Thermogravimetric analysis of pulps part II: Kinetics for dynamic thermogravimetric analysis

Summary This paper surveys the different kinetic schemes that have been employed with dynamic thermogravimetric analysis and discusses their advantages and shortcomings with particular reference to cellulose. It is concluded that the differential method of Friedman [1965] and the integral method of Flynn and Wall [1966] are the best approaches for kinetic analysis in each category. Both these methods are consistent with and analogous to the isothermal kinetic methods previously given by Cardwell and Luner [1975].Contribution No. 101 from the Empire State Paper Research Institute, State University of New York College of Environmental Science and Forestry, Syracuse, New York 13210     

Surface analysis of explosion pulps by ESCA

Summary The oxygen (1s) ESCA peak for aspen explosion pulp consists of two components, O1 and O2. A tentative assignment was made for them. O1 with lower binding energy is assigned to oxygen in lignin; while O2 comes mainly from the oxygen elements in carbohydrates. Thus, an O1 area percentage might be viewed as a measure of lignin exposed on the fiber surface. Sulfur (2p) spectra show that the sulfur on the fiber surface of the pulps studied here is in the form of sulfonate groups. Compared to conventional pulps, the lower percentage of O1 and higher sulfur-to-carbon ratio for explosion pulps imply higher number of hydrophilic groups exposed on their fiber surface.     

Enzymic isolation of lignin from wood and pulps

After enzymic hydrolysis of polysaccharides in milled wood or pulp the unhydrolysed lignin residue becomes soluble in certain polar solvents. Extensive disintegration of the wood is necessary to obtain a sufficient accessibility toward the enzyme. For milling a porcelain rotary ball mill is recommended. A relationship has been found between the milling energy, which is proportional to the size of the mill, the milling time, and the yield of ball-milled wood lignin (BMWL). Enzymatically isolated lignin (EIL) requires a critical milling time which is shorter than that for obtaining maximum yields of BMWL. A procedure for isolation of the total lignin content from wood and pulps in the form of three fractions has been developed, giving a water soluble, low molecular carbohydrate-lignin complex by water extraction of ball-milled wood, a BMWL-carbohydrate complex by subsequent extraction with dioxane, and a EIL-carbohydrate complex by dioxane extraction of the residue after enzymic hydrolysis.     

Accurate determination of the limiting viscosity number of pulps

The viscosity of copper ethylenediamine (CED) solutions of pulps exhibits a decrease with time, while the viscosity loss is insignificant when the time between dissolution and measurement is just 15–20 min. Time of 1 h or longer would lead to noticeable differences from the initial viscosity. The viscosity of the solution at the beginning can be estimated from a series of measurements performed under strict conditions. In particular, tight control of the temperature of the solution and accurate measurement of the flow time are of importance. The plot of efflux times against elapsed times to the measurements results in a almost linear correlation, which enables to determine the initial viscosity.     

On the selectivity of ozone delignification of softwood kraft pulps

Summary Ozonation of kraft pulp and oxygen-delignified kraft pulp in acetic acid/water mixtures has been studied at different pulp consistencies with and without an inhibitor to obtain information about the limitations of the selectivity of the ozone treatment. The experiments have been performed according to a full factorial design and data have been analysed by stepwise regression analysis. The results show that a better delignification selectivity can be achieved when ozone is applied in acetic acid media instead of conventional aqueous media. By combining conventional oxygen delignification and ozonation in acetic acid, pulps with equal strength properties and better optical properties compared to those of conventional O(DC)E prebleached pulps can be obtained. This study has also revealed that the reagent is utilized far more efficiently in ozonation at high pulp consistency (35%) than in ozonation at low consistency (1%), and that a similar selectivity can be achieved in both types of ozonation by choosing appropriate conditions. The greater selectivity of ozonation in acetic acid than in water is interpreted in terms of different stabilities of the oxidant in these reaction media. The relation between the formation of hydroxyl radicals and the extent and selectivity of delignification during ozonation has been investigated. The final bleaching of pulps prebleached with ozone in acetic acid medium has been studied. Two final bleaching sequences are presented, by which pulps with ISO brightness levels of 79% and 90% can be produced.The authors are indebted to the Swedish National Board for Technical Development (Styrelsen för Teknisk Utveckling) for financial support for this work and to STORA Technology for pulp tests and analyses     

Surface analysis of explosion pulps by ESCA Part 1. Carbon (1s) spectra and oxygen-to-carbon ratios

Summary The surface composition of explosion pulp and conventional CMP and CTMP underwent ESCA spectroscopy. Explosion pulps exhibited a higher oxygen-to-carbon ratio and less C1 peak areas compared to conventional CMP/CTMP. Based on the theoretical O/C ratios and C1 contents for the main components of wood fibers (i.e., carbohydrates, lignin and extractives), a triangular graph was used to illustrate the relative amounts of the three components on the surface. This analysis indicated that explosion pulps had more carbohydrates exposed on their fiber surface, which may explain their high physical strength. A bulk analysis indicated that these differences could not depend on their bulk compositions, since the latter were similar.     

