Key Characteristics of a Novel Silk Yarn from Fresh Cocoons

We studied the key characteristics of a novel silk yarn reeled from fresh cocoons. Compared with traditional silk yarn, this novel silk yarn displayed better mechanical properties, especially in terms of a higher breaking stress and toughness, and exhibited a different surface morphology. A cross-sectional observation and the sericin content results illustrated that different sericin coatings on the silk yarn reeled from fresh cocoons surface did not improve the mechanical properties. The degumming and tensile testing analysis indicated that degummed silk fibroin of novel silk yarn is able to resist deformation and fracture better than silk fibroin of traditional silk yarn. The FTIR results revealed that the selected techniques is an important contributor to the silk fibroin mechanical properties, because novel technique brought higher percentage beta-sheet structures in novel silk yarn fibroin than traditional silk yarn. The new technique that using novel silk yarn has improved its mechanical properties and it is expected that the silk yarn with superior mechanical properties could be used in fabrics transistors, electrodes and reinforced biomaterials.     

Effect of sericin blending on molecular orientation of regenerated silk fiber

The use of regenerated silk fiber is limited due to its inferior mechanical properties in spite of high potential in a wide variety of applications. Many studies have been conducted in order to improve the mechanical properties of the regenerated silk materials, but no one has so far suggested an obvious solution. Meanwhile, some reports showed evidence that structural development of silk protein can be manipulated by physical interactions between silk fibroin (SF) and silk sericin (SS) during the regeneration process, especially in recrystallization process of SF. Such a hypothesis suggests a promising clue to enhance the mechanical properties of silk-based materials. Therefore, in this study, we tried to elucidate how SS can promote developing the molecular chain orientation of SF, resulting in an improvement of mechanical properties of regenerated silk fiber during spinning process. The tensile properties of the regenerated silk fiber were significantly improved compared to those of pure SF fiber when a proper amount of SS was blend with SF; both tenacity and breaking elongation increased by approximately 30 % and 70 % at three fold draw ratio, respectively. Quantitative analysis of X-ray diffraction and Herman’s orientation coefficient confirmed that such an improvement of tensile property was mainly caused by an increase of molecular orientation induced by sericin during the drawing process.     

Preparation and characterization of silk sericin/glycerol/graphene oxide nanocomposite film

Sericin (SS) is a protein that is secreted by silkworms, but it is usually discarded during the degumming process. To obtain and make use of the sericin, we prepared sericin/glycerol/graphene oxide nanocomposite film. The inherent brittleness of pure sericin film was improved by the addition of glycerol (Glc) as a plasticizer. To compensate for the reduced stiffness, we added graphene oxide (GO) into the SS/Glc film. At concentrations of up to 0.8 wt% relative to SS, GO dispersed evenly in the SS matrix without any agglomeration. The maximum tensile strength (9.5±0.7 MPa) and Young’s modulus (414.4±23.2 MPa) were obtained when the GO content was 0.8 wt% relative to SS. The elongation of SS/Glc/GO nanocomposite film also increased by approximately 40 % compared to SS/Glc film. The strong interfacial interaction between the SS and the GO was responsible for the increased stiffness. The increased elongation was due to the reduced crystallinity of the sericin matrix in the presence of GO.     

Characteristics of Electrical Heating Elements Coated with Graphene Nanocomposite on Polyester Fabric: Effect of Different Graphene Contents and Annealing Temperatures

