落叶松和毛白杨制备纳米结晶纤维素的性能对比

本研究以落叶松和毛白杨浆粕为原料,用酸水解法、超声处理分别制备纳米结晶纤维素,并研究原料的α-纤维素含量和聚合度等性质对制备所得纳米结晶纤维素得率、结构、结晶度和热稳定性的影响。实验所选用落叶松浆粕的α-纤维素质量分数为 88.93 %,平均聚合度达到1048.11,而毛白杨浆粕的α-纤维素质量分数为 85.90 %,平均聚合度为976.07。结果表明:酸水解处理对浆粕纤维中排列致密的结晶区影响不明显,但是会破坏非结晶区造成结晶度提高,而超声处理会使结晶度下降;由落叶松浆粕制备所得纳米结晶纤维素的得率高、晶面特征吸收峰显著,且热稳定性较好(热降解温度为 295.2 ℃),而由毛白杨浆粕制备所得的纳米结晶纤维素的热降解温度为 283.1 ℃。     

纤维素的酸预处理研究

以硫酸为纤维素的预处理剂,讨论了酸浓度、酸液温度、处理时间对纤维素聚合度的影响,结果表明:酸液浓度高于0.285mol/L,酸液温度应高于60℃,纤维素聚合度下降明显;当酸液浓度低于0.285mol/L,温度低于60℃时,纤维素聚合度下降缓慢;随降解时间的延长,纤维素聚合度下降趋势先快后慢.     

Lyocell纤维活化工艺探讨

纤维素浆粕活化工艺的主要目的是打开纤维素的结晶区,利于溶剂进入。介绍了Lyocell活化工艺的原理及重要性,活化工艺控制参数为:选用纤维素活化酶,其与纤维素质量比为0.003~0.006,活化p H值5~6,活化温度40~60℃,活化时间40~60 min,活化终止p H值10~13。经过活化工艺,纤维素聚合度略有降低,浆液过滤指数好,浆粕的选型范围更宽,有利于产品品种的开发。     

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。     

离子液体与水混合溶剂应用于微晶纤维素溶剂液化研究

将离子液体氯化1-丁基-3-甲基咪唑（[BMIM]C1）、水、固体酸催化剂组成的混合溶剂应用于微晶纤维素的预处理过程中,并尝试把经过预处理的微晶纤维素应用于随后的溶剂液化的研究中,对经过混合溶剂处理后的微晶纤维素进行表征分析。通过测定纤维素的聚合度、官能团基变化、热重分析、结晶结构和表面结构等对微晶纤维素结构进行比较分析。通过对苯酚溶剂液化的基本表征、残渣物的结晶结构以及生成物相对分子质量的变化了解了混合溶剂对微晶纤维素的处理效果。结果表明,通过混合离子液体[BMIM]C1和水并且添加固体酸催化剂形成新的混合溶剂体系对微晶纤维素进行预处理,发现溶剂在保留纤维素主要葡萄糖单元的同时能够有效地降低聚合度。聚合度从未处理时的190降到样品[B]C1（10）的165和样品[B]C1（10）＋NR50的151。混合溶剂对非结晶或低结晶物质具有一定的溶解能力,并且对高结晶性纤维素部分的氢键结构起到破坏作用和造成整体结晶结构的歪曲。在随后的液化过程中,处理后的纤维素液化效率有所提高,在反应2min时,固体酸加混合溶剂处理的微晶纤维素液化残渣率为19％,而未处理的液化残渣率29％。表明使用了混合溶剂添加固体酸的溶剂体系对加速液化的效果更佳,预处理对最终液化生成物的性质影响不大。     

纤维素/磷酸纺丝溶液再生性能研究

利用磷酸/多聚磷酸混合体系溶解纤维素,用铜乙二胺法测定溶解过程的不同时间阶段纤维素的聚合度,通过XRD和IR表征溶解前后纤维素性能变化情况.并初步探讨了纤维素在混酸体系中的溶解机理和降解机理.结果表明,混酸体系溶解纤维素时间较以往溶剂体系短,由于溶解温度比较低,热降解作用不明显.XRD表明经过溶解再生的纤维素品体类型已经由纤维素Ⅰ转变为纤维素Ⅱ.红外谱图中没有新峰出现,说明没有新的官能团产生,混酸溶解纤维素没有衍生物形成.     

