天然纤维素结晶结构的表征

以木醋杆菌1.1812菌株为菌种,分别在30℃静态培养和12℃下振荡(振荡速率150 r/min)培养5 d,制得细菌纤维素,通过X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)和固体13C核磁共振(CP/MAS ~(13)C-NMR)分析了细菌纤维素的结晶结构。结果表明:木醋杆菌1.1812菌株在12℃恒温振荡培养得到细菌纤维素微球,由扭曲的扁平状带子交织而成,XRD分析表明其为完全无定形结构,而CP/MAS ~(13)C-NMR分析其结晶指数为9.7%,表明这种完全无定形结构中包含了有序的次晶结构;30℃静态培养得到细菌纤维素膜,由直径40~100 nm纤维层层堆积而成,为纤维素Ⅰ晶型结构,XRD分析其结晶指数高达90.3%,FTIR法得到的结晶指数为4.75,CP/MAS ~(13)C-NMR分析其结晶指数为86.7%。     

玉米秸秆木质素降解过程的CP/MAS 13CNMR和SEM表征

利用黄孢原毛平革菌对玉米秸秆木质素进行降解处理,通过CP/MAS 13 CNMR和SEM研究降解过程中木质素的结构变化。CP/MAS 13 CNMR结果表明:玉米秸秆木质素降解过程中,作为木质素结构单元主要连接方式的β-O-4键基本上没有被降解;木质素单位苯环的甲氧基含量稍有增加;S/G值降低,推断反应过程中紫丁香基优先参与反应。SEM结果表明:降解后的木质素空穴增多且增大、颗粒物质减少,主要是由于酶解木质素中大量碳水化合物的降解所致;比木质素更容易降解的纤维素和半纤维素也存在于样品中。CP/MAS 13 CNMR为木质纤维原料结构的定性和初步定量提供了可能,是传统定量表征手段的有力补充,具有一定的研究意义。     

二羟甲基脲与三聚氰胺共缩聚反应研究

采用高分辨超导13C-NMR(核磁共振碳谱)法和ESI-MS(电喷雾电离质谱)法对碱性条件下模型化合物UF2(N,N′-二羟甲基脲)与M(三聚氰胺)的共缩聚反应进行了分析。研究结果表明:在UF2的反应体系中,UF2发生了一定程度的缩聚反应,产物中亚甲基醚键占主导地位;经典理论认为碱性条件下很难生成亚甲基桥键,但13C-NMR谱图中观测到化学位移为47.77×10-6、54.36×10-6和54.54×10-6处是亚甲基桥键的特征峰。在UF2/M的反应体系中,UF2大量水解并导致M羟甲基化和UF2/M的共缩聚反应;仅根据13C-NMR谱图难以确认M/UF2反应体系中发生了共缩聚反应,但结合ESI-MS谱图可以确认质荷比为221~341的对应结构是共缩聚反应产物。     

H_2O_2/电化学法联合处理粘胶纤维生产废水的研究

以化学需氧量(COD)去除率为考核指标,采用H2O2/电化学法联合处理粘胶纤维生产废水,并与单独H2O2氧化法、单独电化学法的处理结果进行对比。研究结果表明:将COD为1 020 mg/L的粘胶纤维生产废水稀释至一定比例后,当V(H2O2)=1.5 m L、电解电压为5.5 V和处理时间为90 min时,分别采用单独H2O2氧化法、单独电化学法、联合H2O2/电化学法处理粘胶纤维生产废水时,废水的COD去除率分别达到28%、50%和82.6%;H2O2/电化学法可互相促进两者对粘胶纤维生产废水的氧化反应,同时降低了运行成本,是一种行之有效的废水处理方法。     

硫酸铵/氯化铵处理对粘胶纤维热裂解行为的影响

利用热重分析方法对硫酸铵/氯化铵处理粘胶纤维的热裂解行为进行了研究,并求解出粘胶纤维热裂解反应的动力学参数。结果表明,硫酸铵/氯化铵处理粘胶纤维与传统的硫酸/尿素处理粘胶纤维相比,其裂解反应的温度更低,收率更大;硫酸铵/氯化铵催化体系的活性催化组分在一个宽温度范围内缓慢释放,对粘胶纤维裂解反应的催化效果更佳;粘胶纤维经硫酸铵/氯化铵催化剂处理后,反应级数由1.1增大到3.2,反应活化能由237kJ/mol降低到94kJ/mol。采用此催化体系制备的粘胶碳纤维抗拉强度达到1.05GPa。     

