Polymer Chemistry
·
2022
·Vol. 13
·期 16
·2375-2382
·
IF 5.364
Shuai Zheng,Lei Jiang,Changqi Zhang,Ning Ma,Xueqiang Liu
This study described a facile and environmentally friendly method for preparing polyimide (PI) aerogels via a sol–gel process and freeze-drying without the use of organic solvents. The prepared PI aerogels showed excellent mechanical properties. Their compressive strength can reach 4 MPa, which was mainly due to the 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA) and phenylenediamine (PDA) used in the synthesis of their fully aromatic backbone. The PI aerogels obtained here showed low bulk densities (0.098–0.143 g cm−3), low shrinkage (10%), high specific surface areas (334–389 m2 g−1) and high porosity (92%). In addition, the PI aerogels exhibited excellent thermal stability and thermal insulation properties. The onset decomposition temperature of the PI aerogel was up to 560 °C while the thermal conductivity at room temperature was 0.036–0.038 W m−1 K−1.
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JOURNAL OF MEMBRANE SCIENCE
·
2022
·
IF 10.53
Zitian Liu,Rongrong Qiang,Ligang Lin,Xuesong Deng,Xu Yang,Kongyin Zhao,Jing Yang,Xinyang Li,Wensong Ma,Meina Xu
Selective filtration of dyes and inorganic salts is a challenge for the treatment of textile wastewater containing high salt contents. In this study, selective separation performance of PI/SiO 2 nanofiltration (NF) membrane for dye/inorganic salt mixtures was substantially improved through directional modulation of its thermal treatment parameters after phase inversion. After thermal modification, the pore size, porosity and roughness were reduced, and the mechanical strength was improved. The PI/SiO 2 membrane under optimized thermally-modified conditions (M6, heat treatment conditions: 50 °C for 8 min) possessed high porosity of 79.95%. Besides, the thermally-modified PI/SiO 2 membrane revealed high water permeance of 152.87 L m −2 h −1 ·bar −1 with efficient rejection performance for a variety of typical dyes. In single dye filtration tests, the thermally-modified PI/SiO 2 membrane displayed high rejection (>90%) for Coomassie Brilliant Blue (CBB), Congo Red (CR), Trypan Blue (TB) and Direct Black 38 (DB 38), and exhibited excellent permeance (84.21–133.76 L m −2 h −1 ·bar −1 ). In addition, the thermally-modified PI/SiO 2 membrane could selectively separate dyes and inorganic salts. The membrane exhibited high dye rejection (>90%) and low inorganic salt rejection (<10%) for the filtration tests of CR + NaCl/Na 2 SO 4 and CBB + NaCl/Na 2 SO 4 mixed solutions (2 g L −1 ). In particular, the permeances of the thermally-modified PI/SiO 2 membrane (89.45–130.21 L m −2 h −1 ·bar −1 ) were higher than those of many contemporary NF membranes used for the same type of dye/inorganic salt separation. In conclusion, the present study presents a simple, inexpensive and effective thermal modification means, which shows great promise in the selective filtration of industrial dye wastewater.
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HIGH PERFORMANCE POLYMERS
·
2022
·
IF 1.73
Kangkang Tao,Fei Qin,Yahui Li,Shuai Zhang,Shihui Han,Guangmin Liu,Jun Wang,Jun Shen,Zailin Yang,Yi Tang,Gaohui Sun
Polyimide (PI) films with excellent mechanical and electrical properties were produced at a low temperature assisted by microwave. Depending on the reciprocating movement of dipole molecules excited by microwave, even though under a low temperature, the rotation and conformational changes of functional groups could also be promoted. Thus, reaction between N-H bond and -OH in carboxyl which could realize dehydration and cyclization of polyamic acid proceeded normally. Results revealed that the combination between ambient temperature only at 70°C and microwave power at 2000 W or higher could also produce PI films with imidization degree of 100%. For PI-2000W, compared with traditional PI film (PI-300°C) that generated only at temperature of 300°C, even though on the basis of no any change in molecular structure and addition of filler, the tensile strength, elastic modulus, crystallinity, and apparent density increased by about 21%, 51%, 37%, and 5%, respectively. For electrical properties, conductivity enhanced by one to two orders of magnitude comparing with PI-300°C. Results indicated that while keeping the original molecular structure of PI films unchanged, this work provided a new and effective method to assist the enhancement in mechanical and electrical properties of PI films.
