最新刊期
      卷 52 ， 期 2 ， 2021

        Reviews

      • Ming-qing Yu,Yao-zu Liao,Mei-fang Zhu
        Vol. 52, Issue 2, Pages: 113-123(2021) DOI: 10.11777/j.issn1000-3304.2020.20186
        摘要：Polymer hydrogels are cross-linked polymeric materials with three-dimensional networks that can maintain 1000%−2000% of deformation under certain stress. Conjugated polymer hydrogels (CPHs) are the hydrogels made from conjugated polymers. From the point of view of molecular structure, CPHs exhibit an inherent rigidity and extended π-π bond of conjugated polymers, which can synergize the advantages of organic semiconductors and hydrogel networks. By means of physical and chemical doping, CPHs also display adjustable electroconductive properties. Therefore, CPHs combine the good mechanical properties, swelling properties of hydrogels and the excellent electrochemical properties of conjugated polymers. A diversity of methods have been applied to prepare CPHs. Owing to their unique properties mentioned, CPHs have been widely used in many fields such as drug release, energy conversion, energy storage, sensors, tissue damage repair and sewage treatment. Over decades, various new types of CPHs have been successfully synthesized, and their water absorption capacity, electrical conductivity and other properties have been continuously optimized. At present, CPHs are mainly prepared through in situ polymerization, direct filling, physical crosslinking and chemical crosslinking, etc. Chemical modifications and functionalization are also applied to adjust the properties of CPHs, which amplify their functionalities and applications. In this review, the preparation methods and applications of CPHs are systematically summarized, and the main issues existing in this research and the future development direction are analyzed.  
        关键词：Conjugated polymer hydrogels;Functional polymers;Preparation methods;Functional applications   
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        发布时间：2021-01-26
      • Shao-fan Li,Xiang-ning Wen,Wei-long Ju,Yun-lan Su,Du-jin Wang
        Vol. 52, Issue 2, Pages: 146-157(2021) DOI: 10.11777/j.issn1000-3304.2020.20189
        摘要：The inclusion of nanoparticles (NPs) or polymer-grafted nanoparticles (PGNPs) can impart the polymeric materials with enhanced properties in polymer nanocomposites (PNCs). Compared to the traditional polymer materials, the excellent performances of PNCs such as superior mechanical, thermodynamic, and optical properties have become a prominent aspect of scientific research. However, it still remains unclear about the relationship between interfacial interactions and mechanical enhancement in PNCs because the various factors i.e., grafting density σ (chains/nm2), the chain length of matrix versus the grafted polymer (P/N) and nanoparticle size can complicatedly affect the interfacial characteristics. Understanding the enhancement mechanism of the NPs/PGNPs in PNCs is, therefore, of crucial importance to modulate the properties of PNCs. Based on the successes and failures of the previous study, this review summarizes the mechanism of mechanical enhancement in PNCs, mainly from two perspectives: "particle-polymer interaction" and "particle-particle interaction". According to the different structural and conformation properties in PNCs, these two aspects are discussed in polymer/NPs nanocomposites and polymer/PGNPs nanocomposites, respectively. Strong reinforcement in PNCs inclusion of unmodified NPs is obtained at low NPs contents due to the overlapping of the glassy layer between NPs, and the network structure occurring at high NPs contents can significantly improve the mechanical properties of the polymer/NPs system. The decoration of grafted chains on the NPs surface can remarkably enhance the interfacial interactions between NPs and matrix. Mechanical properties of the grafted system can be affected by the different dispersion states of PGNPs, through controlling σ, P/N and NPs size. The "particle-particle interaction" under different aggregates is the main contribution to the enhancement of the mechanical properties in polymer/PGNPs system. It is anticipated that this review can be helpful to establish the relationship between the microstructure and macroscopic performance in PNCs and to provide guidance on modulating the mechanical properties of PNCs.  
