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51.
52.
Benzylated pulps from sugar cane bagasse 总被引:1,自引:0,他引:1
R. PEREIRA S. P. CAMPANA FILHO A. A. S. CURVELO A. GANDINI 《Cellulose (London, England)》1997,4(1):21-31
An optimized ethanol/water process has been employed for the pulping of fibres from sugar cane bagasse. After pretreatment
with aqueous NaOH, unbleached pulps were subjected to benzylation at 110 °C for different periods of time. The resulting purified
products were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), gel permeation chromatography
(GPC) and infrared spectroscopy (IR). The results showed that benzylation proceeded to various extents depending on the reaction
time, as assessed by weight gain. During the first 3 h, a loss of mass was observed due to the occurrence of benzylation of
low molecular weight polyoses, which were eliminated in the purification step. After that period of time a drastic weight
increase was observed probably because crystalline regions had developed. The samples with low degrees of benzylation were
insoluble, whereas the more benzylated counterparts showed limited solubility in THF. Partially soluble samples and a completely
soluble one showed very different GPC elution profiles. This may be attributed to the efficiency of the pre treatment which,
in the latter case, employed more concentrated alkali. Thermogravimetric analyses showed that all samples were degraded above
310 °C. Glass transition temperatures ranged between 42 °C and 65 °C, increasing as the extent of benzylation increased
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
53.
灰色多层次综合评判在柳树材性分析中的应用 总被引:2,自引:1,他引:1
用灰色关联度与层次分析(AHP)法选出了柳树作矿柱和造纸用材不同无性系的优良品种,其结果是:作造纸用材J903>J799>J172>J308>J795>J802,作矿柱用材J903>J799>J308>J172>J795>J802,为木材工业的发展进一步提供了信息和科学根据。 相似文献
54.
Bagasse, corn husk, and switchgrass were pretreated with ammonia water to enhance enzymatic hydrolysis. The sample (2 g) was
mixed with 1–6 mL ammonia water (25–28% ammonia) and autoclaved at 120°C for 20 min. After treatment, the product was vacuum-dried
to remove ammonia gas. The dried solid could be used immediately in the enzymatic hydrolysis without washing. The enzymatic
hydrolysis was effectively improved with more than 0.5 and 1 mL ammonia water/g for corn husk and bagasse, respectively. In
bagasse, glucose, xylose, and xylobiose were the main products. The adsorption of CMCase and xylanase was related to the initial
rate of enzymatic hydrolysis. In corn husks, arabinoxylan extracted by pretreatment was substantially unhydrolyzed because
of the high ratio of arabinose to xylose (0.6). The carbohydrate yields from cellulose and hemicellulose were 72.9% and 82.4%
in bagasse, and 86.2% and 91.9% in corn husk, respectively. The ammonia/water pretreatment also benefited from switchgrass
(Miscanthus sinensis and Solidago altissima L.) hydrolysis. 相似文献
55.
L. RAHKAMO L. VIIKARI J. BUCHERT T. PAAKKARI T. SUORTTI 《Cellulose (London, England)》1998,5(2):79-88
Dissolving pulp was solubilized in 9% NaOH, resulting in 32% solubilization of the pulp. Most of the pulp hemicelluloses were solubilized during this treatment. During the alkaline treatment the cellulose crystalline form was converted from cellulose I to cellulose II. The alkaline insoluble residue was further treated with cellulases in order to render it more alkaline soluble (two-step process). The cellulose II was readily hydrolysed by Trichoderma reesei endoglucanases. Considerably higher hydrolysis yields and lower viscosities were obtained in the hydrolysis of the alkaline insoluble residue as compared with the original pulp. Compared with direct enzymatic treatment with subsequent solubilization in alkali, the overall alkaline solubility of the two-step process was slightly higher at the same enzyme dosage. However, when compared at the same hydrolysis levels, slightly lower overall alkaline solubilities were obtained in the two-step method. 0969--0239 © 1998 Black ie Academic & Professional 相似文献
56.
A spectroscopic study of cellulose transformation processes, such as alkali treatment and annealing, showed that, in combination with multivariate data analysis techniques, a detailed understanding of the crystalline transformation processes could be reached.13C cross-polarization magic-angle spinning (CPMAS) NMR and near-infrared (NIR) spectroscopy of cotton linters and softwood pulps analysed during the processing revealed information, after data reduction using principal components data analysis, that could be connected to structural changes of the cellulose polymorphs. The data showed that alkali treatment of cotton linters led to a cellulose conversion from cellulose I to II, while annealing, both for linters and pulps, yielded a transformation from I to I. 相似文献
57.