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POLYMER COMPOSITES
·
2022
·Vol. 43
·期 12
·8737-8748
·
IF 3.531
Qingtao Lv,Xin Sun,Chunhong Zhang,Yanjian Liu,Qiang Wang,Lijia Liu,Chao Wang,Hao Wei,Xiaohui Liang
Excellent impedance matching plays a crucial role in the design of absorbers to tackle the growing problem of electromagnetism pollution. Here, a porous nickel–zinc ferrite/polyaniline/polyimide (Ni Zn Fe 3 O 4 /PANI/PI) composite was prepared by in-situ polymerization and thermally assisted non-solvent-induced phase separation (TNIPS). The impedance matching of porous Ni Zn Fe 3 O 4 /PANI/PI composite can be improved by controlling the composition ratio of Ni Zn Fe 3 O 4 /PANI absorbing filler. When the absorbing filler satisfied a molar ratio of 8:2 for Ni to Zn and a mass ratio of 2:8 for PANI to Ni Zn Fe 3 O 4 , the porous Ni Zn Fe 3 O 4 /PANI/PI composite with 20% absorbing filler content displayed the minimum reflection loss of −30.01 dB, effective absorption bandwidth of 4.05 GHz (6.91–10.96 GHz), and the impedance matching (Z) value almost equal to 1 at 9.36 GHz. In addition, the initial thermal decomposition temperature ( T 5 %) of porous Ni Zn Fe 3 O 4 /PANI/PI composite beyond 544°C in nitrogen, demonstrates superior thermal stability properties. The porous Ni Zn Fe 3 O 4 /PANI/PI composite in this research has great application potential in electromagnetic wave absorption at high-temperature environment.
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PROGRESS IN ORGANIC COATINGS
·
2022
·
IF 6.206
Kaiming Yang,Junshan Yuan,Yuanbo Zhang,Rui Liu,Weixu Feng,Gaofeng Shang,Hongxia Yan
The weak adhesion and tribological properties of polyimide (PI) restrict its practical application as bonded solid lubricating coatings in high-tech fields. Herein, a novel PI bonded solid lubricating coating was prepared using hyperbranched polysiloxane containing Si-O-C chain segments (HBPSi) and MoS 2 /reduced graphene oxide (rGO) heterostructured particles. Surprisingly, the adhesion, average coefficient of friction, wear life and load carrying capacity of the PI bonded solid lubricating coating can achieve level 1, 0.03, 550 s and 3400 N, respectively. In particular, the average coefficient of friction in the stabilization stage is reduced by 91.4 % compared to the pure PI coating, which is superior to that of most reported polyimide coatings. This is attributed to the synergistic enhancement effect of “soft-hard” particles between HBPSi and MoS 2 /rGO heterostructured particles. Furthermore, this work provides an important direction for the design and preparation of high-performance bonded solid lubricating coatings.
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高影响因子
CHEMICAL ENGINEERING JOURNAL
·
2021
·
IF 13.273
Shuaizhen Li,Zhibo Zheng,Siwei Liu,Zhenguo Chi,Xudong Chen,Yi Zhang,Jiarui Xu
High-efficiency heat-dissipation materials are in urgent need in microelectronics industry in 5G era. However, large-scale, low-cost, and high-efficiency preparation technologies still have great challenges. Here, ultrahigh thermal and electric conductive graphite films prepared by graphite-phase carbon nitride (g-C 3 N 4 ) catalyzed graphitization of polyimide film (PI) were reported for the first time. The graphite film obtained from 0.25 wt% g-C 3 N 4 catalyzed polyimide graphitization (G0.25) has homogeneous and perfect graphene structure and state-of-the-art properties. The d -spacing of the graphite layers is about 0.335 nm, which is similar to the ideal layer thickness of graphene (0.334 nm). The thermal conductivity is 1781 W·m −1 ·K −1 and the conductivity is 1.63 × 10 6 S·m −1 , which is 1.49 and 2.18 times of graphite film from pure PI film, 1.94 and 2.34 times of graphite film from commercialized Kapton film (I-film), respectively. The thermal conductivity of G0.25 film is 4.52 times of Cu and 7.46 times of Al. More importantly, the addition of g-C 3 N 4 can reduce the graphitization temperature from 2800 to 2500 ℃, which can reduce the energy consumption by 20.5% in the whole polyimide graphitization process. The developed preparation technology has important guiding significance and very attractive industrial application value for the preparation of large-scale, low cost and high-quality heat dissipation materials.
