水引发L-丙交酯开环聚合工艺研究

针对L-丙交酯本体开环聚合中富羟基水的存在导致产物聚乳酸相对分子质量偏低的问题,选用辛酸亚锡为催化剂,研究了L-丙交酯重结晶次数、精制L-丙交酯干燥时间及聚合前反应釜内真空干燥时间3项关键水分控制工艺对聚乳酸相对分子质量的影响。借助核磁共振仪、红外光谱仪、差示扫描量热仪和热重分析仪表征并分析了聚乳酸的化学结构和热力学性能。结果表明:增加L-丙交酯重结晶次数,延长精制L-丙交酯干燥时间以及延长聚合前反应釜内真空干燥时间,均不同程度上有助于提高聚乳酸的黏均分子量;与低黏均分子量聚乳酸相比,高黏均分子量的聚乳酸熔点提高至175 ℃,有较好的热稳定性。     

由乳酸合成聚乳酸的研究

由乳酸合成乳酸的环状二聚体丙交酯,丙交酯在辛酸亚锡催化剂引发下开环聚合得到聚乳酸,讨论了单体纯度、引发剂与单体比例、反应温度、聚合时间对聚乳酸合成的影响,通过平均分子量、红外光谱和核磁共振光谱对聚乳酸进行了表征。     

聚乳酸的制备与性能研究

采用二步法由乳酸制备丙交酯,由丙交酯的开环聚合制备高分子量的聚乳酸。实验采用正交设计方法,通过改变催化剂种类、催化剂用量、脱水时间、环化时间四个主要影响因素进行实验,根据实验结果选择最好的丙交酯制备的实验方案。再次运用正交设计方法,通过改变催化剂种类、催化剂用量、反应时间、反应温度得到性能和分子量不同的聚乳酸,采用乌氏黏度计方法测定聚乳酸的分子量,利用傅立叶红外光谱和扫描电镜对聚乳酸的结构和形貌进行表征。     

聚乳酸/低密度聚乙烯共混聚合物的制备及表征

聚乳酸（PLA）是一种来源于玉米及甜菜根的脂肪类聚合物,可被降解为无毒的化合物。目前,常用的PLA合成方法为直接由乳酸或丙交酯开环聚合制得PLA。首先用乳酸合成低分子量的PLA,随后使其解聚成丙交酯（不稳定的二聚物）,最后经催化剂开环聚合成可控的高分子聚合物,其制备过程免溶剂处理。该方法能够以低成本生产高分子量的PLA,故在市场上得到了广泛的应用。     

α,ω二羟基二甲基硅氧烷齐聚物的合成与研究

本文介绍了用自制酸性催化剂、乙酸酐作助催化剂对八甲基环四硅氧烷进行开环聚合制备出低分子量的α,ω-二羟基二甲基硅氧烷齐聚物(PSi)的方法;研究过程中发现,通过改变乙酸酐用量可调节PSi分子量的大小,其收率可达90％以上。     

欧盟InnoREX项目——开发制备聚乳酸的新技术

正目前,由德国化学研究所协调、欧盟资助的InnoREX'项目,目的在于开发制备聚乳酸(PLA)产品的新技术,以改善PLA的均匀性,并停止使用目前用来改善内酯聚合速率的金属催化剂。研发团队中的12位合作者正在寻找一种新的制备聚乳酸的聚合方式,即通过反应挤出进行持续、精     

L-丙交酯/meso-丙交酯的共聚反应及其产物性能

为研究工业化生产中左旋(L-)丙交酯和内消旋(meso-)丙交酯的聚合反应及产物性能，通过对L-丙交酯进行高温热处理制备更加符合工业生产的meso-丙交酯，并以L-丙交酯和meso-丙交酯为聚合单体，探究丙交酯性质对开环聚合反应产物的分子量及其性能的影响。借助凝胶渗透色谱仪、核磁共振波谱仪、傅里叶红外光谱仪、热重分析仪、差示扫描量热仪和二维X射线衍射仪分析了聚乳酸共聚产物的分子量、化学结构、热性能和结晶性能。结果表明：含有0～5.0%meso-丙交酯的L-丙交酯可以成功进行开环聚合得到聚乳酸共聚物，并且meso-丙交酯的存在不会显著影响聚合物分子量的分布均一性。随着meso-丙交酯含量的增加，聚乳酸的热分解温度、玻璃化转变温度、熔点和熔融焓等热性能参数均明显降低。与聚左旋乳酸(PLLA)相比，共聚物的结晶速度与结晶能力降低，二者的最佳结晶温度均在100℃左右。meso-丙交酯的加入使共聚物大分子链的有序化程度降低，但不会改变聚乳酸的晶体结构。     

