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Design and Fabrication of Silk Fibroin-based Fibers and Functional Materials
Su-na Fan, Jie Chen, Zhang-hong Gu, Xiang Yao, Yao-peng Zhang
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20172 doi: 10.11777/j.issn1000-3304.2020.20172
[Abstract](264) [FullText HTML] (104) [PDF 3646KB](0)
With the advent of environmental pollution, resource depletion, and medical and health problems, the fabrication of new materials that meet specific performance standards, green safety and reproducibility has become the focus of current research. Silk fibroin, originating from natural silkworm cocoons, is among the most important renewable material due to its excellent biocompatibility, biodegradability, optical properties, thermal stability, and mechanical strength. Furthermore, silk fibroin can be processed, functionalized and produced in a variety of forms, such as porous scaffolds, hydrogels, membranes, and fibers, which endows silk fibroin-based materials (SFBM) with special structure, unique performance and increases their potential fields of application into biomedicine, bioelectronics, and intelligent sensing. However, there are still many challenges to fabricate SFBM with excellent performance on a large scale. Firstly, conventional methods of processing destroy the multilevel structure of silk firoin, which restricts its biomimetic design and results in degradation of its performance. Secondly, it is difficult to precisely regulate the structure of silk fibroin and ensure consistent performance across different batches. Thirdly, the performance of SFBM is comparatively inferior to that of synthetic polymers and can easily deteriorate when exposed to light, heat, or radiation. Therefore, the development of simple, efficient, biomimetic processing strategies to regulate the structure, improve the performance, and clarify the structure-function relationships of SFBM is of considerable significance. The present review summaries the latest achievements and developments of silk fibroin-based fibers and functional materials, focusing on the progress of research into biomimetic preparation of regenerated silk fibroin, the construction and functionalization of biomedical scaffolds, the design of intelligent electronic materials, and the fabrication of natural multi-functional silk and its building blocks. The aim of this review is to provide guidance and a reference for the design and construction of high-performance SFBM.
Study on the Regulation of Living Anionic Alternating Copolymerization of 1-(4-Dimethylsiloxphenyl)-1-styrene and Isoprene
Cheng-wei Dong, Xue-fei Leng, Li Han, Chao Li, Lin-can Yang, He-yu Shen, Hong-wei Ma, Yang Li
, Available online  , doi: 10.11777/j.issn1000-3304.2021.20204 doi: 10.11777/j.issn1000-3304.2021.20204
[Abstract](22) [FullText HTML] (22) [PDF 0KB](0)
The alternating regulation of living anionic copolymerization of 1-(4-dimethylsiloxphenyl)-1-styrene (DPE-SiH) and isoprene (Ip) was studied. By combining in situ 1H-NMR with MALDI-TOF technologies, the sequence distribution and apparent rate constant of monomers in the copolymer, as well as the reactivity ratio of Ip were determined. The results showed that the amount of DPE-SiH unit entring in the copolymer was less obvious than that of Ip, and the site of DPE-SiH unit was mainly gathered at the end of copolymer when without the addition of regulators. Meanwhile, the gradient copolymer was obtained with the reactivity ratio rIp=9.28. The apparent rate constants of DPE-SiH and Ip unit were KD=0.00134 min−1 and KIp=0.01421 min−1, respectively. In addition, the sequence distribution characteristics of the two monomers in the copolymer chain were investigated after the addition of the regulators [N'N'N'N-tetramethylethylenediamine (TMEDA) and potassium tert-butoxide (t-BuOK)] were also investigated. The copolymer with the alternating sequence feature was obtained when the regulator TMEDA and t-BuOK were added, achieving the sequence controlled of DPE-SiH and Ip unit in the copolymer chain. Meanwhile, the alternating entry of two monomers in the copolymer chain and the improvement of trans-1,4 Ip contents of copolymer were attributed to the “space-limited” living species resulted by the addition of regulators according to the results of Gaussian simulation.
Progress in Preparation and Applications of Conjugated Polymer Hydrogels
Ming-qing Yu, Yao-zu Liao, Mei-fang Zhu
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20186 doi: 10.11777/j.issn1000-3304.2020.20186
[Abstract](207) [FullText HTML] (197) [PDF 2774KB](2)
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. Chemically 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.
Study on Crystallization Kinetics of Crosslinked Poly(ε-caprolactone)/Styrene-acrylonitrile Copolymer Blends Prepared through Irradiation by Electron Beam
Jia Wang, Cui Xu, Juan Zhang, Xue-hui Wang, Zhi-gang Wang
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20168 doi: 10.11777/j.issn1000-3304.2020.20168
[Abstract](223) [FullText HTML] (89) [PDF 1447KB](1)
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.
Flame Retardant and Toughening Modification of Poly(lactic acid) with Phenylhypophosphate Ionomer/Ammonium Polyphosphate
Cong Wu, Dan-dan Yang, Gang Wu, Si-chong Chen
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20161 doi: 10.11777/j.issn1000-3304.2020.20161
[Abstract](228) [FullText HTML] (152) [PDF 1468KB](3)
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).
