共查询到19条相似文献,搜索用时 171 毫秒
1.
CP/MAS 13C-NMR技术对桉木浆纤维素微观结构的研究 总被引:1,自引:0,他引:1
利用交叉极化结合魔角旋转技术13C 核磁共振法(CP/MAS 13C NMR)对桉木浆纤维的微观结构进行研究, 为进一步研究木质纤维素材料开发过程中反应障碍特征奠定基础. 通过对NMR光谱C1区(δ 102~108)进行洛仑兹拟合, 得到桉木浆纤维中纤维素Iα的相对含量为26.92%, 纤维素Iβ的相对含量为52.04%, 主要以纤维素Iβ晶体形式为主. 通过计算纤维素C4结晶区(δ 86~92)和非结晶区(δ 80~86)的相对含量得到桉木浆的纤维素结晶度为47%. 通过洛仑兹和高斯函数的混合模型对NMR光谱C4区(δ 80~92)进行拟合得到基原纤尺寸和微原纤横向尺寸分别为4.0与17.9 nm, 并通过计算不同形态的结晶纤维素的相对含量得到纤维素结晶度为51%, 证实了在微原纤内部次晶纤维素的存在. 相似文献
2.
固体核磁共振和原子力显微镜分析不同半纤维素含量植物纤维的微观结构 总被引:1,自引:0,他引:1
采用交叉极化结合魔角旋转技术13C核磁共振法和原子力显微镜研究了半纤维素的脱除对纤维微观结构的影响。分别对NMR光谱C1区(δ102~108)和C4区(δ80~92)进行拟合。结果表明,随着半纤维素的脱除,次晶纤维素的相对含量从20%增加到33%,基原纤尺寸在4.0~4.3nm之间相对稳定,而基原纤聚集尺寸从17.9nm增加至22.2nm,且与半纤维素含量呈良好的线性关系。AMF图像观察到高半纤维素含量的纤维具有疏松的表面结构,而低半纤维素含量的纤维由于基原纤聚集尺寸的增加使得表面结构更加紧密。随着半纤维素含量的降低,向内收紧的拉力使得纤维细胞壁上的孔隙发生关闭,平均孔径减小。但是当半纤维素的脱除累积到一定量时,纤维孔隙结构反而能够得到改善。 相似文献
3.
为缓解我国木浆供应压力,满足混合原料制浆的实际需求,该文进行了近红外光谱快速分析混合制浆原料的研究。采集145个人为控制尾巨桉含量的尾巨桉-马占相思混合样品的近红外光谱,用常规方法测定其综纤维素、聚戊糖、Klason木质素含量。对原始光谱进行一阶导数与标准正态变换预处理后,分别运用偏最小二乘法、支持向量机法、人工神经网络法和LASSO算法建立尾巨桉、综纤维素、聚戊糖、Klason木质素含量分析模型。其中LASSO法建立的尾巨桉和综纤维素含量分析模型最优,预测均方根误差(RMSEP)分别为1.80%、0.60%;绝对偏差(AD)分别为-3.03%~3.17%、-1.03%~0.98%,模型性能可满足较精确的快速分析。偏最小二乘法建立的聚戊糖含量分析模型最优,RMSEP为0.75%,AD为-1.26%~1.33%;支持向量机法建立的Klason木质素含量分析模型最优,RMSEP为0.48%,AD为-0.82%~0.86%,两个模型性能适用于非精确性的分析。该研究为混合制浆原料的快速分析提供了可能,同时也证实了LASSO算法的适用性。 相似文献
4.
