明胶的微生物降解

<正> 明胶发生微生物降解后会造成明胶分子中多肽链的肽键水解。任何具有能破坏肽键的溶朊酶的微生物都可使明胶发生微生物降解。有好几种不同类型的微生物含有此类溶朊酶。某些霉菌可使明胶液化,但由于它们生     

胰蛋白酶降解琥珀明胶的研究

对以胰蛋白酶为催化剂,琥珀明胶为底物的酶解反应体系进行了考察。结果表明,胰蛋白酶不仅可以切断琥珀明胶主链上的肽键,对琥珀酸分子上羧基和侧链氨基所形成的酰胺键也具有反应活性,导致降解产物的酰化度下降。研究了胰蛋白酶降解琥珀明胶的反应中,底物质量浓度、反应时间、温度、pH值和酶用量等条件对该反应的影响规律。找出了胰蛋白酶催化水解琥珀明胶的最适反应条件为:反应温度T=40℃,底物质量浓度约为100g L,体系pH=8 5,酶和底物质量比≥0 005。     

明胶的酶降解反应动力学研究 Ⅰ.影响明胶酶降解反应的因素

系统研究了酸度、温度、酶量、明胶浓度及反应时间等因素,对明胶酶降解反应的影响;确定了最适反应条件。     

氯化天然橡胶的热降解研究

用傅立叶变换红外光谱法和热失重分析法研究了氯化天然橡胶(CNR)的热氧降解和热降解过程。结果表明,CNR的热降解为一步反应,在160～390 ℃时CNR 发生脱氯化氢反应,在390 ℃时CNR 仍有质量分数为0.35的残留物存在,而且较稳定。CNR的热氧降解为两步反应,在160～390 ℃时,产生氯化氢和二氧化碳;在390～575 ℃时分解产物为二氧化碳,且分解彻底。     

聚乙烯的热降解动力学研究

采用三种不同的动力学分析方法,即Freeman方法、Flynn-Wall-Ozawa以及Kissinger方法对不同类型聚乙烯的热分解动力学进行了探讨。结果表明,Flynn-Wall-Ozawa法I、Friedman法的测试结果与三者聚乙烯的结构特征较吻合,不同聚乙烯降解活化能的大小顺序为HDPE>LLDPE>LDPE。     

明胶水解程度测定方法的探讨

本文探讨了FDNB、紫外分光光度法、甲醛反应滴定法、粘度法测定明胶水解程度的可能性,并对他们作了一定的研究。实验结果表明,紫外分光光度法、甲醛反应滴定法简便易行,有可能在水解明胶的工业生产中获得应用,但关键是要采用一个合适的测试液浓度和合适的滴定用的碱液浓度,才能确切地反应出明胶水解的规律,从而可以测得明胶的水解程度。     

水解明胶的喷雾干燥

<正> 喷雾干燥技术的应用非常广泛。这里着重探讨应用于水解明胶的喷雾干燥。一、概述水解明胶系以工业明胶、食用明胶等为主要原料,原料液在酸、碱、热或酶的作用下,其分子的某些肽键将不断地水解,从而制得小分子明胶液。水解后的明胶仍保持着明胶某些优良的品质,但也导致了某些性能的变化。如,分子量的降低和溶解度的增大,特别是凝冻能力的丧失及粘度的减小。正是这些性能的变化,才使其可采用喷雾干燥而制成水解明胶粉末。     

酶法生产水解明胶工艺研究

介绍以明胶为原料酶法生产水解明胶的原理及工艺，推荐了产品质量标准，并对水解明胶生产的前景进行了分析。     

木瓜蛋白酶水解明胶制备多肽的工艺研究

以明胶为原料,用木瓜蛋白酶降解制备多肽。试验中用甲醛滴定法和三氯醋酸法(TCA)测定明胶水解度,并将两种方法进行比较。得出甲醛滴定法简单易行便于过程控制,适合于工业生产需要。并系统的研究了pH、温度、酶量、底物浓度、以及反应时间等因素对明胶降解的影响,确定了制备护发调理剂最佳的水解工艺条件:底物浓度5%(w/v)明胶溶液,pH=7.0,木瓜蛋白酶量0.20%～0.30%,反应温度60℃,反应时间60 min。     

