酶载体壳聚糖制备的研究

本文分别采用电热法、连续微波法和问歇微波法制备了几种性能不同的壳聚糖,并对产品的脱乙酰度和分子量进行了比较.结果表明,间歇微波法制备的壳聚糖具有制备时间短、产品脱乙酰度高和分子量大等特点,能更好地满足酶载体的要求.     

壳聚糖理化性能:粘均分子量、脱乙酰度及结晶性能测定

使用粘度法测定了阿拉丁牌低粘、中粘、高粘和沪试牌四种壳聚糖的分子量,分别约为126万,115万,69万和56万。分别使用酸碱滴定法和双突跃电位滴定法测定了脱乙酰度,结果表明后者更精密,四类壳聚糖的脱乙酰度值均在78%～86%之间。X射线衍射测得阿拉丁牌壳聚糖具有相对较低的结晶度,脱乙酰度降低导致结晶度下降。     

高脱乙酰度壳聚糖的制备及结构与性能研究

本文系统地研究了从虾壳制备高脱乙酰度、高分子量壳聚糖的方法。在一定条件下可得到脱乙酰度达97％,分子量达5×10~5左右的壳聚糖。用IR、NMR、DTA、TGA等分析技术对壳聚糖的结构与性能进行了研究。     

壳聚糖在活性染料染羊毛织物上的应用工艺探讨

本文对壳聚糖处理过的羊毛织物用活性蓝BET染色工艺进行了探讨.讨论了壳聚糖脱乙酰度、壳聚糖浓度对羊毛染色性能的影响,并比较了经壳聚糖处理与未处理羊毛染色性能的差异.结果表明,提高处理液中壳聚糖的浓度或脱乙酰度都能提高活性染料的固色率,提高织物表面色深值K/S,而且对染色样的各项牢度影响不大.     

壳聚糖在醋酸溶液中的溶解行为及动力学模型

用电导和粒度测试两种方法研究了壳聚糖在醋酸溶液中的溶解行为。结果显示:醋酸浓度、溶解温度和壳聚糖样品本身的脱乙酰度及分子量都会影响壳聚糖的溶解,但溶解初期壳聚糖因吸附醋酸根离子而产生聚集现象。一般情况下,温度高有利于壳聚糖的溶解。当壳聚糖脱乙酰度非常高,分子量差距又并不是非常大时,前者将对溶解起主导作用,同时脱乙酰度越高越有利于其溶解。     

止血性壳聚糖的制备及其凝血效果的研究

在温和均相条件下,对较高脱乙酰度的壳聚糖进行乙酰化,制备不同脱乙酰度的壳聚糖;测试不同脱乙酰度和分子量的壳聚糖醋酸溶液的凝血效果。中药—壳聚糖复合止血材料的制备及其止血功能的研究。     

甲壳素制备壳聚糖脱乙酰度可控性的研究

介绍了甲壳素（ehintin）和壳聚糖（ehitosan）的性质、用途及发展前景；分析了国内外对壳聚糖的研究状况及取得的成果；描述了制备壳聚糖的实验原理；初步研究了在保证能获得大分子量的情况下提高壳聚糖的脱乙酰度的实验方法；介绍了测定壳聚糖脱乙酰基的实验方法；分析了影响壳聚糖脱乙酰度（Degree　of　 Deacetylation缩写：D．D．）的主要因素。     

壳聚糖脱乙酰度测定方法的总结与比较

测定壳聚糖脱乙酰度(DD)的方法主要分为三类:①光谱法:紫外、红外光谱和核磁法;②破坏样品法:色谱法、差示扫描量热和元素分析法;③滴定法:酸碱、电位和胶体滴定等方法。对壳聚糖脱乙酰度测定方法进行总结与比较,为研究者选择最佳的壳聚糖脱乙酰度测定方法提供理论依据。     

微波技术提取高脱乙酰度高黏度壳聚糖的实验研究

壳聚糖作为一种具有独特性能的天然高分子生物材料，其应用越来越广泛，并且对壳聚糖品质的要求也越来越高。高脱乙酰度和高黏度是壳聚糖的二个重要质量指标，传统制备工艺中，通过提高反应温度和延长反应时间，能得到高脱乙酰度的壳聚糖产品，但由于过长的反应时间使黏度大大降低。本文采用微波技术和传统工艺相结合，通过正交试验确定了从虾壳中提取高脱乙酰度高黏度壳聚糖的较优工艺条件。     

N-乙酰化制备水溶性壳聚糖研究

以高脱乙酰度壳聚糖为原料,在不使用吡啶的无水乙醇均相体系中用乙酸酐通过N-乙酰化制备了水溶性壳聚糖,采用酸碱滴定、XRD、IR对壳聚糖原料和所制得水溶性壳聚糖的脱乙酰度、结晶状态、红外光谱分别进行了测试分析,并探讨了水溶性壳聚糖的结构与水溶性机理。     

Effect of degree of deacetylation of chitosan on the kinetics of ultrasonic degradation of chitosan

