Stress relaxation and inverse stress relaxation in silk fibers

Stress‐relaxation experiments on four varieties of Indian silk fiber show that stress relaxation is significantly greater in non‐Mulberry silks than in the Mulberry silk and that the differences among non‐Mulberry silk fibers are relatively small. All the fibers studied also exhibit inverse stress relaxation. It has been shown that the Maxwell–Wiechert model, with two Maxwell elements in parallel, can be used to analyze and explain both the stress‐relaxation and inverse stress‐relaxation behaviors. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1147–1154, 2001     

Synthesis and characterization of some disulfonyl azides as potential crosslinking agents for textile fibers

The syntheses of 1,6‐hexanedisulfonyl azide, 1,10‐decanedisulfonyl azide, 1,3‐benzenedisulfonyl azide, 1,5‐naphthalenedisulfonyl azide, 2,6‐naphthalenedisulfonyl azide, and 4,4′‐biphenyldisulfonyl azide are described in this article. The compounds are characterized according to their melting temperature, infrared spectra, mass spectra, and carbon‐13 and proton nuclear magnetic resonance spectra, with the intention of assessing their potential as crosslinking agents for textile fibers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1092–1100, 2001     

Spectral dispersion curves of polymeric birefringent textile fibers

Optical Fourier transform (OFT) polarizing microscopy combined with variable‐wavelength interferometry (VAWI) was used for the determination of the spectral dispersion curves of birefringent textile fibers. We observed that the maximally bright circular fringe from the OFT technique corresponded to the anticoincidence case of the fiber fringe with the empty fringe from the VAWI technique and that the maximally dark fringe from the OFT technique corresponded to the coincidence case. With this combination of the two techniques, we identified the positions of the anticoincidence and coincidence when the VAWI technique was applied to overcome the difficulties of manually determining these positions. The intensity of the OFT patterns at the center was grabbed with a charge couple device camera and analyzed with a photodiode electrical circuit. The new observation was used for the determination of the spectral dispersion curves of the birefringence of polyethylene and aramide fibers. Microinterferograms are provided as illustrations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2481–2488, 2002     

Stress relaxation studies on wool fibers

Stress relaxation studies were made on single fibers of Lincoln, Chokla, and Merino wool in water in the temperature range 2–80°C. Differences in the viscoelasticity of the three wool types were related to differences in their fine structure and morphology. Of the three wools, Merino fibers have the lowest crystalline content and the poorest fibril orientation and packing. This results in greater viscoelastic effects in this wool. Stress relaxation studies have been made in the Hookean, yield, and postyield regions, and the molecular mechanisms of stress relaxation have been discussed.     

Dyeing of pet textile fibers and films in supercritical carbon dioxide

Polyethylene terephthalate (PET) textile fibers were dyed with a disperse dye in the presence of supercritical carbon dioxide at three temperatures of 333.2, 363.2 and 393.2 K and at pressures between 15 and 25MPa. The PET film was also dyed at 393.2 K. It was found that the dye uptake in the fiber increased 2–5 times when a small amount of acetone was added as a cosolvent. The equilibrium dye uptake increased with increasing pressure at all temperatures. At 393.2 K the pressure effect appeared to be much larger. It was explained with the shift of the glass transition temperature of the polymers at high pressures. These results may be useful in designing and developing the pollution-free supercritical dyeing technique, a potential alternative to the conventional dyeing of polyesters that produces a lot of wastewater.     

A comparative study of the stress‐relaxation behavior of untreated and alkali‐treated jute fibers

In this study, we examined the effect of alkali treatment and its variables, namely, the time (2, 4, 6, or 8 h) and the concentration of alkali (1, 5, or 17.5% w/w), on the linear density, strength, and stress‐relaxation properties of jute fiber. It was demonstrated that this kind of treatment led to the creation of several voids and fiber fibrillation. Properties were measured for the alkali‐treated and dewaxed fibers. The linear density and tenacity of the fibers were reduced at higher alkali concentration and at longer dipping times. The strength increased with treatment with mild alkali and decreased with treatment with the strong alkali. A very low alkali treatment (1%) rendered low relaxation. At a 5% alkali concentration, interfibrillar matrix softening also played an important role and was prominent in the stress‐relaxation behavior. The stress‐relaxation value was much higher in the fibers treated with 17.5% NaOH compared to the dewaxed fibers; this was probably due to a loss in the fibrillar arrangement. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

