Fiber Entanglement Research Articles

Effect of shape morphology on mechanical, rheological and tribological properties of polyoxymethylene/aramid composites

This paper highlighted the morphological effect of aramid, i.e. fibers and particles, on friction and wear properties of polyoxymethylene (POM)/aramid composites under dry frictional conditions. Meanwhile, the mechanical, rheological and crystalline properties were also studied as a function of filler content. Results showed that addition of aramid short fibers (ASF) and particles (AP) affected the frictional behavior of POM in two different ways due to distinguished packing structure in composites. The mechanical performance of aramid short fibers filled POM composite outweighed that of POM/AP composite because of quite well length retention of aramid fibers, however this kind of morphology appeared not helpful to the enhancement of wear resistance. Dynamic rheology analysis confirmed the existence of network structure of POM filled with aramid short fiber, which was consistent with SEM observation of the worn scar surfaces. Compared with aramid particles, the entanglement and overlap of aramid fibers made it hard to deform under the same frictional conditions and could not to protect the matrix effectively, thus led to poor wear resistance.

Anatomie de la symphyse pubienne

Pubic symphysis is an original joint, because its vertical fibro-cartilaginous disc, inserted between the two ‘endplates’ of pubic bones, is reminiscent of a vertebral disc. It must resist compression, tearing, and shearing stresses, and physiological vertical shift can reach 2 mm and rotation 1°. During pregnancy, relaxin induces the resorption of the edges of symphysis, leading to widening of the joint. Structural changes within the disc also increase its mobility. Rectus abdominalis, adductor longus and obliquus externus control those shifts, but the sites of insertions of those muscles around the symphysis are still disputed. The pattern of entanglement of collagen fibers within the disc has been poorly studied. The same hold true for the central cleft, which develops over time, as also observed in some vertebral discs. The biomechanics and motility of symphysis according to sex and anatomic variations should be further studied, as well as the inter-individual changes in joint innervations, to better explain the changing occurrences of pubalgia across the population, either in sports or pregnancy.

Thermal and photo reversible gel–sol transition of azobenzene based liquid crystalline organogel

Abstract Azobenzene based photoresponsive gelator, 1,2-bis[4-(4-(10-decyloxy)phenylazo)]-benzoylhydrazine showing selective gelation in alcoholic solvent is described. Whilst their thermodynamic behaviors are investigated by polarized optical microscopy and differential scanning calorimetry, the related layer arrangement is measured by X-ray diffraction techniques in which the organogel shows monotropic liquid crystalline phase. Present work shows that the non-liquid crystalline gelator can be converted into liquid crystalline organogel in the presence of alcoholic solvent in which the trans-cis isomerization of the azobenzene moiety disrupts the entanglement of gel fibers of self-assembly resulting in gel–sol transition. The present result also shows that the organogel is capable of the thermal and photo induced transition from gel–sol and vice versa.

Biodegradable mulch fabric by surface fibrillation and entanglement of plant fibers

We evaluated the feasibility of producing biodegradable mulch fabrics from bast fibers using a low-cost nonwoven fabric production process. Commercially available low-cost hemp and linseed flax fibers were carded, lightly needle-punched and then consolidated using a hydroentanglement process to produce fabrics around 200 g/m2 and 0.5 mm thickness. The hydroentanglement process liberated micro and nanofibers that formed a continuous fibrous network entangling and linking the parent fibers to produce fabrics with good tensile properties. Preliminary field trials of the fabrics demonstrate that they can be used to suppress weeds when colored with a commercially available carbon black-based mulch colorant. When in contact with soil the fabric biodegraded and lost strength in a matter of a few months.