本文测定了原生态聚乙烯粒子样品的固体核磁宽线氢谱,并应用三组分(晶相、无定形相以及两者的界面相)分析的方法对谱图进行了分解,从而得到各相质量分率以及相区内分子运动性的信息。对谱图进行三组分解析的依据是:1)结晶相内大分子链运动受阻,对谱线的贡献可用高斯函数描述;2)无定形相内分子运动具有类似液体中的性质因而对谱线的贡献用洛仑兹函数描述;3)两者的界面相内亚甲基绕C-C键的转动部分受阻,用高斯和洛仑兹函数的组合函数进行描述。所选取的聚乙烯粒子包括改变聚合条件的系列单峰线性高密度聚乙烯、双峰高密度聚乙烯以及双峰线性低密度聚乙烯。研究发现,核磁结晶度与WAXD方法所测得的结晶度较为吻合并大大高于DSC方法所测得的结晶度,表明核磁结晶度中仍包含非晶区分子链的贡献。对于改变聚合条件所得到的同一组系列线性高密度聚乙烯,其固体核磁相结构受聚合条件的影响不大,然而核磁结晶相中的“缺陷区”含量受到聚合条件的影响较大。通过单峰线性高密度聚乙烯和双峰高密度聚乙烯的三相结构对比,发现核磁界面相的性质与晶区间系带分子的含量联系紧密,因此将对聚合物的力学性能产生重要影响。 相似文献
5.
以85%的食品级磷酸为原料,三聚氰胺为缩合剂,合成了一种具有网状结构的结晶V型聚磷酸铵,对其水溶性、XRD、13C NMR、红外光谱、热重等进行了测试与表征,并与结晶I型、结晶Ⅱ型产品进行了对比。结果表明,本实验制备产品具有良好的耐水性, 其XRD图谱与结晶V型完全一致,其13C NMR及红外图谱表明该物质是以三嗪环为基本骨架的聚磷酸铵链交联网状结构。热重分析表明,700℃时该产品残重53.6%,大于结晶I型的40.29%及结晶II型的36.16%,初步显示该产品具有良好的高温热稳定性。 相似文献
6.
聚(L-丙交酯)/聚(DL-丙交酯)的结晶性能及相溶性 总被引:2,自引:0,他引:2
用共溶液沉淀法制备了聚 (L 丙交酯 ) 聚 (DL 丙交酯 )共混物 (PLLA PDLLA) ,然后用成纤模压法压制成3 2mm的棒材 .用差示扫描量热法研究了共混物的结晶性能和相溶性 .结果表明 ,PLLA组分在共溶液沉淀过程中可生成结晶 ,共混物中PDLLA含量直到 30 %时 ,PLLA组分的结晶熔融温度和结晶度与纯PLLA相同 ,但PDLLA含量为 5 0 %时 ,PLLA组分的结晶熔融温度和结晶度明显下降 .由于加工成型条件的不一致性 ,共混物棒材中的PLLA组分的结晶熔融温度和结晶度呈较大的分散性 .共混物从熔体降温 ,在其后的升温DSC扫描中出现分别相应于PDLLA和PLLA的玻璃化转变 ,表明PDLLA与未结晶的PLLA形成的非晶相是不相溶的 相似文献
7.
聚己内酯在有机/无机杂化体系中的受限结晶行为 总被引:3,自引:0,他引:3
通过Sol Gel技术合成了聚己内酯 (PCL) /二氧化硅 (SiO2 )杂化材料 ,并对杂化样品进行了DSC和WAXD测试 .实验结果表明杂化样品中PCL的结晶度随二氧化硅含量增加而减小 ,当样品中二氧化硅含量达到 60 %时 ,PCL为非晶态 ;含有PCL结晶的杂化样品中PCL熔融温度基本相同 ,但是比纯PCL的熔融温度低 .杂化样品中结晶PCL的结晶结构和微晶尺寸和纯PCL的一致 .这说明杂化材料中PCL的结晶行为和结晶度受到了限制 ,含PCL结晶的样品中PCL的结晶结构和微晶尺寸并没有受到影响 . 相似文献
8.
9.
