醋酸纤维素的降解性研究进展

介绍了醋酸纤维素的生物降解、水解、光解的降解机理与研究现状,并对影响醋酸纤维素降解速率的因素进行了探究。从现有研究中可知,影响醋酸纤维素降解速率的主要因素为醋酸纤维素自身的分子结构（如取代度、取代度分布及结晶性等）,物理改性、化学改性及增塑改性会通过改变醋酸纤维素的分子结构,进而影响醋酸纤维素的降解性能。最后,总结了醋酸纤维的应用领域,并做出了展望。     

我国纤维素衍生物工业现状及发展

我国纤维素衍生物工业已有数十年历史,除硝酸纤维素和粘胶纤维已有相当规模的大、中型厂外,按甲基纤维素近年来已发展至数十中小型厂,形成了2万ua以上的生产规模。但醋酸纤维素尚不足0．5万Ua规模。我国纤维素衍生物与国外相比,不论在品种,产量,质量和价格上都有较大的差距。1纤维素酯类产品该类产品主要品种有硝酸纤维素、二醋酸纤维素、三醋酸纤维素、丁醋酸纤维素和丙醋酸纤维素。1．l硝酸纤维素虽然目前电影片基几乎全部为三醋酸纤维和涤纶树脂所代替,但硝酸纤维素由于价格低廉,尚有相当用量,而用于清漆、塑料和薄膜的硝酸纤…     

醋酸纤维素衍生物反渗透膜对低分子量有机物分离特性研究

研究用醋酸纤维素衍生物氰乙基醋酸纤维素、羟丙基醋酸纤维素和醋酸纤维素反渗透膜对有机醇、有机酸及有机胺类水溶液的分离特性,考察操作压力对反渗透分离特性的影响,并应用不可逆热力学过程得出的Spiegler—Kedem膜输送方程解析实验数据,获得了反射系数σ、溶质渗透系数ω和溶剂水渗透系L_p等膜参数。     

纤维素醋酸酯接枝己内酯的合成与表征

以冰醋酸为溶剂,浓硫酸为催化剂,将三醋酸纤维素水解为不同取代度的醋酸纤维素(CA),再用此醋酸纤维素同ε-己内酯(ε-CL)接枝共聚合成醋酸纤维素/聚己内酯接枝共聚物(CA-g-PCL).研究了醋酸纤维素取代度和原料配比对单体转化率(C)、接枝率(G)、接枝效率(EG)的影响,结果表明在醋酸纤维素取代度为0.7时接枝共聚反应C、G、EG可分别达到46%、238.6%、88.5%;m(ε-CL)m(CA)=51时可分别达48.3%、140.553%、58.2%,并对相应的接枝共聚物进行了FTIR和1H-NMR的表征分析.     

醋酸纤维素取代基分布与性质的关系

分析了以吡啶为溶剂的醋酸纤维素的13C-NMR核磁共振谱,得出了三种不同位置羟基的取代度。结合X—射线和DSC分析,初步说明具有相同取代度但未经水解和经过水解的醋酸纤维素(CA) 性质上的差异是由于三个羟基上的取代度分布不同及消晶程度差异所致。     

大麻秆浆制备醋酸纤维素的研究

以大麻秆浆和醋酸为原料制备了醋酸纤维素。考察了硫酸用量、保温温度、保温时间、醋酐用量和冰醋酸用量对醋酸纤维素取代度和聚合度的影响。采用红外光谱和X射线衍射分析对醋酸纤维素进行了表征。实验结果表明:增加硫酸用量、提高保温温度和延长保温时间可提高醋酸纤维素的取代度,但聚合度下降;增加醋酸酐用量可提高醋酸纤维素的取代度,对聚合度影响不大;增加冰醋酸用量可提高醋酸纤维素的聚合度,对取代度影响不大。制备醋酸纤维素的适宜条件为:硫酸、醋酸酐和冰醋酸对大麻秆浆的质量比分别为0.13、9.0和9.0,保温温度为50℃,保温时间为1 h。该条件下制备的醋酸纤维素取代度为2.92,聚合度为121。由醋酸纤维素的红外光谱可证实纤维素与醋酸酐之间醋化反应的发生。X射线衍射分析表明大麻秆浆经醋化反应后,纤维素晶型发生了明显的变化。     

三醋酸纤维素与片基质量的关系

本文比较了三醋酸纤维素摄影片基的国内外质量指标;讨论了影响三醋酸纤维素片基质量的一些因素,如制备三醋酸纤维素的工艺线路、醋酸结合量、分子量和分子量分布、胶液配方以及流涎工艺过程。提出了改进三醋酸纤维片基的质量应从稳定棉短绒原料着手,抓好酯化工艺,把住流涎制片关,才能在保证质量的前提下,向高速流涎方向发展。     

