Mechanical properties and structure of glassy and semicrystalline random copolymers of poly(ethylene terephthalate) and poly(ethylene naphthalene-2,6-dicarboxilate)

The microhardness,H, of random copolymers of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalene-2,6-dicarboxilate) (PEN) was determined over a wide range of compositions. It is shown that microhardness of the materials is strongly affected by the composition. The mechanical property,H, of the quenched amorphous copolyester films is discussed in terms of a simple model given by the additivity values of the single componentsH _a ^PET andH _a ^PEN . In materials containing up to 30% PEN, crystals of PET are found after annealing at temperatures 10 °C below their melting points. In materials containing 80% PEN, after annealing at about 20 °C below the melting point, crystals of PEN are formed. The observed deviation ofH for the crystallized films from the additive behaviour of the single components can be quantitatively related to two factors: the changes occurring in the crystallinity value and in the thickness of PET and PEN crystals.     

Correlation of microhardness and morphology of poly(ether-ether-ketone) films

We have applied microindentation to a series poly(ether-ether-ketone) films crystallized at different temperatures from the melt and from the glass to measure their microhardness. The morphology of the samples was characterized by X-ray diffraction, density measurements and differential scanning calorimetry. The results show that a relationship between microhardness, density and degree of crystallinity can be established for samples crystallized at various temperatures from both the glass and the melt. The values of the microhardness of the crystalline component of the samples can be correlated with the lamellar thickness of the polymer crystals.     

聚醚醚酮纤维的制备、性能及应用

介绍了聚醚醚酮(PEEK)纤维的制备方法及纺丝工艺,总结了PEEK纤维的优异性能;阐述了PEEK纤维的应用领域;综述了PEEK纤维当前国内外的研究开发概况;并提出我国应加大PEEK纺丝级原料及相应纺丝设备的研发,尽快实现PEEK纤维国产化。     

Preparation and characterization of poly(indole-3-carboxaldehyde) film at the glassy carbon surface

Indole-3-carboxaldehyde (In3C) monomer was oxidized by electrochemical methods at the glassy carbon (GC) electrode in 0.05 M tetrabutylammonium tetrafluoroborate in acetonitrile, with the aim to prepare a modified electrode. Modification was performed using cyclic voltammetry (CV) scanning from 0.0 V to 2.0 V at a scan rate of 50 mV s^− 1 for 10 cycles in 1 mM In3C monomer solution. The modified GC surface (In3C-GC) was characterized by CV response of potassium ferricyanide and ferrocene redox probes as well as by the electrochemical impedance spectroscopy. The modified surface was analyzed by reflection-absorption infrared spectroscopy and compared with the spectrum of the monomeric In3C. Elemental composition of the surface was determined by X-ray photoelectron spectroscopy. Contact angle measurements was also performed to check the changes in hydrophobic character of the bare GC and compared to that of In3C-GC surface. Thickness of the oligomeric/polymeric film was investigated by ellipsometric measurements and a surface confined polymerization mechanism was proposed.     

原位聚合羟基磷灰石/聚醚醚酮复合材料

通过原位聚合法制备HA/PEEK复合材料,利用X射线衍射仪、红外光谱仪、差示扫描量热仪、扫描电镜对PEEK、HA/PEEK复合材料进行表征。研究表明,基体PEEK的聚合过程受到一定的影响;HA颗粒在基体之中有着优异的分散性。将PEEK、HA/PEEK复合材料压模成型,通过拉伸试验和硬度测量检测材料的力学性能,结果表明,HA的加入对复合材料的力学性能产生较大的影响。     

Fracture mechanisms and fracture toughness in semicrystalline polymer nanocomposites

Polymer nanocomposites, especially nanoclay composites, have received much attention in recent years. While it is the functional properties of these composites that are the driving force, good mechanical properties are necessary in most applications. Although claims are made that the mechanical properties of nanocomposites should be excellent, in practice the mechanical properties are often disappointing. Soft or hard spherical particles can toughen semicrystalline polymers, but plate-like nanoclay particles have not produced any significant toughening action and frequently cause significant embrittlement. In this paper the toughening of semicrystalline polymers with nanoparticles, and particularly the difference in behaviour of spherical and plate-like particles is reviewed.     