The objective of the study was to explore the effect of the degree of deacetylation (DD) of the chitosan used on the degradation rate and rate constant during ultrasonic degradation. Chitin was extracted from red shrimp process waste. Four different DD chitosans were prepared from chitin by alkali deacetylation. Those chitosans were degraded by ultrasonic radiation to different molecular weights. Changes of the molecular weight were determined by light scattering, and data of molecular weight changes were used to calculate the degradation rate and rate constant. The results were as follows: The molecular weight of chitosans decreased with an increasing ultrasonication time. The curves of the molecular weight versus the ultrasonication time were broken at 1‐h treatment. The degradation rate and rate constant of sonolysis decreased with an increasing ultrasonication time. This may be because the chances of being attacked by the cavitation energy increased with an increasing molecular weight species and may be because smaller molecular weight species have shorter relaxation times and, thus, can alleviate the sonication stress easier. However, the degradation rate and rate constant of sonolysis increased with an increasing DD of the chitosan used. This may be because the flexibilitier molecules of higher DD chitosans are more susceptible to the shear force of elongation flow generated by the cavitation field or due to the bond energy difference of acetamido and β‐1,4‐glucoside linkage or hydrogen bonds. Breakage of the β‐1,4‐glucoside linkage will result in lower molecular weight and an increasing reaction rate and rate constant. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3526–3531, 2003     

The effect of reaction time and temperature during heterogenous alkali deacetylation on degree of deacetylation and molecular weight of resulting chitosan

The objective of the study is to elucidate the effect of reaction time and temperature during heterogenous alkali reaction on degree of deacetylation (DD) and molecular weight (MW) of the resulting chitosans, and to establish the reaction conditions to obtain desired DD and MW chitosan products. Chitin was extracted from red shrimp process waste. DDs and MWs were determined by infrared spectroscopy (IR) and static light scattering, respectively. The results are as follow: The DD and MW of chitin obtained were 31.9% and 5637 kDa, respectively. The DD of the resulting chitosan increased along with reaction time and/or reaction temperature. The DDs of the resulting chitosan that were obtained from 140°C were higher than those reacted at 99°C. The highest DD of the resulting chitosans after alkali deacetylation at 99 and 140°C were 92.2 and 95.1%, respectively. The DDs of chitosans increased fast at the beginning of reaction process then slowed over time. The reaction rate and rate constant of the deacetylation reaction decreased with increasing DD of the reactant. The MWs of chitosans decreased along with the deacetylation time. MW of those chitosans reacted at 140°C are smaller than those at 99°C. The rate of chitosan degradation was above 43.6%/h in the initial stage, then decreased to about 20%/h. The degradation rate constants raised substantially in the late stage. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2917–2923, 2003     

聚合度对纤维素表面性能的影响

根据Washburn浸渍理论和van Oss-Good-Chaudhury组合理论及应用柱状灯芯技术测试了具有不同聚合度(DP)的纤维素的表面性能,同时与已报道的纤维素的表面能进行了比较。结果表明:纤维素的表面能随分子量的增加而增大,但主要是其Lifshitz-van der Waals力在起主导作用。研究还发现纤维素的表面能γS与聚合度DP之间的关系大致可以描述为:γS=37.56+0.02 DP,而纤维素的极性率P与聚合度DP之间的关系则是一种非线性关系,如:P=11.88-0.02 DP+9.10 DP2。     

Effect of the Characters of Chitosans Used and Regeneration Conditions on the Yield and Physicochemical Characteristics of Regenerated Products

The objective of this study was to explore the effect of the character of chitosans used, and the regeneration conditions employed on, the yield and physicochemical characteristics of regenerated products. Different concentrations of acetic acid were used to dissolve chitosans of 61.7% and 94.9% degree of deacetylation (DD), and weight-average molecular weight (Mw) of 176 and 97 kDa, respectively; they were then precipitated with an 8 N NaOH solution, followed by washing and neutral and freeze drying to get the regenerated products. Yields of regenerated products and their physicochemical properties, such as ash content, bulk density, Mw, polydispersity index (PDI), DD, and crystallinity were measured. A higher concentration of acetic acid used resulted in a higher yield. The purity of the regenerated product increased significantly, whereas the bulk density and crystallinity decreased significantly after regeneration. The regeneration process showed its merits of narrowing down the PDI of regenerated products. The DD and structure of chitosan was changed insignificantly after the regeneration process.     

Acid hydrolysis of commercial chitosans

Commercial chitosans were subjected to controlled acid hydrolysis and their degrees of deacetylation (DD), molecular size and rheological flow profiles determined (pre‐ and post‐hydrolysis) by ¹H‐NMR spectroscopy, high‐performance size‐exclusion chromatography and rheometry, respectively. Hydrolysis resulted in DD increases between 4 and 11%. Unhydrolysed chitosans had M_w and M_n values in the ranges 700–1200 and 130–210 kDa, respectively. Chitosan with the smallest initial molecular size averages had the smallest averages after hydrolysis; however, a chitosan with an intermediate initial molecular size proved to be most resistant to hydrolysis. Molecular size trends were paralleled by zero shear viscosity (η₀) measurements determined by application of the Williamson model to rheological flow profile data. Viscosity is obviously related to molecular size, but does not necessarily reflect relative ease of hydrolysis, since specific hydrolysis conditions affect structurally similar polysaccharides in different ways (in terms of rate of depolymerisation and de‐N‐acetylation, etc), which are not simply due to differences in molecular size profiles pre‐hydrolysis. Copyright © 2005 Society of Chemical Industry     

