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
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 multiaxial 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
It is a daunting task to develop a promising strategy at an industrial scale for simultaneously ameliorating ductility and gas barrier performance of poly(lactic acid)(PLA)films in the application of green packaging.I...It is a daunting task to develop a promising strategy at an industrial scale for simultaneously ameliorating ductility and gas barrier performance of poly(lactic acid)(PLA)films in the application of green packaging.In this work,biaxial stretching and constrained annealing were employed to prepare transparent PLA films with superior ductility and barrier properties.The oriented nano-sized crystals induced by biaxial stretching were developed into regularαform during constrained annealing,which could not only serve as“nano-barrier wall”to impede the diffusion and dissolution of gas molecules,but also strengthen amorphous chain entanglement network as physical crosslink to enhance ductility.As a result,the as-prepared PLA films exhibited an outstanding comprehensive performance with a low oxygen and water vapor permeability coefficient of 0.733×10^(-14) cm^(3)·cm·cm^(-2)·s^(-1)·Pa^(-1) and 3.82×10^(-14) g·cm·cm^(-2)·s^(-1)·Pa^(-1),respectively,outstanding ductility with elongation at break of 66.0%,high yield strength of 84.2 MPa,and good transparency of more than 80%at 550 nm.The new insight in the relationship between microscopic amorphous and crystalline structure and macroscopic performance is conducive to alleviating the intrinsic defects of brittle and insufficient barrier PLA films without the aid of any heterogenous modifiers,facilitating their widespread commercialization in the booming sustainable packaging market.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 multiaxial 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financially supported by the National Key Research and Development Program of China(No.2018YFB0704200)the National Natural Science Foundation of China(Nos.51803140,52033005,51822305 and 21776186)+2 种基金the Science and Technology Department of Sichuan Province(No.2018JY0584)the Postdoctoral Science Foundation of China(No.2019M663496)the State Key Laboratory of Polymer Materials Engineering(No.sklpme2021-4-03)。
文摘It is a daunting task to develop a promising strategy at an industrial scale for simultaneously ameliorating ductility and gas barrier performance of poly(lactic acid)(PLA)films in the application of green packaging.In this work,biaxial stretching and constrained annealing were employed to prepare transparent PLA films with superior ductility and barrier properties.The oriented nano-sized crystals induced by biaxial stretching were developed into regularαform during constrained annealing,which could not only serve as“nano-barrier wall”to impede the diffusion and dissolution of gas molecules,but also strengthen amorphous chain entanglement network as physical crosslink to enhance ductility.As a result,the as-prepared PLA films exhibited an outstanding comprehensive performance with a low oxygen and water vapor permeability coefficient of 0.733×10^(-14) cm^(3)·cm·cm^(-2)·s^(-1)·Pa^(-1) and 3.82×10^(-14) g·cm·cm^(-2)·s^(-1)·Pa^(-1),respectively,outstanding ductility with elongation at break of 66.0%,high yield strength of 84.2 MPa,and good transparency of more than 80%at 550 nm.The new insight in the relationship between microscopic amorphous and crystalline structure and macroscopic performance is conducive to alleviating the intrinsic defects of brittle and insufficient barrier PLA films without the aid of any heterogenous modifiers,facilitating their widespread commercialization in the booming sustainable packaging market.
