Zone drawn NEW-TPI thermoplastic polyimide and its blends with Xydar liquid crystalline polymer

In this work we report the effects of single stage zone drawing on the properties of NEW-TPI thermoplastic polyimide homopolymer, and its blends with Amoco's Xydar liquid crystalline polymer. Zone drawing was performed first on homopolymer NEW-TPI films to determine the effect of load weight, heater speed, and drawing temperature on the attainable draw ratio. Degree of crystallinity and chain orientation increase as the draw ratio increases for NEW-TPI. Blends of NEW-TPI/Xydar compositions 90/10 and 70/30 were studied next. In blends, the Xydar component is not molecularly dispersed, and is initially preferentially oriented along the machine direction during the film processing stage. Xydar acts as a nucleation site and lowers the temperature for crystallization of the NEW-TPI from the rubbery amorphous state. Zone drawing was performed either parallel or perpendicular to Xydar's initial preferred orientation direction. Blends with lower Xydar fraction could be zone-drawn to higher ratios. Zone drawing perpendicular to Xydar's initial orientation direction also resulted in increased draw ratio. Dynamic mechanical properties of the zone drawn materials were studied. In homopolymer NEW-TPI, dynamic modulus increased by a factor of two to 4.0 GPa in zone drawn films, largely as a result of the formation of oriented crystallites. In the blends, the modulus parallel to Xydar's initial orientation direction was greater than that in the transverse direction. Depending upon composition and test direction, zone drawing increased the dynamic moduli of the blends from 1.5 up to 2.7 times, in the temperature range from 150°C to 300°C.     

Coating carbon fibers with a thermoplastic polyimide using aqueous foam

Many techniques have been developed to coat carbon fibers with thermoplastic resins to form a prepreg. These techniques include melt impregnation and solution/slurry coating. The applicability of these techniques, however, may be restricted by high melt viscosities or significant drying times. Recent emphasis has been towards a dry powder coating technique using a fluidized bed. This technique may be limited by difficulties in fluidization of the polymer powders. To overcome these difficulties, a technique has been developed to continuously coat carbon fibers with thermoplastic resins using aqueous foam as a carrier medium. The polymer is slurried in a surfactant solution, into which air is dispersed using a foam-generating device. A predetermined amount of this foam is then applied to a moving carbon fiber tow using a foam application unit. The tow is then pulled through ovens where the foam is collapsed and the power fused to the fibers. Other aspects that are addressed include the stability of foams in the presence of powders, the mechanical properties of the composites formed using foam prepregging, and the effect of surfactant on composite properties.     

Oxidative aging of thermoplastic polyimide films

Two linear polyimides were subjected to accelerated isothermal aging at temperatures between 300 and 400°C. Losses in toughness correlated well with changes in glass transition temperature (T_g) of the films, but not with weight loss. Both materials have extrapolated lifetimes of 100,000 h near their T_g's. © 1995 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Thermal properties of a thermoplastic polyimide blend

Differential scanning calorimetry and dynamic mechanical analysis of blends of a new thermoplastic polyimide (TPI) and poly(ether imide) (PEI) have confirmed the full miscibility of the system over the whole composition range. Annealing of the blends above the glass transition temperature of TPI, but below its crystallization temperature, did not produce a shift in the glass transition, while physical ageing of the annealed blends also failed to reveal any indication of phase separation. The rate of crystallization of TPI was slowed by the addition of PEI, and the temperature of the maximum crystallization rate shifted upwards. The β‐relaxation behavior of the blends followed a linear trend between the response of the component polymers, while the low‐temperature γ‐relaxation was unchanged by blending. The time scale of physical ageing of the blends did not behave in a linear fashion, and the enthalpy loss on ageing also deviated from the average. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 543–552, 1999     

热塑性聚酰亚胺微电子薄膜的制备

以微电子业所急需的聚酰亚胺薄膜为背景,采用一种热塑性聚酰亚胺树脂(TPI),实验测定了聚合物溶液特性、干燥工艺及热拉伸性能。在化学环化过程中聚合物溶液粘度随时间逐步增大;15 h后粘度和重均相对分子质量及分布趋于稳定。薄膜溶剂含量在干燥初期急剧下降,干燥速率随干燥温度升高而增大。TPI树脂表现出良好的热塑拉伸性能,当温度高于其玻璃化温度时,最大拉伸比随升温速率降低而增大,而随拉伸载荷增加呈现出先增后降。TPI薄膜经拉伸处理后其力学性能得到明显提高,综合性能与日本钟渊TP E薄膜相当。     

