Abstract:
China has abundant resource of corn stalk, but the stalk utilization has low added-value and outstanding problems of combustion and idleness. Corn stalk has different components whose chemical constituents vary, among which corn stalk rind, as one of the most constituents, consists of rich lignin and cellulose similar to wood properties, has high mechanical strength and can be used as raw material of stalk artificial board and paper. Therefore, efficient application based on corn stalk's different constituent is significant for increasing farmers' income, relieving energy crisis and protecting ecological environment. However, the recent researches related to mechanical property mostly start with crop physiological characteristics, stalk mechanical model, stalk mechanical property index and equipment performance parameters, but make little analysis of internal factors of corn stalk rind like microstructure and fiber morphology. Taking full consideration of the impact of variety, growing environment and various conditions on corn stalk constituent, this paper has adopted the corn stalk rind of the same variety under the same planting condition to analyze fiber morphology characteristic distribution rule among different sampling heights and the changes of fiber morphology parameters, the tensile strengths of different sampling heights were tested, the correlation between tensile property and fiber morphology parameters of corn stalk rind was analyzed, and the internal mechanism of crop stalk mechanical property was researched from the microscopic view to offer theoretical basis for physicochemical property research and deep processing and utilization of corn stalk rind. Nitric acid technique was adopted to obtain fiber and morphology parameters of corn stalk rind at different heights, meanwhile radial and axial tensile strength were tested, and grey correlation method was applied to analyze the correlation between fiber morphology parameters (like fiber length-width ratio and wall-cavity ratio) and tensile property of corn stalk rind. Through the experiments, it was confirmed that there was significant (P<0.01) difference between fiber morphology parameters and tensile property of corn stalk rind at different sampling heights; with the increase of sampling heights, the fiber length-width ratio of corn stalk rind firstly increased slightly and then reduced significantly, and the wall-cavity ratio of corn stalk rind fiber reduced gradually; the average axial tensile strength of corn stalk rind was significantly (P<0.01) larger than the average radial tensile strength; the maximum radial tensile strength of corn stalk rind occurred at the root and the mean was 2.44 MPa, and the maximum axial tensile strength of corn stalk rind occurred at the middle and lower part and the mean was 94.47 MPa; with the increase of sampling heights, radial tensile strength reduced gradually while axial tensile strength firstly increased and then reduced gradually. There was correlation between tensile property and fiber morphology of corn stalk rind, between radial tensile strength and fiber wall-cavity ratio (r=0.9972), between axial tensile strength and length-width ratio (r=0.8885) and wall-cavity ratio (r=0.6648) of the fiber. Corn stalk rind tensile property was in correlation with fiber morphology parameters like fiber length-width ratio and wall-cavity ratio, of which the radial tensile strength was related to fiber wall-cavity ratio while the axial tensile strength was related to both fiber length-width ratio and fiber wall-cavity ratio. The research findings provide the theoretical basis for the design of corn stalk processing equipment and promote the utilization of corn stalk rind as material.