This paper reports the fabrication of electrical heating elements based on the graphene/waterborne polyurethane (WPU) composite coated on polyester fabric with toughness like that of artificial leather. Samples were prepared with 0, 4, 8, and 16 wt% of graphene by using the knife edge method, and then, the samples were annealed from 100 oC to 160 °C. The graphene content had a large effect on the electrical and electrical heating properties. The surface resistivity was decreased by approximately 6 orders of magnitude with an increase from 0 wt% to 16 wt% graphene/WPU composite fabric. The electric heating properties were also improved, as indicated by the percolation threshold. Samples with various graphene contents were annealed, and it was found that the electrical and electrical heating properties were improved, and the most enhanced properties were obtained when the samples were annealed at 120 °C. The initial modulus and tensile strength were increased in comparison with those of 0 wt% and 16 wt% graphene/WPU composite coated on fabrics, but the elongation at break value was slightly decreased with an increasing graphene content. When the samples were annealed, initial modulus and tensile strength of samples were improved at 120 °C and 140 °C, and they were slightly decreased at 160 °C. However, the elongation at break showed an opposite tendency to the tensile strength. With the increase in content of graphene and annealing at 120 °C and 140 °C, the samples were more stiff and tough, and at 160 °C, the samples were softer. Therefore, graphene/WPU composite coated on polyester fabric by use of the annealing process may have applications in electrical heating elements due to its excellent heating performance and toughness like that of artificial leather.     

Effect of molecular weight and concentration on crystallinity and post drawing of wet spun silk fibroin fiber

Wet spun silk fibroin (SF) filaments have attracted considerable attention because of their potential in biotechnological applications including surgical sutures, tissue engineering and wound dressing. Although the molecular weight (MW) of polymers is one of key factors affecting the wet spinnability of dope along with the structural characteristics and properties of wet spun filament, no related study has been conducted. In this study, regenerated SFs with different MWs and concentrations were prepared by wet spinning. The effects of the SF concentration and MW on 1) wet spinnability and rheology of silk dope solution and 2) crystallinity index and post drawing performance of wet spun silk filament were examined. Their relationships were also investigated. The rheological measurements showed that an 80 mPa·s viscosity is needed to obtain a continuous wet spun SF filament. As the MW of SF increased, the peak position of the maximum draw ratio shifted to a lower SF concentration with a concomitant increase in the maximum draw ratio value at the peak. Interestingly, the crystallinity index obtained from Fourier transform infrared spectroscopy (FTIR) revealed a similar trend to the maximum draw ratio suggesting that the post drawing ability is strongly affected by the quantity of short-ordered crystalline regions in wet spun SF filaments. On the other hand, X-ray diffraction did not detect any crystallinity change in the SF filament produced from the formic acid solvent system. It was concluded that MW strongly affected the dope solution viscosity and the crystallinity index from FTIR and these determined the fiber formation of dope and post drawing performance of fiber.     

Properties and performance of polypyrrole (PPy)-coated silk fibers

Different silk substrates in form of spun silk tops, nonwoven web, yarn, and fabric were coated with electrically conducting doped polypyrrole (PPy) by in situ oxidative polymerization from an aqueous solution of pyrrole (Py) at room temperature using FeCl₃ as catalyst. PPy-coated silk materials were characterized by optical (OM) and scanning electron (SEM) microscopy, FT-IR spectroscopy, and thermal analysis (DSC, TG). OM and SEM showed that PPy completely coated the surface of individual silk fibers and that the polymerization process occurred only at the fiber surface and not in the bulk. Dendrite-like aggregates of PPy adhered to the fiber surface, with the exception of the sample first polymerized in the form of tops and then spun into yarn using conventional industrial machines. FT-IR (ATR mode) showed a mixed spectral pattern with bands typical of silk and PPy overlapping over the entire wavenumbers range. DSC and TG showed that PPy-coated silk fibers attained a significantly higher thermal stability owing to the protective effect of the PPy layer against thermal degradation. The mechanical properties of silk fibers remained unchanged upon polymerization of Py. The different PPy-coated silk materials displayed excellent electrical properties. After exposition to atmospheric oxygen for two years a residual conductivity of 10–20 % was recorded. The conductivity decreased sharply under the conditions of domestic washing with water, while it remained essentially unchanged upon dry cleaning. Abrasion tests caused a limited increase of resistance. PPy-coated silk tops were successfully spun into yarn either pure or in blend with untreated silk fibers. The resulting yarns maintained good electrical properties.     