Cellulose Nanocrystals vs. Cellulose Nanofibrils: A Comparative Study on Their Microstructures and Effects as Polymer Reinforcing Agents

Both cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) are nanoscale cellulose fibers that have shown reinforcing effects in polymer nanocomposites. CNCs and CNFs are different in shape, size and composition. This study systematically compared their morphologies, crystalline structure, dispersion properties in polyethylene oxide (PEO) matrix, interactions with matrix, and the resulting reinforcing effects on the matrix polymer. Transparent PEO/CNC and PEO/CNF nanocomposites comprising up to 10 wt % nanofibers were obtained via solution casting. Scanning electron microscopy (SEM), wide-angle X-ray diffraction (WXRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), dynamic mechanical analyzer (DMA), and tensile testing were used to examine the above-mentioned properties of nanocellulose fibers and composites. At the same nanocellulose concentration, CNFs led to higher strength and modulus than did CNCs due to CNFs' larger aspect ratio and fiber entanglement, but lower strain-at-failure because of their relatively large fiber agglomerates. The Halpin-Kardos and Ouali models were used to simulate the modulus of the composites and good agreements were found between the predicted and experimental values. This type of systematic comparative study can help to develop the criteria for selecting proper nanocellulose as a biobased nano-reinforcement material in polymer nanocomposites.

Laccase-Catalyzed Fiber Functionalization with Different Phenolic Compounds for Enhancing Pulp Strength

Chemo-enzymatic functionalization offers an innovative approach to produce paper and board products with enhanced performance. Unbleached softwood kraft pulps were functionalized by laccase with methyl syringate(MS), p-hydroxybenzoic acid(HBA), gallic acid(GA), and syringaldehyde(SyA). The wet strength of fibers treated with MS and SyA increased by 57.9% and 31.9%, respectively. The dry strength of fibers treated with HBA, GA, and SyA increased from about 64 N•m/g to 68 N•m/g. The opacity of MS-treated fibers was the highest, and the surface lignin coverage increased. The kappa number and surface lignin of HBA-treated fibers changed little; however, the total carboxyl group significantly increased. The participation of phenolic compounds enhanced the reactivity of fibers to laccase in varying degree. However, the reactivity of phenols to laccase did not show a direct relation to the paper strength. All treatments with phenols decreased the brightness and the curl index of fibers. The syringyl-type phenols with hydrophobic groups (OCH3) were shown to be effective for improving the pulp wet strength. The compounds with carboxyl groups enhanced the pulp dry-strength. The observed pulp strength improvement could be attributed to the formation of covalent bonding via radical coupling, the attachment of the functional group, increased bonding area, and fiber entanglement.

Analysis of Elastic Recovery Property Based on the Mesh Structure of Spun-Laced Nonwovens

By means of entanglement and consolidation, fibers form stable web in spun-laced nonwovens, it initially conceived fibers entanglement structure and analyzed morphological changes in the stress state, the result showed that the elastic recovery property of spun-laced nonwovens could be adjusted through the deformation resilience of water mesh and the elastic fiber itself. Meanwhile the mathematical model demonstrated the most common "u-shaped" entanglement method between fibers,so fiber I slip from the fiber Π which met the equation T1 = T0×e μ θ. Under the same water jet pressure condition, larger static friction coefficient (μ) or fiber coated Angle (θ) equals better fiber entanglement, more stable structure and better elasticity. Combining the actual production with ideal mesh model, the size relations of horizontal and longitudinal extension deformation about Δ L and Δ L' was discussed. The results showed that the elastic recovery property of nonwovens could be improved through changing fibers arrangement of the fiber web.

