherulitic morphology of a glass fibre-reinforced nylon 6,6 were investigated. The annealing effects on matrix crystallinity of nylon 6,6 composites with varying glass fibre contents were measured and the morphology of the composites were examined using both the microtomed bulk samples and thin composite films prepared by melt crystallization. It was found that fibre breakage during injection moulding was significant for composites with glass content higher than 20 wt%, and the spherulite size as well as the crystallinity were reduced by the additions of glass fibres. Upon annealing, the start of a log time rate increase of matrix crystallinity was delayed by the addition of glass fibres. Glass fibre-induced transcrystallinity was not observed in injection-moulded composites; however, columnar spherulites were found to develop along the glass fibres in melt-crystallized thin composite films. Differences in morphological observations between the two sample preparation methods are also discussed.     

Manufacturing techniques and property evaluations of conductive composite yarns coated with polypropylene and multi-walled carbon nanotubes

This study uses a melt extrusion method, a method for producing wires, to coat polyester (PET) yarns with polypropylene (PP) and multi-walled carbon nanotubes (MWCNTs). The resulting PP/MWCNTs-coated PET conductive yarns are tested for their tensile properties, processability, morphology, melting and crystallization behaviors, electrical conductivity, and applications. The test results indicate that tensile strength of the conductive yarns increases with an increase in the coiling speed that contributes to a more single-direction-orientated MWCNTs arrangement as well as a greater adhesion between PP/MWCNTs and PET yarns. 8 wt% MWCNTs results in an 18 °C higher crystallization temperature (T_c) of PP and an electrical conductivity of 0.8862 S/cm. The test results of this study have proven that this form of processing technology can prepare PP/MWCNTs-coated PET conductive yarns that have satisfactory tensile properties and electrical conductivity, and can be used in functional woven fabrics and knitted fabrics.     

Nanofibre fabrication in a temperature and humidity controlled environment for improved fibre consistency

Fabricating nanofibres with reproducible characteristics is an important demand in the membrane industry in order to establish commercial viability. In this study, the effect of controlled atmospheric conditions on electrospun cellulose acetate (CA) nanofibres was evaluated for temperatures ranging 17.5–32.5 °C and relative humidity ranging 20–70%. CA solution (0.2 g/mL) in a solvent mixture of acetone/dimethylformamide/ethanol (2:2:1) was electrospun into nonwoven fibre mesh with the fibre diameter ranging from 150 nm to 1 μm. The resulting nanofibres were analysed by differential scanning calorimetry, showing a correlation of reducing melt enthalpy with increasing atmospheric temperature. The opposite was seen with increasing atmospheric humidity, which conferred increasing melt enthalpy. Analysis of scanning electron microscopy images provided a correlation of reducing average fibre diameter with increasing atmospheric temperature and increasing fibre diameter with increasing atmospheric humidity. These results correlate with the melt enthalpy results, suggesting that finer CA nanofibres infer a lower melt enthalpy. Together these studies provide strong evidence that the controlled atmospheric conditions affect the fibre diameter of the resulting electrospun nanofibres. A salient observation in this study was that increased humidity reduced the effect of fibre beading yielding a more consistent and therefore better quality of fibre. This has apparent implications for the reproducibility of nanofibre production and offers a new method of controlling fibre morphology. This study has highlighted the requirement to control atmospheric conditions during the electrospinning process to fabricate reproducible fibre mats.     

