Improvement of tensile properties of ramie yarns by applying a winding machine with heat treatment

A winding machine with heat treatment was newly developed to strengthen ramie yarns. During the treatment process, ramie yarn in normal or wet state was wound on a winding machine and passed continuously through a heater at 100 and 150°C, respectively, with different winding speeds and tensions. Higher tensile strength and stiffness of ramie yarn was achieved after heat treatment on wet yarn and winding speed had a significant influence on the tensile properties of yarns. However, a little decline in tensile strength was found for ramie yarns after heat treatment in normal state. This implies that the water‐swollened structure of ramie yarn during the heat treatment is crucial in strengthening yarns. In the case of heat treatment on wet yarns, the effect of winding tension on the tensile properties of yarns was studied. It was found that the tensile strengths and Young's moduli of ramie yarns first increased and then reached equilibrium as the winding tension was increased. The crystallinity calculated from X‐ray diffraction diagrams showed a slight decrease in heat‐treated ramie yarns whereas the crystalline orientation factors had no appreciable change. It was considered that the improved effect was related to the more oriented molecular chains in amorphous region and optimized yarn structure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of heat treatment on the structure and properties of Lyocell fibers

Lyocell fibers were heat‐treated under different conditions. The tensile strength and initial modulus of the heat‐treated Lyocell fibers increased sharply, whereas the elongation at break decreased. Moreover, applying tension to the fibers during the heat treatment further improved the tensile strength and initial modulus. In addition, the crystallinity of the heat‐treated fibers increased slightly, and there was no obvious change with an increase in the tension; the general orientation of the heat‐treated fibers increased, the crystalline orientation little changed, and the amorphous orientation improved. Also, the improved mechanical properties of the Lyocell fibers via the heat treatment could not be preserved for long. The reason may be that the crystalline structure of the Lyocell fibers was not destroyed and no new crystallites were formed during the heat‐treatment process. Therefore, the heat‐treated Lyocell fibers reverted to their original state with time because there was no crosslinking point to fix the orientation, although the cellulose molecules of the amorphous region of the Lyocell fibers were more oriented by the heat treatment with tension. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1738–1743, 2006     

Preparation of hyperbranch-structured polyester fiber via thiol-ene click reaction under UV light irradiation for asphalt binder modification

This study reports the application of UV induced “thiol-ene click reaction” by coupling the covalent bonds of venyl-terminated dendritic polyester (VTDP) and polyester (PET) fiber and resulting in the fabrication of hyperbranch-structured PET named as VTDP-PET fiber. The PET fiber or VTDP-PET fiber as additives were blended with styrene-butadiene-styrene modified asphalt (SBSMA) to prepare fiber/SBSMAs. Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectrometry, and X-ray photoelectron spectroscopy characterizations indicated that VTDP-PET fiber was linked with spherical three-dimensional dendritic molecular structure. Cone penetration, dynamic shear rheometer, multistress creep recovery, and thermogravimetric analysis tests showed that VTDP-PET/SBSMA exhibited enhanced resistance to flow, viscoelasticity, resistance against rutting, and thermal stability as compared to those of PET/SBSMA. The newly designed PET fiber and VTDP-PET fiber can be envisioned as effective alternative candidate for the fabricated of modified SBSMA with enhanced performances for practical applications in construction and highway industries.     

Insights into process–structure–property relationships of poly(ethylene terephthalate) industrial yarns by synchrotron radiation WAXD and SAXS

Synchrotron radiation wide angle X‐ray diffraction (WAXD) and small angle X‐ray scattering (SAXS) were performed to study the structures of four typical types of poly(ethylene terephthalate) (PET) industrial yarns. Three‐dimensional structural models of the yarns and comprehensive insights into the process–structure–property relationships were gained. High spinning speed, low draw ratio, and high heat‐setting temperatures lead to HMLS yarns with high crystallinity, high amorphous orientation, densely packed lamellar stacks, and a small tilting angle of crystalline lamellae. High draw ratio tends to result in PET industrial yarns with large long period and a large tilting angle of lamellae. Heat‐setting process has a significant influence on the amorphous orientation and crystalline structures, such as crystallinity, crystallite size, as well as crystal grain number. Compared with other structure characteristics, amorphous orientation plays a more important role in determining the tenacity, initial modulus, part load elongation, ultimate elongation, as well as shrinkage of PET industrial yarns. The crystal grain number seems to have an effect on the initial modulus, while the long period influences the elongation of the yarns to some extent. In addition, the small tilting angle of crystalline lamellae may relate to the dimensional stability of PET yarns. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42512.     