Impacts of Gin and Mill Cleaning on Medium-Long Staple Stripper-Harvested Cotton

The quality of upland cotton grown in the Texas Plains, which in good seasons constitutes nearly 40% of all U.S. cotton, has changed radically over the past decade. However, production practices, particularly pertaining to harvesting and ginning, remain largely unchanged, with a predominately stripper-harvested crop. Hence, the necessity to subject the lint to vigorous cleaning at the gin could adversely impact the use value of the cotton in high-value added applications more typically served by picker-harvested cotton. This research was conducted to provide a systemic analysis, combining perspectives from both the gin and the spinning mill, of the impacts of mechanical cleaning on the emerging stripper-harvested cotton with improved fiber properties that appear suitable for ring-spinning. Five cotton varieties grown over three seasons were processed through various sequences of gin and spinning mill cleaning processes. Analysis of the properties of individual fibers across the gin and spinning mill processing chain revealed significant interactions impacting fiber entanglements (neps), mean length, and short fiber content. Both neps and length distribution parameters appeared significantly impacted by fiber damage in both the ginning and spinning processes. However, the damage inflicted through both ginning and spinning may be a function of only fiber maturity. Mature cottons have lower fiber damage potential and appear to be less affected by the processes of lint cleaning and spinning preparation than immature cottons. The latter have higher fiber damage potential, which is reached even with minimal cleaning at the gin because if those immature fibers are preserved at the gin, they will ultimately break in spinning preparation.

A new t-PA releasing concept based on protein–protein displacement

A new tissue plasminogen activator (t-PA) releasing concept based on a unique protein-displacement triggering mechanism is reported. This concept takes advantage of the fact that plasminogen has higher affinity than t-PA for surface bound lysine. t-PA bound to lysine-modified materials through specific interactions is thus displaced from the surface (released) by plasminogen when in contact with plasma. The concept was investigated using a lysine-modified polyurethane (PU) material in the form of fibrous mats fabricated by electrospinning. The mats are of high surface area to volume ratio and are effectively porous due to fiber entanglement. They were successively modified with poly(2-hydroxyethyl methacrylate) (PHEMA) and lysine, such that the e-amino and carboxyl groups were free (e-lysine). These materials were shown to be significantly resistant to nonspecific protein adsorption and to take up large amounts of t-PA through specific interactions with lysine residues. The role of plasminogen-mediated displacement in t-PA release was fully confirmed, and efficient clot lysis by the t-PA loaded materials was demonstrated in an in vitro plasma assay. Release of t-PA by plasminogen displacement endows the t-PA-loaded materials with dual mechanisms for clot-lysis, i.e. by t-PA released from the material to generate plasmin in the fluid phase and by plasmin generated on the surface.

폴리믹스 혼입 고강도 콘크리트의 펌프압송 성상에 관한 실험적 연구

기존 내화성능 확보기술인 섬유혼입 콘크리트의 경우 내화성능을 높이기 위해 섬유량이 과다하게 투입되면 초고압 펌핑시 엉킴현상이 발생하여 압송효율이 급격히 저하되는 문제점이 있다. 이에 이 연구에서는 기존 섬유 이외에 추가로 유동성 개선효과 및 내화성능을 확보할 수 있는 폭렬방지재를 개발하여 이를 활용한 60~80 MPa 고강도 콘크리트의 펌프압송성능 개선을 이 연구의 목표로 설정하였다. 이 연구에서 사용된 폭렬방지재는 pp섬유, 나일론 섬유 및 폴리머 분말을 혼입한 폴리믹스로서 이를 활용한 결과는 다음과 같다. 섬유혼입 유무에 따른 굳지않은 특성 중 슬럼프 플로우는 섬유투입시 압송 후 기존 대비 약 70% 물성이 개선되었고, 공기량은 섬유혼입에 관계없이 압송 후 다소증가하였다. 압축강도는 재령 28일에서 설계기준강도를 상회하였고, 휨 강도는 압축강도 발현율 대비 12~15%로 기존 경향과 유사하게 나타났다. 탄성계수는 섬유혼입시 감소하였지만, 기준값 이상으로 문제는 없을 것으로 사료된다.