        关键词：Polymer nanocomposites;Polymer-nanoparticle interaction;Nanoparticle-nanoparticle interaction;Mechanical properties   
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        发布时间：2021-01-26
      • Ge-ge Wang,Ju-zhong Zhang,Shui-ren Liu,Xiang-hong Wang,Xu-ying Liu,Jin-zhou Chen
        Vol. 52, Issue 2, Pages: 124-145(2021) DOI: 10.11777/j.issn1000-3304.2020.20179
        摘要：Cross-linked liquid crystal polymer (CLCP), as a combination of the order of liquid crystal orientation and the entropy elasticity of the polymer network, has exhibited unique properties such as actuation, soft elasticity, and birefringence. CLCP can mimic the behavior of organisms in a dynamically adjustable and reversible way to achieve actuation. When subjected to a specific external stimulus (such as light, heat, magnetism, or humidity), CLCP responds to the stimuli by presenting changes in LC arrangement at the micro level and reversible shape or size changes at the macro level. Because of the initial arrangement of the mesogen memorized through the network, the macroscopic deformation of CLCP is reversible. Materials with photothermal conversion effect, such as graphene, carbon nanotubes, and gold nanorods, can be combined with polymers to convert the absorbed light energy into heat energy so as to realize photothermal actuation. In addition, when photo-response moieties like azobenzene are appropriately added to CLCP, the reversibletrans-cis isomerization of azobenzene under specific wavelengths of light will cause the change of LC director, thus bringing out its photodeformation performance. Moreover, there is also magnetic stimulation driven by magnetic fields and humidity stimulation based on CLCP reversible anisotropic contraction or expansion. In this review, the synthesis methods of CLCP (one-step cross-linking, two-step cross-linking, post-crosslinking, and dynamic covalent bond cross-linking) and molding technology (inkjet printing, microfluidic transportation, soft lithography, direct laser writing, and 4D printing) are described. Through reasonable structure and material design, CLCP can be fabricated into a variety of flexible actuators. Herein, this review mainly summarizes the recent research progress in the applications of intelligently responsive cross-linked liquid crystal polymer in the field of the biomimetic actuators, such as artificial muscles, and microfluidic transportation. The future development and challenges of intelligently responsive cross-linked liquid crystal polymer in actuator field are also discussed.  
        关键词：Liquid crystal polymer;Synthesis method;Molding technology;Stimulus response;Bionic actuator   
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        Research Article

      • Yu Tao,Kai Gu,Zheng-zhong Shao
        Vol. 52, Issue 2, Pages: 158-165(2021) DOI: 10.11777/j.issn1000-3304.2020.20151
        摘要：A well dispersed aqueous suspension of reduced graphene oxide (RGO) enriched with silk fibroin nanofibrils and regenerated silk fibroin (RSF) was properly prepared, taking the advantage of the so called selective aggregation of silk fibroin nanofibrils on reduced graphene oxide nanosheets, and then a series of composited sponges with different proportions of RGO and RSF were obtained by the process of freezing and ethanol treatment at low temperature. To improve the pressure-sensitive conductivity of those composited sponges, the extra RGO nanosheets were deposited on the surface of the sponge by solution immersion. SEM observation and mechanical testing showed that the introduction of RGO not only made the corresponding micro/nano structure in RSF based sponge benefit the adhering of extra RGO nanosheets, but also favorited to the mechanical properties of the sponge. Moreover, the RGO/RSF sponges displayed significant strength and elasticity under the completely wet state, and could achieve good compression recovery effect and pressure sensing performance between compression strain of 0%−80%. Among them, the sensitivity of such composited sponge with the optimal proportion of the component could reach 0.15 kPa−1 regarding its resistance change under low pressure. Also, it worked efficiently under the pressure in the range of 0−17.3 kPa and presented excellent electrical stability and durability. Therefore, such pressure sensing material based on RGO/RSF sponge is expected to apply in energy-saving and environmental friendly flexible electronic devices due to its high sensitivity, wide working range, adjustable structure, renewability, good plasticity and so on.  
