Linear thermoelastic characterization of anisotropic poly(ethylene terephthalate) films

All nine independent elastic constants have been determined for a biaxially stretched poly(ethylene terephthalate) (PET) film using novel mechanical methods. The orthotropic directions and the in‐plane Poisson's ratios were first characterized using vibrational holographic interferometry of tensioned membrane samples. The out‐of‐plane Poisson's ratio was obtained by measuring the change in tension with the change in pressure for constant strain conditions. Pressure–volume–temperature (PVT) equipment was used to measure the bulk compressibility as well as the volumetric thermal expansion coefficient (TEC). The in‐plane Young's moduli were obtained by tensile tests, while the out‐of‐plane modulus was calculated from the compressibility and other elastic constants that describe the in‐plane behavior. The in‐plane TECs in the machine and transverse directions were determined using a thermal mechanical analyzer (TMA). The out‐of‐plane TEC was determined using these values and the volumetric TEC determined via PVT. The resulting compliance matrix satisfies all of the requirements of a positive‐definite energy criterion. The procedure of characterization utilized in this article can be applied to any orthotropic film. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2937–2947, 2002     

Simulation and Validation of Thermo‐mechanical Stresses in Planar SOFCs

To study possible failure modes of the Hexis Galileo solid oxide fuel cell stack, various stack components such as nickel/yttria stabilised zirconia anodes, lanthanum strontium manganese cathodes, 3 mol%‐yttria stabilised zirconia electrolytes and chromium alloy metallic interconnectors have been characterised with respect to their thermo‐mechanical properties. Specifically, coefficients of thermal expansion, Young's moduli, bending strengths, Poisson's ratios and fracture toughnesses have been measured. Furthermore, the temperature‐dependent warpage of complete cells has been investigated by video analysis. All experimental data were taken as input parameters for a set of finite element models to analyse various thermo‐mechanical phenomena on different length scales. The simulations offer an explanation for the often observed ‘saddle‐like‘ deformations of cells at room temperature. They also show that cracks that first develop within the anode induce local tensile stresses within the electrolyte and hence represent a weakening mechanism for the cells. It is shown that the induced electrolyte stresses depend on the anode crack density. The electrolyte stresses decrease as the distances between the anode cracks become smaller.     

Auxetic polypropylene films

Auxetic materials are those exhibiting negative Poisson's ratio (ν) behavior. Polymeric auxetic extruded products in the form of cylinders and fibers have previously been reported. This article reports the successful production of auxetic polypropylene films (～0.15‐mm thick) using a melt extrusion process. Video extensometry and tensile testing techniques have been used to measure the in‐plane Poisson's ratios and Young's moduli of the auxetic film, both on an Instron tensile testing machine and a Deben microtensile testing machine. The film is elastically anisotropic with the Poisson's ratio and Young's modulus along the extrusion (x) direction being ν_xy = ?1.12 ± 0.06 and E_x = 0.34 ± 0.01GPa, respectively, while the Poisson's ratio and Young's modulus in the transverse (y) direction to the extrusion direction are ν_yx = ?0.77 ± 0.01 and E_y = 0.20 ± 0.01GPa, respectively. POLYM. ENG. SCI., 45:517–528, 2005. © 2005 Society of Plastics Engineers     

Determination of poisson's ratio for polyimide films

The Poisson's ratios of polyamic acid and polyimide films were determined using a high pressure gas dilatometer. In this technique, a sample is held at constant length and a hydrostatic pressure is applied to the sample. The resulting change in stress on the sample with applied pressure provides a measure of Poisson's ratio. For fully cured polyimide films based on pyromellitic dianhydride and oxydianiline, Poisson's ratio was measured to be 0.34 at approximately 1% strain. This value increases to 0.48 as the strain is increased to 5%.     

