Correlation between structure characteristics and adsorption properties of regenerated cellulose fibers

We correlate fine structure with the adsorption behavior of new (lyocell) and conventional (viscose, modal) regenerated cellulose fibers. We have studied the molecular structure, the fine structure and, most important of all, the amorphous regions and voids in the system. Differences in adsorption properties of all three-fiber types were determined by using several methods for quantification of water, dye and iodine adsorption. The structural analysis shows that higher molecular weight, a higher degree of crystallinity and a higher molecular orientation are found in lyocell fibers [1]. Our results obtained by several independent methods demonstrate clearly that the adsorption properties of cellulose fibers depend, with the exception of the portion and orientation of amorphous regions, predominantly on the void system (diameter, volume and inner surface of voids) [2]. Electronic Publication     

Thermal and mechanical properties of porous Y-PSZ/zircon composites

 The thermal and mechanical properties of sintered porous composites of yttria-partially-stabilized-zirconia (Y-PSZ) and zircon (ZrSiO₄) were investigated for a broad range of compositions. Fracture strengths of these composites were significantly improved with the zircon addition (0 to 50wt%). The addition of zircon also improved the thermal shock resistance. Specimens sintered at 1500^oC for 6 h with 15–20% porosity were shown to have superior strength and thermal shock resistance. These findings have been used in the manufacturing of ceramic permanent molds for brass casting. Received: 5 December 1997 / Accepted: 13 December 1997     

Reinforcement of ramie fibers on regenerated cellulose films

All-cellulose composite films reinforced with ramie fibers were prepared from aqueous NaOH–urea solvent system via a simple pathway. The structure and physical properties of the modified ramie fibers and composite films were characterized by scanning electron microscope (SEM), wide angle X-ray diffraction (WAXD), Fourier transform infrared spectrometer, ultraviolet–visible spectroscope, thermogravimetry, biodegradation tests and tensile tests. The results revealed that a good compatibility existed between the modified ramie fibers and cellulose matrix. The all-cellulose composite films exhibited high tensile strength, good optical transmittance, thermal stability, and biodegradability. The tensile strength and elastic modulus of the composite films increased with an increase of the ramie fibers. These high-strength biodegradable films prepared by a “green” pathway have potential applications as packaging materials and biomaterials.     

Effect of coupling treatment on mechanical properties of bacterial cellulose nanofibre-reinforced UPR ecocomposites

Bacterial cellulose nanofiber-reinforced unsaturated polyester resin composites (BC/UPR) were prepared using vinyl-triethoxy silane coupling modified BC fibres by the method of resin transfer molding (RTM) and subjected to mechanical tests in order to study the effect of surface treatment on the properties of composites. The results show that coupling treatment did not change the morphology of BC nanofibers, while it changed the chemical states of the BC fiber's surface. The XPS result indicates that chemical bonding was formed at the interface between UPR matrix and BC fibers after surface treatment, which enhanced the mechanical properties of composites. After treatment, tensile strength, flexure strength, shear strength and tensile modulus of the composites with a fiber volume fraction (V_f) of 10% were increased by 117.7%, 38.4%, 38.7% and 27.6%, respectively.     

Microstructure and mechanical properties of Y2O3/SiC nanocomposites

 Y₂O₃-based nanocomposites were fabriacted by hot-press and the microstructures and mechanical properties were investigated. Transmission-electron-microscope observations revealed that the SiC particles were distributed both within Y₂O₃ matrix grains and at the grain boundaries. Significant mechanical properties improvements were identified particularly at high temperatures above 1000 oC both in air and inert atmospheres. Received: 2 January 1997 / Accepted: 27 March 1997     

Effect of surface modification of bamboo cellulose fibers on mechanical properties of cellulose/epoxy composites

Bamboo cellulose fibers were treated with NaOH aqueous solution and silane coupling agent, respectively, before they were applied into epoxy composites. The effect of surface modification on mechanical properties was evaluated by tensile and impact tests under controlled conditions. Compared with the untreated cellulose filled epoxy composites, the NaOH solution treatment increased the tensile strength by 34% and elongation at break by 31%. While silane coupling agent treatment produced 71% enhancement in tensile strength and 53% increase in elongation at break. The scanning electron microscopy (SEM) was used to observe the surface feature of the cellulose fibers and the tensile fractures as well as cryo-fractures of the composites. The Fourier transform infrared (FTIR) was employed to analyze the chemical structure of the cellulose fibers before and after modifications. The results indicated different mechanisms for the two modifications of cellulose. The NaOH solution partly dissolved the lignin and amorphous cellulose, which resulting in splitting the fibers into smaller size. This led to easier permeating into the gaps of the fibers for epoxy resin (EP) oligmer and forming effective interfacial adhesion. Based on the emergence of Si–O–C and Si–O–Si on the cellulose surface, it was concluded that the enhancement of mechanical properties after coupling agent modification could be ascribed to the formation of chemical bonds between the cellulose and the epoxy coupled with the coupling agent.     

