Effect of the type of nanoaddition on the thermal properties of polyacrylonitrile fibres

Thermal properties of precursor polyacrylonitrile fibres containing nanoparticles of additives such as SiO₂, hydroxyapatite and montmorillonite have been examined. The thermal curves of the fibres under investigation obtained by the derivatographic method in air and DSC in a neutral gas atmosphere were interpreted from the point of view of physical and chemical changes in the fibre-forming polymer. Based on the thermogravimetric curves, the coefficients of thermal stability of the fibres were found. It has been found that the thermal stability of PAN fibres is affected by the type of nanoadditives and the value of the as-spun draw out ratio used during fibre spinning.     

Thermal properties of fibres from a new polymer of the polyimideamide group

The paper presents the thermal properties of fibres made of a modified polyimideamide. The effects of as-spun draw ratio and deformation during the fibre drawing stage on the structure, thermal properties, moisture absorption and tenacity of the obtained fibres have been determined. Based on the findings obtained by the DTA and DSC methods, it has been found that the modification of the polymer under investigation causes its glass transition temperature to decrease through the increase of molecular mobility. At the same time, the heat-resistant fibres with the amorphous oriented structure are characterized by a tenacity of 16 cN/tex, good absorption properties and increased porosity. The thermal stability indices of the examined fibres have been determined on the basis of thermogravimetric curves obtained both under air and inert gas. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal degradation and decomposition of jute/vinylester composites

Thermal analysis of jute fibre reinforced vinylester resin with 30 vol% of fibre were performed by TG/DTG under dynamic conditions. The fibres were treated with alkaline solution at different temperatures and the final composition (cellulose, hemicellulose and lignin) of the fibre was determined by chemical analysis. Apparent activation energies were determined using a variety of conventional thermogravimetric methods. Two peaks were found in the composite differential curves: the first peak close to 327 and the second peak at 408°C. The apparent activation energy values for the second peak decreased when fibre were treated. The addition of the jute fibres produced a slightly decrease in the thermal stability of the composites.     

Thermal Analysis of Acrylonitrile Polymerization and Cyclization in the Presence of N,N-Dimethylformamide

This paper examines the polymerization of acrylonitrile to poly(acrylonitrile)(PAN), and its cyclization, in bulk form and using N,N-dimethylformamide (DMF) as solvent in which both monomer and polymer are soluble. Thermal analysis of the resultant products after polymerization has been performed by DSC and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). Scanning electron microscopy has been used to study the morphology of the resultant products and after thermal treatments. The DSC thermal curve of PAN-DMF sample is quite different from the PAN bulk sample, showing a single sharp exothermic peak associated with nitrile group polymerization (cyclization) of PAN at lower temperature (240°C) than that of bulk PAN sample (314°C). Cyclization of PAN was confirmed by IR spectroscopy. It was found that the amide molecules are difficult to eliminate completely in the product obtained after the polymerization reaction, even after prolonged heating at 110°C, and remain occluded. The formation of a complex by dipolar bonding is also possible and it is discussed. It is concluded that the amount of heat evolved as well as the temperature interval over which it is released are influenced by the chemical processing of PAN when using DMF as solvent of both monomer and polymer. Pyrolysis of these PAN samples revealed the release of occluded molecules of DMF, and several compounds containing nitrogen produced from the thermal degradation processes. All these results are interesting to know the chemical processing of carbon fibres and activated carbon fibres from PAN modified precursors.This revised version was published online in November 2005 with corrections to the Cover Date.     

