Creep and shrinkage behavior of improved ultrathin polymeric films

Long‐term creep‐deformation and shrinkage characteristics of improved ultrathin polymeric films for magnetic tapes are presented. These films include poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN), and aromatic polyamide (ARAMID). PET film is currently the standard substrate used for magnetic tapes, and thinner tensilized‐type PET, PEN, and ARAMID have recently been used as alternate substrates with improved material properties. The thickness of the films ranges from 6.2 to 4.8 μm. More dimensional stability is required for advanced magnetic tapes, and the study of creep and shrinkage behavior is important for estimating the dimensional stability. Creep measurements were performed on all available substrates at 25, 40, and 55°C for 100 h. Based on these data, master curves were generated using time–temperature superposition to predict dimensional stability after several years. The amount of creep deformation is considerably smaller for ARAMID and tensilized‐type PET than for PEN, although Standard PET shows the largest amount of creep. In addition, creep measurements under high humidity also show similar trends. Shrinkage measurements at 55°C for 100 h show that the shrinkage of ARAMID is lower than that of PET and PEN. The relationship between the polymeric structure and dimensional stability are also discussed. Based on the creep and shrinkage behavior, ARAMID and tensilized‐type PET seem to be suitable for advanced magnetic tapes. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1477–1498, 2002; DOI 10.1002/app.10012     

Viscoelastic and shrinkage behavior of ultrathin polymeric films

Viscoelastic and shrinkage characteristics of five ultrathin polymeric films are presented. These films include poly(ethylene terephthalate) or PET, poly(ethylene naphthalate) or PEN, an aromatic polyamide (ARAMID), a polyimide (PI), and poly(benzoxazole) or PBO. PET film is currently the standard substrate used for magnetic tapes, and the other four films represent alternative substrates with improved material properties. Thicknesses of the films range from 14.4 μm for PET to 4.4 μm for ARAMID. A creep apparatus is used to measure the viscoelastic and shrinkage characteristics of the films. The largest amount of creep compliance was measured for PET followed by PI, PEN, ARAMID, and PBO. Creep velocity was highest for PET and PI, followed by ARAMID, PEN, and PI. Shrinkage measurements at 50°C for 100 h show that PEN shrinks more than all the other substrates. Time–temperature superposition is used to predict long-term creep behavior, and relationships between polymeric structure and viscoelastic behavior are also discussed. Based on their relative cost and creep behavior, PEN and ARAMID substrates appear to be suitable alternatives to PET. © 1995 John Wiley & Sons, Inc.     

Tensile and dynamic mechanical properties of improved ultrathin polymeric films

Tensile and dynamic mechanical properties of improved ultrathin polymeric films for magnetic tapes are presented. These films include poly(ethylene terephthalate) or PET, poly(ethylene naphthalate) or PEN, and aromatic polyamide (ARAMID). PET film is currently the standard substrate used for magnetic tapes; thinner tensilized‐type PET, PEN, and ARAMID were recently used as alternate substrates with improved material properties. The thickness of the films ranges from 6.2 to 4.8 μm. Young's modulus of elasticity, F5 value, strain‐at‐yield, breaking strength, and strain‐at‐break were obtained at low strain rates by using a tensile machine. Storage (or elastic) modulus, E′, and the loss tangent, tan δ, which is a measurement of viscous energy dissipation, are measured by using a dynamic mechanical analyzer at temperature ranges of ?50 to 150°C (for PET), and ?50 to 210°C (for PEN and ARAMID), and at a frequency range of 0.016 to 29 Hz. Frequency–temperature superposition was used to predict the dynamic mechanical behavior of the films over a 28 decade frequency range. Results show that ARAMID and tensilized films tend to have higher strength and moduli than standard PET and PEN. The rates of decrease of storage modulus as a function of temperature are lower for PET films than those for PEN and ARAMID films. Storage modulus for PEN films are higher than that for PET films at high frequencies, but this relationship reverses at low frequencies. ARAMID has the highest modulus and strength among the films in this study. The relationship between polymeric structure and mechanical properties are also discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2225–2244, 2002     

