Papers by Keyword: Polyimide

Abstract: In this paper, we treated MWNTs by Fendon oxidation method and mixed acid method, finding the factors of functionalized effect affecting MWNTs. And added MWNTs treated to PI matrix for the study of the impact of MWNTs treated on thermal properties of the films. We using 3,3^/,4,4^/-diphenyl ether tetraacid dianhydride (ODPA) and 4,4'-diamino diphenyl ether (ODA) as raw material, mixing functional MWNTs and monomer by situ polymerization, then MWNTs / PAA hybrid glue was prepared. The molecular weight and distribution of the polyamic acid were measured by gel permeation chromatography (GPC), and the effects of different addition amounts on the product were examined. The PI/MWNTs films were prepared using an automatic film applicator, and finally the PI films were obtained by thermal imidization. The thermal behavior of the imidization process of the product was determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). The results showed that the PAA film has thermodynamic behavior at 150 ° C and 280 ° C approximately, which could be regarded as the kinetic interruption temperature of the imidization reaction. The dehydration cyclization reaction mainly occured in these two temperature ranges, moreover, the addition of MWNTs had no significant effect on the thermal decomposition temperature of the material which doping amount that does not affect the mechanical strength.

Abstract: This study presents the results of an analysis of the influence of joint mechanical activation of a polyimide matrix and tungsten (IV) oxide (WO₂) on the mechanical properties of their composites. Mechanical activation of the powder components of the matrix and the filler is performed in a vortex jet mill. The ultimate tensile strength, tensile modulus and relative elongation at break of the composites are all investigated. When using mechanical activation, an increase in tensile strength of 9% is observed with a content of 30 wt.% WO₂ filler and of 12% with a content of 70 wt.% WO₂ filler compared to composites in which the joint mechanical activation of components is not used. Using scanning electron microscopy, it is shown that the use of mechanical activation by dispersing in a jet-vortex mill made it possible to achieve a uniform distribution of highly dispersed filler based on tungsten dioxide in a polyimide matrix.

Abstract: A new approach for manufacturing ultrathin free-standing polyimide film was proposed. This approach involves casting polyamic acid solution to a Al-doped zinc oxide film coated substrate sputtered at room temperature and to form polyamic acid film. The polyamic acid film was released from substrate in 0.5% diluted hydrochloric acid. Then polyamic acid was reattached to glass substrate and was transformed into polyimide film by thermal imidization with gradient heat treatment process. After that, thickness of the1000 nm polyimide film was reduced by KrF excimer laser ablation with 100 pulses at 45 mJ/cm² and 30 pulses at 75 mJ/cm², and 200 nm free-standing polyimide film was obtained. By this method, free-standing polyimide films of 1000 nm and 200 nm thickness were fabricated without and with excimer laser ablation reduction, respectively.

Abstract: Poly (diethylene glycol) adipate diol, tolylene-2,4-diisocyanate, 1,3-bis (3',4-dicarboxylphenoxy) benzene and 1,4-bis (4'-aminophenoxy) biphenyl were used as monomers to form statistical copoly (urethane-imide) s with variable content of imide blocks (from 37 to 65% (wt)). The copolymers imide blocks on the T_g and T_m values relative content increasing effect was traced, which is associated with the phase separation of hard imide and flexible polyester blocks in the systems studied.

Abstract: Selective Laser Sintering (SLS) is close to be accepted as a production technique (Additive Manufacturing). However, one problem limiting employment of SLS for additive manufacturing in a wide-ranging industrial scope is the narrow variety of applicable polymers.In the present work, a thermoplastic semi-crystalline polyimide powder was synthesized.. The shape, size and fractional composition of such powder were investigated by scanning electron microscopy. As a result, polyimide powders with a fairly narrow particle size distribution were formed. On the basis of the polyimide powder, samples were obtained in the form of films by the method of selective laser sintering (SLS). The mechanical properties of these samples were investigated depending on a laser energy density. The morphological study of the films cross-sections showed that monolithic sample having insignificant pores and irregularities in the structure was formed