聚乳酸纤维原液着色用改性炭黑的制备及其性能

针对聚乳酸纤维原液着色过程中炭黑与聚乳酸相容性差导致其力学性能下降的问题,采用原位聚合法制备了聚乳酸改性炭黑,并对聚乳酸纤维进行原液着色。探讨丙交酯用量、反应温度、聚合时间对聚乳酸改性炭黑的粒径及粒径分布的影响,并对其在聚乳酸纺丝溶剂中的分散稳定性进行测试,同时对加入改性与未改性炭黑前后的聚乳酸纺丝液及聚乳酸膜进行分析与表征。结果表明:在丙交酯单体的用量为1.5 g、聚合时间为6 h、聚合温度为70 ℃时制备出的改性炭黑的粒径最小,为184.2 nm,且其在聚乳酸纺丝溶剂中可以稳定分散,与聚乳酸相容性较好;与未改性炭黑相比,加入改性炭黑后聚乳酸的力学性能得到提升。     

不同温度下酸催化有机硅单体开环共聚制备含氢硅油的研究

以98%浓硫酸为催化剂,进行了八甲基环四硅氧烷(D4)与四甲基环四硅氧烷(DH4)的阳离子开环共聚并得到含氢硅油,重点考察了不同共聚温度对聚合产物转化率、含氢值及其分子量分布的影响。研究结果表明:在温度30℃条件下,制备得到的聚合物分子量和含氢值接近理论值,增加共聚温度对聚合物转化率的提高帮助不大,且会使聚合物的分子量分布变宽。     

提高聚合物质量，改善纺丝加工性能

我厂二期聚合釜开车，一、二期调聚合釜催化剂流量相差很大，二期聚合釜运行周期短，易结疤，催化剂用量比一期聚合釜多60-70kg／h，二期聚合物分子量分布宽，造成纺丝毛丝多，既造成了催化剂消耗高，聚合釜清理周期短，又影响了最终产品质量。为此，探讨二期聚合釜反应过程中参数控制及影响因素，来延长聚合釜运行周期，改善A-7聚合物的质量及加工性能。     

两种分子量壳聚糖抗疲劳作用的研究

目的:以小鼠为实验对象,研究两种分子量和剂量的壳聚糖对小鼠的抗疲劳作用的影响。方法:用相对分子质量为2.4×103和7.6×104的壳聚糖给小鼠灌胃18d,测定游泳时间、血糖和乳酸含量;至24d测定肝糖原和肌糖原含量。结果:两种分子量和不同剂量的壳聚糖均能延长小鼠游泳时间、加速游泳后血糖恢复和乳酸清除并提高游泳前后肝糖原和肌糖原的含量;与同剂量的高分子量壳聚糖相比,低分子量壳聚糖显示了更优的抗疲劳作用。结论:壳聚糖具有抗疲劳作用且与其分子量有关。     

Enhancement of low molecular weight ginsenosides from low-quality ginseng through ultra-high-pressure and fermentation processes

This study aimed to analyze the conversion pattern of high to low molecular weight ginsenosides in low-quality ginseng during lactic acid fermentation associated with an ultra-high-pressure process. It was found that the relative quantities of various low molecular weight ginsenosides were increased by 20 min of pressure treatment at 500 MPa following fermentation with Bifidobacterium longum. Specifically, after ultra-high-pressure extraction, the triol-type, low molecular weight Rg2 was the most abundant ginsenoside, at 1.213 mg/g. However, when low-quality ginseng was fermented, the concentrations of diol-type, low molecular weight ginsenosides (e.g., Compound-K (CK), Rh2, and Rg3) largely increased to 1.52, 1.241, and 0.947 mg/g, respectively. These data indicate that high molecular weight ginsenosides in ginseng could be broken down by two different hydrolysis mechanisms. In the fermentation process, the β-1,2 and β-1,4 glycosidic bonds in high molecular weight ginsenosides such as Re, Rc, and Rb1 were hydrolyzed to diol-type, low molecular weight ginsenosides by the β-glucosidase enzyme of the lactic acid bacterium. Meanwhile, the physical energy of the ultra-high-pressure process specifically hydrolyzed relatively weak bonds of the sugars in high molecular weight ginsenosides such as Re to form the low molecular weight ginsenoside Rg2. Rg2, Rg3, Rh2, and CK increased to 2.043, 1.742, 1.834, and 2.415 mg/g, respectively, possibly due to a synergistic effect of combining both processes. Therefore, low molecular weight ginsenosides with higher biological activities than high molecular weight ginsenosides can be selectively obtained from low-quality ginseng using both fermentation and ultra-high-pressure processes.     

传统培养结合分子生物学法分析传统发酵食品中乳酸菌的多样性

利用传统分离培养法和基于PCR-DGGE的分子生物学方法来分析酸菜和酸奶等广西特色传统发酵食品中乳酸菌的多样性.结果显示,用传统分离培养结合分子生物学方法共获得7个属的乳酸菌,其中乳杆菌属是主要优势菌群.传统分离法与分子生物学法法结合能够更有效的分析传统发酵食品中乳酸菌的多样性,获得更全面的信息.     

