γ-射线辐照对壳聚糖相对分子质量影响

壳聚糖是地球上蕴藏量最丰富的有机物之一.常用的壳聚糖相对分子质量大,不易溶于水等普通溶剂,使其应用受到极大限制.使用γ-射线(3x1015Bq钴-60装置)辐照壳聚糖,研究了溶液浓度、辐照剂量、辐照气氛、pH值和样品状态等因素在壳聚糖γ-射线辐照过程中对相对分子质量的影响.结果表明壳聚糖辐射降解产物的平均分子量随着溶液浓度增加和辐照剂量增大而降低,而与溶液的pH值无关.水对于壳聚糖辐射裂解有加速效应,溶液态壳聚糖辐照降解比固态辐照可以提高效率约50倍.     

磷钨酸催化壳聚糖氧化降解的工艺优化

采用磷钨酸作催化剂,催化H_2O_2氧化降解天然大分子壳聚糖制备水溶性壳聚糖。通过单因素实验研究了降解温度、降解时间、催化剂用量(磷钨酸与壳聚糖的质量比)、H_2O_2用量(H_2O_2与糖单元物质的量比)对壳聚糖降解的影响,采用正交实验优化了最佳制备工艺条件。结果表明,水溶性壳聚糖最佳制备工艺条件为:降解温度70℃、降解时间4 h、催化剂用量0.02、H_2O_2用量2.0,在最佳工艺条件下,得到了产率58%左右、数均分子量1 500 Da左右的浅黄色水溶性壳聚糖。     

降温母粒对控制降解聚丙烯结晶性能的影响

研究了共聚聚丙烯和均聚聚丙烯加入降温母粒降解前后结晶性能的变化。发现适量的降温母粒含量(质量分数0.6%)可以改善均聚聚丙烯的结晶性能,但对控制降解共聚聚丙烯的结晶性能影响更为复杂。同时发现相对分子质量分布(MWD)对控制降解聚丙烯结晶形态的变化规律更为显著。     

电子束辐照聚四氟乙烯微粉的制备与表征

采用电子束辐照降解法制备了PTFE微粉,并对不同剂量下制备的PTFE微粉的结构、热性能及形态分布进行了研究。结果表明,通过电子束辐照可以使聚四氟乙烯有效降解,且主要以C-C主链断裂为主;辐照剂量对结晶温度、相对分子质量及粒径尺寸以及粒径尺寸分布有较大影响。随着辐照剂量的上升,样品相对分子质量逐渐下降,粒径变小,初始结晶温度向低温方向偏移,但耐热性变化不大,粒径分布变窄且服从正态分布。     

壳聚糖季铵化衍生物结构表征及特性研究

采用壳聚糖(CTS)与2,3-环氧丙基三甲基氯化铵(GTA)制备了不同取代度的水溶性壳聚糖季铵盐(HACC),通过红外、扫描电镜对壳聚糖、壳聚糖季铵盐结构进行表征,同时测试了壳聚糖季铵盐的水溶性、表面张力.结果表明:取代主要发生在壳聚糖的氨基上,改性后产物外观与粒度有很大变化;壳聚糖季铵化改性产物具有比壳聚糖更优良的水溶性、表面活性,且随着取代度的增加而提高.     

水溶性甲壳低聚糖的制备与结构表征

以H_2O_2为氧化剂,在中性介质中使壳聚糖氧化降解为水溶性甲壳低聚糖,并研究了H_2O_2用量、反应温度和保温时间对产物收率的影响;用双突跃电位滴定法测定了产物的脱乙酰度,FT-IR和~1H NMR表征了产物结构。实验结果表明,H_2O_2在中性介质中使壳聚糖氧化降解为水溶性甲壳低聚糖的同时,也会使产物进一步降解;产物中含醛基的链式结构组成明显高于壳聚糖,并且过高的反应温度和H_2O_2用量不利于水溶性甲壳低聚糖的生成;适宜的H_2O_2用量为3.0~3.5 m L(30%H_2O_2)/g(CTS),而反应温度和保温时间则分别为60℃和7.0~8 h。     