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COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS
·
2021
·
IF 4.539
Yizhi Zhao,Zhigang Shen,Xiaojing Zhang
Graphene and graphene/nanoparticles were explored to enhance the atomic oxygen (AO) corrosion resistance of polyimide (PI) composites. Graphene flakes (EGs) were produced by electrochemical method using alternating current (AC). A series of EGs/PI composite films were prepared by in-situ polymerization. After exposure to AO, although all EGs/PI composite films were resistant to AO, we found a much greater enhancement, i.e. adding 1.5 wt% EGs can reduce the mass loss of the composite by 42%. On this basis, EGs/SiO 2 and EGs/Al 2 O 3 co-doping fillers were firstly used to further enhance the AO corrosion resistance of PI. The sample co-doped 1.5 wt% EGs with 3 wt% SiO 2 could achieve a 71% decrease in the composite’ mass loss. Bonding effect and barrier effect of graphene fillers are responsible for the enhanced protective performance. At the same time, the “synergistic effect” between EGs and nanoparticles also plays a role in the enhancement. These preliminary but interesting results pave a novel way for the study of AO corrosion resistance.
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MACROMOLECULAR MATERIALS AND ENGINEERING
·
2021
·Vol. 307
·期 2
·2100645
·
IF 4.367
Weiwang Chen,Sha Liu,Yueyan Sun,Xiaomeng Zhou,Fenglei Zhou
Polyimide aerogels are promising for diverse applications owing to their nano-porous structure and superior properties. However, the shrinkage of melamine-crosslinked polyimide (MPI) aerogels has greatly compromised their performance in practical applications. In this study, supercritical drying with ethanol rather than CO 2 is employed to enhance their in-use shape stability at high temperatures. The structure, thermal insulation, mechanical strength of the resultant aerogels as well as their shape stability are characterized. Experimental results reveal that the shape stability of MPI aerogels during use is greatly improved thanks to the in-advance baptism of supercritical ethanol drying. The aerogel shrinks by only 2.64 vol.% after being treated at 280 °C for 72 h. Besides, the MPI aerogel shows enhanced compressive strength and can easily support a load more than 20 000 times its own weight. The thermal conductivity of these aerogels varies from 0.034 to 0.046 W m −1 k −1 , indicative of remarkable performance in thermal insulation. In addition, the aerogels that started to decompose at as high as 500 °C also perform well in thermal stability and char forming. It can be envisaged that the developed MPI aerogels with greatly improved in-use shape stability may have broad prospects for thermal insulation at high temperatures.
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SEPARATION AND PURIFICATION TECHNOLOGY
·
2021
·
IF 7.312
Peiyu Jia,Junjie Liu,Jingjing Kong,Mingming Hu,Ning Qi,Zhiquan Chen,Shan Xu,Nanwen Li
Two series of 6FDA-based co-polyimide membranes were synthesized by adding different diamine monomer containing special functional groups: APAF (containing OH) and DABA (containing -COOH). The ODA/APAF and ODA/DABA series were heat treated at 450 °C and 350 °C, respectively. Thermal rearrangement of polymer chain segments is confirmed in ODA/APAF membranes by infrared spectroscopy, while addition of DABA in ODA/DABA membranes causes decarboxylation crosslinking. Positron lifetime measurements reveal existence of ultramicropores in polyimides. The thermal rearrangement in ODA/APAF membranes induces remarkable increase in both size and number of ultramicropores and therefore increase in fractional free volume (FFV), but the crosslinking in ODA/DABA causes significant decrease in both size and number of ultramicropores. The increase in FFV is favorable for gas permeation, but too large size of the micropore drastically deteriorates the gas selectivity. Finally, the ODA/APAF(3:7) shows a high CO 2 permeability of 127.4 Barrer with CO 2 /CH 4 selectivity of 34.2, which surpasses the 1991 Robeson upper bound. Besides, the ODA/DABA(3:7) exhibits a H 2 permeability of 22.6 Barrer with H 2 /CH 4 selectivity of 256.8, which also exceeds the 1991 Robeson upper bound. Our results indicate that the gas permeability and selectivity of polymer membranes can be effectively adjusted by tailoring the ultramicropore structures, and positron can provide precise information about micropores.