热重法研究木材热解反应动力学

本文应用热重分析法研究了木材热解过程，结果表明：１．失去水分后的试样木粉，α－纤维素热解反应分两阶段进行，克拉松木素热解反应只有一个阶段，２．热解反应的表观活化能α－纤维素〉试样木粉〉克拉松木素，在低温阶段热解时α－纤维素表以活化能远大于试样木粉，而在高温阶段热解时α－纤维素和试样木粉反应表观活化能基本相同，３．试样木粉和α－纤维素各阶段反应级数均为１，克拉松木素的热解反应级数因树各种的不同而有较     

Thermogravimetric Analysis and Kinetics of Walnut Shell and Coal Co-pyrolysis

利用热重分析在不同升温速率(5 ～50 K/min)和氮气气氛下对核桃壳、褐煤以及核桃壳-褐煤(质量比1∶1)混合物的热解失重行为进行了研究,求取了热解动力学参数.实验结果表明,随着升温速率的提高,3种原料的失重率下降,热失重速率升高;核桃壳与褐煤共熟解时存在协同作用;三者的平衡熟解温度分别为568.9、709.9和571.0K.应用Coats-Redfern方法进行热解动力学过程分析表明,3种原料均可由一级反应过程描述.核桃壳快速热解和残余物缓慢热解阶段的平均活化能分别为50.6、17.3 kJ/mol,褐煤的平均活化能为21.1 kJ/mol,核桃壳-褐煤混合物快速热解和残余物缓慢热解阶段的平均活化能分别为34.2和14.5 kJ/mol.     

核桃壳与煤共热解的热重分析及动力学研究

利用热重分析在不同升温速率(5～50 K/min)和氮气气氛下对核桃壳、褐煤以及核桃壳-褐煤(质量比1∶1)混合物的热解失重行为进行了研究,求取了热解动力学参数。实验结果表明,随着升温速率的提高,3种原料的失重率下降,热失重速率升高;核桃壳与褐煤共热解时存在协同作用;三者的平衡热解温度分别为568.9、709.9和571.0K。应用Coats-Redfern方法进行热解动力学过程分析表明,3种原料均可由一级反应过程描述。核桃壳快速热解和残余物缓慢热解阶段的平均活化能分别为50.6、17.3 kJ/mol,褐煤的平均活化能为21.1 kJ/mol,核桃壳-褐煤混合物快速热解和残余物缓慢热解阶段的平均活化能分别为34.2和14.5 kJ/mol。     

阻燃刨切薄竹的热重分析

利用磷酸氢二铵[(NH4)2HPO3]和硼砂(Na2B4O7·10H2O)(质量比4∶1)复配的阻燃剂对刨切薄竹进行阻燃处理,采用热重(TG)、微商热重(DTG)法对阻燃和未阻燃刨切薄竹的热解性能进行研究.结果表明:阻燃刨切薄竹与未阻燃处理的刨切薄竹相比,在其热解过程中质量损失率明显降低,未阻燃薄竹的残余质量百分比为17.96％,载药量3％、4％、7％的阻燃刨切薄竹的残余质量百分比分别为23.75％、25.54％、27.4％,其残余质量百分比分别比未阻燃簿竹增加了32.2％、41.98％、52.56％,而成炭率显著提高;热分解的起始温度也有所提前,说明阻燃刨切薄竹获得了较好的阻燃效果,随着刨切薄竹载药量的增加,阻燃效果也越明显.     

Thioacidolytic analysis of residual lignins isolated from the chemical pulps of spruce (Picea abies) and beech (Fagus sylvatica) wood

Eight different residual lignins isolated from unbleached chemical pulps [sulfite, kraft, alkaline sulfite-anthraquinone-methanol (ASAM), soda/AQ/MeOH] of spruce and beech were characterized using gel permeation chromatography (GPC), thioacidolysis, and desulfurization to determine average molecular weight, amounts of uncondensed β-O-4 linkages, and dimeric linkage patterns, respectively. The total amounts of G-CHSEt-CHSEt-CH₂SEt and S-CHSEt-CHSEt-CH₂SEt were markedly reduced in residual lignins to 40% to 80% of the values for the corresponding milled wood lignins (MWLs). The number of dimeric units determined by thioacidolysis and desulfurization of the residual lignins was decreased by onehalf to one-fifth compared to the MWLs. Among the diverse types of dimeric units, reduction of β-1 and β-5 units was significant in most of the residual lignins, with the exception of beech ASAM residual lignin. Compared to beech MWL, 40% more C6–C3 main monomers were detected, whereas the relative composition of the dimeric units in the beech residual lignin was very similar to that in the beech MWL. The average molecular weights of residual lignins were less than those of the MWLs. However, the average molecular weights of the spruce kraft and soda residual lignins were determined to be higher than those of the corresponding MWLs.     

