Microstructure and thermal stability of low-oxygen SiC fibers prepared by an economical chemical vapor curing method

Continuous SiC fibers (SiC-CVC fibers) with low oxygen content (~2 wt%) were prepared by pyrolysis of polycarbosilane (PCS) fibers cured with chemical vapor curing (CVC). PCS fibers were cured by cyclohexene vapor as curing agent. Their structure and properties were compared with those of SiC fibers obtained from electron beam irradiation curing (SiC-EB fibers). SiC-CVC fibers were similar to SiC-EB fibers, with distinctly better thermomechanical stability than that of fibers cured by thermal oxidation curing (commercial KD-I fibers). CVC is a more economical and practicable approach for preparing high-performance SiC fibers than other strategies.     

Surface modification of UHMWPE fibers by ozone treatment and UV grafting for adhesion improvement

In this study, the surface of ultra-high-molecular-weight-polyethylene (UHMWPE) fibers was modified by ozone pretreatment, followed by ultraviolet (UV) grafting, to enhance the interfacial properties of UHMWPE fibers/rubber composites. The fibers were first pretreated by ozone to introduce oxygen-functional groups. The graft polymerization of glycidyl methacrylate (GMA) onto the ozone-treated fibers was implemented by UV irradiation. The effects of time and GMA concentration on the grafting efficiency were investigated. The modified fibers were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). The XPS and FTIR results revealed that GMA was successfully grafted onto the fibers with epoxy groups. SEM images confirmed that a continuous layer of poly-(GMA) (PGMA) was grafted onto the fibers. The interfacial adhesion force of UHMWPE fibers with rubber matrix was characterized by H pullout testing, which showed that the maximum force the fibers/rubber composites increased by 79% over that of the untreated fibers.     

聚丙烯／接枝木纤维复合材料相容性及性能的研究

为了改善木纤维与聚丙烯基体间的相容性，用马来酸酐接枝聚丙烯（ＭＡＰＰ）对木纤维进行接枝处理。通过红外光谱分析，证明了马来酸酐接枝聚丙烯和木纤维之间产生了酯化反应，提出了木纤维和聚丙烯基体的粘合性。通过扫描电镜（ＳＥＭ）的观察及示差扫描量热计（ＤＳＣ）的分析，证明了接枝木纤维比未接枝的木纤维与聚丙烯基体间的界面相容性有了明显的改善，使木纤维能均匀地分散在聚丙烯基体中，从而提高了复合材料的加工性能和力     

Characterization of differently shaped carbon fiber composites prepared from naphtha cracking bottom oil

Different shaped carbon fibers (R-, I-, C-, Y-, and X-type) were prepared from melt-spinning of reformed naphtha cracking bottom oil precursors through various shaped spinnerets. These different shaped CFs (carbon fibers) and PVC (polyvinyl chloride) resin were compounded, and then CF/PVC composites were prepared. Precursor pitch, carbon fibers, and composites were characterized and their properties were compared. Mechanical properties of carbon fibers and composites were characterized relating to external surface area and ratio of perimeter to cross-sectional area of carbon fibers. The tensile strength of tetralobal fibers (X-type) showed five times higher than that of round-shaped fibers (R-type) due to extended external surface area. Their tensile strength of CF/PVC composite increased as ratio of perimeter to cross-sectional area of carbon fibers. The magnitude of the ratio was in order to X-, C-, I-, Y-, and R-type.     

Surface modification of henequen (Agave fourcroydes) fibers by ultraviolet curing with 2‐hydroxyethylacrylate and ethylacrylate: Effect of additives on degradable properties

Henequen fibers were grafted with a double impregnating monomer 2‐hydroxyethylacrylate (HEA) and ethylacrylate (EA) to improve the physicomechanical properties. The fibers soaked in different concentration (1–10%) of monomer + MeOH solution along with photoinitiator Irgacure 907 [2%] were cured under ultraviolet (UV) lamp at different UV radiation intensities (2–14 passes). Concentration of monomer at different radiation intensities was optimized with extent of mechanical properties such as polymer loading, tensile strength, and elongation at break. Enhanced tensile strength (268%) and elongation at break (110%) were achieved by the polymer treated fibers than untreated virgin fibers. We observed that, henequen fibers treated by 3% EA showed better physico‐mechanical properties than those treated by 5% HEA. The tensile properties of henequen fibers treated by 3% EA can be enhanced by adding aloxysilane; 3‐(trimethoxysilyl) propylmethacrylate additives with bulk monomer EA (3%). The degradability of the treated and untreated fibers due to accelerated weathering were also studied and it has been found that surface modified henequen fibers produced more resistivity towards different weathering conditions than untreated fibers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4000–4006, 2006     