Mechanical,hygroscopic, and thermal properties of metal particle and metal evaporated tapes and their individual layers

Mechanical and thermal properties of magnetic tapes and their individual layers strongly affect the tribology of magnetic head–tape interface and reliability of tape drives. Dynamic mechanical analysis, longitudinal creep, lateral creep, Poisson's ratio, the coefficient of hygroscopic expansion (CHE), and the coefficient of thermal expansion (CTE) tests were performed on magnetic tapes, tapes with front coat or back coat removed, substrates (with front and back coats removed), and never‐coated virgin films of the substrates. Storage modulus and loss tangent values were obtained at a frequency range from 0.016 to 28 Hz, and at a temperature range from ?50 to 150 or 210°C. Longitudinal creep tests were performed at 25°C/50% RH, 40°C/25% RH, and 55°C/10% RH for 50 h. The Poisson's ratio and lateral creep were measured at 25°C/50% RH. CHE was measured at 25°C/15–80% RH. CTE values of various samples were measured at a temperature range from 30 to 70°C. The tapes used in this research included two magnetic particle (MP) tapes and two metal evaporated (ME) tapes that were based on poly(ethylene terephthalate) and poly(ethylene naphthalate) substrates. The master curves of storage modulus and creep compliance for these samples were generated for a frequency range from 10^?20 to 10¹⁵ Hz. The effect of tape manufacturing process on the various mechanical properties of substrates was analyzed by comparing the data for the substrates (with front and back coats removed) and the never‐coated virgin films. A model based on the rule of mixtures was developed to determine the storage modulus, complex modulus, creep compliance, and CTE for the front coat and back coat of MP and ME tapes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1319–1345, 2004     

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     

Viscoelastic analysis applied to the determination of long‐term creep behavior for magnetic tape materials

Creep‐compliance experiments were performed for three representative magnetic tapes. Two of these tapes used a magnetic particle (MP) coating, and one used a metal‐evaporated (ME) coating. The MP tapes used the following polyester substrates: semitensilized poly(ethylene naphthalate) (PEN) and supertensilized poly(ethylene terephthalate). The ME tape used an aromatic poly(amide) or aramid substrate. Time–temperature superposition was used to make creep‐compliance predictions at 30 and 50°C reference temperatures. Comparisons were made with dimensional stability requirements based on position error signal (PES) specifications for magnetic tape drives along with in‐cartridge creep specifications based on PES measurements. Circumferential and lateral creep strains were determined that account for storage of the tapes in a reel, and creep strains were predicted for future tapes with thinner, lower compliance coatings. A rule of mixtures method was also used to extract compliance information for individual layers of MP‐PEN tapes, and stress profiles through the thickness of the tapes were determined. Additional measurements and analyses were performed to determine the creep recovery and shrinkage characteristics for the magnetic tapes. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1106–1128, 2006     

Correlations between creep,shrinkage, and dynamic mechanical characteristics of magnetic tape materials

Creep compliance, shrinkage, and dynamic mechanical analysis (DMA) results are presented and discussed for developmental magnetic tapes made from PEN and metalized PET (Spaltan®) substrates as well as PEN substrate samples cut from wide‐stock in the machine and transverse directions. Curve fit parameters from the Kelvin‐Voigt model are discussed to shed light on the creep‐compliance characteristics, particularly the roll‐off characteristics observed at elevated temperatures and long time periods. Characteristic peaks observed in storage and loss moduli measured using DMA that correspond with molecular movement provide information that assists with the understanding of creep‐compliance and shrinkage behavior for these materials. Such movement corresponds with dimensional instabilities that need to be understood for future generations of advanced digital magnetic tapes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Dynamic mechanical analysis of magnetic tapes at ultra‐low frequencies