乙醇中碱纤维素的结构变化

在乙醇中,用氢氧化钠对纤维素进行活化处理,借助X-射线、扫描电镜及CP/MAS-13C-NMR等手段研究了纤维素在活化过程中的形态结构变化。X-射线衍射图谱显示,随碱化中碱浓度的提高,纤维素的结晶度逐渐降低,活性逐渐增强,但当碱的浓度超过16%(W)时,结晶度的下降变化缓慢;电镜图片显示:纤维素表面裂痕增加,表面积增大;从CP/MAS-13C-NMR图谱中可以看出原纤维素和经碱处理的纤维素之间的化学位移区别较大,表明纤维素和氢氧化钠之间发生了化学变化,即生成了碱纤维素(Cell-Na)。     

光催化环己烷选择氧化合成环己酮/环己醇催化研究进展

环己烷选择性氧化合成环己醇/酮具有重要工业价值,工业上热氧化路线反应温度高、副反应多、转化率低、选择性不高,亟需条件更温和、更环保的替代路线。以太阳光为驱动的光催化环己烷氧化路线可在常温常压下实现环己烷的选择性氧化,受到极大关注。本文综述了近10年来光催化环己烷选择性氧化催化体系、反应机理和反应影响因素的研究情况,对光催化环己烷选择性氧化催化循环中环己烷分子活化、环己酮/醇形成、活性自由基再生的基元过程和催化剂失活机理进行总结和分析;对影响光催化环己烷选择性氧化的反应参数进行深入分析和讨论;指出·OH为主要的活性自由基,环己基过氧化氢是重要的中间产物,环己酮/醇主要通过环己基过氧化氢的光催化分解形成,光辐射条件（光强和波长）、溶剂、催化剂结构和表面性质都是光催化环己烷选择性氧化的重要影响因素。最后指出光催化环己烷选择性氧化规模化应用的关键是进一步提高光催化剂的寿命和稳定性以及设计结构合理、高效利用光能的光催化反应装置。     

细菌纤维素结构与性质的初步研究

对A. xylinum X-2的发酵产物进行纤维素酶水解液的纸层析实验,发现样品的Rf值与标准葡萄糖液的Rf值相近,水解液主成分为葡萄糖。通过对细菌纤维素的的X-射线衍射图谱和固体CP/MAS 13C-NMR谱分析,表明细菌纤维素结晶度高,Iα/Iβ比例大。对细菌纤维素干膜进行渗透性实验,发现干膜透气性小,透湿性大,结构致密,含有大量极性基团。     

碳基质新型离子印迹聚合物的制备及离子识别性能研究

溶胶-凝胶法制备二氧化钛/羧基碳纳米管(Ti O2/MWNTs-COOH),接枝壳聚糖并通过乙烯基三甲氧基硅烷化反应制备生物碳基质功能单体-乙烯基碳纳米管双功能基壳聚糖。利用Cu2+为模板离子,通过交联反应制备生物基质新型离子印迹聚合物(Novel ion imprinted polymer on biological carbon matrix,NIIPs-BCM)。傅里叶变换红外光谱(FT-IR)、固体核磁共振波谱(CP/MAS 13C-NMR)和扫描电镜(SEM)对中间产物和NIIPs-BCM进行结构表征,表观形貌分析法考察生物降解性能并利用同步热分析仪(DSC-TG)进行热稳定性测试,原子吸收光谱仪(AAS)进行离子印迹聚合物识别性能研究。结果表明,成功制备了对金属Cu2+具有选择性吸附的NIIPs-BCM。NIIPs-BCM具有显著生物降解性,热稳定性分析结果表明NIIPs-BCM具有良好的热稳定性,热失重率为67%。原子吸收法分析NIIPs-BCM的离子识别性能表明,其对Cu2+的特异识别性明显优于非离子印迹聚合物(Non-novel ion imprinted polymer on biological carbon matrix,NNIIPs-BCM),识别理论符合静态等温吸附方程。     

(T_(p-Cl)PPFe)_2O/Co(OAc)_2催化对二甲苯空气氧化反应及条件优化

对二甲苯液相氧化是目前石油化工领域最重要的碳氢化合物氧化反应之一,本文报道了μ-氧双[四对氯苯基卟吩]合铁/醋酸钴[(Tp-ClPPFe)2O/Co(OAc)2]复合催化体系在无溶剂体系中催化空气氧化对二甲苯的反应,初步考察了(Tp-ClPPFe)2O/Co(OAc)2复合催化体系的催化过程,在单因素考察催化剂种类和使用量对反应转化率和产物选择性影响的基础上,使用正交实验全面考察了该反应中时间、温度、压力、空气流速、金属卟啉用量、醋酸钴/金属卟啉质量比对反应转化率和产物选择性的影响,获得了优化反应条件。通过实验对优化条件进行了确认。实验表明,在上述优化条件下,对二甲苯转化率达65.0%,对甲基苯甲酸和对苯二甲酸选择性分别为81.0%和13.0%。     