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TRIBOLOGY INTERNATIONAL
·
2021
·
IF 4.872
Xinle Yao,Sen Liu,Zhongying Ji,Rui Guo,Chufeng Sun,Yuxiong Guo,Xiaolong Wang,Qihua Wang
Three-dimensional (3D) target-region-lubrication printing of photosensitive polyimide (PSPI) filled with polytetrafluoroethylene (PTFE), i.e., PSPI-PTFE, with excellent tribological properties for self-lubricating devices was realized by digital light processing of PSPI-PTFE ink and thermal post-treatment. The 3D-printed PSPI-PTFE composites exhibited the friction coefficients and wear rates sharply reduced by 88% and 98%, respectively, and good mechanical properties , thermal stability and interlayer bonding as well. Importantly, the surfaces with lubricating only in regions where needed were readily realized due to the layer-by-layer manufacturing manner of 3D printing . As proof-of-concept, a target-region-lubricating bearing was demonstrated successfully, which run stably with a speed ranged from 60 to 180 rpm/min, indicating that the 3D-printed PSPI-PTFE composites are suitable for fabricating devices with complex and special shapes.
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Advanced Fiber Materials
·
2021
·Vol. 4
·期 1
·108-118
·
IF 0
Li Jianwei,Zhang Xuanning,Lu Yuyan,Linghu Keliang,Wang Chen,Ma Zhonglei,He Xinhai
The separator with excellent mechanical and thermal properties are highly required for lithium ion batteries (LIBs). Therefore, it is crucial to develop novel nanofibrous membranes with enhanced mechanical strength and thermal stability. In this work, the fluorinated polyimide (FPI) was synthesized and blended with polyvinylidene fluoride (PVDF) to fabricate composite nanofibrous membranes (CNMs) via electrospinning method. Benefiting from the introduction of aromatic FPI, the prepared PVDF/FPI nanofibrous membranes were endowed with enhanced mechanical strength and thermal stability. When the FPI content increased from 0 to 30 wt%, the tensile strength of composite nanofibrous membranes enhanced from 1.57 to 2.30 MPa. Moreover, there are almost no dimensional shrinkage for the CNM-30 containing 30 wt% FPI after heat treatment at 160 °C for 1 h. Furthermore, the prepared CNMs show improved electrochemical performances in comparison with neat PVDF and commercial Celgard membranes. The electrolyte uptake and ionic conductivity of the CNMs could reach to 522.4% and 1.14 ms·cm −1 , respectively. The prepared CNMs could provide an innovative and promising approach for the development and design of high-performance separators.
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TRIBOLOGY INTERNATIONAL
·
2021
·
IF 4.872
Lisong Dong,Jian Wu,Danyang Cao,Xin Feng,Jiahua Zhu,Xiaohua Lu,Liwen Mu
Liquid metal (LM) can be well distributed in polyimide (PI) coatings by ultrasonic shear into 1–2 μm diameter. The LM incorporated PI (PI-LM) coatings show remarkably enhanced tribological properties when the coating slide against GCr15 steel ball at room temperature, while the mechanical properties are slightly reduced. When the filling amount is 8%, the wear is just 10% of pure PI and the friction coefficient can be reduced by 31.6%. During friction process , the LM microspheres are squeezed to the frictional interface and form a transfer film together with PI debris, achieving lower wear and friction coefficient. These results show that PI-LM coatings have high potential as advanced self-lubricating materials.
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