蔗渣碱木素的热裂解特性

利用热重分析法研究了蔗渣碱木素的热解特性,并利用TG-FTIR和Py-GCMS对碱木素的热解产物种类及分布规律进行了分析。结果表明,木素热解呈现宽温度区域,可分为4个阶段,主要裂解温度范围为200～500℃,在400℃左右失重率最大,残余物得率较高。TG-FTIR分析显示了木素热解过程中气体产物的释放规律,300～500℃为主要热解挥发阶段,大部分气体产物在400℃左右产率达到最大。Py-GCMS分析表明,木素的热解产物大致可分为杂环、苯类芳香族、酚类芳香族、酯和酸等化合物,在主要热分解阶段,随着热解温度的升高,苯类和酚类芳香族化合物的含量增多,600℃时酚类物质的含量最高。     

Thermochemical characteristics of sugar cane bagasse pellets

Pelletisation facilitates utilisation of sugar cane bagasse as a fuel and storage for year-round electricity generation. The present work determines thermochemical characteristics of bagasse pellets of different sizes and origins, using various temperatures (600, 750 and 900 °C) and gas flow rates (4, 7 and 10 L/min) with varying concentrations of oxygen (5, 10 and 15%) in mixtures with nitrogen. Of major interest are the effects of raw material, origin and size of pellets, and the treatment conditions on the rate of pyrolysis and the structure and reactivity of char in combustion. The char yield of the larger pellets of high-ash content bagasse was practically independent of treatment conditions. Smaller pellets gave better mechanical stability of the char but lower reactivity.     

Thermal behavior of ungrafted and grafted bagasse and wood pulps

The effect of grafting of methyl methacrylate (MMA) and acrylonitrile (AN) on the thermal behavior of the pulp of sugar cane loaded with CaCO₃ and the pulp of a broad-leaved tree has been studied by thermal methods. Different experimental conditions of grafting AN onto the eucalyptus pulp have been used, including both water and organic solvent systems as the medium of reaction. To optimize the grafting of MMA onto wood pulp, the effect of pulp swelling and the contact time of the monomer with the pulp have been examined. Ungrafted as well as grafted cellulose samples with different levels of grafting were characterized by differential scanning calorimetry (DSC) and the thermogravimetric analysis (TGA). The CaCO₃ filler makes the pulp of bagasse thermally more stable. The grafting of MMA onto the bagasse or the wood pulps improves their thermal stability. This is not the case for wood grafted with poly(AN). The thermal stability of the grafted and ungrafted samples varies after a few weight percent has been lost. The glass transition temperature (T_g) of the copolymers have been measured and they are in good agreement with the calculated data. © 1993 John Wiley & Sons, Inc.     

蔗渣碱法造纸黑液回收木质素的结构及其燃烧特性

以酸析法从蔗渣碱法造纸黑液中回收蔗渣木质素（BL）,通过红外光谱（FTIR）,核磁共振氢谱（¹H NMR）和凝胶渗透色谱（GPC）对其进行了表征。结果表明,BL主要由愈创木基丙烷单元（G）和紫丁香基丙烷单元（S）通过C-O、C-C键合方式连接而成,其分子量分布较宽,分子之间存在较大差异。通过热重分析法（TG）研究了BL的燃烧特性,结果表明BL的燃烧主要发生在300~500℃的阶段,在此过程中BL分子中的C-C键发生断裂形成挥发分和焦炭,并迅速燃烧,失重率超过80%。通过扫描电子显微镜（SEM）和X射线荧光光谱（XRF）研究了BL在300、600、900和1100℃燃烧灰渣（BLR）的微观形貌和元素组成,结果表明BL呈结实、饱满的颗粒状,而BLR则表现为多孔的疏松堆积体或规则的片状结晶颗粒。随着燃烧温度的升高,BLR中的Na和K质量分数逐渐减少,而其他元素质量分数变化不大。     