Complexes of starch polysaccharides and poly(ethylene co-acrylic acid): Structural characterization in the solid state

The structural characterization of model complexes of amylose (AM) and amylopectin (AP) with poly(ethylene-co-acrylic acid) (EAA) was undertaken in order to better understand the interactions that occur between the polysaccharides and EAA in starch-EAA-polyethylene films. X-ray diffraction and CP/MAS ¹³C-NMR studies showed that precipitates from solution mixtures of AM and EAA form crystalline, helical V -type inclusion complexes. The proportion of AM forming the V -type complex in the EAA/AM blends, estimated from shifts in the C1 resonance of AM, increased with increasing EAA/AM ratio, reaching a value of about 80% at EAA/AM = 0.5 (w/w). Similar measurements for EAA/AP complexes showed < 10% V structure. Approximately 80% of the AM and 4% of the AP in these blends was resistant to amylase digestion, in good agreement with their V -structure contents as determined above. Resonances at 184 and 181 ppm were observed for the carboxyl carbon of EAA in the EAA/AM and EAA/AP complexes. The resonance at 181 ppm, which was not observed in pure EAA, probably reflects greater shielding of the carboxyl inside the polysaccharide helix as well as changes in hydrogen bonding. The intensity of this peak was 2–3 times larger for the EAA/AM than for the EAA/AP complexes. FTIR experiments suggest that most (> 50%) of the EAA carboxyl groups were hydrogen bonded to polysaccharide hydroxyl groups in both AM and AP complexes when EAA/polysaccharide < 1.     

Synthesis of Crosslinked Copolymers based on Acrylonitrile Containing Carboxyl and Amidrazone Groups

Summary Chelating networks based on modified chemically acrylonitrile with hydrazine at alkaline solution were synthesized. The resin beads with different porosities were obtained by aqueous suspension copolymerization of acrylonitrile (AN) and divinylbenzene (DVB). The unmodified and modified resins were characterized by bulk density, surface area, average pore diameter, elemental analysis (CHN), FTIR, ¹³C CP/MAS NMR and scanning electronic microscopy. Elemental analyses were used to observe the increasing of nitrogen and oxygen contents due to chemical modification. Spectroscopic techniques (FTIR and ¹³C CP/MAS NMR) were employed to study the structural changes provoked by the modification with hydrazine. The contents of carboxyl and amidrazone group into the copolymer structure were dependent on the reaction conditions.     

Structure and formation of cellulosic chars

The formation and structure of chars produced on heating of cellulose, lignin, and wood have been investigated by FTIR and CP/MAS ¹³C-NMR, and the results have been discussed in conjunction with parallel permanganate oxidation studies reported before. These data show that when cellulose is heated for 5 min within the temperature range of 325–350°C, the IR bands associated with hydroxyl and glycosidic groups in cellulose disappear, and new bands signal the formation of unsaturation and carbonyl groups by dehydration and rearrangement. The NMR data also show the disappearance of the glycosyl carbons at 60–110 ppm and the appearance of methyl and other paraffinic carbons at 0–60 ppm, aromatic carbons at 110–170 ppm, carboxyl carbons at 170–190 ppm, and carbonyl carbons at 190–220 ppm. On heating at 400°C the IR and NMR signals for the glycosyl groups completely disappear, the signals for carbonyl and carboxyl groups diminish, and those for the aromatic and paraffinic groups expand. At this stage the char contains about 69% aromatic and 27% paraffinic carbons. At the temperature range of 400–500°C the paraffinic carbon content is reduced to 12%, and a highly aromatic (88%) char is produced. This is consistent with the permanganate oxidation studies which show the production of polycyclic aromatic structures resulting from extensive condensation and crosslinking at these temperatures. The chars produced from wood and lignin at 400°C had about the same aromatic carbon content as the corresponding cellulose char; however, the char yields were higher due to the presence of the methoxy phenyl groups that survive the heating process, as indicated by strong NMR signals at 55 and 148 ppm.     

