Modification of polypropylene fibers by electron beam irradiation. I. Evaluation of dyeing properties using cationic dyes

The dyeing properties of hydrophobic polypropylene fibers using cationic dyes were investigated to improve dyeability by electron beam irradiation and sulfonic acid incorporation. The color strength of polypropylene fibers after irradiation was examined according to the dyeing conditions including the pH of the dyebath, absorbed doses, and the introduction of a functional group to the fiber substrate. The best dyeing result was obtained when polypropylene fibers incorporated by sulfonic acid group after electron beam irradiation were dyed with cationic dyes at alkaline conditions and 30∼75 kGy irradiation ranges.     

Water repellent treatment of cotton fabrics by electron beam irradiation

In this study, traditional dip-pad-cure (DPC) process and electron beam (EB) irradiation were used to graft cotton fabrics with fluorine containing chemical, 1H,1H,2H,2H-perfluorooctyl acrylate (PFA). The grafted cotton fabrics were characterized by FT-IR and SEM. The water repellent properties were measured by contact angle, hydrostatic pressure, and spry test. It was found that there was no significant difference between the grafted cotton fabrics with DPC and EB methods, and the treated fabrics showed good water-resistant properties. The grafted cotton fabrics also showed good washing stability. By measuring the bending rigidity and bending hysteresis, it was found that the cotton fabrics grafted with PFA became softer than untreated samples.     

Elastic property of polyolefin elastomer film cross linked by electron beam irradiation

Polyolefin elastomers were extruded to form films and subjected to electron beam (EB) irradiation at various energy levels. The film samples were characterized to illuminate the effects of EB-induced cross-linking through measurements of gel contents, Fourier transform infra-red (FT-IR) spectroscopy, and variations of tensile properties of the films after the EB irradiations. The EB irradiations introduced crosslinking among the molecular chains resulting increases in initial modulus. The elastic recovery was 83 % at 30 % stain, which is increased by 10 % at 150 kGy compared with pristine. The maximum stain was 1,400 % at 150 kGy which is comparable with commercial polyurethane elastomer.     

Synthesis and characterization of boron doped alumina stabilized zirconia fibers

Boron doped PVA/Zr-Al acetate nanofibers were prepared by electrospinning using PVA as a precursor. The effect of calcination temperature on morphology and crystal structure was investigated at 250, 500, and 800 °C. The study also establishes the effect of boron doping on the morphology of PVA/Zr-Al acetate nanofibers at various calcination temperatures. The measurements showed that the conductivity, pH, viscosity and the surface tension of the hybrid polymer solutions have increased with boron doping. In addition, the fibers were characterized by FTIR, DSC, XPS, XRD and SEM techniques. The addition of boron did not only increase the thermal stability of the fibers, but also increased the average fiber diameters, which gave stronger fibers. The DSC results indicated that the melting temperature (Tm) of the fibers was increased from 256 to 270 °C with the addition of boron. XRD peak patterns showed that after further heat treatment at 800 °C, zirconia exists in two phases of tetragonal and monoclinic modifications. Moreover, alumina does not transform into the γ-Al₂O₃ and θ-Al₂O₃ phase at 800 °C. The SEM appearance of the fibers showed that the addition of boron resulted in the formation of crosslinked bright surfaced fibers.     

Study on polyacrylonitrile fibers modified by blending with polyethylene glycol

A series of water absorbent porous modified polyacrylonitrile (PAN) fibers were prepared using the blends of PAN and various molecular weight of polyethylene glycol (PEG) by wet-spinning process and water bath post-treatment. The chemical structure and morphologies of the modified PAN fibers were studied. The water transportation, water retention, moisture absorption and mechanical properties of the fibers were discussed. Results show that there is no residual PEG in modified PAN fibers after drawing process in hot water bath and post-treatment. With the increase in PEG molecular weight, the fiber surface grooves become deeper, the inner pore size increases, while the mechanical properties decrease. The water absorbing and transferring capabilities of the modified PAN fibers can be improved in varying degrees due to the different pore structures left by series molecular weight of PEG removing.     

