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1.
Defence reactions of embryonal suspensor mass (ESM), precotyledonary, cotyledonary and desiccated cotyledonary somatic embryos of Abies numidica were tested by dual cultures with Phaeolus schweinitzii. Defence reactions were expressed at a very early stage of somatic embryo development. Both ESM and early somatic embryos inhibited mycelial growth, but the strongest defence was shown by the precotyledonary somatic embryos. The cotyledonary and desiccated cotyledonary embryos also showed defence reactions but with less intensity. Eight major components of soluble proteins, already present in the ESM, increased in concentration during subsequent developmental stages. Synthesis of two low‐molecular components of 6 and 3 kDa appeared in desiccated embryos. Probable regulation of defence reactions by auxins in early somatic embryos, as well as by abscisic acid content and storage proteins in subsequent developmental stages, is discussed. 相似文献
2.
J. Gierer 《Wood Science and Technology》1985,19(4):289-312
Summary Delignification processes comprising various pulping and bleaching reactions are reviewed in the light of a general concept dividing these reactions into nucleophilic and electrophilic categories. It is shown by numerous examples that pulping is due to the action of external nucleophilic species attacking electron-deficient centres in carbonyl and conjugated carbonyl (=enone) structures and to the presence of neighbouring nucleophilic groups attacking the -carbon atom of side chains. On the other hand, bleaching is initiated by electrophilic species attacking electron-rich centres in aromatic nuclei and unsaturated, ring-conjugated side chains. These initial bleaching reactions are followed by nucleophilic reactions taking place during the same or during subsequent bleaching steps.The efficiency of a particular delignification procedure is determined by the extent of cooperation between nucleophilic and electrophilic reactions.During delignification processes carbohydrate constituents of wood are subject to reactions which follow mechanisms analogous to those of lignins. This provides an explanation for the fact that the selectivity of pulping and bleaching processes is limited.Academy Lecture presented at the Ninth Cellulose Conference, Syracuse, USA, May 24–27, 1982. Extended Version of a survey article published in Holzforschung 36 (1982): 43–51 and 55–64 Part 2: Reactions of lignins during bleaching, will be published in No. 1/86 and contains all literature references 相似文献
3.
Kinetics of the self-condensation of 2,4-dihydroxymethylphenol (2,4-DHMP) and 2,4,6-trihydroxymethylphenol (THMP) were investigated to elucidate the mechanisms of the condensation of hydroxymethylphenols (HMPs). Rate equations were derived on the assumptions of the formation of quinone methide intermediates as unimolecular reactions and the occurrence of bimolecular reactions between undissociated HMPs, between undissociated HMP and dissociated HMP, and between dissociated HMPs. Rate constants were determined numerically by comparing the calculated reaction rates with observed ones. The results of analyses are as follows: (1) Both unimolecular and bimolecular reactions occur as the rate-determining steps during the self-condensation of 2,4-DHMP and THMP with low concentrations. (2) Nothing but bimolecular reactions occur as the rate-determining steps during the self-condensation of THMP with high concentrations. (3) Differences in the activation energy and the reaction rate due to the unimolecular process between 2,4-DHMP and THMP are small. (4) Rates of bimolecular reactions of THMP are about five times as large as those of 2,4-DHMP. (5) The values of the rate constants and the activation energy for the bimolecular reactions of THMP of low concentrations differ from those of THMP of high concentrations, indicating the difference in reaction mechanisms. 相似文献
4.
The liquefied product of Salix psammophila wood was separated by thin-layer chromatography (TLC) and column chro-matography, and its structure was identified by nuclear magnetic resonance (NMR) spectra in our study. The separation result indi-cates that the sample of liquefied S. psammophila contained at least two categories of components. The structure of the main compo-nents was guaiacyl C-1, C-2 of the hydroxyphenyl propane, i.e., the aromatic nucleus protons of lignin. Degradation and polycon-densation reactions occurred when the S. psammophila wood was liquefied in phenol. Polycondensation reactions occurred among the depolymerization products from cellulose, the aromatic depolymerization products from lignin and the products of the displace-ment reactions between phenoxide ion and cellulose. 相似文献
5.
H. Matsuda 《Wood Science and Technology》1987,21(1):75-88
Summary Preparation and utilization of esterified woods bearing carboxyl groups are reviewed. The esterified woods are prepared by the addition reactions of wood with dicarboxylic acid anhydrides in the presence or absence of a solvent such as dimethylformamide. The reactions without solvent are industrially advantageous and can give esterified woods with a wide range of monoester contents. The esterified woods can be molded into sheets by hot pressing. By addition reactions of the esterified woods with epoxide, or epoxide and anhydride at high temperatures, epoxide-adducted esterified woods and oligoesterified woods are obtained. These can also be molded by hot pressing. The addition of epoxide to esterified woods results in an improvement in moisture resistance of the molded sheets. When esterified woods are subjected to crosslinking reactions with bisepoxide both at high temperatures and under high pressures, the wood components plasticize to give reddish brown, yellowish brown, or blackish brown crosslinked wood boards whose surfaces are smooth, glossy, and plastic-like. Among the plastic-like crosslinked wood boards, the phthalic anhydride-based board shows the best physical properties. Especially, this board exhibits very high compressive strength and water resistance. 相似文献
6.
