| Using agricultural and forestry biomass to produce bio-energy,chemicals and biomaterials is a crucial way for tackling energy crisis and relieving environmental pollution pressure.In order to utilize the wheat straw as high-value materials,the methods including fractional isolation,structural analysis,and deep utilization of cellulose and lignin separated from wheat straw were carried out.The obtained cellulose was used for producing cellulose nanofibrils(cnf)to prepare nanocomposite through chemical bonds and electrostatic adsorption.The obtained lignin was used for producing lignin-based polyurethane.In this paper,the high efficiency utilization system was gradually formed by separation and coproduction of component of forestry and agricultural residues.Firstly,the chemical components of wheat straw were analyzed,and the data showed that wheat straw has more holocellulose,ash content and less lignin than other raw materials used in pulping industry.Based on this,Fourier Transform Infrared Spectroscopy(FT-IR),1H NMR,13 C NMR,2D–HSQC NMR,X-Ray Diffraction(XRD)and Thermal Gravimetric Analysis(TGA)were employed to characterize the chemical structures and physical properties of the cellulose,hemicellulose and lignin in wheat straw.The results showed that the crystallinity of cellulose was 51.9%,and the main thermal degradation temperature of cellulose in wheat straw ranged from 200 to 400 °C.The main chemical structure of hemicellulose isolated from wheat straw was L–arabinose–(4–O–methyl–D–glucuronic acid)–D–xylan,and the thermal stability of hemicellulose was weaker than cellulose and lignin.The mass loss temperature of hemicellulose was 258.6 °C.The lignin in wheat straw is composed of guaiacyl(G),syringyl(S),and p–hydroxyphenyl(H)units.And aliphatic hydroxyl structure was the main hydroxyl structure in lignin of wheat straw,which was 3.49 mmol/g.The content of phenolic hydroxyl structure was in a relative proportion of 1.01 mmol/g and the lowest carboxyl structure content(0.88 mmol/g).The main thermal degradation temperature phase of lignin was in the range from 200 to 500 °C,and the mass loss temperature was at 352.8 °C.The necessity of the pretreatment on the subsequent alkali cooking performance was evaluated.It was found that NaOH combined with Na2 S can be used for the pretreatment of wheat straw before alkali cooking.This mothed can prevent holocellulose from being excessively hydrolysis,and enhance the dissolution ratio of lignin.Response surface method was employed to design and optimize the process parameters during alkali cooking.The results showed that kappa number decreased sharply with increasing the NaOH content.Meanwhile,the yield of screened pulp and the viscosity of the wheat–straw pulp were decreased,while the brightness increased obviously.The kappa number decreased after alkali cooking with higher sulfidity,and the yield of screened pulp and the viscosity of the wheat-straw pulp slowly declined with significantly higher brightness.Prolonged heating time caused higher viscosity and brightness of the wheat–straw pulp,while the kappa number and the yield of the wheat-straw pulp.In our experiment,the Design–Expert software was employed to optimize processing of alkali cooking.The results showed a better results in prediction and optimization.By optimizing the technological parameters,the optimum condition to obtain higher kappa value and fined pulp yields were sodium hydroxide dosage of 9.94 %,sulfidity of 13.61 %,and heating time of 140 min and heating temperature of 155 °C.And the actual result of fined pulp yields and kappa value were 50.45 % and 17.2,respectively.The optimum condition to obtain low kappa value and better viscosity of pulp were sodium hydroxide dosage of 10.27 %,sulfidity of 18 %,and heating time of 100 min and heating temperature of 155 °C.And the actual result of fined pulp yields and kappa value were 43.78 % and 11.6,respectivelyThe cellulose nanofibrils(cnf)and chitin nanowhisker(cnw)were separated by TEMPO-oxidation and acid hydrolysis with high pressure homogenization.Zeta potential indicated that the differences in the suspended mechanism in cnf and cnw dispersions.Fourier Transform Infrared Spectroscopy(FTIR),X–ray diffraction(XRD)revealed that the chemical and crystal structure had changed during chemical separation process.Meanwhile,a series of hybrid cnf/cnw films was prepared via casting and evaporation.The films had better mechanical properties because of multivalent electrical interaction between cnf and cnw.cnw content higher than 50% negatively affected the mechanical properties of hybrid films.Second derivative FTIR spectra data results showd that the formation of hydrogen–bonded was crucial reson for improving the mechanical properties of the hybrid films.To enhance the mechanical strength for individual pulp fibers,we deposited nanoscale multilayer film consisting of chitin nanowhisker(cnw)and anionic cellulose nanofibrils(cnf)on pulp fibers using the layer–by–layer(Lb L)technique.The deposition behavior of cnw / cnf on surface of pulp was analyzed.And the buildup of the multilayer film was investigated using X–ray photoelectron spectroscopy(XPS).The results confirmed that LbL deposition process was through electrostatic interaction,coordination and hydrogen–bond interaction between pulp and nanowhiskers.Assembled pulp fibers were then applied to prepare paper sheets.Physical and mechanical test were conducted to evaluate the mechanical enhancement of paper sheets as a function of the number of layers deposited on fibers.The results indicated that the deposition behavior of cnw / cnf on thepulp surface is an effective way to enhance the mechanical quality to pulp and the paper sheets made from these pulp fibers.The behavior of lignin was investigated during the alkali cooking process with different alkali doses,and the structural characteristics were illustrated by spectroscopic analyses.Gel permutation chromatography(GPC)and nuclear magnetic resonance(NMR)indicated that the lignin were typical grass structures,generally with S and G units and small amounts of H units.The main substructures present were ?–O–4 aryl ether linkages with some ?–? and ?–5 linkages.Alkali treatment conditions had evident effects on the chemical structures and properties of lignin.Moreover,NMR indicated that alkali cooking caused lignin to depolymerize more easily and led to aggregation of lignin.Higher content of phenolic hydroxyl groups in the S3–lignin was favor for applying lignin to prepare lignin–based polyurethane.Research indicated that lignin has a good compatibility with polyurethane at 0.5 wt.% adding amount.Under this condition,the mechanical property of lignin–based polyurethane was enchanced.The oil–absorption capability of lignin–based polyurethane was also investigated.The results showd that lignin–based polyurethane has a good adsorption capacity with polyurethane at 0.5 ~ 1.0 wt.% adding amount.And the maximum absorption of benzene,dimethyl benzene,and ethyl acetate were 50.2 %,44.0 %,41.5 %.TGA analysis showed that the thermal stability of lignin–based polyurethane was improved by incorporation with lignin. |
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