三氧化二铝对甘蔗渣灰熔融特性的影响

采用红外光谱分析、环境扫描电镜分析、X射线衍射分析等方法,分析了酸性氧化物Al_2O_3在不同比例下对甘蔗渣灰熔融特性的影响。灰熔点测试和SEM实验结果表明,随着Al_2O_3添加比例的增加,甘蔗渣的灰熔点逐渐升高,但是升高的速率逐渐降低。红外光谱中特征峰的明显与否体现了Al_2O_3的加入对甘蔗渣灰中硅酸盐含量的影响,添加比例越大,硅酸盐的特征峰越不明显。XRD实验表明,添加Al_2O_3后甘蔗渣灰中的主要成分含量发生改变,其中K_2SO_4含量降低,SiO_2、Al_6Si_2O_(13)的含量增多,说明Al_2O_3的加入能有助于减少甘蔗渣灰中非晶态低温共熔体的生成。由于低灰熔点K_2SO_4、硅酸钙盐的减少和高灰熔点SiO_2、Al_2O_3、Al_6Si_2O_(13)的增加,因此添加Al_2O_3能显著提高甘蔗渣的灰熔点。     

Thermal characteristics of rice hulls

Evaluation of the thermal characteristics of rice hulls is described. Decomposition was negligible below 200°C, but on heating above 200°C, the amount of volatile matter evolved increased steadily with increasing temperature up to 450°C, where > 90 % of the total volatile matter was separated. Decomposition is rapid and is temperature dependent. The effect of temperature on the composition of the residues is also described. The carbon content of the residues increased while the oxygen and hydrogen content decreased sharply when the temperature of pyrolysis was increased.     

板式蒸发式冷凝器热工性能实验

对影响板式蒸发式冷凝器热工性能的主要因素——空气的湿球温度、冷凝温度、相对湿度做了实验研究。结果显示：冷凝温度和冷凝压力均随着入口空气湿球温度的升高而升高;入口空气相对湿度对压缩机功耗的影响与湿球温度对压缩机功耗的影响均比较大;对基于同一压缩系统的实验比较表明,在冷凝温度为38℃时,板式蒸发式冷凝器的热流密度比管式蒸发式冷凝器平均大30.5%;且在相同的冷凝温度下,入口空气湿球温度越低,板式蒸发式冷凝器的热流密度比管式蒸发式冷凝器大得越多。     

Saccharification of bagasse pith

Work is reported here on a process for the saccharification of bagasse pith, as the second part of a study of bagasse processing aimed at establishing an integrated industry. A method for pentose preparation from bagasse pith is designed on the basis of the conclusions reached in the first part of the study. It is preferable to Scholler's process in recovery of sugar and in concentration of the sugar solution. A process for glucose production from pentose-exhausted cellulosic residue is also developed to avoid the difficulties encountered in the Udic-Rheinau process. It seems to be a promising continuous process capable of giving a higher yield of glucose with less acid at a higher speed and affording favourable conditions for crystallising the dissolved glucose.     

Thermoplasticization of bagasse. I. preparation and characterization of esterified bagasse fibers

This research was to investigate the conversion of bagasse into a thermoformable material through esterification of the fiber matrix. For this purpose, bagasse was esterified in the absence of solvent using succinic anhydride (SA). The reaction parameters of temperature reaction, time, and amount of succinic anhydride added were studied. Ester content, Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA) were used to characterize the chemical and thermal properties of the esterified fibers. The results showed that on reacting bagasse with SA in the absence of solvent, ester content up to about 48% could be obtained. Diester formation increased with increasing reaction time and temperature at high levels of ester content. Ester content determination of the esterified fibers and their corresponding holocelluloses showed that the reaction took place in the lignin and holocellulose components of bagasse. The IR results showed that the crystallinity index of different esterified bagasse samples did not decrease as a result of increasing the ester content. DSC and TGA results showed that esterified‐bagasse fibers were less thermally stable than the untreated fibers. DMTA results showed that esterification of the fibers resulted in a decrease in the tan δ peak temperature of the esterified fibers compared to the untreated fiber. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 561–574, 2000     