Lyocell fibers as the precursor of carbon fibers

In this work, Lyocell fibers, used as carbon fiber precursors, were investigated. Lyocell fibers used for the carbon precursors and the carbon fibers themselves were produced in our laboratory. The mechanical properties morphology and structure of the precursors and the obtained carbon fibers were studied and compared to those of rayon. The results show that Lyocell fibers have higher tenacity and modulus, and better thermal stability than rayon fibers. Scanning electron microscopy (SEM) experiments show that Lyocell precursors have round cross‐sections and fewer defects in the fibers, while rayon fiber has an oval cross‐section and many defects. Wide angle X‐ray diffraction (WAXD) results for the Lyocell precursors indicate that the degree of crystallinity of the Lyocell precursor is higher than that of a rayon precursor. They also show that Lyocell based carbon fibers have better mechanical properties than those that are rayon‐based. WAXD data of the obtained carbon fibers show that the crystallinity of Lyocell‐based carbon fiber is higher than that of rayon‐based carbon fiber. It is concluded that the Lyocell fibers are better precursors for carbon fibers than rayon. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1941–1947, 2003     

Uniaxial tensile properties of TiO2 coated single wool fibers by sol‐gel method: The effect of heat treatment

Single wool fibers were coated with TiO₂ by using the sol‐gel method. The uniaxial tensile properties of TiO₂ coated single wool fibers heated at different temperatures from 25 to 200°C were investigated and compared with those of uncoated single wool fibers. It was observed that the shape of the stress–strain curve of TiO₂ coated wool fibers became the same as uncoated wool fibers and showed a similar tendency of change to uncoated wool fibers with increasing temperature. But, the TiO₂ coated wool fibers obtained higher rigidity than uncoated wool fibers and up to their rupture points; they obtained higher stress levels in three deformation regions in the stress–strain curves, which indicates stronger wool fibers. Although the breaking extension of TiO₂ coated wool fibers decreased little by about 8%, the Young's modulus of TiO₂ coated wool fibers increased significantly by 19%, which was caused mostly by an increment in the stiffness of the cuticle layer of the wool fiber, and remained relatively higher than that of uncoated wool fibers after heat treatments. Structural changes in both uncoated and TiO₂ coated single wool fibers due to thermal effect, which caused the changes in the uniaxial tensile properties and the thermal behaviors of these fibers were discussed by using spectroscopic and thermal analysis methods in detail. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 898‐907, 2013     

Fundamental influences on quasistatic and cyclic material behavior of short glass fiber reinforced polyamide illustrated on microscopic scale

In this work, the influences of fiber orientation and weld lines on the morphological structures and the mechanical behavior of polyamide 6.6 (PA6.6‐GF35) are investigated. In quasistatic and fatigue tests tensile and 3‐point‐bending loads are applied. Test temperatures vary between RT and 150°C. Two different specimen types are produced by using injection moulding process to create different fiber orientations as well as weld lines. Fiber orientations are determined using computer tomography. Scanning electron microscopy is used to investigate fracture surfaces of tested specimens. Results show that mechanical properties and morphological structures depend highly on fiber orientation and temperature. Transversely oriented fibers in weld lines result in brittle failure mechanisms and decreased mechanical properties. Different stress distributions in the specimens under tensile and flexural loads have influence on the material behavior as well. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40842.     

Thermosetting bismaleimide resins generating covalent and multiple hydrogen bonds

Prepolymerizations of 4,4′‐bismaleimidodiphenylmethane (BMI), diallyl isocyanurate (DAIC), and melamine (ML) at 160–170°C and subsequent compression molding at 200–280°C yielded cured BMI/DAIC/ML resins with feed molar ratios of 4/1/1, 3/1/1, and 2/1/1 (BMI‐DAIC‐ML411, 311, and 211). Similarly, cured BMI/DAIC 1/1 and BMI/ML 3/1 resins (BMI‐DAIC11 and BMI‐ML31) were prepared. The FT‐IR analysis revealed that the maleimide and allyl groups were almost consumed for all the cured resins, and the hydrogen bonding interaction became stronger with decreasing BMI contents for BMI‐DAIC‐MLs. Based on the cured structures elucidated from the FT‐IR result, the numbers of multiple hydrogen bonds and cross‐linking covalent bonds (N_MHB and N_CB), and total cross‐linking bond energy (E_TB) were evaluated to be 0, 7.92, and 618 for BMI‐DAIC‐ML411, 0.71, 7.81, and 627 for BMI‐DAIC‐ML311, and 0.95 mol kg^?1, 7.61 mol kg^?1, and 617 kcal kg^?1 for BMI‐DAIC‐ML211, respectively. A higher order of glass transition and 5% weight loss temperatures for BMI‐DAIC‐MLs was 411 > 311 > 211 in accordance with a higher order of N_CB. BMI‐DAIC‐MLs displayed a weak tan δ peak at 70–150°C due to dissociation of the hydrogen bonds. The flexural strength and modulus of BMI‐DAIC‐ML311 were higher than those of BMI‐DAIC‐ML411 in accordance with the difference of E_TB. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43121.     

