Tensile Behavior Characterization Of Tube Fiber And Its Composite Films In Coir Fiber

Coir fiber is rich in resources,but the research on the structure and properties of coir fiber and its tube fiber is not very perfect,especially the lack of effective mechanical models to describe the mechanical properties of coir fiber,and its application is not very reasonable.In this paper,the coir fiber and its tube fiber as the research objects,on the basis of clarifying its complex structure,its mechanical properties,fracture mechanism and the relationship between fiber structure and mechanical properties were studied;by the establishment of a mechanical model for the coir fiber and its tube fiber to analyze and to characterize the mechanical behavior of coir fiber.The single coir tube fiber was taken as reinforcement to prepare the all cellulose composite material and the performance test was carried out to improve the theoretical research of coir fiber and expand the application range of coir fiber.First,the length,fineness and chemical composition of coir fiber and its tube fiber were measured and analyzed.The results showed that the length of the coir fiber is 15~289mm,the linear density is 8.23~75.60tex,the diameter is 80.8~340.7?m,and the fiber length-quantity distribution is lognormal distribution.The relationship between linear density and length of fiber is linear,and the relationship between the diameter and the length is two times.The length of the coir tube fiber is 81.04~1386.1?m,the diameter is 4.41~20.37?m,and the fiber length-quantity distribution is also lognormal distribution.The contents of cellulose,hemicellulose and lignin in coir fiber were 35.5%,24.1%and 40.4%,so coir fiber contained more hemicelluloses,and lignin content exceeded cellulose content.The contents of cellulose,hemicellulose and lignin in the tube fiber were 77.4%,5.7%and 16.9%,and the cellulose content of tube fiber increased significantly.Then,assume coir fiber as a plurality of unit-cell(n)tube fiber piled up,and the bonding between the tube fiber is regarded as the outer matrix of tube fiber,that is,the tube fiber is an independent unit.The coir fiber can be regarded as the mechanical behavior of a tube fiber.the coir fiber and its tube fiber were tested for tensile strength and the cross section was observed by SEM.The deformation mechanism of coir fiber was discussed.It is concluded that the tensile curve of coir fiber is composed of three parts:linear elastic area,platform area and reinforcing area.There is no obvious linear relationship between the three stage strain interval and the fracture strain of fiber.The tensile curve of tube fiber consists of two parts of the line elastic zone and the platform area,and the slope of the platform area is more inclined.The average values of fracture strength,fracture strain,initial modulus and fracture specific work of coir fiber are93.02MPa,0.28,1.56GPa and 17.34MPa,respectively.The average values of fracture strength,fracture strain,initial modulus and fracture specific work of tube fiber are 157.48MPa?0.25?1.62GPa and 20.62 MPa,and there is no significant linear relationship between the four parameters of both coir fiber and tube fiber.The deformation of coir fiber is mainly caused by the decrease of the spiral angle caused by the torsion and the smaller diameter of the tube fiber.The elongation is caused by the elongation of the intercellular matrix between the spiral crystal belt,the elongation of helix angle changes,the crystal belt is separated from the matrix and torsional contraction of crystal belt and the elongation of matrix between tube fibers.These three parts exist at the same time.The second and third parts play a major role.The final tube fiber fracture is the spiral belt can not afford greater torsion from outside to inside the results of the tear.There are two main types of tube fiber fracture,one is the deformation of the spiral fracture,and to the fiber cross-section of the fiber Center shrinkage;the other is the overall fracture of the wall of the tube fiber.Thus,the coir fiber is assumed to be a tube fiber,a multilevel structure model of coir fiber was established.Based on this,a four-element mechanical model for coir fiber structure was established,fitting with the measured tensile curve.Meanwhile,compared with the modified Vangheluwe model shows:the fitting correlation between the four-element model and the measured typical tensile curve of coir fiber is greater than 0.997,which is slightly lower than that of the modified Vangheluwe model with the correlation R~2=0.999.However,in the one-to-one correspondence of structural viscoelastic properties and in the initial linear section,the fitting yield point and the post yield platform area of the tensile behavior,the four-element model is superior,and can estimate the modulus value and viscosity coefficient of each part.While the fitting correlation between the four-element model and the measured typical tensile curve of tube fiber is greater than 0.999,which is better than that of coir fiber 0.997.The fitting curve of four-element model and the actual tensile curve in two linear or nearly linear regions in good agreement.The estimated value of the modulus and viscosity coefficient of each part is closer to the measured value of the tube fiber,and the four-element structure model is more accurate for the characterization of the tube fiber.Finally,the single coir tube fibers were successfully separated by alkali oxidation method and the coir tube fiber reinforced cellulose composite films with different tube fiber contents were obtained.The morphology and properties of the tube fibers and composite films were tested,obtained:coir tube fibers can be combined with the cellulose matrix through hydrogen bonds,with the increase of coir tube fiber,the content of the composite membrane crystallization degree increased,mechanical properties improved,and when the coir and tube fiber content is too large,the performance of the composite films become worse because of the agglomeration of the tube fiber.When the content of coir tube fiber is 20%,the performance of the composite film is the best,the breaking strength and initial modulus of the composite film reach the maximum value of 54.28MPa and 2.48GPa,respectively,compared with the pure cellulose film increased by81.17%and 113.79%.And the toughness of the composite film has also been effectively improved,but the excellent elongation properties of coir tube fibers have not been fully utilized.