A custom, ultra‐low frequency, dynamic mechanical analyzer (ULDMA) has been developed to study the correlated effects of temperature and frequency on the viscoelastic behavior of magnetic tapes. It has been used to acquire data needed for the development of future magnetic tapes that require an archival life of up to 100 years. A range of elevated temperatures is used to simulate real‐world storage environments, which enables the investigation of how the viscoelastic characteristics of tape samples influence the extent to which the tape deforms. The experiments and subsequent analysis examine the influence of the molecular structure on the viscoelasticity of magnetic tapes. Experiments were performed on a variety of magnetic tapes, including poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN), metalized PET (M‐PET), and metalized Spaltan (M‐SPA). Additional experiments examined PEN and PET substrates by removing the front and back magnetic layers from the tape sample. Because of the viscoelastic behavior of the tapes, a time delay was present between the strain and stress signals, which was determined using a Fourier transform program. The elastic modulus (E), storage modulus (E′), loss modulus (E″), and loss tangent (tan δ) were obtained from the time delay for each of the ULDMA experiments at 25, 50, and 70°C over the frequency range of 0.0100–0.0667 Hz. Plots of these mechanical characteristics demonstrate the ability of frequency and temperature to affect trends associated with mechanical and thermal properties. Finally, some samples displayed an initial relaxation during the ULDMA experiments, which, when modeled using Maxwell's viscoelastic model, provided an insight into the relaxation characteristics of the samples. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Dynamic mechanical and thermal analyses of magnetic particle and metal evaporated tapes and their individual layers

The mechanical and thermal properties of magnetic tapes and their individual layers strongly affect the tribology of the magnetic head–tape interface. Dynamic mechanical analysis and thermomechanical analysis tests were performed on magnetic tapes, tapes with front coat or back coat removed, substrates (with front and back coats removed), and never‐coated virgin films of the substrates. Storage modulus and loss tangent were obtained at a frequency range from 0.016 to 28 Hz, and at a temperature range from ?50 to 150 or 210°C. Coefficients of thermal expansion (CTE) of various samples were measured at a temperature range from 30 to 70°C. The tapes used in this research include two magnetic particle (MP) tapes and two metal evaporated (ME) tapes based on poly(ethylene terephthalate) and poly(ethylene naphthalate) substrates. The master curves of storage modulus for these samples were generated for a frequency range from 10^?20 to 10¹⁵ Hz. The effect of the tape manufacturing process on the dynamic mechanical properties of substrates was analyzed by comparing the data for the substrates (with front and back coats removed) and the never‐coated virgin films. A model based on the rule of mixtures was developed to determine the storage modulus, complex modulus, and CTE for the front coat and back coat of MP and ME tapes. To validate the procedure, data for these individual layers were then used to calculate the corresponding properties of the finished tape. The predicted results were compared with the experimental measurements. The data obtained in the study are also discussed in light of previously published lateral contraction, Poisson's ratio, CTE, and CHE (coefficient of hygroscopic expansion) data. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 548–567, 2003     

The influence of cross‐linking reaction on the mechanical and thermal properties of polyarylene ether nitrile

The processing of cross‐linked polyarylene ether nitrile (PEN), which has a triazine rings structure, has been investigated under different reaction times and temperatures. In this study, the PEN films prepared by the tape‐casting formed the thermally stable triazine rings by catalytic cross‐linking reaction gradually, which was characterized by Fourier transform infrared spectroscopy. The chemical cross‐linking reaction occurred as the CN group absorption of PEN at 2221 cm⁻¹ decreased and a new absorption peak, at 1682 cm⁻¹, was observed, and the absorption peak intensity would be progressively larger, with the extension of the processing time. After the formation of cross‐linking networks, the cross‐linking degree and thermal and mechanical properties of the processed films were improved substantially, compared with the untreated films. The film with added ZnCl₂ as the catalyst was more rapidly cross‐linked, and its properties were better than that without catalyst at the same treatment conditions. The glass‐transition temperature (T_g) of PEN films processed at 350°C for 4 h (213.65°C) was higher than that of PEN films before the treatment (161°C), and the tensile strength was also improved significantly. The PEN was processed at 350°C for 2 h, whose initial decomposition temperature increases by about 10°C, compared with that of untreated film, at one time. The rheology behavior of the cross‐linked films was processed on dynamic rheometer to monitor and track the process of polymer cross‐linking reaction. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Dynamic mechanical analysis of barium ferrite magnetic tapes with aramid and poly(ethylene naphthalate) substrates