Properties of cotton fabrics treated by protease and its multienzyme combinations

A commercial serine‐type protease preparation (Alcalase) was examined as a scouring agent for cotton fabrics. Application of the enzyme induced moderate changes in the composition of fibers that were mainly associated with the removal of protein and waxes. The relationship between the compositional modifications and structural transformations, which were reflected in the crystallinity index of the bioscoured cotton fibers, was demonstrated. The protease‐treated textiles displayed superior whiteness and outstanding compressional resilience but exhibited a poor hydrophilicity and dyeing capacity. One‐step scouring at neutral conditions, where proteolytic activity was supported by multienzyme combinations, could generate textiles with sufficient water absorbency and advanced performance. The implementation of the appropriate scouring conditions (concentration and combination of enzymes) could form fabrics with the desired physicochemical and micromechanical properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of high-performance deproteinized natural rubber/chitosan composite films via a green and sulfur-free method

To solve the environment and health issues arose from the sulfur vulcanization, a facile and completely eco-friendly method of latex-assembly and in situ cross-linking is developed to prepare fully bio-based and high-performance rubber films. The films are featured by a “reinforced concrete” structure composed of dynamically cross-linked chitosan framework and unvulcanized deproteinized natural rubber (DPNR) matrix. The self-assembly of DPNR latex particles and chitosan, as well as the in situ cross-linking of chitosan in the film forming process are confirmed by transmission electron microscope and dynamic light scattering. As green rubbers without vulcanization, the as-designed composite films possess excellent mechanic properties comparable to those of the sulfur vulcanized DPNR film, whose tensile strength and toughness reach 15.2 MPa and 77.6 MJ m⁻³ respectively. Moreover, the films exhibited appropriate permeability to moisture and achievable reprocessing, which have potential applications in wearable devices.     

Use of a bis(aminoalkyl)-calix[4]arene derivative as cross-linking agent to enhance functional and mechanical properties of a maleated polypropylene

An isotactic polypropylene grafted by 1 wt% of maleic anhydride (iPP-g-MAH) was chemically modified to provide it with new functional abilities and improved mechanical properties. The specific additive considered in this work is a derivative of bis(aminoalkyl)-calix[4]arene. Not only this molecule serves as a cross-linking agent, but it offers grafting sites for metallic ions that confer electrolytic conductivity to the initially insulating polyolefin. Materials were synthesized by reactive extrusion, and subsequently manufactured as plates by injection molding. The three-dimensional macromolecular architecture was optimized by adjusting the NH₂:MAH molar ratio in a range from 0.5:1 to 1:1. Fourier transform infrared spectroscopy revealed the amine/ anhydride chemical reactions, while gel content measurements were used to determine the degree of cross-linking. The crystalline microstructure of the different materials was characterized by two complementary methods: (a) overall crystallinity by differential scanning calorimetry; (b) lamellar thickness by thermal fractionation using the self-successive auto-nucleation procedure. Only a small decrease of the crystalline lamellae is observed. The mechanical properties were determined by a video-controlled tensile testing method and by Brillouin spectroscopy. A transition from brittle to ductile behavior was observed for increasing cross-links density. Scanning electron microscopy on fracture surfaces showed that ductile fracture was favored by the development of fibrils.     

Supramolecular thermoplastic elastomer with thermally scratch repairable effect from 3‐amino‐1,2,4‐triazole crosslinked maleated polyethylene‐octene elastomer/nylon 12 blends

In this study, nylon 12 (5–25 wt %) was melt blended with a supramolecular thermally repairable thermoplastic elastomer (ATA‐POE), which was generated by crosslinking of maleated polyethylene‐octene elastomer (mPOE) with 3‐amino‐1,2,4‐triazole (ATA), in an internal mixer. The effect of nylon 12 content on the phase morphology, thermomechanical properties, and thermally triggered scratch repairing effects of the ATA‐POE/nylon 12 blends was investigated. Scanning electron microscopy results showed that nylon 12 formed a dispersed phase with submicron scale in a continuous ATA‐POE phase. Fourier transform infrared spectroscopy and differential scanning calorimetry analysis revealed that there are extensive hydrogen bonding interactions between the ATA‐POE and nylon 12 in the blends, which was manifested by a decrease in the melting temperature of each polymer component. Tensile and dynamic mechanical test showed that tensile modulus increased with increasing nylon 12 contents in the blend with maintaining fairly high elastic recoverability. Furthermore, the blends containing up to 20 wt % of nylon 12 showed good scratch repairing effects when they are heated above melting temperature of the ATA‐POE phase in the blend. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41511.     

