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Chinese Journal of Polymer Science 2023年第8期41卷 1287-1297,I0010页

作者： Zhou-xian li Yi-Ran Kong xiang-Fei Chen Ya-Jiang Huang Ya-Dong Lv guang-xian li College of polymer science and engineering State key laboratory of polymer materials engineering of ChinaSichuan UniversityChengdu 610065China

The aging of natural rubber(NR)at high temperatures will seriously affect its service lifetime in many key *** the present work,the changes in microstructure and mechanical properties of semi-efficient vulcanized NR/carbon black(CB)vulcanizates during thermooxidative aging at high temperatures(150-200℃)and a moderate temperature(95℃)were *** high temperatures,a two-stage aging behavior,which was characteristic of a first rapid decline and then a continuous rise in the crosslinking density(ve),was identified and was found to be closely related to the depletion behavior of *** surface cracking behavior observed in the second stage of high-temperature aging was discussed in terms of the grafting reaction of macromolecular radicals on CB particles and thermal *** contrast,the aging of NR at moderate temperatures was much mild,which featured a continuous increase in ve and an oxidation mechanism dominated by peroxy radicals attacking double *** general,the mechanical properties of NR vulcanizates during high-temperature aging depended on the competition effects of structural evolution in the crosslinked network and oxidation-induced chain scission.

关键词： Natural rubber nanocomposites High-temperature Thermo-oxidative aging

Highly Improved Creep Resistance in Polypropylene Through Thermally Reduced Graphene Oxide and Its Creep lifetime Prediction

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Chinese Journal of Polymer Science 2024年第2期42卷 256-266,I0010页

作者： Can-Can Zhang Jun-Long Yang Ya-Jiang Huang guang-xian li College of Polymer Science and Engineering State Key Laboratory of Polymer Materials Engineering of ChinaSichuan UniversityChengdu610065China

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% TrGO 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 criterion, generalized creep compliance curves for PP and its composites were established, facilitating the prediction of material creep failure lifetimes, with a strong agreement between experimental and predicted lifetime values. This research proposes a novel strategy aimed at developing 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.

关键词： Thermally reduced graphene oxide Polypropylene Creep failure and lifetime prediction

Dynamics of Poly(methyl methacrylate)in Ionic liquids with Different Concentration and Cationic Structures

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Chinese Journal of Polymer Science 2023年第2期41卷 315-324页

作者： Huan Luo Xi He Gang liu Yan-Hua Niu guang-xian li College of Polymer Science and Engineering State Key Laboratory of Polymer Materials Engineering of ChinaSichuan UniversityChengdu610065China

The dynamic behavior of entangled poly(methyl methacrylate)(PMMA)chains in both the traditional monocationic ionic liquid(MIL)and synthetic dicationic ionic liquid(DIL)with the same anion bis[(trifluoromethyl)sulfonyl]imide([TFSI]−)has been examined over the wide composition range using differential scanning calorimetry and rheological ***/DIL and PMMA/MIL systems exhibit two glass transitions in the midrange of composition due to self-concentration *** in DIL shows slower relaxation behavior,however,after the iso-free-volume correction,the terminal relaxation timeτ_(0)of PMMA in both the DIL and MIL presents the power law behaviorτ_(0)∼ϕ^(v)with exponent v conforming to experimental results for conventional polymer solutions(v=2.0±0.2).At high ILs concentration(70%),the entanglement molecular weight M_(e)of PMMA/DIL system is lower than that of PMMA/MIL system owing to the formation of additional physical network in DIL,while the difference of M_(e)is reversed at low ILs *** composition dependence might be related to the fact that the probability of formation of physical cross-linking points in linked double imidazolium ring increases with the increase of DIL *** recovered creep strain of PMMA/DIL is almost 18 times of PMMA/MIL,exhibiting significantly better viscoelastic behavior.

关键词： Ionic liquids Terminal relaxation time Entanglement molecular weight Creep-recovery behavior

Crystallization Kinetics and the Fine Morphological Evolution of Poly(ethylene oxide)/Ionic liquid Mixtures

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Chinese Journal of Polymer Science 2017年第11期35卷 1402-1414页

作者： Wen-ze li 牛艳华 Chen-ting Zhou Huan Luo guang-xian li College of Polymer Science and Engineering State Key Laboratory of Polymer Materials Engineering of ChinaSichuan University

