Viscoelastic properties of ternary in situ elastomer composites based on fluorocarbon, acrylic elastomers and thermotropic liquid crystalline polymer blends

Dynamic mechanical analysis was performed to characterize the viscoelastic properties of binary and ternary blends of fluorocarbon elastomer (FKM), acrylic elastomer (ACM) and liquid crystalline polymer (LCP). The results showed that the storage and loss modulus of all the blends increased significantly with the weight percentage of the LCP. The glass transition temperature evaluated at the loss modulus peak, were in the range of −10-+5 °C for all the blends. The time temperature superposition principle was applied for the FKM/ACM and 20% LCP filled FKM/ACM blend in order to evaluate the changes in the viscoelastic properties of FKM/ACM blend by the addition of LCP. The Arrhenius and William-Landel-Ferry (WLF) equations were used to quantify the viscoelastic behaviour at the glass transition region. Both the blends exhibited a single relaxation, which is glass transition, observed as a peek in the loss modulus at 1 Hz. The glassy moduli of these two systems were found to be comparable, but the rubbery moduli of the LCP filled FKM/ACM was much higher than the LCP unfilled system. However, the viscoelastic behaviour of these two systems and their sensitivity to time temperature may be considered to be quite similar.     

Effect of γ-radiation on the dynamic mechanical properties of styrene–butadiene rubbers

Three different styrene–butadiene, gum rubbers were exposed to γ-radiation doses ranging from 0 to 200 Mrad. The crosslink densities, hardness, and the dynamic mechanical properties were evaluated. All specimens increased in hardness and crosslink density during radiation. This was reflected in an increased storage modulus, broadened loss tangent maximum, and increased relaxation spectrum. The dynamic data are presented in master curves which were developed by using the WLF equation.     

含能粘结剂低温动态力学性能的临界温度

采用ＤＭＡ（动态机械热分析仪）研究了几种含能粘结剂的机械松弛,从动态力学性能的ＴＴＳ（时温叠加１）原理,求得时间位移与频率对数的关系曲线及ＷＬＦ方程的常数Ｃ１和Ｃ２,应用ＷＬＦ方程,把时间位移与频率对数曲线的拐点作为材料由高弹态变为玻璃态的判据,计算求得火箭发动机点火瞬间粘结剂系统的临界温度Ｔｃ,根据自由体积理论模型和结晶理论解释了Ｔｃ的物理意义。并研究了临界温度与玻璃化转变温度之间的关系     

Equivalent processing time analysis of glass transition development in epoxy/carbon fiber composite systems

The cure kinetics and glass transition development of a commercially available epoxy/carbon fiber prepreg system, DMS 2224 (Hexel F584), was investigated by isothermal and dynamic‐heating experiments. The curing kinetics of the model prepreg system exhibited a limited degree of cure as a function of isothermal curing temperatures seemingly due to the rate‐determining diffusion of growing polymer chains. Incorporating the obtained maximum degree of cure to the kinetic model development, the developed kinetic equation accurately described both isothermal and dynamic‐heating behavior of the model prepreg system. The glass transition temperature was also described by a modified DiBeneditto equation as a function of degree of cure. Finally, the equivalent processing time (EPT) was used to investigate the development of glass transition temperature for various curing conditions envisioning the internal stress buildup during curing and cooling stages of epoxy‐based composite processing. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 144–154, 2002; DOI 10.1002/app.10282     

Thermal and dynamic mechanical properties of organic–inorganic hybrid composites of itaconate‐containing poly(butylene succinate) and methacrylate‐substituted polysilsesquioxane