聚醚醚酮增韧改性环氧树脂

采用共混法用聚醚醚酮(PEEK)改性环氧树脂(EP),借助差示扫描量热分析(DSC)确定了环氧树脂的固化工艺,测试了共混体系的工艺性能,研究了聚醚醚酮含量对环氧树脂力学性能的影响。借助扫描电子显微镜(SEM)对材料断裂面的形态结构进行了分析,探讨了体系的形态结构与冲击性能之间的关系。结果表明,在改性材料的韧性有所提高的同时,压缩强度、马丁耐热都没有降低。从断裂面的形态来看,是属于韧性断裂。当PEEK的加入量为6%时,韧性最好,达到19．1kJ/m~2,比纯的环氧树脂增加了107．6%。     

聚醚醚酮增韧改性环氧树脂

采用共混法用聚醚醚酮(PEEK)改性环氧树脂(EP),借助差示扫描量热分析(DSC)确定了环氧树脂的固化工艺,测试了共混体系的工艺性能,研究了聚醚醚酮含量对环氧树脂力学性能的影响.借助扫描电子显微镜(SEM)对材料断裂面的形态结构进行了分析,探讨了体系的形态结构与冲击性能之间的关系.结果表明,在改性材料的韧性有所提高的同时,压缩强度、马丁耐热都没有降低.从断裂面的形态来看,是属于韧性断裂.当PEEK的加入量为6%时,韧性最好,达到19.1 kJ/m2,比纯的环氧树脂增加了107.6%.     

Constitutive model for large strain deformation of semicrystalline polymers

A constitutive model for large strain deformation of semicrystalline polymers has been formulated to predict the complex elasto-viscoelastic-viscoplastic material response. The general form of this model can be represented by three parallel rheological components corresponding to each of the modes of deformation. It will be shown that such a configuration is well suited to the mechanical nature of polymers as observed in recent studies. The constitutive stress-strain-time relationships are drawn from continuum mechanics which are more suitable than simple linear expressions from rheology. The result is a large strain, fully three-dimensional constitutive model, derived from a thermodynamic basis. The proposed model can be fit to macroscopic experimental data and is highly suited to numerical analysis. The paper reviews the literature relevant to constitutive representation of semicrystalline polymers, provides conclusion and validation of the most suitable form of constitutive model and presents the relevant constitutive mathematics.     

Sputter deposition of semicrystalline tin dioxide films

Tin dioxide is emerging as an important material for use in copper indium gallium diselenide based solar cells. Amorphous tin dioxide may be used as a glass overlayer for covering the entire device and protecting it against water permeation. Tin dioxide is also a viable semiconductor candidate to replace the wide band gap zinc oxide window layer to improve the long-term device reliability. The film properties required by these two applications are different. Amorphous films have superior water permeation resistance while polycrystalline films generally have better charge carrier transport properties. Thus, it is important to understand how to tune the structure of tin dioxide films between amorphous and polycrystalline. Using X-ray diffraction (XRD) and Hall-effect measurements, we have studied the structure and electrical properties of tin dioxide films deposited by magnetron sputtering as a function of deposition temperature, sputtering power, feed gas composition and film thickness. Films deposited at room temperature are semicrystalline with nanometer size SnO₂ crystals embedded in an amorphous matrix. Film crystallinity increases with deposition temperature. When the films are crystalline, the X-ray diffraction intensity pattern is different than that of the powder diffraction pattern indicating that the films are textured with (101) and (211) directions oriented parallel to the surface normal. This texturing is observed on a variety of substrates including soda-lime glass (SLG), Mo-coated soda-lime glass and (100) silicon. Addition of oxygen to the sputtering gas, argon, increases the crystallinity and changes the orientation of the tin dioxide grains: (110) XRD intensity increases relative to the (101) and (211) diffraction peaks and this effect is observed both on Mo-coated SLG and (100) silicon wafers. Films with resistivities ranging between 8 mΩ cm and 800 mΩ cm could be deposited. The films are n-type with carrier concentrations in the 3 × 10¹⁸ cm^− 3 to 3 × 10²⁰ cm^− 3 range. Carrier concentration decreases when the oxygen concentration in the feed gas is above 5%. Electron mobilities range from 1 to 7 cm²/V s and increase with increasing film thickness, oxygen addition to the feed gas and film crystallinity. Electron mobilities in the 1-3 cm²/V s range can be obtained even in semicrystalline films. Initial deposition rates range from 4 nm/min at low sputtering power to 11 nm/min at higher powers. However, deposition rate decreases with deposition time by as much as 30%.     