The Investigation from Animal Silks to Silk Protein-based Materials
Gong-wen Yang, Kai Gu, Zheng-zhong Shao
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20142 doi: 10.11777/j.issn1000-3304.2020.20142
[Abstract](425) [FullText HTML] (126) [PDF 2919KB](2)
Animal silk, especially silkworm silk, which has a long history and good practical performance, is one of the outstanding representatives for natural biomaterials. Although both of silkworm silk and spider dragline silk (abbr. as spider silk below) are formed by natural proteins with the similar molecular weight as well as amino acid composition, the comprehensive mechanical properties (especial the toughness) of the silkworm cocoon silk are much worse than those of spider silk, Previously, it was reasonably thought that such contrast on the mechanical properties of the silks was caused by the different amino acid sequences of silkworm silk protein (named as fibroin) and spider silk protein (named as spidorin). Nevertheless, the properties of the silk fibers formed by these recombinant spidroins still show less competitive with those of natural animal silks (including silkworm silk) in terms of mechanical properties besides the extremely high cost for the production so far. Indeed, it must be recognized that animal silk is naturally processed and can be directly used as a fiber. Therefore, the reasonable routine for basic research and practical development of animal silk and silk protein-based materials should be (1) exploration of intrinsic properties and investigation of multi angle/multi-level structure-property relationships of natural silk fiber; (2) acquisition/regeneration of silk protein and the research on its molecular chain behavior; (3) according to the understanding on its molecular chain behavior based on the multi-level structure-property relationship of regenerated silk protein molecular chain, endowing silk protein based-materials with various sharps, morphologies as well as functions, especially those non-fiber materials, in order to achieve diversified applications. Based on a few of achievements in our group, this article reviewed the way mentioned above regarding the investigation on animal silks and fibroin-based materials, while emphasized that the hierarchical structure and structure-function relationship in the natural fiber could not spontaneously extend to silk protein-based materials. We also expected this concept would lead the research on the preparation of animal silk proteins represented non-physiologically active biomacromolecule-based materials with different morphologies and site-specific functions.
Pressure Sensing Material Based on Reduced Graphene Oxide/Silk Fibroin Sponge
Yu Tao, Kai Gu, Zheng-zhong Shao
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20151 doi: 10.11777/j.issn1000-3304.2020.20151
[Abstract](205) [FullText HTML] (114) [PDF 1759KB](0)
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.
Injectable Hydrogels for Regenerative Medicine
Qian Feng, Kun-yu Zhang, Rui Li, Li-ming Bian
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20126 doi: 10.11777/j.issn1000-3304.2020.20126
[Abstract](251) [FullText HTML] (142) [PDF 10775KB](9)
Injectable therapeutics enabled by engineered biomaterials are becoming increasingly popular, transforming traditional clinical practice to become less invasive and more effective. Compared with traditional biomaterials, injectable biomaterials allow for more precise implantation into deeply enclosed anatomical locations and for the repair of irregularly shaped lesions, demonstrating great translational potential. Injectable hydrogels have become increasingly important in the fields of drug delivery, tissue engineering and regenerative medicine due to their tunable physical and chemical properties, controllable degradation, biomimetic water content, and the ability to achieve delivery in a minimally invasive manner. Researchers have developed a series of injectable hydrogels with unique properties through in situ gelation, macroporous hydrogels, microgels, and shear thinning. Importantly, these hydrogels can be used to achieve the delivery of bioactive molecules and cells during the injection process and provide the three-dimensional microenvironment required for cell culture. Rationale modifications of the hydrogel biophysical and biochemical properties enable precise regulation on cellular behaviors such as adhesion, proliferation, and differentiation. This article aims to review the recent advances in the design and preparation of injectable hydrogels and their applications in regenerative medicine and the key challenges to be addressed in future research work.
The Progress in Thermogels Based on Synthetic Polymers for Treating Ophthalmic Diseases
Min-hua Liu, Kai-hui Nan, Yang-jun Chen
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20152 doi: 10.11777/j.issn1000-3304.2020.20152
[Abstract](569) [FullText HTML] (288) [PDF 3847KB](0)
Due to the presence of several physiological barriers, including corneal barrier, blood-aqueous humor barrier and blood-retinal barrier, efficient drug delivery remains a huge challenge in the treatment of ocular diseases. In recent years, in situ forming thermogels have emerged as ideal drug delivery systems (DDSs) with sustained-release feature, receiving extensive attention in the field of ocular drug delivery. At room temperature, thermogels in liquid form can be easily administrated by topical instillation or intravitreal injection. Once in contact with the eye, physical crosslinking induced sol-gel transition will take place in-situ when the liquid temperature exceeds the critical gelation temperature. Thus, drug retention time can be prolonged and drugs can be continuously released for a longer term to enhance drug bioavailability. Benefiting from the advantages of synthetic polymers in terms of material diversity and versatility, thermogels based on synthetic polymers are the current hotspot in the research of temperature-induced hydrogels. Poloxamer, polyethylene glycol/polyester and poly(N-isopropylacrylamide) are the three most common synthetic thermo-gelling polymers. In this review, we will first introduce preparation methods and gel-forming properties of these synthetic polymer-based thermogels. Then, the research progress of the application of synthetic thermogels in the treatment of ophthalmic diseases, including corneal disorders, dry eye syndrome, glaucoma, ocular inflammation, and others, is mainly discussed. Last but not the least, the advantages and disadvantages of these three thermogels are compared, and future perspectives on the design of novel synthetic thermogels for ophthalmic applications are suggested.
Research Progress of Poly(aryl ether ketone) on Spinnability and Structure Optimization
Da-lin Dong, Yue-zhen Bin, Xi-gao Jian
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20130 doi: 10.11777/j.issn1000-3304.2020.20130
[Abstract](411) [FullText HTML] (165) [PDF 2190KB](7)
As a kind of special engineering plastics, poly(aryl ether ketone) has excellent comprehensive properties, making poly(aryl ather ketone) have broad application prospects in many fields. Research progress of poly(aryl ether ketone) fibers and structure optimization of poly(aryl ether ketone) on spinnability are introduced from amorphous poly(aryl ether ketone) and crystalline poly(aryl ether ketone). There are some differences in solubility, processing methods, aggregation structure and application fields between amorphous poly(aryl ether ketone) and crystalline poly(aryl ether ketone) fibers. At present, more studies have been done on crystalline poly(aryl ether ketone) fibers than on amorphous poly(aryl ether ketone) fibers. In terms of physical modification, poly(aryl ether ketone) blends with inorganic lubricants, thermotropic liquid crystalline polyester and thermotropic liquid crystalline poly(aryl ether ketone). Processability of the blend and mechanical properties of the fibers are improved significantly. In terms of chemical modification, poly(aryl ether ketone) is modified by sulfonation, chloromethylation, ring opening polymerization, multicomponent copolymerization, introduction of mesogenic units or different side groups, introduction of twisted non-coplanar structure and introduction of thermotropic liquid crystalline polyester. Processing methods of poly(aryl ether ketone) are expanded and the solubility of poly(aryl ether ketone) is improved. Ionic conductivity of poly(aryl ether ketone) nanofiber membrane is also improved. Blending with inorganic lubricant, blending with thermotropic liquid crystalline polyester, blending with thermotropic liquid crystalline poly(aryl ether ketone), sulfonation, introduction of different side groups and introduction of twisted non coplanar structure play an important role in crystalline poly(aryl ether ketone). While, chloromethylation, ring opening polymerization, multicomponent copolymerization and introduction of thermotropic liquid crystalline polyester play an important role in amorphous poly(aryl ether ketone). By chemical modification, the application of poly(aryl ether ketone) nanofiber membrane in ion-exchange membrane of fuel cell and many other promising fields are expanded. In corresponding fields, the structure and properties of amorphous and crystalline poly(aryl ether ketone) still have great potential for improvement. Hope this paper could provide reference for the other researchers.