Itaconate‐unit‐containing poly(butylene succinate) (PBSI) was synthesized by the reaction of 1,4‐butanediol, succinic acid, and itaconic acid in a molar ratio of 2.0 : 1.0 : 1.0, and the obtained PBSI was reacted with methacryl‐group‐substituted polysilsesquioxane (ME‐PSQ) in the presence of benzoyl peroxide (BPO) at 130°C to produce PBSI/ME‐PSQ hybrid composites. The thermal and dynamic mechanical properties of the PBSI/ME‐PSQ hybrid composites were investigated in comparison with those of PBSI cured at 130°C in the presence of BPO. As a result, the hybrid composites showed a much higher thermal degradation temperature and storage modulus in the rubbery state than the cured PBSI (C‐PBSI). The thermal degradation temperature and storage modulus of the hybrid composites increased with increasing ME‐PSQ content. The glass‐transition temperature, measured by dynamic mechanical analysis of the hybrid composites, somewhat increased with increasing ME‐PSQ content. However, the glass‐transition temperatures of all the hybrid composites were lower than that of C‐PBSI. Although the IR absorption peak related to C?C groups was not detected for C‐PBSI, some olefinic absorption peaks remained for all the hybrid composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Some considerations concerning the dynamic mechanical properties of cured styrene–butadiene rubber/polybutadiene blends

The dynamic mechanical response of several binary mixtures of a styrene–butadiene copolymer and high cis‐polybutadiene has been studied. The loss tangent and shear modulus were measured with a free damping torsion pendulum at temperatures between 143 and 343 K in argon atmosphere. From the loss tangent data the glass transition temperature of each sample was evaluated. The results can be represented by the Fox equation that relates the glass transition temperature of the blend with that of constituent polymers. The influence in the loss tangent data of the crystallization of the high cis BR used in the blend is discussed. A study of the separation of the crystalline and amorphous parts in the polybutadiene using the storage modulus data is presented. Finally, the loss of crystallinity at different contents of SBR in the blend is analysed using the dynamic mechanical data. © 2000 Society of Chemical Industry     

The effect of kevlar fiber reinforcement on the curing,thermal, and dynamic‐mechanical properties of an epoxy/anhydride system

Curing, thermal, and dynamic‐mechanical relaxational behavior of an epoxy/‐anhydride resin and a Kevlar‐fiber/epoxy composite were compared. Reinforcement by Kevlar fibers had a catalytic effect on the curing reaction. Reinforced formulations produced higher extents of reaction than neat formulations at the same curing time. Curing kinetics was also studied by means of DSC heating scans. When the Kevlar content increased, the heat flow curves and the exothermic peak temperature shifted significantly to lower temperatures. The glass transition temperature of the matrix also decreased as the Kevlar content increased. Postcuring reduced the differences between the neat and reinforced formulations. Loss tangent and storage modulus versus frequency master curves were obtained from isothermal dynamic‐mechanical measurements. The effect of fiber addition on the main dynamic‐mechanical relaxation was analyzed with a simple mechanical model.     

Viscoelastic properties and characterization of inorganic particulate‐filled polymer composites

To identify effects of glass bead (GB) content on the dynamic mechanical properties of filled low‐density‐polyethylene (LDPE) composites, the storage modulus, loss modulus, glass transition temperature, and mechanical damping of these composites were measured using a Du Pont dynamical mechanical analysis instrument in temperature range from ?150 to 100°C. It was found that the storage modulus increased nonlinearly with an increase of the GB volume fraction. On the basis of Eshelby's method and Mori's work, an equation describing the relationship between the relative storage modulus (E′_R) and filler volume fraction for polymeric composites was proposed, and the E′_R of LDPE/GB composites were estimated by means of this equation at temperatures of ?25, 0, and 25°C, and the calculations were compared with the experimental data, good agreement was showed between the predictions and the measured data. Furthermore, this equation was verified by the experimental from Al(OH)₃ filled EPDM composites at glassy state reported in a reference. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Viscoelastic behavior of Cytec FM73 adhesive during cure