水解明胶对明胶凝冻强度的影响探究

明胶凝冻强度是评价其质量的一个重要指标,影响的因素有很多。本文专就明胶的水解物对明胶凝冻强度的影响进行了研究,考察了明胶水解物的含量对明胶凝冻强度值降低程度。研究证明了明胶水解物对明胶的凝胶强度影响显著。     

Kinetic study on the first stage during thermal degradation of polystyrene

The kinetic parameters of the first stage of polystyrene degradation have been investigated to elucidate the reaction mechanisms using the flow reactor system. The decrease in molecular weight of polystyrene was recorded at minute intervals over the temperature range 310°–390°C. Generally, the first and second stages were observed by thermogravimetric analysis (t.g.a.), however in the early stage of the degradation volatile yields of at least 5% occurred. Therefore, using t.g.a. analysis it is difficult to detect this earlier stage. It became evident that the first stage in the earlier part of the reaction could be detected by g.p.c. analysis. We have observed the hidden kinetic parameters of the nature of the first stage of the polystyrene degradation. The results indicate that the main chains were degraded randomly with the small quantitative volatile groups in the first stage and the rates of decrease in molecular weight in the first stage against reaction temperatures were evaluated as log k_s = 12.0 ? 41300/RT.     

溴化天然橡胶的热降解研究

用傅立叶变换红外光谱法和热失重分析法研究了溴质量分数分别为31%、51%和69%的溴化天然橡胶（BNR）的热降解和热氧降解过程。结果表明,BNR热降解为两步反应,第1步BNR发生脱溴化氢反应,失重率近似等于其溴含量;第2步BNR31、BNR51和BNR69在475℃降解时仍有9.7%、15.6%和12.7%的残留物存在,且较稳定。BNR热氧降解分3步进行,第1步反应的温度及降解率与热降解相近,产物主要是溴化氢,此外还有少量二氧化碳;第2步和第3步产物为二氧化碳,且分解彻底。     

The effects of clay on the thermal degradation behavior of poly(styrene-co-acrylonitirile)

The thermal degradation of poly(acrylonitrile-co-styrene) (SAN) and its clay nanocomposites were studied using TGA/FTIR and GC/MS. Virgin SAN degrades by chain scission followed by β-scission, producing monomers, dimers and trimers. The degradation pathway of SAN in clay nanocomposites contains additional steps; extensive random chain scission, evolving additional compounds having an odd number of carbons in the chain backbones, and radical recombination, producing head-to-head structures. Since acrylonitrile-butadiene-styrene copolymer (ABS) has butadiene rubber incorporated as a grafted phase in a SAN matrix, ABS follows a similar degradation pathway as that of SAN. The effect of butadiene rubber is similar to that of clay, leading to extensive random scission and an increase in thermal stability, but as not effective as clay due to its shorter duration. Eventually, the butadiene rubber phase degrades to small aliphatic molecules.     

New kinetic aspects on the mechanism of thermal oxidative degradation of polypropylenes with various tacticities

Thermal oxidative degradation behavior of polypropylene (PP) with different tacticities was studied based on the activation energy (ΔE) data obtained by thermogravimetric analysis (TGA). The ΔE value showed a negative proportion to the content of meso pentad fraction (mmmm) in all of isotactic PP (iPP) samples, and that of syndiotactic PP sample considerably deviated from this negative proportion relationship. Since the value of mmmm was directly related to polymer chain conformation, the ΔE value was thought to have close connection with the concentration of 3₁ helix conformation in the iPPs. The ΔE changes would be caused by the competition between uni- and bimolecular hydroperoxide decomposition, which was controlled by concentration and character of conformations of PPs.     