Characterization of sugar palm (Arenga pinnata) fibres

The aim of this study was to characterize tensile and thermal properties of sugar palm (Arenga pinnata) fibres obtained from different heights (1, 3, 5, 7, 9, 11, 13, and 15?m) of sugar palm tree. This study has confirmed that in a mature sugar palm tree, degradation was occurred and altered the properties of its fibre. Fibres obtained at the area of live (green) palm frond were found to have a better tensile properties as a result of its optimum chemical composition especially cellulose, hemicelluloses and lignin. For the fibre obtained from the upper part of sugar palm tree, it shows slightly decreasing trend in tensile properties compared to mature fibres. It is due to the fibres are juvenile where their cell walls are progressively built up thus give slightly lower properties than matured fibres. For the fibre obtained from the area of dead palm frond, the fibres are considered to be degraded biologically. It is believed that polymeric chains in microfibrils were broken and their cellulose content was decreased which demonstrated inferior properties (tensile strength, modulus, elongation at break and toughness). The use of such fibre for application as reinforcing fibre in composite is not recommended since the strength of the fibre and composite will be reduced. There were four phases of decomposition of the fibres where the sequence of decomposition started with decomposition of moisture, followed by hemicelluloses, then cellulose and next is lignin while the ash was the last component left. The thermal degradation of these components were found in ranges of 45?C123, 210?C300, 300?C400, 160?C900 and 1723?°C, respectively. Thermogravimetric analysis and derivative thermogravimetric analysis curves showed that the fibre of 1?m showed higher thermal stability than the fibres of 3?C15?m. The different thermal stability for each fibre was due to different chemical compositions especially when the fibre containing high ash content which result in higher thermal stability.     

A review of the role of DSC analysis in the design of fluorozirconate glasses for fibre optic applications

The relatively poor thermal stability of fluorozirconate glasses is a major factor preventing the realisation of their true potential for fibre optic applications. A range of methods based on both isothermal and non-isothermal DSC techniques, which can be employed to evaluate the thermal stability of fluorozirconate glasses, are described. The relevance of these thermal stability criteria to the design of fluorozirconate compositions capable of yielding high quality optical fibres is discussed.     

Thermal and crystallization studies of short flax fibre reinforced polypropylene matrix composites: Effect of treatments

The effect of fibre treatments on thermal stability of flax fibre and crystallization of flax fibre/polypropylene composites was investigated. For thermal stability study, flax fibres have been treated using maleic anhydride, maleic anhydride polypropylene copolymer, vinyltrimethoxy silane and alkalization. In order to compare thermal stability of flax fibres thermogravimetry (TG) analysis has been used. Kinetic parameters have been determined by Kissinger method. Results showed that all treatments improved thermal stability of flax fibres. For crystallinity analysis, three different techniques have been used, differential scanning calorimetry analysis (DSC), pressure–volume–temperature (PVT) measurements for analysis of volume shrinkage and polarized optical microscopy (POM). All techniques results showed that addition of flax fibre increased crystallization rate. Besides, depending on fibre surface treatment and crystallization temperature, flax fibre/PP composites can show transcrystallinity.     

Effect of the fibre-forming material structure and silica nanoparticles

The paper discusses the thermal properties of alginate fibres made from alginic acid or sodium alginate and from alginates substituted with divalent metal ions during the fibre-forming stage. Alginate fibres with an addition of silica nanoparticles have also been examined. The selection of fibre-forming parameters was intended to obtain the best either sorption or strength properties depending on the specific fibre application. Thermal curves of the fibres under investigations obtained by under air atmosphere and differential scanning calorimetry (DSC) under neutral gas atmosphere have been interpreted from the view of physical and chemical changes in the fibre-forming material. Based on thermogravimetric curves, the fibre thermal stability indices have been determined. It has been found that the addition of silica nanoparticles exerts a positive influence on the thermal properties of the examined fibres.     