Chain Structure and Mechanical Properties of Ethylene Copolymers in Two Operating Modes of Fluidized Bed Polymerization Reactor
Xiao-bo Hu, Yao Yang, Bin-bo Jiang, Jing-dai Wang, Yong-rong Yang
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20140 doi: 10.11777/j.issn1000-3304.2020.20140
[Abstract](356) [FullText HTML] (78) [PDF 1466KB](0)
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.
The Study on the Application of Pectin Binder in Lithium-Sulfur Batteries
Han-tao Xu, Zhen-yu Zou, Ben Tang, Zhou Chen, Huan-rui Zhang, Jin-chun Chen, Guang-lei Cui
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20157 doi: 10.11777/j.issn1000-3304.2020.20157
[Abstract](371) [FullText HTML] (177) [PDF 1749KB](2)
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.
A Novel Aging Evaluation System and the Application to Polyethylene Composites
Zhen-hua An, Rui Yang
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20150 doi: 10.11777/j.issn1000-3304.2020.20150
[Abstract](469) [FullText HTML] (244) [PDF 1214KB](2)
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.
Lattice Self-consistent Field Calculations of Phase Behavior of Symmetric Star Block Copolymers AmBm Confined between Two Parallel Surfaces
Jing-xue Zhang, Jia-ping Wu, Qiang Wang, Bao-hui Li
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20119 doi: 10.11777/j.issn1000-3304.2020.20119
[Abstract](565) [FullText HTML] (188) [PDF 0KB](2)
We studied the lamellar structures formed by incompressible melts of symmetric star block copolymer (BCP) AmBm confined between two identical, homogeneous and parallel surfaces with their separation equal to the bulk lamellar period, using the self-consistent field calculations on a simple cubic lattice. All the star BCPs have the same χNAB value, where χ is the Flory-Huggins parameter characterizing the repulsion between two nearest-neighbor A and B segments, and NAB is the number of segments on one pair of A- and B-arms. The effects of total chain length N and the number of A or B arms m in each AmBm chain on the lamellar structure and orientation were investigated in detail. We found that the normalized A-B interfacial widths of the confined lamellae increase with decreasing m at fixed N or NAB = (N − 1)/m. The calculated Helmholtz free energy per chain shows that perpendicular lamellae are stable over parallel lamellae when the two confining surfaces are neutral. As the surface preference Λ (e.g., for B-segments) increases, all systems exhibit a first-order phase transition from perpendicular to parallel lamellae. At a fixed m value, the star BCPs with smaller N have larger Λ range to form perpendicular lamellae. At a fixed N (or NAB), the star BCPs with larger m have larger Λ range to form perpendicular lamellae. These findings may provide useful information for the lithographic applications of BCPs.
Recycling and Chemical Upcycling of Waste Disposable Medical Masks
Hai-ming Chen, Xia Dong, Ying Zhao, Du-jin Wang
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20136 doi: 10.11777/j.issn1000-3304.2020.20136
[Abstract](791) [FullText HTML] (366) [PDF 2216KB](9)
Since the COVID-19 epidemic, the global demand for medical supplies, e.g., disposable medical masks (DMMs), have been largely increasing. Blocking bacteria and viruses via wearing masks, according to the pre-judgment of epidemic infectious disease experts, will be a normal phenomenon within a long future period. Therefore, how to process the large number of waste DMMs properly is becoming an important issue for various countries and regions all over the world. From the view of chemical upcycling, this paper reviews the current status of recycling, and prospects the upcycling of polypropylene (PP), which is the main component of DMMs. The upcycling methodologies here mainly include mechanical blending, chemical modification, controllable degradation and physical process modification. Both the advantages and disadvantages of these methodologies have been discussed based on the analysis of technological feasibility and economic benefit. On the basis of the formation of public awareness of recycling and treatment of waste DMMs, by exploring the mechanism of decomposition, reconstruction and re-functionalization of PP, developing new selective green catalysts, degradants, in situ collaborative detection technologies, utilizing the residual value of the existing waste DMMs, etc. will greatly promote the upcycling of waste DMMs. It is believed that converting waste PP selectively into a single type of chemicals, fuels and high value-added material by chemical ways is the fundamental method to realize the transformation of waste DMMs from “waste” to “treasure” and sustainable development.
