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1.
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  相似文献   

2.
    
This article discusses the viscoelastic behavior of a vinyl ester (Derakane 411‐350) reinforced with 1.25 and 2.5 wt % nanoclay and exfoliated graphite nanoplatelets during short‐term creep and relaxation tests with a dynamic mechanical analyzer. Linear viscoelastic models are generally composed of one or more elements such as dashpots and springs that represent the viscous and elastic properties. Stress relaxation data from the dynamic mechanical analyzer have been used to obtain the elastic parameters based on model constitutive equations. The standard linear solid model, which is a physical model, has been used for predicting the creep deformation behavior of the vinyl ester nanocomposites over a wide temperature range. Some correlations have been made with the mechanical model, such as the effect of temperature on the deformation behavior, which is well explained by the dashpot mechanism. At lower temperatures, higher creep compliance has been observed for the vinyl ester versus the nanocomposites, whereas at temperatures near the glass‐transition temperature of the vinyl ester, creep compliance in the nanocomposites is closer in magnitude to that for the vinyl ester. The creep response of the pure vinyl ester and its nanocomposites appears to be modeled reasonably well at temperatures lower than their glass‐transition temperatures. A comparison of the predictions and experimental data from the creep tests has demonstrated that this model can represent the long‐term deformation behavior of these nanoreinforced materials reasonably well. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010  相似文献   

3.
    
Two chemically modified phenolic resins (PFs) designed and developed for the matrix resins of organic friction materials were characterized. The braking performance of organic brake pads based on the two modified resins and reinforced with hybrid fibers was investigated on a full‐scale test bench. The results indicate that the modified PF with more internal friction units possessed much higher impact and compression strengths, greater toughness, and better braking stability. We concluded that the matrix resin with more adjustable structural units allowed for an adjustable Young's modulus and dynamic mechanical properties and, hence, could indirectly allow an adjustable friction coefficient for organic brake pads during braking process and, furthermore, enable the optimization of braking stability of the friction couples. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012  相似文献   

4.
    
The energy approach for evaluation of the limits of linear viscoelastic (LVE) behavior is considered. The approach of Foux and Bruller based on the Reiner‐Weissenberg dynamic theory of strength is developed for the temperature effect. Value of the stored energy at the limit of LVE is considered as the material characteristic independent on loading conditions and temperature. Time–temperature superposition principle is extended for the energy calculations. Curves of the stored energy calculated for different temperatures are shifted to each other in the logarithmic time axes similarly as creep compliance and relaxation modulus curves in creep and tension tests, respectively. Temperature is considered as a factor that accelerates transition form linear to non‐LVE at the same stored energy threshold. This is proved by example of polyvinylchloride by comparing temperature dependences of the stress limits of LVE determined in two independent test series: tensile creep and constant strain rate tests. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009  相似文献   

5.
    
In this study, the creep behavior of semicrystalline polymers was investigated based on time-dependent thermomechanical characteristics of the amorphous and crystalline sections. To this end, different equivalent box models (EBMs) with simple or complex structures were designed to interconnect the system components and cover all of their likely interactions. To induce time-dependency to the model, a variety of viscoelastic models (e.g., Maxwell, Kelvin–Voigt, Maxwell representation of standard linear viscoelastic [SLV] model, Kelvin representation of SLV model, Burger and developed Bingham–Norton) were incorporated with the EBM structures as its crystalline/amorphous components. A specific strategy was devised in order to separately indicate the particular effects of crystalline and amorphous sections along with stress concentration on the temperature-dependent creep behavior of the system. This approach combined with validating the theoretical data against the creep test results, performed at 20, 40, and 60°C, helped to indicate the most efficient structure for EBM and the best applicable viscoelastic model component. Accordingly, based on the findings of the present study, it was revealed that the series arrangement of the amorphous and crystalline model components, represented by the Burger viscoelastic model, could provide the best predictions regarding the temperature-dependent creep in semicrystalline polymers.  相似文献   

6.
The variations of the dynamic mechanical properties (at 5 Hz) of bitumen–SBS mixes in the function of their composition (polymer content, bitumen composition) have been established. The relationships between the viscoelastic measurements and the morphological characteristics, previously determined, have been used to interprete these variations in terms of change of morphological characteristics (phase composition, phase content in the blends). Finally, a theoretical approach based on the thermodynamics of mixing is proposed to explain the relationships between the composition and the morphological characteristics. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1609–1618, 1997  相似文献   

7.
    