热塑性聚酰亚胺增韧环氧树脂胶粘剂的研制

利用热塑性聚酰亚胺粉末增韧改性环氧树脂,得到了综合性能优异的胶粘剂体系,并对其凝胶化时间、接触角、表面能、疏水性、耐热性等各项性能进行了研究。     

Microhardness of carbon fiber reinforced epoxy and thermoplastic polyimide composites

We have examined the micro indentation hardness of a series of carbon fiber reinforced epoxy and thermoplastic polyimide (TPI) composites. In the epoxy systems, the influence of Nylon particles was studied. The effect of crystallization of the thermoplastic polyimide upon the microhardness values of the resin was also investigated. The microstructure of the TPI-composites was characterized by X-ray diffraction. The results show that the addition of carbon fibers to the neat resins greatly increases the microhardness and thus the yield stress of the composite. The value of the microhardness technique is highlighted in emphasizing the heterogeneity of the CFRC.     

Semicrystalline thermoplastic polyimide + polymer liquid crystal blends: Nonisothermal calorimetry and thermogravimetry

Blends of a thermoplastic polyimide (TPI) and a polymer liquid crystal (PLC) were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The presence of PLC enhances orientation in the system and lowers the crystallization temperature-—a manifestation of the channeling effect predicted theoretically (38). The degradation studies show high temperature stability of all blends with the degradation onset consistently above 520°C. The onset decreases with PLC concentration but reaches a plateau above 30 wt% PLC when the PLC-rich islands are formed. The amount of moisture absorbed decreases with the PLC concentration while the moisture does not affect the degradation of the samples significantly. A phase diagram is constructed for the PLC + TPI blends from the DSC and TGA data. A comparison of amorphous and semicrystalline TPI and the characterization of amorphous TPI + PLC blends will be reported later.     

Dynamic relaxation characteristics of Matrimid polyimide

The dynamic relaxation characteristics of Matrimid^® (BTDA-DAPI) polyimide have been investigated using dynamic mechanical and dielectric methods. Matrimid exhibits three motional processes with increasing temperature: two sub-glass relaxations (γ and β transitions), and the glass—rubber (α) transition. The low-temperature γ transition is purely non-cooperative, and displays an identical time-temperature response to both the dynamic mechanical and the dielectric probes with a corresponding activation energy, E_A = 43 kJ/mol. The β sub-glass transition shows a more cooperative character as assessed via the Starkweather method. Comparison of dynamic mechanical and dielectric data for the β process suggests that the dynamic mechanical test (E_A = 156 kJ/mol) is sensitive to a broader, more strongly correlated range of sub-glass motions as compared to the dielectric probe (E_A = 99 kJ/mol). Time-temperature superposition was used to establish mechanical master curves across the glass-rubber (α) relaxation, and these data could be described using the Kohlrausch-Williams-Watts function with an exponent value, β_KWW = 0.34. The corresponding shift factors were used as the basis of a cooperativity plot for the determination of dynamic fragility. The relation between fragility index (m = 115) and β_KWW for the Matrimid polyimide was in good agreement with the wide correlation reported in the literature.     

Blends of thermoplastic polyurethanes and polyamide 12: Structure,molecular interactions,relaxation, and mechanical properties

Studies were done to understand the effects of polyamide 12 (PA 12) incorporation on microphase separation (microsegregation) in thermoplastic polyurethanes (TPU) based on oligoether (polytetramethylene oxide, molecular weight, 1000) and oligoester (polyethylene butylene glycol adipate, molecular weight, 2000), and relaxation transitions, compatibility, and molecular interaction energy in polymer blends. It was learned that the addition of PA 12 caused partial degradation of the domain structure in the oligoester‐containing polyurethane, whereas interaction of hard blocks in the oligoether‐containing polyurethane increased. Analyzing compatibility and interphase interactions in blends is possible in the frame of the quantum theory of relaxation processes. Also, interferences of the components on characteristic temperatures of relaxation transitions were studied. Partial compatibility was detected between PA 12 and the soft block of oligoether‐based TPU over the whole range of components concentrations tested. For oligoester‐based TPU, partial compatibility was observed only at low polyamide concentrations (up to 20 wt %). Effects of a polyurethane phase on PA 12 crystallization in the blends along with the pattern of concentration—mechanical properties dependencies are discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1054–1070, 1999     