Limited effect of diameter of fibres on spalling protection of concrete in fire

This study investigates the effect of diameter, length and melting point of fibres on spalling protection of concrete in fire. Three different diameters (0.012, 0.02 and 0.04 mm), three different lengths (9, 12 and 19 mm) and two different types (nylon and polypropylene) of fibres were investigated. Fibre volume (v%) or fibre weight per unit volume of concrete are commonly used parameters for fibre addition, but are dependent parameters on diameter of fibres. This study reports a better parameter for the expression of fibre addition which is independent of diameter, namely, number of fibres per cubic centimeter (N). When 12 mm length polypropylene fibre addition is expressed by v%, the minimum requirement for spalling protection is v = 0.20% for 0.04 mm diameter fibres and v = 0.05% for 0.02 mm diameter fibres. If the fibre addition is expressed in N, the minimum requirement is N = 133/cm³ for both cases regardless of fibre diameter. Hence, the diameter of fibres has limited effect on spalling protection of concrete. If the fibre addition is expressed in v%, the diameter seems to have an effect due to the fact that parameter v% is a function of diameter. In addition, increasing the length of fibres has the effect of reducing the required N for spalling protection. When fibre length is increased from 12 to 19 mm, the minimum requirement is reduced from N = 133 to 42/cm³. The melting point of the fibres also has an influence on spalling protection, which is discussed in detail by comparing nylon and polypropylene fibre results.     

Reinforcement of polyethylene with polypropylene by a blending and deformation process

The blending of polymers to achieve either unique or intermediate properties has become a rather common practice. High density polyethylene (HDPE) and isotactic polypropylene (PP) are immiscible in the melt state and phase segregate. This behaviour and their difference in melting point (132 against 165° C) has been exploited to produce a uniaxial reinforcement of HDPE with PP fibres by a process of melt blending, and tensile drawing followed by annealing. Tensile drawing of the blends results in the transformation of each phase to a fibrous structure having an increased modulus and tensile strength. The annealing of this material to melt and recrystallize the HDPE converts it to a lower modulus ductile lamellar structure which is reinforced with the fibrous PP regions. Both the modulus and tensile strength in the fibre direction fit simple composite theory for isotropic HDPE filled with higher modulus PP fibres over the entire composition range.     

Effect of amphiphilic coupling agent on heat flow and dielectric properties of flax–polypropylene composites

The study on heat transport in composites is of fundamental importance in engineering design and for tailoring thermal and mechanical behaviour of materials. In this study, the thermal conductivity and thermal diffusivity of flax reinforced polypropylene (PP) composites were determined at room temperature. Chemical modification in the form of a biodegradable zein coating was applied to the flax nonwovens. The effect of fibre loading and chemical modification on the thermo-physical properties was investigated. Dielectric permittivity studies were also evaluated and the dielectric constant of fibre reinforced composites was found to be higher than that of PP. The heat flow and crystallinity effects of the composites were also determined by differential scanning calorimetric (DSC) studies. Zein modification of the flax fibres resulted in a decrease of thermal conductivity and diffusivity which was attributed to a decrease in velocity and mean free path of phonons due to increase in interfacial adhesion.     

Lead magnesium niobate-lead titanate fibres by a modified sol-gel method

Lead magnesium niobate-lead titanate (PMN-PT) ceramic fibres with the nominal composition of 0.65Pb(Mg_1/3Nb_2/3)O₃-0.35PbTiO₃ have been fabricated by a modified sol-gel method. Due to the difficulty of dissolving the magnesium component, the mixed oxide method was used together with the traditional sol-gel method. To obtain crack-free fibres, pyrolysis was carried out at a very slow heating rate under specific atmosphere to control the organic burnout. The thermal and microstructural properties were investigated using thermogravimetric analysis, scanning electron microscopy and X-ray diffraction. The optimum sintering temperature is 1200 °C and yields a fibre with a final diameter of around 100 μm. A single PMN-PT fibre has been poled and its electrical properties were measured. The properties of the fibre are found to be better than that of a ceramic disc.     

Wool fibres functionalised with a silane-based coupling agent for reinforced polypropylene composites

Polypropylene (PP)-based composites containing 20 wt.% wool fibres were successfully prepared using a simple melt blending procedure. A blend of a commercial-grade PP and a maleinised PP was chosen as the matrix. To investigate the effects of modifying the fibre surface on the fibre/matrix adhesion, wool fibres were used as received, oxidised, or functionalised with a silane-based coupling agent, capable in principle of reacting with both the fibres and the polyolefinic matrix. The silanisation of the fibres and the consequent surface modifications were assessed using infrared spectroscopy and scanning electron microscopy. The resulting PP-based composites were thoroughly characterised in terms of their morphology, thermal stability and mechanical behaviour.     

