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Optimization of the spark plasma sintering processing parameters affecting the properties of polyimide 下载免费PDF全文
Maxime Schwertz Pierre Ranque Sébastien Lemonnier Elodie Barraud Adele Carradò Marie‐France Vallat Michel Nardin 《应用聚合物科学杂志》2015,132(9)
The present study deals with the optimization of polyimide (PI) mechanical properties, obtained by Spark Plasma Sintering (SPS), by using a method combining Design of Experiments (DOE) with physical, structural, and mechanical characterizations. The effects of SPS parameters such as temperature, pressure, dwell time, and cooling rate on the density, mechanical properties, and structure of PI were investigated. The experimental results revealed that the mechanical properties of the material were optimized by raising the sintering temperature up to 350°C. The optimized SPS processing parameters were a temperature of 350°C, a pressure of 40 MPa, and a dwell time of 5 min. Under these conditions, a relative density of 99.6% was reached within only a few minutes. The corresponding mechanical properties consisted of Young's modulus of 3.43 GPa, a Shore D hardness of 87.3, and a compressive strength of 738 MPa for a maximum compressive strain of 61.8%. Moreover, when working at 320°C and at 100 MPa, an increase in the dwell time was necessary to enhance the properties. Contrary to the other parameters, the cooling rate appeared to be a non‐significant parameter. Finally, correlations between the PI structure and the mechanical properties were made to demonstrate the densification mechanisms. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41542. 相似文献
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The copolyimide (co‐PI) fibers with outstanding mechanical properties were prepared by a two‐step wet‐spinning method, derived from the design of combining 4,4′‐oxydianiline (ODA) with the rigid 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA)/p‐phenylenediamine (p‐PDA) backbone. The mechanical properties of PI fibers were drastically improved with the optimum tensile strength of 2.53 GPa at a p‐PDA/ODA molar ratio of 5/5, which was approximately 3.7 times the tensile strength of BPDA/p‐PDA PI fibers. Two‐dimensional wide‐angle X‐ray diffraction indicated that the highly oriented structures were formed in the fibers. Two‐dimensional small‐angle X‐ray scattering revealed the existence of the needle‐shaped microvoids aligned parallel to the fiber axis, and the introduction of ODA led to the reduction in the size of the microvoids. As a result, the significantly improved mechanical properties of PI fibers were mainly attributed to the gradually formed homogeneous structures. The co‐PI fibers also exhibited excellent thermal stabilities of up to 563°C in nitrogen and 536°C in air for a 5% weight loss and glass transition temperatures above 279°C. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42474. 相似文献
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《Journal of Adhesion Science and Technology》2013,27(1):245-253
Ar ion beam etching (IBE) can be used to roughen a Cu surface and thus improve the adhesion of subsequently spin-coated polyimide (PI) films. During Ar IBE, the surface morphology of sputter-deposited Cu changes from round bumps to a rough cone structure. The ultimate tensile strength (UTS) of the PI/Cu interface is increased for certain specific beam conditions. Under optimal conditions, the UTS of the etched PI/Cu interface (6.2 MPa) is twice that of the unetched PI/Cu interface (3.1 MPa). Cu is detected in the deposited PI by Rutherford backscattering spectrometry (RBS). The amount of Cu at the top surface of the 2.5 μm thick PI film is 0.1 at. %; this is determined by RBS and XPS. While the Cu is dissolved by polyamic acid and diffuses into the PI, an oxygen-rich region is formed in the Cu. The oxygen-rich region in Cu grows from 50 A (approximately Cu2O) before PI deposition to more than 2000 A (where the oxygen concentration is about 5 at. %) after PI deposition. The oxygen source is not the PI itself but either dissociated oxygen from the water vapor in the PI imidization process or a product of the chemical reaction between Cu and polyamic acid. 相似文献
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Polyimide (PI)/modified layered double hydroxide (m‐LDH) nanocomposites were prepared in this study. For this work, m‐LDHs were prepared from layered double hydroxides (LDHs) through an anionic exchange reaction with pyromellitic dianhydride (PMDA), succinic acid or terephthalic acid. PMDA and 4,4′‐oxydianiline were used to make the poly(amic acid) precursor for PI. X‐ray diffraction and transmission electron microscopy measurements confirmed that the PMDA‐modified LDH (PMH) and terephthalic acid‐modified LDH (TMH) were well dispersed in the PI matrix. For the succinic acid‐modified LDH, some of the LDH was intercalated with the succinic acid molecules but most maintained its original structure. Thus, the PI/PMH and PI/TMH nanocomposites exhibited improved mechanical, thermal and electrical properties compared to pure PI. The PMH has aromatic groups and is expected to have better π–π interactions with the PI chains than the other m‐LDHs. Thus, the PI/PMH nanocomposites exhibited the best properties among the nanocomposites investigated. Copyright © 2010 Society of Chemical Industry 相似文献
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Xu Wang Shengliang Chen Yijun Yang Yi Chen Ming Li Xiangyang Liu 《Polymer International》2010,59(12):1622-1629
A series of polyimides (PIs) with side chains were fabricated from 6‐(4‐phenylphenoxy)hexyl‐3,5‐diaminobenzoate of various ratios with 4,4′‐oxydianiline and 4,4′‐oxydiphthalic anhydride. After PI alignment, films were directly fluorinated using a 10 vol% fluorine/nitrogen mix. The pretilt angle of liquid crystals on the PI films is much improved to more than 20°, and can be continuously controlled by changing the side‐chain content of the PI films from 20 to 100%. The change of the pretilt angles is ascribed to the fluorinated microstructure of molecules at the surface rather than to the surface energy or surface morphology. Moreover, the improvement of rigidity and the steric repulsion of the fluorinated side chains result in an upright conformation of the side chains that leads to the high pretilt angle. Copyright © 2010 Society of Chemical Industry 相似文献
50.
《Journal of Adhesion Science and Technology》2013,27(6):615-637
Ti-6A1-4V/FM-5 polyimide adhesively bonded double cantilever beam (DCB) specimens were aged for 12 months at elevated temperatures (177°C and 204°C) in one of three different environments: ambient atmospheric air pressure and reduced air pressures of 2 psi (13.8 kPa) and 0.2 psi (1.38 kPa), to assess bond durability. The FM-5 polyimide adhesive (Tg~ 250°C) is based on a polyimide developed by NASA Langley Research Center and is produced by Cytec Industries, Inc. Bonds aged for different times were tested to measure the critical strain energy release rate as a function of the temperature and environment. The greatest loss in bond strength occurred after aging in air at 204°C. Following thermal rejuvenation of the aged bonds at 300°C for 2 h, part of the strength loss could be recovered. This strength recovery was attributed to the reversal of physical aging in the adhesive resin. Further evidence for physical aging, which is a thermo-reversible phenomenon, was obtained from tests conducted on neat resin specimens using DMA (dynamic mechanical analysis) and DSC (differential scanning calorimetry). The unrecovered portion of the loss in bond strength following longer-term aging was attributed to chemical aging/degradation of the bonded 'system'. The 'system' in this study includes the adherends, the adhesive, the surface pretreatment (chromic acid anodization, CAA), and their respective interphase/interface regions. Evidence for chemical aging was also seen from weight loss, and Soxhlet extraction data on neat resin specimens. 相似文献