Development of nanofibrous membranes with far-infrared radiation and their antimicrobial properties

This study investigated the incorporation of nanoscale germanium (Ge) and silicon dioxide (SiO₂) particles into poly(vinyl alcohol) (PVA) nanofibers with the aim of developing nanostructures with far-infrared radiation effects and antimicrobial properties for biomedical applications. Composite fibers containing Ge and SiO₂ were fabricated at various concentrations of Ge and/or SiO₂ using electrospinning and layered on polypropylene nonwoven. The morphological properties of the nanocomposite fibers were characterized using a field-emission scanning electron microscope and a transmission electron microscope. The far-infrared emissivity and emissive power of the nanocomposite fibers were examined in the wavelength range of 5-20 μm at 37 °C. The antibacterial properties were quantitatively assessed by measuring the bacterial reductions of Staphylococcus aureus, Klebsiella pneumoniae, and Escherichia coli. Multi-component composite fibers electrospun from 11 wt% PVA solutions containing 0.5 wt% Ge and 1 wt% SiO₂ nanoparticles exhibited a far-infrared emissivity of 0.891 and an emissive power of 3.44·102 W m^?2 with a web area density of 5.55 g m^?2. The same system exhibited a 99.9 % bacterial reduction against both Staphylococcus aureus and Escherichia coli, and showed a 34.8 % reduction of Klebsiella pneumoniae. These results demonstrate that PVA nanofibrous membranes containing Ge and SiO₂ have potential in medical and healthcare applications such as wound healing dressings, skin care masks, and medical textile products.     

Sericin-fixed filk fiber as an immobilization support of enzyme

In this study, we attempted to evaluate a novel use of sericin-fixed silk fiber (SFx) as an immobilization support of enzyme. Sericin was fixed on the silk fiber using glutaraldehyde as a fixation reagent. After 6 hours of fixation, the degree of fixation increases linearly with linear decrease of the amount of bound α-chymotrypsin (CT). This suggests that the increase of the degree of fixation is due to the further crosslinking of free aldehyde groups on the surface of sericin-fixed silk fiber (SFx). Even though perfect fixation was not achieved, sericin did not dissolve seriously and could be removed by further washing. The specific activity did not differ significantly after 6 hours of fixation. The activity of immobilized CT on SFx decreased to its half after 6 hours of incubation at 50°C. However, it retained 78% of initial activity even after 1 hour of treatment with 100% ethanol. As a result, the SFx could be used as an immobilization support of enzyme in non-aqueous media at ambient temperature.     

Influence of fibre contents on mechanical and thermal properties of roselle fibre reinforced polyurethane composites

The aim of this paper is to study the effect of fibre content on mechanical and morphological properties and thermal stability of roselle fibres (RFs) reinforced polyurethane (TPU) composites. The RF/TPU composites were prepared at difference fibre contents; 10, 20, 30, 40 and 50 wt% by melt mixed mixer and hot press at 170 °C. Mechanical (tensile, flexural and impact strength) and Thermogravimetric analysis (TGA) properties of RF/TPU composites were measured according to ASTM standard. Obtained results indicated that effect of fibre contents display improved tensile and flexural and impact strength properties. RF/TPU composites show the best mechanical and thermal properties at 40 wt% roselle fibre content. Scanning electron microscopy (SEM) micrograph of fractured tensile sample of the roselle composite revealed good fibre/matrix bonding. TGA showed that RF/TPU with difference fibre contents had improved thermal stability.     

Fabrication and characterization of mechano-modulated PET/BPU nanofibrous mats as potential vascular grafts materials

Polyethylene terephthalate (PET)/biomedical polyurethane (BPU) composite nanofibers with modulated mechanical properties are electrospun by varying the weight ratios of PET and BPU polymers in the mixture. The effect of BPU content on the morphology, porosity, thermal properties, and crystalline structures are systematically investigated. It is shown that uniform PET/BPU nanofibers can be formed through optimization. When the content of BPU is low (0?C7 %), better elongation of the nanofibrous mats is obtained with the increase of BPU content, whereas further increasing the BPU polymer (up to 15 %) results in a decreased breaking elongation as well as the mechanical strength of composites. The formed nanofibrous mats may find potential applications in tissue engineering and vascular graft.     