Multiresponsive Network Surface Wrinkle Based on PEA Polymernetwork Contained on Boronic Bond
Yi-jie Zhang, Tian-tian Li, Xiao-dong Ma, Jie Yin, Xue-song Jiang
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20133 doi: 10.11777/j.issn1000-3304.2020.20133
[Abstract](533) [FullText HTML] (211) [PDF 1298KB](5)
Dynamic surface pattern with responsive morphology to environmental stimuli can possibly enable the on-demand control of the encoded surface properties, providing an important alternative to realize smart surfaces. In this study, we fabricated a series of mutli-responsive wrinkle patterns by using poly(ether amine) (PEA)-based dyanmic crosslinked network containing boronic ester and photodimer of AN as toplayer for bilayer wrinkling systems. Upon the irradiation of 365 nm UV-light and thermal treatment, the resulting crosslinked polymer network caused by photodimerization of AN and boronic ester bond with the increasing modulus induced the compressive strain in the bilayer systems, resulting in the formation of microscale wrinkling pattern. And the wrinkle pattern can be erased under the irradiation of 254 nm UV light or water due to the decrosslinking of polymer network. Owing to the spatial and temporal features of light, the dynamic hierachical pattern of wrinkle can be obtained through selective exposure with photomask. This strategy based on respsosnive polymer network containing dyanmic chemical bond provides an important alternative approach to fabricate multi-responsive patytern of wrinkle, and has potential applications in the field of sensor and anticonterfeiting.
Preparation and Properties of Photo-cured Electrolyte Based on Polyethylene Glycol Grafted Acrylic Resin
Peng-xuan Zheng, Xiang-wei Wang, Dong Wang, Zhi-wei Yu
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20121 doi: 10.11777/j.issn1000-3304.2020.20121
[Abstract](413) [FullText HTML] (188) [PDF 1146KB](2)
Polyethylene oxide (PEO) (polyethylene glycol (PEG)) grafted acrylic resin had been widely used as polymer electrolytes. In this paper, quasi-solid polymer electrolytes (QSPE) with high conductivity were prepared and studied by UV-curing of polyethylene glycol dimethacrylate (PEGDA) and methoxypolyethylene glycol methacrylate (PEGMA). The electrolytes could be easy to be fabricated into membranes and simply encapsulated in electrochemical devices, espacially in electrochromic devices (EDCs). The process of the PEGDA and PEGMA polymerization was mainly confirmed by Fourier-transform infrared spectroscopy (FTIR). The electrochemical performance of the electrolytes was characterized by an electrochemical workstation, and the ion conductivities with the various concentrations of liquid electrolyte and weight ratios of monomers were investigated. When the content of lithium salt solution was 75% and the weight ratio of PEGMA to PEGDA was 75:25, the ionic conductivity of the electrolytes reached 1.96 × 10−3 S·cm−1 , which was 14 times higher than that of the original. In order to verify its application performance, electrochromic devices was assembled with the obtained electrolyte membrane as an ion transport layer and exhibited high efficiency of color changes. The EDCs still exhibited stable and reversible color switching between gray blue and bright yellow even after 580 cycles, and the response time was less than 3 s. Because of its good electrochemical property and easy encapsulating, the electrolytes based on polyether grafted acrylic resins also held extensive prospects in other electrochemical devices.
Research Progress in Zwitterionic Hydrogels
Ping Li, Liang-peng Zeng, Hong-lei Guo, Hui Guo, Wei-hua Li
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20124 doi: 10.11777/j.issn1000-3304.2020.20124
[Abstract](727) [FullText HTML] (348) [PDF 4155KB](19)
Zwitterionic hydrogels have received considerable attention owing to their characteristic structures and properties. Bearing high density of oppositely charged groups within polymer networks at the micro-scale, the zwitterionic hydrogels exhibit a macroscopic electro-neutrality. As a result, the soft matter exhibits various specific features, such as high hydrophilicity owing to their dense charged groups, “anti-polyelectrolyte behavior” due to salt clearable associations between oppositely charged groups, and UCST-type thermo-responsiveness as a result of temperature-sensitive polymer inner and inter-chain associations. In this review, the unique properties of the materials are described at first, and their potential applications including biomedicine, gel polymer electrolyte, sensor, and actuator are subsequently illustrated in detail. Thereafter, the possible constraints that hinder their current practical application are well discussed. The difficulty in monomer synthesis, the relatively poor chemical stability against long term hydrolysis and oxidization in aqueous media, and unsatisfactory mechanical performance are three main plausible reasons. Developing zwitterionic hydrogels with ameliorated chemical structures effectively enhances their chemical stability, while the exploration of polyzwitterionic composite hydrogels with nanoparticles is a possible way to figure out the existing drawback of poor mechanical performance. In the end, current status as well as future prospect of the zwitterionic hydrogels are finely presented.
Cavitation in Tensile Stretched HDPE Revealed by Synchrotron Ultrasmall-angle X-ray Scattering
Lian-lian Fu, Ying Lu, Zhi-yong Jiang, Yong-feng Men
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20147 doi: 10.11777/j.issn1000-3304.2020.20147
[Abstract](429) [FullText HTML] (184) [PDF 1615KB](0)
A series of high-density polyethylene samples with different microstructures obtained via isothermal crystallization at various temperature 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.
The Controllable Surface Structure and Oil-Water Separation Performance of Reinforced Poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) Hollow Fiber Membranes
Xi Shu, Chang-fa Xiao, Kai-kai Chen, Tai Zhang, Hao-yang Ling
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20101 doi: 10.11777/j.issn1000-3304.2020.20101
[Abstract](598) [FullText HTML] (178) [PDF 1947KB](1)
In order to solve the problem of oily wastewater, the poly(m-phenyleneisophthalamide) (PMIA) braided tube reinforced (PBR) poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether)(PFA) hollow fiber membrane was prepared via dipping-sintering method with the PFA and poly(vinyl alcohol)(PVA) as membrane-forming polymer and bonding agent, respectively. The membrane surface structure was adjusted by changing the sintering temperature and graphene (GE) content, and the influence of membrane structure and oil-water separation performance were investigated by scanning electron microscopy (SEM), thermogravimetric (TG), Fourier transform infrared (FTIR), pore size analysis and oil-water separation experiment. The morphology observation shows that the surface PFA melts and permeates into the PMIA braided tube after sintering, and separation layer is closely combined with the support layer. The experiment results also indicate that with sintering temperature increasing, the oil flux decreases. On the other hand, with GE content increasing, the water contact angle, roughness, and porosity of PBR-PFA/GE hollow fiber membrane decrease, however, the oil flux increases initially and then decreases, the oil-water separation efficiency increases gradually. Furthermore, the introduction of GE not only has a similar effect on the increase of sintering temperature, but also results in two different ways of pore formation on the membrane surface. The PBR-PFA/GE hollow fiber membrane exhibits excellent hydrophobicity and lipophilicity with more than 97% separation efficiency for different oil products at −0.02 MPa. In addition, the membrane shows higher separation ability to the water-in-oil emulsion, and maintains a fine flux recovery rate after recycling, making it possible to apply in the field of wastewater treatment.