Ultrasonic determination of mechanical moduli of oriented semicrystalline polymers

Ultrasonics has been used for the determination of the mechanical properties of oriented semicrystalline polymers through time-of-flight measurements of elastic waves propagating in various directions within the material. While being nondestructive, such a method allows one to obtain more mechanical moduli with a better accuracy than the conventional tensile tests, especially regarding the shear properties and the Poisson's coefficients. Until now, the approach used to interpret the data was approximate and not rigorous. We present here a self-consistent rigorous approach for interpreting time-of-flight data based on the group velocity including allowance for lateral displacement of the transmitted beam. Results are presented for roll-drawn PET with various draw ratios. These samples are considered to have transversely isotropic symmetry. For the Young's moduli, comparisons are made with conventional tensile tests and the differences observed are interpreted in terms of viscoelastic efforts considering both the amorphous and crystalline phases.     

Elastic properties of adhesive polymers. I. Polymer films by means of electronic speckle pattern interferometry

The elastic modulus and Poisson's ratio of seven different polymers frequently used as wood adhesives and/or matrix polymers in wood‐ and natural‐fibre‐reinforced composites, respectively, were determined by means of tensile tests. Specimen deformation during testing was measured by means of a mechanical extensometer and an electronic speckle pattern interferometry system, respectively. The results from both methods show an excellent correlation for the elastic modulus. The elastic moduli of the studied polymers cover a wide range from 0.47 GPa for polyurethane to 6.3 GPa for melamine–urea–formaldehyde, whereas Poisson's ratios show less variability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3936–3939, 2007     

Ester-type photosensitive polyimide precursor with low thermal expansion coefficient

For an ester-type photosensitive polyimide precursor of low thermal expansion coefficient, the oxygen concentration in the curing process and the molecular weight of the polyimide precursor were found to control the properties of the polyimide. The effects of these factors on the thermal expansion coefficient, tensile strength, and modulus of polyimide film were investigated. Based on these results, a photosensitive polyimide with low thermal expansion coefficient, called the PIMEL TL-series, was developed. Crack and delamination free multilayers were successfully achieved using this newly developed product.     

Preparation and properties of APPSSQ‐like/polyimide hybrid composites

Hydrolysis and condensation proceeded to generate 3‐aminopropyl polysilsesquioxane‐like (APPSSQ‐like) particles from 3‐aminopropyl triethoxysilane. An APPSSQ‐like particle includes two domains: crosslinking Si? O? Si networks inside and 3‐aminopropyl groups outside the particle. The APPSSQ‐like/polyimide (APPSSQ‐like/PI) hybrid composites were prepared from a solution of poly(amic acid) (PAA, polyimide precursor) and APPSSQ‐like particles using N,N‐dimethylacetamide as a solvent. Scanning electron microscopy (SEM) showed that the APPSSQ particle sizes were about 100 nm, and there was no obvious phase separation between the APPSSQ‐like particles and the PI matrix in the fracture surfaces of the hybrid films. Owing to the highly crosslinked Si? O? Si networks inside the APPSSQ‐like particles, the APPSSQ‐like/PI hybrid composites possessed desired properties such as improved thermal resistance and reduced coefficients of thermal expansion (CTE). The presence of covalent bonds between the APPSSQ‐like particles and the PI molecules improved the compatibility between these two components. Thus, the tensile strength increased with the APPSSQ‐like content, and the elongation at break also slightly increased with the APPSSQ‐like content. The initial tensile and storage moduli of the APPSSQ‐like/PI hybrid composites increased with the APPSSQ‐like content, which indicates that the mechanical properties of these hybrid composites were enhanced by the incorporation of the APPSSQ‐like content in the PI matrix. Furthermore, the glass transition temperatures of these composites increased with the APPSSQ‐like content because the adhesion between the APPSSQ‐like particles and the PI molecules restricts the PI chains' mobility. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2865–2874, 2003     

Solid and thermal properties of ABA‐type triblock copolymers designed using difunctional fluorine‐containing polyimide macroinitiators with methyl methacrylate