Flow-induced crystallization of polypropylene in the presence of graphene nanoplatelets and relevant mechanical properties in nanocompsoite fibres

Flow-induced crystallization of polypropylene (PP) in the presence of graphene nanoplatelets (GnPs) was experimentally observed for the first time. Monofilaments of PP and PP/GnPs in the presence and absence of polypropylene grafted maleic anhydride (PP-g-MA) as a compatibilizer were produced via masterbatch dilution technique. Morphology, crystalline and super molecular structures, thermal and mechanical characteristics of the nanocomposite fibres were investigated by means of SEM, WAXD, DSC, DMTA, TGA, polarized light microscopy and tensile testing. The fractured cross-section images indicated a reasonably good GnPs dispersion in the compatibilized nanocomposite fibres since a few large GnPs aggregates were observed. Based on DSC, XRD, and polarizing optical microscopy results, it can say that GnPs acted as a nucleating agent and increased the crystallization temperature and simultaneously acted as a physical barrier, reducing crystallite growth of PP. The introduction of PP-g-MA into PP/GnPs nanocomposite fibre increased storage modulus. Upon inclusion of PP-g-MA, the most significant improvement of 48% was observed for tensile modulus with the incorporation of 0.5 wt.% GnPs. The observed results suggested that the presence of PP-g-MA changed the internal structure and morphology of PP/GnPs nanocomposite fibres rather than improving the interface of PP/GnPs. We concluded that using extensional flow and having proper dispersion of GnPs, flow-induced crystallization could be occurred in PP/GnPs nanocomposite fibres. About 20% increase in crystallinity was found for the compatibilized PP/GnPs nanocomposite fibres as compared to that of the virgin PP.     

Impact fatigue behaviour of vinylester resin matrix composites reinforced with alkali treated jute fibres

An impact fatigue study has been made for the first time on 35% jute/vinylester composites containing both untreated and alkali treated fibres. Longer alkali treatment removed the hemicellulose and improved the crystallinity and gave better fibre dispersion. The flexural strength properties of the composites made from treated fibre were superior. 4 h alkali treated jute fibres gave the optimum combination of improved interfacial bonding and fibre strength properties. However this was not reflected in their impact fatigue behaviour. On the contrary, the composites reinforced with 8 h alkali treated fibres displayed superior impact fatigue properties. Here, the fibres suffered catastrophic fracture with microfibrillar pull-out at some places and improved the fatigue resistance property of the composites as evident from SEM micrographs.     

Characterisation and utilization of natural coconut fibres composites

Two thousand fibres were randomly taken from a coir fibre stack, characters of the fibres were analysed. It was shown that length of the fibres was in the range between 8 and 337 mm. The fibres amount with the length range of 15–145 mm was 81.95% of all measured fibres. Weight of fibres with the length range of 35–225 mm accounted for 88.34% of all measurement. The average fineness of the coir fibres was 27.94 tex. Longer fibres usually had higher diameters.Composite boards were fabricated by using a heat press machine with the coir fibre as the reinforcement and the rubber as matrix. Tensile strength of the composites was investigated.     

Effects of hydrogen annealing on the structural, optical and electrical properties of indium-doped zinc oxide films

Indium-doped zinc oxide (IZO) films were fabricated by radio-frequency magnetron sputtering. The effects of hydrogen annealing on the structural, optical and electrical properties of the IZO films were investigated. The hydrogen annealing may deteriorate the crystallinity of the films. The surfaces of the films would be damaged when the annealing temperature was higher than 350 °C. After the annealing, the surface roughness of the films would decrease, and high transparency of 80–90% in the visible and near-infrared wavelength would be kept. Meanwhile, the resistivity decreased from 1.25 × 10⁻³ Ωcm of the deposited films to 6.70 × 10⁻⁴ Ωcm of the annealed films. The work function of the IZO films may be modulated between 4.6 and 4.98 eV by varying the hydrogen annealing temperature and duration.     