A study on structural characterization of thermal stabilization stage of polyacrylonitrile fibers prior to carbonization

Structural transformations taking place during the thermal stabilization of polyacrylonitrile (PAN) fiber used for the production of carbon fiber were characterized using a combination of polarized infrared spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and density measurements. Direct relationship between the increasing oxygen content and the density values was confirmed with increasing stabilization time. Linear density values were found to be directly influenced by the stabilization time. Thermal stability of stabilized precursor fibers was evaluated in terms of weight loss and residual weight fraction. The results showed that a residual weight fraction of 65 % at 1000 °C can be obtained but longer stabilization time resulted in a loss of residual weight fraction due to excessive thermal degradation. SEM was used for the observation of surface morphological features of stabilized precursor fibers. Polarized infrared spectroscopy showed the loss of molecular orientation of methylene (CH₂), nitrile (Ct=N), and carbonyl (C=O) groups in direct response to the effects of cyclization, dehydrogenation, and amorphization (i.e. decrystallization) processes taking place during the stabilization stage.     

电子束辐射诱变及克隆选择培育好好芭抗寒无性系的研究

利用电子辐射处理好好芭试管苗，从改变基因型入手提高其抗寒力，以获得稳定遗传的好好芭株系。研究表明150GY的辐射量是诱发好好芭发生变异的最佳剂量，结合生化标记，抗寒相关的酶类——淀粉酶和过氧化物酶活性分析，人工模拟低温实验的克隆检测，筛选出了具有较高抗寒能力的好好芭株系，这些株系通过无性系繁殖可用于抗寒育种。     

Spinnability in pre-gelled gel spinning of polyacrylonitrile precursor fibers

The spinnability in pre-gelled gel spinning of polyacrylonitrile (PAN) precursor fibers was investigated. The spinning solutions were aged at 25 °C for different times prior to fiber spinning. The pre-gelled spinning solution aged for 2.5 h was much more strain hardening than the ungelled one, which can increase the spinnability of the solution. The maximum take-up velocity of the first winding roller V _1m, which reflects the spinnability of the spinning solutions, was found to be largest when the aging time was 1.5 h. The spinnability increased with the increase of the air gap length and the lengthdiameter ratio L/D of the spinnerette. Once the L/D increased beyond 15, the spinnability hardly changed. The fibers spun from the spinning solution aged for 1.5 h had the best mechanical properties and favorable structure, showing that good spinnability favors the performance increase of resultant PAN precursor fibers.     

The demonstration of a dense and stable circumferential layer in the subsurface of polyacrylonitrile fibers for carbon fibers

The radial structure of polyacrylonitrile (PAN) copolymer fibers was investigated quantitatively by etching layer by layer in an improved permanganic etchant; meanwhile the effect of the etchant on the fiber surface was taken into consideration. The aggregated structure (crystal size, crystallinity, orientation and density) and thermal stability of each circumferential layer of PAN fibers were determined in detail according to a model proposed in the study. A denser layer with a thickness of about 1 µm was observed in the subsurface (2 µm from the PAN fiber surface), possessing a greater crystal size and crystallinity as well as a relatively higher thermal stability than other layers. This layer was considered to be a barrier for the diffusion of oxygen into PAN fibers during the stabilization and accelerated the formation of a core-shell structure in the resulting carbon fibers.     

Effect of boric acid on oxidative stabilization of polyacrylonitrile fibers

The coating modification of polyacrylonitrile (PAN) fibers with boric acid to enhance the controllability of thermally oxidative stabilization process. The stabilization process, cross-section morphologies of oxidized and carbonized products were investigated by means of optical microscopy, SEM, XPS and in-situ thermal shrinkage indicator. The results indicated that the coating with boric acid on fiber surface was effective to avoid skin-core heterogeneity on the cross section and, in the stabilization process, that boric acid as a crosslinking agent to tie together the adjacent oxidative molecular chains was confirmed. It was suggested that the crosslinked structures should play an essential role in controlling the formation of uniform oxidized structures, which is favorable for tensile properties of carbon fibers.     

