Research progress on chemical modification of silk fibroin and its applications北大核心CSCD

Mulberry silk is composed of the two major parts of two triangle-like silk fibroin fibers and sericin covering the fibers and a few lipids. After removing the sericin on the raw silk what is left is the silk fibroin fiber. Silk fibroin is the main part of silk accounting for about 75% of the total weight. Silk fibroin contains 18 natural amino acids such as glycine Gly alanine Ala serine Ser serine aspartic acid Asp and tyrosine Tyr . The secondary structure of silk fibroin has three main conformations α-helix β-fold and random coil. Under certain conditions the three conformations can transform into each other and change the mechanical properties of the silk fibroin material. Silk fibroin extracted from silk fiber is a natural polymer with biocompatibility and biodegradability. It can be further processed into different forms of materials nanoparticles films hydrogels sponges etc. It has been applied in many fields such as biomedicine and cosmetics. In order to meet the needs of different fields researchers have conducted further chemical modification treatment based on the original excellent properties of silk fibroin. Meanwhile the active groups on various amino acid residues in silk fibroin also provide chemical reaction sites for the chemical modification of silk fibroin. The chemical modification methods of silk fibroin mainly include amino acid residue modification macromolecular grafting modification and crosslinking reaction modification. Among them amino acid residue modification can modify protein amino acid residues by chemical reagents and some groups can be introduced into the side chains of silk fibroin macromolecules. Grafting modification of silk fibroin macromolecules is one of the main means to bind functional compounds to silk fibroin macromolecular chains. The properties of grafted silk fibroin are affected by the type and grafting rate of the grafts. The chemical crosslinking reaction modification of silk fibroin macromolecules is to make the macromolecular chains connected by covalent bonds and form a network structure by means of crosslinking agents enzymes or ultraviolet irradiation. The cross-linking reaction can not only form covalent bonds within and between the molecular chains of silk fibroin thus changing its structural properties and improving its stability but be used to form covalent bonds with other polymers. At present the chemical modification of silk fibroin is mainly applied in the fields of silk textiles biomedicine and environmental science. In the field of silk textiles graft copolymerization modification of vinyl and other monomers crosslinking agent modification and other methods are used to overcome the shortcomings of silk like being easy to wrinkle. The graft modified monomers mainly include ethylene methacrylate and methylacrylamide. The active groups on crosslinking agents such as polycarboxylic acid / anhydride and epoxide are covalently combined with carboxyl hydroxyl and amino groups on macromolecules of silk fibroin to improve the wrinkle resistance of silk fabrics. In the field of biomedicine silk fibroin materials with appropriate chemical modification have better biological activity drug delivery ability antimicrobial properties and mechanical properties. The optimization of these properties enables silk fibroin materials to show great potential in drug control delivery tissue regeneration and wound repair. The applied research in the field of environmental science mainly focuses on the adsorption separation and catalysis of impurities in water. Therefore the modification of amino acid residues grafting and cross-linking of protein macromolecules can change some important properties of silk fibroin and meet the requirements of various applications and functionalization of silk fibroin. In many fields of chemical modification and application of silk fibroin protein fruitful results have been achieved which has laid a good foundation for the further development of related fields and also shows that the chemical modification of silk fibroin material has great potential and application prospects. However there are still some problems that need to be overcome and further improved in the current chemical modification methods such as mild modification conditions and accurate adjustment of the degree of modification which will be the research direction of related fields in the future. © 2022 Authors. All rights reserved.     

Study on the structure and properties of modified silk with ultraviolet absorbent北大核心CSCD

