壳聚糖水溶性改性研究进展

介绍了壳聚糖水溶性改性的八种主要方法。     

水溶性壳聚糖的开发与应用

壳聚糖经改性提高其水溶性后可广泛应用于食品、医药、化妆品等领域，前景广阔。本文介绍了壳聚糖的制备和应用等。     

水溶性壳聚糖的制备及其应用研究进展

由于壳聚糖的结晶性.它只能溶于一些稀的无机酸或有机酸,不能直接溶于水中.文章介绍了几种水溶性壳聚糖的制备方法-控制壳聚糖的脱乙酰度、降低分子量和化学修饰,以及水溶性壳聚糖在医药、食品、化妆品等方面的应用进展.     

低聚水溶性壳聚糖的制备方法及研究进展

低聚水溶性壳聚糖的制备是目前非常热门的一个研究课题,本文对壳聚糖降解以制备低聚水溶性壳聚糖的各种方法及目前的研究进展情况进行了综述。     

水溶性壳聚糖改性天然胶乳的性能研究

采用乙酰化反应制备的水溶性壳聚糖改性天然胶乳(NRL),并对其性能和结构进行研究.结果表明:当pH值小于11时,水溶性壳聚糖在水中能够获得最佳溶解度.水溶性壳聚糖改性NRL胶膜的表面平整,致密性和耐溶剂性能优于纯NRL胶膜.当水溶性壳聚糖用量为1.5份时,NRL胶膜的综合物理性能最佳.水溶性壳聚糖赋予了NRL胶膜良好的生物相容性,达到了改善过敏性的目的,在医疗卫生领域具有广阔的应用前景.     

水溶性二羟丙基壳聚糖的制备及性能研究

以壳聚糖(Chitosan,CTS)为原料进行改性制备成水溶性更为优良的多羟基壳聚糖。首先利用α-氯甘油醇与NaOH反应生成醚化剂——缩水甘油(glycidol)。再用异丙醇溶液为反应体系,对壳聚糖进行碱化、醚化、中和以及提纯处理,得到了二羟丙基壳聚糖。最佳反应条件为:壳聚糖2 g,NaOH 30%～40%,缩水甘油15 mL,温度60℃,反应时间8 h。     

水溶性壳聚糖开发和应用前景广阔

甲壳素是主要来源于海洋无脊椎动物的外壳、真菌细胞壁和昆虫的外角质层及内角质层的一类高分子聚合物，在自然界中资源十分丰富，是地球上数量仅次于纤维素的有机天然化合物。     

水溶性壳聚糖的制备

以壳聚糖为原料,利用H2O2 NaClO在醋酸溶液中进行氧化降解反应,制备了水溶性壳聚糖。考察了H2O2和NaClO的浓度对壳聚糖降解率的影响,确定了最佳降解条件为:反应温度80℃,反应时间2h,H2O2和NaClO的浓度分别为5%和6%。利用红外和元素分析对产物进行了表征。     

壳聚糖改性最新研究进展

壳聚糖富含羟基和氨基,通过改性可以得到特定的功能高分子。本文总结了壳聚糖改性的研究进展,主要介绍了它的结构、理化性质、改性方法和应用,展望了壳聚糖改性研究的发展趋势。     

水溶性磺化壳聚糖的研制

以工业壳聚糖为原料,先后用浓硫酸和氯磺酸为磺化试剂,在适当条件下进行磺化,获得了水溶性较好,含硫量较高的磺化壳聚糖,考察了磺化剂用量、反应温度、反应时间等因素对硫含量的影响,结果表明,较优的磺化条件为:浓硫酸∶氯磺酸=1∶1,反应温度为5℃,反应时间为4h。IR光谱分析表明,该衍生物具有与肝素相似的结构,是一种非常具有潜力的新型的类肝素。     

Polydimethylsiloxane-modified chitosan I. Synthesis and structural characterisation of graft and crosslinked copolymers