Effects of electron beam irradiation on dry matter degradation of wheat straw in the rumen

The effect of electron beam irradiation at doses of 100, 200 and 300 kGy on ruminal dry matter degradation kinetics of wheat straw was investigated. Samples were irradiated by electron beam irradiator under identical conditions of temperature and humidity. Nylon bags of untreated or irradiated wheat straw were suspended in the rumen of three Taleshi steers for up to 96 h and resulting data were fitted to non-linear degradation model to calculate degradation parameters of dry matter. Results show that the washout fractions of dry matter increased linearly (p<0.001), but potentially degradable fraction and degradation rate decreased linearly (p<0.001) by electron beam irradiation. As a consequence, the effective degradability of dry matter increased linearly (p<0.001) with increasing irradiation dose. Electron beam irradiation at doses of 100, 200 and 300 kGy increased the effective degradability of dry matter at rumen outflow rate of 0.05/h by about 7, 15 and 18%, respectively. In the condition of this study, electron beam irradiation at dose of 200 kGy appeared to be a suitable dose for improving dry matter degradability of wheat straw in the rumen.     

The role of thermal stabilization on the structure and mechanical properties of polyacrylonitrile precursor fibers

The thermal stabilization stage of polyacrylonitrile (PAN) fibers is characterized by a steady and continuous reduction in fiber diameter and linear density values together with color changes from reddish brown to shiny black with increasing stabilization time. Thermally stabilized PAN fibers acquire infusible and nonburning characteristics prior to the carbonization stage. Structural characterization of thermally stabilized polyacrylonitrile fibers was carried out using an indepth analysis of equatorial X-ray diffraction traces. Curve fitting of X-ray diffraction traces provided accurate peak parameters which were subsequently used for the evaluation of apparent crystallinity, apparent crystallite size and X-ray stabilization index. The results showed the loss of crystallinity due to the amorphization processes together with a steady and continuous decrease in lateral crystallite size with increasing stabilization time. With the progress of thermal stabilization, a new amorphous phase with a crosslinked and aromatized structure is formed which is expected to withstand high carbonization temperatures. Mechanical properties of the thermally stabilized PAN precursor fibers were found to be adversely affected with the progress of stabilization time. Due to the influence of thermal degradation mechanisms heavily involving chain scission along the fiber axis direction, tensile strength and tensile modulus values were found to decrease by significant proportions with the prolonged stabilization times.     

Thermal performance and flammability of poly(ethylene terephthalate) fabrics grafted with different monomers followed by electron beam irradiation

Electron beam irradiation grafting of acrylic acid (AAc), acrylamide (AAm), and dimethyl vinylphosphonate (DMVP) onto poly(ethylene terephthalate) (PET) fabrics was performed using a high-energy electron accelerator. Parameters affecting the graft polymerization of PET fabrics, including absorbed dose and monomer concentration, were investigated. Fourier transform infrared spectroscopy analysis confirmed that the monomers were grafted onto the PET fabrics. The thermal behavior of the grafted PET fabrics was investigated with thermogravimetric analysis. Findings showed that grafting with AAm could improve the thermal stability of PET. The limiting oxygen index values and vertical flammability test results showed that PET fabric graft-polymerized with AAc could improve the flammability and prevent melt dripping. Grafting with AAm and DMVP could improve the flame retardation property of PET fabric. Scanning electron micrographs showed that the surface morphology of the PET fabric samples was significantly influenced by graft polymerization, and that grafting with AAc could promote the formation of residual char and impart an anti-dripping quality to PET fabrics.     