An unsaturated polyester, based on maleic anhydride, 1,6‐hexanediol, and trimethylol propane, was formulated with tetraethylorthosilicate (TEOS) oligomers and a coupling agent to prepare inorganic/organic hybrid films. TEOS oligomers were prepared through the hydrolysis and condensation of TEOS with water, and 3‐(triethoxysilyl)propylisocyanate was used as the coupling agent between the organic and inorganic phases. The hybrid materials were cured by moisture via sol–gel chemistry and by the UV curing of unsaturated polyesters. To compare the properties of the moisture‐cured inorganic/organic hybrid films, a conventional 2K polyurethane system was also prepared. The tensile, adhesion, abrasion, and fracture toughness properties were investigated as functions of the coupling agent and relative amount of UV cure versus thermal cure. Although no difference could be observed in the tensile properties, the abrasion resistance, fracture toughness, and adhesion were enhanced by the incorporation of TEOS oligomers into polyurethane films. Also, the abrasion resistance, fracture toughness, and tensile properties were increased with both moisture and UV exposure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 115–126, 2006  相似文献   

8.
    
In a preceding publication this author introduced a new universal viscoelastic model to describe a definitive relationship between constant strain rate, creep, and stress relaxation analysis for viscoelastic polymeric compounds. One extremely important characteristic of this new model is that it also characterizes secondary creep very well. Because secondary creep is the linear portion of creep after the completion of primary creep, then a straight line with a slope and an intercept can describe secondary creep. To effectively define a straight line in the secondary creep region it was found necessary to obtain averages of the instantaneous slope and the instantaneous intercept strain by averaging over a series of equally spaced data points in the secondary slope region. Most importantly, this average intercept strain was found to be independent of creep stress and creep time. This means that all the secondary creep straight lines must pass through the same intercept creep strain for all creep stresses. The results presented in this study strongly indicate that this secondary creep intercept strain is independent of creep stress and creep time, and appears to increase as the value of the efficiency of yield energy dissipation decreases. Because a decrease in the efficiency of yield energy dissipation, n, appears to correlate with an increase in the elastic solid like character of a material, then it appears that this secondary creep intercept strain should be a direct measure of the strain that the material can survive to retain its full elastic character. Therefore, this secondary creep intercept strain has been designated as the “Projected Elastic Limit” of a given viscoelastic material. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2923–2936, 2003  相似文献   

9.
    
Thermally Stimulated Creep (TSCr) mechanical spectroscopy has been used to analyze molecular movements in KMU‐4lcarbon/epoxy composite material around the glass transition temperature. This technique is powerful to characterize the microstructure and micromechanical properties of the epoxy matrix and their evolution upon thermal aging. Three cooperative submodes have been distinguished by resolving the fine structure of the material complex α‐retardation mode. The elementary processes constituting this mode possess activation enthalpies and preexponential factors that strongly depend on the thermal history of the sample. The activation parameters of the composite are subject to perceptible evolution due to postcuring degradation. The α‐mode associated complex spectrum shifts towards higher temperatures by 27°C as a consequence of a series of quenching in the temperature range 260 to 0°C; the material shows a rise in the fragility and a deterioration in the crack‐growth resistance qualities. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 342–350, 2002  相似文献   

10.
    
The strain response and influence of elevated temperature on the viscoelastic behavior of fabric in the compaction process cannot be described and predicted by current viscoelastic models. Here, a viscoelastic model, verified by compaction experiments, is originally proposed to depict the stress and strain responses in different stages of the compaction, especially considering the effects of added binder and elevated temperature. The model effectively captures that with the rising temperature, the interaction among fibers is enhanced due to the fiber volume expansion. Accordingly, the elastic modulus is enlarged in the compression stage. In the relaxation stage, the interaction suppresses the fiber realignment, leading to the reduction of stress relaxation. In the creep stage, the elevated temperature increases the deformation stiffness, indicating the strain is declined. In the relaxation stage, the adhesive effect of added binder facilitates the stress relaxation, and then the increasing stress relaxation promotes the increment of strain in the creep stage.  相似文献   

11.
    