Impact of harvest aid timing and machine spindle harvesting on neps in upland cotton

Neps are fiber entanglements created during the mechanical processing of cotton and are often associated with immature fibers. Even in small amounts neps can affect textile quality and cotton marketability. Machine harvesting, lower fiber linear density (fineness), and more immature bolls at harvest are factors that contribute to neps. However, it is not clear whether differences in fiber linear density or immature bolls at harvest combine with harvest method to substantially affect neps. The aim of this study was to compare machine spindle and hand-harvested cotton collected from four field studies with treatments that differed in percentage of immature bolls and fiber linear density at harvest (resulting from differences in harvest aid timing) and to test for statistical interactions. By systematically varying the timing of harvest aids to cease crop growth, removing fruiting branches, or both, differences in the percentage of immature bolls and fiber linear density were generated. In all studies spindle harvesting increased neps, but there were no significant statistical interactions between the harvest method with harvest aid timing or branch removal treatments. When all measurements of neps were combined across studies there was a multiple regression that explained the level of neps with the harvest method and fiber linear density ( R2 = 0.66). These responses supported the individual season analyses, finding no statistical interaction of harvest method with either variable. Spindle harvesting increased neps by an average of 53 count/g compared to hand harvesting. Identifying reasons for differences in nep levels between cotton growing regions may assist in developing strategies to reduce neps.

Effect of Laundering Hydroentangled Cotton Nonwoven Fabrics

To study the effect of household machine laundering on hydroentangled cotton nonwoven developmental fabrics, several sets of such fabrics, uniformly made with cottons of different fiber quality characteristics, were sequentially laundered repeatedly for their performance evaluation after one washing and drying cycle (1 W), 5 W, 10 W, and 20 W, using a standard AATCC method for washing. The control greige fabrics (i.e., before any wash) and their respective versions after the 1 W, 5 W, 10 W and 20 W were examined for their physical and mechanical properties. The laundering results showed that the fabrics, even after 20 wash cycles, had held up unexpectedly well. Nonwovens generally are not considered wash-durable, and more than a third of nonwovens today are used in durable applications that necessarily do not require laundering since most nonwovens inherently are considered “disposable” after one end-use application. At any rate, all the researched fabrics, irrespective of their fiber quality origin, showed a significant drop in tensile strength, mainly after the first wash. The drop was more severe in the machine direction (MD) than in the cross direction (CD). To primarily investigate the cause of the declined fabric tensile strength due to washing, SEM images of the fabrics before and after the washing(s) were studied for any structural deformation. The SEM images clearly showed that the fabrics before the wash had symmetrical, almost uniformly spaced clusters of well-defined fiber entanglements (corresponding to the geometric locations of the orifices in the water jet-strip). After the first wash, those entanglements somewhat appeared to have been considerably “loosened,” disintegrated, and even lost. It seemed that the washing affected the fabric structure mostly in the (hydroentangling) MD. A possible reason for this phenomenon could be the fact that the cotton card used in preparing the native batt for hydroentanglement had aligned and stressed the fibers mostly in the machine direction. The subsequent crosslapping operation to some extent had been altered (randomized), and the fiber orientation in its web output was subjected to the hydroentangling, water jet forces that also stressed the fibers mostly in the MD. Upon washing the hydroentangled fabric in water, the stressed fibers, as expected, somewhat relaxed by releasing some of the stored mechanical energy that originally had held the fibrous structure together by creating strong inter-fiber cohesion or frictional or mechanical bonds. In other words, the washing basically loosened or broke up some of the “mechanical entanglements” and, consequently, their (MD) frictional bonds that had been created by the forceful water jets of the fabric formation process. Research has been planned to stabilize these mechanical bonds by means of special finishing, such as blending cotton with fusible/bonding fibers, resin finishing, and/or even layered fabric-film reinforced composites.

An Analysis on the Effect of Fiber Entanglement in the Hydroentangled Nonwovens and the Initial Research of Influencing Factor

The hydroentangled nonwovens have be widely used today. But the basic research of the hydroentangled nonwoven technology is relatively weak. It is not very clear so far that how the fibers are entangled with each other in the spunlaced nonwoven fabrics. In this paper, the pulling-out behavior of single fiber from hydroentangled nonwoven was first studied and analyzed the stress situation of the entanglement points in order to investigate the entanglement of the fibers in the hydroentangled nonwovens. It is found that the bigger of the pulling-out force, the more fibers are broken and the resultant hydroentangled nonwovens show better tensile property. So the pulling-out force can be used to weight the fiber entanglement effect in the hydroentangled nonwovens. Moreover, in this paper we also discover the fiber performance which can influence the fiber entanglement effect during the hydroentangled process by the cohesive of fibers, and the theory instruction will be provided to develop new fibers in the spunlaced process.