Thermal properties of biocomposites

Thermal properties of new biocomposites prepared from modified starch matrix reinforced with natural vegetable fibres were studied. DSC and TG methods were applied to study thermal behaviour of biocomposites. Biocomposites were obtained in the laboratory twin-screw extruder. Two kinds of natural fibres were used, i.e. flax and cellulose in the amount of 0–40 mass%. DSC curves of biocomposites reveal glass transition temperature, attributed to the amorphous nature of the plasticized starch matrix. In general, incorporating natural fibres into modified starch matrix leads to an increase in glass transition temperature. Thermal degradation of modified starch matrix and cellulose reinforced biocomposites proceeds in three steps, whereas the degradation process of flax reinforced biocomposites occurs in two steps. For unreinforced matrix as well as for all biocomposites, regardless of type and amount of reinforcement, the major mass loss is observed at the temperature above 300°C. The increase in thermal stability with introduction of natural fibre is observed for both flax and cellulose reinforced biocomposites.     

IFSS, TG, FT-IR spectra of impregnated sugar palm (Arenga pinnata) fibres and mechanical properties of their composites

This study aimed to investigate the effect of resin impregnation on the interfacial shear strength (IFSS), thermogravimetric (TG) and fourier transform infrared (FT-IR) of sugar palm (Arenga pinnata) fibres. In addition, the effect of resin impregnation on the mechanical properties of sugar palm fibre reinforced unsaturated polyester (UP) composites was also studied. The fibres were impregnated with UP via vacuum resin impregnation process at a pressure of 600 mmHg for 5 min. Composites of 10, 20, 30, 40 and 50 % fibre loadings were fabricated and tested for tensile and flexural properties. It was observed that the impregnation process caused the fibres to be enclosed by UP resin and this gave a strong influence to the increase of its interfacial bonding by the increase of its IFSS from single fibre pull-out test. It was also observed with TG and FT-IR spectra that the impregnated fibre had lower moisture uptake than the control and there was no significant increase in thermal stability of the impregnated fibre. The sequence of fibre decomposition started from the evaporation of moisture, hemicelluloses, cellulose, lignin and finally ash content and the presence of these components were proven by FT-IR spectra. For the composite specimens, due to the high interfacial bonding of the impregnated fibre and the matrix, the impregnated composites showed consistently higher tensile strength, tensile modulus, elongation at break, flexural strength, flexural modulus and toughness than the control samples. It was also observed that 30 % fibre loading gave optimum properties.     

Dye diffusion in anisotropic polyamide fibres

Radioactive tracer techniques have been used to study the diffusion of three dyes in polyamide fibres produced under different conditions. It has been shown that drawn nylon fibres have a surface barrier layer which limits diffusion. The permeability of the layer is reduced by drawing, and varies with drawing conditions. The dependence of dye diffusion on concentration, ionic size and draw ratio is less in the surface than in the bulk of the fibre, but variations in dyeing behaviour have been shown to follow surface rather than bulk diffusion characteristics.     

Radial structure and property relationship in the thermal stabilization of PAN precursor fibres

Here we report on the role of oxygen in the evolution of radial heterogeneity in the fibre structure and properties of PAN fibres stabilized in air and vacuum at different temperatures. Modulus mapping by Nano-indentation showed heterogeneous modulus distribution in the fibres treated in air, while no variation in modulus was observed in fibres processed in vacuum. Raman spectroscopy and elemental analysis revealed that the temperature dependent oxygen diffusion from skin to core of the fibres assisted in the evolution of higher extent of sp²-hybridized carbons in the skin compared to core of the air treated samples. Conversely, no radial structure variations were observed in the vacuum treated fibres. Higher modulus in the skin of air-treated fibres was due to the formation of compact structures which was associated with the enhanced intermolecular interactions facilitated by the formation of C=C bonds within the polymer backbone, promoted by oxidative-dehydrogenation reaction. Supporting these observations, the fracture morphology examined by SEM showed a brittle fracture in the skin and ductile fracture in the core.     