Mechanical and scratch behaviors of polyrotaxane-modified poly(methyl methacrylate)

The mechanical and scratch behaviors of polyrotaxane (PR) modified poly(methyl methacrylate) (PMMA) were investigated. PR is a necklace-like supramolecule with rings threaded onto a linear backbone chain that is capped by bulky end groups. Cyclodextrin (CD) serves as the ring structure and can be functionalized to induce specific interactions with the hosting polymer matrix. To systematically investigate the effect of CD functionalization on the mechanical properties of PMMA, PR with polycaprolactone (PCL) grafted chains on CD, and PR with methacrylate functional groups at the terminal of the PCL grafted chains on CD were chosen for this study. Tensile and compressive true stress–strain tests, ASTM scratch test, and coefficient of friction measurements were conducted to fundamentally understand how PR influences the mechanical and scratch behaviors of PMMA. Additionally, dielectric relaxation spectroscopy and dynamic mechanical analysis were conducted to explore how PR influences the relaxation dynamics of PMMA. The above findings suggest that the methacrylate functional group on PR induces favorable molecular interactions with PMMA matrix, leading to enhanced molecular cooperativity during deformation, which in turn improves tensile and compressive properties and achieves greatly improved scratch resistance.     

Solvent‐induced modifications in polyester yarns. I. Mechanical properties

The mechanical properties of polyester (PET) yarns, fine filament, and microdenier (original and heat‐set), treated with a trichloroacetic acid–chloroform (TCAC) mixture were investigated. The treatments were carried out in an unstrained state with various concentrations of the TCAC reagent at room temperature. The TCAC treatment on PET yarns resulted in notable changes in the tensile behavior. The TCAC‐treated yarns exhibited higher extensibility and work of rupture without much loss in strength. The improvement in elongation was less in the case of heat‐set polyester yarns due to solvent treatment. The depression of the glass transition temperature (T_g) of TCAC‐treated PET yarns, even at the minimum concentration, showed its effectiveness to plasticize the fibers and the closeness of the solubility parameter of TCAC and PET. The T_g depression favors molecular relaxation, which has resulted in a higher shrinkage percentage of TCAC‐treated PET yarns and the effective shrinkage was reached more easily for the original fine‐filament polyester (FFP) and microdenier polyester (MDP) yarns at the lowest concentration. The effects of the concentration of TCAC on the strength, elongation, yield behavior, and work of rupture on PET were also investigated. A significant plastic flow was observed in the TCAC‐treated yarns. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1500–1510, 2003     

Strengthening,toughening, and self-healing for carbon fiber/epoxy composites based on PPESK electrospun coaxial nanofibers

A carbon fiber/epoxy composite modified by electrospun coaxial dicyclopentadiene/poly(phthalazinone ether sulfone ketone) (DCPD/PPESK) nanofibers was successfully fabricated, and the addition of DCPD/PPESK fibrous membranes made the composite have remarkable self-healing ability, and meanwhile effectively improve its mechanical properties. Results of polarization microscope observation and thermogravimetric analysis confirmed liquid DCPD as the healing agent was encapsulated into the PPESK coaxial nanofiber. Three-point bending test was utilized to evaluate the mechanical properties and self-healing effect of the composite. Experimental results indicated that the embedded nanofibers significantly improved the toughness of the composite, and maintained good mechanical properties even at low resin content. Most importantly, the flexural strength of the composite recovered to close to 90% observed 2 h after the bending failure.     

Radiation effect on the thermal conductivity and diffusivity of ramie fibers in a range of low temperatures by γ rays

To understand the influence on the thermal conductivity by the length of the molecular chain in the polymer fiber, the thermal conductivity and thermal diffusivity of ramie fibers and those irradiated by γ rays, which induced molecular chain scission of cellulose, were investigated in a range of low temperatures. The degrees of polymerization, crystallinities, and orientation angles of ramie fibers and those irradiated by γ rays (γ‐ray treatment) were measured by the solution viscosity method, solid‐state NMR, and X‐ray diffraction. Only the degree of polymerization decreased with the γ‐ray treatment, and the crystallinities and orientation angles were almost independent of the γ‐ray treatment. The thermal conductivities of the ramie fibers with and without γ‐ray treatments decreased with decreasing temperature. The thermal diffusivities of the ramie fibers and those irradiated by γ rays were almost constant from 250 to 100 K, increased slightly with the temperature decreasing from 100 to 50 K, and increased rapidly with the temperature decreasing below 50 K. The thermal conductivity and thermal diffusivity of the ramie fibers decreased with the γ‐ray treatment. The mean free path of the phonon in the ramie fibers was reduced by the γ‐ray treatment. This decrease of the thermal diffusivity and thermal conductivity was explained by the reduction of the mean free path of the phonon by molecular chain scission with γ rays. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 5007–5018, 2006     