Molecular relaxations in the composites of liquid crystalline cellulose derivatives with poly(acrylic acid)

The molecular relaxation phenomena of the specific polymer composites obtained by photopolymerisation of the oriented lyotropic liquid-crystalline systems composed of cellulose derivatives dissolved in photopolymerisable acrylic acid are studied. We have investigated the composites based on two cellulose derivatives, which differ by the length of their side-chains and consequently by their physical properties. In this work, the molecular relaxations of such anisotropic composites were studied by dielectric relaxation spectroscopy and by thermooptical analysis. In the dielectric relaxation spectroscopy two representations were analysed: temperature dependences of dielectric loss ɛ"(T) and of electric modulus M "(T). The electric modulus representation is especially convenient to monitor the relaxations in a high temperature range where the ionic conductivity dominates the dielectric response. Received: 9 October 2000 / Reviewed and accepted: 10 October 2000     

Influence of the sampling area of the stem on the mechanical properties of hemp fibers

Natural fibers appear to be a promising alternative to glass fibers for the reinforcement of polymer matrix composites. However, the wide dispersion of their mechanical properties slows down their development.The aim of this study was to evaluate the influence of the sampling area of the stem on the mechanical properties of hemp fibers. Tensile tests were carried out on fibers extracted from the bottom, the middle, and the top of one stem. The results show there is only slight variations between the different areas: fibers from the middle exhibit higher tensile strength and ultimate elongation than top and bottom fibers, but there are no differences in terms of stiffness. A strong dependence of the fiber mechanical properties on their diameter is observed. This dependence induces more dispersion of the properties than the sampling area, thus it seems relevant to consider the whole stem to extract fibers, without defining distinct areas.     

Influence of fiber length on the mechanical properties of wood-fiber/polypropylene prepreg sheets

Natural fiber based composites have the potential to improve the mechanical properties of plastics while reducing the cost and weight. This study shows a practical method of blending natural-fiber with polypropylene to form a mat and then consolidated into a sheet by hot pressing. The natural fibers assessed were Pinus radiata and Eucalyptus regnan high temperature thermomechanical pulps and sisal (Agave sisalana) fibers. The tensile strength was shown to decrease with an increase in fiber content, while the tensile modulus was shown to increase. Tensile and flexural modulus were positively influenced by fiber length. The water performance tests of the sheets generally showed approximately 20% weight gain and approximately 3% thickness swell at 30% fiber content. The natural fiber surface chemical composition was determined by X-ray photoelectron spectroscopy and shown to be primarily covered with hydrophobic material such as lignin and extractives, while polypropylene was shown to be partially oxidized. Received: 18 September 2000 / Reviewed and accepted: 20 September 2000     

温度、炭纤维和硅土粉对轻量混凝土力学性能的影响

研究了温度、炭纤维和硅士粉含量对轻量混凝土力学性能的影响.制备了含硅土粉(质量分数0%和10%)及炭纤维(质量分数0%,0.5%,1%,和2%)的混合物,测定了高温(400℃,600℃和800℃)暴烤后轻理混凝土的压缩强度和弯曲强度.采用三个控制因素(硅土粉含量、炭纤维含量及处理温度),应用Taguchi法确定最佳条件并减少实验次数,采用方差(Anova)法确定主要实验参数与轻量混凝土力学性能的基准.结果表明:轻量混凝土力学性能最实效的参数是加热程度,而抗拉强度与抗弯强度的最佳参数各不相同.     

Preparation and properties of microfibrillated cellulose polyvinyl alcohol composite materials

This work reports the preparation of MFC–PVA composite films, and the thermal and mechanical properties of these films. Microfibrillated cellulose (MFC), which was separated from kraft pulp by a mechanical process, was used as the reinforcement in polyvinyl alcohol (PVA) matrix. This MFC reinforcement has an interconnected web-like structure with fibrils having a diameter in the range of 10–100 nm, as observed by TEM. MFC–PVA composite films were created by casting from a water suspension to produce a homogeneous dispersion of MFC in the polymer matrix. DMA shows an increase of the storage modulus in the glassy state with increasing MFC content, but a more significant increase in modulus is detectable above the glass transition temperature. There is a steady increase in both the modulus and strength of the composite films until a plateau is reached at 10 wt% MFC. The thermal stability of the PVA composite films is slightly increased with the addition of MFC.