BACKGROUND: ABA‐type poly(methyl methacrylate) (PMMA) and fluorine‐containing polyimide triblock copolymers are potentially beneficial for electric materials. In the work reported here, triblock copolymers with various block lengths were prepared from fluorine‐containing difunctional polyimide macroinitiators and methyl methacrylate monomer through atom‐transfer radical polymerization. The effects of structure on their solid and thermal properties were studied. RESULTS: The weight ratios of the triblock copolymers derived using thermogravimetric analysis were shown to be almost identical to the ratios determined using ¹H NMR. The solid properties (film density and maximum d‐spacing value) and thermal properties (glass transition and thermal expansion) were shown to be strongly dependent on the weight ratios of both PMMA and polyimide components. Furthermore, a porous film, which showed a lower dielectric constant of 2.48 at 1 MHz, could be prepared by heating a triblock copolymer film to induce the thermal degradation of the PMMA component. CONCLUSION: The use of the polyimide macroinitiator was useful in the preparation of ABA‐type triblock copolymers to control each block length that influences the solid and thermal properties. Additionally, the triblock copolymers have great potential in preparing porous polyimides in the application of electric materials as interlayer insulation membranes of large‐scale integration. Copyright © 2009 Society of Chemical Industry     

高温热处理对聚酰亚胺薄膜性能的影响

研究了高温热处理对聚酰亚胺(PI)薄膜拉伸性能和热性能的影响。在薄膜完全环化后,随着热处理温度的升高,薄膜的拉伸强度、弹性模量先增大后基本保持不变,断裂伸长率先保持不变后明显降低,热膨胀系数也显著降低,而薄膜的玻璃化转变温度略有增大。高温热处理工艺可制备高强度和低热膨胀系数的高性能PI薄膜。     

Synthesis,structure and properties of polyimide–silica hybrid composites based on biphenyltetracarboxylic dianhydride

A simple and efficient way of synthesizing nanocomposite films using a dispersion technique is reported, with the resulting films having improved mechanical and thermal properties. Nano‐SiO₂ was used in a biphenyltetracarboxylic dianhydride‐based poly(amic acid) precursor and found to be dispersed up to 7 wt% without any additives. The composites were cast to make 10 µm solid films to establish structure and property relationships between liquid and solid film. The structures of the liquid composite materials were studied using NMR and Fourier transform infrared spectroscopy. Solid film properties such as tensile strength, contact angles and thermal behaviour were evaluated for comparison. The properties of the composite films were found to be enhanced compared to polyimide film itself. Atomic force microscopy and macroscale mechanical measurements showed that composite films with more dipolar bonding interactions have higher elastic moduli and are more deformable. They yield higher adhesion energies, and therefore composite coatings offer greater adhesion. There was a limitation in the film formation beyond 5 wt% of silica. Copyright © 2011 Society of Chemical Industry     

Grafting of telechelic poly(lactic‐co‐glycolic acid) onto O2 plasma‐treated polypropylene flakes

An operating window, which is bounded by two temperatures and draw ratios, defines the stable and defect‐free stretching region of a polymer film. Physical properties including the coefficient of thermal expansion (CTE), birefringence, and Young's modulus of a recyclable polyimide (PIR) film were measured under stretching conditions. While values of birefringence and Young's modulus increased with increasing stretching stress in the machine direction, the CTE was found to decrease. A semiempirical model for the prediction of birefringence and Young's modulus under stretching conditions was developed, from which the CTE could be estimated from the Young's modulus data. Theoretically evaluated physical properties were found to be in qualitative agreement with the experimental data. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Carbon nanotube reinforced rigid‐rod polyimide

Multiwalled carbon nanotube/rigid‐rod polyimide composite films have been prepared by casting a solution of precursor polymer (polyamide acid) containing multiwalled carbon nanotubes (MWNTs) into thin films, followed by a thermal imidization treatment. The composite films were characterized by FTIR, TEM, DSC, TGA and TMA, and the film tensile properties were also examined. The presence of 1.0% MWNTs in the polymer matrix led to more than twofold increase in tensile strength of the rigid‐rod polyimide composite films and improved thermal stability, but reduced in thermal deformation. However, the tensile property did not show further increase when the film contained higher composition of MWNTs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Technique development and measurement of Poisson's ratio,lateral creep behavior,and thermal and hygroscopic expansion of individual layers in magnetic tapes