Virgin injection‐molded tensile specimens without any inserted film and four kinds of film insert molded (FIM) tensile specimens were prepared. They were annealed at 80°C to investigate the effect of residual stresses and thermal shrinkage of the inserted film on thermal deformation of tensile specimens. The FIM specimens with the unannealed film were bent after ejection in such a way that the film side was protruded and the warpage was reversed gradually during annealing and the film side was intruded. Warpage of the FIM specimen with the film annealed at 80°C for 20 days was not reversed during annealing. Processing of the FIM specimens have been modeled numerically to predict thermoviscoelastic deformation of the part and to understand the warpage reversal phenomenon (WRP). Nonisothermal three‐dimensional flow analysis was carried out for filling, packing, and cooling stages. The flow analysis results were transported to a finite element stress analysis program for prediction of deformation of the FIM part. The WRP was caused by the combined effect of thermal shrinkage of the inserted film and relaxation of residual stresses in the FIM specimen during annealing. It is expected that this study will contribute towards the improvement of the FIM product quality and prevention of large viscoelastic deformation of the molded part. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009  相似文献   

12.
    
Hybrid coatings, based on poly(ethylene oxide) (PEO) or polycaprolactone (PCL) and silica (SiO2), at different organic–inorganic compositions have been used to coat PET films employed in the electric industry to produce capacitors. The overall electrical behavior of the coated films has been investigated. The electrical strength of the coated films increases up to 10–15% of the uncoated ones regardless of polymer type (PEO/PCL) and amount of inorganic phase, as far as the thickness of the coating is below 5 μm. A systematic increase of surface electrical conductivity is found in all coated samples which however still behave as insulators. Permittivity and loss factor also increase particularly at low frequencies (< 10 Hz) on account of the presence of ions deriving from the sol–gel process and on the presence of interfacial polarization probably related to the coatings nanostructurated morphology which leads to phase separation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4870–4877, 2006  相似文献   

13.
    
Viscoelastic behavior has a remarkable impact on the functional realization of shape memory polymers and their composites. Our previous work reported that a series of shape memory epoxies with varied curing agents and contents were synthesized and exhibited higher shape fixture and recovery rates. The viscoelastic behavior of the materials at different temperatures is experimentally investigated in this study. Stress–strain hysteresis under uniaxial tension, stress relaxation, and creep tests are performed. The energy dissipation factor and residual strain factor as functions of temperatures are presented in the basis of stress–strain hysteresis tests. Moreover, the effects of test temperature, curing‐agent type, and content on the viscoelastic behavior of these materials are discussed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013  相似文献   

14.
    
The effects of thermomechanical properties of dissimilar polymer plates on thermal bonding were investigated and the resultant deformation of cover Topas COC plate was modeled using a simplified quasi‐creep model. The appropriate conditions for thermal bonding for minimal deformation of both the Topas cover and substrate plates could be established through simulation using the quasi‐creep model. Both the cover plate and the substrate containing microchannels were fabricated by injection molding. The elastic modulus of the COC plate at different temperatures was measured using three‐point bending test. The thermal bonding was conducted at different temperatures, pressures, and holding times. The deformation of the cover plate (consisting of Topas with a lower glass transition temperature, Tg) into the microchannel of the substrate plate (consisting of Topas with a higher Tg) was found to be significant even at lower bonding pressures when the bonding temperature was higher than a critical temperature. Such deformation was dependent on the viscoelastic creep behavior of the material and the thermal bonding temperature and load. This deformation behavior was predicted by the numerical model, and the predicted results agree well with the experimental data. The bonding strength of the sealed microchannels was evaluated using the burst test. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011  相似文献   

15.
    
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  相似文献   

16.
    
In general, the universal viscoelastic model evaluated in this study was found to adequately predict constant strain rate, creep, and/or stress relaxation measurements from the constants determined from constant strain rate measurements. The elastic and viscous components for two acrylonitrile–butadiene–styrene (ABS) viscoelastic materials were also easily isolated using this new universal viscoelastic model. The creep measurements for ABS‐A (25383‐A) and ABS‐N (LL‐4102‐N) at three different stresses allowed elucidation of the common creep intercept strain of the calculated creep slopes that was designated as the “projected elastic limit.” Once the values for n and β were evaluated from creep measurements, then the creep variation of the universal viscoelastic model yielded a reasonably good fit of the measured creep data for both ABS‐A and ABS‐N. The extensional viscosity constant λE was found to be 7.2% greater for ABS‐A than for ABS‐N. Consequently, ABS‐N was found to have a lower extensional viscosity in secondary creep than that of ABS‐A at any specific strain rate. The value of the efficiency of yield energy dissipation n for ABS‐N as determined from creep measurements was also 37.6% larger than the value of n for ABS‐A. In addition, the projected elastic limit ?I for ABS‐A was 2% greater than the projected elastic limit for ABS‐N. These observations indicated that ABS‐A should be slightly more solidlike than ABS‐N. However, both ABS‐A and ABS‐N were significantly more solidlike than liquidlike because both of their values for the efficiency of yield energy dissipation n were very close to zero. In general, values of n range from 0 < n < 1 with a material characterized as being essentially pure elastic having a value of n = 0. Using the yield strain as the failure condition for constant strain rate and stress relaxation measurements and the strain at critical creep, the failure condition for creep, it was found that the universal viscoelastic model allowed these failure criteria to yield remarkably good agreement on a projected time scale. This agreement resulted even though separate and independent data were used to evaluate these three different techniques for both ABS‐A and ABS‐N. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1298–1318, 2003  相似文献   