Application of electrospun silk fibroin nanofibers as an immobilization support of enzyme

Silk fibroin (SF) nanofibers were prepared by electrospinning and their application as an enzyme immobilization support was attempted. By varying the concentration of SF dope solution the diameter of SF nanofiber was controlled. The SF nanofiber web had high capacity of enzyme loading, which reached to 5.6 wt%. The activity of immobilizedα-chymotrypsin (CT) on SF nanofiber was 8 times higher than that on silk fiber and it increased as the fiber diameter decreased. Sample SF8 (ca. 205 nm fiber diameter) has excellent stability at 25°C by retaining more than 90 % of initial activity after 24 hours, while sample SF11 (ca. 320 nm fiber diameter) shows higher stability in ethanol, retaining more than 45% of initial activity. The formation of multipoint attachment between enzyme and support might increase the stability of enzyme. From these results, it is expected that the electrospun SF nanofibers can be used as an excellent support for enzyme immobilization.     

Polyester-based thermoplastic elastomer/MWNT composites: Rheological, thermal, and electrical properties

Polyester-based thermoplastic elastomer (Hytrel®) was melt-compounded with multi-walled nanotubes (MWNTs) using an internal mixer and the changes in the thermal, electrical and rheological properties were investigated using a range of nanotube contents (from 0.1 to 7 wt%). Even at nanotube concentrations as low as 0.1 wt%, the crystallization temperature was remarkably elevated by 15 °C and it increased further up to 22 °C with a 5 wt% loading. On the contrary, the melting temperature increased by 2 °C with 0.1 wt% MWNTs and it was slightly decreased by further additions of MWNTs. Electrical conductivity measured by the four probe method was detected from the 1 wt% MWNTs, indicative of electrical percolation. In addition, MWNTs starting from 4 wt% and above had no significant effect on the electrical conductivity, while it rapidly increased with nanotube contents below 4 wt%. Dynamic rheological properties were measured using a strain controlled rotational rheometer. The complex viscosity increased with MWNT contents giving an abrupt increase between 0.5 and 1 wt% loadings. In addition, the storage and loss modulus increased in a different manner depending on the range of the nanotube concentration. In the Cole-Cole plot, the slope of the nanocomposites decreased from 1.63 to 0.74 with increasing nanotube contents. In the Casson plot, the addition of MWNTs up to 0.5 wt% did not show any yield behavior giving an extremely low value for the yield stress, but further additions of nanotubes increased it notably. The presence of nanotubes in the elastomer increased the relaxation time with nanotube contents and their effect became weak as the frequency increased.     

施氮量对糯小麦和非糯小麦籽粒淀粉组分与理化特性的影响

为探明氮肥对小麦籽粒淀粉组分和理化特性的影响,采用田间试验,分析了4个施氮量(0、100、200、300kg·hm~(-2))对糯小麦(农大糯50222)和非糯小麦(轮选987)籽粒淀粉组分与理化特性的影响。结果表明,随施氮量的增加,小麦籽粒淀粉含量降低,轮选987籽粒中B型淀粉粒的数目占比增加,而农大糯50222籽粒的B型淀粉粒数目占比呈减少趋势;增施氮肥能显著提高小麦籽粒淀粉的峰值黏度和谷值黏度。相同施氮量处理下,轮选987淀粉的被测糊化特征参数(除谷值黏度外)均大于农大糯50222。施氮量不同,2个品种籽粒淀粉X-衍射图谱中各峰的位置和相对强度明显不同。随施氮量的增加,轮选987淀粉的相对结晶度增大,而农大糯50222淀粉的相对结晶度减小。相关分析表明,小麦籽粒的直链淀粉含量和直支比与最终黏度、稀澥值、反弹值、糊化温度和峰值时间呈显著正相关,与谷值黏度和相对结晶度呈显著负相关;支链淀粉含量反之。小麦籽粒的B型淀粉粒数目占比与峰值黏度、稀澥值呈显著负相关。综上所述,施氮量可影响小麦籽粒的淀粉含量和粒度分布,进而改变其糊化特性和晶体特征。     