烟用滤棒二醋酸纤维素的回收及静电纺丝研究

为实现废弃烟用滤棒中有用资源的回收和利用,对废弃烟用滤棒进行除杂、除纸、解纤、筛分处理,回收了其中的二醋酸纤维素,并采用静电纺丝方法制备了二醋酸纤维素膜,对纤维素膜的过滤性能及吸附性能进行了表征。结果表明:回收的二醋酸纤维素表面光滑,无机械损伤,单根纤维呈Y型,长度为3~10 mm的纤维素占纤维总量的62.34%,三醋酸甘油酯含量为6.11 mg/g;当纺丝液中二醋酸纤维素的质量分数为12%时,静电纺二醋酸纤维素膜中纤维表面光滑,粗细纤维相互缠结,纤维素膜的纯水通量为1.125×10~4L/(m~2·h),对卵清蛋白的截留率为48.7%,对分散红染料的吸附率为59.8%。     

二醋酸纤维素纺丝的研究现状

二醋酸纤维具有无毒、无味、截滤效果高、悬垂性及吸湿性好等优点,因此成为烟用滤嘴行业的首选材料,并且在高档服装方面受到人们的广泛关注。综述了二醋酸纤维素的纺丝方法,并对二醋酸纤维素纺丝的最新研究进行了分析。     

我国醋酸纤维素市场前景广阔

醋酸纤维素可分为三个主要系列产品 :醋酸纤维素 (ＭＣＡ)、二醋酸纤维素 (ＣＡ )、三醋酸纤维素(ＴＣＡ)。ＭＣＡ主要用于制造苯甲酸醋酸纤维ＣＡＰ ,ＣＡＰ是肠溶衣的主要材料。ＣＡ是醋酸纤维素中用途最广 ,产量最大的品种 ,可用于制造香烟过滤咀 ,世界生产年增长率超过 3 %     

NMR法研究羧甲基羟丙基纤维素的取代结构

羧甲基羟两基纤维素(CMHPC)经水解和乙酰化反应后,利用~1H NMR和~(13)C NMR谱确定其取代度和取代基分布,提出了纤维素葡萄糖单元上羟基的相对反应活性顺序。     

Preparation of polymer brush-type cellulose β-ketoesters using LiCl/1,3-dimethyl-2-imidazolidinone as a solvent

Cellulose β-ketoesters with branched alkenyl chains were prepared using cis-9-octadecenyl ketene dimer (OKD) and LiCl/1,3-dimethyl-2-imidazolidinone (DMI) as the esterifying reagent and cellulose solvent, respectively. Relationships between degree of substitution (DS) of the cellulose/OKD β-ketoesters and reaction conditions were studied in detail. The results showed that DS values of the products were controllable up to 2.1 by selecting the reaction conditions. Solution- and solid-state ¹³C-NMR analyses revealed that cellulose backbones of the cellulose/OKD β-ketoesters with DS 2.1 behave like solid in chloroform owing to strong restriction on movement of cellulose chains by the long and branched alkenyl substituents introduced. Size-exclusion chromatographic analysis showed that little depolymerization occurred on cellulose during β-ketoesterification at room temperature, and that molecules of the cellulose/OKD β-ketoesters with DS 2.1 had semi rigid-rod conformation in tetrahydrofuran. Thus, cellulose β-ketoesters with densely substituents like polymer brushes or comb-shaped polymers were prepared in this study.     

Aerobic biodegradation of cellulose acetate

Two separate assay systems were used to evaluate the biodegradation potential of cellulose acetate: an in vitro enrichment cultivation technique (closed batch system), and a system in which cellulose diacetate (CDA) films were suspended in a wastewater treatment system (open continuous feed system). The in vitro assay employed a stable enrichment culture, which was initiated by inoculating a basal salts medium containing cellulose acetate with 5% (v/v) activated sludge. Microscopic examination revealed extensive degradation of CDA (DS = 2.5) fibers after 2–3 weeks of incubation. Characterization of the CA fibers recovered from inoculated flasks demonstrated a lower average degree of substitution and a change in the mol wt profiles. In vitro enrichments with CDA (DS = 1.7) films were able to degrade > 80% of the films in 4–5 days. Cellulose acetate (DS = 2.5) films required 10–12 days for extensive degradation. Films prepared from cellulose triacetate remained essentially unchanged after 28 days in the in vitro assay. The wastewater treatment assay was less active than the in vitro enrichment system. For example, approximately 27 days were required for 70% degradation of CDA (DS = 1.7) films to occur while CDA (DS = 2.5) films required approximately 10 weeks before significant degradation was obtained. Supporting evidence for the biodegradation potential of cellulose acetate was obtained through the conversion of cellulose [1-¹⁴C]-acetate to ¹⁴CO₂ in the in vitro assay. The results of this work demonstrate that cellulose acetate fibers and films are potentially biodegradable and that the rate of biodegradation is highly dependent on the degree of substitution. © 1993 John Wiley & Sons, Inc.     

