In this work,the lamellar structural evolution and microvoids variations of βpolypropylene(β-PP)during the processing of two different stretching methods,sequential biaxial stretching and simultaneous biaxial stretc...In this work,the lamellar structural evolution and microvoids variations of βpolypropylene(β-PP)during the processing of two different stretching methods,sequential biaxial stretching and simultaneous biaxial stretching,were investigated in detail.It was found that different stretching methods led to significantly different lamellae deformation modes,and the microporous membranes obtained from the simultaneous biaxial stretching exhibited better mechanical properties.For the sequential biaxial stretching,abundant coarse fibers originated from the tight accumulation of the lamellae parallel to the longitudinal stretching direction,whereas the lamellae perpendicular to the stretching direction were easily deformed and separated.Those coarse fibers were difficult to be separated to form micropores during the subsequent transverse stretching process,resulting in a poor micropores distribution.However,for the simultaneous biaxial stretching,theβcrystal had the same deformation mode,that is,the lamellae distributed in different directions were all destroyed,forming abundant microvoids and little coarse fibers.展开更多
A biaxial stretching equipment was designed and constructed to enable fundamental studies of the relationship between film processing conditions and structures of oriented film products. With programmable drive motors...A biaxial stretching equipment was designed and constructed to enable fundamental studies of the relationship between film processing conditions and structures of oriented film products. With programmable drive motors and scissorlike mechanism, all stretching modes, including uniaxial stretching with constant and free width, simultaneous and sequential biaxial stretching, can be applied to a square-shaped sheet. Parameters related to film stretching manufacturing, such as temperature, draw ratio and stretching speed can be set independently to meet the requirement of different polymers. The force information during stretching is recorded by two miniature tension sensors in two directions independently, which can monitor the mechanical stimulus and stress response. Using this equipment, experiments are conducted to investigate the influence of stretching parameters on the structure of polypropylene films, which provides an effective method to tailor the processing conditions to obtain the films with desired properties.展开更多
By virtue of the rational interpolation procedure and logarithmic strain, a direct approach is proposed to obtain elastic potentials that exactly match uniaxial data and shear data for elastomers. This approach reduce...By virtue of the rational interpolation procedure and logarithmic strain, a direct approach is proposed to obtain elastic potentials that exactly match uniaxial data and shear data for elastomers. This approach reduces the determination of multi axial elastic potentials to that of two one-dimensional potentials, thus bypassing usual cumbersome procedures of identifying a number of unknown parameters. Predictions of the suggested potential are derived for a general biaxial stretch test and compared with the classical data given by Rivlin and Saunders （Rivlin, R. S. and Saunders, D. W. Large elastic deformation of isotropic materials. VII： experiments on the deformation of rubber. Phill. Trans. Royal Soc. London A, 243, 251-288 （1951））. Good agreement is achieved with these extensive data.展开更多
Expanded polytetrafluoroethylene(ePTFE)is promising in biomedical fields such as covered stents and plastic surgery owing to its excellent biocompatibility and mechanical properties.However,ePTFE material prepared by ...Expanded polytetrafluoroethylene(ePTFE)is promising in biomedical fields such as covered stents and plastic surgery owing to its excellent biocompatibility and mechanical properties.However,ePTFE material prepared by the traditional biaxial stretching process is with thicker middle and thinner sides due to the bowing effect,which poses a major problem in industrial-scale fabrication.To solve this problem,we design an olive-shaped winding roller to provide the middle part of the ePTFE tape with a greater longitudinal stretching amplitude than the two sides,so as to make up for the excessive longitudinal retraction tendency of the middle part when it is transversely stretched.The as-fabricated ePTFE membrane has,as designed,uniform thickness and node-fibril microstructure.In addition,we examine the effects of mass ratio of lubricant to PTFE powder,biaxial stretching ratio and sintering temperature on the performance of the resultant ePTFE membranes.Particularly,the relation between the internal microstructure of the ePTFE membrane and its mechanical properties is revealed.Besides stable mechanical properties,the sintered ePTFE membrane exhibits satisfactory biological properties.We make a series of biological assessments including in vitro hemolysis,coagulation,bacterial reverse mutation and in vivo thrombosis,intracutaneous reactivity test,pyrogen test and subchronic systemic toxicity test;all of the results meet the relevant international standards.The muscle implantation of the sintered ePTFE membrane into rabbits indicates acceptable inflammatory reactions of our sintered ePTFE membrane fabricated on industrial scale.Such a medical-grade raw material with the unique physical form and condensed-state microstructure is expected to afford an inert biomaterial potentially for stent-graft membrane.展开更多
基金supported by the National Natural Science Foundation of China(No.51721091).