Porous Electrospun PES/PEG Ultrafine Fibers for the Removal of Endocrine Disruptors

In this work, porous polyethersulfone (PES)/polyethylene glycol (PEG) ultrafine fibers were prepared via electrospinning technique, and then were used to removing endocrine disrupters from their aqueous solutions. The surface and the internal structures of PES/PEG ultrafine fibers were characterized by scanning electron microscopy (SEM) and the result showed that they were both porous. The porous electrospun PES/PEG ultrafine fibers can remove endocrine disrupters such as biphenyl A (BPA) and biphenyl (BP) effectively. Compared with pure PES ultrafine fibers, PES/PEG ultrafine fibers showed larger adsorption capacity and faster kinetics of uptaking target species. The hydrophilic properties and the porosity of porous PES/PEG ultrafine fibers can be controlled by adding hydrophilic materials such as polyethylene glycol (PEG), which can improve the adsorption properties of porous PES/PEG ultrafine fibers significantly. The results showed that porous electrospun PES/PEG ultrafine fibers had the potential to be used in environmental application and water treatment.     

Synthesis of carbon nanotubes on Ni/carbon-fiber catalysts under mild conditions

Methane, n-hexane, benzene, and cyclopentadiene were decomposed at a relatively mild temperature (773 K) over a Ni catalyst supported on either vapor grown carbon fibers (VGCF) or graphitized carbon fibers (GCF). Transmission electron microscopy showed that the morphology of the fibers changed according to hydrocarbon and particle size. Decomposition of methane and n-hexane produced fishbone-type fibers. The fibers from n-hexane sometimes showed intermittent hollow structures but the diameters of the fibers were widely distributed. Decomposition of benzene and cyclopentadiene mainly produced winding type carbon nanotubes of relatively uniform diameters (10-20 nm). Bidirectional fishbone-type fibers (fibers growing outward from a central catalyst particle) were also observed as a by-product. Small Ni particles (10-20 nm) with stretched tails were present on the tips of tubular fibers, some of which frequently changed growth direction. The varying tubular morphologies can be ascribed to liquid-like Ni particles resulting from the freezing point depression due to a fast dissolution of carbons during decomposition of benzene or cyclopentadiene. The formation of bidirectional fibers was also observed in the decomposition of n-hexane. Relatively large well-faceted Ni particles (diameter 50-110 nm) grew bidirectional fibers.     

Elastic response of copolyether-ester fiber on its phase morphology under different heat-treatment condition

In order to verify the elastic response of copolyether-ester (PEE) fibers on their phase morphology and structure, the PEE fibers based on poly(butylene terephthalate) (PBT) as hard segments and poly(terramethylene glycol) (PTMG) as soft segments were prepared by melt spinning, the as-spun fibers were then heat-drawn and heat-set at different conditions. From the analysis of the mechanical properties, it is shown that the tenacity as well as elastic recovery of the fibers increased with the increasing heat-draw ratios, the elongation at break decreased. The morphological and structural were evaluated by small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS) and birefringence. When the melt-spun PEE fibers were heat-drawn, higher crystallinity and orientation, larger size of lamellae structure was formed within the fibers, it is also much easier to form higher phase separation. This structure will contribute to better elastic performances of PEE fibers.     