Investigation on jet stability,fiber diameter,and tensile properties of electrospun polyacrylonitrile nanofibrous yarns

Electrospinning is a flexible and efficient method for producing nanofibers by using relatively dilute polymer solution. However, there are many parameters related to material and processing that influence the morphology and property of the nanofibers. This study investigates the influence of electric field and flow rate on diameter and tensile properties of nanofibers produced using polyacrylonitrile (PAN)‐dimethylformamide (DMF) solution. Stability of the spinning jet is investigated via fiber current measurement and an image system at different electric fields and solution flow rates. It is observed that a set of electric field and flow rate conditions favor producing thinnest, strongest, and toughest nanofibers during electrospinning process. Other conditions may lead to instability of the Taylor cone, discontinuous jet, larger diameter fiber, and lower mechanical properties. Finally, a simple dynamic whipping model is adopted to correlate the nanofiber diameter with volumetric charge density and is found to be excellent validating our experimental results. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41918.     

Surface modification of UHMWPE fibers by means of polyethylene wax grafted maleic anhydride treatment

A novel surface modification method for ultrahigh molecular weight polyethylene (UHMWPE) fibers to improve the adhesion with epoxy matrix was demonstrated. Polyethylene wax grafted maleic anhydride (PEW‐g‐MAH) was deposited on the UHMWPE fibers surface by coating method. The changes of surface chemical composition, crystalline structure, mechanical properties of fiber and composite, wettability, surface topography of fibers and adhesion between fiber and epoxy resin before and after finishing were studied, respectively. The Fourier transform infrared spectroscopy spectra proved that some polar groups (MAH) were introduced onto the fiber surface after finishing. The X‐ray diffraction spectra indicated that crystallinity of the fiber was the same before and after finishing. Tensile testing results showed that mechanical properties of the fiber did not change significantly and the tensile strength of 9 wt % PEW‐g‐MAH treated fiber reinforced composite showed about 10.75% enhancement. The water contact angle of the fibers decreased after finishing. A single‐fiber pull out test was applied to evaluate the adhesion of UHMWPE fibers with the epoxy matrix. After treatment with 9 wt % PEW‐g‐MAH, a pull‐out force of 1.304 MPa which is 53.59% higher than that of pristine UNMWPE fibers was achieved. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46555.     

Influence of fiber treatment on the performance of sisal–polypropylene composites

This article concerns the effectiveness of MAPP as a coupling agent in sisal–polypropylene composites. The fiber loading, MAPP concentration, and fiber treatment time influenced the mechanical properties of the composites. It was observed that the composites prepared at 21 volume percent of fibers with 1% MAPP concentration exhibits optimum mechanical strength. SEM investigations confirmed that the increase in properties is caused by improved fiber‐matrix adhesion. The viscoelastic properties of the treated and untreated composites were also studied. From the storage modulus versus temperature plots, an increase in the magnitude of the peaks was observed with the addition of MAPP and fiber reinforcement, thus showing an improvement in stiffness of the treated composites. The damping properties of the composites, however, decreased with the addition of the fibers and MAPP. The thermal properties of the composites were analyzed through DSC and TGA measurements. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1336–1345, 2004     

Molecular modeling approach to the prediction of mechanical properties of silica‐reinforced rubbers

Recently, we have suggested a nanomechanical model for dissipative loss in filled elastomer networks in the context of the Payne effect. The mechanism is based on a total interfiller particle force exhibiting an intermittent loop, due to the combination of short‐range repulsion and dispersion forces with a long‐range elastic attraction. The sum of these forces leads, under external strain, to a spontaneous instability of “bonds” between the aggregates in a filler network and attendant energy dissipation. Here, we use molecular dynamics simulations to obtain chemically realistic forces between surface modified silica particles. The latter are combined with the above model to estimate the loss modulus and the low strain storage modulus in elastomers containing the aforementioned filler‐compatibilizer systems. The model is compared to experimental dynamic moduli of silica filled rubbers. We find good agreement between the model predictions and the experiments as function of the compatibilizer's molecular structure and its bulk concentration. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40806.