Abstract The overall crystallization kinetics and spherulite morphologies of miscible poly（ethylene oxide）（PEO）/1-butyl-3- methylimidazolium hexafluorophosphate （[BMIM][PF6]） mixtures were studied by differential scanning calorimetry （DSC）, polarized optical microscopy （POM） and rheological measurements. The finer crystal structures were further detected by wide angle X-ray diffraction （WAXD） and small angle X-ray scattering （SAXS）. Crystallization of PEO is largely suppressed by [BMIM][PF6] addition especially at higher ionic liquid （IL） concentrations above 20 wt%. Both the overall crystallization rate and the spherulite growth decrease with the increase of IL content and crystallization temperature; however, the crystallization mechanism keeps unchanged as evidenced by the similar Avrami exponent n and WAXD results. The addition of [BMIM][PF6] could induce more nuclei to some extent, but the induction time of crystallization is evidently prolonged, and a linear to non-linear transition of the spherulite growth （R ∝ t to R ∝t^1/2） can be observed. At higher IL concentration, the spherulite texture changes apparently from particular serrated to branch surface due to the diffusion-controlled growth and the dilution effect, which also as a main factor contributes to the increasing trend of the long period of crystals.

关键词： PEO [BMIM][PF6] Crystallization kinetics Spherulite morphologies

Accelerated Aging Behaviors and Mechanism of Fluoroelastomer in Lubricating Oil Medium

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Chinese Journal of Polymer Science 2020年第8期38卷 853-866,I0007页

作者： Qi-Long Wang Jing-Ke Pei Gao li Xi He Yan-Hua Niu guang-xian li College of Polymer Science and Engineering State Key Laboratory of Polymer Materials Engineering of ChinaSichuan UniversityChengdu 610065China

The aging behaviors and mechanism of fluoroelastomer(FKM)under lubricating oil(FKM-O)and air(FKM-A,as a comparison)at elevated temperatures were studied from both physical and chemical *** obvious changes of mechanical and swelling performances indicate that the coupling effect of lubricating oil and temperature causes more serious deterioration of FKM-O compared to that of ***,much stronger temperature dependence of both bulk properties and micro-structures for FKM-O is ***-stage physical diffusion process is defined in FKM-O due to the competition between oil diffusion and elastic retraction of *** results reveal that the dehydrofluorination reaction causes the fracture of C-F bonds and produces a large number of C=C bonds in the *** coupling effect of oil medium and high temperature could accelerate the scission of C=C bonds and generate a series of fragments with different molecular *** TGA results,crosslinking density Ve,and glass transition temperature Tg derived from different measurements coherently demonstrate the network destruction in the initial stage and the simultaneous reconstruction occurring at the final *** newly formed local network induced by reconstruction cannot compensate the break of the original rubber network and thus only provides lower tensile strength and thermal stability.

关键词： Fluoroelastomer Aging behaviors Mechanism Lubricating oil Network reconstruction

Coalescence Suppression in Flowing Polymer Blends Using Silica Rods with Different Surface Chemistries

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Chinese Journal of Polymer Science 2021年第4期39卷 474-483,I0007页

作者： Si-Ying xiang li-Sa-Ya Ye Ya-Jiang Huang Ya-Dong Lv Mi-Qiu Kong guang-xian li College of Polymer Science and Engineering State Key Laboratory of Polymer Materials Engineering of ChinaSichuan UniversityChengdu 610065China

Silica rods with homogeneous(hydrophilic or hydrophobic)and amphiphilic surface properties were synthesized and their efficiencies in suppressing the flow-induced droplet coalescence of immiscible polyisobutylene(PIB)/polydimethylsiloxane(PDMS)blends were evaluated via in situ visualization *** flow-induced coalescence behavior of blends was found to strongly depend on the surface nature and concentration of silica rods added as well as the blend *** a trace amount of rods promoted coalescence,all kinds of rods demonstrated a morphology refinement effect at high rod *** compatibilization effects were obtained at high rod concentrations,especially for hydrophilic and amphiphilic *** on confocal laser scanning microscopy results,these phenomena observed were interpreted reasonably in terms of the selective distribution and aggregation of silica rods,which were suggested to be decisive for the stabilization mechanism and efficiency of these rods.