机械活化对木薯淀粉糊透明度的影响

采用搅拌球磨机对木薯淀粉进行机械活化,分别研究了机械活化对木薯淀粉糊透明度的影响和淀粉糊储藏过程中机械活化时间与淀粉糊浓度对其透明度的影响. 并通过X射线衍射研究了机械活化对木薯淀粉结晶结构的影响. 结果表明,机械活化作用时间越长,淀粉糊透明度越高. 这是由于机械活化使木薯淀粉颗粒结晶结构受到破坏,结晶程度降低,最终由多晶态转变成非晶态. 淀粉糊储藏过程(储藏温度4℃)中发生老化是引起透明度变化的主要因素. 机械活化时间为2 h的样品易老化,淀粉糊透明度迅速下降,而机械活化时间达3 h后木薯淀粉则过度降解,淀粉糊透明度下降变慢. 同时还发现,机械活化淀粉糊储藏过程其透明度的变化与糊浓度密切相关,当浓度在10 g/L左右时,机械活化淀粉糊不易老化,而浓度提高到50 g/L后,则老化加速,淀粉糊透明度迅速下降.     

丁基磺酸纤维素醚减水剂的合成及表征

以纤维素棉桨粕经酸水解得到具有确定聚合度的微晶纤维素(MCC)为原料,在氢氧化钠活化下,与1,4-丁烷磺内酯(BS)反应,得到了具有良好水溶性的丁基磺酸纤维素醚(SBC)减水剂.采用红外光谱(FT-IR)、核磁共振谱(NMR)、扫描电镜(SEM)、X射线衍射(XRD)等分析方法对产品结构进行了表征,并考察了MCC聚合度、原料配比、反应温度、反应时间、悬浮剂种类等合成工艺条件对产品减水性能的影响.结果表明:当原料MCC聚合度为45,反应物物质的量比为:AGU(纤维素葡萄糖苷单元):n(NaOH):n(BS)=1.0:2.1:2.2,悬浮剂为异丙醇,原料室温活化时间为2h,产物合成时间为5h,温度为80℃时,所得产品丁磺酸基取代度最高,产品减水性能最优.     

棉纤维在LiCl/DMAc极性溶液中的溶解性能研究

采用不同方法将棉纤维活化并溶解在LiCl/DMAc极性溶液中,研究了活化方法、溶解温度、时间及LiCl浓度对棉纤维素溶解性的影响。结果表明:DMAc热活化法为较好的活化方法;提高溶解温度,延长溶解时间及提高LiCl浓度均有利于棉纤维溶解;棉纤维在LiCl质量分数为12%的LiCl/DMAc溶液中,150℃下搅拌4h,溶解度可达3%。碱活化法使棉纤维素聚合度大幅度降低,可提高棉纤维溶解度至8%。通过扫描电镜和X射线衍射方法研究了棉纤维在前处理和溶解过程中的形态和结构变化,初步揭示了纤维素高温处理后在低温下发生溶解的机理。     

纤维素在离子液体中的溶解特性研究

测定了纤维素在不同结构的离子液体——1-烯丙基-3-甲基咪唑氯化物([AMIM]Cl)和1-丁基-3-甲基咪唑氯化物([BMIM]Cl)中的溶解度和溶解速率。结果发现:相同条件下,纤维素在[AMIM]Cl中具有较大的溶解度和较快的溶解速率;随着纤维素聚合度的增大,相同条件下,纤维素在离子液体中的溶解度降低。进一步通过WXRD、FT-IR、13C NMR和黏度法分析了溶解前后纤维素的化学结构、结晶结构和聚合度,结果表明:纤维素在离子液体中的溶解属于直接溶解,纤维素经离子液体溶解和再生后,晶型由纤维素I转变为纤维素II;溶解时间和温度对再生纤维素的聚合度有较大的影响,随着溶解时间的延长和溶解温度的提高,再生纤维素聚合度降低。     