Population balance models for the thermal degradation of PMMA

A widely accepted view of the thermal degradation of polymers such as PMMA is that an initiation reaction produces radical fragments that undergo rapid depropagation and are also converted back to molecules by a termination reaction. This mechanism is applied to a population of linear molecules and radicals and the evolution of the population is modelled by appropriate discrete sets of ordinary differential equations. In particular, end-chain and random initiation reactions with first-order termination are analysed and compared with experimental data. We find on comparison with TG data for PMMA that the initiation reaction is important in dictating the qualitative behaviour of the overall rate of thermal degradation. Furthermore, the behaviour of degradation rate with initial degree of polymerisation is also investigated and interpreted within the framework of the model.     

Influence of thermal treatments on the structure and stability of gelatin gels

The influence of thermal history on the structure of gelatin gels has been investigated by measuring the specific optical rotation [α]_λ at λ = 436 nm. The helix content χ in the gels was derived by reference to the native collagen. Two types of thermal treatments have been applied: (a) cooling and heating at constant rates, and (b) quenching and annealing for long periods. Our results support the idea that the gels are non-equilibrium systems and exhibit thermal hysteresis. The kinetics of helix formation were analysed by the Avrami theory and compared to other techniques. The stability of the structures formed suggests the existence of several mechanisms of hydrogen bonding of the helices: disordered aggregation or partial collagen renaturation.     

SIS-g-AN热降解性能的研究

采用热重分析法和差示热重分析法研究丙烯腈(AN)接枝热塑性弹性体SIS(SIS g AN)的热降解性能。结果得出,SIS g AN的平衡起始降解温度、平衡最大降解速率温度和平衡终止降解温度分别为659. 17, 713. 94 和740.05 K;热降解反应活化能为195.2 kJ·mol-1;热降解机理是Deceleration中的D3 降解机理;不同质量损失率下的热寿命与温度呈线性关系。     

明胶及其酰化产物的沉降性能

本文研究了明胶和酰化明胶溶液的沉降性能,考察了试剂用量及pH值对沉降性能的影响,找出了一些基本的规律,发现了氯化钠盐析与乙醇、丙酮溶剂沉降时,明胶和酰化明胶沉降效率的不同,并从理论上进行了初步的探讨。     

Further insights on the thermal degradation of aluminum metaphosphate prepared from aluminum dihydrogen phosphate solution

A study of the high temperature (up to 1200 °C) degradation of aluminum metaphosphate Al(PO₃)₃ has been carried out to evaluate the stability of this compound used for many purposes. For the preparation of Al(PO₃)₃, an aluminum dihydrogen-phosphate Al(H₂PO₄)₃ solution has been heated at 700 °C. Thermal degradation of Al(PO₃)₃ has been followed through the measurement of weight loss on isothermal mode at 1000 and 1200 °C and by thermogravimetric analysis coupled with mass spectroscopy (TGA-MS). Structural data have been obtained by ²⁷Al, ³¹P and ¹H MAS NMR spectroscopy. NMR analyses have shown that [A] and [B] allotropic forms of Al(PO₃)₃ are formed after the preparation procedure. In addition, NMR revealed that hydroxyls groups are also present in the sample, and they form POH groups. TGA-MS showed that they are decomposed at a temperature of 875 °C, while the decomposition of Al(PO₃)₃ into AlPO₄ and P₂O₅ begins at 1000 °C.     

PA 1111的热降解过程和机理研究

通过热重分析研究了聚酰胺(PA)1111在N_2气氛中以不同升温速率时的热降解过程和机理。PA1111的热降解实验表明,PA 1111的热降解是一步过程,热降解温度为419.5℃。用Kinssinger和Flynn-Wall-Ozawa方法求得PA 1111的热降解表观活化能分别为239.3 kJ/mol和240.9 kJ/mol。用Coats-Redfern方法证明了PA 1111的热降解为减速机理。