以氯丙烯和N-乙基咪唑为原料合成了离子液体氯化1-烯丙基-3-乙基-咪唑盐([AEIM]Cl),利用FT-IR和1HNMR对其化学结构进行了表征。采用微波加热法溶解微晶纤维素(MCC),考察 [AEIM]Cl对纤维素的溶解性能。研究了NaOH、微波和高压等3种预处理方式对微晶纤维素的相对结晶度、聚合度及溶解率的影响。利用FT-IR、XRD、TGA和SEM分别对溶解后得到的再生纤维素的化学结构、晶型变化、热稳定性及表观形貌进行测试与分析。结果表明,合成的离子液体是目标产物,对微晶纤维素表现出很好的溶解能力,且高温高压条件下15%的NaOH水溶液对微晶纤维素处理后,得到的纤维素相对结晶度最小,聚合度最低,溶解率最高。溶解过程中纤维素没有发生衍生化反应,溶解后得到的再生纤维素的相对结晶度和微晶尺寸变小,热稳定性降低。 相似文献
10.
以酚和氯乙酸为初始原料,经一系列反应,合成出了10个新型的含苯并咪唑环二酰肼衍生物7a~7j.利用1HNMR,13C NMR,2D NMR(包括HMBC,HSQC,1H-1H COSY和NOESY)和变温1H NMR技术对代表化合物7c进行了1H和13C NMR谱归属并确定了其空间结构,证明了其在室温及DMSO中存在着A和B两种互变异构体,并且A异构体占优势(87.65%).据此,对其它目标化合物的1H NMR也进行了归属,A异构体含量为80.55%~89.90%. 相似文献
11.
Kristina Wickholm Eva-Lena Hult Per Tomas Larsson Tommy Iversen Helena Lennholm 《Cellulose (London, England)》2001,8(2):139-148
In this paper, we present a chemometric model for quantifying the cellulose forms with different states of order found within cellulose I fibrils. The relative amounts of the different cellulose forms, that is crystalline cellulose I, para-crystalline cellulose and cellulose at accessible and inaccessible cellulose surfaces, were determined by non-linear least squares fitting of the C4-region in CP/MAS 13C-NMR (Cross-Polarisation Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance) spectra. By correlating these results from the C4-region with the full spectral data we obtained a model which is able to provide an assessment of the relative amounts of the different cellulose forms directly from NMR-spectra of complex lignocellulosic samples. Furthermore, this model enabled new assignments to be made in the C1-region for signals from cellulose at accessible fibril surfaces. 相似文献
12.
Benjamin Briois Tsuguyuki Saito Christian Pétrier Jean-Luc Putaux Yoshiharu Nishiyama Laurent Heux Sonia Molina-Boisseau 《Cellulose (London, England)》2013,20(2):597-603
Aqueous suspensions of dispersed Glaucocystis cellulose microfibrils were sonicated at 4 °C for 3 h, using 24 kHz ultrasonic waves. This treatment induced a variety of ultrastructural defects, as the microfibrils became not only shortened, but also presented substantial damage materialized by kinks and subfibrillation. Upon analysis by X-ray diffraction and 13C solid-state NMR spectroscopy, it was found that the initial sample that contained 90 % of cellulose Iα allomorph became, to a large extent, unexpectedly converted into the Iβ phase, while the loss of crystallinity was only moderate during the sonication treatment. 相似文献
13.
High resolution data from all-atom molecular simulations is used to parameterize a Martini 3 coarse-grained (CG) model of cellulose I allomorphs and cellulose type-II fibrils. In this case, elementary molecules are represented by four effective beads centred in the positions of O2, O3, C6, and O6 atoms in the D-glucose cellulose subunit. Non-bonded interactions between CG beads are tuned according to a low statistical criterion of structural deviation using the Martini 3 type of interactions and are capable of being indistinguishable for all studied cases. To maintain the crystalline structure of each single cellulose chain in the microfibrils, elastic potentials are employed to retain the ribbon-like structure in each chain. We find that our model is capable of describing different fibril-twist angles associated with each type of cellulose fibril in close agreement with atomistic simulation. Furthermore, our CG model poses a very small deviation from the native-like structure, making it appropriate to capture large conformational changes such as those that occur during the self-assembly process. We expect to provide a computational model suitable for several new applications such as cellulose self-assembly in different aqueous solutions and the thermal treatment of fibrils of great importance in bioindustrial applications. 相似文献
14.