Magnetic polyacrylonitrile-Fe@FeO nanocomposite fibers - Electrospinning, stabilization and carbonization

Uniform and bead-free pure polyacrylonitrile (PAN) and its magnetic polymer nanocomposite (PNC) fibers reinforced with different core-shell Fe@FeO nanoparticles (NPs) loadings are prepared using electrospinning method. The morphology of the resulting products is correlated to the corresponding rheological behaviors of the pure PAN and PAN/Fe@FeO solutions. The diameter of the PAN fibers is linearly related to the polymer solution concentration. However, with a fixed PAN concentration of 10 wt%, the Fe@FeO NP loading shows a negligible effect on the morphology of the PNC fibers. Thermogravimetric analysis (TGA) results indicate an enhanced thermal stability of the PNC fibers than that of the pure PAN fibers. Magnetic carbon nanocomposite (MCNC) fibers are prepared through the stabilization and carbonization of the electrospun PNC fibers. The effects of the heating procedures, including the stabilization and carbonization temperature and time, on the fiber morphology are systematically investigated. Both short and long MCNC fibers could be easily produced by changing the heat procedures. Room temperature magnetic properties of the nanocomposite fibers based on different heating procedures are also studied in this work.     

Electrospinning of thermo-regulating ultrafine fibers based on polyethylene glycol/cellulose acetate composite

Ultrafine fibers of polyethylene glycol/cellulose acetate (PEG/CA) composite in which PEG acts as a model phase change material (PCM) and CA acts as a matrix, were successfully prepared as thermo-regulating fibers via electrospinning. The morphology observation from the electrospun PEG/CA composite fibers revealed that the fibers were cylindrical and had a smooth external surface. PEG was found to be both distributed on the surface and within the core of the fibers. Differential scanning calorimeter (DSC) was used to characterize the thermal properties of the composite fibers. The results indicated that the fibers imparted balanced thermal storage and release properties for their thermo-regulating function and the thermal properties were reproducible after 100 heating-cooling cycles.     

High-strength–high-modulus polyimide fibers II. Spinning and properties of fibers

The polyimides based on 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) described in Part I of this series were dissolved in p-chlorophenol and spun into fibers using a coagulating bath of ethanol. The fibers as spun had in general low tenacities and low moduli, but a heat treatment at 300–500°C under tension produced a remarkable increase in strength and modulus, and fibers with a tensile strength of 26 g/den (3.1 GPa) and an initial modulus higher than 1,000 g/den (120 GPa) could be obtained. Thus, the annealed fibers of polyimides are comparable to aramid fibers in mechanical properties. To heating in air and in the saturated steam, the polyimide fibers showed higher resistance than the aramid fibers. The polyimide fibers surpassed the aramid fibers in resistance to acid treatment and ultraviolet (UV) irradiation, but were inferior in resistance to alkali treatment. The annealed fibers of polyimides displayed distinct X-ray diffraction patterns. The chain repeat distance of 20.5 Å determined on the fibers of polyimide prepared from BPDA and o-tolidine, and 20.6 Å determined on the fibers of polyimide derived from BPDA and 3,4′-diaminodiphenyl ether are reasonable when the dimensions of monomeric units and the shapes of the molecular chains are considered. The X-ray reflections of both polyimide fibers were indexed satisfactorily on the basis of postulated unit cells.     

Properties of differently shaped activated carbon fibers

Differently shaped carbon fibers (R-, I-, C-, Y-, and X-type) were prepared from melt-spinning of reformed naphtha cracking bottom oil precursors through various shaped spinnerets. These carbon fibers were activated by steam and activation properties were compared. The decrease of hydraulic radius resulted in the extending of the external surface area of carbon fibers. Activation energy and rate of differently shaped carbon fibers were affected by external surface area. Especially, the activation rate of tetralobal carbon fibers (X-type) appeared much larger than other shaped carbon fibers due to the smallest hydraulic radius. Adsorption capacity of tetralobal activated carbon fibers was also larger than other shaped activated carbon fibers.     