An experimental technique was developed to measure the Poisson's ratio (lateral contraction over longitudinal elongation), lateral creep, and both thermal and hygroscopic expansion of thin polymeric films. A so‐called profile‐matching method was developed to measure the lateral and longitudinal deformation with the help of a laser scan micrometer. A thermomechanical analyzer was used to measure the coefficient of thermal expansion (CTE). The laser scan technique was also used to measure the coefficient of hygroscopic expansion (CHE). The measurements were performed on magnetic tapes, substrates, and tapes with front coat or back coat, or with both coats stripped. A model based on the rule of mixtures was developed to determine the Poisson's ratio, lateral and longitudinal deformation behavior, and thermal expansion of the front coat and back coat. To investigate the mechanical degradation of the substrates during tape manufacturing, the data for substrate with the front and back coats removed from the tape, were compared with the data for the never‐coated virgin film. The relationship between the molecular structure and the degradation mechanism of the substrates is discussed. The magnetic tapes used in this research include two metal particle (MP) tapes and two metal evaporated (ME) tapes that use polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) substrates. Longitudinal and lateral deformation tests were performed at 25 ± 0.5°C and 50 ± 2%RH, and thermal expansion was measured from 15 to 70°C. The CHE was measured at 25 ± 0.5°C and 15–80%RH. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2082–2096, 2003     

Correlations of the temperature and pressure dependencies of the elastic constants of zircon

The temperature dependencies of the single crystal elastic constants and the isotropic elastic moduli of zircon were reevaluated using the ultrasonic in-phase frequencies vs. temperature data and the thermal expansion coefficients. The bulk moduli of zircon at different temperatures were also calculated using the recently derived analytical expression by Garai and Laugier (J. Appl. Phys. 101, 023514 (2007)) utilizing the Anderson–Grüneisen parameter (δ) obtained from the pressure dependencies of the single crystal elastic constants. The temperature derivatives of the bulk modulus of zircon evaluated from the temperature derivatives of the single crystal elastic constants agree well with the corresponding values calculated from the analytical expressions utilizing the pressure derivative of the bulk modulus (δ). The results reveal good correlations between the ultrasonic measurements of the pressure and temperature derivatives of the single crystal elastic constants of zircon.     

Facile fabrication of macroporous polyimide films with pores distributing on one side

Herein, we report on direct preparation of macroporous polyimide (PI) films with pores distributing on one side, the method of which relies on sedimentation of ceramic spheres in polyamic acid (PAA) solutions in a gravitational field and imidization of PAA/ceramic spheres mixtures to obtain PI/ceramic spheres hybrid films followed by curing in dilute hydrofluoric (HF) acid. In this strategy, the curing of the hybrid films in HF acid leads to the formation of pores. The introduction of pores makes the room‐temperature dielectric constants of the macroporous films lower than that of pure PI film. Moreover, the macroporous PI films have improved Young's moduli and higher thermal stability in nitrogen atmosphere. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 261–266, 2007     

Preparation and characterisation of polyamide–polyimide organoclay nanocomposites