Araujo E Rodríguez-Malave AJ González AM Rojas OJ Peñaloza N Bullón J Lara MA Dmitrieva N 《Applied biochemistry and biotechnology》2002,97(2):91-103
In this work, the effect of Fento’s reagent on the degradation of residual Kraft black liquor was investigated. The effect
of Fenton’s reagent on the black liquor degradation was dependent on the concentration of H2O2. At low concentrations (5 and 15 mM) of H2O2, Fenton’s reagent caused the degradation of phenolic groups (6.8 and 44.8%, respectively), the reduction of reaction medium
pH (18.2%), and the polymerization of black liquor lignin. At a high concentration (60 mM) of H2O2, Fenton’s reagent induced an extensive degradation of lignin (95–100%) and discoloration of the black liquor. In the presence
of traces of iron, the addition of H2O2 alone induced mainly lignin fragmentation. In conclusion, Fenton’s reagent and H2O2 alone can degrade residual Kraft black liquor under acidic conditions at room temperature. 相似文献
58.
Rodrigues Denise C. G. A. Da Silva Silvio S. Almeida E Silva J. B. Vitolo Michele 《Applied biochemistry and biotechnology》2002,98(1-9):875-883
Xylose reductase activity of Candida guilliermondii FTI 20037 was evaluated during xylitol production by fed-batch fermentation of sugarcane bagasse hydrolysate. A 24-1 fractional factorial design was used to select process variables. The xylose concentrations in the feeding solution (S
F
) and in the fermentor (S
0), the pH, and the aeration rate were selected for optimization of this process, which will be undertaken in the near future.
The best experimental result was achieved at S
F
=45 g/L, S
0=40 g/L, pH controlled at 6.0, and aeration rate of 1.2 vvm. Under these conditions, the xylose reductase activity was 0.81
U/mg of protein and xylitol production was 26.3 g/L, corresponding to a volumetric productivity of 0.55 g/(L·h) and a xylose
xylitol yield factor of 0.68 g/g. 相似文献
59.
CP/MAS 13C-NMR spectroscopy in combination with spectral fitting was used to study the supermolecular structure of the cellulose fibril in spruce wood and spruce kraft pulp. During pulping, structures contributing to inaccessible surfaces in the wood cellulose are converted to the cellulose I allomorph, that is, the degree of order is increased. This increase is also accompanied by a conversion of cellulose I to cellulose I. Cellulose from wood composed of different cell types, that is, compression wood, juvenile wood, earlywood, latewood and normal wood exhibited a similar supermolecular structure. Assignments were made for signals from hemicellulose which contribute significantly to the spectral C-4 region (80–86 ppm) in kraft pulp spectra but substantially less to the corresponding region in wood spectra. 相似文献
60.
The effect of Trichoderma reesei cellulases and hemicellulases on the paper technical properties of never-dried bleached kraft pulp 总被引:1,自引:0,他引:1
Four purified cellulases, a xylanase and mannanase from Trichoderma reesei were used to treat never-dried bleached pine kraft pulp prior to refining, and the effects on pulp properties were evaluated.
The enzymatic treatments hydrolysed up to 0.8% of pulp dry weight. The results demonstrated that the individual cellulases
have profoundly different modes of action in modifying pulp carbohydrates. This is especially clear when comparing their effects
at the same level of hydrolysis. Pretreatment with cellobiohydrolases I (CBH I) and II (CBH II) had virtually no effect on
the development of pulp properties during refining, except for a slight decrease in strength properties. On the contrary,
endoglucanase I (EG I) and endoglucanase II (EG II) improved the beatability of the pulp as measured by Schopper--Riegler
value, sheet density and Gurley air resistance. Of the endoglucanases, EG II was most effective in improving the beating response.
The combinations of CBH I with EG I and EG II had similar effects on the pulp properties as the endoglucanases alone, although
the amount of hydrolysed cellulose was increased. Pretreatments with xylanase or mannanase did not appear to modify the pulp
properties. The same enzyme treatments which improved the beatability, however, slightly impaired the pulp strength, especially
tear index at the enzyme dosages used. When compared at a given level of cellulose hydrolysis, the negative effect of EG II
on strength properties was more pronounced compared with EG I. Thus, the exploitation of cellulases for fibre treatments requires
careful optimization of both enzyme composition and dosage. Since the endoglucanases had no positive effect on the development
of tensile strength, it is suggested that the explanation for the increased beating response is increased fibre breakage and
formation of fines, rather than improved flexibilization.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献