Gelation Modification of Alginate Nonwoven Fabrics

Calcium alginate nonwoven fabrics were gelation-modified by two-stage with aqueous HCl solution and then ethanolic NaOH solution. The structure and crystallinity properties of the samples were characterized by FT-IR, SEM, and XRD. The preparation conditions and modification mechanism were investigated. The results indicated that the crystal structure of calcium alginate fibers was destroyed; the crystallinity and calcium ion content decreased after HCl treatment. This resulted from the formation of ester bonds among the hydrolytic molecules after NaOH treatment. The best gel performance was obtained at the HCl concentration of 0.05-0.1 wt% with the NaOH concentration in ethanol of 2–4 mol/l. The liquid absorption of nonwoven alginate fabrics increased by 145 %. The water capability increased by 2673 % after modification, while the thickness, mass per unit area, permeability, and tensile strength of nonwoven alginate fabrics changed little.     

Characterization of plant and animal based natural fibers reinforced polypropylene composites and their comparative study

Natural fibers are largely divided into two categories depending on their origin: plant based and animal based. Plant based natural jute fiber reinforced polypropylene (PP) matrix composites (20 wt% fiber) were fabricated by compression molding. Bending strength (BS), bending modulus (BM), tensile strength (TS), Young’s modulus (YM), and impact strength (IS) of the composites were found 44.2 MPa, 2200 MPa, 41.3 MPa, 750 MPa and 12 kJ/m², respectively. Animal based natural B. mori silk fiber reinforced polypropylene (PP) matrix composites (20 wt% fiber) were fabricated in the same way and the mechanical properties were compared over the silk based composites. TS, YM, BS, BM, IS of silk fiber reinforced polypropylene composites were found 55.6 MPa, 760 MPa, 57.1 MPa, 3320 MPa and 17 kJ/m² respectively. Degradation of composites in soil was measured upto twelve weeks. It was found that plant based jute fiber/PP composite losses its strength more than animal based silk fiber/PP composite for the same period of time. The comparative study makes it clear that mechanical properties of silk/PP composites are greater than those values of jute/PP composites. But jute/PP composites are more degradable than silk/PP composites i.e., silk/PP composites retain their strength for a longer period than jute/PP composites.     

Effect of coir fiber content and compatibilizer on the properties of unidirectional coir fiber/polypropylene composites

The main objective of this research was to study the effect of fiber content variation and stearic acid (SA) treatment on the fundamental properties of unidirectional coir fiber (CF) reinforced polypropylene (PP) composites. Several percentages of filler contents were used (10–40 wt %) in order to gain insights into the effect of filler content on the properties of the composites. Coir/PP composites were fabricated by compression molding, and the properties of composites were studied by physico-mechanical and thermal properties. The results from mechanical properties such as tensile strength (TS), tensile modulus (TM) and impact strength (IS) of the CF/PP composites were found to be increased with increasing fiber content, reached an optimum and thereafter decreased with further increase in fiber content. Treatment of the coir with SA as the coupling agent enhanced the mechanical properties, crystallization temperature and crystallinity of virgin PP and water desorption of the resulting composites, resulting from the improved adhesion between the CF and PP matrix. Scanning electron micrographs (SEM) of the tensile fractured samples showed improved adhesion between fiber and matrix upon treatment with SA. Interfacial shear strength (IFSS) of the composites was measured by single fiber fragmentation test (SFFT).     

Thermal and mechanical properties of environment-friendly ‘green’ plastics from stearic acid modified-soy protein isolate