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。     

双氧水均相氧化降解制备水溶性壳聚糖的研究

在酸性条件下,利用H2O2在均相条件下对壳聚糖进行降解,通过控制反应时间、反应温度、反应物浓度等条件,制备一系列不同分子量(0.23×104～6.5×104)的水溶性壳聚糖,用FT-IR、TG-DTA对其降解产物进行表征,并对影响降解的主要因素及降解机理进行了讨论。     

Mn(Ⅱ)对壳聚糖降解制备低聚壳聚糖的影响

将壳聚糖进行液态均相配合反应制得壳聚糖锰配合物，IR、元素分析及热分析等检测证实了壳聚糖锰配合物中配位键的存在，且显示壳聚糖锰配合物存在有利于壳聚糖高分子链断裂的弱势结构。以H2O2对壳聚糖．Mn(Ⅱ)配合物及壳聚糖进行氧化降解，考察降解过程中粘度的变化及降解产物分子量分布，在相同的降解条件下，壳聚糖锰配合物的降解速度明显高于壳聚糖，且降解产物分子量分布较壳聚糖直接降解窄。对壳聚糖锰配合物降解反应动力学研究表明壳聚糖锰配合物对H2O2分解不存在催化作用，其降解反应与壳聚糖的差异只与其结构有关。对降解产物进行脱金属处理，所得低聚壳聚糖含锰量为0。     

PCL及PCL-PEG-PCL共聚物的合成与表征

以辛酸亚锡[Sn(Oct)2]作为引发剂,采用ε-己内酯(ε-CL)开环均聚合制备聚ε-己内酯(PCL),考察了n(ε-CL)/n[Sn(Oct)2]、反应温度和反应时间等因素对聚合产物特性黏数的影响。以Sn(Oct)2为催化剂,聚乙二醇(PEG)为引发剂,合成了不同相对分子质量的PCL-PEG-PCL三嵌段共聚物,研究了ε-CL均聚物及共聚物的结构、热性能和结晶形态。PCL最佳合成工艺为:n(ε-CL)/n[Sn(Oct)2]为400,温度130℃,反应时间4 h。随着PEG相对分子质量从2×103增加到8×103,三嵌段共聚物的熔融温度、熔融焓和结晶温度逐渐升高;结晶温度及PEG相对分子质量对PCL-PEG-PCL三嵌段共聚物球晶的形态和尺寸影响很大。     

固相法化学降解等规聚丙烯

在剪切力作用和较低温度下,利用过氧化物对等规聚丙烯（PP）化学降解,得到了具有超高熔体流动速率（MFR）的PP降解产品。考察了降解时间对降解产品的MFR及相对分子质量的影响,发现随着降解时间的增加,MFR提高幅度逐渐减小,相对分子质量下降。用红外光谱和差示扫描量热法表征发现,降解PP出现了羰基和碳碳双键吸收峰．且羰基吸收峰随降解时间的增加而增强;PP降解产品在不同温度下的结晶结构未改变。     

Effect of sonolysis on kinetics and physicochemical properties of treated chitosan

Low molecular weight chitosan with weight‐average molecular weight from 161 to 22,000Da were obtained by sonolysis. Optimal conditions for sonolysis were described. The influence of sonolysis condition and the molecular parameters of initial chitosan on the degradation rate and degradation rate constant were investigated in detail. Weight‐average molecular weight (M_w) and molecular weight dispersion (M_w/M_n) of samples were measured by gel permeation chromatography. The structure of degraded chitosan were characterized by Fourier transform infrared, X‐ray diffraction, and electrospray ionization mass spectrometry. For a given sonolysis time, the decrease in molecular weight has been found to be greatest at lowest reaction temperature and lowest chitosan concentration. Molecular weight of samples decreased exponentially with increasing sonication time at early stages. The action mode of ultrasound on the splitting of molecular chain of chitosan has been discussed. The degree of deacetylation of the main hydrolysis products almost unchanged compared with the initial chitosan. The decrease of molecular weight led to transformation of crystal structure but the chemical structures of residues were not modified. Ultrasonic treatment on chitosan is an alternative, safe method to prepare chitosan having different molecular weights, which are more suitable for biomedical and food applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of immobilized neutral protease on the preparation and physicochemical properties of low molecular weight chitosan and chito‐oligomers