The roles of the degree of substitution and the degree of polymerization on the behaviour of cellulose ethers applied as adhesives for artwork conservation

Quite recently cellulose ethers have been introduced into the conservation field as an adhesive agent. Cellulose ethers are available in a wide range of products. Their properties are related not only to the nature of the substituent but also to the degree of polymerization (DP) and the degree of substitution (DS). Thus, the number of OH groups that are bound to C1 and C4 or to C2, C3 and C6 carbon atoms of the cellulose ether molecule affect their properties. Paper traction resistance is increased by using cellulose ethers as an adhesive to paste Tenguyo paper, a paper with a low density of fibres usually used by restorers. This increase is directly related to the molecular structure of the cellulose ethers. Therefore, the nature of substituents, the DP and the DS of cellulose ethers have to be taken into account in conservation practice. DP equals the number of anhydroglucose units in the chain and DS equals the number of hydroxyl groups replaced by the substituent in every anhydroglucose unit in the chain. As this information is not usually provided by suppliers, viscosity measurements are proposed as a means of predicting the behaviour of different products in relation to the conservation of paper artefacts, or to any other field where cellulose ethers solutions are used.     

Biosynthesis of (Z,Z)-6,9-heptacosadiene in the American cockroach

The biosynthesis of (Z,Z)-6,9-heptacosadiene, the major cuticular hydrocarbon component of the American cockroach, was examined by radiotracer and¹³C-nuclear magnetic resonance (NMR) techniques. Sodium [1-¹⁴C] acetate was incorporated about equally into the saturated and diunsaturated hydrocarbons, whereas [1-¹⁴C] linoleate preferentially labeled the C₂₇ alkadiene and [9,10-³H] oleate labeled the C₂₇ alkadiene almost exclusively.¹³C-NMR demonstrated that [2-¹³C] acetate labeled carbons 25 and 27 but not carbon 3 of the C₂₇ alkadiene. In addition, ozonolysis of the diene labeled from [1-¹⁴C] acetate followed by radio-gas liquid chromatography showed that carbons 1–6 were not labeled, whereas the fragment containing carbons 10–27 was labeled. The data presented in this paper indicate that linoleate from the diet or synthesized de novo is elongated by the addition of acetate units and is then decarboxylated.     

On the polarity and donor-acceptor-properties of polysaccharides

Summary Acidic parameters according to the GUTMANN's acceptor numbers (AN) of cellulose acetates and unmodified cellulose have been determined by means of the negatively solvatochromic probe dye Fe(phen)₂(CN)₂. Unmodified cellulose possesses a relatively high acceptor strength due to cooperative hydrogen bonds while increasing acetate contents in the polymer chain lower the acceptor strength. The dependence of AN on the acetate content can be used to estimate the degree of substitution (DS). Pecularities in the substitution interval (DS=0 to DS=1.5) are discussed.     

Solvent-free Synthesis of Cellulose Acetate by Solid Superacid Catalysis

Herein a novel process to synthesize cellulose acetate (CA) is reported in a solvent-free ball-milling reactor in the presence of solid superacid SO₄ ²⁻/ZrO₂ as green catalyst. FT-IR and H¹-NMR spectra reveal that the maximum degree of substitution (DS) of formed cellulose acetate can achieve 1.8, and the DS depends on the reaction time. This method provides a new environmental benign and simple way to synthesize cellulose acetate.     

Differentiation of Fish Oils According to Species by <Superscript>13</Superscript>C-NMR Regiospecific Analyses of Triacyglycerols

The aim of this study was to use ¹³C-nuclear magnetic resonance (NMR) regiospecific analyses of triacylglycerols to distinguish fish oils from different fish species for authentication purposes. ¹³C-NMR data of muscle lipids from Atlantic salmon (Salmo salar L.), mackerel (Scomber scombrus) and herring (Clupea harengus) were obtained, and the distribution of omega-3 polyunsaturated fatty acids between the sn-1,3 and sn-2 glycerol chains calculated from the carbonyl region. The results show that there were significant differences in the sn-2 position specificity of the fatty acids 22:6n-3, 20:5n-3 and 18:4n-3 among the species investigated. The most pronounced difference was that herring had a higher proportion of its 22:6n-3 in the sn-2 position compared to the two other species. Principal component analysis of data points in the carbonyl-region showed that there were also differences in the level and regiospecific distribution of monounsaturated/saturated fatty acids, which made it possible to distinguish oils of these three species solely from the carbonyl region of ¹³C-NMR spectra.     

Homogeneous hydroxyethylation of cellulose in NaOH/urea aqueous solution

Summary The 6 wt.% NaOH/4 wt.% urea aqueous solution was proved to be an aqueous non-derivatizing solvent for cellulose by ¹³C NMR. O-(2-hydroxyethyl)cellulose (HEC) was prepared by a totally homogeneous hydroxyethylation of cellulose using this new solvent for the first time, and the distribution of substituents within anhydroglucose units (AGU) was examined by ¹³C NMR. It was found that the relative reactivity of the hydroxyl groups within AGU and the new hydroxyl group was in the order C-x > C-6 > C-2 > C-3, an analogous functionalization pattern as HEC obtained by the heterogeneous slurry process. The ethylene oxide efficiency in this homogeneous etherification reaction was 20 – 30%.