Frequency‐ and temperature‐dependent viscoelastic characteristics of advanced materials used for high‐capacity digital magnetic tapes were analyzed using a custom ultra‐low frequency dynamic mechanical analyzer (ULDMA). The magnetic tapes studied both use barium ferrite (BaFe) magnetic particles. One tape uses an aromatic poly(amide) or aramid substrate, and the other tape uses a poly(ethylene naphthalate) or PEN substrate. ULDMA studies were performed for both types of tape materials using samples cut from reels and the substrates after the front and back coats were removed. Two‐hour experiments were performed at 25, 30, 50, and 70°C temperatures, and four test frequencies were used at each temperature: 0.006, 0.010, 0.033, and 0.065 Hz. Properties determined were the peak strain‐based elastic modulus, E, and the storage modulus, E′, loss modulus, E″, loss tangent, tan(δ), complex modulus, E*, and complex loss, E″/E*, expressed as a percentage. When compared with the PEN tape and substrate materials, the peak elastic modulus, storage modulus, and complex modulus were higher for the aramid materials. Substrates for each material exhibited higher elastic, storage, and complex moduli compared with their respective tapes. Through the complex loss percentage, comparisons were made between the aramid and PEN materials related to their viscoelastic characteristics. Finally, the influence of frequency was shown to have increasing relevance at higher temperatures, with the PEN tape and substrate exhibiting an increase in complex loss modulus in the 50°C range because of the β* secondary transition. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41478.     

Study on phase separation of PET/PEN blends by dynamic rheology

Blends of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) were processed into biaxially drawn films, and samples taken from the bi‐oriented films were then investigated by dynamic rheology experiments in the melt state. Storage modulus G′ and loss modulus G″ were determined in the frequency range of 10^?2–10² rad/s at temperatures between 260 and 300°C. Although the time–temperature superposition (TTS) principle was found to hold in the high frequency regime, a breakdown of TTS was observed at low frequencies, and the terminal behavior of the storage modulus G′ of the blends departs drastically from the terminal behavior observed for the blend components. This is caused by interfacial surface tension effects. The results indicate that despite the effect of transesterification reactions, the PET/PEN blend systems investigated consist of a microseparate phase of PEN platelets in a matrix of PET. This morphology is produced when the blends are processed into biaxially oriented PET/PEN films, and droplets of PEN are deformed into a lamellar structure consisting of parallel and extended, separate layers. The large interfacial surface area of the bi‐oriented PET/PEN blends leads to remarkably strong interfacial tension effects in dynamic rheology measurements. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Shrinkage behavior after the heat setting of biaxially stretched poly(ethylene 2,6‐naphthalate) films and bottles