Effect of Deacetylation Degree in Chitosan Composite Membranes on Pervaporation Performance

ABSTRACT

The effect of the degree of deacetylation in chitosan composite membranes on their pervaporation performance for ethanol dehydration was investigated. The degree of deacetylation of chitosans was measured by using an infrared spectroscopic method and elemental analysis. The chitosan composite membranes were prepared by coating a chitosan solution onto a microporous polyethersulfone membrane with 3–7 nm pore sizes. Then the surface of the top layer (chitosan) of well-dried membranes was crosslinked with sulfuric acid, and pervaporation experiments for binary mixtures (water—ethanol) were carried out at various conditions. In the case of a chitosan membrane with a high degree of deacetylation, the flux increases while the separation factor decreases compared with membranes with a low degree of deacetylation.     

取代基及分子量对非离子型纤维素醚表面特性的影响

根据Washburn的浸渍理论(Penetration Theory)和van Oss-Good- Chaudhury的组合理论(Combining Theory)及应用柱状灯芯技术(Column Wicking Technique),对几种非离子型纤维素醚,如甲基纤维素、羟丙基纤维素和羟丙基甲基纤维素的表面特性进行了测试。由于这些纤维素醚的取代基、取代度和分子量不同,所以它们的表面能及其组成部分有着明显的差异。数据说明,非离子型纤维素醚Lewis碱大于Lewis酸,表面自由能的主要成分是Lifshitz-van der Waals力。羟丙基的表面能及其成分都大于羟甲基。而在相同取代基和取代度的前提下,羟丙基纤维素的表面自由能正比于分子量;而羟丙基甲基纤维素的表面自由能则正比于取代度,反比于分子量。实验还发现非离子型纤维素醚中的取代基羟丙基和羟丙基甲基的表面能似乎都大于纤维素的表面能,而实验证明所测试得出的纤维素的表面能及其成分的数据是与文献所吻合的。     

竹纤维的表面化学特性及与棉纤维的比较

报道了竹纤维的表面化学性能,如:表面能、Lifshitz-vanderWaals力、Lewis酸性和碱性。为了认识竹纤维的表面性能,同时还对棉纤维的表面性能进行了测试以作对比。结果表明,竹纤维的表面性能与棉纤维基本相同,但两者具有一个非常明显的差异,即前者的Lewis酸性是后者的一倍。这个发现极好地解释了人体皮肤在夏天接触竹纤维时感到舒适的现象。研究还指出,竹纤维的取向性略差于棉纤维,这可能会导致竹纤维的柔软性、面料性能略逊于棉纤维。     

Chitosan as Scaffold Materials: Effects of Molecular Weight and Degree of Deacetylation

In this study, we investigated in vitro the role of the degree of deacetylation and molecular weight on some biological properties of chitosan films. The influence of different degree of deacetylation and molecular weight of chitosan on the hydrophilicity, degradation, mechanical properties and biocompatibility were evaluated. The results showed that the degree of deacetylation affected the hydrophilicity and biocompatibility of the chitosan films. The molecular weight, on the other hand, affected the rate of degradation and the mechanical properties. Chitosan with higher degree of deacetylation and molecular weight was more suitable for tissue engineering applications. Alginate could be added into chitosan to modify the rigidity and hydrophilicity of chitosan. Higher hydrophilicity, biocompatibility, and elongation were found after modification.     

Effect of recovery methods and conditions on the yield,solubility, molecular weight,and creep compliance of regenerated chitosan

The objective of this study is to explore the effect of using different recovery methods and conditions on the yield, solubility, molecular weight, and creep compliance of the regenerated chitosan. The results show that yields obtained by dialysis were higher than those using recovery medium of alkali solutions, organic solvents, or alkali–alcohol–water mixtures. For those chitosans employing alkali solutions as the recovery medium, the higher the alkali concentration used, the higher the yields obtained, although the total quantity of alkali in the solution were the same. Solubilities of regenerated chitosans were similar and independent at the methods of using alkali solution, organic solvent or alkali–alcohol–water mixture or at different concentrations of alkali solution. The molecular weight of regenerated chitosan decreased from 2.37 × 10⁷ to 1.68 × 10⁷ Da proportionally with the concentration of the alkali solution of the recovery medium from 1N to 8N. Creep compliance of regenerated chitosan gel obtained from 65% degree of deacetylation (DD) chitosan was lower than that of either 72 or 89% DD chitosan gel. Of the same DD chitosan, compliance of regenerated chitosan gels obtained by using a higher concentration of alkali solution was lower than that of a lower concentration ones. Hydrogels regenerated from different DD chitosans and/or different recovery mediums have different structure and tactile properties. Therefore, they can be used as wound dressings suited to different applications. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 193–202, 2002; DOI 10.1002/app.10296