Multifunctional single-crystal tellurium core multimaterial fiber via thermal drawing and laser recrystallization

In the field of multimaterial optical fibers, the demand for high-performance single-crystal core glass-clad multimaterial optical fibers is increasing. However, the applications of single-crystal fibers are restricted by the complex fabrication processes and the slow growth of single-crystal materials. Here, a two-step method is demonstrated to achieve single-crystal tellurium (Te) core fibers with high crystal quality over the length of the fiber. This method starts with the thermal drawing of a fiber preform into polycrystalline Te core multimaterial fibers (precursor fibers) that are long and mechanically stable. A 532-nm continuous laser is then employed to recrystallize the Te core in the precursor fiber into a single crystal state along the entire length of the fiber. Experimental studies of these single-crystal fibers demonstrate that the single-crystal Te core fibers possess high transmittance (>90% at 2–10 μm) and high thermoelectric performance (ZT values from 0.03 to 0.13 at 300 K temperature). They are superior to previous reports and our previous work. This method works for fabricating various single-crystal fibers and has important applications in the field of optical fibers, functional fibers, and their integrated devices.     

Novel route to pure and composite fibers of polypyrrole

An organic salt (FeAOT) is synthesized by the reaction of sodium 1,4‐bis(2‐ethylhexyl)sulfosuccinate (AOT) and ferric chloride. It is fabricated into fibers by manual drawing and electrospinning. Long polypyrrole (PPy) fibers are obtained for the first time by a vapor deposition reaction of pyrrole on the FeAOT fibers, and this technique is extended to the synthesis of PPy composite fibers with multiwalled carbon nanotubes (PPy–MWCNT fibers). The PPy and PPy–MWCNT fibers have a nanoporous morphology, a conductivity of 10–15 S cm^?1, and a tensile strength of 12–43 MPa. The electrochemistry and current–voltage characteristics of the PPy fibers are also studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1490–1494, 2007     

Maleated high oleic sunflower oil‐treated cellulose fiber‐based styrene butadiene rubber composites

Surface treatment of cellulose fibers was performed with maleated high oleic sunflower oil (MSOHO). The MSOHO‐treated cellulose fibers and unmodified cellulose fibers were dispersed in styrene butadiene rubber (SBR) using a two roll mill. Vapor grown carbon nanofibers (VGCNF) were also incorporated at only one parts per hundred rubber (phr) in unmodified cellulose fibers/SBR composites. The curing characteristics, mechanical properties, and water absorption of the resulting composites were determined. MSOHO‐treated fibers completed curing at much slower rate and also decreased the cure density of composites, compared to unmodified fibers. In contrast, the combination of VGCNF and unmodified cellulose fibers accelerated the SBR curing process, but reduced the cure density. MSOHO treatment improved the dispersion of the fibers in the SBR, which resulted in improved mechanical properties of composites. The composite incorporating 1 phr VGCNF and 15 phr unmodified cellulose fibers showed the greatest increase in tensile strength as compared with neat SBR. POLYM. COMPOS. 37:1113–1121, 2016. © 2014 Society of Plastics Engineers     

Moisture sorption on the wetting behavior of poly(p-phenylene terephthalamide) fibers in water and epoxy resin

The moisture sorption of poly(p-phenylene terephthalamide) (PPTA) fibers and the effects of moisture on the wetting behavior of these fibers in water and in an epoxy resin were studied. The moisture regains in the Kevlar 149 fibers followed a third order polynomial dependency on increasing relative humidity at 23°C. When preconditioned at 0% relative humidity (R.H.), water wettability of Kevlar 49 fibers was superior to that of Kevlar 149 fibers. Resin wettability of the dried Kevlar 49 fibers, on the other hand, was lower than that of Kevlar 149 fibers. Wettability in water and resin of these two fiber types was affected differently by moisture. Exposure to 97% R.H. moisture level significantly lowered water wettability of Kevlar 49 fibers but did not affect the wettability of Kevlar 149 fibers in water. Resin wettability of Kevlar 49 fibers was improved upon exposure to moisture, but the opposite was observed on Kevlar 149 fibers.     