As a result of this research, it has been shown that MFC is an excellent reinforcement comparable to cellulose nanowhiskers. Furthermore, by combining MFC with PVA in addition to good mechanical properties, this composite has good chemical resistance and biodegradability. The water soluble characteristics of PVA combined with a water dispersion of MFC are also easily processable.     

Influence of compatibilizing system on morphology,thermal and mechanical properties of high flow polypropylene reinforced with short hemp fibers

Simultaneous influence of polypropylene-graft-maleic anhydride (MAPP) and silane-treated hemp fibers (HF) on morphology, thermal and mechanical properties of high-flow polypropylene (PP) modified with poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) was studied in this paper. The addition of SEBS reduced the efficiency of MAPP in PP composites with HF, thus silane-treated fibers (HFs) were used to improve polymer–fiber interface. Thermal stability of HF was improved after silane treatment and less than 2% weight loss was observed at 240 °C in composites with 30 wt% HF. Better dispersion of fibers and better efficiency in enhancing static and dynamic mechanical properties of PP, doubling its strength and stiffness were observed in composites with treated fibers compared to untreated ones. High ability to absorb and dissipate energy and well-balanced strength and stiffness were showed by PP modified with SEBS and MAPP containing 30 wt% HFs. These composites were studied as an alternative to conventional PP/glass fibers composites for injection molding of small to medium auto parts.     

Fabrication and mechanical properties of Cu-coatedwoven carbon fibers reinforced aluminum alloy composite

Cu-coatedwoven carbon fibers/aluminum alloy composite (C_f/Al) was prepared by spark plasma sintering. Microstructure and mechanical properties of the composite were investigated. Microstructure observation indicates that the interface reaction is evidently inhibited by Cu coating. Woven carbon fibers are adhered to the matrix alloy by anchor locking effect of matrix alloy immersing into the interstices between carbon fibers. Under the quasi-static and dynamic compressive conditions, the composite exhibits excellent ductility even when the strain reaches 0.8. Adding carbon fibers into ZL205A alloy has no obvious influence on compressive flow stress of the composite. The compressive true stress–true strain curves show that the composite is a strain rate insensitive material. During the tensile tests, the elongation of the composite shows a sharp increase from 4.5% to 13.5% due to the adding of woven carbon fibers. Meanwhile, the tensile strength of the composite is increased slightly from 168 MPa to 202 MPa compared to that of ZL205A alloy. The good ductility of the composite is ascribed to the cracks deflection, fibers pulling out, debonding and breakage mechanisms.     

Influence of fiber content on mechanical,morphological and thermal properties of kenaf fibers reinforced poly(vinyl chloride)/thermoplastic polyurethane poly-blend composites

Kenaf (Hibiscus Cannabinus) bast fiber reinforced poly(vinyl chloride) (PVC)/thermoplastic polyurethane (TPU) poly-blend was prepared by melt mixing method using Haake Polydrive R600 internal mixer. The composites were prepared with different fiber content: 20%, 30% and 40% (by weight), with the processing parameters: 140 °C, 11 min, and 40 rpm for temperature, time and speed, respectively. After mixing, the composite was compressed using compressing molding machine. Mechanical properties (i.e. tensile properties, flexural properties, impact strength) were studied. Morphological properties of tensile fracture surface were studied using Scanning electron microscope (SEM). Thermal properties of the composites were studied using Thermogravimetric Analyses (TGA). PVC/TPU/KF composites have shown lower tensile strength and strain with increase in fiber content. Tensile modulus showed an increasing trend with increase in fiber content. Impact strength decreased with increase in fiber content; however, high impact strength was observed even with 40% fiber content (20.2 kJ/m²). Mean while; the 20% and 30% fiber contents showed higher impact strength of 34.9, 27.9 kJ/m²; respectively. SEM showed that there is poor fiber/matrix adhesion. Thermal degradation took place in three steps. In the first step, composites as well as the matrix had a similar stability. At the second step, matrix showed a slightly better stability than the composites. At the last step, composites showed a better stability than the matrix.     

石墨化温度对炭纤维微观结构及其力学性能的影响

以通用型PAN基炭纤维为原材料，通过1800℃～3000℃连续高温石墨化处理，制备了不同性能的炭(石墨)纤维；采用SEM、XRD、RAMAN、元素分析仪、万能材料测试机等分析手段研究了石墨化温度对炭(石墨)纤维微观结构、元素含量、表面形态及其力学性能的影响。实验表明：随着热处理温度的提高，炭纤维中非碳元素(氮、氢)的含量逐渐减少而碳元素质量分数却从92．62％增加到99．99％；纤维的微观结构也从二维乱层石墨结构向有序的三维层状结构发展，表现为石墨晶体层间距d。随处理温度的提升逐渐减小、d100和d110与La和Lc不断增大，纤维抗拉强度呈下降趋势、弹性模量呈上升趋势。     