        关键词：Reduced graphene oxide;Silk fibroin;Sponges;Pressure sensing material   
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        发布时间：2021-01-26
      • Han-tao Xu,Zhen-yu Zou,Ben Tang,Zhou Chen,Huan-rui Zhang,Jin-chun Chen,Guang-lei Cui
        Vol. 52, Issue 2, Pages: 166-175(2021) DOI: 10.11777/j.issn1000-3304.2020.20157
        摘要：Lithium-sulfur batteries (LSBs) are regarded as one of the ideal candidates of next-generation energy storage devices due to their high theoretical energy density (2567 Wh·kg−1), low cost and environmental friendliness. However, there are still some obstacles towards the mass production of LSBs. For example, the cathode active material exhibits large volume change during the charge-discharge process, and low electronic conductivity, and the LSBs usually suffer from severe polysulfide shuttle effect, which result in the fast capacity fade. To alleviate these issues, the development of advanced binders for sulfur cathodes should be an effective solution since polymer binder plays an important role in stabilizing the structure of the sulfur cathode and suppressing polysulfide shuttle. Here we first present pectin as the binder for sulfur cathodes in LSBs. As a result, the as-prepared LSBs with pectin binder deliver a high initial discharge capacity of 1210.6 mAh·g−1, as well as a discharge capacity of 837.4 mAh·g−1 after 200 cycles, which is far better than the carboxymethyl cellulose-styrene butadiene rubber (CMC-SBR) counterpart. Cyclic voltammetry and electrochemical impedance characterization confirmed that the LSB using pectin binder exhibits better kinetic characteristics than CMC-SBR binder. It is evidenced by the polysulfide adsorption test and UV-Vis characterization that one mechanism behind such enhanced performance of pectin binder is that pectin binder can effectively suppress polysulfide shuttle. Furthermore, the scanning electron microscope and energy despersive spectroscopy mapping imaging demonstrate that pectin binder has the ability of ensuring the structural stability of MWCNT/S composite cathodes. This study shows that pectin is a high-performance sulfur cathode binder with widely potential applications.  
        关键词：Lithium-sulfur battery;Binder;Pectin;Carboxymethyl cellulose-styrene butadiene rubber (CMC-SBR)   
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        发布时间：2021-01-26
      • Cong Wu,Dan-dan Yang,Gang Wu,Si-chong Chen
        Vol. 52, Issue 2, Pages: 176-185(2021) DOI: 10.11777/j.issn1000-3304.2020.20161
        摘要：Poly(lactic acid) (PLA), as a kind of aliphatic polyester derived from biomass with excellent mechanical strength, biocompatibility and biodegradability, is a kind of green polymers with promising potential application. However, the application of PLA as a commodity polyester has been restricted dramatically because of its brittleness and flammability nature. It is still a great challenge to improve flame retardancy and toughness of PLA simultaneously by a simple blending method. In this work, copolymer ionomer (PCLA-PIU) was prepared by chain extension copolymerization of hydroxyl terminated poly(ε-caprolactone) (PCL), PLA prepolymer and phenylhypophosphate, and then incorporated with ammonium polyphosphate (APP) for synergistic modification of PLA. The ionomer can act as a compatibilizer to enhance the dispersion of APP in PLA matrix because of its PLA segments and phenylhypophosphate groups. The SEM observation shows that the APP particles dispersed in PLA/PCLA-PIU/APP composite has significantly smaller size and uniform dispersity, compared to the PLA/APP20. The phenyl hypophosphate groups in the ionomer also has an excellent synergistic effect with APP for improving the flame-retardance of PLA. The flame-retardant properties and mechanism of the PLA and its composites were investigated by LOI, UL-94, Cone calorimeter test, SEM, EDS, Raman spectroscopy, etc. Compared with neat PLA and PLA/APP, the composite PLA/PCLA-PIU10/APP10 containing 10 wt% of PCLA-PIU and 10 wt% of APP10 achieves the V-0 rating in UL-94 burning test with limiting oxygen index (LOI) as high as 27.6%. The heat release rate and total heat release of PLA/PCLA-PIU10/APP10 are also reduced significantly to 254.9 kW/m2 and 55.8 MJ/m2, respectively. SEM and Raman analysis for char residues after Cone calorimeter test suggest PCLA-PIU and APP had synergistic effect on promoting charring of PLA, which result in compact char residue with high graphitization degree, therefore effectively improving the flame-retardant efficiency. Moreover, the toughness of PLA is improved effectively by the flexible PCL segments of ionomers, resulting in a PLA/PCLA-PIU/APP composite with improved flame retardancy and toughness simultaneously. The mechanical properties test results show that the toughness of the modified PLA (10.3 kJ/m2 of PLA/PCLA-PIU10/APP10) is significantly improved compared to those of neat PLA (3.7 kJ/m2) and PLA/APP20 (2.5 kJ/m2).  