Amorphous preforms of poly(ethylene 2,6‐naphthalate) (PEN) were biaxially drawn into bottles up to the desired volume under industrial conditions. These bottles were used to characterize the shrinkage behavior of the drawn bottles with or without heat treatment and to study structural variations during heat setting. During drawing, a rigid phase structure was induced, and the amount of the induced rigid phase structure was linearly related to the square root of the extra first strain invariant under equilibrium conditions. During the production of these bottles, this equilibrium was not attained because of high stretching conditions and rapid cooling after stretching. The structure after orientation contained a rigid amorphous phase and an oriented amorphous phase. The shrinkage behavior was a function of the temperature and time of heat setting. Long heat‐setting times, around 30 min, were used to characterize the possible structural variations of the oriented PEN after heat setting at equilibrium. Under the equilibrium conditions of heat setting, the start temperature of the shrinkage was directly related to the heat‐setting temperature and moved from 60°C without heat treatment up to a temperature of 255°C by a heat‐setting temperature of 255°C; this contrasted with poly(ethylene terephthalate) (PET), for which the start temperature of shrinkage was always around 80°C. For heat‐setting temperatures higher than 220°C, the structural variations changed rapidly as a function of the heat‐setting time, and the corresponding shrinkage of the heat‐set samples sank below 1% in a timescale of 30–60 s for a film thickness of 500 μm. The heat treatment of the oriented films taken out of the bottle walls with fixed ends stabilized the induced structures, and the shrinkage of these heat‐set films was zero for temperatures up to the heat‐setting temperature, between 220 and 265°C, if the heat‐setting time was sufficient. According to the results obtained, a heat‐setting time of 30 s, for a film thickness of 500 μm, was sufficient at a heat‐setting temperature of 255°C to stabilize the produced biaxially oriented PEN bottles and to take them out the mold without further shrinkage. During the drawing of PEN, two different types of rigid amorphous phases seemed to be induced, one with a mean shrinkage temperature of 151°C and another rigid amorphous phase, more temperature‐stable than the first one, that shrank in the temperature range of 200–310°C. During heat setting at high temperatures, a continuous transformation of the less stable phase into the very stable phase took place. The heat‐set method after blow molding is industrially possible with PEN, without the complicated process of subsequent cooling before the molds are opened, in contrast to PET. This constitutes a big advantage for the blow molding of PEN bottles and the production of oriented PEN films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1462–1473, 2003     

Prestressed polymeric matrix composites: Longevity aspects

Elastically prestressed polymeric matrix composites (EPPMCs) are produced by stretching fibers (e.g., glass) within the composite during matrix curing. The resulting prestress can enhance mechanical performance, without increasing section dimensions or weight. Viscoelastically prestressed polymeric matrix composites (VPPMCs) can provide similar benefits, these being produced by subjecting polymeric fibers (e.g., nylon 6,6) to a creep load, which is released prior to molding. Although VPPMCs offer simplified processing and flexibility in product geometry, long‐term viscoelastic activity within the prestressing fibers is sensitive to time‐temperature limitations. In this study, nylon 6,6 fiber‐polyester resin samples were subjected to accelerated ageing. Using time‐temperature superposition, the samples were maintained at 70°C for 2,298 h, representing a 20‐fold ageing increase over previous work. Subsequent Charpy impact testing (at 20°C) demonstrated that the VPPMC samples absorbed ∼40% more energy than corresponding control (unstressed) counterparts; i.e., no deterioration in impact performance was observed, over a duration equivalent to ∼25 years at 50°C. In contrast, the longevity of EPPMCs remains unknown, but it is suggested that progressive localized matrix creep at the fiber‐matrix interface regions may cause a deterioration in elastically generated prestress with time and/or elevated ambient temperatures. POLYM. COMPOS., 37:2092–2097, 2016. © 2015 Society of Plastics Engineers     

Hot compaction of polyethylene naphthalate

In this article, we describe the production of single polymer composites from polyethylene naphthalate (PEN) multifilaments by using the hot compaction process. In this process, developed at Leeds University, highly oriented tapes or fibers are processed at a critical temperature such that a small fraction of the surface of each oriented element is melted, which on cooling recrystallizes to form the matrix of the composite. This process is, therefore, a way to produce novel high‐volume fraction polymer/polymer composites where the two phases are chemically the same material. A variety of experimental techniques, including mechanical tests and differential scanning calorimetry, were used to examine the mechanical properties and morphology of the compacted PEN sheets. Bidirectional (0/90) samples were made at a range of compaction temperatures chosen to span the melting range of the PEN multifilaments (268–276°C). Measurement of the mechanical properties of these samples, specifically the in‐plane modulus and strength, allowed the optimum compaction temperature to be ascertained (～ 271°C), and hence, the optimum mechanical properties. The optimum compacted PEN sheets were found to have an initial modulus close to 10 GPa and a strength of just over 200 MPa. The glass transition temperature of the optimum compacted sheets was measured to be 150°C, nearly 40°C higher than compacted poly(ethylene terephthalate) (PET) sheets. In previous work on polypropylene and PET hot compacted materials, it proved instructive to envisage these materials as a composite where the original oriented multifilaments are regarded as the reinforcing phase, and the melted and recrystallized material are regarded as the matrix phase. Dynamic mechanical bending tests (DMTA) were used here to confirm this for PEN. DMTA tests were carried out on the original fibers and on a sample of completely melted material to determine the fiber and matrix properties, respectively. The composite properties were then predicted by using a simple rule of mixtures and this was found to be in excellent agreement with the magnitude and measured temperature dependence of the hot compacted PEN material. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 796–802, 2004     