Graft and crosslinked polydimethylsiloxane (PDMS)-chitosan copolymers were prepared through the reaction between mono and difunctional glycidoxypropyl-terminated PDMSs and chitosan. The transformation of amino groups of chitosan through the reaction with epoxy groups was confirmed by FT-IR and ¹³C cross-polarization (CP) magic-angle spinning (MAS)-NMR analysis. Chitosan-based materials modified with about 40% and 60% hydrophobic polydimethylsiloxane were obtained, respectively. As proved by wide angle X-ray analysis, the crystallinity of chitosan was strongly decreased through the incorporation of PDMS sequences. However, both graft and crosslinked copolymers still present a partial crystalline structure. Their X-ray patterns are not only different as compared to chitosan but also as compared to each other. For the graft copolymer, three diffraction peaks were observed at 2θ = 8.4°, 11.2° and 21.2°, indicating the formation of a new partially crystalline phase and the modification of the interplanar distances for the phases similar to chitosan. The crosslinked copolymer is even less crystalline, the peak around 2θ = 20° being strongly decreased. Different thermal behaviour of siloxane modified chitosan was registered for graft and crosslinked copolymers; the graft sample is less stable than chitosan, while the crosslinked copolymer showed an intermediate stability between chitosan and polydimethylsiloxane precursors.     

水溶性粘合剂的配制及其性能研究

先通过聚乙酸乙烯酯(PVAc)的醇解制备出聚乙烯醇(PVA),再用聚乙烯醇在酸性条件下与甲醛缩合,得到聚乙烯醇缩甲醛(PVF),再以聚乙烯醇和聚乙烯醇缩甲醛为基料,以邻苯二甲酸二丁酯(DBP)为增塑剂,聚乙二醇-400(PEG-400)为增韧剂,水为溶剂,以鱼油为分散剂,配制了不同工艺配方的水基粘合剂,考察了增塑剂、增韧剂的加入量对粘合剂的透明度、稳定性、溶解度、粘弹性等的影响。实验结果表明,当质量比PVA∶PVA∶水=9.6∶9.6∶80.8,鱼油、聚乙二醇-400、DBP的添加量分别为4%、1.6%、2.0%时,所配制的粘合剂有相对较好的综合性能。     

NMR study of the phosphonomethylation reaction on chitosan

N-Phosphonomethylation of chitosan reaction was studied and optimized using different reaction conditions. NMR spectroscopy was an important tool in this work to study this reaction and the α-aminomethylphosphonic acid function introduced onto chitosan was unequivocally characterized by ³¹P and ¹³C NMR analyses. But surprisingly, whatever the reaction conditions used, N-phosphonomethylation reaction of chitosan cannot be dissociated from a side reaction: the N-methylation reaction of chitosan. A mechanism was proposed to explain the formation of this side product.     

Amorphous reprecipitated chitosan as a novel morphological form

In order to overcome the intractable nature of chitosan, which has delayed the basic and utilization research of this biopolymer having remarkable biological activities, destruction of the crystalline structure was studied. Chitosan was dissolved in aqueous acid, reprecipitated in alkali, and freeze-dried under appropriate conditions to prepare a fluffy cotton-like material, which was amorphous and had almost the same molecular weight as the original chitosan. It exhibited highly improved chemical reactivity as confirmed by the acetylation and enhanced adsorption capability toward copper ion. Full N-acetylation of the reprecipitated chitosan afforded structurally uniform chitin, which was also found to be amorphous. These results indicate the high potential of this new morphological form of chitosan possibly leading to a wide range of utilizations of this under-utilized biological resource.     

Large-scale and controllable synthesis of metal-free nitrogen-doped carbon nanofibers and nanocoils over water-soluble Na2CO3

Using acetylene as carbon source, ammonia as nitrogen source, and Na₂CO₃ powder as catalyst, we synthesized nitrogen-doped carbon nanofibers (N-CNFs) and carbon nanocoils (N-CNCs) selectively at 450°C and 500°C, respectively. The water-soluble Na₂CO₃ is removed through simple washing with water and the nitrogen-doped carbon nanomaterials can be collected in high purity. The approach is simple, inexpensive, and environment-benign; it can be used for controlled production of N-CNFs or N-CNCs. We report the role of catalyst, the effect of pyrolysis temperature, and the photoluminescence properties of the as-harvested N-CNFs and N-CNCs.     