The silk fiber has an irreplaceable position in textile fibers and related silk fabrics have the advantages of light and airy texture good moisture absorption and breathability comfort in wear etc. It is also widely used in other fields such as the biomedical sector. However silk also has its own limitations poor light resistance and susceptibility to ultraviolet light especially the ultraviolet light of 290-400 nm wavelength in daylight such as under which condition it is prone to yellowing and photodegradation. The yellowing of silk is due to the photo-oxidation of tyrosine and tryptophan in silk protein under the action of ultraviolet light from sunlight and due to the production of yellow substances which affects the whiteness of silk. In addition from the molecular structure of silk most of the amino acids susceptible to UV light are distributed in the amorphous region. As the amorphous region is affected the structure of the crystalline region is also gradually relaxed the local degradation begins and the silk protein macromolecule chain is cleaved which leads to the decrease of the mechanical properties of silk fibers and accelerates the aging of silk fibers and fabrics. Therefore it is necessary to modify the silk products outside the anti-purple line. The current methods used to modify silk are mostly for post finishing modification including coating impregnation and chemical grafting methods but these methods often affect the original color or feel of the fabric and the durability of the modified effect is also poor. The feeding method is a green method to obtain modified silk by spraying mulberry leaves or artificial feed mixed with modifier which is ingested by silkworm and transferred to silk gland. In this study five aminobenzene UV absorbers were used as exogenous additive food for silkworms. The effect of molecular polarity on the transport of modifiers to silk glands was investigated and their effects on silkworm development and silk structural properties were studied. It was found that the aminobenzene UV absorbers were more easily transferred to the central silk gland silk glue and less to the posterior silk gland (fibroin). 4-dimethylaminobenzoic acid was found to be the highest in the posterior silk gland with a content of 3. 27 μg / strip. The cocoon width and cocoon quality of this group were significantly lower than those of the control group and the silk gum content was increased when this group was used as the study object. Compared with the control group the relative content of β-folded structure and crystallinity of the silk in the addition feeding group decreased slightly. The silkworm silk in the feeding group showed a certain UV absorption ability. After 330 h UV irradiation the breaking strength and elongation of the control group decreased by 48. 95% and 43. 52% respectively while those of the feeding group decreased by 42. 03% and 34. 18% respectively. In this paper UV absorbers were added to silkworms to obtain modified silk mainly focusing on the transfer of the modifier to the silk gland and the structural properties of the modified silk only for the most UV absorbers to enter the silk gland of the posterior group of silk. Other properties of the modified silk such as washing resistance have not been studied and some more in-depth studies are required. For instance it needs to be studied in depth for the limited absorption of exogenous additives by silkworms additive food's being not always absorbed by silkworms and transferred to the silk gland and the mechanism of action between the additive food and silk protein after the former's entering the silk gland. © 2022 Authors. All rights reserved.     

Preparation and Applications of Soybean Residue CNF Films

In this study, soybean residues were treated with HCl and soybean residue cellulose was extracted, which was used to prepare cellulose nanofiber (CNF) using the high-pressure homogenization method. The maximum yield of CNF, the reaction temperature, reaction time, and HCl concentration were optimized. The optimum HCl concentration for acid treatment was 6%, the reaction time was 60 min, the reaction temperature was 80℃, and the maximum yield of soybean residue cellulose was 78.8%. The different CNF films were then prepared; the color, mechanical property, and light transmittance of the CNF films were studied. Compared to the properties of the CNF film prepared with the soybean residue cellulose by high-pressure homogenization 15 times (HGT-15 film), the mechanical properties of the CNF film with soybean residue cellulose by decolorizing treatment decreased, but the light transmittance increased. The film prepared by adding HGT-15 CNF to whey protein was investigated for its mechanical property, light transmittance, and solubility. Unlike the pure whey protein film, addition of 2.0% CNF to the whey protein enhanced the mechanical property and water vapor transmission rate (WVT) of the film. With the increase in CNF content, the solubility of the whey protein film decreased, and then stabilized.     

Facile Fabrication of Conductive Paper-based Materials from Tunicate Cellulose Nanocrystals and Polydopamine-decorated Graphene Oxide

Conductive papers made from graphene and its derivatives are important for the development of electronic devices; however, elastomerbased matrices usually make it difficult for the conductive sheets to form continuous conductive networks. In this work, we used tunicate-derived cellulose nanocrystals(TCNC) instead of traditional elastomers as the matrix for polydopamine(PDA)-coated and reduced graphene oxide(GO) to prepare conductive paper, which, at a low concentration, were better for the formation of conductive networks from conductive sheets. It was found that the Young's modulus of the conductive paper produced via this strategy reached as high as 7 GPa. Meanwhile, owing to the partial reduction of GO during the polymerization of dopamine, the conductivity of the conductive paper reached as high as 1.3×10-5 S/cm when the PDA-coated GO content was 1 wt%, which was much higher than the conductivity of pure GO(～4.60×10-8 S/cm). This work provides a new strategy for preparing environmentally friendly conductive papers with good mechanical properties and low conductive filler content, which may be used to produce high-performance, low-cost electronic devices.     