聚乙烯纤维的紫外光交联

在光引发剂和交联剂的存在下,用紫外光成功地交联了聚乙烯纤维,并使交联后的纤维具有良好的耐热性和抗蠕变性能。这一方法对超高强高模聚乙烯纤维的改性具有良好的应用前景。     

Mechanical properties of carbon fiber composites modified with nano-SiO2 in the interphase

The performance of carbon fibers-reinforced composites is dependent to a great extent on the properties of fiber–matrix interface. To improve the interfacial properties in carbon fibers/epoxy composites, nano-SiO₂ particles were introduced to the surface of carbon fibers by sizing treatment. Atomic force microscope (AFM) results showed that nano-SiO₂ particles had been introduced on the surface of carbon fibers and increase the surface roughness of carbon fibers. X-ray photoelectron spectroscopy (XPS) showed that nano-SiO₂ particles increased the content of oxygen-containing groups on carbon fibers surface. Single fiber pull-out test (IFSS) and short-beam bending test (ILSS) results showed that the IFSS and ILSS of carbon fibers/epoxy composites could obtain 30.8 and 10.6% improvement compared with the composites without nano-SiO₂, respectively, when the nano-SiO₂ content was 1 wt % in sizing agents. Impact test of carbon fibers/epoxy composites treated by nano-SiO₂ containing sizing showed higher absorption energy than that of carbon fibers/epoxy composites treated by sizing agent without nano-SiO₂. Scanning electron microscopy (SEM) of impact fracture surface showed that the interfacial adhesion between fibers and matrix was improved after nano-SiO₂-modified sizing treatment. Dynamic mechanical thermal analysis (DMTA) showed that the introduction of nano-SiO₂ to carbon fibers surface effectively improved the storage modulus of carbon fibers/epoxy.     

A comparison of ablative resistance properties of liquid silicone rubber composites filled with different fibers

Flexible ablative materials play a key role in thermal protection systems to protect space vehicles during hypersonic flight missions. In this work, epoxy resin modified liquid silicone rubber was adopted as elastomeric matrix. Two inorganic fibers (carbon fibers (CF) and quartz fibers (QF)) and two organic fibers (aramid fibers (AF) and poly (p-phenylene benzobisoxazole) fibers (PBO)) were chosen as functional fillers. The ablation resistance and thermal insulation properties were evaluated using oxyacetylene torch test. Microstructure and phase composition of the char layer was fully characterized to investigate the ablation mechanism. SEM observations revealed that the fibers are well dispersed and integrated in the matrix. TGA analysis indicated that the inorganic fibers possess significantly higher thermal stability than organic fibers. In addition, a molten silica film can be formed on the material surface, which can exert a better thermal protection effect on the matrix. Furthermore, the ablation test shows that the linear ablation rate decreases first and then increases with an increase of fiber content. This work provides basic data to guide optimal selection of fibrous ablatives to enhance ablation performance.     

Effect of graphene nanoplatelets presence on the morphology,structure, and thermal properties of polypropylene in fiber melt‐spinning process

Melt spinning of graphene nanoplatelets (GnPs)‐polypropylene (PP) nanocomposite fibers are reported for the first time. PP/GnPs fibers were spun with a pilot‐plant spinning machine with varying concentration of GnPs by mixing PP/GnPs masterbatch with PP. The effect of inclusion of GnPs on the morphology and crystalline structure of PP fibers was investigated. The thermal stability of the fibers was also evaluated by thermogravimetric analysis. The light microscopy images showed that the GnPs are uniformly distributed over the PP matrix. The differential scanning calorimetry (DSC) results revealed that presence of GnPs affects both the melting and crystallization behaviors. The melting peaks of PP/GnPs nanocomposite fibers were broader than that of neat PP fibers, indicating a broader crystal size distribution in PP/GnPs nanocomposite fibers as compared to the neat PP fibers. Besides, an obvious increment in the crystallization peak temperature was observed in GnPs‐PP nanocomposite fibers. The wide‐angle X‐ray diffraction spectra (WAXD) results showed that the crystal type of nanocomposite fibers did not change and was still the α‐monoclinic crystal form. Moreover, the morphology of spherulites demonstrated that GnPs increased the nucleation sites in the nanocomposite fibers which in turn restricted the crystal growth of PP chains. This finding supported the DSC and WAXD results. Activation energies were calculated by Horowitz and Metzger's method as 77.87 and 105.41 kJ/mol for neat PP and PP/0.2 wt% GnPs fibers, respectively, suggesting an increase in the thermal stability of GnPs‐PP nanocomposite fibers. POLYM. COMPOS., 36:367–375, 2015. © 2014 Society of Plastics Engineers