Real time SAXS/stress-strain studies of thermoplastic polyurethanes at large strains

Simultaneous small angle X-ray scattering (SAXS) and force measurements have been recorded during tensile deformation of two contrasting polyurethane elastomers. The elastomers comprise the same hard and soft chemical segments; in Sample A, the length of the hard blocks is randomised while in Sample B the hard blocks are monodisperse. During deformation of Sample A, the SAXS halo from the mesophase structure deforms to an ellipse with intensification on the meridian. In Sample B, the halo transforms into a four point pattern. The ellipse patterns of A are interpreted in terms of a model based on particles located on a statistical lattice which is subjected to an affine deformation scheme. According to this model, the SAXS patterns of A are consistent with the hard phase regions behaving as embedded particles which separate from each other in an affine manner and which are not impeded by interconnections during the mechanical yield process. In B, the interconnection of the hard phase prevents affine deformation of the structure and involves the formation of a four point ‘lattice’ structure which then subsequently deforms in an affine manner. The differences in behaviour are linked with the segment sequencing which result in the phase regions of Sample A having a lower volume fraction and are consistent with variation in applied stress.     

Carbon plastics based on thermoplastic polyimide binders modified with nanoparticles

Polyimides (PIs) crystallized from melts are promising thermally stable, heat-resistant plastics with high destruction viscosities. Nanocomposites that in turn serve as matrixes for carbon plastics can be obtained on the basis of PIs filled with carbon nanoparticles of various structures and morphologies. The presence of the composite-in-composite structure gives rise to the enhancement of dissipation properties of the polymer matrix in particular and to an increase in the crack resistance of the carbon plastic in general.     

Dynamic stress relaxation of thermoplastic elastomeric biomaterials

In this paper we present the results of comparative dynamic stress relaxation studies performed with poly(styrene-b-isobutylene-b-styrene) (SIBS), polyurethane (PU) and polyester (PED) biomaterials in air and simulated body fluid (SBF) at 24 °C and 37 °C. SIBS showed the highest value of relieved stress under constant strain (24.1% after 100,000 cycles in air) with PED and PU having similar relative change (12.2% and 10.5%). In spite of its softness (Shore A 56 vs. 80), the dynamic modulus (E_dyn) and stiffness of SIBS were in between PED and PU. The behavior of the materials was correlated to their structure: SIBS is an amorphous block copolymer with a long elastomer midblock, while PU and PED are semicrystalline segmented copolymers with much shorter soft blocks, and hydrogen bonding. SIBS and PED were relatively insensitive to SBF and temperature changes, while PU experienced the largest changes in physical properties in vitro (simulated body fluid, 37 °C).     

Polyether–polyimide thermoplastic elastomers. I. Synthesis and properties

A series of polyether–polyimides based on polycondensation of poly(tetramethylene oxide) glycol di-p-aminobenzoate with different molecular weights (650, 1000, 2000) and benzenetetracarboxylic acid dianhydride (BTDA) or 3,3′,4,4′-benzenetetracarboxylic acid anhydride (BPTDA) was synthesized. Infrared spectroscopy (IR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and stress–strain tests were used to follow the imidization process and to study the structure–property relations of this family of polymers. FTIR data showed that the imidization was completed after 6 h at 140°C, which is a much lower temperature than that required for polyimides synthesized from low molecular weight diamines. DSC and DMA results indicated that the block copolymer exhibited a well-phase-separated structure and had a broad rubbery plateau from about ?70°C to 260°C, which varied with dianhydride type and hard-segment content. The BTDA series had enhanced mechanical properties compared to the BPTDA series. The excellent tensile properties of the polyether–polyimides suggest that they could be potentially used as heat-resistant thermoplastic elastomers.     