Impact of pulp rheological behavior on selective separation of Ni minerals from fibrous serpentine ores

Froth flotation based on selective separation of the Ni minerals from ores containing large amounts of fibrous serpentines (chrysotile) has been a long lasting challenge. One underlying reason has largely been considered to be slime-coating. The findings from this investigation, on the other hand, show that the pulp rheological behavior of the flotation pulp is the underlying basic reason. Flotation pulp (25% solids) appeared atypically viscous in the flotation tests carried out with copper ore containing either chrysotile or nylon fibers, where fibers (1–6% by wt fibers) were deliberately added in the grinding stage. With an increase in the pulp fiber (chrysotile and nylon) content, an increase in the pulp yield stress values and a corresponding decrease in the Copper recovery were observed. Notably, pulp was immovable when the copper ore contained more than either 6% of chrysotile or 2% of nylon fibers. Increase in the pulp yield stress values has been proposed to be due to the entanglement of fibers, further resulting in the formation of fiber networks in the pulp. The height, texture, and consistency of the froth phase were observed to be different with increases in the pulp yield stress values. Thus, the above findings evidently suggest that pulp rheological behavior plays a critical role in effective flotation beneficiation of ore containing fibrous minerals. Most importantly, at lower (∼2% by wt in ore) fiber concentrations a subtle change (e.g., increase in pulp yield stress) in rheological behavior may result, however, could possibly contribute to a decrease in the value mineral recovery.

Characterisation of the z-directional tensile strength of composite hydroentangled nonwovens

Composite nonwovens are fabrics consisting of two or more layers that are combined by cohesion, fusion or adhesion. The z-directional tensile strength (ZTS) of such fabrics is important in various applications, including wound dressings, absorbent hygiene products, roofing carrier fabrics, absorbent wipes, filter media and wall coverings. Whilst the determination of tensile strength in the x and y directions in composite nonwoven fabrics is readily undertaken, characterisation of the resistance to delamination can be challenging, particularly when there is intensive mechanical entanglement of the constituent fibres between the layers. In this paper, the BS ISO 15754 method for determining the ZTS of paper and board has been adapted to characterise the ZTS or tensile strength in the thickness direction, of nonwoven fabrics using a universal tensile tester. The adapted method was found to be suitable for the study of ZTS in a variety of nonwoven assemblies, including mechanically bonded composite nonwovens comprised of more than one layer. Application of the modified experimental method was demonstrated following the preparation of composite nonwoven fabrics comprised of polyethylene terephthalate (PET) and glass fibre layers, mechanically-integrated by hydroentanglement. A full-factorial experiment was completed in which the main effects and interactions of water jet pressure, conveyor speed, nozzle diameter and number of injectors on the ZTS were analysed. A four-way significant interaction was observed wherein water jet pressure and conveyor speed were empirically found to influence the ZTS of the composite nonwoven fabric. The average through-thickness location at which failure of the composite nonwoven fabric occurred was characterised by a gravimetric approach and was influenced by the total specific energy and ZTS of the fabric.

Characterisation of fibre entanglement in nonwoven fabrics based on knot theory

Owing to the structural complexity, the entanglement of fibres within nonwoven fabrics is generally characterised in indirect way by determining fabric mechanical properties using destructive testing and empirical modelling. Using elements of knot theory, a new approach is presented in this paper to characterise degree of entanglement in webs and nonwoven fabrics by topological representation of the fibrous assembly. The identification of fibre crossings followed by calculation of splitting number gives a numerical estimate of the degree of entanglement that can be potentially linked to the mechanical properties of the fibrous assembly.