Abstract: In this paper, melamine was used as porogen to prepare porous polyimide film by in-situ polymerization. The mechanical properties, thermal properties, dielectric properties, oil content and friction and wear properties of polyimide films with different porosity were investigated. The tensile strength of porous films decreases obviously with increase of melamine content. It shows the lower thermal decomposition temperature and the faster decomposition speed compared with the non-porous film, indicating higher heat exchange rate due to holes in porous films. As the porogen content increases, the dielectric constant decreases significantly, and the film with melamine content of 20 wt.% has the lowest dielectric constant of 2.43. The holes lead to good oil storage performance and the wear rate and the friction coefficient decrease with the increase of porosity. Keywords: polyimide; porous; melamine; dielectric; friction

Abstract: Polyimide films with Al₂O₃ composite layers were prepared by KOH solution surface hydrolysis, ion exchange and heat treatment. Scanning electron microscope (SEM), atomic force microscopy (AFM), X-ray diffractometry (XRD), thermo gravimetric analyzer (TGA), breakdown voltage tester, high frequency pulse voltage machine were performed to characterize the micromorphology, thermal stability, mechanical properties, electric breakdown strength, and corona resistance time of composite films. Results indicated that the thermal properties of the composite film are better than the original film. The corona resistance time of the composite film was longer than that of the pristine film. The composite film had the longest corona resistance time and reached 101.2min while the KOH treatment time was 90min.

Abstract: Interaction of high energy electrons with spacecraft materials, such as polyimide (PI, Kapton-H®), is known to cause their physical degradation. However, understanding of the chemical nature of this damage and the effect on the electrical and optical properties of PI is still limited. This lack of understanding limits predictive spacecraft models (charging, thermal, etc) as only pristine material properties are used for calculation. This is a major source of error in spacecraft construction and anomaly resolution, since PI properties change after exposure to the space environment. In the presented study, we analyze the chemical, electrical, and optical changes to polyimide after exposure to 90 keV electrons.

Abstract: Space exploitation and development need high-performance polymer based tribo-materials in order to reduce the weight and improve the reliability of mechanical moving components. However, the wear resistance of polymer composites will decrease after space irradiation. In order to improve the anti-irradiation and wear resistance, the high performance polyimide (PI) composites reinforced with aramid fibers (AF), filled with polytetrafluoroethylene (PTFE) and Al₂O₃ were designed and prepared using hot press sintering. The effect of the individual atomic oxygen or proton irradiation as well as both on the tribological properties of the PI composites were systematically investigated against Si₃N₄ ball on a ball-on-disk test rig under simulating space environment system, and coefficient of friction and wear rate were considered as responses. The worn surfaces of the composites were observed by scanning electrical microscopy to reveal wear mechanisms of the materials’ damage. Experimental results indicated that the wear rate of the PTFE/AF/PI greatly increased after atomic oxygen and proton irradiation due to oxidation degradation effect on the polymer matrix. However, filling Al₂O₃ nano-particles into polyimide matrix can improve the wear resistance because of oxidation layer, gradually formulated during the process of atomic oxygen irradiation, which can protect the polymer composites and avoid further oxidation. This study will expect to provide the helpful guidance for designing high performance polymer based frictional materials in the application of space science.

Abstract: Recently, many researchers focus on the nanoscale fillers to enhance electrical properties of composite due to the uniqueness of material. In this study, polyimide/barium titanate (BaTiO₃) nanofibers films were prepared by incorporating electrospun BaTiO₃ nanofibers with polyimide derived from 2,2-Bis [4-(4-aminophenoxy) phenyl] propane (BAPP) and 3,3',4,4'-Biphenyl tetracarboxylic dianhydride (BPDA). The obtained nanofibers were modified with (3-Glycidyloxypropyl) trimethoxysilane as coupling agent before integrating into the polyimide matrix. Microstructure and dielectric properties of BaTiO₃ nanocomposites were investigated. The results showed BaTiO₃ nanofibers were successfully produced at nanoscale regime and well dispersed in the hybrid film after modification and ultrasonication method. Dielectric constant of the nanofibers films were improved and increased with increasing of BaTiO₃ nanofibers concentration while dielectric loss remains relative low.