Synthesis and characterization of nanocrystalline CoWO4@silk fibers with antibacterial activity under ultrasound irradiation

The present investigation reports the novel synthesis of CoWO₄ nanoparticles@silk fiber under ultrasound irradiation. The effect of temperature, power of ultrasound irradiation and sequential dipping steps in growth of the CoWO₄ particles were studied. Results show a decrease in the particles size as the temperature and power of irradiation decreased. The fibers containing CoWO₄ nanoparticles were tested for their antibacterial efficacy against E. coli and S. aureus and were found to possess significant antibacterial activity. The results show the CoWO₄ nanoparticles@silk with strongest fluorescence characteristics can be obtained in this method. The physicochemical properties of the nanoparticles were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and fluorescence spectroscopy.     

Dyeing behavior of polyacrylonitrile nanofibers: Physicochemical parameters of dyeing with basic dye in comparison with regular polyacrylonitrile fibers

Polyacrylonitrile nanofibers were produced using the electrospinning method and dyed with a basic dye alongside regular polyacrylonitrile fibers. In order to investigate the effect of high surface area to volume ratio of nanofibers on their adsorption behavior in comparison with regular fibers, the dyeing conditions for both types of fibers were kept just the same. Physiochemical parameters of dyeing such as adsorption isotherm, standard affinity, enthalpy change, rate of dyeing constant, diffusion coefficient, and activation energy of diffusion were investigated for both types of fibers. The results showed that the adsorption process can be well described with the Langmuir adsorption isotherm for both types of fibers whereas the standard affinity of dye to nanofibers was higher than regular fibers and the higher negative values of enthalpy changes were obtained for regular fibers. The nanofibers rate of dyeing was faster than regular fibers with higher amounts of diffusion coefficients and lower amounts of activation energy of diffusion. This study also revealed that in spite of the approximately same amount of dye exhaustion for both types of fibers, the color strength of regular fibers was noticeably higher than nanofibers.     

Quantification of degradation and surface morphology of NB7 silk fibers irradiated by 8 MeV electron beam using XRD and SEM techniques

NB7 silk fiber (Bombyx mori) was irradiated with the maximum dose range of 100 kGy using 8 MeV electron beam at room temperature. Irradiation effect in these fibers is quantified in terms of the changes in microstructural parameters employing X-ray diffraction line profile analysis technique. For this purpose we have used three asymmetric distribution functions for column lengths in a crystal. The decreasing trend of crystallite size values (〈N〉 as well as D _s ) and crystallinity with increasing dosage of radiation clearly indicates the degradation of fiber. Of the several factors responsible for such a behavior, we presume that the chain scission of polymer network is a significant one over others and it is well pronounced here, leading to low molecular weight of the samples. This degradation is attributed to many changes in tensile properties of the polymer. Comparison of SEM photographs also confirms the X-ray results.     

The influence of thermal stabilization stage on the molecular structure of polyacrylonitrile fibers prior to the carbonization stage

Structural transformation from a linear chain structure to crosslinked chain structure, occuring during the thermal stabilization stage of carbon fiber manufacture, was followed through the use of infrared spectroscopy, differential scanning calorimetry (DSC), elemental analysis and gel-fraction measurements. The results obtained from the analysis of IR spectroscopy showed the gradual and continuous loss of intensity of the nitrile (C≡N) vibration at 2242 cm⁻¹ closely associated with the cyclization reactions whereas the intensity loss of the methylene (CH₂) groups vibration around 2920–2939 cm⁻¹ has been attributed to the loss of hydrogen atoms as part of the dehydrogenation reactions. The dehydrogenation index, evaluated using the absorbance ratio of A₁₄₅₂/A₁₃₆₈, also indicated the gradual loss of hydrogens in agreement with decreasing hydrogen content with progressing stabilization process. IR spectroscopy also showed the emergence of new absorption bands attributed to the formation of crosslinked ladder-like structure in the 1590–1600 cm⁻¹ region. The amount of newly formed crosslinked structure was characterized using DSC conversion index, IR conversion index and gel-fraction measurements. The results are compared and discussed in detail.     