Cellulose microfibrils are viewed as imperfect array of elementary fibrils. We have investigated the possible defects in Valonia cellulose microfibrils, which are such that the microfibrils can be broken into elementary fibrils by deformation, but are not sufficient to allow for a small angle maximum corresponding to the elementary fibril dimension. The microfibril has been constructed by convolution of th elementary fibril with a two dimensional point lattice. Defects have been incorporated in the microfibril, first by introduction of gaps between the elementary fibrils. These regular gaps were then replaced by a statistical distribution of the elementary fibrils about the lattice points, modeled by Hosemann distortions of the first type. The cylindrically averaged transforms of such structures show that significant distortions can be incorporated within the microfibril without producing large scale changes in the equatorial intensity distribution. Larger distortions are necessary before a small angle maximum corresponding to the 35 A elementary fibril is predicted, by which stage the wide angle x-ray pattern is unacceptable. 相似文献
15.
The hierarchic organization of cellulose fibrils (microfibrils) was investigated in holocellulose, sulphite pulp and kraft pulp using TEM, XRD, ED and FTIR. There were remarkable differences in both the fibril structure and fibril aggregation between the samples. TEM observations revealed more intimately associated fibrils in the kraft pulp compared to the sulphite pulp and the holocellulose, results in agreement with previous CP/MAS 13C-NMR data [Hult E.-L. et al. (2002) Holzforschung 56: 231–234]. Furthermore, the cellulose crystallinity was higher in the kraft pulp sample. With respect to the cellulose I and I allomorphs, these samples were controversial when different analytical techniques were applied. Due to the small fibril size and the low degree of order of cellulose in these samples, the concept of crystalline triclinic and monoclinic components as determined by diffraction analysis may not be adequate. Instead the fibril can be regarded to have different degrees of lateral order (including paracrystalline ordering) that can be reoriented to I type conformation and packing upon pulping. 相似文献
16.
The supramolecular architecture and the morphological structure of cellulose play an important role in its accessibility.
In order to evaluate the effect of the crystalline form of organization on the accessibility, we selected cellulosic materials
with significant variations in the aforementioned characteristics. The assessment of the accessibility of cellulosic materials
was performed experimentally through a water vapor sorption method. The kinetics and the thermodynamic parameters of water
vapor sorption process were determined, and a correlation between the Flory–Huggins interaction parameters and the crystallinity
index was derived. We concluded that the allomorph involving the most accessible crystal surfaces and amorphous regions was
Cellulose II. The correlation of the accessibility values with those of the crystallinity index allowed us to evaluate the
accessibility of the allomorphic forms of cellulose at different crystallinity indexes. The obtained experimental data allowed
us to quantify the accessibility for crystal surfaces and amorphous regions of the different allomorphs in the order Cellulose
II (38%) > Cellulose I (24%) > Cellulose III (10%). 相似文献
17.
Qining Sun Marcus Foston Daisuke Sawada Sai Venkatesh Pingali Hugh M. O’Neill Hongjia Li Charles E. Wyman Paul Langan Yunqiao Pu Art J. Ragauskas 《Cellulose (London, England)》2014,21(4):2419-2431
One commonly cited factor that contributes to the recalcitrance of biomass is cellulose crystallinity. The present study aims to establish the effect of several pretreatment technologies on cellulose crystallinity, crystalline allomorph distribution, and cellulose ultrastructure. The observed changes in the cellulose ultrastructure of poplar were also related to changes in enzymatic hydrolysis, a measure of biomass recalcitrance. Hot-water, organo-solv, lime, lime-oxidant, dilute acid, and dilute acid-oxidant pretreatments were compared in terms of changes in enzymatic sugar release and then changes in cellulose ultrastructure measured by 13C cross polarization magic angle spinning nuclear magnetic resonance and wide-angle X-ray diffraction. Pretreatment severity and relative chemical depolymerization/degradation were assessed through compositional analysis and high-performance anion-exchange chromatography with pulsed amperometric detection. Results showed minimal cellulose ultrastructural changes occurred due to lime and lime-oxidant pretreatments, which at short residence time displayed relatively high enzymatic glucose yield. Hot water pretreatment moderately changed cellulose crystallinity and crystalline allomorph distribution, yet produced the lowest enzymatic glucose yield. Dilute acid and dilute acid-oxidant pretreatments resulted in the largest increase in cellulose crystallinity, para-crystalline, and cellulose-Iβ allomorph content as well as the largest increase in cellulose microfibril or crystallite size. Perhaps related, compositional analysis and Klason lignin contents for samples that underwent dilute acid and dilute acid-oxidant pretreatments indicated the most significant polysaccharide depolymerization/degradation also ensued. Organo-solv pretreatment generated the highest glucose yield, which was accompanied by the most significant increase in cellulose microfibril or crystallite size and decrease in relatively lignin contents. Hot-water, dilute acid, dilute acid-oxidant, and organo-solv pretreatments all showed evidence of cellulose microfibril coalescence. 相似文献
18.
