| Wheat straw was an important crop in the world,to relieve the increasing scarcity of wood resources,while solving the waste of resources and environmental pollution problems caused by burning wheat straw,research on the properties and components of wheat straw wasextremely significant.In this paper,properties of wheat straw of six varieties(Jimai22、Jiamai66 and Taian23 from Heze Shandong、Sumai188 and Zhengmai9023 from Nanjing Jiangsu、Aboafu from Bijie Guizhou)were studied.The difference of physical properties、tensile properties、main chemical functional groups through FT-IR、thermal properties including TG and DSC、microstructure of outside surface and internal surface of straws and wheat leaves through SEM and the determination of the main components in strawsand wheat leaves throughVan Soest were compared.And changes of these properties above of wheat straw with different internodes、temperatures and physical and chemical treatments were explored.The main conclusions can be drawn as follows:(1)Moisture content and 24h water absorption of wheat straw from the same areas was proportional and had a small difference,the moisture content and 24h water absorption from high to low were Taian23、Jimai66、Jimai22.The difference of moisture content of wheat straw from different areas was small and they had a certain degree of saturation,zhengmai9023 had the lowest moisture content,5.71%,but moisture content of the other three areas was not very different,from high to low as follows:Sumai188(6.24%)、Aboafu(6.072%)、Taian23(6.02%).Difference of 24hwater absorption ofwheat straw from different areas was obvious,from high to low as follows:Taian23、Sumai188、Zhengmai9023、Aboafu.The moisture absorption from the same areaswas not very different,while different areas not,the saturation of moisture of wheat straw was reached after 8 hours.Contact angle of untreated wheat straw was greater than 90 degrees,contact angle of 6 varieties decreased after acid,alkali,hydrothermal and microwave treated in different degree,Effect of different treatments on wax layer of Jimai 22,Sumai 188 and Aboafu wasmore obvious,But it was not obvious for Tai’an23,effect of 2%oxalic acid and 2%NaOH treatment were both obvious,but microwave treatment was not.(2)The maximum tension of wheat straw from the same areas were increased when internodes were increased,but tensile strength and elastic modulus were decreased when internodes were increased.The trend of maximum tension,tensile strength and elastic modulus of Taian23(Heze Shandong),Sumail88(Nanjing Jiangsu),Zhengmai9023(Yancheng Jiangsu)were similar to wheat straw from the same areas.Tensile strength and elastic modulus of Aboafu(Bijie Guizhou)were higher than the other three areas,and the second internodes were higher than the third and fourth.Wheat straw from the same areas after treatments at different temperatures(80 ℃,110℃,140℃),the tensile strength was maximum when the temperature was 80℃.The change of the tensile strength of wheat straw from different areas was not obvious after treatments at different temperatures.All in all,temperatures had not an obvious effect on the tensile strength of wheat straw.The different treatments(hydrothermal,microwave treatment,2%oxalic acid and 2%NaOH treatment)had an obvious effect on the tensile properties of the same and different areas of wheat straw.And the improvement of tensile properties on wheat straw with 2%NaOH treated was the obviousest.The 2%oxalic acid treatment was the worsest.Compared to the untreated,the tensile properties treated by hydrothermal or microwave treatment were not changed much.(3)The pyrolysis process of wheat straw was divided into four stages:drying volatile stage in 30℃-100℃;heating stage in 100℃～250℃;thermal decomposition stage in 250℃～400℃;The remaining material heated stage over 400℃.TG curves of different varieties had the same trends.But their residual masses ratio were different.The DSC curves of different varieties were different.Jimai 22 reached the end-point temperature earlier than the others of the same areas,and Aboafu reached earlier of the different areas.Thermal properties of wheat straw after different treatments were different,the end-point temperature was the minimum after 2%NaOH treated.(4)Absorption peaks of different inste:modes from the same and different areas were quite different,absorption peaks including 2230～2400cm-1 and 1640～1735cm-1 had obvious difference.The absorption peaks intensity of lignin and hemicellulose of wheat straw of different varieties were different,the absorption peaksof the second internodes had strong,but the third and fourth had weakened or even disappeared.Wheat straw treated with different temperatures(80℃,110℃,140℃),which the absorption peak intensity at 2230～2400cm-1 and 1640～1735cm-1 increased slightly.It shows that the temperature rising promoted stretching vibration of C-O,lignin and hemicellulose content was increasedrelatively,the cellulose content was reduced relatively and mechanical properties was lowerrelatively.After different treated(2%oxalic acid treatment,2%NaOH treatment,hydrothermal treatment,microwave treatment),more absorption peaks of FT-IR disappeared,increased or decreased.Effects of acid and alkali treatment were more obvious then microwave and hydrothermal.2%NaOH treatment made absorption peak at 1735 cm-1 disappeared,indicating that 2%NaOH treatment dissolved the lignin and hemicellulose so that the percentage of celluloseincreased,mechanical properties such as tensile strength also increased.2%oxalic acid treatment made absorption peak at 1735 cm-1 increased slightly,indicating thatoxalic acid treatment increased the hemicellulose and lignin so that the percentage of cellulose decreased relatively,mechanical properties alsodecreased compared with untreated.Effect of microwave and hydrothermal treatment of lignin and hemicelluloses was not obvious.(5)Different treatments affected microstructure of both outside surface and internal surfaceof wheat straw.2%oxalic acid treatment,microwave treatment and hydrothermal treatment had little effect and their influences descending were as follows:2%oxalic acid treatment,microwave treatment,hydrothermal treatment.2%NaOH treatment had significant effect.NaOH dissolved part of hemicellulose,lignin and lipids,wax and ash in the surface,so that more fiber bundles exposed,and internal fiber structure was clearly visible.Compared with the outside surface of wheat straw,there were more waxy and crystal silicon cells in the outside surface of the wheat leaves.Its main component was SiO2,which affected the glued performance of wheat leaves and plastic or resin.There was a layer of smooth parenchyma in the internal surface,tiny fiber structure regularly distributed and a vertical arrangement was visible.(6)After different treatments of wheat straw from the same and different areas,contents of the cellulose,hemicellulose,lignin and ash had changed a lot.Contents of cellulose and hemicellulose increased both after 2%oxalic acid,hydrothermal treatment and microwave treatment,but after 2%NaOH treatment,contents of cellulose increased significantly greater than the other three treatments,and the hemicellulose and ash content decreased.It was showed that NaOH treatment could improve the tensile properties and waterproof properties of wheat straw,and remove part of wax layer inthe surface,which was conducive to the infiltration of adhesive,therefore,wheat straw after 2%NaOH treatmenthad the best properties.Contents of cellulose,hemicellulose,lignin and ash of different varieties of wheat straw and wheat leaves were very different,cellulose and lignin contents in the wheat straw were higher than which in wheat leaves,while hemicellulose and ash contents in wheat leaves were higher than which in wheat straw.It is predicated that compared with wheat leaves,wheat straw was hard,and had better mechanical performance,waterproof properties and bonding properties.Therefore,trying to get rid of wheat leaves,retaining only the wheat straw when manufacturing wheat straw board or polymerization with plastic and resin in the industry would be more conducive to processing and get better mechanical properties and waterproof properties when compoundedwith other materials. |
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