聚醚醚酮/碳纤维复合材料的界面结构以及结晶形态的研究

本文采用扫描电子显微镜观察经氩等离子刻蚀后PEEK/碳纤维复合材料的界面层结构和PEEK树脂的结晶形态。无论是从熔体还是从橡胶体结晶,PEEK树脂的结晶都是从碳纤维表面诱导开始,最后形成横穿晶体结构。在高碳纤维含量的复合材料中,PEEK的球晶尺寸主要由碳纤维之间的距离控制,受温度的影响较小。在PEEK/碳纤维复合材料的结晶过程中,第一片晶片在碳纤维表面取向生长方式为:晶体的ā轴(厚度方向)平行于维纤径 向。b轴(晶片生长方向)与纤维最小圆截面的切线重合,(?)轴(垂直晶片平面的方向)平行于纤维轴向。由于球晶成核过程是取向生长,因而生成的球晶也按一定的方式取向。     

PEEK-PEDEK嵌段共聚物非等温结晶动力学研究

PEEK以其优异的热稳定性和耐溶剂性被广泛应用在航空航天和电子电气等领域^[1].经过增强后的PEEK长期使用温度(UL温度指数)可达523 K.但在温度高于523 K的情况下,模量下降较快,这在一定程度上限制了其应用.在PEEK的分子链上引入刚性较强地联苯基团,可以有效的提高分子链的刚性,使聚合物的玻璃化转变温度得以提高^[2,3].我们曾合成了一系列含有刚性单体联苯二酚的嵌段共聚物,并对其热性能进行了研究^[4],本文着重对这一系列共聚物的非等温结晶动力学进行研究.     

Synthesis and properties of new fluorinated polymers bearing pendant imidazole groups for fuel cell membranes operating over a broad relative humidity range

New alternating copolymers comprising a chlorotrifluorinated backbone and imidazole‐terminated pendant ethylene oxide groups have been prepared with a view to their use as a component of proton‐conducting membranes in polymer electrolyte fuel cells. A vinyl ether containing an imidazole (Imi) function protected by a benzyl group (BVI) was first synthesized in a three‐step reaction. It was then copolymerized in solution with chlorotrifluoroethylene (CTFE) by conventional radical copolymerization leading to alternating poly(BVI‐alt‐CTFE) copolymers in good yields. Deprotection of the benzyl group under hydrogen produced a chlorotrifluorinated poly(Imi‐alt‐CTFE) copolymer. The polymer was subsequently used to form blend membranes with sulfonated poly(ether ether ketone) (sPEEK). The conductivity of blend membranes of poly (Imi‐alt‐CTFE) with sPEEK lies in the range of 4–10 mS cm^?1 at 40–70 °C and, for blend membranes rich in poly(Imi‐alt‐CTFE), is little dependent on relative humidity between 30 and 100%. It is surmised that the polymer and membrane composition favor microstructural phase separation into chlorotrifluorinated polymer backbone domains and regions in which imidazole groups are clustered. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 223–231, 2010     

Photodegradation of PEEK sheets under tensile stress

The photochemical reaction of poly(ether ether ketone) (PEEK) sheets under tensile loads has been investigated. Two types of UV irradiation tests were carried out in a vacuum environment: with and without a cooling apparatus. Chemical structures, thermal properties, and mechanical properties were measured to clarify photo-deterioration. Chemical analysis based on Fourier Transform Infrared Spectrometry (FT-IR) and X-ray Photoelectron Spectroscopy (XPS) showed photochemical scission caused by UV exposure. Thermal properties, measured by Differential Scanning Calorimetry (DSC), indicated that a crosslinking reaction occurred during the radiation tests. Tensile properties of PEEK sheets after UV radiation clearly showed a tendency to embrittlement affected not only by crosslinking but also by the orientation of molecular chains resulting from the temperature rise of the specimens. Furthermore, applied tensile stress during exposure accelerated molecular scission and disturbed the crosslinking effects of the tensile properties.     

Immunoaffinity chromatographic isolation of prostate-specific antigen from seminal plasma for capillary electrophoresis analysis of its isoforms

Prostate-specific antigen (PSA) concentration in serum has been the biomarker employed for prostate cancer diagnosis in the last two decades. However, new more specific biomarkers allowing a better differentiation of cancer from non-malignant prostate diseases are necessary. Glycosylation of PSA gives rise to different forms of the protein which can be separated into several isoforms by analytical techniques, such as CE. Because PSA glycosylation is influenced by pathological conditions, the CE pattern of PSA isoforms could be different in prostate cancer than in non-malignant prostate diseases. To study this CE pattern of PSA, prior purification of the protein from the biological fluid is mandatory. In this study an immunoaffinity chromatography method which allows PSA purification without altering the CE pattern is developed. An in-house prepared column produced with commercial anti-PSA antibodies is employed. The use of 1 M propionic acid as elution agent provides higher than 40% recovery of high purity PSA. CE analysis of PSA immunopurified from seminal plasma of a healthy individual shows the same 8 peaks as the commercially available PSA standard. Sample preparation only requires dilution with phosphate buffered saline prior to immunoaffinity purification. High repeatability for the sample preparation step was achieved (RSD% for percentage of corrected peak area in the range 0.6–5.3 for CE analysis of three independently purified seminal plasma aliquots compared to range 0.8–4.9 for a given aliquot analyzed three times by CE). IAC of five microliters seminal plasma provided enough PSA to achieve signal/noise ratio larger than 5 for the smallest CE isoforms.     