Highly Conductive Fractal-structured Silver Particles for Preparing Flexible Printed Circuits via Screen Printing

Fractal-structured silver particles(FSSPs) are conductive materials with a micron-scale trunk and nanoscale branches, and are characterized with high electrical conductivity and high connectivity. In this study, FSSPs were added to an aqueous additive solution for synthesizing a conductive ink,which was used to prepare two types of printing electrodes via screen printing. The first type included two flexible printed electrodes(FPEs): an FPE on a polyethylene terephthalate(PET) film and an FPE on paper. The second one was a polydimethylsiloxane(PDMS)-embedded FPE. The PETbased FPE exhibited high electrochemical stability when its sheet resistance was 0.38 Ω/sq for a 50%(w/w) content of FSSPs in the prepared conductive ink. Moreover, the embedded FPE demonstrated excellent mechanical properties and high chemical stability. In addition, the embedded structure was endowed with stretchability, which is important for different devices,such as flexible biomedical sensors and flexible electronics.     

Biomass-derived Porous Carbon Materials for Supercapacitor Electrodes: A Review

The development of renewable,cost-efficient,and environmentally friendly electrode materials with excellent performance is urgently needed for improving supercapacitors(SCs).Recently,biomass-derived porous carbons(BPCs)have received increasing attention due to their excellent physical and chemical properties,widespread availability,and low production cost.In this review,the progress in preparing BPCs and the properties of prepared BPCs are presented and discussed.In addition,the applications of BPCs as electrode materials for supercapacitors are also summarized.More importantly,the pore structure and surface properties of BPCs are all determining factors to improve electrochemical performance.Moreover,a high energy density and power density can be pursued by using composites based on BPCs as electrode materials,of which combining transition metallic oxide with BPCs is one of the most attractive selections.Therefore,rational design of BPCs with respect to the supercapacitor's performance should be conducted in the future.     

Study on the anions and moisturizing function of vitamin e fiber intertexture北大核心CSCD

To explore the impacts of different functional fiber contents, different yarn types and different fabric weaves on the functionality of textiles, this paper takes mulberry silk as the warp yarn and takes vitamin E yarn, combed cotton/'vitamin E fiber/Modal(40/40/20) blended yarn and viscose fiber as weft yarns, to prepare 9 tyj>es of vitamin E yam and viscose yarn with different weft ratios, 5 types of combed cotton/vitamin E fiber/Modal(40/40/20) blended yarns and viscose fiber with different weft ratios, 5 types of vitamin E yarn and viscose fabrics with a weft ratio of 1 • 1 and different weaves, and then tests the anions and moisturizing compound function of three series of fabrics.The results show that the anion production and moisturizing properties of fabric grow with the increase of vitamin E fiber content.Both yarn type and fabric! weave will affect the anion production and moisturizing properties of fabrics. © 2021 China Silk Association. All rights reserved.     

Cellulose-based Antimicrobial Composites and Applications: A Brief Review

Cellulose-based antimicrobial composites, typically in the form of functional films and cloth, have received much attention in various applications, such as food, medical and textile industries. Cellulose is a natural polymer, and is highly biodegradable, green, and sustainable. Imparting antimicrobial properties to cellulose, will significantly enhance its applications so that its commercial value can be boosted. In this review paper, the use of cellulose for antimicrobial composites’ preparation was discussed. Two different approaches: surface loading/coating and interior embedding, were focused. Three most widely-applied sectors: food, medical and textile industries, were highlighted. Nanocellulose, as a leading-edge cellulose material, its unique application on the antimicrobial composites, was particularly discussed.     

One-step Fabrication of Cellulose/Graphene Conductive Paper

In this study,a straightforward,one-step wet-end formation process was employed to prepare cellulose/graphene conductive paper for antistatic packing materials.Cationic polyacrylamide was introduced into the cellulose/graphene slurry to improve the graphene loading on the surfaces of the cellulose fibers.The effect of the super calender process on the properties of the cellulose/graphene conductive paper was investigated.When 55 wt% graphene was added,the volume resistivity of the cellulose/graphene conductive paper was 94.70 W·cm,decreasing to 35.46 W·cm after the super calender process.The cellulose/graphene conductive paper possessed excellent anti-static ability and could be used as an anti-static material.     