Phase Change Azobenzene/Fabric Composite Material Based on Rapid Heat Release Function
Tian-yu Xu, Yi-yu Feng, Wei Feng
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20146 doi: 10.11777/j.issn1000-3304.2020.20146
[Abstract](435) [FullText HTML] (236) [PDF 1077KB](3)
Due to the instant conversion of traditional photothermal conversion, solar energy could be stored for a short time, which limits its utilization in solar energy storage. Using photosensitive molecules as photothermal conversion materials, solar energy is stored in chemical bond, which becomes a common solution in this field and an important part of photothermal conversion field. As a common photothermal conversion material with simple synthesis, low cost and not easy to degrade, azobenzene (azo) can change from trans-structure to cis-structure in the light of specific wavelength and store the light energy in the chemical bond. When return to trans-structure under external stimulation, cis-azo release energy in the form of heat energy, completing a light heat storage and release cycle. In view of the difficulties in the slow heat release rate and controlling the temperature of azo-based photosensitive molecules, based on the molecular structure design, 4,4'-dihexylazobenzene (AZO-L6) with solid-liquid phase change function was prepared by the oxidation coupling method. The successful preparation of AZO-L6 was proved by relevant tests. Due to the low intermolecular force, the azo molecule is characterized by low melting point and fast isomerization, and when the trans to cis isomerization transition occurs, the melting point of the azo molecule greatly reduced. The process of solid-liquid phase changing realizes the storage of photothermal energy and phase change latent heat, and simultaneously releases the stored energy (231.8 kJ/kg) when returning to the cis-structure. We apply AZO-L6 to the wearable polymer composite fabric. It is proved that azo is fully filled into the fabric, and the isomerization of azo is hindered, while the recovery process is not affected. Under the stimulation of blue light (440 nm), the phase change azo molecule can make the material temperature go up 0.8 °C within 60 s, and a wearable composite fabric with self-heating function is obtained, which provides research ideas for exploring multifunctional self-insulating wearable devices.
Preparation and Properties of Catechol Modified Chitosan-based Injectable Biological Adhesives with Near-infrared-light-controlled Release Behavior
Li-an Wang, Zhi-qing Ge, Mo-zhen Wang, Xue-wu Ge
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20005 doi: 10.11777/j.issn1000-3304.2020.20005
[Abstract](620) [FullText HTML] (232) [PDF 1907KB](5)
Chitosan (CS) hydrogel based adhesives have good biocompatibility, but poor adhesive property. In this paper, catechol modified chitosan (CS-pC) was synthesized by modifying CS with 3,4- dihydroxybenzoic acid. The mass ratio of catechol group of CS-pC is 14.4%. When the CS-pC acetic acid aqueous solution and the aqueous solution of β-glycerol phosphate disodium salt (β-GP) is mixed, an injectable CS-pC/β-GP sol is formed, which can be transformed into CS-pC/β-GP hydrogel under heating. The sol-gel transition time decreases exponentially with the increase of the temperature, and is around seven minutes at 37 °C. The CS-pC/β-GP hydrogel has good biocompatibility, showing no cytotoxicity to Hela cells, MCF-7 cell, as well as 293T cells. It has excellent antibacterial properties on killing Escherichia coli and Staphylococcus aureus. It is noted that the CS-pC/β-GP hydrogel has brilliant adhesion property. The CS-pC/β-GP hydrogel can adhere to the porcine skin tightly. The critical peel strength is up to 4.9 kPa, eight times higher than that of the hydrogel prepared from unmodified CS (0.6 kPa). Furthermore, the water-soluble drug doxycycline hydrochloride (DH) and near-infrared (NIR) photothermal agent gold nanorods (AuNR) can be loaded into the CS-pC/β-GP sol to form an injectable CS-pC/β-GP/DH/AuNR sol, which can also be transformed into CS-pC/β-GP/DH/AuNR hydrogel rapidly at 37 °C. The strong NIR photothermal conversion effect of the loaded AuNR offers the hydrogel a remarkable NIR light controlled release function. The release rate of the loaded DH will increase six times under the irradiation of 808 nm NIR laser, which indicates that the CS-pC/β-GP/DH/AuNR hydrogel adhesive can also achieve a controlled wound healing. This work provides a new way for the development of safe, high-performance, and multifunctional injectable catechol modified chitosan based biological adhesives.