BACKGROUND: Ternary nanocomposites containing an organomodified layered silicate polyimide additive within a polyamide matrix have been investigated to gain greater insight into structure–property relationships and potential high‐temperature automotive applications. RESULTS: Polyamide nanocomposite blends, containing 3 wt% of organoclay, were prepared and compared with organoclay‐reinforced polyamide and neat polyamide. Nanoclay addition significantly increased heat distortion temperature, as well as both the tensile and flexural moduli and strength. The addition of polyimide demonstrated further increases in heat distortion temperature, glass transition temperature and the flexural and tensile moduli by about 17, 21 and 40%, respectively. The tensile and flexural strengths were either unaffected or decreased modestly, although the strain‐to‐failure decreased substantially. Morphological studies using transmission electron microscopy (TEM) and X‐ray diffraction showed that the nanoclay was dispersed within the ternary blends forming highly intercalated nanocomposites, regardless of the presence and level of polyimide. However, TEM revealed clay agglomeration at the polyamide–polyimide interface which degraded the mechanical properties. CONCLUSIONS: A range of improvements in mechanical properties have been achieved through the addition of a polyimide additive to a polyamide nanocomposite. The decrease in ductility, arising from the poor polyamide–polyimide interface and nanoclay clustering, clearly requires improving for this deficiency to be overcome. Copyright © 2008 Society of Chemical Industry     

以BAPP为原料的热塑性PI薄膜的合成及性能

以芳香长链二胺2,2-双[4-(4-氨基苯氧基)苯基]丙烷(BAPP)为二胺原料,与最具商业价值的四种酸酐均苯四甲酸二酐(PMDA)、3,3′,4,4′-联苯四酸二酐(BPDA)、3,3′,4,4′-二苯酮四酸二酐(BTDA)、3,3′,4．4′-二苯醚四酸二酐(ODPA)为二酸酐原料,采用二步溶液缩聚法制得了一系列均聚和共聚聚酰亚胺薄膜。利用FTIR表征了聚酰亚胺的结构,并用DSC、TOA、TMA DMA等手段测得了不同聚酰亚胺的Tg、5%与10%热失重温度、线膨胀系数、拉伸强度、断裂延伸率、热压粘接T型剥离强度等性能数据。     

Effects of dispersion and arrangement of clay on thermal diffusivity of polyimide‐clay nanocomposite film

Polymer‐clay nanocomposites are well‐known high‐performance materials with a superior tensile modulus. However, in the case of composites with polyimide (PI), additional functions require study because PI is a high‐performance material in itself. Significant enhancement of thermal conductivity, which is closely related to the state of clay dispersion, is expected for a polymer‐clay nanocomposite. In this study, variations in the thermal diffusivity of PI‐clay nanocomposite films prepared by different methods were investigated. The thermal diffusivity of PI‐clay nanocomposite film increased at low clay content only when unmodified clay was used, where the clay morphology was a layered structure dispersed on a nanometer scale. Moreover, the thermal diffusivity could be enhanced by controlling the tensile stress induced by spontaneous shrinkage of the film during thermal imidization. These results demonstrated that the thermal diffusivity of PI‐clay nanocomposite films is significantly affected by the dispersion and/or arrangement states of the clay. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Structure and properties of polyimide‐g‐nylon 6 and nylon 6‐b‐polyimide‐b‐nylon 6 copolymers

Polyimide‐g‐nylon 6 copolymers were prepared by the polymerization of phenyl 3,5‐diaminobenzoate with several diamines and dianhydrides with a one‐step method. The polyimides containing pendant ester moieties were then used as activators for the anionic polymerization of molten ε‐caprolactam. Nylon 6‐b‐polyimide‐b‐nylon 6 copolymers were prepared by the use of phenyl 4‐aminobenzoate as an end‐capping agent in the preparation of a series of imide oligomers. The oligomers were then used to activate the anionic polymerization of ε‐caprolactam. In both the graft and copolymer syntheses, the phenyl ester groups reacted quickly with caprolactam anions at 120°C to generate N‐acyllactam moieties, which activated the anionic polymerization. All the block copolymers had higher moduli and tensile strengths than those of nylon 6. However, their elongations at break were much lower. The graft copolymers based on 2,2′‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]propane dianhydride and 2,2′‐bis[4‐(4‐aminophenoxy)phenyl]propane displayed elongations comparable to that of nylon 6 and the highest moduli and tensile strengths of all the copolymers. The thermal stability, moisture resistance, and impact strength were dramatically increased by the incorporation of only 5 wt % polyimide into both the graft and block copolymers. The graft and block copolymers also exhibited improved melt processability. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 300–308, 2006