Reinforcement of elastomeric poly(dimethylsiloxane) by glassy poly(diphenylsiloxane)

Some novel approaches were taken to provide the improvements in mechanical properties that are almost always necessary to prepare a commercially useful elastomer from poly(dimethylsiloxane) (PDMS) [-Si(CH₃)₂O-]. The reinforcement was provided by poly(diphenylsiloxane) (PDPS) [-Si(C₆H₅)₂O-], a hard glassy polymer, which was introduced into the PDMS by two rather different techniques. In the first, the PDPS was prepared separately by condensation polymerization of diphenylsilanediol and then solution-blended into the PDMS. In the second, it was generated by in situ polymerization of the same monomer absorbed into the PDMS network. The resulting materials were characterized by scanning electron microscopy and by stress-strain isotherms in elongation. At least under some conditions both techniques were found to be successful, leading to increases in ultimate strength by a factor of two or more.     

Studies on interface structure and crystal texture of poly(ether-ether-ketone)-carbon fibre composite

The interface structure of poly(ether-ether-ketone) (PEEK)-carbon fibre composite and the crystal texture of PEEK matrix have been studied by scanning electron microscopy (SEM) after the samples were properly etched by argon plasma. We find that most of the PEEK'S crystals are induced by nucleating carbon fibre and then they developed the transcrystalline or spherulite shape, depending on the crystallization conditions. Because the volume fraction of the carbon fibre is 60%, and the space distance between two adjacent carbon fibres is about 10 m–20 m, the crystal size of PEEK matrix is mainly controlled by the space distance between adjacent carbon fibres, and the crystallization temperature has little effect on it. The detail of the oriented crystal growth of the PEEK relative to carbon fibre was first observed by SEM. Our results show that the nucleation process of PEEK-carbon fibre composite is as follows: The first lamella is formed orientationally in the carbon fibre surface in the way that thea crystallographic direction is parallel to the radial direction of carbon fibre, theb direction parallel to the tangent line of cross section of carbon fibre, and thec direction parallel to the axis of the carbon fibre. Therefore, the crystals finally formed are oriented.     

Physical ageing studies in semicrystalline poly(ethylene terephthalate)

The physical ageing of semicrystalline poly(ethylene terephthalate) (c-PET) of different crystallinities and morphological structures was studied using differential scanning calorimetry. Samples of c-PET of crystallinity content _c = 0.12, crystallized at low temperatures (105 °C for 13 min), submitted to physical ageing in a temperature range between 50 and 65 °C for different periods of time, showed two endothermic peaks. The first peak (P₁) of higher intensity, appeared at a temperature close to the glass transition temperature, T _g, of the amorphous PET, and the other peak (P₂) of lower intensity, merged as a shoulder of the first one, at a higher temperature. These peaks have been attributed to the enthalpy relaxation process of two different amorphous regions: one amorphous phase outside the spherulitic structure (interspherulitic amorphous region) and another amorphous phase inside the spherulites (interlamellar amorphous region). The separation between P₁ and P₂ indicates that DSC, via enthalpy relaxation, is a good technique to detect the real double glass transition of the semicrystalline PET. However, the physical ageing of a semicrystalline PET of _c = 0.32, crystallized at 114 °C during 1 h, showed a main endothermic peak shifted to a higher temperature, which probably corresponds to the enthalpy relaxation of the more restricted interlamellar amorphous region, and a small endothermic peak at lower temperature which could be a reflection of the hindered interspherulitic amorphous region.     

The yield behaviour of poly(phenylenebibenzimidazole)

The compressive yield behaviour of poly(2,2-m-phenylene-5,5-bibenzimidazole) (PBI) has been studied over a wide range of temperatures. The tensile behaviour was also studied under superimposed hydrostatic pressure. In both cases wet and dry samples were examined and the results revealed the considerable effects of moisture on the mechanical properties of PBI. The results of all these tests show that PBI has a remarkably high shear yield stress at room temperature. This results in a very high compressive yield stress and a very high tensile yield stress observed under superimposed hydrostatic pressure when brittle failure from surface flaws is prevented. It is concluded on the basis of quantitative analysis that the yield mechanism in PBI at room temperature is initiation controlled, as in a metal or ceramic, rather than a velocity controlled, thermally activated, viscoelastic process which is generally considered applicable in polymers.     