Neutral protease was immobilized on glutaraldehyde‐pretreated N‐succinyl chitosan hydrogel beads and the biocatalyst obtained was used for the preparation of low molecular weight chitosan and chito‐oligomers with molecular weight of 1.9–23.5 kDa from commercial chitosan. Factors affecting the chitinolytic hydrolysis were described. The degradation was monitored by gel permeation chromatography. The structure of degraded chitosan was characterized by Fourier transform infrared, X‐ray diffraction and liquid chromatography‐mass spectrometry. Immobilized neutral protease showed optimal depolymerization at pH 5.7 and 50°C. The degree of deacetylation of the hydrolysates did not change compared to that of the initial chitosan. The decrease of molecular weight led to transformation of crystal structure but the chemical structures of residues were not modified. The degree of polymerization of chito‐oligomers was mainly from 3 to 8. The method allows cyclic procedures of immobilized enzyme and N‐succinyl chitosan support utilization, and is suitable for a large‐scale production of the low molecular weight chitosan and chito‐oligomers free of protein admixtures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:4185–4193, 2006     

壳聚糖及丁二酸酐酰化壳聚糖双氧水降解行为的研究

在简单均相体系下．研究了壳聚糖及丁二酸酐酰化壳聚糖在双氧水中的降解特性。采用鸟氏粘度计,利用一点法测量了降解过程中壳聚糖及丁二酸酐酰化壳聚糖的分子量,讨论了该体系下壳聚糖及丁二酸酐酰化壳聚糖的降解速率．通过红外光谱分析了双氧水对低分子量壳聚糖和低分子量丁二酸酐酰化壳聚糖结构的影响。结果表明．在该体系下·壳聚糖及丁二酸酐酰化壳聚糖的降解主要发生在反应开始后的2～3h内．此后降解产物的分子量逐渐趋于20000;相同条件下,丁二酸酐酰化壳聚糖的降解程度高于壳聚糖;红外光谱表明．采用该降解体系制备的降解产物主链结构基本没有发生变化。     

Thermal stability and degradation of chitosan modified with phenylacetic acid

N-(phenylacetyl) chitosan (NPAC) polymer was synthesized by the reaction of phenylacetic acid with chitosan. The chemical structure of the formed polymer was characterized by IR and microanalysis. Thermogravimetric analysis revealed that the thermal stability of the NPAC polymer was less than that of chitosan. The products of NPAC thermal degradation were identified by the GC-MS technique. The results indicate that the mechanism of degradation of NPAC polymer is characterized by the elimination of low-molecular weight radicals. A combination of these radicals and a random scission mechanism along the backbone chain are the main source of the degradation products.     

新型水溶性壳聚糖衍生物的制备

以醋酸和丙酮为反应介质,利用马来酸酐在均相条件下对壳聚糖进行水溶性N-酰化改性;与壳聚糖相比,改性后的壳聚糖衍生物的水溶性有了很大改善。实验表明：对壳聚糖的N-酰化改性程度越高,其改性产物的水溶性越好;同时,制备的3种样品的产率均在90％以上。     