Most plastics, at present, are petroleum-based and do not degrade over many decades under normal environmental conditions. As a result, efforts towards developing environment-friendly and biodegradable ‘green’ plastics for various commercial applications have gained significant momentum in recent years. Soy protein isolate (SPI)-based ‘green’ plastics have been shown to suffer from high moisture sensitivity and low strength. These properties have limited their use in most commercial applications. They are also difficult to process into sheets without any plasticizer. The commonly used plasticizer, glycerol, tends to leach out over time producing time-dependent properties, which is highly undesirable for commercial applications. The objectives of the current research are to reduce the moisture sensitivity and simultaneously improve the tensile properties of SPI by incorporation of stearic acid without affecting its biodegradability. The effect of stearic acid and glycerol on the tensile and thermal properties of SPI has been characterized using various techniques to determine the interaction mechanisms between stearic acid and soy protein. Mechanical properties were characterized using Instron tensile tester. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA) and X-ray diffraction (XRD) techniques have been used to determine the effects of stearic acid and glycerol on the surface chemistry, thermal transitions and thermal degradation of the stearic acid modified SPI plastic (resin). The tensile test results show that Young’s modulus increased on increasing the stearic acid content, reaching the maximum value at about 25% (by weight of SPI powder) stearic acid. Further increase in stearic acid content from 25 to 30% led to a reduction in Young’s modulus. The moisture content, fracture stress, strain, and energy at break decreased steadily on increasing the stearic acid from 0 to 30% for SPI containing 30% glycerol. At 25% stearic acid content, the modulus and the fracture stress increased significantly, whereas the fracture strain, energy at break and the moisture content decreased on reducing glycerol content. Scanning electron microscopy photomicrographs of fractured surfaces showed a layered structure for stearic acid modified-SPI resin. TGA measurements showed that the thermal degradation of stearic acid modified-SPI resin initiated at higher temperature than the SPI resin. DSC scans indicated that stearic acid modified-SPI resin had a small degree of crystallinity, which was confirmed by X-ray diffraction patterns. Modifying SPI resin with stearic acid has been successful in obtaining better tensile and thermal properties as well as reduced moisture sensitivity without any processing problems.     

Shape memory effects of polyurethane block copolymers cross-linked by celite

The shape memory polyurethane (PU) copolymers cross-linked by celite, a porous inorganic material with enormous surface area and hydroxyl groups on the surface, were prepared to see if the shape memory effect and the mechanical properties were improved. The PU copolymers with different celite contents were compared and characterized by IR, DSC, DMA, and UTM. The melting temperatures of PU soft segment were around 20 oC independent of celite content. The shape memory effect and mechanical properties were dependent on the celite content, and the celite addition into the reaction mixture should be made in the middle of polymerization to get the best shape memory and mechanical properties. The best mechanical properties were found at 0.2 wt% celite content and its shape retention rate went up to 98 %. The inclusion of celite as a cross-linker increased both shape memory effect and mechanical properties. The reasons underlining the improvements by adopting celite as a cross-linker are discussed in this paper.     

High water content silk protein-based hydrogels with tunable elasticity fabricated via a Ru(II) mediated photochemical cross-linking method

Silk is very promising in the field of biomaterials as a natural biomacromolecule. Silk protein can be made into various forms of materials, including hydrogels. However, silk protein-based hydrogels have not attracted much attention due to its weak mechanical properties. Here, we report high water content silk protein-based hydrogels with tunable elasticity which were fabricated through Ru(II) mediated photochemically cross-linking tyrosine residues in regenerated silk protein. The regenerated silk protein was characterized by Fourier transform infrared spectroscopy (FTIR). The gelation kinetics of the silk protein was studied by rheology measurements. The compressive mechanical properties of the silk protein-based hydrogels was investigated using compressive tests and dynamic mechanical analysis (DMA). Compressive modulus of the hydrogels reached 349±64 MPa at 15 % strain. The fabricated silk protein-based hydrogels were also characterized by Scanning electron microscopy (SEM), revealing an interconnected porous network structure, typical of hydrogels, with an average pore size of approximately 130 μm. Finally, biocompatibility of the silk protein-based hydrogels was demonstrated through cell culture studies using a human fibroblast cell line, HFL1. The reported silk protein-based hydrogels represent a promising candidate for biomaterial applications.     

Effect of oxidized alginate on its electrospinnability

The electrospinnability of alginate was improved by opening of uronate ring. The uronate rings were oxidized and opened by sodium periodate. The effects of the oxidant and the solution concentrations on the spinnability and the characteristics were studied. As the alginate was more oxidized, the solution viscosity was decreased and the finer and more uniform fibers were obtained. As a result of the ring opening and the degradation by oxidation, the crystallinity and the thermal stability of the electrospun oxidized alginate web were decreased.