文摘In this work,the lamellar structural evolution and microvoids variations of βpolypropylene(β-PP)during the processing of two different stretching methods,sequential biaxial stretching and simultaneous biaxial stretching,were investigated in detail.It was found that different stretching methods led to significantly different lamellae deformation modes,and the microporous membranes obtained from the simultaneous biaxial stretching exhibited better mechanical properties.For the sequential biaxial stretching,abundant coarse fibers originated from the tight accumulation of the lamellae parallel to the longitudinal stretching direction,whereas the lamellae perpendicular to the stretching direction were easily deformed and separated.Those coarse fibers were difficult to be separated to form micropores during the subsequent transverse stretching process,resulting in a poor micropores distribution.However,for the simultaneous biaxial stretching,theβcrystal had the same deformation mode,that is,the lamellae distributed in different directions were all destroyed,forming abundant microvoids and little coarse fibers.
基金financially supported by the National Natural Science Foundation of China(Nos.51227801,51325301)
文摘A biaxial stretching equipment was designed and constructed to enable fundamental studies of the relationship between film processing conditions and structures of oriented film products. With programmable drive motors and scissorlike mechanism, all stretching modes, including uniaxial stretching with constant and free width, simultaneous and sequential biaxial stretching, can be applied to a square-shaped sheet. Parameters related to film stretching manufacturing, such as temperature, draw ratio and stretching speed can be set independently to meet the requirement of different polymers. The force information during stretching is recorded by two miniature tension sensors in two directions independently, which can monitor the mechanical stimulus and stress response. Using this equipment, experiments are conducted to investigate the influence of stretching parameters on the structure of polypropylene films, which provides an effective method to tailor the processing conditions to obtain the films with desired properties.
基金Project supported by the National Natural Science Foundation of China(No.11372172)the 211-Plan of the Education Committee of China(No.A.15-B002-09-032)the Research Innovation Fund of Shanghai University(No.A.10-0401-12-001)
文摘By virtue of the rational interpolation procedure and logarithmic strain, a direct approach is proposed to obtain elastic potentials that exactly match uniaxial data and shear data for elastomers. This approach reduces the determination of multi axial elastic potentials to that of two one-dimensional potentials, thus bypassing usual cumbersome procedures of identifying a number of unknown parameters. Predictions of the suggested potential are derived for a general biaxial stretch test and compared with the classical data given by Rivlin and Saunders （Rivlin, R. S. and Saunders, D. W. Large elastic deformation of isotropic materials. VII： experiments on the deformation of rubber. Phill. Trans. Royal Soc. London A, 243, 251-288 （1951））. Good agreement is achieved with these extensive data.
基金supports from National Natural Science Foundation of China(grant no.52130302)National Key R&D Program of China(grant no.2016YFC1100300)。
文摘Expanded polytetrafluoroethylene(ePTFE)is promising in biomedical fields such as covered stents and plastic surgery owing to its excellent biocompatibility and mechanical properties.However,ePTFE material prepared by the traditional biaxial stretching process is with thicker middle and thinner sides due to the bowing effect,which poses a major problem in industrial-scale fabrication.To solve this problem,we design an olive-shaped winding roller to provide the middle part of the ePTFE tape with a greater longitudinal stretching amplitude than the two sides,so as to make up for the excessive longitudinal retraction tendency of the middle part when it is transversely stretched.The as-fabricated ePTFE membrane has,as designed,uniform thickness and node-fibril microstructure.In addition,we examine the effects of mass ratio of lubricant to PTFE powder,biaxial stretching ratio and sintering temperature on the performance of the resultant ePTFE membranes.Particularly,the relation between the internal microstructure of the ePTFE membrane and its mechanical properties is revealed.Besides stable mechanical properties,the sintered ePTFE membrane exhibits satisfactory biological properties.We make a series of biological assessments including in vitro hemolysis,coagulation,bacterial reverse mutation and in vivo thrombosis,intracutaneous reactivity test,pyrogen test and subchronic systemic toxicity test;all of the results meet the relevant international standards.The muscle implantation of the sintered ePTFE membrane into rabbits indicates acceptable inflammatory reactions of our sintered ePTFE membrane fabricated on industrial scale.Such a medical-grade raw material with the unique physical form and condensed-state microstructure is expected to afford an inert biomaterial potentially for stent-graft membrane.
