The Basic Study On Resinification Of Walnut Shell

With the shortage of petrescence resource increasingly, the chemical utilizations of renewable woody biomass resources were more and more important in the world. As an abundant resource of forestry fruit wastes, walnut shell is burn at present. But this way of utilizations of walnut shell is both low worth and polluting environment. Base on utilization of walnut shell, without the second pollution, the resinification of walnut shell was studied. As a material of resinification, the walnut shell of Juglans Sigillata Dode was studied as following characteristics: chemical components, microstructure, physical and chemical properties. In order to know more characteristics of walnut shell, the properties of main components of walnut shell were studied, including lignin, cellulose and hemicellulose of walnut shell. Base on the foundation of material characteristics of walnut shell, the liquefaction, the preceding way of resinification, of walnut shell and its main component (including lignin, cellulose and hemicellulose) was studied respectively. The study of continuous liquefaction process from 5min to 120 min was emphasized firstly, with phenol/walnut shell (or its main components) weight ratio 3/1, liquefaction temperature 120℃ and 3% (phenol weight percent) sulfuric acid (98%). In order to study the variation of characteristics of liquefaction resultant system at different liquefaction time, the physical and chemical methods of determination, modern instrument analysis, such as FTIR, ¹H-NMR, ¹3C-NMR, GPC and DSC, were used to determine the residue rate, free phenol, brominable substance, chemical group, chemical structure, molecular weight and its distribution, and so on. Depend on the above studies, the possible mechanism of liquefaction of walnut shell lignin, cellulose and hemicellulose and the possible effects of their resultant on the next resinification were analyzed. The role of phenol in liquefaction under acid condition was analyzed, too. The model of liquefaction process of walnut shell was also established firstly. At last, resinifications of walnut shell lignin and walnut shell were studied. As results, the following could be obtained:(1) Chemical component characteristics of walnut shell: Lignin is the most main component with 56.65%, which includes 53.81% acid-insoluble lignin and 2.84% acid-soluble lignin. The content of Cellulose and pentosan is 22.06% and 19.90%, respectively. The content of cold water solubility, hot water solubility, one percent sodium hydroxide solubility is 8.62%, 11.04% and 37.65%, respectively. The main element is C, H, O, N, S, and the minim element is Ca, Mg, Fe, Si, P, and so on. The content of sugar is 11.99%.(2) Microstructure of walnut shell: The microstructure of walnut shell is very different to microstructure of wood. Without fiber cell, without fiber of bundle type, with stone cell of high lignification are the main characteristics of microstructure of walnut shell.(3) The basic characteristics of walnut shell lignin: The content of C, H and O element in walnut shell lignin is 67.15%, 5.73% and 27.12%, respectively. The content of methoxyl group of the lignin is 18.19%. The empirical formulas of C₉ is C9H_9.22O_1.99(OCH₃)_1.05 based on itsmethoxyl group content and elemental composition, and the relative molecular weight of C9 structure unit is 181.61. The lignin of walnut shell belongs to GS-type (Guaiacyl-Syringyl type) lignin, which includes 80.68% G-type lignin. The content of OHPh and OHaijPh is 32.21% and 67.79% in the lignin, respectively. In the structure of lignin, there are many structures of p-O-4, P-5 and P-p. The molecular weight of weight-average and number-average is 22521 and 8758, respectively. The molecular weight extent of dispersing is 2.57.(4) The basic characteristics of walnut shell cellulose: The characteristics of FTIR spectra of walnut shell cellulose are very similar to FTIR spectra of beech cellulose. According to the FTIR spectra, The relative crystal extent of walnut shell cellulose is 94.00%, lower than beech cellulose.(5) The basic characteristics of walnut shell hemicellulose: There is a lot of xylan in the hemicellulose. The main chain of hemicellulose is essentially a (1—>4) linked P-D-xylan with 4-O-methyl-a-D-glucopyranosyluronic acid attached at position C2.(6) The physical and chemical properties of walnut shell: The density of walnut shell is 1.07g/cm3. The value of pH is less than 6, representing weak acid. The acid and alkaline buffering capacity of walnut shell is 4.92mL and 10.68mL, respectively. The content of brominable substance of walnut shell is 7.00%.(7) Walnut shell, the natural lignified material enriched lignin, could be liquefied quickly. When the liquefaction time is 5min, the residue content of walnut shell and its lignin is 25.58% and 13.27%, but the residue content of cellulose is 72.52%. That shows cellulose could be more difficult to liquefy than walnut shell and its lignin. The rate of liquefaction of walnut shell is compositive of the rate of liquefaction of its lignin, cellulose and hemicellulose, which eould be described to the multiplication of weight percent of main component and their liquefaction rate. The relationship between liquefaction rate of walnut shell (including the main component lignin, cellulose) and liquefaction time is exponential obviously. That means the liquefaction of walnut shell and its main component (lignin and cellulose) submits to the bimolecular type second-order reaction. With the extending of the liquefaction time, the residue content of walnut shell and its lignin, cellulose will become lower and lower, but the trend of reduction is more and more slowly, especially after lOmin. And there is some residue in the liquefaction resultant system at 120min.(8) When the liquefaction time is 5min, is reduced quickly in the liquefaction resultant system of walnut shell and its lignin, cellulose. Among these, the reduction of the content of free phenol and brominable substance in the liquefaction resultant of the lignin is obvious. With the extending of the liquefaction time, the content of free phenol and brominable substance will be reduced slowly, but the content of brominable substance is little higher than that of free phenol at the same liquefaction time.