17.
    
Woodfiber–polypropylene and woodfiber–waste polyethylene composites have been produced by injection molding and by hot pressing the thermoplastic between woodfiber mats. The stress relaxation under constant strain in these composites has been studied at 25, 50, and 80°C. The results have been compared with similar experiments performed on neat thermoplastics. It is interesting to note that the presence of woodfibers as reinforcement in the composites restricts the stress relaxation, but their effectiveness decrease with the increase in ambient temperature. Composites made by hot pressing the woodfiber mat and the thermoplastic are found to exhibit a lesser amount of relaxation than those made by injection molding the same combination. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 401–407, 2006  相似文献   

18.
    
Epoxy–amine was blended with two resol resins to study the influence of the final network and void content on the water absorption of these systems. To characterize the network structure of the blends, infrared analyses were performed. It was observed that a diminution in the crosslink density of the network and the reaction between the epoxy and resol have been occurred. From dynamic–mechanical analyses, a diminution in the Tg value and an increment in the height of the tan δ peak with the epoxy–amine content added to the resol were observed. Thermogravimetric analysis showed that the thermal stability of the resol was reduced by the addition of epoxy–amine as well as a lesser crosslink network for the blends with higher epoxy–amine content. The maximum water uptake and the diffusion coefficient were related with the chemical structure and void content of the specimens. On one hand, the maximum water uptake was observed to depend on the void content of the blends. On the other hand, the diffusion coefficient appears to be related with the local motions of the polymeric chains and with the hydrophilic character of the materials. This behavior was observed for the two resols studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 588–597, 2006  相似文献   

19.
Using a modified torsional dynamic rheometer, strain and torque signals are captured and analyzed through Fourier transform. A thorough analysis of strain signal is first performed to document the quality of the applied deformation and to define the optimum conditions for signal capture, and hence, for Fourier transform calculation. A specific calculation procedure is developed that allows the error associated with FT calculation to be estimated, in terms of mean harmonic peaks and their standard deviation. Scatter is observed on low strain results that nearly vanishes when the applied deformation is larger than 14%, thus giving confidence in data gathered under non‐linear viscoelastic conditions. Results on a series of gum EPDM with different macromolecular characteristics (MWD and long chain branching, LCB) are reported and discussed, with respect to a simple four parameters model for the variation on deformation of the relative third harmonic component. Processing additives are found to mask expected LCB effects. Results on a series of SBR 1500 samples, collected from various manufacturers, are presented that illustrate the capability of FT rheometry to detect differences between materials expected to be similar. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1101–1115, 2003  相似文献   

20.
    
The research aims to investigate the effects of natural and accelerated weathering on polyethylene‐based films. At this regard, monolayer films of low density/linear low density polyethylene blends, containing commercially available organic pigments and an UV absorber of the benzophenone type, have been considered. The samples were weathered on field (natural weathering) or using two different artificial procedures: UV lamp and QUV chamber. Conditioned film samples were, then, analyzed by performing several physical tests taking as‐received films as a reference. Rheological measurements showed an increase in viscosity of weathered sample melts as a consequence of photodegradation phenomena, inducing the formation of double bonds and crosslinks. This latter result was also confirmed by gel content measurements. UV–visible spectroscopic tests indicated that in both cases of natural and artificial weathering an increase of the transmittance of films occurred. Tensile tests indicated the increase of films stiffness, especially in case of samples conditioned using the UV lamp, and a large decrease of the strain at break, both in machine and in transverse directions, especially for film weathered using the QUV chamber. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013  相似文献   

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