Thermal and flow property–morphology relationship of sugarcane bagasse fiber‐filled polyamide 6 blends

The structure–property relationship of sugarcane bagasse fiber‐filled polyamide 6 blends at different blend compositions has been investigated. Blends were prepared in the composition of wt % PA6/wt % bagasse as follows: 98/2, 95/5, and 90/10 for three fiber length ranges (<100, <250, and <500 μm) using a twin‐screw extruder. Thermal properties were evaluated by measuring the glass transition temperature T_g, enthalpy of fusion ΔH_f, crystallinity X_c and thermogravimetry, TG. Results showed that T_g of the composites changed with change in fiber loading and length. The X_c as well as ΔH_f of the blends reduced to almost half its value for the neat PA6. The thermogravimetric curves TG showed that the thermal stability of the composites was lower than that of the neat PA6. Rheological properties were studied as a function of fiber loading, fiber length, shear rate, and temperature. The viscosity of composites increased with increasing fiber loading and length at low shear rates but decreased below that of neat PA6 at high shear rates. It was also found to be temperature sensitive, and influenced by fiber lengths particularly at higher temperatures. The morphology of the blends was studied using a Leica laser scanning confocal microscopy at two different regions: at the wall, and the core. The micrographs of the blends showed that fibers present in the form of bundles were found at the wall of the extrudates and increased in volume with increase in both length and concentration, at the same temperature and shear stress. In the core region, there is laminar flow, presenting striation morphology, with the omnipresent bundles of fibers dispersed in the matrix. At higher shear rates, the bundles were pushed to the wall. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3744–3754, 2004     

Thermoplasticization of bagasse by cyanoethylation

To develop a new technique for the effective utilization of bagasse, cyanoethylation was attempted to see if bagasse could be converted into a thermoplastic material. The effects of various reaction parameters (temperature, time, alkali concentration, and acrylonitrile‐to‐bagasse ratio) on the extent of the cyanoethylation reaction were studied. Fourier transform infrared spectroscopy was done to demonstrate the occurrence of cyanoethylation; thermogravimetric analysis, to study the thermal stability of the produced cyanoethylated bagasse; X‐ray diffraction, to follow the change in the supramolecular structure; and scanning electron microscopy of hot‐pressed cyanoethylated bagasse to show the occurrence of thermoplasticization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1965–1978, 2001     

Thermal response characteristics of fire blanket materials

The thermal response characteristics of over 50 relatively thin (0.15–3.7 mm) fire blanket materials from four different fiber groups (aramid, fiberglass, amorphous silica, and pre‐oxidized carbon) and their composites have been investigated. A plain or coated fabric sample was subjected to a predominantly convective or radiant heat flux (up to 84 kW/m²) using a Meker burner and a cone heater, respectively. In addition to conventional thermal protective performance ratings for protective clothing, two transient thermal response times (for the fabric back‐side temperature to reach 300 °C and for the through‐the‐fabric heat flux to reach 13 kW/m²) and a steady‐state heat‐blocking efficiency (HBE) were introduced for both convective and radiant heat sources. For most woven fabrics, the HBE values were approximately 70 ± 10% for both convection and radiation and only mildly increased with the fabric thickness or the incident heat flux. Nonwoven (felt) fabrics with low thermal conductivity exhibited significantly better insulation (up to 87%) against convective heat. Highly reflective aluminized materials exhibited exceptionally high HBE values (up to 98%) for radiation, whereas carbon and charred aramid fabrics showed lower HBEs (down to 50%) because of efficient radiation absorption. A relatively thin fire blanket operating at high temperatures can efficiently block heat from a convective source by radiative emission (enhanced by its T⁴‐dependence and high surface emissivity) coupled with thermal insulation and from a radiant heat source by surface reflection while the aluminum surface layer remains. Copyright © 2013 John Wiley & Sons, Ltd.     