Continuous Bacterial Cellulose Aerogel Fibers with High Strength
Jun-yan Zhang, Si Meng, Wen-ping Chen, Yan-hua Cheng, Mei-fang Zhu
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20143 doi: 10.11777/j.issn1000-3304.2020.20143
[Abstract](674) [FullText HTML] (342) [PDF 1471KB](6)
Aerogel fibers have attracted increasing interests due to their high outside specific surface area and high flexibility for applications in energy management systems. However, aerogel fibers usually suffer from weak mechanical properties and complicated fabrication process, thus severely restricting their broad application. In this paper, the never-dried bacterial cellulose (BC) with high molecular weight was firstly dissolved in NaOH/urea/thiourea aqueous solution at −15 °C. Followed by wet spinning, solvent exchange and freeze-drying, the BC aerogel fiber with high mechanical properties was simply obtained. The dissolution process was observed by polarized optical microscope (POM), 13C nuclear magnetic resonance (NMR) and viscoelastic measurements. The variations of structure and properties on original BC and regenerated BC aerogel fibers were characterized by attenuated total reflection-Fourier transform infrared spectrometry (ATR-FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The structure and properties of BC aerogel fiber were studied by field emission scanning electron microscopy (FESEM), specific surface area and pore size distribution analyzer (BET) and fiber strength tester. The results show that the never-dried BC can be dissolved in NaOH/urea/thiourea solution at low temperature. The maximum concentration of BC in the solution reaches up to 3 wt%. The resulted BC solution behaves as pseudoplastic fluid and stays stabe at room temperature. To fabricate BC aerogel fibers, wet-spinning technology and freeze-drying were utilized using BC solution as spinning dope. After regeneration, the crystal structure of BC transforms from I to II without derivatization. Meanwhile, highly porous structure in axial alignment with a high specific area of 192 m2/g was demonstrated in the BC aerogel fibers. Due to the high molecular weight of BC, strong intramolecular and intermolecular interactions, and molecular chain orientation, the tensile strength and Young’s modulus of BC aerogel fibers could reach up to (9.36 ± 1.68) MPa and (176 ± 17.55) MPa, which are higher than those of state-of-the-art aerogel fibers. The lightweight BC aerogel fiber can withstand a load of more than 5 × 104 times its own weight. Such BC aerogel fibers show high potentials in flexible biological scaffolds, drug carriers, bio-adsorbents and advanced thermal insulation textiles.
Effect of Mixed Ionic Liquids on Chain Entanglement and Relaxation of Poly(methyl methacrylate)
Xi He, Huan Luo, Yan-hua Niu, Guang-xian Li
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20116 doi: 10.11777/j.issn1000-3304.2020.20116
[Abstract](616) [FullText HTML] (232) [PDF 0KB](0)
A kind of dicationic ionic liquid (DIL) [C8(MIM)2][TFSI]2 with double charged imidazole rings was successfully synthesized and mixed with a monocationic ionic liquids (MIL) [C8(MIM)][TFSI]. Compared with MIL, the double imidazolium rings on the DIL cation greatly limits the vibration ability of the alkyl chain, which shows a much higher wavenumber in infrared spectrum. The DIL/MIL mixtures show Arrhenius fluid behaviour, and their viscosities follow the logarithmic mixing rule. With the increase of DIL content in the ILs mixtures, the viscosity and flow activation energy gradually increase, which is closely related to the molecular size and intermolecular interaction of DIL. Then, the effect of mixed ILs on the entanglement and relaxation of poly(methyl methacrylate) (PMMA) was extensively investigated by rheological tests. The master curves obtained by time-temperature superposition principle show that DIL could significantly change the relaxation behaviour and entanglement state of PMMA chains in mixed ILs. With increasing DIL content in the mixed ILs, both the terminal relaxationτ1 and entanglement relaxation τe of PMMA chains were retarded, and the entanglement network of the PMMA/ILs becomes more compact, showing higher plateau modulus and greater viscosity. More interaction sites could be formed between PMMA chains and DIL molecules due to its unique double imidazolium rings structure, which results in more cohesive entanglements among PMMA chains and thus restrict their relaxation. Moreover, there is a mathematical relationship between the rheological parameters (such as τ1 and τe) of PMMA/ILs and the viscosity of ILs mixtures, so the rheological behaviour of the system could be approximately predicted. On the other hand, thermal stability, glass transition and ion conductivity of PMMA/ILs were also discussed. The thermal decomposition temperature and glass transition temperature of PMMA/ILs increased with the DIL content, while the ionic conductivity decreased slightly.
The Investigation on Foamability Behavior of Polybutene Based on Melt Grafting
Chong Han, Bing-zhen Sun, Rui-ying Gong, Chao-xu Li
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20109 doi: 10.11777/j.issn1000-3304.2020.20109
[Abstract](778) [FullText HTML] (317) [PDF 1616KB](8)
The melt strength of polyolefin materials could be enhanced by graft modification, since the introduction of long side chains could result in entanglement among the chains and thus improve the foaming properties. Herein, polybutylene (PB) with the improved foaming property was produced by melt grafting of octadecyl methacrylate (SMA) as long side chains. It was found that the chain entanglement was increased and the foaming behavior was improved. The structure was characterized by infrared (IR) spectroscopy, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Compared with un-modified PB, the tensile strength of the modified PB decreased, whereas its impact strength firstly increased and then decreased when increasing the amount of SMA. DSC curves showed that the crystallinity of PB decreased when increasing the grafting dosage. The SEM images showed that all the parameters including the average cell size, cell size distribution, and cell density of foam beads were improved after introducing the longside chains. When the weight ratio of SMA/PB was 3/100, the average cell diameter of PB was 12.3 μm, the cell density was 38 × 107 cells/cm3, and the expansion ratio was 12. The cell density and expansion ratio of PB with longside chains were 9.2 times and 1.6 times respectively as many as those of un-grafted PB produced with the same foaming method. Additionally, the grafted PB exhibited a wider foaming temperature range.