Viscoelastic behavior of polymer tape in a wound roll

A viscoelastic computational model is developed that uses experimentally determined viscoelastic material properties as input and can be used to predict the behavior of a tape material in a wound roll as stresses relax over time. Experimental creep test results are used to find best‐fit creep‐compliance parameters to describe two high density data storage tape media. The two tapes used in the analysis are a developmental tape with a poly(ethylenenaphthalate) (PEN) substrate and metal particle (MP) front coat similar to linear tape open (LTO4) (referred to in this work as “Tape C”), and LTO3, a commercially available tape with a PEN substrate and MP front coat. Sets of best‐fit creep‐compliance parameters are determined for both tapes. The differences between the predicted behavior using three‐, five‐, and seven‐parameter Kelvin–Voigt models are evaluated, both for a benchmark case and in a viscoelastic wound roll model. The choice of material model is found to significantly influence the predictions of the wound roll model. The differences between different material models for the same material are on the order of the differences found between the two different materials. A material model with a higher number of creep‐compliance parameters, although more computationally expensive, produces better results, particularly over long spans of time. The relative differences between the three‐, five‐, and seven‐parameter models are shown to be qualitatively consistent for several variations in the computational model setup, allowing predictions to be made based on simple benchmarks. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of fiber size on short‐term creep behavior of wood fiber/HDPE composites

When natural fiber‐thermoplastic composites are used in long‐term loading applications, investigating creep behavior is essential. The creep behavior of high‐density polyethylene (HDPE)‐based composites reinforced with four sizes of wood fibers (WFs) (120–80, 80–40, 40–20, and 20–10 mesh) was investigated. The instantaneous deformation and creep strain of all WF/HDPE composites increased at a fixed loading level when the temperature was increased incrementally from 25 to 85°C. At a constant loading level, composites containing the larger‐sized WFs had better creep resistance than those containing smaller‐sized fibers at all measured temperatures. The creep properties of composites with smaller‐sized WFs were more temperature‐dependent than those with larger‐sized WFs. Two creep models (Burger's model and Findley's power law model) were used to fit the measured creep data. A time–temperature superposition principle calculation was attempted for long‐term creep prediction. The Findley model fitted the composite creep curves better than the four‐element Burger's model. From the predicted creep response of the WF/HDPE composites, two groups of small fibers (120–80 and 80–40 mesh) had the lowest creep resistance over long periods of time at the reference temperature of 25°C. The largest WFs (10–20 mesh) provided the best composite creep resistance. POLYM. ENG. SCI., 55:693–700, 2015. © 2014 Society of Plastics Engineers     

Mechanical,thermal, electrical,and interfacial properties of high‐performance bisphthalonitrile/polyarylene ether nitrile/glass fiber composite laminates