Separation of liquefied product of Salix psammophila by column chromatography and structure analysis of its components 总被引：2，自引：1，他引：1
The liquefied product of Salixpsammophila wood was separated by thin-layer chromatography （TLC） and column chromatography, and its structure was identified by nuclear magnetic resonance （NMR） spectra in our study. The separation result indicates that the sample of liquefied S. psammophila contained at least two categories of components. The structure of the main components was guaiacyl C-1, C-2 of the hydroxyphenyl propane, i.e., the aromatic nucleus protons of lignin. Degradation and polycondensation reactions occurred when the S. psammophila wood was liquefied in phenol. Polycondensation reactions occurred among the depolymerization products from cellulose, the aromatic depolymerization products from lignin and the products of the displacement reactions between phenoxide ion and cellulose. 相似文献
7.
Curing kinetics of phenol formaldehyde resin and wood-resin interactions in the presence of wood substrates 总被引：1，自引：0，他引：1
The curing kinetics of resol PF resin and resin–wood interactions in the presence of wood substrates have been studied by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. The activation energy of cure of PF resin generally increases when PF resin is mixed with wood, mainly due to the decrease of the pH values resulting from the presence of wood. However, wood decreases the curing enthalpy of PF resin through diffusion and the change in the phase of the curing system, which suggests that the curing reactions reached a lower final degree of conversion for the mixtures of PF resin with wood than for the PF resin alone. Moreover, DSC curves and the variation of activation energy with conversion indicate that wood accelerates the addition reactions and retards condensation ones during the curing process of PF resin with wood. The study also revealed that almost no chemical reactions occur between PF resin and wood, but the secondary force interactions of hydroxyl groups between PF resin and wood have been detected. These most significant secondary forces can catalyze the self-condensation reactions of PF resin, although their effect is not vital on the curing kinetics of PF resin. 相似文献
8.
Mitsuo Higuchi Shoichi Nohno Mitsuhiro Morita Shin-ichiro Tohmura 《Journal of Wood Science》1999,45(4):306-312
The reaction course of the sodium hydroxidecatalyzed hydroxymethylation of phenol was analyzed by use of high-performance liquid chromatography (HPLC), and the rate constants for the seven reactions taking place consecutively and competitively were evaluated by means of a computer simulation technique. Calibration was done at the quantification of the six phenolic monomers from the peak areas in the HPLC chromatogram, taking the differences in molar ultraviolet absorption intensities of the six compounds into account. The values of the energies of activation for the seven reactions obtained differed greatly from those reported by Eapen and Yeddanapalli. Simulation experiments carried out by use of the newly obtained rate parameters showed that the amounts of phenol left unreacted and 2,4,6-trihydroxymethylphenol in the final reaction product increased as the reaction temperature was increased and the alkali/phenol molar ratio decreased. These phenomena can be attributed to the differences in the energies of activation for the seven reactions and differences in the acid strengths of the six phenolic monomers.Part of this paper was presented at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998 and at the 1998 annual meeting of the Forest Products Society, Merida, Mexico, June 1998 相似文献
9.
木材阻燃剂FRW的阻燃机理 总被引：10，自引：2，他引：10
在综合分析热分析法、锥形量热仪法和FTIR法获得的FRW阻燃机理研究结果并吸收木材阻燃机理研究现有成果的基础上,推导进而提出了木材阻燃剂FRW的阻燃机理。其主要内容是:1)FRW阻燃木材受热时,阻燃剂FRW分解产生不燃性气体和不挥发的酸性熔融物质,具有降低体系温度和氧气浓度及屏蔽热辐射的作用,降低了木材的热解速度;2)FRW的组分硼酸和GUP的酸性分解产物催化木材脱水、降解,以及木材热解产物的缩合、聚合、芳构化等反应,能改变木材的热解途径并使其向着有利于炭化的方向变化,FRW显著的催化成炭作用,使阻燃木材的燃烧放热量大大降低,这是FRW阻燃机理的主要方面;3)硼酸与GUP起阻燃作用的温度和方式不同,并且有相互补充的作用,因而表现出阻燃协同效应。 相似文献
10.
Mohsen Sheikholeslami Antonio Pizzi Ahmad Mirshokraie 《Wood material science & engineering》2018,13(1):1-6
Acid copper chromate fixation reactions on oak (Quercus castaneifolia C. A. Mey) sapwood were characterized by at least two distinguished reaction periods which differ in their kinetic behavior, particularly reaction rate. In this research, chemical rate equation parameters were studied in detail as a function of chromium fixation time. Theoretically, the kinetic data were distinguished between the adsorption and reduction reactions and consequently, the rate parameters were determined for each stage distinctly. The obtained results showed that at the investigated thermal range (25–33°C), almost for every 3°C increase in temperature the reaction duration has decreased 20.4?min for the first reaction period and 78?min for the second reaction period. Besides that, in all sample replications, up to 58.3% of hydrogen ions function at the reduction reactions of the initial period, demonstrating that acidity (H+ ions) has a major effect on reaction rate constant. Accordingly, adsorption reactions of the hexavalent chromium at the starting point follow a pseudo-first-order kinetic reaction. Different to the adsorption reaction the CrVI reduction reaction is exothermic with a measured exothermal energy of 48.2?kJ/mol. 相似文献