On-line sample processing involving microextraction techniques as a front-end to atomic spectrometric detection for trace metal assays: A review

Within the last decade, liquid-phase microextraction (LPME) and micro-solid phase extraction (μSPE) approaches have emerged as substitutes for conventional sample processing procedures for trace metal assays within the framework of green chemistry. This review surveys the progress of the state of the art in simplification and automation of microextraction approaches by harnessing to the various generations of flow injection (FI) as a front end to atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS) or inductively coupled plasma atomic emission spectrometry or mass spectrometry (ICP-AES/MS). It highlights the evolution of flow injection analysis and related techniques as vehicles for appropriate sample presentation to the detector and expedient on-line matrix separation and pre-concentration of trace levels of metals in troublesome matrices. Rather than being comprehensive this review is aimed at outlining the pros and cons via representative examples of recent attempts in automating green sample preparation procedures in an FI or sequential injection (SI) mode capitalizing on single-drop microextraction, dispersive liquid-phase microextraction and advanced sorptive materials including carbon and metal oxide nanoparticles, ion imprinted polymers, superparamagnetic nanomaterials and biological/biomass sorbents. Current challenges in the field are identified and the synergetic combination of flow analysis, nanotechnology and metal-tagged biomolecule detection is envisaged.     

Strength of poly-ether-ether-ketone: Effects of sterilisation and thermal ageing

This paper investigates the strength of polyether-ether-ketone (PEEK) after sterilisation and thermal ageing. PEEK specimens were divided into five groups, according to whether the specimens had been annealed, sterilised or aged. Specimens were subjected to either static or dynamic three-point bend tests. Static tests involved loading the specimens until a maximum displacement of 40 mm was reached. Dynamic tests involved applying a sinusoidally varying force at a frequency of 5 Hz. The maximum force applied to a specimen was based on a percentage of the static yield strength. Testing continued until failure or run out of 10 million cycles. Sterilisation and ageing resulted in no significant change in the static yield strength. Annealing was found to significantly increase the yield strength. For the dynamic tests, the fatigue strength was in the range 99.4 to 107.4 MPa; sterilisation and thermal ageing were found to have no effect on fatigue strength.     

Porosity‐dependent Young's modulus of membranes from polyetherether ketone

The porosity‐dependent Young's modulus for PEEK membranes was determined and the data compared to several empirical and semiempirical equations often applied to porous systems. The Spriggs equation, Wang's approximation, Sudduth's equation, and the foam modulus‐density relationship were all tested against the data. The relatively wide range of porosities tested in these experiments shows the Spriggs equation to be inadequate to fitting the data, especially above 50% porosity where the Young's modulus decreases rapidly. Wang's approximation to second order fitted the data well, and the porosity‐modulus relations had non‐negative coefficients as required and consistent with the ceramic data obtained by others. The data also fitted Sudduth's equations, usually applied to sintered ceramics, but equivalently good fits were obtained with nonunique fitting parameters. The foam modulus‐density relationship fitted the data for foamlike membranes but fitted less well to nonfoam morphology membranes. Finally, the data were used to determine the range of porosities and hollow fiber dimensions necessary for microfiltration and composite membrane application. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1168–1174, 2003     

Aminated polyacrylonitrile blends with cellulose acetate

Polyacrylonitriles (PANs) were synthesized and aminated with ethylene diamine (2DA), hexamethylene diamine (6DA), and dodecane diamine (12DA), followed by blending with cellulose acetate (CA). Effects of amination and chain length of diamine on the miscibility of the aminated PAN with CA were studied. Scanning electron microscopy (SEM) micrographs of cryogenically fractured surfaces of the blends showed coarse elliptical dispersions of CA in PAN. The dispersed CA domains decreased in size with an increase in aminated PAN content. The dispersed domain size further decreased with increasing chain length of diamine. and eventually the morphology became almost homogeneous with 12DA-modified PAN blends. With increasing chain length of the diamines, the dynamic loss peak temperature of PAN in blends showed a movement toward that of CA. Fourier transform infrared (FTIR) measurements showed that the specific interaction between the aminated PAN and cellulose acetate is the hydrogen bonding between aprotic hydrogen in aminated PAN and the ester carbonyl of CA, the interactions being increased with increasing chain length of diamine.     

Yielding behavior of glassy polymers. I. Free-volume model

Rigid, glassy polymers show a diversity of tensile behavior-ranging from apparently brittle to ductile. To delineate some of the factors that control the toughness or impact resistance of these polymers, the yielding behavior of poly (methyl methacrylate) (PMMA) was studied. Results of other workers have shown that the cold flow exhibited by many glassy polymers can be explained qualitatively by a free-volume model. The treatment assumes that molecular flow is permitted when the free volume increase, resulting from the dilatational component of the applied stress, is sufficient to bring the total free volume to that characteristic of the polymer liquid. The present study refines this approach by introducing an “effective temperature,” defined as that hypothetical temperature at which the glass would have an equilibrium free volume equal to the total free volume of the nonequilibrium glass at temperature T. Equations are derived which more satisfactorily describe the temperature and strain-rate dependences of the tensile yield strain of PMMA glass from -10° to 90°C at rates between 0.015 and 120%/sec.