Nanofibrillation of cotton fibers by disc refiner and its characterization

Nanofibrils of cellulose were prepared from short staple cotton by refining process using a lab disc refiner that exerts a combination of shear and frictional forces. The nanofibrils were characterized by scanning electron microscope (SEM), atomic force microscope (AFM), X-ray diffractometer (XRD) and Fourier transform infrared spectroscopy (FTIR). From SEM and AFM, it was found that starting average diameter of the cotton fiber (∼25 μm) was reduced to 242 nm after 30 passes of refining. FTIR analysis revealed the increase in amorphous nature of cotton cellulose due to refining process. Supportively, XRD analysis showed a steady decline in percent crystallinity of the cotton fibers as the cotton fibres were passed through the refiner for more number of passes. Similarly, degree of polymerization (DP) was reduced from 2720 to 740 due to the refining process. Nanofibrils of cellulose from short staple cotton have a huge potential for application in nanofilters and as biodegradable fillers in nanocomposites.     

Influences of organic-modified Fe-montmorillonite on structure, morphology and properties of polyacrylonitrile nanocomposite fibers

The Fe-montmorillonite (Fe-MMT) combined catalysis effects of Fe ion with barrier effects of silicate clays, was firstly synthesized by hydrothermal method, and then was modified by cetyltrimethyl ammonium bromide (CTAB). The organic-modified Fe-montmorillonite (Fe-OMT) was dispersed in the N, N-dimethyl formamide (DMF) and then compounded with polyacrylonitrile (PAN) solution which was dissolved in DMF. The composite solutions were electrospun to form PAN/Fe-OMT nanocomposite fibers. The influences of the Fe-OMT on the structure, morphology, thermal, flammability and mechanical properties of PAN nanocomposite fibers were respectively characterized by X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM), Scanning electron microscopy (SEM), Thermogravimetric analyses (TGA), Micro Combustion Calorimeter (MCC) and Electronic Single Yarn Strength Tester. It was found from XRD curves that there was not observable diffraction peak of silicate clay, indicating that the silicate clay layers were well dispersed within the PAN nanofibers. The HRTEM image indicated that the multilayer stacks of nanoclays could be found within the nanofibers and were aligned almost along the axis of the nanofibers. The SEM images showed that the diameters of nanocomposite fibers were decreased with the loading of the Fe-OMT. The TGA analyses revealed that the onset temperature of thermal degradation and charred residue at 700°C of PAN nanocomposite fibers were notably increased compared with the pure PAN nanofibers, contributing to the improved thermal stability properties. It was also observed from MCC analyses that the decreased peak of heat release rate (PHRR) of the PAN nanocomposite fibers reduced the flammability properties. The loadings of Fe-OMT increased the tensile strength of PAN nanocomposite fibers, but the elongation at break of PAN nanocomposite fibers was lower than that of the PAN nanofibers.     

Electrospinning and microwave absorption of polyaniline/polyacrylonitrile/multiwalled carbon nanotubes nanocomposite fibers

Electrical conductive nanocomposite fibers were prepared with polyaniline (PANI), polyacrylonitrile (PAN) and multi-walled carbon nanotubes (MWCNTs) via electrospinning. The morphology and electrical conductivity of the PANI/PAN/MWCNTs nanocomposite fibers were characterized by scanning electron microscope (SEM) and Van De Pauw method. Electrical conductivity of nanocomposite fibers increased from 1.79 S·m^?1 to 7.97 S·m^?1 with increasing the MWCNTs content from 3.0 wt% to 7.0 wt%. Compared with PANI/PAN membranes, the mechanical property of PANI/PAN/MWCNTs nanocomposites fiber membranes decreased. The microwave absorption performance of composite films was analyzed using waveguide tube, which indicated that with the thickness increasing the value of R_L reduced from ?4.6 to ?5.9 dB.