聚醚酰亚胺热焓松弛的分子量依赖关系

采用ＤＳＣ对不同分子量的聚醚酰亚胺的等温及动态热焓松弛行为进行了研究，并以ＫＷＷ方程对实验数据进行了非线性拟合。结果表明，分子量对热焓松弛的影响是由高分子端基引起自由体积的差异所致。不同分子量的聚醚酰亚胺分子具有不同数量的端基，淬冷时端基数目的差异将产生不同数量的过剩自由体积，从而影响松弛热焓及松弛速率、低分子量的聚醚酰亚胺松弛相对较快，且起始热焓高，松弛的表观活化能亦较小。     

Preparation of aligned polyetherimide fiber by electrospinning

Fifteen to 20 wt % polyetherimide (PEI) solutions with 1-methyl-2-pyrrolidinone (NMP) were prepared. The electrical conductivity and surface tension of the solutions were determined. The fiber spinning technique of electrospinning was optimized in order to prepare unidirectionally aligned, structurally oriented nanofiber tows. The morphology of the PEI fibers was investigated using field emission scanning electron microscopy (FESEM). The well-aligned fibers with diameters between 0.58 and 0.90 μm (FESEM) were collected by electrospinning 20 wt % PEI solutions with NMP in the range of 8–10 kV onto a target rotating with a surface velocity 9.8 m/s. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Wear characteristics of some internally lubricated and reinforced engineering polymer composites

An interesting characteristic of abrasion is the dependence of the wear rate on the particle size of the abrasive grits used to lubricate the abrasive papers. Three types of polymers, PTFE, PA, PI, several of their composites, and three metals were selected for studying the effect of particle size on wear rate. The pins were abraded against Sic abrasive papers of various mesh sizes under constant loading in multi-pass conditions. For some of the polymers and their composites (PA and PEI) the size effect on wear rate was similar to that for the metals. Beyond a critical particle size, no increase in wear was found with increasing particle size. On the other hand, PTFE, PI, and their composites showed the opposite effect. SEM and EDAX were used to investigate the related mechanisms.     

Toughening of epoxy resins with thermoplastics. Ii. Tetrafunctional epoxy resin-polyetherimide blends

A series of blends has been prepared by adding a polyetherimide (PEI), in varying proportions, to a tetrafunctional epoxy resin, tetraglycidyl-diaminodiphenylmethane (TGDDM), cured with 4,4′-diaminodiphenylsulphone (DDS). All the materials exhibited two-phase morphologies which were characterised by dynamic mechanical thermal analysis and scanning electron microscopy. Addition of the thermoplastic gave a modest improvement in fracture properties (K_1c and G_1c), as determined by three-point bending experiments, although no obvious correlation with the marked morphological changes was observed.     

Interlaminar Fracture Toughness of CF/PEI and GF/PEI Composites at Elevated Temperatures

An experimental study has been conducted to assess temperature effects on mode-I and mode-II interlaminar fracture toughness of carbon fibre/polyetherimide (CF/PEI) and glass fibre/polyetherimide (GF/PEI) thermoplastic composites. Mode-I double cantilever beam (DCB) and mode-II end notched flexure (ENF) tests were carried out in a temperature range from 25 to 130°C. For both composite systems, the initiation toughness, G _IC,ini and G _IIC,ini, of mode-I and mode-II interlaminar fracture decreased with an increase in temperature, while the propagation toughness, G _IC,prop and G _IIC,prop, displayed a reverse trend. Three main mechanisms were identified to contribute to the interlaminar fracture toughness, namely matrix deformation, fibre/matrix interfacial failure and fibre bridging during the delamination process. At delamination initiation, the weakened fibre/matrix interface at elevated temperatures plays an overriding role with the delamination growth initiating at the fibre/matrix interface, rather than from a blunt crack tip introduced by the insert film, leading to low values of G _IC,ini and G _IIC,ini. On the other hand, during delamination propagation, enhanced matrix deformation at elevated temperatures and fibre bridging promoted by weakened fibre/matrix interface result in greater G _IC,prop values. Meanwhile enhanced matrix toughness and ductility at elevated temperatures also increase the stability of mode-II crack growth.     