In this work, the viscoelastic properties of Cytec FM73 structural film adhesive were characterized. Several resin plates were cured using various process cycles to achieve a range of final cure states. Specimens cut from these plates were tested using a dynamic mechanical analyzer (DMA) and the glass‐transition temperature at each degree of cure was determined. Stress relaxation tests at different temperatures were then performed using DMA in stress relaxation mode and time‐temperature superposition was used to generate master stress relaxation curves and associated shift functions for each degree of cure. Several different constitutive models were examined for their ability to describe relaxation modulus development during cure. A simple three‐parameter model consisting of a stretched exponential with cure‐dependent terms was found to provide the best results. The results indicate that of the parameters used in the model, relaxation time strongly depends on cure state. The empirical DiBenedetto equation was used to obtain an expression for glass‐transition temperature as a function of degree of cure. This expression was in turn used to derive a new relation to describe stress relaxation time as a function of degree of cure. The shift function was modeled using a simplified form of the Vogel equation with cure‐dependent coefficients. Good correlation between measured relaxation modulus and model predictions was observed. © 2003 Wiley Periodicals, J Appl Polym Sci 91: 2548–2557, 2004     

高聚物的低温动态力学性能

用ＤＭＡ（动态机械热分析仪）研究了几种高聚物的低温动态力学性能,测定了样品的动态力学性能参数,并且应用动态力学性能的ＴＴＳ（时温叠加）原理,求得了ＷＬＦ方程的常数Ｃ１和Ｃ２,由Ｃ１和Ｃ２进一步计算出材料的脆性参数,同时从分子结构角度解释了本文所研究试样之间贮能模量和脆性参数的差别。     

Effect of Thermal History on Structural Changes in Melt‐Intercalated Poly(ε‐caprolactone)/Organoclay Nanocomposites Investigated by Dynamic Viscoelastic Relaxation Measurements

Poly(ε‐caprolactone) (PCL) nanocomposites were prepared using two different types of organically modified nanosilicates by melt intercalation with an internal mixer. Dynamic mechanical analysis revealed possible structural changes in the nanocomposites even during the small deformation occurring during shear oscillatory measurements, as evidenced by a V‐shaped modulus change in the plot of the dynamic storage modulus as a function of stepwise increased temperature. X‐ray diffraction patterns were recorded at different simulated temperatures during the various stages of dynamic measurements. The X‐ray data indicate that the structural changes can be ascribed to a further intercalation of the PCL matrix chains into the silicate layers. This further intercalation is a consequence of the heat treatment during the dynamic mechanical measurements. Furthermore, there is a considerable vertical shift in addition to the horizontal shift in the higher temperature regime, which allows the mapping of a master curve through the application of the time‐temperature superposition principle to the dynamic storage and the loss modulus data obtained at various isothermal temperatures. The present study is also concerned with the relative molecular mobility of both PCL nanocomposites in the given experimental conditions considering the Williams‐Landel‐Ferry (WLF) equation and the Arrhenius relationship between the horizontal shift factor and the activation energy of flow. Moreover, the extent of the vertical shift as a function of temperature made it possible to determine the apparent activation energy of the further intercalation of PCL into the silicate layers. This intercalation is caused by the additional exposure to heat during the dynamic mechanical measurements after mixing, which led to a comparison of the relative diffusivity of the PCL matrix in the two nanocomposites.

Dynamic shear storage moduli G′ of PCLOC25A and PCLOC30B as a function of temperature with increase increments of 20 °C from 60 to 260 °C. The G′ data were obtained from isothermal frequency sweep G′(ω) data at ω = 1 rad · s^?1 at the corresponding temperatures.     

Dynamic mechanical analysis of particulate‐filled epoxy resin

The dynamic mechanical properties of epoxy composites filled with different amounts of quartz powder were investigated. The storage modulus and loss tangent were measured at frequencies between 7.8 and 323 Hz from room temperature up to 460 K. The influence of the filler content on the temperature and frequency behavior of the dynamic mechanical properties is discussed and explained in terms of models presented in the literature. In particular, the dependence of the composite damping with the quartz content is explained with regard to damping due to particle–particle and polymer–particle interaction. Also, the glass‐transition temperature as a function of filler content was obtained and was related to the results obtained for the apparent activation energies of the α relaxation, which were estimated with the Williams, Landel, and Ferry equation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 883–892, 2003     