Ultrasound-assisted Biodiesel Production from Waste Cooking Oil at Room Temperature

Waste cooking oil (WCO) is considered to be a promising alternative for vegetable oils that have been traditionally used for biodiesel production. In this study, WCO with a fairly high free fatty acid content was transesterified into biodiesel in a one-step procedureat room temperature (25℃ ) under ultrasound irradiation and in the presence of potassium hydroxide (KOH) as catalysts. Response surface methodology (RSM) was used to investigate the effects of the methanol/oil molar ratio, reaction time, and catalyst loading on the fatty acid methyl ester (FAME) yield and the biodiesel yield. The optimal reaction conditions for the production of WCO biodiesel were found to be a methanol/oil molar ratio of 8.6:1, a reaction time of 25 min, and a catalyst loading of 2.43 wt%. Under these optimal settings, the FAME and biodiesel yields were 96.4% and 92.7%, respectively. The properties of the resultant WCO biodiesel, including kinetic viscosity, acid number, water content, and flash point, were measured according to ASTM D6751 standards. The obtained results provide useful information for the large-scale production of WCO biodiesel.     

Effect of Thermal Treatment on the Properties of TEMPO Oxidized Cellulose Film for the Flexible Substrate of Solar Cell

The 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidized cellulose film (TOCF) has been attempted to be used as a substrate in electronic and optoelectronic devices, but the changes in the TOCF properties before and after annealing treatment have usually been neglected during device fabrication. In this study, TOCF was treated in different atmospheres (air, vacuum, and N₂) and at different temperatures, and the properties were investigated. The results indicate that the optical properties are slightly affected by atmosphere and temperature; only slight transmittance loss and haze increase have been observed when TOCF is exposed to an air atmosphere at temperatures of above 120℃. In contrast to the slight effects on the optical properties, cellulose degradation and a loss of film strength have been observed regardless of the atmosphere used when placed at temperatures of above 100℃. Specifically, TOCF was exposed to air, followed by N₂ and vacuum atmospheres. Additional Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) results showed that increasing the temperature had no significant effect on the structure of TOCF. Therefore, the annealing temperature should be controlled at a temperature of lower than 100℃ and a vacuum atmosphere is preferred.     

Studies of Microstructure of Kernels of Macadamia integrifolia and Its Hybrids through MRI, X-Ray Tomography and Confocal Microscopy

The aim of this study was to apply the existing techniques that enable examination ofmacadamia kernels to provide a better understanding of physico-chemical properties of kernels during postharvest processing. These techniques, such as X-ray tomography, could be applied for quality monitoring in the macadamia industry. The objectives of this study were to investigate the browning centre symptoms that usually occur in macadamia nuts-in-shell. The applied techniques included confocal microscopy, X-ray tomography and magnetic resonance imaging （MRI）. Five different varieties of macadamia nuts （A38, 246, 816, 842 and Daddow） were selected to include distinct characteristics, such as drop pattern and growing location. Analysis of the microstructure of kernels by confocal microscopy showed the distribution of possible brown pigment compounds as well as the distribution of lipids, carbohydrates and proteins inside macadamia cells. Physical properties data, including shell density and seed to volume ratio, were obtained by X-ray tomography. Magnetic resonance diffusion tensor imaging used in this study showed marked differences in microstructure which indicate that different varieties exhibit different microstructures expressed as fraction ofanisotropy and apparent diffusion coefficient that appear to be related to the occurrence of the brown centre. Hence, the findings of this study have potential to improve the existing postharvest techniques used in the macadamia processing industry. They will be of benefit to the industry in terms of improved quality control and cost reduction.     