A flame retarded chitosan binder for insulating miscanthus/recycled textile fibers reinforced biocomposites

The main objective of this study is devoted to the development of new insulating and ignifuged miscanthus fibers (Mf)/recycled textile fibers (RTf) reinforced biocomposites (BCs) using chitosan as polysaccharide-based binder and aluminum trihydroxide (ATH) fillers while focusing on the fire behavior. To achieve this goal, a preliminary study was carried out on flame retarded chitosan-based films with various ATH-filler ratios (20, 33, 50, and 60 wt %). ATG and pyrolysis-combustion flow calorimeter analysis showed significant improvement of chitosan thermal behavior with the addition of 33 wt % and above of ATH. Mechanical properties of films were, however, degraded. Thereafter, different ratios of miscanthus/RTf reinforced BCs (fibers content up to 89.5–90 wt %) were elaborated through thermocompression process using neat chitosan and chitosan/ATH (67/33 wt %) as a binder. Mechanical, thermal, and fire behavior were evaluated. Higher mechanical properties were found for hybrid materials containing the association of both RTf and Mf in comparison to those containing only RTf or Mf. Fireproof BCs (E rating: according to the NF EN ISO 11925-2), with thermal conductivity values between 0.07 and 0.09 W m⁻¹ K⁻¹ and density range between 270 and 299 kg m⁻³ were successfully elaborated. The results of this study show a promising use of the chitosan/ATH system as flame retardant for biobased insulating building materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47306.     

Stress relaxation in carbon nanotube-based fibers for load-bearing applications

Carbon nanotube (CNT) based continuous fiber, a CNT assembly that could retain the superb properties of individual CNTs on a macroscopic scale, has emerged as a promising candidate for reinforcement in multifunctional composites. While existing research has extensively examined their short-term mechanical properties based upon quasi-static measurements, the long-term durability of CNT fibers has been largely neglected. Here we report time-dependent behavior of CNT fibers, with a particular focus on tensile stress relaxation. Both the pure CNT fiber and the CNT/epoxy composite fiber exhibited significant stress decay during the relaxation process, and this time-dependent behavior became more significant at a higher initial strain level, a lower strain rate and a greater gauge length. The present approach signifies a fundamental difference in the load-bearing characteristics between CNT fibers and traditional advanced fibers, which has major implications for the long-term durability of CNT fibers in load-bearing multifunctional applications.     

Penetration mechanics of textile structures: Influence of non-linear viscoelastic relaxation

A numerical simulation of ballistic impact and penetration on woven textile panels is described which can easily incorporate a wide variety of realistic constitutive and fracture models. The use of this model in assessing Viscoelastic relaxation effects is illustrated, and is further extended to include non-linear Viscoelastic effects. Since a variety of non-linear models is presently available and there is insufficient evidence to indicate the superiority of any single one in this instance, the Eyring non-linear model was chosen arbitrarily to indicate the ease with which these models may be implemented into the numerical treatment. The results obtained using the non-linear model are compared with comparable computer experiments using linear elastic and linear Viscoelastic models.     

Surface characterization of intact fibers by inverse gas chromatography

Inverse gas chromatography (IGC) was used to determine adsorption isotherms and isosteric heats of adsorption for several normal alkanes on a number of intact textile fibers and to determine the specific surface areas of these fibers. Surface areas obtained by IGC were in excellent agreement (except for cotton) with those calculated from the geometric dimensions of circular cross-section fibers and with those obtained by the adsorption of krypton. Heats of adsorption were found to be only slightly higher than the corresponding heats of liquefaction of the probes. The effect of fiber surface purity on adsorption behavior as well as computerized data reduction are briefly discussed.     

Dielectric relaxation studies in some Polymer-PZT composites

Composites of PZT with different polymeric compositions viz. Vinyl Acetate-Vinyl Chloride (VA-VC) co-polymer, Amide cured Epoxy (ACE), Nitrile Rubber-Poly Vnyl Chloride (NR-PVC) blend and piezoelectric poly Vinyledene Fluoride (PVDF) were prepared and the dielectric properties were studied. New dielectric relaxation peaks were observed in the VA-VC and PVDF containing composites owing to the interaction of the molecular motion of the polymer chains with PZT.     