Combined effect of relative humidity and temperature on dynamic viscoelastic properties and glass transition of poly(vinyl alcohol)

On the basis of the experimental studies on viscoelastic properties of poly vinyl alcohol (PVA) films at various relative humidity (RH) and temperature conditions by dynamic mechanical analysis (DMA), the influence of both temperature and RH on the glass transition are discussed and an improved property model is developed to relate the dynamic modulus to RH and temperature. The results indicate that (1) with increasing the RH, the storage modulus of PVA decrease remarkably, while both loss modulus and tanδ sharply increase to reach the peak and then markedly drops. The intensity of this variation is highly dependent upon temperature. (2) Moisture increase will cause the glass transition of PVA at isothermal condition and the transition point can be detected by glass transition relative humidity (RH_g) that obtained by isothermal RH scans. (3) Similar to the relationship between T_g and RH, the RH_g of PVA vary linearly with temperature. The state diagram of RH_g versus temperatures is nearly consistent with that of T_g versus RH. (4)The present equation based on model of Mahieux and Reifsnider (Mahieux and Reifsnider, Polymer 2001, 42, 3281) can predict well the dynamic modulus of PVA at various RHs and temperatures. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3161–3167, 2013     

Reinforced polystyrene via solvent‐exfoliated graphene

Solvent‐exfoliated graphene (SEG)‐reinforced polystyrene (PS) composites were prepared using a straightforward solution‐casting method. SEG sheets, obtained by sonication‐assisted solvent direct exfoliation from natural graphite, were well dispersed in the PS matrix as evidenced from scanning electron microscopy and transmission electron microscopy observations. Addition of 0.5 wt% SEG resulted in a 6% increase in tensile strength and a 77% improvement in Young's modulus over pure PS due to the effective load transfer between SEG and PS matrix. The Young's moduli of the PS/SEG composites were obtained from both tensile experiments and calculations using the well‐established Halpin–Tsai model. Results from dynamic mechanical analysis indicated that the storage modulus of the PS/SEG composites was significantly improved relative to neat PS. The glass transition temperatures of the composites were found to increase substantially upon addition of SEG, consistent with differential scanning calorimetry analysis. © 2017 Society of Chemical Industry     

Dynamic mechanical properties of extruded nylon–wood composites

Dynamic mechanical properties determine the potential end use of a newly developed extruded nylon–wood composite in under‐the‐hood automobile applications. In this article, the dynamic mechanical properties of extruded nylon–wood composites were characterized using a dynamic mechanical thermal analyzer (DMTA) to determine storage modulus, glass transition temperature (T_g), physical aging effects, long‐term performance prediction, and comparisons to similar products. The storage modulus of the nylon–wood composite was found to be more temperature stable than pure nylon 66. The T_g range of the nylon–wood composite was found to be between 23 and 56°C, based on the decrease in storage modulus. A master curve was constructed based on the creep curves at various temperatures from 30 to 80°C. The results show that the relationship between shift factors and temperature follows Arrhenius behavior. Nylon–wood composites have good temperature‐dependent properties. Wood fillers reduced the physical aging effects on nylon in the wood composites. The comparison of the nylon–wood composite with other similar products shows that nylon–wood composites are a promising low cost material for industrial applications. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Mechanical,thermal, and dynamic mechanical properties of long glass fiber‐reinforced thermoplastic polyurethane/polyoxymethylene composites

Long glass fiber (LGF)‐reinforced thermoplastic polyurethane (TPU) elastomers and polyoxymethylene (POM) (LGF/TPU/POM) composites were prepared by using self‐designed impregnation device. Dynamic mechanical properties of the LGF/TPU/POM composites have been investigated by using dynamic mechanical thermal analysis. The results indicated that the storage modulus and glass transition temperature of the composites increase with increasing the glass fibers content and scanning frequencies. In addition, the Arrhenius relationship has been used to calculate the activation energy of α‐transition of the LGF/TPU/POM composites. The thermal stability of the LGF/TPU/POM composites was investigated by thermogravimetric analysis. The consequence demonstrated that the thermal stability increase with augmenting the content of glass fibers. The mechanical properties of the composites are investigated by a universal testing machine and a ZBC‐4 Impact Pendulum. The results demonstrated the mechanical properties of the composites aggrandize with augmenting the glass fibers content. The good dispersion of the LGFs in the matrix resins is obtained from scanning electron micrographs. POLYM. COMPOS., 35:2067–2073, 2014. © 2014 Society of Plastics Engineers     