Studies on thermal degradation of cellulose and cellulose phosphoramides

Reaction of cellulose with hexamethylphosphoric acid triamide has been investigated under various physical conditions. Dimethylamine hydrochloride was found to be an efficient catalyst for the system. The thermal degradation of cellulose and its phosphoramide products in air was studied by DTA, TG, and DTG techniques from ambient temperature to 500°C. The data were processed for the various thermodynamic parameters following the methods of Freeman and Carroll, of Broido, and of Dave and Chopra. The energies of activation, E_a, for the degradation for various cellulose phosphoramide samples were found to be in the range of 92–136 kJ mol^?1. These values were found to decrease with increase in the degree of substitution. A mechanism for the thermal degradation of cellulose phosphoramide has been proposed. The IR spectra of char residues of cellulose phosphoramide gave an indication of the formation of compounds containing C?O and P?O groups.     

Thermal degradation behaviors of spherical cellulose nanocrystals with sulfate groups

A kind of spherical cellulose nanocrystals was prepared by hydrolysis of microcrystalline cellulose with mixed acid. In order to improve the thermal stability, two methods were used: diminishing the acid sulfate groups by desulfation and neutralizing them by using NaOH solution. The thermal degradation behaviors were characterized by thermogravimetric analysis and differential scanning calorimetry at nitrogen current. The results indicated that the degradation of cellulose nanocrystals with acid sulfate groups started at lower temperature and showed two remarkable pyrolysis processes. Profile analysis of the derivative thermogravimetric curves showed that each pyrolysis process was composed of multi-step reactions. When neutralized by NaOH solution, the degradation shifted to the higher temperature and occurred within a narrow temperature range. The influence of particle size of cellulose on degradation was also investigated. The results indicated that the degradation of cellulose with small size took place at lower temperature and facilitated the char residue formation.     

Hβ沸石催化降解聚烯烃的研究

将Hβ沸石进行水热处理和酸处理改性后,其比表面积、总孔容及平均直径均增大,二次孔孔容占总孔容的387%以上,说明改性后的沸石具有更通畅的孔道和较多的二次孔, 总酸量减少,酸强度分布降低。热重分析研究了处理前后的Hβ沸石作催化剂对聚苯乙烯及聚乙烯催化降解的作用。结果表明,Hβ沸石能显著降低聚乙烯的热降解温度,对聚苯乙烯的热降解温度影响不大。催化剂的酸量对聚乙烯降解温度、活化能及积炭生成有很大的影响。催化剂酸量增加,聚乙烯的降解温度和活化能均明显下降,但积炭量增加。催化剂对聚苯乙烯的热降解影响主要取决于孔结构。     

Thermal degradation studies of cellulose phosphates and cellulose thiophosphates

The thermal degradation of cellulose, cellulose phosphates, and cellulose thiophosphates was studied by differential thermal analysis, dynamic thermogravimetry, and derivative thermogravimetry from ambient temperature up to 750°C. Various thermodynamic parameters for different stages of thermal degradation of cellulose and its derivatives have been obtained following the methods of Broido, and Freeman and Carroll. Infrared spectra of thermally degraded samples were obtained. The data were analyzed in an effort to obtain more information concerning the flame-retardant mechanisms of cellulose phosphates and cellulose thiophosphates. Lower values of decomposition temperatures and activation energies of decomposition and higher char yields of cellulose phosphates as compared to cellulose lead to the conclusion that cellulose phosphorus esters are good flame retardants, and this property is retained even when these esters were subjected to ion exchange by Na⁺ and K⁺ ions. However, with the introduction of sulphur atoms, there was some decrease in this property.     