        关键词：Poly(lactic acid);Flame retardant;Toughening;Ammonium polyphosphate;Ionomer   
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        发布时间：2021-01-26
      • Xiao-bo Hu,Yao Yang,Bin-bo Jiang,Jing-dai Wang,Yong-rong Yang
        Vol. 52, Issue 2, Pages: 186-195(2021) DOI: 10.11777/j.issn1000-3304.2020.20140
        摘要：Two ethylene/1-butene/1-hexene terpolymers (sample A and sample B) produced in the fluidized bed polymerization reactor with two different operation modes were fractionated by prepared temperature rising elution fractionation (P-TREF), and the structures of obtained fractions were characterized by the gel permeation chromatography (GPC), differential scanning calorimetry (DSC), nuclear magnetic resonance (13C-NMR), and successive self-nucleation and annealing thermal analysis (SSA). Meanwhile, the tensile yield strength, tensile strength, impact strength, elongation and haze of these two sampled were also tested according to the National Standard of the People’s Republic of China. Results showed that compared with sample B produced in the condensed operation mode, the sample A produced in the liquid containing operation mode had better tensile yield strength, tensile strength, impact strength, elongation and haze. The relative content and the molecular weight of the low-temperature elution fraction of sample A was lower than those of sample B, but for high-temperature elution fraction, the relative content and the molecular weight of sample A were both higher than those of sample B. Sample A possessed the broader distribution of lamellar thickness than sample B. The distribution of short branches between molecular chains of sample A was also wider than that of sample B. From the analysis of branching degree and molecular weight, sample A’s short chain branches were more likely to grow in the high molecular weight chains than sample B. In summary, the sample A produced in the liquid containing operation mode has more excellent physical performance than sample B produced in the condensed operation mode, which was suitable for the preparation of high-performance stretch film material.  
        关键词：Polyethylene;Liquid containing mode operation;Condensed mode operation;Prepared-temperature rising elution fractionation;Short chain branch distribution   
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        发布时间：2021-01-26
      • Zhen-hua An,Rui Yang
        Vol. 52, Issue 2, Pages: 196-203(2021) DOI: 10.11777/j.issn1000-3304.2020.20150
        摘要：A novel aging evaluation system has been developed to realize a rapid, sensitive, non-destructive aging evaluation of polymer materials under various environmental conditions. Available conditions include irradiation, temperature, oxygen and humidity. This system can be used in the stability evaluation, aging status analysis and aging kinetics measurement by in situ detecting trace gaseous degradation products, such as CO2, in a specially designed reaction cell by FTIR. In this study, polyethylene (PE) composites were used as an example. The generation rate of CO2 of PE composites during a 4-h in situ detection corresponded well to the carbonyl index during a 120-day natural weathering, and the same stability ranking was obtained. In particular, there was a linear relationship between the generation rate of CO2 and the natural logarithm of carbonyl index, indicating that the generation rate of CO2 could be taken as a new evaluating index to rapidly detect aging status of PE composites. The activation energy of PE photo-oxidative aging was calculated based on the generation rates of CO2 at different temperatures in the range of 30−80 °C, which was in agreements with the results reported in literature. The above facts prove the reliability and efficiency of this novel aging evaluation system. Meanwhile, the high sensitivity of the system would enable the determination of activation energies at low temperatures close to the actual operating conditions of materials, avoiding the uncertainty caused by the extrapolation of accelerated results from high temperature.  