Electrical conductivity of polyethylene-carbon-fibre composites mixed with carbon black

The study of electrical conductivity of high-density polyethylene-carbon-fibre composites mixed with different concentrations of carbon black is reported. The influence of the mixing procedure of the additives and material preparation is examined with regard to the conductivity values. The use of these two filler types in polyethylene composites combines the conducting features of both. Thus, while fibres provide charge transport over large distances (several millimetres), carbon black particles improve the interfibre contacts. Results are discussed with reference to simple electrical models. It is shown that for composites in which the segregated carbon black-polyethylene component lies above the percolation threshold the electrical interfibre contacts are activated through carbon black particle bridges, leading to a conductivity rise. This effect is more relevant in the case of shorter fibres. Processing of the material involving fibre orientation, such as in injection-moulding, decreases drastically the conductivity level reached.     

Mechanical performance of heat/fire damaged novel flame retardant glass-reinforced epoxy composites

Novel glass-reinforced epoxy composites containing a phosphate-based intumescent and inherently flame retardant (cellulosic (Visil, Sateri) and phenol-formaldehyde (Kynol)) fibres have been fabricated. These components are added both as additives in pulverized form and as fibre interdispersed with intumescent as a fabric scrim for partial replacement of glass fibre. Fire testing has been performed using a cone calorimeter at an incident heat flux of 50 kW/m² and the results have shown that introduction of the intumescent/FR fibre to the matrix can significantly reduce the peak heat release values and smoke intensities evolved by composites. Mechanical testing in tensile and flexural modes of these samples has shown that inclusion of the intumescent/fibre system does not adversely influence their tensile and flexural properties. The effect of heat on mechanical properties has been observed by heating the samples in a furnace at 400 °C for 5 min and tested for their flexural and tensile strength retentions. The charred samples remaining after cone exposure were also tested for stiffness test. Some of the samples retained up to 21% of the initial stiffness after being exposed to high heat flux in the cone calorimeter whereas, the control sample was rendered unusable after cone calorimeter exposure.     

Effects of doping concentration on the microstructural and optoelectrical properties of boron doped amorphous and nanocrystalline silicon films

Boron doped hydrogenated amorphous silicon thin films were prepared by plasma-enhanced chemical vapor deposition technique at various flow rate of diborane (F_B). As-deposited samples were thermally annealed at the temperature of 800 °C to obtain the doped nanocrystalline silicon (nc-Si) films. The effect of boron concentration on the microstructural, optical and electrical properties of the films was investigated. X-ray photoelectron spectroscopy (XPS) measurements demonstrated the presence of the substitutional boron in the doped films. It was found that thermal annealing can efficiently activate the dopants in films accompanying with formation of nc-Si grains. Based on the temperature-dependent conductivity measurements, it was shown that the dark conductivity of doped amorphous samples increases monotonously with the increase of doping content. While the dark conductivity of doped nc-Si films is not only determined by the concentration of dopant but also the crystallinity of the films. As increasing the flow rate of diborane, the crystallinity of doped nc-Si films decreases, which causes the decrease of dark conductivity. Finally, the high dark conductivity of 178.68 S cm⁻¹ of the B-doped nc-Si thin films can be obtained.     

Structure and properties of electrospun PLLA single nanofibres

An electrospinning method was used to spin semi-crystalline poly(L-lactide) (PLLA) nanofibres. Processing parameter effects on the internal molecular structure of electrospun PLLA fibres were investigated by x-ray diffraction (XRD) and differential scanning calorimetry (DSC). Take-up velocity was found as a dominant parameter to induce a highly ordered molecular structure in the electrospun PLLA fibres compared to solution conductivity and polymer concentration, although these two parameters played an important role in controlling the fibre diameter. A collecting method of a single nanofibre by an electrospinning process was developed for the tensile tests to investigate structure-property relationships of the polymer nanofibres. The tensile test results indicated that higher take-up velocity caused higher tensile modulus and strength due to the ordered structure developed through the process.