有关制浆中木素的简单介绍

木素存在于维管束中,木材中含量达20％～30％。化学构造是以3种类苯丙烷为构成单位的复杂聚合的枝状构造。在天然情况下与纤维素和其它糖类结合在一起,充填在细胞壁的纤维素胶囊中,起着强固组织的作用。然而在制浆中我们在保留大部分纤维素和部分半纤维素的同时,还必须尽可能多的除去木素,因而我们对木素有必要进行些了解。     

Effect of methyl jasmonate on cell wall modification of loquat fruit in relation to chilling injury after harvest

Loquat fruit were pretreated with 10 μM methyl jasmonate (MeJA) for 24 h at 20 °C, and then stored at 1 °C for 35 days to investigate the effect of MeJA treatment on cell wall modification in relation to chilling injury. Loquat fruit developed chilling injury, manifested as increased fruit firmness and internal browning, decreased extractable juice during storage. These chilling injury symptoms were significantly reduced by MeJA treatment. MeJA also markedly delayed the increases in lignin, alcohol insoluble residues, hemicellulose and cellulose. Meanwhile, the MeJA-treated fruit exhibited significantly lower activities of phenylalanine ammonia lyase, peroxidase, polyphenol oxidase and higher polygalacturonase activity than the control during storage. The levels of water- and CDTA-soluble pectins in MeJA-treated fruit were also significantly higher than that in the control. These results suggest that the reduction in chilling injury by MeJA may be due to inhibited lignin accumulation and enhanced cell wall polysaccharides solubilisation.     

The capability of ultrafiltrated alkaline and organosolv oil palm (Elaeis guineensis) fronds lignin as green corrosion inhibitor for mild steel in 0.5 M HCl solution

The inhibitive effect of ultrafiltrated oil palm fronds (OPF) lignins on the corrosion of mild steel in 0.5 M HCl solution has been investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PP) and weight loss measurement. The presence of smaller lignin fractions reduces remarkably the corrosion rate of mild steel. The highest corrosion inhibition efficiency for all ultrafiltrated lignins were attained at maximum concentration of 500 ppm (IE_P.Soda: 87% > IE_P.Organosolv: 83% > IE_P.Kraft: 81%). The results from this corrosion test clearly reveal that all ultrafiltrated lignins behaved as a mixed-type inhibitor with predominant anodic (organosolv lignin) or cathodic (alkaline lignin) effectiveness. It was deduced that the inhibition process was spontaneous and the inhibitors were mainly physically adsorbed onto the mild steel surface.     

Detection of wood cell wall porosity using small carbohydrate molecules and confocal fluorescence microscopy

A novel approach to nanoscale detection of cell wall porosity using confocal fluorescence microscopy is described. Infiltration of cell walls with a range of nitrophenyl‐substituted carbohydrates of different molecular weights was assessed by measuring changes in the intensity of lignin fluorescence, in response to the quenching effect of the 4‐nitrophenyl group. The following carbohydrates were used in order of increasing molecular weight; 4‐nitrophenyl β‐D‐glucopyrano‐side (monosaccharide), 4‐nitrophenyl β‐D‐lactopyranoside (disaccharide), 2‐chloro‐4‐nitrophenyl β‐D‐maltotrioside (trisaccharide), and 4‐nitrophenyl α‐D‐maltopentaoside (pentasaccharide). This technique was used to compare cell wall porosity in wood which had been dewatered to 40% moisture content using supercritical CO_2, where cell walls remain fully hydrated, with kiln dried wood equilibrated to 12% moisture content. Infiltration of cell walls as measured by fluorescence quenching, was found to decrease with increasing molecular weight, with the pentasaccharide being significantly excluded compared to the monosaccharide. Porosity experiments were performed on blocks and sections to assess differences in cell wall accessibility. Dewatered and kiln dried wood infiltrated as blocks showed similar results, but greater infiltration was achieved by using sections, indicating that not all pores were easily accessible by infiltration from the lumen surface. In wood blocks infiltrated with 4‐nitrophenyl α‐D‐maltopentaoside, quenching of the secondary wall was quite variable, especially in kiln dried wood, indicating limited connectivity of pores accessible from the lumen surface.     

造纸黑液中回收木素制备粘合剂的研究

以黑液为原料,利用酸析法提出木素,并以其代替部分苯酚制备出低成本的木材用酚醛胶粘剂,最佳工艺条件下产品的粘结强度为2.7Mpa;将制得的粘合剂和骨胶共混,改性既增加了酚醛胶的粘结强度,又大大降低了骨胶的凝固点,改性粘合剂的粘度为61 mPa·s,粘结强度为9.9Mpa.     

Removal of water pollutants with activated carbons prepared from H3PO4 activation of lignin from kraft black liquors

Activated carbons with a high BET surface area and a well-developed porosity have been prepared from pyrolysis of H3PO4-impregnated lignin precipitated from kraft black liquors. Impregnation ratios within the range of 1-3 and activation temperatures of 623-873 K have been used, giving rise to carbons with different porous and surface chemical structure. Increasing the activation temperature and the impregnation ratio leads to a widening of the porous structure with a higher relative contribution of mesoporosity. The potential application of these carbons for the removal of water pollutants has been investigated by measuring their adsorption capacities for phenol, 2,4,5-trichlorophenol and Cr (VI) as representative of toxic contaminants found in industrial wastewaters. The results obtained compare well and even favorably with those reported in the literature for other activated carbons. An impregnation ratio and an activation temperature around 2 g H3PO4/g lignin and 700 K, respectively, are recommended as the best combination of operating conditions to prepare activated carbons for aqueous phase applications although at lower values of these two variables carbons with good adsorption capacities are also obtained.     

木质素磺化的研究

木质素磺酸盐是一种具有广泛用途的高分子物质,开发利用木质素磺酸盐具有很广阔的前途。对造纸黑液及酸析木质素的磺化进行了研究,得出了黑液及酸析木质素磺化的工艺条件。     

酶促木质素与酚共聚反应速率研究

进行了过氧化物酶催化木质素与酚聚合反应及其动力学实验研究。确定了木质素浓度(Y)与吸光度 (X)的关系 ,并得到关联式 :Y =0 .0 916X。通过测定反应剂中酚的浓度 ,得到酚单体消耗速率 ,从一个侧面探索了反应速率。结果表明 ,在反相微乳液系统中 ,酶促反应速率很大。     

酶促木质素与酚共聚反应及产物表征

在反相微乳液系统中 ,用辣根过氧化物酶进行了酶促木质素与酚共聚反应 ,并进行了红外光谱分析及差示扫描量热分析。结果表明 ,由于在木质素分子间引入了聚甲酚片段 ,共聚物的热性能有较大改善。聚合物的重均分子量随反应温度的升高而增加     

The explained variation by lignin and extractive contents on higher heating value of wood

The Higher Heating Value (HHV) of 17 wood fuels was correlated with their Klason lignin (L) and extractive contents (Ext). There was a highly significant correlation between higher heating value, Klason lignin and extractive contents. The HHV (MJ/kg) of wood fuels as a function of lignin and extractive contents can be calculated using the following equation: qv,gr,d = 14.3377 + 0.1228 (L) + 0.1353 (Ext).The correlation coefficient (r) was 0.915. The standard error for Klason lignin was 0.017 and to extractive contents of 0.024. The proportion explained by Klason lignin was 56.4% and explained by extractive contents was 43.6%.