Influence of reduced graphene oxide on mechanical behaviors of sodium carboxymethyl cellulose

Sodium carboxymethyl cellulose/reduced graphene oxide (NaCMC/rGO) nanocomposite films were prepared by a simple solution mixing-evaporation method. The NaCMC/rGO nanocomposite films were characterized and compared with sodium carboxymethyl cellulose/graphene oxide (NaCMC/GO) nanocomposite films. The stability of the rGO dispersion, and the structural and mechanical properties of the composite films were investigated by UV–Vis spectrophotometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and using a universal testing machine (UTM). The results revealed that CMC and rGO were able to form a homogenous mixture. Compared with pure CMC, the tensile strength and Young's modulus of the CMC/rGO nanocomposite films were considerably enhanced (by 72.52% and 131.79%, respectively) upon incorporation of 2 wt% rGO.     

高透明羧甲基纤维素/纤维素纤维复合薄膜的制备及其力学性能

针对传统电子器件衬底柔韧性差、不可生物降解的问题,研究了以羧甲基纤维素（CMC）和纤维素纤维为原料,结合抄纸和浸渍工艺,制备在柔性电子器件领域具有潜在应用的高透明CMC/纤维素纤维复合薄膜衬底。分别探究了CMC与北木纤维的配比和CMC分子量对薄膜透明度和力学性能的影响。研究了纤维素纤维的种类（北木、桉木、马尼拉麻和蔗渣纤维）对高透明CMC/纤维素纤维复合薄膜力学性能的影响。结果表明：CMC与北木纤维质量比为7∶3、CMC分子量为700 000时,所制备CMC/北木纤维复合薄膜的透明度为90%,拉伸强度约为111 MPa,耐折度达到2 526次。这种可生物降解、高柔韧性、高强度和高透明的CMC/纤维素纤维复合薄膜有望作为衬底用于构建下一代绿色、柔性电子器件,促进人类社会的可持续发展。     

Preparation and characterization of regenerated fiber from the aqueous solution of Bombyx mori cocoon silk fibroin

The regenerated silk fibers with high strength and high biodegradability were prepared from the aqueous solution of Bombyx mori silk fibroin from cocoons with wet spinning method. Although the tensile strength of the regenerated silk fibroin fiber, 210 MPa is still half of the strength of native silk fiber, the diameter of the fiber is about 100 μm which is suitable for monofilament of suture together with high biodegradability. The high concentration (30%, w/v) of the aqueous solution of the silk fibroin which corresponds to the high concentration in the middle silkgland of silkworm was obtained. This was performed by adjusting the pH of the aqueous solution to 10.4 which corresponds to pK_a value of the OH group of Tyr residues in the silk fibroin. The mixed solvent, methanol/acetic acid (7:3 in volume ratio) was used as coagulant solvent for preparing the regenerated fiber. The structural change of silk fibroin fiber by stretching was monitored with both ¹³C solid state NMR and X-ray diffraction methods, indicating that the high strength of the fiber is related with the long-range orientation of the silk fibroin chain with β-sheet structure.     

牵伸石墨化对石墨纤维结构和力学性能的影响

借助XRD和力学测试研究了不同石墨化温度下牵伸率（0％～2．5％）对PAN基石墨纤维结构和力学性能的影响。结果表明：在2400℃、2700℃和3000℃石墨化温度下，分别采用1．25％，1．50％和2．20％的牵伸率，可获得的抗拉强度最大值相应为3．1GPa、2．55GPa和2．25GPa。在相同的石墨化温度下与未牵伸的样品相比，抗拉强度提高了10％-20％。弹性模量亦随牵伸率的增大而增加，在牵伸率为2．50％时，弹性模量上升15％。同时，石墨微晶尺寸Lc（3．612nm～7．094nm）和La（12．909nm～24．400nm）及取向度逐渐增大，而d002，（0．3465nm～0．3418nm）逐渐减小。微观结构的改善是石墨纤维抗拉强度和弹性模量提高的主要原因。     

Characterization and mechanical properties of electrospun cellulose acetate/graphene oxide composite nanofibers

Graphene oxide incorporated cellulose acetate composite nanofibers were prepared via an electrospinning technique. The weight percentage of graphene oxide varied from 0.05 to 1.5 wt.% in the polymer solution. The morphologies and crystal structures of the resultant composite nanofibers were investigated by scanning electron microscopy and X-ray diffraction. The specific interaction was demonstrated by Fourier-transform infrared spectroscopy. Tensile test was performed to measure the mechanical properties of the prepared cellulose acetate/graphene oxide composite nanofibers. 1.5 wt.% cellulose acetate/graphene oxide composite nanofibers showed the highest tensile strength and Young's modulus.