聚乙二醇改性聚乳酸吸湿性能研究

以美国聚乳酸、自制聚乳酸和聚乙二醇为原料,分别熔融共聚得到聚乳酸-聚乙二醇共聚物(PLEG)。以L-乳酸与聚乙二醇为原料,熔融共聚后再固相聚合得到PLEG。用凝胶渗透色谱(GPC)、红外光谱(FTIR),熔点测试、吸湿率测试等手段对其进行表征,发现相同条件下,L-乳酸与聚乙二醇熔融共聚后再固相聚合得到的PLEG吸湿率最高。     

Quality characteristics of reduced-fat Chinese-style sausage as related to chitosan's molecular weight

Microbiological and physicochemical characteristics of reduced-fat (approximately 22%) Chinese-style sausages containing 0.1% chitosan (in 1% lactic acid solution) with three different molecular weights [low molecular weight chitosan (CHL), MW= 150 kDa; medium molecular weight chitosan (CHM), MW=600 kDa; high molecular weight chitosan (CHH), MW=1250 kDa] were demonstrated. Sausages were also subject to oven heating or deep-fat frying for sensory evaluation. Treatments containing chitosan were lower in pH at any storage periods than the control (CONT). Generally speaking, total plate counts and lactic acid bacteria counts of all treatments slightly increased, with CHL being the lowest. However, all bacterial counts were lower than 7 [log colony forming unit (CFU)/g] at the end of storage. Results from sensory evaluation showed that deep-fat fried sausages from treatments CHL and CHM were higher in overall acceptability. This study demonstrated that the addition of chitosan to reduced-fat Chinese-style sausage resulted in no detrimental effect on textural properties.     

Effect of different manufacturing parameters on the characteristics of Graviera Kritis cheese

The objective of the present study was to improve the characteristics of Graviera Kritis cheese. The influence of lactic acid and propionic acid starters was studied and then the effect of washing and salting the curd combined with the use of starters was investigated. Although the traditional technology without starters resulted in the highest organoleptic characteristics, it was shown that the use of starters could improve texture characteristics of the cheeses if it is combined with a curd wash to control acidity development. Lower pH values and higher contents of low molecular weight nitrogenous substances were consistent with texture defects. Moreover, the ripening at higher temperatures increased proteolysis levels and decreased cheese quality.     

Chitosan Treatment Affects Yield, Ascorbic Acid Content, and Hardness of Soybean Sprouts

ABSTRACT: The effects of molecular weights, concentrations and solvents of chitosan, soaking times, and soybeans/chitosan solution ratios on growth and quality of soybean sprouts were investigated. Among 5 chitosans, treatment with 493 kDa chitosan was the most effective in increasing total weight, vitamin C content, and hardness. Use of acetic acid rather than lactic acid as a chitosan solvent increased hypocotyl weight and vitamin C content. Soaking of soybeans in chitosan solution for 8 h increased total weight by 13% and vitamin C content by about 10%. Optimal cultivation conditions involve soaking in 0.05% chitosan with 493 kDa in 0.05% acetic acid for 8 h and a soybean/chitosan solution ratio of 1:4.     

多分散性树状大分子的合成和性质

以亚酒石酸为单体,采用缩合聚合方法合成了低分子聚合物,测定了低聚物的分子量,并用5%的低聚物水溶液对染料罗丹红Ⅲ的正己烷溶液进行萃取,用紫外分光光度法测定了萃取液的染料质量浓度。结果表明,合成的低聚物分子量达到较高数值时,低聚物就会产生对染料罗丹红Ⅲ的包合作用,表明低聚物中有树枝状大分子结构,树枝状大分子的内部空腔是疏水性的,可以容纳疏水性的染料分子。研究了低聚物的合成条件,结果表明,单体含量10%～20%、温度100℃、聚合时间140～160min,合成的低聚物对染料罗丹红Ⅲ的正己烷溶液有较高的萃取浓度。     

Pressurized acidified water extraction of black carrot [<Emphasis Type="Italic">Daucus carota</Emphasis> ssp. <Emphasis Type="Italic">sativus</Emphasis> var. <Emphasis Type="Italic">atrorubens</Emphasis> Alef.] anthocyanins

The anthocyanins present in black carrot were extracted with pressurized water acidified with sulfuric, citric and lactic acids. Anthocyanin degradation became significant above 100 °C and there was no improvement when extraction pressure was increased to 100 bar. Therefore, the extraction from black carrot was carried out at temperatures 50, 75 and 100 °C under 50 bar pressure. The extraction efficiencies in terms of acylated and non-acylated anthocyanins were comparable for all three acids used to acidify water at 50 °C, while similar results were observed at 75 °C for both citric and lactic acids. Water acidified with lactic acid showed significantly higher extraction efficiency at 100 °C compared to water acidified with sulfuric and citric acids. Highest degree of polymerization together with increasing degree of browning was observed within extracts when sulfuric acid was used. On the other hand, when organic acids were used to acidify water, a higher extraction efficiency of anthocyanins, accompanied with a relatively low polymerization and browning was observed, with lactic acid giving the best results.