Preparation and characterization of sulfonated polyetherimide/polyetherimide blend membranes

Polyetherimide (PEI) was sulfonated by chlorosulfonic acid (CSA) in 1,2‐dichloroethane for the first time. With the increase of the CSA/PEI repeat unit ratio and/or reaction time, the ion‐exchange capacity (IEC) of the sulfonated polyetherimide (SPEI) increased accordingly. Water‐uptake testing and contact‐angle measurement showed that the hydrophilicity of the SPEI increases with the increase of the IEC. Membranes were fabricated from SPEI/PEI blends with different ratios. The morphologies of the blend membranes were examined by scanning electron microscopy, which showed that the membrane pore size is larger when SPEI with higher IEC was used. With the increase of SPEI ratio in the blend membranes, the membrane pore size also increased. The contact‐angle data of the membranes showed that the hydrophilicity of the blend membrane was elevated because of the sulfonate group on the SPEI molecular backbone. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1709–1715, 2004     

Optimization of high temperature energy storage properties of PEI-based composite dielectric based on rapid in-situ growth of inorganic functional layer

The serious deterioration of the energy density of polymer energy storage dielectrics in high temperature environment is the main reason to curb the in-depth application of dielectric film capacitors in the field of modern electrical and electronic engineering. Here, aiming at the problem of low dielectric constant of polymer dielectric, a simple, low-cost method is proposed to grow inorganic polar functional layer on surface of polymer film in situ, which effectively improves the polarization characteristics of polymer dielectric at high temperature. The in situ growth of Ti(OH)₄ inorganic polar functional layer on surface of polyetherimide (PEI) film noteworthy to improve the energy storage performance of dielectric film. The energy storage density of 4.59 J/cm² is obtained at 150°C and 600 MV/m, which is 1.18 times that of PEI film under the same condition. The significant enhancement of high temperature energy storage density can be attributed to introduction of functional layer, which effectively improves the dielectric properties and polarization intensity of dielectric film. Furthermore, the facile preparation method provided in this paper can be applied to various thin films under the premise of controllable cost, which is of great significance to improve the high temperature energy storage characteristics of polymer dielectric.     

ODPA-ODA型聚醚酰亚胺膜的预氧化机理

为了开发新型高性能炭膜前驱体材料,研究了ODPA-ODA型聚醚酰亚胺膜经430~530℃空气氛围的预氧化机理.借助热重分析、红外光谱、元素分析及x-射线衍射等手段,分析了预氧化温度对预氧化膜的溶解度、柔韧度、表面官能团、元素质量分数及微观结构的影响.结果表明:优化预氧化过程是制备无缺陷高质量炭膜的关键.预氧化可提高热稳定性,形成的交联结构有利于提高残炭量和成膜性.随预处理温度的提高,交联程度提高,但当温度高于490℃时会发生过渡氧化.     

Dehydration of Isopropanol by Pervaporation Using Aromatic Polyetherimide Membranes

Abstract

Aromatic polyetherimide membranes were prepared by the phase inversion method and tested for the pervaporation separation of water from isopropanol with emphasis on the breaking of azeotropic composition and the dehydration of high concentrations of isopropanol. It was found that the membrane selectivity was enhanced by partial evaporation of the solvent in the cast polymer films prior to the gelation step during membrane formation. The membrane performance was shown to be dependent on the feed concentration and the operating temperature. At a feed temperature of 25°C and a permeate pressure of 133 Pa, separation factors of 173 and 384 were achieved for the dehydration of isopropanol solutions at 0.68 (azeotropic composition) and 0.96 mole fractions isopropanol, respectively, with reasonably high permeation rates. The utility of the membranes for the proposed separation was demonstrated; however, these membranes were not prepared under optimized conditions and thus a continuous study is required to rationalize the effects of membrane preparation parameters on membrane performance.