壳聚糖在水处理中的应用研究进展

壳聚糖作为一种来源广泛的无毒无害的高分子聚合物,因其在酸性溶液中其氨基可结合H＋,是一种典型的阳离子聚电解质,能够吸附絮凝废水中有机物,同时其氨基还能鳌合去除许多重金属离子,是一种优良的水处理剂。本文介绍了它在水处理中的研究和应用情况。     

Chemoselective protection of chitosan by dichlorophthaloylation: preparation of a key intermediate for chemical modifications

In order to expand the scope of protection of the amino group of chitosan for synthesizing a key intermediate that would allow regioselective modification reactions, dichlorophthaloylation behavior was studied in detail. The reaction proceeded in a similar manner to phthaloylation, and chemoselectively protected N-dichlorophthaloyl-chitosan could be prepared either by partial hydrolysis of N,O-dichlorophthaloylated chitosan or by one-step dichlorophthaloylation in N,N-dimethylformamide/water. Deprotection of N-dichlorophthaloyl-chitosan was achieved by hydrazinolysis followed by alkaline hydrolysis. GPC measurements revealed that the number–average molecular weight was reduced to about a half after the protection–deprotection process, indicating the cleavage of the main chain to be not pronounced. In the triphenylmethylation, N-dichlorophthaloyl-chitosan exhibited adequate reactivity for facile protection of the C6 hydroxy group. The dichlorophthaloyl group has thus proved to be a promising candidate to prepare a novel precursor for controlled chemical modifications of chitosan.     

A novel method for immobilization of chitosan onto nonporous glass beads through a 1,3-thiazolidine linker

A new method for the surface modification of nonporous glass beads (average diameter, 6 μm), which characterized by formation of a 1,3-thiazolidine ring between l-cysteine linkers on the glass bead and reducing ends of chitosan, has been developed. γ-Aminopropyltriethoxysilane (APES)-treated glass bead was first subjected to condensation with an l-cysteine derivative, l-4-carboxy-3-formyl-2,2-dimethylthiazolidine (CFMT), in the presence of water-soluble carbodiimide hydrochloride (WSC) and HOBt. After deprotection by diluted hydrochloric acid, the glass beads with activated cysteine linkers on the surface were treated with reducing chitosan in aqueous acetic acid solution at room temperature. The maximum content of chitosan immobilized on the glass beads estimated by acid-hydrolysis and subsequent glucosamine analysis by Svennerholm method after was 0.73% (w/w). This was obtained by using chitosan having an average molecular weight of 14 kD. Model reactions of the cysteine derivatives with reducing chitosan were also performed and the product was examined by IR and NMR spectroscopy to verify the linkage between cysteine and chitosan.     

A fundamental study of chitosan/PEO electrospinning

A highly deacetylated (97.5%) chitosan in 50% acetic acid was electrospun at moderate temperatures (25-70 °C) in the presence of a low content of polyethylene oxide (10 wt% PEO) to beadless nanofibers of 60-80 nm in diameter. A systematic quantitative analysis of the solution properties such as surface tension, conductivity, viscosity and acid concentration was conducted in order to shed light on the electrospinnability of this polysaccharide. Rheological properties of chitosan and PEO solutions were studied in order to explain how PEO improves the electrospinnability of chitosan. Positive charges on the chitosan molecule and its chain stiffness were considered as the main limiting factors for electrospinability of neat chitosan as compared to PEO, since surface tension and viscosity of the respective solutions were similar. Various blends of chitosan and PEO solutions with different component ratios were prepared (for 4 wt% total polymer content). A significant positive deviation from the additivity rule in the zero shear viscosity of chitosan/PEO blends was observed and believed to be a proof for strong hydrogen bonding between chitosan and PEO chains, making their blends electrospinnable. The impact of temperature and blend composition on the morphology and diameter of electrospun fibers was also investigated. Electrospinning at moderate temperatures (40-70 °C) helped to obtain beadless nanofibers with higher chitosan content. Additionally, it was found that higher chitosan content in the precursor blends led to thinner nanofibers. Increasing chitosan/PEO ratio from 50/50 to 90/10 led to a diameter reduction from 123 to 63 nm. Producing defect free nanofibrous mats from the electrospinning process and with high chitosan content is particularly promising for antibacterial film packaging and filtration applications.