关键词： Immiscible polymer blends Flow Morphology Silica rods Surface chemistry

Detection of the Destruction Mechanism of Perfluorinated Elastomer(FFKM)Network under Thermo-oxidative Aging Conditions

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Chinese Journal of Polymer Science 2022年第5期40卷 504-514页

作者： Wen-Yue Zhuo Qi-Long Wang Gao li Guo Yang Huan Zhang Wen Xu Yan-Hua Niu guang-xian li College of Polymer Science and Engineering State Key Laboratory of Polymer Materials Engineering of ChinaSichuan UniversityChengdu 610065China Aerospace Research Institute of Materials&Processing Technology Beijing W0076China

The changes of crosslinking network of perfluorinated elastomer(FFKM)cured by TAIC and DBPH under thermo-oxidative aging conditions were *** competitive processes including post-curing and network destruction occur simultaneously,which directly affect the storage modulus and crosslinking *** the increase of aging temperature,the network destruction becomes *** and XPS characterizations further reveal that the network destruction happens preferentially on the crosslink points of TAIC structure,and the post-curing is mainly caused by the decomposition of residual curing agent *** the easier breaking of TAIC structure in the crosslinking network,both the backbone and the pendent groups of FFKM itself are much more *** further figure out the destruction mechanism,TGAFTIR-GC-MS test was also conducted and a schematic degradation process of TAIC structure was *** is found that the destruction of TAIC crosslinking points happens first on the unstable exocyclic C―N bonds and the intermediate ring radicals could eventually decompose into volatile hydrogen isocyanate(HCNO)under extreme condition.

关键词： Perfluorinated elastomer(FFKM) Thermo-oxidative aging Destruction mechanism Crosslinking point

Highly Hydrolysis-Resistant Polyimide Fibers Prepared by Thermal Crosslinking with Inherent Carboxyl Groups

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Chinese Journal of Polymer Science 2024年第2期42卷 247-255,I0010页

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 produced 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 hotdrawn 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 improved 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 solutions at 90 ℃ for 1 h, providing a guarantee for its application in alkaline corrosive environments.

关键词： Polyimide Carboxyl group Crosslinking Hydrolysis-resistance

Structural Evolution in Flowing Immiscible Blends in the Presence of Rough Particles:Dependence of Shear Rate and Blend Ratio

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Chinese Journal of Polymer Science 2021年第8期39卷 1059-1068,I0008页

作者： Si-Ying xiang Ying-Chun Yao Miao-Miao Lu Ya-Jiang Huang Mi-Qiu Kong guang-xian li College of polymer science and engineering State key laboratory of polymer materials engineering of ChinaSichuan UniversityChengdu 670065China

The influence of polystyrene particles with different nanoscale roughnesses on the morphology of polyisobutylene/poly-dimethylsiloxane blends was studied under shear flow by using confocal laser scanning *** was found that the surface roughness of particles strongly affected their diffusion and distribution behaviors,thereby determining the size and spatial arrangement of droplets in the *** roughness effect of particles was found to possess a strong dependence on both the blend ratio and the shear *** result suggested that the particle roughness can serve as a new parameter to control the structure-property correlation in particle-filled polymer blends,especially under slow flow.

关键词： Rough particles Immiscible polymer blends Shear flow

Crosslinking Kinetics of Polyethylene with Small Amount of Peroxide and Its Influence on the Subsequent Crystallization Behaviors

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Chinese Journal of Polymer Science 2016年第9期34卷 1117-1128页

作者：牛艳华 Wen-bin liang Yin-ling Zhang Xue-lian Chen Shih-yaw Lai guang-xian li Du-jin Wang College of Polymer Science and Engineering State Key Laboratory of Polymer Materials Engineering of ChinaSichuan UniversityChengdu 610065China Performance Material Center National Institute of Clean-and-low-carbon Energy(NICE)Beijing 102209China CAS Key Laboratory of Engineering Plastics Beijing National Laboratory for Molecular SciencesInstitute of ChemistryChinese Academy of SciencesBeijing 100190China

Crosslinking reactions of high density polyethylene with low peroxide concentrations ranging from 0.1 wt% to 1.0 wt% at temperatures of 170, 180 and 190 ℃ were monitored by rheological measurements. A critical gel forms at the peroxide concentration of 0.2 wt%, where the transition from long chain branching generation to crosslinking network formation could occur. Rheokinetics of crosslinking can be fitted well by Ding-Leonov＇s model. The curing rate k2 at the earlier stage exhibits about 3 times acceleration per 10 ~C with increasing temperature, while the equilibrium modulus G＇ at the fully cured stage is almost independent of temperature. Influences of crosslinking on the subsequent crystallization behaviors were detected by DSC measurements. Above the critical gel concentration, crystallization is largely retarded as evidenced by the lower crystallization temperature Tc and crystallinity Xc due to the network formation. The secondary crystallization valley located at the temperature near 80 ℃ can be observed above the critical concentration, which becomes more evident with the increasing peroxide concentration and curing temperature. This phenomenon provides another evidence of crystallization retardation by the crosslinking network.

关键词： Polyethylene Rheology Crosslinking kinetics Crystallization.