Structural FTIR analysis and thermal characterisation of lyocell and viscose-type fibres

The microstructure and thermal properties of lyocell and other regenerated cellulose fibres (viscose and modal) were analysed using DSC, TG and FTIR. The FTIR spectral analysis showed that lyocell is the most crystalline fibre and is composed principally of crystalline cellulose II and amorphous cellulose. Likewise, the thermal analysis showed that lyocell has a higher thermal stability than viscose and modal fibres, as the difference between the onset temperature for its decomposition process was as high as 20 °C.     

Two-beam interference detection of the changes in fibre structural parameters during low drawing process

A Pluta polarizing interference microscope with a fibre stretching device attached was used to detect the changes in molecular structure that occur during the fibre cold drawing process. Fibres drawn with low draw ratios show different types of deformation mechanisms. The interference patterns recorded at different draw ratios are used to relate the deformation mechanisms with the measured structural parameters. Some optical parameters are measured such as; refractive indices nand n birefringence n, the polarizability per unit volume , the orientation distribution function f(θ), the angle θ between the stretching direction and the chain axis, and the angle θ_m which the transition dipole moment of the molecular species makes with the molecular axis (chain axis). Three polymeric fibres (Polyethylene terephthalate PET, Polypropylene PP and Polyamide PA) were used in this study and their interferograms are illustrated.     

Effect of dope flow rate on the morphology,separation performance,thermal and mechanical properties of ultrafiltration hollow fibre membranes

We have determined the effects of dope extrusion speed (or shear rate within a spinneret) during hollow fibre spinning on ultrafiltration membrane's morphology, permeability and separation performance, and thermal and mechanical properties. We purposely chose wet-spinning process to fabricate the hollow fibres without drawing and used water as the external coagulant in the belief that the effects of gravity and elongation stress on fibre formation could be significantly reduced and the orientation induced by shear stress within the spinneret could be frozen into the wet-spun fibres. An 86/14 (weight ratio) NMP/H₂O mixture was employed as the bore fluid with a constant ratio of dope fluid to bore fluid flow rate while increasing the spinning speed from 2.0 to 17.2 m/min in order to minimise the complicated coupling effects of elongation stress, uneven external solvent exchange rates, and inner skin resistance on fibre formation and separation performance. Hollow fibre UF membranes were made from a dope solution containing polyethersulphone (PES)/N-methyl-2-pyrrolidone (NMP)/diethylene glycol (DG) with a weight ratio of 18/42/40. This dope formulation was very close to its cloud point (binodal line) in order to speed up the coagulation of nascent fibres as much as possible so that the relaxation effect on molecular orientation was reduced. Experimental results suggested that a higher dope flow rate (shear rate) in the spinneret resulted in a hollow fibre UF membrane with a smaller pore size and a denser skin due to a greater molecular orientation. As a result, when the dope extrusion speed increased, pore size, water permeability, CTE and elongation of the final membranes decreased, but the separation performance, storage modulus, tensile strength and Young's modulus increased. Most surprisingly, for the first time, we found that there was a certain critical value, when the dope extrusion rate was over this value, the final fibre performance could not be influenced significantly. The results suggested that it was possible to dramatically enhance the production efficiency of hollow fibre UF membranes with the same fibre dimension and similar separation performance by the method proposed in this paper.     

Effect of the air-jet and the false-twist texturing processes on the thermomechanical behaviour of polyamide 6.6 yarns

Polyamide 6.6 multifilament yarns are converted to crimped fibres by texturing in order to simulate the properties of natural staple fibre yarns for textile applications. Texturing is carried out by mechanical stresses (turbulences or twisting) in different atmospheres which affect crystallinity and thermal stability of yarns. Two polyamide yarns with the same linear density but consisting of filaments of different fineness were textured by the air-jet and the false-twist procedures. The influence of texturing conditions and filament fineness on crystallinity and thermomechanical behaviour and dimensional stability were studied by TMA and DSC. The air-jet texturing procedure leads to a slight increase in crystallinity of yarns whereas the false-twist texturing procedure was more effective especially when thicker filaments were textured. The inflection point of the shrinkage curve before melting was a good estimator of the effective temperature of yarn texturing.     