Triethylamine-catalyzed Isomerization of Glucose to Fructose under Low Temperature Conditions in Aqueous Phase

Isomerization of glucose derived from lignocellulosic biomass is an important step in biorefinery. Fructose isomerized from glucose, is used as a highly attractive sweetener in the food and beverages industries. However, the prevalence of side reactions at high glucose concentrations is a serious issue, leading to a significant reduction in the fructose yield, especially in the aqueous phase. In this study, an efficient method for the conversion of highly concentrated glucose into fructose under low temperature conditions using triethylamine as the catalyst was developed. It was demonstrated that high fructose yield could be maintained at high glucose concentration. At 60℃, fructose yield of 38.7% and fructose selectivity of 80.6% were achieved in 1 mol/L (approximately 17 wt% ) glucose. When glucose concentration was increased to 2 mol/L (approximately 31 wt%), the fructose yield and selectivity were maintained at 34.7% and 77.4%, respectively. ¹³C nuclear magnetic resonance (NMR) spectrometer was used to examine the glucose isomerization reaction. Compared to the NaOH catalytic system, triethylamine acted as a buffer to provide a stable alkaline environment for the catalytic system, further maintaining a high level of catalytic efficiency for the isomerization of glucose to fructose.     

Ministry of Environmental Protection Issued Regulations on Environmental Protection of Imported Waste Paper

正In order to implement the Implementation Plan for Prohibition of Foreign Refuse Entry and Promoting the Reform of the Management System for the Import of Solid Waste,and to further strength the import management of solid wastes that can be used as raw materials,the Ministry of Environmental Protection issued the Regulations on Environmental Protection of     

Pore Structure Regulation of Carboxyethylated Microfibrillated Cellulose Films

Carboxyethylation is a recent chemical pretreatment for preparation of microfibrillated cellulose(MFC).The carboxyethylated MFC film prepared by coating method has compact structure and high mechanical properties.In order to expand its application,three approaches including using organic solvents,different drying methods and cationic additives,have been adopted in this paper to enrich and regulate the pore structure of MFC film.The results show that all the approaches can improve the pore structure but decrease the mechanical properties of MFC film.When organic solvents such as ethanol,isopropanol and n-butanol were used to replace the water in MFC suspension or pre-dried MFC film,the pore structure of films were increased.Additionally,the film obtained by freeze-drying or air-drying after freezing in liquid nitrogen or freezer has high porosity but poor strength.The best drying process is to rewet dry MFC film,freeze in liquid nitrogen and then freeze-dry.Moreover,the addition of cationic polyelectrolytes or alkene ketone dimer(AKD)in MFC suspension can also significantly increase the film's porosity.Through the above approaches,the porosity of carboxyethylated MFC film can be regulated between 20% and 90%.     

Application of Selected Natural Antimicrobial Formulations for the Control of Food Pathogens in Fresh-Cut Cauliflower

In recent years, research on biopolymer based-coating containing natural antimicrobial agents is developing significantly. The objective of this study was to evaluate the antimicrobial efficiency of six formulations containing pre-selected natural antimicrobial compounds against Listeria monocytogenes, Escherichia coli O 157：H7, Salmonella typhimurium, the total bacteria and total yeasts and molds in cauliflower. Each formulation was subjected to a sensory test in parallel to microbiological analysis and the efficiency during storage at 5 ℃ was evaluated for the two best formulations, based on their ability to eliminate the target microorganisms. Both formulations were able to reduce all pathogens and total flora below detectable levels after 24 h of storage at 5 ℃. Using washing or spraying treatments, the two formulations were able to reduce Listeria to undetectable levels for 3 d. This efficiency was extended to 7 d when the formulations were incorporated into an edible coating. Washing treatment with the two formulations was also able to limit the growth of yeast and molds at levels lower than 2 log, for more than 7 d. The population of E. coli was reduced to below the detection limit during 14 d of storage, after washing treatment with the two formulations. The spraying treatment of cauliflower with the formulations allowed the use of very small amounts of antimicrobials while maintaining a fairly good efficiency, greatly reducing the potential costs of implementing this method in the industry. Future research may focus on development of nanoemulsion of antimicrobial formulations based on the developed antimicrobial formulations in this study to improve the better coating efficiency.     