Bisphthalonitrile (BAPh)/polyarylene ether nitrile end‐capped with hydroxyl groups (PEN‐OH) composite laminates reinforced with glass fiber (GF) have been fabricated in this article. The curing behaviors of BAPh/PEN‐OH prepolymers have been characterized by differential scanning calorimetry and dynamic rheological analysis. The results indicate that with the introduction of PEN‐OH the curing temperature of BAPh has decreased to 229.6–234.8°C and BAPh/PEN‐OH prepolymers exhibit large processing windows with relatively low melt viscosity. The BAPh/PEN‐OH/GF composite laminates exhibit tensile strength (272.4–456.5 MPa) and modulus (4.9–10.0 GPa), flexural strength (507.1–560.9 MPa), and flexural modulus (24.0–30.4 GPa) with high thermal (stable up to 538.3°C) and thermal stabilities (stable up to 475.5°C). The dielectric properties of BAPh/PEN‐OH/GF composite laminates have also been investigated, which had little dependence on the frequency. Meanwhile, scanning electron microscopy results show that the BAPh/PEN‐OH/GF composite laminates display excellent interfacial adhesions between the matrix and GFs. Herein, the BAPh/PEN‐OH matrix can be a good matrix for high‐performance polymeric materials and the advanced BAPh/PEN‐OH/GF composite laminates can be used under high temperature environment. POLYM. COMPOS., 34:2160–2168, 2013. © 2013 Society of Plastics Engineers     

Synthesis and crosslinking behavior of a soluble,crosslinkable, and high young modulus poly(arylene ether nitriles) with pendant phthalonitriles

Poly(arylene ether nitriles) (PEN) with pendant phthalonitrile groups (PEN? CN) were obtained via the Yamazaki‐Higashi phosphorylation route of 4‐(4‐aminophenoxy)phthalonitrile (APN) with acid‐contained PEN (PEN? COOH) in the presence of CaCl₂. The chemical structure and molecular weight of PEN? CN were characterized by ¹H‐NMR, Fourier transform infrared spectroscopy, and Gel permeation chromatography. The synthesized PEN? CN had superior solubility in polar organic solvent and can be easily processed into thin films from the solutions of N‐methylpyrrolidone, dimethylsulfoxide, N,N′‐dimethylformamide, dimethylacetamide, and tetrahydrofuran. Compared with PEN? COOH, PEN? CN showed higher thermal stability with 5% weight loss temperatures (T_5%) up to 430°C. The glass transition temperature of PEN? CN was improved from 211 to 235°C measured by differential scanning calorimetry (DSC). In addition, it also exhibited excellent mechanical properties that Young's modulus reached to 3.5 GPa. Meanwhile, the effects of different aromatic amines and Lewis acid on the crosslinking behavior of PEN? CN were investigated by DSC. The results indicated that anhydrous Zinc chloride (ZnCl₂) was the best catalyst to lower the curing temperature among 2,6‐bis(4‐diaminobenzoxy) benzonitrile, 4,4‐diaminediphenyl sulfone, APN and ZnCl₂. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Long‐term mechanical and viscoelastic behavior of constitutive polymeric materials used for magnetic tapes

Creep‐compliance behavior of specially prepared magnetic tape materials was measured at elevated temperature levels to facilitate the use of a time–temperature superposition (TTS) process. This TTS process allowed for the construction of master curves at a reference temperature of 30°C, which were used to predict the long‐term viscoelastic behavior of the magnetic particle (MP) and metal‐evaporated (ME) tapes used in the study. The specially prepared samples allowed for the use of a rule of mixtures technique to determine the long‐term creep compliance of the front coat and back coat used for the magnetic tapes. To test the validity of this procedure, the front coat, substrate, and back coat data determined through separate experiments were used to calculate creep compliances of simulated tapes. These calculated creep‐compliance curves were then compared to measured data for the actual magnetic tapes. After determination and validation of the front coat, substrate, and back coat creep‐compliance data sets, they were used to determine strain distributions when the tapes are stored in a reel. Strain distributions were calculated for two cases, which reflect how tapes are stored in different drives: (1) the front coat (magnetic + nonmagnetic layer) is oriented away from the hub, and (2) the front coat is oriented toward the hub. Results showed that strain in the critical front coat of a tape is lower if it is stored with the front coat oriented toward the hub. In addition, the use of the creep‐compliance data showed that the MP tape front coat is more susceptible to creep than the ME tape front coat. The strain distributions in future magnetic tapes were also simulated by reducing the thickness and compliance of the layers. Results showed the importance of using lower compliance front coat, substrate, and back coat materials if thinner tapes are to be developed to increase the volume of information that can be stored in a magnetic tape reel. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1142–1160, 2001