Acrylic rubber‐fluorocarbon rubber miscible blends: Effect of curatives and fillers on cure,mechanical, aging,and swelling properties

The cure characteristics and mechanical properties of gum and filled acrylic rubber (ACM), fluorocarbon rubber (FKM), and their blends of varying compositions were studied both under unaged and aged conditions. The rheometric study showed that optimum cure properties were obtained using a mixed curing system of blocked diamine, hexamethylenediamine carbamate (Diak #1), and ammonium benzoate. From varying the curing agents, the optimum levels of Diak #1 and ammonium benzoate were found to be 1.5 and 2.5 phr, respectively. The addition of different fillers and their loading influenced the cure properties, with increased torque and reduced scorch safety. The gum and filled 50:50 (w/w) ACM‐FKM showed overall performance in strength properties. Postcuring improved the strength of all the systems, especially the systems with a higher proportion of FKM. None of the properties changed significantly during aging of the blends. FKM and the blends containing a higher proportion of FKM were affected least by aging. Swelling of the blends was reduced by the addition of fillers. Dynamic mechanical thermal analysis showed a single tan δ peak corresponding to a single phase transition for both cured and filled blends. The storage modulus of the blend increased from the gum blend to the filled blend, indicating the presence of polymer‐filler interaction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1442–1452, 2003     

Effect of molecular relaxation of acrylic elastomers on impact toughening of polybutylene terephthlate

In this study, we examined the performance of two core‐shell acrylic‐based impact modifiers (AIM) prepared by emulsion polymerization. The rubber core was prepared from ethyl hexyl acrylate (EHA) and n‐octyl acrylate (n‐OA). In such as process, the particle size and particle‐size distribution of the modifiers were precisely controlled, so that performance differences observed in polybutylene terephthlate (PBT), used as matrix resin, could only be interpreted in terms of the nature of the elastomeric component of the modifiers. When isolated, the rubber core of the modifiers showed identical glass transition temperatures (T_g) by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) despite the fact that they were made from two different acrylic monomers. Temperature‐frequency superposition principle inferred from the classical WLF equation showed that the rubber components exhibit the same T_g at all frequencies including at the time scale at which mechanical impact typically occurs. However, significant differences in low temperature impact performance measured at ?30°C using notched Izod impact test according to ASTM D 256 were obtained even though their rubber components had identical T_g. Such differences were attributed to the dynamic relaxation behavior of the rubber components and identified as inherent properties of the elastomers due to the structure of the monomers' repeat units. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Influence of water absorption on the mechanical properties of a DGEBA (n = 0)/1, 2 DCH epoxy system

The diffusive, calorimetric, and mechanical behavior of a system composed of a diglycidyl ether of bisphenol‐A (DGEBA, n = 0) and 1, 2 diamine cyclohexane (1, 2 DCH) were investigated during water sorption at different temperatures (23, 47, 58, 77, and 100°C). Experimental results showed that the water absorption at these temperatures fitted well to Fick's law. The water moisture content at the equilibrium temperature and the water moisture content at the equilibrium‐curing conditions dependences have been checked. The activation energy for diffusion was calculated obtaining a value 26.01 kJ/mol. Dynamic mechanical analysis of several samples immersed in water at 100°C during different periods of time showed no significant changes in the glass transition temperature, and a decrease in the storage modulus at 2% of water content was observed. Storage modulus remained essentialy constant above that water content. Values of glass transition temperature were corroborated by differential scanning calorimetric measurements. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 353–358, 1999