Experimental Design as a Tool for the Development of Citric Acid Production by Yarrowia lipolytica Using Glycerol as a Feedstock

Due to the scarcity of fossil fuels in the world, there is increasing interest in the commercial production of biodiesel, which leads to obtaining large amounts of glycerol as a byproduct. If not disposed of properly, glycerol can generate environmental impact. One of the promises, the application of the crude glycerol is the production of citric acid by microbial fermentation. Citric acid is industrially produced by a submerged fermentation process with Aspergillus niger, using sucrose as carbon source, but due to increased demand for citric acid, alternative processes using renewable sources or waste materials as substrates and the cultivation of yeast strains are being studied. The aim of the study was to determine the best culture condition for maximum citric acid synthesis and lower isocitric acid production from crude glycerol through experimental design tool. For this purpose, the yeast strain Yarrowia lipolytica IMUFRJ-50682 was cultivated in nitrogen-limited glycerol-based media. Therefore, glycerol and yeast extract concentrations and agitation speed were evaluated as independent variables. With pure glycerol, the highest citric acid production achieved was 16.5 g/L with an isocitric acid production of 7.7% （in relation to citric acid）. With crude glycerol, citric acid production reduced to 6.7 g/L because of higher biomass yield. Therefore, an increase in the initial carbon to nitrogen molar ratio from 714 to 1,561 was necessary to increase citric acid production to 9.2 g/L, reducing isocitric acid production and to achieve a yield of 0.41 g of citric acid per glycerol consumed. In this condition, less nitrogen source was used, reducing production costs.     

Highly Improved Microstructure and Properties of Poly(p-phenylene terephthalamide) Paper-based Materials via Hot Calendering Process

In this study,the effect of hot calendering process on the microstructure and properties of poly(p-phenylene terephthalamide)(PPTA) paper-based materials was investigated.The microstructures of the fracture surface,crystalline structure,and single fiber strength of the PPTA paperbased materials as well as the different bonding behaviors between the PPTA fibers and PPTA fibrids obtained before and after the hot calendering process were examined.The results indicated that a high linear pressure would result in a limited improvement of the strength owing to the unimproved paper structure.The optimal values of tensile index and dielectric strength of 56.6 N·m/g and 27.6 kV/mm,respectively,could only be achieved with a synergistic effects of hot calendering temperature and linear pressure(240℃ and 110 k N/m,respectively).This result suggested it was possible to achieve a significant reinforcement and improvement in the interfacial bonding of functional PPTA paper-based materials,and avoid the formation of unexpected pleats and cracks in PPTA paper-based materials during the hot calendering process.     

Improvement of solubility and Emulsifying Properties of Soy Protein Isolates by Glucose Conjugotion

Soy Protein Isolate(SPI)was modified with glucose(G-) through the amino-carbonyl reaction (Maillard Reaction).Solubility and emulsifying properties of the modified proteins were investigated.G-SPI conjugate was highly soluble at wide pH while untreated SPI was hardly soluble especially at pH4-PH6.Solubility of modified SPI showed the resistance to heat treatment and high ionic concentration.Emulsifying activity and emulsion stability of G-SPI conjugate was much higher than those of native SPI were.Comparing with some commercial emulsifiers,the G-SPI conjugate showed as good or better emulsifying properties in high salt concentration and in neutral pH.SDS-PAGE was also used to confirm the formation of G-SPI conjugate.     

Green and Effective Ammonium Carbonate-assisted Process for Drying Hemicellulose Obtained through Alkali Extraction of Bleached Bamboo Kraft Pulp

Hemicellulose has a wide range of applications,including that as an emulsifier for the food industry and raw material for the synthesis of bioethanol/biochemicals and biodegradable films.Hemicellulose is usually present as a spent liquor,such as the prehydrolysis liquor of the prehydrolysis kraft dissolving pulp production process and the alkali extraction liquor of the cold caustic extraction of pulp fibers.Due to its dilute nature,hemicellulose needs to be dried for practical utilization,and this is challenging.In this study,cellulose and hemicellulose in a bleached bamboo kraft pulp were separated using an alkali extraction process.Hemicellulose obtained from the extraction liquor was dried by an ammonium carbonate-assisted drying process.The effects of drying time and drying temperature were determined.Structure of the hemicellulose obtained by the ammonium carbonate-assisted drying process was similar to that of original hemicellulose,as revealed by detailed Fourier transform infrared and X-ray diffraction analyses.The novel drying method was more energy efficient and required a shorter drying time than the conventional freeze drying method,and the excellent solubility in alkaline solutions favored the chemical modification of hemicellulose.The dried hemicellulose can be used as a renewable raw material for the preparation of hydrogels and other substances such as bioethanol/biochemicals and biodegradable films.