Study on the Organometallic [N,P] Titanium Catalysts for Ethylene Polymerization without Cocatalyst
Zi-hai Shi, Jiao-jiao Zhang, Ding-kun Yuan, Shao-meng Zhang, Xiao-qi Xia, Ke-jing Gao, Hong-ming Li, Qiu-can Wang, Jian-jun Yi, Qi-gu Huang, Zhong Zhao
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20098 doi: 10.11777/j.issn1000-3304.2020.20098
[Abstract](789) [FullText HTML] (294) [PDF 1074KB](25)
The soft and hard acid-base theory (HSAB) is a new acid-base theory created by Sir. Pearson based on the theory of Lewis acid-base electron. It can be used to explain various chemical reactions, especially in coordination chemistry. In this study, the synthesized Cat. 1 − Cat. 6 [N,P]Ti catalysts containing ligands with electron withdrawing groups were prepared for ethylene polymerization without the addition of cocatalyst. The other optimal conditions for ethylene polymerization were determined through optimizing the polymerization behavior. Cat. 5 with ligand L5 containing tetrafluorobenzene ring showed a catalytic activity of to 2.83 × 105 gP∙(molM) −1∙h−1 for this polymerization. The obtained polyethylene featured high weight average molecular weight of 8.6×105 g/mol. The molecular weight distribution of polyethylene obtained by these six catalysts were in 2.2 ~ 2.5, and the melting point was about 135 °C The reaction mechanism of ethylene polymerization was explored by HSAB. The results showed that when the substituent on the catalyst aniline was an electron withdrawing group, both the polymerization activity and the molecular weight of the obtained polymer were higher. Density Functional Theory (DFT) results indicated that ethylene was more inclined to react with one of the M―C bonds of the catalyst. The energy barrier for the ethylene insertion reaction by Cat. 5 was the lowest, compared to other catalysts except Cat. 1 , which made ethylene insertion reaction easier. These ligands containing electron withdrawing groups on aniline ring made the catalytic active species more stable. Much higher molecular weight of polyethylene was produced by utilizing these catalysts with the ligands containing electron withdrawing groups on aniline ring. These experimental results were consistent with those of HSAB and DFT.
Effect of Uniaxial Tension on Piezoelectric Response of PVDF Film
Ji-tian Wang, Zhuo Chen, Yu-qi Wang, Yi-fan Chu, Meng Pan, Li-jie Dong
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20099 doi: 10.11777/j.issn1000-3304.2020.20099
[Abstract](959) [FullText HTML] (531) [PDF 1192KB](2)
In order to prepare organic piezoelectric materials with good piezoelectric properties and enhance the intrinsic piezoelectric properties of the poly(vinylidene fluoride) (PVDF) crystal phase, a solution coating film-forming process was adopted to prepare PVDF films. The films with different stretch ratios (R = 3,5,7) were made by uniaxial stretch process. The morphology and structure of the films were investigated by scanning electron microscope (SEM), transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC). Gold electrode is sprayed on the surface of the film and then the film is subjected to high-voltage electric field polarization treatment. Connect the films to the sampling multimeter to further study the piezoelectric properties of the films. It shows that uniaxial stretch can increase the crystallinity of PVDF and promote the transformation of α phase into β phase. During the stretch process, the molecular segments of PVDF are highly oriented to form the β phase of the all-trans conformational structure. The larger the stretch ratio, the higher the crystallinity of PVDF and the higher the relative content of the polar β phase. When the stretch ratio is 7, the relative content of β phase increases to 85.12%, which is 1.5 times higher than that of the unstretched film. Since the intrinsic piezoelectric properties of PVDF are controlled by its crystalline β phase content, the larger the stretch ratio, the better the ferroelectric and piezoelectric properties of the film. The film exhibits the best electrical properties when it is stretched 7 times: When the applied electric field is 200 MV/m, the residual polarization intensity reaches 2.69 μC/cm2. When the strain is 5%, the average output current density is 58.92 nA/cm2, and the average output voltage is 89.70 mV. In this study, the single-axis stretched PVDF film has a high voltage sensing sensitivity, and a PVDF film in a small area size (22 mm × 4 mm) can provide an output voltage as high as 89.70 mV. Therefore, the material can be used to produce ultra-thin, lightweight portable electronic devices in ideal shape, and is expected to be used as a flexible touchable sensor to obtain biomechanical energy from the human body for health monitoring.
Synthesis of Primary Amine Functionalized Styrene/Butadiene Copolymer and Contol of Its Composition Distribution
He-yu Shen, Xue-fei Leng, Li Han, Lin-can Yang, Chao Li, Song-bo Zhang, Lan Lei, Hong-wei Ma, Yang Li
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20107 doi: 10.11777/j.issn1000-3304.2020.20107
[Abstract](636) [FullText HTML] (385) [PDF 0KB](1)
The styrene/butadiene copolymer is widely used as elastomer in various applications of packing material, such as shoes, asphalt modifiers, etc. The control of structure is the key to control the properties of material. Living anionic polymerization is still state of the art for the precise preparation of SBC. However, the sequence distribution of the copolymerization of styrene and butadiene cannot be as precise as that of styrene and DPE derivatives, because the product of reactivity ratios of styrene and butadiene is not approximately equal to 0. The composition distribution control was proposed to describe the behaviour of monomers in the statistical anionic copolymerisation. Herein, the primary amine DPE derivative was copolymerized with styrene and butadiene. In the terpolymerization, two primary amine functionalized SBC with similar molecular weight but different composition distributions were synthesized by varying feeding orders (i.e. ran-NFSBC and grad-NFSBC). The kinetics of copolymerizations were calculated. In ran-NFSBC, the reactivity ratio of St to DPE derivative was 2.58. The conversion of primary amine DPE derivative was 71.7%. The composition distribution was random distribution. In grad-NFSBC, the primary amine DPE derivative was totally consumed. The composition distribution was determined to be gradient distribution using the timing sample method. Finally, the relationship between composition distribution and thermal behavior of SBC was preliminarily studied by DSC.