机械活化甘蔗渣与丙烯[BF]酸(钠)的接枝共聚反应

采用搅拌球磨对甘蔗渣进行机械活化,以不同活化时间的甘蔗渣为原料,过硫酸铵和亚硫酸钠为引发剂,在水溶液中与部分中和的丙烯酸进行接枝共聚反应。以接枝率和接枝效率为评价指标,考察了活化时间、丙烯酸与甘蔗渣的用量比、反应时间和反应温度等因素对接枝反应的影响。并采用SEM、FT-IR对甘蔗渣和产物进行表征。结果表明：机械活化明显强化了甘蔗渣与丙烯酸的接枝共聚反应,接枝率和接枝效率随着活化时间的延长而增大,主要是由于机械活化破坏了甘蔗渣中木质素对纤维素的包裹作用,降低纤维素的结晶度,提高了其反应活性。以活化1.5 h的甘蔗渣为原料进行接枝共聚反应,在反应时间为3 h、丙烯酸（体积,ml）与甘蔗渣（质量,g）的用量比为6、反应温度为60℃的条件下,制得接枝率和接枝效率分别为165.29%和82.70%的接枝共聚产物。     

Kinetics of acid catalysed degradation of cellulose triacetate in chloroalkane solvents: 1. Dichloromethane

The kinetics of degradation of cellulose triacetate in a dichloromethane-acetic anhydride mixture with perchloric or sulphuric acid catalyst was studied. Decrease in molecular weight with time was followed viscometrically using limiting viscosity numbers, calculated by a single-point method, and Mark-Houwink constants for the solvent mixture. Dependence of first-order rate constants on catalyst concentration and temperature was investigated and Arrhenius parameters, activation entropies and catalytic coefficients were obtained. A suggested reaction mechanism for degradation based on H⁺ and Ac⁺ (acetylium ion) acting as catalytic species is proposed.     

纤维素/NMMO·H_2O溶液体系流变性能的研究

利用 Brookfield DV-Ⅱ型粘度计对纤维素/NMMO·H2O 溶液体系的流变性能进行了研究,讨论了温度、纤维素浓度、浆粕聚合度及添加剂等对溶液粘度的影响。结果表明,纤维素/NMMO·H2O 溶液的流动活化能较低,因此其表观粘度随温度的变化不大;纤维素浓度和浆粕聚合度的增加都可使溶液粘度增大,但纤维素浓度对溶液粘度的影响更显著;抗氧化剂没食子酸丙酯(GPE)的加入减缓了加热时溶液粘度的下降,降低了纤维素的氧化降解;二甲亚砜(DMSO)的加入可有效地控制溶液粘度,改善溶液的加工性能。     

微波条件下植物纤维素降解工艺条件的优化

在微波加热条件下,采用HCl/H<,2>O<,2>催化剂对植物纤维素进行降解.通过中心组合实验优化的适宜降解条件为:催化剂体积分数5.0%、反应温度100℃、反应时间2.0 h,在此条件下,纯植物纤维素的降解率为70.6%,较常规加热降解率提高了32.01%.SEM分析微渡加热和常规加热下降解产物的结构特征,发现微波作...     

醋酸丙酸纤维素的合成与表征

采用非均相催化酯化法合成醋酸丙酸纤维素(CAP),研究了反应时间、温度和催化剂用量对CAP乙酰和丙酰取代度、特性粘度的影响,发现反应温度、反应时间和催化剂浓度增加虽可使产物的取代度增大,但粘度降低,得到优化的反应条件为:催化剂用量1%(wt,相对于纤维素),反应温度60℃,反应时间2 h。酯化反应使纤维素的结晶度降低。     

A kinetic study of ultrasonic degradation of carboxymethyl cellulose

In this study, the effect of power of ultrasound, temperature, and concentration of carboxymethyl cellulose (CMC) solution on the rate of ultrasonic degradation were investigated, and a kinetic model based on viscometry data was used to calculate the rate constants in different conditions. To investigation of effect of ultrasonic power on the degradation of CMC, the power of ultrasound was increased and observed that the viscosity of the CMC solution was decreased with an increase in the power of ultrasound, but the extent of the degradation in a constant power was found to decrease with an increase in concentration or temperature. The ultrasonic degradation of CMC solutions was carried out at different temperatures to investigate the effect of the temperature on the rate of degradation. The calculated rate constants indicated that the degradation rate of the CMC solutions decreased as the temperature increased. The degraded CMCs were characterized by gel permeation chromatography, and average molecular weights of ultrasonicated CMCs were compared in different reaction conditions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012