Topology optimization of thermoelastic structures using level set method

This paper describes the topology optimization of thermoelastic structures, using level set method. The objective is to minimize the mean compliance of a structure with a material volume constraint. In level set method, free boundary of a structure is considered as design variable, and it is implicitly represented via level set model. Objective function of the optimization problem is defined as a function of the shape of a structure. Sensitivity analysis based on continuum model is conducted with respect to the free boundary, which suggests the steepest descent direction. A geometric energy term is introduced to ensure smooth structural boundary. Augmented Lagrangian multiplier method is adopted to enforce volume constraint. Numerical examples are provided for 2D cases, considering design independent temperature distribution.     

含有叔胺结构的聚醚醚酮单体的合成

通过三步反应合成了一种具有叔胺结构的聚醚醚酮单体,其结构经1H NMR1、3CNMR、IR和元素分析确证,同时讨论了影响反应的因素。     

Variational-asymptotic modeling of the thermoelastic behavior of composite beams

This paper deals with steady state thermoelastic problems in composite beam structure by using variational-asymptotic method. First, the original three-dimensional heat conduction problem is reduced to be a two-dimensional thermal cross-sectional analysis along with an optional one-dimensional heat conduction analysis. The one-dimensional heat conduction analysis exists only if the temperature is not prescribed at any point of the cross-section along the span except the end surfaces. Then we reduce the one-way coupled, three-dimensional thermoelasticity problem into a two-dimensional, one-way coupled thermoelastic cross-sectional analysis and a one-dimensional, one-way coupled, thermoelastic beam analysis. The present theory is implemented into the computer program, variational-asymptotic beam sectional analysis (VABS). Several examples are studied using the present theory and the results from VABS are compared with available analytical solutions and the three-dimensional analysis using the commercial finite element package ANSYS.     

A numerical investigation of the potential of rubber and mineral particles for toughening of semicrystalline polymers

The impact strength of many semicrystalline polymers can be improved by the dispersion of second-phase rubber particles. A criterion for the effect of this practice is based on the average interparticle matrix ligament thickness. The critical interparticle distance, below which a substantial toughness increase can be observed, is considered to be an intrinsic material property of the matrix. A toughening mechanism has recently been suggested which considers a layer of transcrystallized material around well-dispersed particles, having a reduced yield strength in certain preferentially oriented directions, thereby opening the possibility of using mineral fillers. In this work, the potential of toughening of semicrystalline polymeric material by local anisotropy in combination with soft rubber and hard mineral filler particles is investigated. The matrix material is modeled within the framework of anisotropic Hill plasticity with a rate dependent and hardening yield stress. Various particle/matrix interface conditions are used to study the role of debonding and cavitation. The presence of debonded moderately stiff or hard fillers is found to affect the shear yielding effect of local anisotropy that was found for voided material.     

聚醚醚酮改性研究进展

聚醚醚酮(PEEK)作为一种新型高性能热塑性工程塑料,在许多工程领域有着广泛的应用.采用不同手段增强PEEK,改善其加工性能和力学性能、热性能、摩擦学性能,有利于降低材料成本和进一步拓展应用范围.本文从纤维增强PEEK、颗粒填充PEEK、PEEK表面改性、与聚合物共混等方面综述了PEEK改性研究的进展情况.     

A mesoscale quantification method of cavitation in semicrystalline polymers using X-ray microtomography

The ability of X-ray microtomography to quantify the cavitation in highly strained semicrystalline polymers is investigated on polyvinylidene fluoride. The cavitation phenomenon is studied on Circumferentially Notched Round Bars tested in tension. The tensile deformation induces void formation as attested by the whitening of the notch and SEM observations. The aim of this paper is to highlight the interest of a non destructive method based on X-ray microtomography in order to quantify the developed porosity in the cavited area and to follow step by step after relaxation, or continuously the evolution of the porosity during a tensile test. As voids may have a submicrometric size, as attested by SEM images in PVF2, the X-ray microtomography does not intend to image all the voids but to quantify them as a whole, including the non resolved voids. The method is designed to be used either with a laboratory microtomograph or with a synchrotron microtomography device. The quantification uses the correlation between the attenuation coefficient of the material and the porosity developed in the material. The measure is first validated on synchrotron images. Then the method is adapted to the laboratory microtomography prone to beam hardening artefacts. The results obtained with both devices are compared to each other and compared to the results obtained from local SEM analysis. Finally, the analysis of notched tensile specimens with varying notch root radius is investigated after interrupted tests. The analyses of the in situ tensile tests and relaxation effects are described in another paper [16].