Enhancement of Nonleaching Antimicrobial PVA/PHMG Hydrogels
Wuling Gong, Dafu Wei , Shaotian Zhang, Jingyun Ye, Anna Zheng, Yong Guan
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20080 doi: 10.11777/j.issn1000-3304.2020.20080
[Abstract](788) [PDF 0KB](16)
A novel nonleaching antimicrobial polyvinyl alcohol/poly(hexamethylene guanidine) hydrochloride (PVA/PHMG) hydrogel was prepared by freezing-thawing method. The Hydrogen bond interaction between PVA and PHMG confirmed by ATR-FTIR spectra endowed the nonleaching characteristic of PVA/PHMG hydrogels. These antimicrobial hydrogels behaved above 99.9% of antimicrobial rates against both Escherichia coli and Staphylococcus aureus. The PVA-0.100% PHMG hydrogel had 120% higher tensile strength than pure PVA hydrogel. Furthermore, PVA/PHMG/GO (graphene oxide) hydrogel and PVA/PHMG/SiO2 hydrogel also showed nonleaching antimicrobial properties and the antimicrobial rates were above 99.99%. The hydrogen bond interactions among reinforcing agents, PVA and PHMG significantly enhanced the tensile strength of the hydrogel. The tensile strengths of PVA/PHMG/GO and PVA/PHMG/SiO2 hydrogels were 1.6 times and 3.3 times of that of PVA/PHMG hydrogels, respectively. This work opens up a simple approach to develop nonleaching antimicrobial PVA hydrogels for potential application in biomedical field.
Effects of Particle-polymer Interactions and Particle-particle Interactions on Mechanical Properties of Polymer Nanocomposites
Shao-fan Li, Xiang-ning Wen, Wei-long Ju, Yun-lan Su , Du-jin Wang
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20189 doi: 10.11777/j.issn1000-3304.2020.20189
[Abstract](64) [PDF 0KB](0)
Polymer nanocomposites (PNCs) possess excellent performance such as superior mechanical, thermodynamic and optical properties compared to the traditional polymer materials. It is a vital issue to probe the enhancement mechanism of the PNCs inclusion of nanoparticles (NPs). However, it is still unclear about the relationship between interaction and mechanical enhancement due to the various factors in PNCs. Considering the successes and failures in the previous study, this review summarizes the enhancement mechanism in PNCs from the perspective of particle-polymer interaction and particle-particle interaction. Moreover, according to the different structural properties of PNCs, the influencing factors are discussed in polymer/unmodified NPs nanocomposites and polymer/polymer-grafted NPs (PGNPs) nanocomposites, respectively. We hope 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.
Effect of Matrix Molecular Motion Ability on PTC Behaviors of PVDF/CF Composite
Ren-peng Liu, Hui-zhao Zou, Yan-hao Huang, Zheng-ying Liu , Wei Yang, Ming-bo Yang
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20181 doi: 10.11777/j.issn1000-3304.2020.20181
[Abstract](7) [PDF 0KB](0)
Conductive polymer composites with positive temperature coefficient (PTC) effect have been widely utilized in electronic industry due to their low density, excellent processibility and abundant adjustability. At the melting temperature, the phase transition of crystalline region results volume expansion, which leads to a dramatic increase of the volume resistivity of the composite. Therefore, the PTC performances are highly correlated with the melting process and melt properties of polymer matrix, which means the motion ability of molecules chain during matrix melting has influences on the performances of the composite such as PTC intensity and reproducibility. Making a thorough inquiry of the effects of polymer molecular motility on PTC behaviors is helpful for the design and fabrication of polymer based PTC materials with highly sensitive response to temperature and stable reproducibility in heating-cooling cycles. In this study, the resistance-temperature characteristic of carbon fibers (CF) filled poly(vinylidene fluoride) (PVDF) composites with varied melt viscosity of PVDF was investigated. All the samples showed significant PTC effect during heating processes without negative temperature coefficient (NTC) effect even at the temperature much higher than the melting point of polymer matrix. It can be found that the PTC transition temperature range depended only on the chemical structure and crystallinity of PVDF, while the cyclic stability of PTC behavior was significantly affected by the motion ability of the matrix molecules. For the PVDF(710)/CF composite with matrix of stronger molecular motion, during the heating cycles, the molecular chains possibly stuck to the fillers surface to form an insulating layer, which resulted in wider gaps between fillers to reduce tunneling current. After cooling, the reconstruction of conductive paths in composites was impeded, resulting in higher resistivity at room temperature and lower PTC intensity and worse reproducibility. On the contrary, in the PVDF(5130)/CF composites with higher matrix viscosity, the molecular chains with weaker motion ability would not cover CF particles. The composite could almost rebuild the conductive paths to the initial condition after heating-cooling cycles, which resulted a better PTC reproducibility and stable resistivity at room temperature. When it was applied in the circuit overheat protection device, the PVDF(5130)/CF composite shut off the current timely at 167°C and recovered the circuit when cooled down, exhibited excellent sensitivity and reproducibility as thermal responsive switch.
Synthesis and mechanical property investigation of epoxy liquid crystal elastomer material
Hai-feng Lu, Meng Wang, Shuai Huang, Xu-man Chen, Zhi-yang Liu, Hong Yang
, Available online  , doi: 10.11777/j.issn1000-3304.2020.20197 doi: 10.11777/j.issn1000-3304.2020.20197
[Abstract](163) [PDF 0KB](1)
This manuscript reports an epoxy liquid crystal elastomer material prepared by photo-initiated cationic polymerization. Most of the traditional liquid crystal elastomers are based on polyacrylate or polysiloxane systems and prepared by thermal or photo-initiated free-radical polymerization. However, the free-radical polymerization is easily inhibited by oxygen gas and causes high volume shrinkage during the curing process, which results in large internal stress. In order to address these drawbacks, we design and synthesize a new liquid crystal monomer and a crosslinking agent bearing epoxy groups. The epoxy liquid crystal elastomer is prepared by in-situ cationic polymerization/crosslinking using iodonium salt as the photo-initiator. Compared with the traditional liquid crystal elastomers, the volume shrinkage is small during the photo-initiated cationic reaction and the photo-curing process will not be interfered by oxygen gas. The liquid crystallinity and mechanical properties of the epoxy liquid crystal elastomer material are systematically characterized. The results show that epoxy liquid crystal elastomer material prepared by photo-initiated cationic polymerization possess advantageous mechanical properties than the traditional polyacrylate/polysiloxane liquid crystal elastomers.
  • Editor: Xi Zhang

    Establishment Time: 1957

    Adminidrated by: Chinese Academy of Sciences

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