        关键词：In situ aging evaluation;Polyethylene composites;Photooxidative aging;Kinetics   
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      • Lian-lian Fu,Ying Lu,Zhi-yong Jiang,Yong-feng Men
        Vol. 52, Issue 2, Pages: 204-213(2021) DOI: 10.11777/j.issn1000-3304.2020.20147
        摘要：A series of high-density polyethylene samples with different microstructures obtained via isothermal crystallization at various temperatures and then cooling down to room temperature were used to explore the structural evolution and cavitation behavior during stretching by means of the ultrasmall-angle X-ray scattering and differential scanning calorimetry techniques. The samples crystallized at temperature higher than 110 °C then naturally cooled to room temperature possess two populations of lamellar stacks with different crystalline thicknesses. The thicker lamellae with well-organized structure were formed in the isothermal crystallization process, and chains crystallized at lower temperatures during cooling down yielded thinner defective lamellar crystallites. The melting temperatures of the two populations of lamellar stacks were around 133 and 110 °C, respectively. When deformed at 30 °C, the cavitation was observed in all samples and accompanied with strain-whitening phenomenon. It turned out that the cavities were more intense for the samples with thicker lamellae generated during isothermal crystallization. During deformation, the cavities first take place with the normal parallel to the stretching direction around yield point, and then changes the normal perpendicular to the tensile direction with the increase of strain. The length of cavities was calculated and the values were around 900 − 1200 nm. On the other hand, the extent of cavitation becomes smaller with the increasing ratio of the thinner lamellae crystallized during cooling down. Moreover, the plastic deformation of the lamellae is facilitated and the degree of cavitation become weaker with the increase of the stretching temperature.  
        关键词：X-ray scattering;Polyethylene;Caivitation;Stretching temperature   
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        发布时间：2021-01-26
      • Jia Wang,Cui Xu,Juan Zhang,Xue-hui Wang,Zhi-gang Wang
        Vol. 52, Issue 2, Pages: 214-222(2021) DOI: 10.11777/j.issn1000-3304.2020.20168
        摘要：Linear PCL (poly(ε-caprolactone)), SAN (styrene-acrylonitrile copolymer) and TAIC (triallyl isocyanurate) were melt blended, and the blends were then subjected to different doses of electron beam irradiation to prepare three series of crosslinked PCL and PCL/SAN blends with different gel contents. The crosslinked PCL/SAN blends were observed by a phase-contrast optical microscope (PCOM), which disclosed that phase separation did not occur, indicating that PCL and SAN components were miscible. Differential scanning calorimetry (DSC) was applied to study isothermal crystallization kinetics of crosslinked PCL and PCL/SAN blends. It was found that for the samples with close crosslinking degrees, the crystallization kinetics of the samples became significantly slower with increasing SAN content. When the SAN contents in the blends were the same, the crystallization rate became slower as the degree of crosslinking increased. For the blends with close degrees of crosslinking, the linear portion and the crosslinked portion were separated from the crosslinked blends, and the study on their respective crystallization kinetics by using DSC and polarized light microscope (POM) revealed that it was the incorporated SAN component rather than the crosslinked network that mainly contributed to the slowdown of crystallization rate of PCL in the crosslinked blends. Furthermore, the non-isothermal crystallization behaviors of the crosslinked blends during the cooling process verified the above conclusion.  
        关键词：Poly(ε-caprolactone);Styrene-acrylonitrile copolymer;Electron beam irradiation;Crosslinked;Crystallization kinetics;Non-isothermal crystallization   
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