Spectral characterization and thermal behaviour of crosslinked poly(hydroxyethylmethacrylate) beads prepared by suspension polymerization

Crosslinked poly(hydroxyethylmethacrylate) [poly(HEMA)] beads were prepared by the suspension copolymerization of 2-hydroxyethylmethacrylate monomer with ethyleneglycol dimethacrylate (EGDMA) in aqueous media which contained only magnesium oxide (MgO) as a suspension stabilizer and also salting-out agent. The procedure gives spherical particles with narrow size distribution. The reaction mechanism, composition and structure of poly(HEMA) beads were studied by solid-state ¹³C CP/MAS NMR, FTIR, ESCA, and elemental analysis. ¹³C NMR implies the existence of unreacted pendant groups in the HEMA-EGDMA copolymer. The surface composition obtained by ESCA is almost the same as the bulk composition determined by elemental analysis. FTIR spectra provide compelling evidence for the presence of carboxyl and hydroxyl groups. The glass-transition temperature and the thermal stability of beads were determined by DSC.     

Pervaporation separation of water/ethanol mixtures through polysaccharide membranes. III. The permselectivity of the neutralized chitosan membrane and the relationships between its permselectivity and solid state structure

The separation of water/alcohol mixtures through chitosan membrane neutralized by various acids was investigated. The permselectivity of the neutralized chitosan membrane was affected by the species of acids and, only when neutralized by polybasic acids, was a marked increase of the selectivity observed and a high selectivity maintained for ion free mixtures. The marked increase of the selectivity could be explained by the contraction of the “holes” produced by the thermal motion of polymer chains due to the conformation change of chitosan molecule caused by the neutralization. The conformation change was confirmed by the analysis of the solid state structure of the neutralized chitosan using CP/MAS ¹³C-NMR.     

New class of cellulose fiber spun from the novel solution of cellulose by wet spinning method

A novel cellulose solution, prepared by dissolving an alkali-soluble cellulose, which was obtained by the steam explosion treatment on almost pure natural cellulose (soft wood pulp), into the aqueous sodium hydroxide solution with specific concentration (9.1 wt %) was employed for the first time to prepare a new class of multifilament-type cellulose fiber. For this purpose a wet spinning system with acid coagulation bath was applied. The mechanical properties and structural characteristics of the resulting cellulose fibers were compared with those of regenerated cellulose fibers such as viscose rayon and cuprammonium rayon commercially available. X-ray analysis shows that the new cellulose fiber is crystallographically cellulose II, and its crystallinity is higher but its crystalline orientation is slightly lower than those of other commercial regenerated fibers. The degree of breakdown of intramolecular hydrogen bond at C₃[X_am(C₃)] of the cellulose fiber, as determined by solid-state cross-polarization magic-angle sample spinning (CP/MAS) ¹³C NMR, is much lower than other, and the NMR spectra of its dry and wet state were significantly different from each other, indicating that cellulose molecules in the new cellulose fiber are quite mobile when wet. This phenomenon has not been reported for so-called regenerated cellulose fibers.     

微波处理对棉纤维结晶结构的影响

对于微波处理后强力显著上升和下降的棉纤维,采用核磁共振碳谱分析其结晶结构的变化,并与原样进行对比。实验结果表明:微波处理前后棉纤维的纤维素Ⅰβ都是占优势的,微波处理后棉纤维的结晶度下降,结晶的完整性受到破坏,主要由更小的晶粒组成。微波处理改变了纤维素的晶型,晶型含量Ⅰα和Ⅰβ均降低,但是比例基本保持不变,微波处理后向次晶转化。     

Synthesis and characterization of colloidal TBA-silicalite-2

Colloidal TBA-silicalite-2 (MEL type) was hydrothermally synthesized in the reactant system TBAOH–TEOS–H₂O. The influences of reactant composition, reaction temperature, and crystallization period on particle size of the zeolite were investigated. The colloidal silicalite-2 was characterized by XRD, SEM, TEM, FT-IR, ²⁹Si MAS NMR, ¹³C CP MAS NMR, thermogravimetric analysis and N₂ adsorption. The as-synthesized colloidal zeolite with a particle size of 100 nm is an agglomerate composed of nano-sized crystals of about 20 nm, displaying unique structural characteristics such as high content of silanol defects in the framework, splitting of the double-ring vibration in FT-IR spectrum and an unusual signal for methyl groups of TBA in ¹³C CP MAS NMR spectrum.     

Synthesis, characterization and thermal behavior of Poly(methyl-n-octadecyl itaconate) a comb-like polymer with crystallizable side chain

The radical polymerization of methyl n-octadecyl itaconate initiated with AIBN, produces poly(methyl n-octadecyl itaconate) with a yield of 47% and a molecular weight of about 10⁵ g/mol. ¹³C-NMR studies point out that this polymer is mainly syndiotactic. The combined studies of DSC and solid state ¹³C CP/MAS NMR indicate that the polymer side chains are able to crystallize in a paraffinic phase, presumably in an hexagonal form which melts at 44°C with a ΔH of 4.8Kcal/mol. Received: 12 September 2001/Revised version: 3 January 2002/Accepted: 10 January 2002