Technique for internal channelling of hydroentangled nonwoven scaffolds to enhance cell penetration

An important requirement in thick, high-porosity scaffolds is to maximise cellular penetration into the interior and avoid necrosis during culture in vitro. Hitherto, reproducible control of the pore structure in nonwoven scaffolds has proved challenging. A new, channelled scaffold manufacturing process is reported based on water jet entanglement of fibres (hydroentangling) around filamentous template to form a coherent scaffold that is subsequently removed. Longitudinally-oriented channels were introduced within the scaffold in controlled proximity using 220 µm diameter cylindrical templates. In this case study, channelled scaffolds composed of poly(l-lactic acid) were manufactured and evaluated in vitro. Environmental scanning electron microscope and µCT (X-ray microtomography) confirmed channel openings in the scaffold cross-section before and after cell culture with human dermal fibroblasts up to 14 weeks. Histology at week 11 indicated that the channels promoted cell penetration and distribution within the scaffold interior. At week 14, cellular matrix deposition was evident in the internal channel walls and the entrances remained unoccluded by cellular matrix suggesting that diffusion conduits for mass transfer of nutrient to the scaffold interior could be maintained.

The role of structure in the nonlinear mechanics of cross-linked semiflexible polymer networks

The microstructural basis of the characteristic nonlinear mechanics of biopolymer networks remains unclear. We present a 3D network model of realistic, cross-linked semiflexible fibers to study strain-stiffening and the effect of fiber volume-occupancy. We identify two structural parameters, namely, network connectivity and fiber entanglements, that fully govern the nonlinear response from small to large strains. The results also reveal distinct deformation mechanisms at different length scales and, in particular, the contributions of heterogeneity at short length scales.

Using polymeric additives to enhance molecular gelation: impact of poly(acrylic acid) on pyridine-based gelators

The effect of polymeric additives on molecular gelation was explored using poly(acrylic acid) and pyridine-based gelators. A significant reduction in the critical gel concentration (cgc) and an increase in gel strength were observed when the polymer was present during gel formation. Detailed studies revealed that the polymer is adsorbing onto the growing fibers, reducing the growth rates, and leading to thinner fibers. These and other morphological changes lead to improved gel properties by increasing the number of fiber–fiber entanglements. Several other polymers were briefly examined and these studies revealed that polymer structure is important. The polymer containing a complementary functional group relative to the gelator (e.g., H-bond donor/acceptor) provided the lowest cgc.

Removal of hexavalent chromium from aqueous solution using polypyrrole-polyaniline nanofibers

Polypyrrole-polyaniline (PPy-PANI) nanofibers as adsorbent of Cr(VI) were prepared without template via coupling of propagating PPy+ and PANI+ free radicals by simultaneous polymerization of Py and ANI monomers in presence of FeCl3 oxidant. Inclusion of both polymeric moieties PPy and PANI in the fibers was confirmed by the Attenuated Total Reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Entanglement and nanostructure of the PPy-PANI fibers were confirmed by field-emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) respectively. Adsorption experiments were carried out in batch sorption mode to investigate the effect of pH, dose of adsorbent, contact time, concentration of Cr(VI) and temperature. The adsorption of Cr(VI) on the nanofibers surface was highly pH dependent and the kinetics of the adsorption followed the Pseudo-second-order model. The adsorption isotherm data fitted well to the Langmuir isothermal model. Thermodynamic parameters for the adsorption system were calculated and suggested that the adsorption process is spontaneous, endothermic and marked with an increase in randomness at the solid–liquid interface. The maximum adsorption capacity of the PPy-PANI nanofibers for Cr(VI) was 227mg/g. Selective adsorption of Cr(VI) from aqueous solution was achieved in the presence of other co-existing ions. The nanofibers retained the original sorption capacity in the first two adsorption–desorption cycles of operation. The Cr(VI) uptake was mainly governed by a physico-chemical process, which included ion-exchange followed by reduction of Cr(VI) by electron rich polymer nanofibers to form Cr(III).