Tiina Liitiä Sirkka Liisa Maunu Bo Hortling Tarja Tamminen Osmo Pekkala Antero Varhimo 《Cellulose (London, England)》2003,10(4):307-316
Solid-state 13C NMR spectroscopy was used to determine the degree of cellulose crystallinity (CrI) in kraft, flow-through kraft and polysulphide–anthraquinone (PS–AQ) pulps of pine and birch containing various amounts of hemicelluloses. The applicability of acid hydrolysis and the purely spectroscopic proton spin-relaxation based spectral edition (PSRE) method to remove the interfering hemicellulose signals prior to the determination of CrI were also compared. For softwood pulps, the spectroscopic removal of hemicelluloses by PSRE was found to be more efficient than the removal of hemicelluloses by acid hydrolysis. In addition to that, the PSRE method also provides information on the associations between cellulose and hemicelluloses. On the basis of the incomplete removal of xylan from the cellulose subspectra by PSRE, the deposition of xylan on cellulose fibrils and therefore an ordered ultrastructure of xylan in birch pulps was suggested. The ordered structure of xylan in birch pulps was also supported by the observed change of xylan conformation after regeneration. Similarly, glucomannan in pine pulps may have an ordered structure. According to the 13C CPMAS measurements conducted after acid hydrolysis, the degree of cellulose crystallinity was found to be slightly lower in birch pulps than in the pine pulps. Any significant differences in cellulose crystallinity were not found between the pulps obtained by the various pulping methods. Only in pine PS–AQ pulp, the degree of cellulose crystallinity may be slightly lower than in the kraft pulps containing less hemicelluloses. 相似文献
19.
Diana Ciolacu Selestina Gorgieva Daniel Tampu Vanja Kokol 《Cellulose (London, England)》2011,18(6):1527-1541
This paper investigates the enzymatic hydrolysis of three main allomorphic forms of microcrystalline cellulose using different
cellulases, from Trichoderma reesei and from Aspergillus niger, respectively. It was demonstrated that both the morphological and crystalline structures are important parameters that have
a great influence on the course of the hydrolysis process. The efficiency of the enzymatic hydrolysis of cellulosic substrates
was estimated by the amounts of reducing sugar and by the yield of the reaction. Changes in the average particle sizes of
the cellulose allomorphs were determined during enzymatic hydrolysis. The accumulation of soluble sugar within the supernatant
was used as a measure of the biodegradation process’s efficiency, and was established by HPLC-SEC analysis. Any modifications
in the supramolecular structure of the cellulosic residues resulting from the enzymatic hydrolysis were determined by X-ray
diffraction. The action of each cellulase was demonstrated by a reduction in the crystalline index and the crystallite dimensions
of the corresponding allomorphic forms. The crystalline structure of allomorphic forms I and II did not suffer significant
modifications, while cellulose III recorded a partial return to the crystalline structure of cellulose I. The microstructures
of cellulose allomorph residues were presented using optical microscopy and scanning electron microscopy. 相似文献