Electrochemical formation of some conducting fibers

A study on the electrochemical grafting of polyaniline onto cotton, silk, and wool fibers was made. These insulating natural fibers became moderately conducting when they were subjected to electrical treatment in the polymerizing solution of aniline in aqueous HBF₄ medium. The weight gain of the fibers increased linearly and electrical resistance decreased with the time of electrolysis. The multiple cycled voltammograms of the solution of aniline in the aqueous solution of HBF₄ at the tip of conducting silk and wool fibers, which functioned as a microelectrode, were successfully recorded. The deep green polyaniline film was deposited on the fiber microelectrodes during electrolysis at +0.85 V vs. an Ag/Ag⁺ electrode. The IR spectra suggest the coordination between the polyaniline and fibers. © 1996 John Wiley & Sons, Inc.     

Photoinitiated surface grafting of synthetic fibers,IV. Applications of textile dyes onto surface-photografted synthetic fibers

High-strength polyethylene (HSPE), polypropylene (PP), poly(ethylene terephthalate) (PET), and poly(vinyl alcohol) (PVA) textile yarns have been surface-photografted with various functional monomers, such as acrylic acid (AA), acrylamide (AM), glycidyl acrylate (GA) and 4-vinyl pyridine (VP), by means of the continuous presoaking process developed. The dyeing of these surface-modified yarns with various textile dyes has been investigated. In general, considerable improvements of dyeability have been observed. The dye adsorption of the surface-photografted fibers is influenced by many factors, such as type of fiber, amount and properties of the functional monomer grafted on the surface of the fibers, type of textile dye, etc. The fibers surface-grafted with a monomer containing basic groups, such as acrylamide and 4-vinyl pyridine, are efficiently dyed with an acid dye. Conversely, a fiber surface-grafted with acidic functional monomer is easily dyed to deep shades with basic dyes. The dye adsorption increases monotonically with increasing grafting measured in ESCA spectra as relative intensities of relevant lines. The ungrafted HSPE, PP and PET fibers can be dyed to some extent with certain dyes. In the present work, the dye adsorption increased by 3.4 times for HSPE fiber grafted with GA and dyed with the metal complex dye IO, by 7.9 times for PP fiber grafted with AA and dyed with the basic dye MB, by 6.1 times for PET with AM and with the direct dye SL, and by about 15.3 times for PVA with VP and with the acid dye TE.     

Comparison of the surface energetics data of eucalypt fibers and some polymers obtained by contact angle and inverse gas chromatography methods

This study compares two approaches to determine the surface energy of solids, and its acid-base components in particular: inverse gas chromatography (IGC) and analysis of contact angle data using the Good-van Oss theory. The comparison is made in the context of wood fibers from Eucalyptus globulus and Eucalyptus regnans pulped by the kraft and neutral sulfite semi-chemical (NSSC) processes, and of selected polymers. Contact angles on wood fibers were measured using the Wilhelmy method and on polymer samples using the sessile drop technique. For the dispersive component of the surface energy, the level of agreement between the two approaches was reasonable, using alkanes for the IGC measurements and diiodomethane for the Wilhelmy and sessile drop techniques. However, agreement was poor for the acid and base characteristics when monopolar probes were used for IGC and water, formamide, and diiodomethane for contact angle measurements. The Good-van Oss approach suggested that all fibers and polymers are monopolarly basic, whereas IGC measurements suggested that they are bipolar. When new values were used for the acid and base components of the surface energy of the liquid probes based on the values for water proposed by Della Volpe and Siboni, all samples still appeared strongly basic. This is inconsistent with the chemical nature of the lignocellulosic fibers. Thus, the Good-van Oss approach provides a poor indication of acid-base properties of the surfaces of solids in suggesting that lignocellulosic fibers and polymers are strongly basic. The above issues as well as potential problems in measuring the surface energy of lignocellulosic fibers using the three-liquid procedure and the Good-van Oss approach are discussed.