加纳龙头竹的热重习性和物理性能

与亚洲国家相比,加纳的竹子利用程度较低。究其原因,主要是对当地竹种的潜力缺乏了解。本研究在加纳选择了3块立地,对龙头竹和黄金间碧竹的热习性及其与与含水率和基本密度的关系进行了研究。结果表明,在热加工过程中可分为3~4个不同的阶段。样品竹的灰含量低于1%,且两种竹之间没有明显的区别。但在物理特性上,来自3块地的不同竹秆存在不同。竹秆含水量在71.7%~145.5%之间,且顶部的含水量比基部的含水量稍低。基本密度值为466~761kg/m³,3块立地之间有明显的区别。     

The influence of acetosolv pulping conditions on the enzymatic hydrolysis of Eucalyptus pulps

Eucalyptus globulus wood was subjected first to HCl–catalysed delignification with 70% acetic acid under conditions realizing an incomplete 3 × 3 × 3 factorial design (HCl concentration 0, 0.025 or 0.05%; temperature 120, 140 or 160 °C; reaction time 1, 2.5 or 4 h), and then to enzymatic hydrolysis. The hydrolysis kinetics conformed to both Ghose's empirical model and a biexponential equation. The biexponential fit implies the presence of both readily and reluctantly hydrolysed cellulose fractions, and the fitted coefficients show hydrolysis yield to depend largely on the digestibility of the latter. Multiple regression of performance variables on pulping conditions showed that neither the rate nor the extent of hydrolysis is greatest for pulps with minimum lignin or xylose contents; we attribute this circumstance to the condensation and precipitation of lignin under severe pulping conditions, which protects the cellulose of the pulp from enzymatic attack. Received 20 June 1998     

NIR PLSR model selection for Kappa number prediction of maritime pine Kraft pulps

A total of 910 maritime pine (Pinus pinaster Aiton) wood discs, belonging to a genetic trial of 80 families with 11–12 trees per family, were used in this study. A near infrared (NIR) partial least squares regression (PLSR) model for the prediction of Kappa number of Pinus pinaster Aiton pulps obtained from samples pulped under identical conditions was calculated. Very good correlations between NIR spectra of maritime pine pulps and Kappa numbers in the range from 58 to 100 were obtained. Besides the raw spectra, spectra pre-processed with ten methods were used for PLS analysis (cross validation with 57 samples), showing that even after test set validation (with 34 samples) no model decision could be made due to almost identical statistics. The final evaluation that proved the predictive power of the models by predicting pulps with unknown Kappa numbers allowed choosing a model according to a minimal number of outliers found during this process. The minimum–maximum normalized spectra in the wave number range from 6,110 to 5,440 cm⁻¹ used for the calculation gave the best model with a root mean square error of prediction of 2.3 units of Kappa number, a coefficient of determination of 95.9%, and one PLS component. The percentage of outliers during evaluation was 0.9%.     

Sulfuric acid bleaching of kraft pulp 1: Bleaching of hardwood and softwood kraft pulps

To develop a new nonchlorine bleaching technology, hardwood and softwood kraft pulps, before and after oxygen-alkali predelignification, were treated with dilute sulfuric acid solutions (pH 1.0-1.8) at 100°C for 1 h and then extracted with aqueous sodium hydroxide at 70°C for l h. Hardwood kraft pulp was successfully bleached. The delignification selectivity was similar to that seen with oxygen-alkali bleaching; and it was greatly enhanced by the addition of sodium nitrate and sodium nitrite. The sulfuric acid bleaching can replace the presently adopted oxygen and chlorine stages if the additives are allowed. This bleaching process was also effective for oxygen-bleached hardwood kraft pulp, but it was less effective for softwood kraft pulp and oxygen-bleached softwood kraft pulp. The effectiveness of the addition of sodium nitrate and sodium nitrite was more apparent for softwood kraft pulp than for hardwood kraft pulp.Part of this report was presented at the 7th International Symposium on Wood and Pulping Chemistry, Beijing, July 1993     

Refining of bleached cellulosic pulps: characterization by application of the colloidal titration technique

Summary The relation between freeness and the cationic demand of fibrous suspensions containing an industrial kraft hardwood bleached pulp (refined at different levels) is studied in this paper. The technique used was the colloidal titration. Results suggest that the fixation on cellulosic fibres is attained through two mechanisms: ionic exchange and adsorption by means of hydrogen bonds and van der Waals forces.     

An improved acetyl bromide procedure for determining lignin in woods and wood pulps

Summary The acetyl bromide procedure for spectrophotometrically determining lignin in wood and wood pulp samples has been modified by adding perchloric acid to the digestion medium. This enables faster dissolution of the materials and the use of coarser samples. Subsequent treatment of the digestion mixtures with larger amounts of sodium hydroxide than those used in the conventional procedure has obviated the need for treatment with hydroxylamine. The modified method has been successfully applied to woodmeals and pulps from Pinus radiata and Eucalyptus species.