Stress relaxation and the domain structure of thermoplastic elastomer

The relationship between the stress relaxation phenomena and domain structure of thermoplastic elastomer (TPE) was studied. Two representative thermoplastic elastomers: styrenebutadiene-styrene block copolymer (SBS) and 1,2-syndiotactic polybutadiene (1,2-PB), representing the amorphous glassy domain and crystalline domain, respectively, were tested in different atmospheres and temperatures. Results show that the structure of the domain has a significant effect on the stress relaxation curve. It is found that the way the glassy domain is formed determines the failure of the domain and hence the stress relaxation rate. In the case of crystalline domain, the history of heat treatment determines the crystal structure and, in turn, the stress relaxation rate.     

The analysis of TSDC peaks with a KWW relaxation function or a distribution of relaxation times in polymers

Summary The analysis of Thermally Stimulated Depolarization Currents (TSDC) spectra in polymers requires the introduction of a distribution of relaxation times. Also, a decay of the induced polarization following a stretched exponential law can be used. Two different ways for introducing this effect in the TSDC equations are compared here together with the decomposition in elementary curves by a Simulated Annealing Monte Carlo procedure to find the distribution. It is found that the stretched exponential applied to computer generated curves corresponds in both cases to a nearly Debye process. Also the analysis of the α-peak of poly(ɛ-caprolactone) with the three approaches are compared. Received: 14 July 1998/Revised version: 16 November 1998/Accepted: 16 November 1998     

Thermal expansivity and thermal conductivity of amorphous thermoplastic polyimide and polymer liquid crystal blends

Linear thermal expansivities α_L and thermal conductivities of polyimide (TPI) and polymer liquid crystal (PLC) blends were studied. The glass transition temperatures T_g of our amorphous TPI and the PLC are, respectively, 240 and 220°C. The addition of the PLC induces orientation through the channeling process, as predicted by an extension of the Flory statistical‐mechanical theory of PLCs (27). Channeling was observed at PLC concentrations as low as 5 wt%. Thermal conductivity decreases with the addition of the PLC to the TPI. The anisotropic expansivity of the blends shows a strong dependence on PLC concentration and orientation direction. The pure PLC shows a maximum on the along‐the‐flow expansivity vs. temperature curves and also negative α_L values. TPI addition moves the expansivities to positive values, but the maximum persists, even for 5% PLC only.     

Low temperature relaxation of DGEBA epoxy resins: A thermally stimulated discharge current (TSDC) study

The effect of curing conditions on the low temperature relaxation behavior of catalyst-cured epoxy systems based on digliycidyl ether of bisphenol A (DGEBA) has been characterized by the thermally stimulated discharge current (TSDC) technique. In these chemically relatively simple epoxy systems, five relaxation processes, designated as γ, β, β′, β_OH, and β″, have been observed: Their molecular origins are discussed in detail. The results are in agreement with prior suggestions of an inhomogeneous cross-link density morphology.     

Dielectric behavior of polyetheretherketone (PEEK) using TSDC technique

The dielectric relaxation behavior of Polyetheretherketone (PEEK) has been investigated by using thermally stimulated discharge current (TSDC) technique. The dependence of TSDC characteristics of PEEK on poling temperature (T_P) [50–200 °C], poling field (E_P) [200–500 kV/cm], storage time (t_S) [2–120 hrs] and various thicknesses 25 μm, 50 μm and 75 μm have been investigated in the temperature range [60–230 °C]. The TSDC spectra shows a prominent maxima around glass transition temperature (T_g) i.e. at 143 °C named as α-peak and the other peak is observed around 200 °C named as β-peak. The α-dipolar relaxation is taking place because of the movement of ketone (>C = 0) dipoles linked to the main chain. The β-peak is attributed to the space charges. It is observed that the magnitude of α-peak increases with the increase in poling field. The peak current and area under the α-peaks are found to be diminished with the increase of storage time (t_s) for electrets. The amplitude of α-peak decreases with the increase in thickness. The activation energies for PEEK sample at different conditions in the present work are found to be 0.38 eV–1.70 eV. The values of activation energy (U) and pre-exponential factor (τ _o) for α- relaxation are determined using Bucci plot method and support the nature of the relaxations.     

Stress relaxation behavior of short kevlar fiber-reinforced thermoplastic polyurethane

Stress relaxation behavior of short Kevlar fiber-reinforced thermoplastic polyurethane (TPU) is studied with respect to strain level, strain rate, fiber loading, and fiber orientation and temperature. The existence of a two-step relaxation mechanism for unfilled stock and a three-stage relaxation mechanism for the fiber-filled stock is reported.