(9) From the FTIR spectra, the characteristics of the residue of lignin liquefaction are similar to the lignin, but there are some reaction in the aryl of lignin reacted with phenol under acid condition. The characteristics of FTIR spectra of the resultant of lignin liquefaction aredifferent to those of lignin. And from the FTIR spectra of the resultant, the reaction has been happened between the resultant and phenol. The characteristics of FTIR spectra of the residue of cellulose liquefaction are very similar to those of cellulose before 60min. But the characteristics of FTIR spectra of the residue of cellulose liquefaction have been changed evidently. That shows cellulose have been decomposed and the residue may be changed to another matter. The characteristics of FTIR spectra of the resultant of cellulose liquefaction are different to those of cellulose, too. And the reaction has been happened between the resultant of liquefaction of cellulose and phenol. From the FTIR spectra, the resultants of liquefaction of hemicellulose are the translated matters which may be the phenolated ones bonded with phenol. From the FTIR spectra of the resultants of liquefaction of walnut shell, there are some new chemical groups in the residue, which are the phenolated ones bonded with phenol. Further more, the resultants of liquefaction of walnut shell are the matters which the low molecular weight matters react with phenol.(10) From the results of NMR spectra of walnut shell lignin: The resultants of liquefaction are mainly low molecular weight matters which formed by decomposer of P-O-4, p-1, P-5 and P"P bond structure of lignin at 5min. Further more, these decompositions are happened at the side chains of benzene-propane units at 5min. But at 60 min of liquefaction, the resultants may be the reactants of the former low molecular weight matters react with phenol, which react at the side chains of benzene ring. The resultants of liquefaction of lignin are very complicated.(11) From the results of NMR spectra of walnut shell cellulose: When the liquefaction time is 5min and 60min, the chains of cellulose are decomposed during liquefaction. But there are some glucose units in the resultant. Though the decomposition of cellulose is very strong before 5min, there are many matters with glucose units in the resultant. And these matters could react with phenol. Contrarily, there are not matters with glucose units in the resultant of liquefaction of 60min. And these matters will be steady and coherent. The resultants of liquefaction of cellulose are very complicated, too.(12) From the results of NMR spectra of walnut shell hemicellulose: The xylan in the hemicellulose is decomposed both in 5min and in 60min. The decomposition could be changed into furfural. But these mesial matters could react with phenol and be changed into more complicated ones. In addition, there is some alkyl hydrocarbon in the resultants.(13) From the results of GPC spectra of resultants of walnut shell and its main components (lignin and cellulose): The molecular weight of resultants of walnut shell and its main components could reduced rapidly when they are liquefied in phenol under acid condition. When the liquefaction time is 5min, the molecular weight of resultants of walnut shell and its main components could reduce rapidly to about 1000. But with the extending of the liquefaction time, the molecular weight and its distribution are only changed slightly, and the molecular weight of resultant will tend to uniformity.(14) From the results of DSC spectra of residue of walnut shell cellulose: In the short liquefaction time, such as 5min, the maximal peak value of melt endothermal peak of DSCspectra reduces rapidly. That means the crystal area of cellulose could be broke quickly in liquefaction, and the crystal extent is reduced. But with the extending of the liquefaction time, the maximal peak value of melt endothermal peak of DSC spectra changes slightly.(15) From the analysis of mechanism of liquefaction of walnut shell and the model of liquefaction process: Phenol, as a reagent of liquefaction, has some functions of dissolution, decomposition, reaction (including oxidation, sulfonic reaction, resinification reacted between phenol and the resultants), and linkage of further resinification under acid condition. So, the functions of phenol under acid condition could be considered as "active-passive sword", that is on the one hand, phenol has functions of decomposition and liquefaction, but on the other hand, it has consumption of active group (including in phenol and in the resultant). The process of liquefaction of walnut shell and its main components is very complicated. Because there is not only decomposition of biomass, resinification of the mesial resultant of liquefaction reacted with phenol, but also the self-condensed reaction of the mesial resultant, the self-oxidation of phenol. So the process of liquefaction is one of decomposition and condensation, which are the adverse process of reaction. In the prophase of liquefaction, the decomposition is dominant, but the condensation will be dominant in the anaphase of liquefaction. In fact, the process of liquefaction of walnut shell and its main components includes decomposition and resinification.(16) The ability of resinification of walnut shell lignin reacted with formaldehyde under alkaline condition is very good. The ability of resinification of walnut shell lignin reacted with phenol under alkaline or acid condition is very good, too.(17) It is feasible that the resinifieation of resultants (unfiltrated) of liquefaction walnut shell in phenol could go along well to produce wood adhesive, which reacted with formaldehyde. When the rate of walnut shell replacing to phenol is 25%, the walnut shell-phenol-formaldehyde resin adhesive could make requirements of the plywood for concrete form manufacture. And the properties of the plywood for concrete bonded with the walnut shell-phenol-formaldehyde resin adhesive could be comparative to that bonded with phenolic formaldehyde resin adhesive.