Physical properties of polyacrylonitrile fibres treated with organotin compounds

A study was made of the effect of the polymerization of the nitrile groups of polyacrylonitrile by organotin compounds on the coloration and on the physical properties of PAN fibres. It is shown that, by controlling reaction parameters such as concentrations, temperature, solvent and type of organotin compound, it is possible to control the coloration of the fibres. Application of this reaction to the fibres results in an increase in their elongation at break with retention of the original modulus and ultimate strength; also, their thermal stability is enhanced.     

Solvent and enzyme induced recrystallization of mechanically degraded hemp cellulose

The structural degradation of cellulose fibre from hemp (Cannabis Sativa L.) by a ball-milling process and the recrystallization behavior of the product were studied. A linear increase in the Brunauer–Emmett–Teller specific surface area was observed; indicating the fibre bundles were being crushed and disrupted to single fibres, which was confirmed by SEM. An increase in the milling duration gradually destroyed the crystalline structure of the cellulose fibres, observed by a reduction of the 002 plane intensity in wide angle X-ray scattering measurements. The crystalline order index calculated from the area ratio of the 002 to the 021, 10 and 002 planes was decreased from 65 to 36 after milling for 330 min. Subsequently the lower thermal stability of ball-milled fibre was observed from a decrease in the temperature at the maximum mass loss rate using thermogravimetry. An increase in solvent polarity, solvent-fibre ratio, agitation speed and drying rate resulted in the rearrangement of ball-milled cellulose crystalline structure to a greater order. Moreover, an increase in the BET specific surface area and the amorphous fraction improved the scouring efficiency of the ball-milled cellulose using the pectate lyase enzyme (EC. 4.2.2.2).     

Carbon nanotube growth on high modulus carbon fibres: Morphological and interfacial characterization

Carbon nanotubes (CNTs) were grown directly on the surface of carbon fibres, using the catalytic chemical vapour deposition. FeCo bimetallic catalysts were deposited on carbon fibres using a simple wet impregnation method. CNTs were synthesized over the prepared catalysts by the catalytic decomposition of acetylene at 750^oC. The uniform CNT formation on the fibre surface was verified using scanning electron microscopy. Raman spectroscopy was employed to evaluate non‐destructively the CNT growth and the CNT quality. Thermo gravimetric analysis and differential thermal analysis were employed as destructive methods to confirm the spectroscopic data. Single CNT‐coated fibre fragmentation tests were performed to examine the interfacial shear strength (ISS) of the modified fibres. Acoustic emission was employed to monitor the fragmentation process in real time. Thus, the coated fibre structural integrity was assessed together with its stress transfer properties. Polarized optical microscopy was employed to cross validate the acoustic emission data. It was found that the ISS of the nanotube‐reinforced interphase was improved without affecting the fibre mechanical properties. Copyright © 2013 John Wiley & Sons, Ltd.     

Development of orientation during electrospinning of fibres of poly(ε-caprolactone)

We explore the influence of a rotating collector on the internal structure of poly(ε-caprolactone) fibres electrospun from a solution in dichloroethane. We find that above a threshold collector speed, the mean fibre diameter reduces as the speed increases and the fibres are further extended. Small-angle and wide-angle X-ray scattering techniques show a preferred orientation of the lamellar crystals normal to the fibre axis which increases with collector speed to a maximum and then reduces. We have separated out the processes of fibre alignment on the collector and the orientation of crystals within the fibres. There are several stages to this behaviour which correspond to the situations (a) where the collector speed is slower than the fibre spinning rate, (b) the fibre is mechanically extended by the rotating collector and (c) where the deformation leads to fibre fracture. The mechanical deformation leads to a development of preferred orientation with extension which is similar to the prediction of the pseudo-affine deformation model and suggests that the deformation takes place during the spinning process after the crystals have formed.