查看更多>>摘要：Poly(aryl ether ketone)(PAEK)films with different crystallinities were obtained by controlling the cooling rate,which were subjected to the absorption and desorption of methylene chloride(CH2Cl2).We employed attenuated total reflection Fourier transform infrared(ATR-FTIR)spectroscopy analyses to investigate the diffusion behavior of CH2Cl2 in PAEK films with different crystallinities.According to the Fickian diffusion model,the calculated diffusion coefficients of CH2Cl2 in PAEK films were observed to decrease with increasing crystallinity.The effect of CH2Cl2 absorption and desorption on the mechanical properties of PAEK films with different crystallinity was further analyzed using tensile tests.The tensile tests exhibited that CH2Cl2 has two concurrent effects:plasticization and solvent-induced crystallization.Differential scanning calorimetry(DSC)and wide-angle X-ray diffraction(WXRD)techniques further confirmed solvent-induced crystallization behavior.The results would be beneficial to understand the solvent resistance of PAEK materials and consequently provide the practical application conditions of PAEK with a theoretical basis.
查看更多>>摘要：Easy hydrolysis in alkaline environments limits the use of polyimide fibers in environmental protection.The hydrolysis resistance levels of polyimide fibers can be improved by crosslinking of the macromolecular chains.In this work,crosslinked polyimide fibers(CPI fibers)were pro-duced by intrinsic carboxyl decarboxylation for the first time.The thermal stability of the polyimide fibers containing the intrinsic carboxyl groups(PIC fibers)was studied,and the temperature of the decarboxylation-crosslinking reaction was determined to be 450 ℃.The PIC fibers were hot-drawn to initiate thermal crosslinking of the carboxyl groups and molecular chain orientation at high temperature.The CPI fibers had high tensile strengths(0.72-1.46 GPa)and compressive strengths(401-604 MPa).The oriented macromolecules and chemically crosslinked structure im-proved the tightness of the molecular chains and endowed the CPI fibers with excellent hydrolytic resistance.The CPI-50 fiber did not dissolve in a 0.5 wt％NaOH solution during heating at 90 ℃ for 10 h,and the tensile strength retention reached 87％when treated in 0.5 wt％NaOH solu-tions at 90 ℃ for 1 h,providing a guarantee for its application in alkaline corrosive environments.
查看更多>>摘要：Polypropylene(PP)exhibits suboptimal creep resistance due to the presence of methyl groups on its main chain,leading to irregular chain segment distribution,diminished inter-chain interaction,and crystallinity.This structural feature causes chain slippage in PP under stress,significantly constraining its service lifetime.In this study,thermally reduced graphene oxide(TrGO)nanosheets were incorporated into the PP matrix,yielding a nanocomposite with exceptional creep resistance performance.Results demonstrated that at a stress of 25 MPa,a 2.0 wt％Tr-GO content could enhance the creep failure lifetime of PP by 21.5 times compared to neat PP.Rheology,transmission electron microscopy(TEM),and scanning electron microscopy(SEM)characterization techniques were employed to analyze the mechanism of TrGO's influence on PP's creep behavior.It was observed that when TrGO content exceeded 1.0 wt％,an effective particle network structure formed within the PP matrix.This homogeneously dispersed TrGO-formed particle network structure restricted the migration and rearrangement of PP molecular chains,enabling prolonged stress resistance without structural failure.By combining the time-strain superposition method with the critical failure strain as a crite-rion,generalized creep compliance curves for PP and its composites were established,facilitating the prediction of material creep failure life-times,with a strong agreement between experimental and predicted lifetime values.This research proposes a novel strategy aimed at develop-ing polypropylene materials and products with enhanced long-term stability and durability,thus extending service life,reducing failure risk,and broadening their potential across various application domains.
查看更多>>摘要：Aiming at the difficult problem of solving the conformation statistics of complex polymers,this study presents a novel and concise conformation statistics theoretical approach based on Monte Carlo and Neural Network method.This method offers a new research idea for in-vestigating the conformation statistics of complex polymers,characterized by its simplicity and practicality.It can be applied to more complex topological structure,more higher degree of freedom polymer systems with higher dimensions,theory research on dynamic self-consistent field theory and polymer field theory,as well as the analysis of scattering experimental data.The conformation statistics of complex polymers deter-mine the structure and response properties of the system.Using the new method proposed in this study,taking the semiflexible ring diblock copolymer as an example,Monte Carlo simulation is used to sample this ring conformation to construct the dataset of polymer.The structure fac-tor describing conformation statistics are expressed as continuous functions of structure parameters by neural network supervised learning.This is the innovation of this work.As an application,the structure factors represented by neural networks were introduced into the random phase ap-proximation theory to study the microphase separation of semiflexible ring diblock copolymers.The influence of the ring's topological proper-ties on the phase transition behavior was pointed out.
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