Radiation degradation of microcrystalline cellulose in solid status

Pulverization and degradation are important pretreatment procedures in producing bio‐ethanol from cellulose. In this study, microcrystalline cellulose (MCC), a pure α‐cellulose, was degraded by γ‐irradiation. The average degree of polymerization, content of reducing sugar, crystalline structure, and molecular structure were investigated to elucidate the radiation effect on the degradation of MCC. The results manifested that γ‐ray destroyed part of the chemical bond and hydrogen bond, leading to the degradation of cellulose and increasing of the reducing sugar content. According to the Fourier transform infrared result, radiation degradation led to the formation of reductive carbonyl group. Meanwhile, radiation had slight influence on the crystalline structures of MCC. Therefore, the radiation degradation procedure is expected to benefit the further proceedings such as ultrafine treatment and enzyme hydrolysis of cellulose. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

纳米纤维素/壳聚糖/明胶复合膜的制备及其性能研究

以明胶（Gel）、壳聚糖（CS）、纳米纤维素（NCC）为原料,采用溶液共混法制备了不同NCC和CS质量比的纳米纤维素/壳聚糖/明胶复合膜。采用紫外-可见分光光度计、扫描电镜（SEM）、红外光谱仪（FT-IR）、X射线衍射仪（XRD）、热分析仪（TGA）和质构仪对所制备复合膜的透光性能、显微结构、化学结构、晶体结构、热学性能和力学性能进行了分析。结果表明：纳米纤维素、壳聚糖、明胶之间形成相互作用较强的网络结构。复合膜表面光滑,分散均匀,具有良好的相容性。随着纳米纤维素含量的增加,复合膜透光率呈下降的趋势。与壳聚糖膜相比,复合膜的热稳定性显著提高。当纳米纤维素与壳聚糖质量比为7：1时,复合膜拉伸强度最高可达到33 MPa,断裂伸长率可达到14.9%,吸水率最大值可达到341%。     

Effect of amine degradation products on the membrane gas absorption process

The effect of the presence of monoethanolamine (MEA) degradation products on membrane hollow fibers was investigated using untreated polypropylene (PP) as a model material. Common amine oxidative degradation products were added to MEA to simulate a degraded solution. The effect of these degradation products on the membrane gas absorption process using PP hollow fiber membrane was quantified. When PP membrane which has been exposed to amine degradation products is used in a membrane gas absorption contactor, the mass transfer rate of CO₂ is reduced relative to the use of unexposed PP. It was found that the presence of oxalic acid reduced the mass transfer rate of CO₂ in MEA most significantly followed by formic acid and then acetic acid. These acids are believed to adsorb into the PP, altering the surface properties and reducing the hydrophobicity of the membrane. This in turn increases the degree of wetting of the membrane pores. The membrane was characterized before and after use in a membrane gas absorption contactor containing degraded MEA solvent and studies showed that membrane pore wetting increased by 22-31% after 69 h of use. SEM images and XPS spectra of exposed PP membrane indicate that wetting may be due to both morphological and chemical changes in the membrane due to contact with the solvent. This study highlights the need to consider reductions in the mass transfer rate of membrane gas absorption processes associated with inevitable changes in the solvent composition that comes with prolonged use.     

Synthesis and characterization of polyurethane elastomers based on chitosan and poly(ε‐caprolactone)

Biodegradable polyurethane (PU) elastomers with potential for biomedical and industrial applications were synthesized by the reaction of poly(ε‐caprolactone) (PCL) and isophorone diisocyanate (IPDI), extended with different mass ratio of chitosan and 1,4‐butane diol (BDO). Their chemical structures were characterized using FTIR, ¹HNMR, and ¹³CNMR, and thermal properties were determined by TGA and DMTA. Incorporation of chitosan contents into the polyurethane backbone caused improvement in thermal stability and thermal degradation rate. Optimum thermal properties and degradation profile were obtained from elastomer extended with chitosan. The crystallinity and hydrophilicity of the prepared polymers were also examined by X‐ray and contact angle measurements. The results showed that hydrophilicity decreased and crystallinity increased with increasing of chitosan content in polyurethane backbone. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009