Thermal characteristics of silver powder-filled polypropylene composites

The thermal properties of silver powder-filled polypropylene composites were studied as a function of filler concentration. Thermal conductivities of the composites increased with filler content. Comparison of the data with theoretical predictive models for two-phase systems showed that the Nielson equation agreed reasonably well with the measured values. A TGA study showed that presence of silver powder increased the thermal stability of polypropylene through an increase in activation energy. The thermal expansion coefficient of the composites exhibited a decreased in the presence of Ag powder. Surface treatment of Ag powder with a titanate coupling agent marginally increased thermal conductivity and decreased thermal expansion coefficient values, implying a degree of enhance adhesion of the filler with the polymer. © 1994 John Wiley & Sons, Inc.     

Thermal and textural characteristics of modified silica

A silica gel characterised as predominently microporous, with the remaining pores of limited dimensions which do not permit capillary condensation, is modified with aqueous solutions of acetic acid, glycine and β-alanine. The modified samples are investigated and compared with a water soaked sample by means of differential thermal analysis, thermogravimetry and i.r. spectroscopy. Textural measurements are also carried out on the parent samples and those produced in the temperature range 110–600°C. Acetic acid is both physically and chemically adsorbed; a surface ester is formed. Both amino acids are physically adsorbed but no chemical interaction has been detected. Glycine and β-alanine decompose differently when adsorbed on to the silica surface than when in the pure state. The specific surface area decreases upon modification, reaching half the value of the pure silica for the β-alanine modified sample. Pore structure analysis, shows that the microporous nature of the modified samples decreases in the modifier order acetic acid < glycine < β-alanine. The adsorbed β-alanine molecules block most of the micropores present.     

Characterization of sugarcane bagasse powders

Sugarcane bagasse is a promising renewable lignocellulosic feedstock. Hence, proper characterization of bagasse powders is important for the development of novel technologies based on this resource. In this work, bagasse powders are prepared by sieve fractionation followed by cutting milling and rotor milling (which acts by impact, shear, and friction). The generated powders are characterized by techniques commonly applied to other particulate systems, namely scanning electron microscopy, light scattering particle sizing, and nitrogen adsorption. Particle size distribution, envelope density, specific surface areas, and effective cell wall thickness are determined. Results obtained from different techniques are compared. Finally, the applicability of the analytical techniques to sugarcane bagasse powders is discussed.     

Thermal characteristics of high-strength and thermostable aromatic fibres

The thermal characteristics of para-aramid, polyoxadiazole, and polyimide fibres were comparatively investigated by dynamic thermogravimetric analysis, differential scanning calorimetry, and thermomechanical analysis. It was shown that thermooxidative degradation of these types of fibres began at 400–450 °C and intensified at higher temperatures. The fibres investigated are characterized by size stability up to the initial temperature of thermooxidative processes (400–450 °C). With respect to thermal stability, these fibres are in the following order: polyimide > polyoxadiazole, and carbocyclic para-aramid fibres. The correlation of the “hydrogen index” I_H and “aromaticity index” I_Ar for thermostable fibres with their thermal stability was demonstrated. Translated from Khimicheskie Volokna, No. 3, pp. 72–74, May–June, 2008.     

Hydrolysis of pentosans in bagasse pith

Work has been conducted on the hydrolysis of pentosans in bagasse pith as the first part of a study of the chemistry of bagasse processing aimed at establishing an integrated industry. Bagasse pith is the fine part screened out and discarded as waste during the preparation of raw material for bagasse pulping plant. By using dilute sulphuric acid at a concentration less than 2% by weight and at a temperature lower than 165°C, pith is hydrolysed to pentoses in a yield of 80–90% based on potential pentoses in pith. Hydrolysis of pentosans in pith, within the scope of experiment, seems to be a first order reaction. However, the semi-logarithmic time plot for the hydrolysis of potential pentoses in the residue consists of two straight lines of different slope. This may be explained on the assumption that bagasse pith contains two major fractions of pentosans that are hydrolysed at different rates. Saeman's equation for hydrolysis of wood with sulphuric acid may be adapted to represent dependence of rate constant K on acid concentration C and reaction temperature T in hydrolysis of the two major parts of pentosans in bagasse pith.