Dynamic Mechanical Spectrometer Research Articles

Relaxation behavior and activation energy of relaxation for polyimide and polyimide–graphene nanocomposite

ABSTRACTThe relaxation behavior of polyimide and its nanocomposite containing 10 wt % of graphene was studied by using the dynamic mechanical spectrometer. Dynamic mechanical analysis of polyimide and its composite was performed as a function of temperature and frequency in the temperature range of 25–480 °C and frequency range between 0.05 and 100 Hz. The effect of increasing frequency of testing from 0.05 to 100 Hz is a significant shift from the glass transition temperature, Tg, to higher temperature from 360 °C at 0.05 Hz to 420 °C at 100 Hz. The tan δ peak height for both α and β transitions decreased with increasing test frequency from 0.24 at 0.05 Hz to 0.08 at 100 Hz, due to increasing restriction to chain motion. At any given testing frequency, the Tg for the composite was shown to be higher than that for the matrix by about 5–10 °C. The Arrhenius equation was used to calculate the activation energy for both α and β transitions. The activation for α and β transitions for the composite and polyimide matrix were determined to be 688 and 537 kJ/mol and 313 and 309 kJ/mol, respectively, indicating that a significant increase in the energy barrier to chain relaxation occurred as a result of reinforcement of polyimide with low weight fraction of graphene. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43684.

Temperature sensitivity and model of stress relaxation properties of cement and asphalt mortar

The stress relaxation properties of two types of cement and asphalt mortar (CA mortar) in the temperature range of −40 to 60°C and at the initial strain of 0.1% was studied by dynamic mechanical thermal spectrometer. The results show that the stress relaxation process of CA mortar can be divided into attenuation stress relaxation stage and steady stress relaxation stage. The lower the temperature is, the higher the initial stress and residual stress are. At the same temperature, the stress relaxation rate and specific stress relaxation of type I CA mortar are larger than that of type II CA mortar, while the initial stress, residual stress and stress relaxation modulus are relatively smaller. The glass transition region of type I CA mortar characterized by the isochronous stress–temperature curves is −20 to 0°C. The established model agrees well with experimental results, and φ, δ are dominated parameters affecting the stress relaxation of CA mortar. This indicates that the established model can effectively predict the time dependence and temperature sensitivity of stress relaxation of CA mortar. The results can provide reference for the calculation of temperature stress of CA mortar filling layer of ballastless slab track.

Mechanism of corrosion protection of aluminum alloy substrate by hybrid polymer nanocomposite coatings

The corrosion protection of polymer clay nanocomposite, PCN coatings consisting of polyurea, siloxanes, epoxy ester and montmorillonite clay was determined. Corrosion resistance of the coating, was assessed by monitoring the polarization resistance and impedance of coated aluminum alloy, Al 2024-T3, coupons immersed in 3.5wt.% of sodium chloride, NaCl, solution. Direct current polarization and electrochemical impedance spectroscopic techniques were used to measure polarization resistance and impedance of the samples, respectively. Diffusion of saturated salt solution into free-standing PCN films was measured gravimetrically and diffusivity of the nanocomposites was determined. The presence of clay decreases diffusivity and increases corrosion resistance of the non-scribed coatings containing up to 10wt.% of clay. A correlation between polarization resistance and diffusivity was made. It was shown that for non-scribed coatings, polarization resistance increases with decreasing diffusivity. A relationship between coating's diffusivity and weight fraction of clay was established. Increasing clay concentration also resulted in decreasing diffusivity. The scribed nanocomposite coatings show slightly decreasing polarization resistance with increasing weight fraction, however, the polarization resistance of scribed coatings containing low clay weight fraction in the range between 0.5 and 2.0wt.% was higher than that for the matrix. A barrier mechanism of corrosion prevention of the coated substrate is proposed for non-scribed coatings. The viscoelastic property of the nanocomposites was determined by using dynamic mechanical spectrometer. A correlation between polarization resistance of the coatings and the rubbery plateau modulus on the one hand and polarization resistance and tanδ peak area for α-transition of the nanocomposites is made. Decreasing tanδ peak area for α-transition and increasing rubbery plateau modulus resulted in increasing coatings polarization resistance.

Effect of clay on the corrosion inhibition and dynamic mechanical properties of epoxy ester–polyurea–polysiloxane hybrid coatings

AbstractThe corrosion resistance of polymeric coatings containing epoxy ester, polyurea, and polymethylhydrosiloxane was significantly improved by the addition of cloisite 15A organoclay. The weight percent of organoclay was varied from 0.5 to 10%. The presence of organoclay in the coatings was confirmed using the Fourier transformed infrared spectroscopy. The effect of organoclay on the surface energy of the coatings was analyzed by measuring contact angle with a video contact angle analyzer and using water and iodomethane as the probing liquids. The surface energy of the coatings increased with increasing organoclay concentration. The corrosion resistant properties were measured by direct current polarization technique. The addition of organoclay enhanced the corrosion resistance of the coatings, and the best corrosion resistance was shown by coating containing 1% organoclay. The dynamic mechanical property of the coatings was determined using the dynamic mechanical spectrometer. The glass transition temperature of the films decreased significantly with the addition of organoclay up to 1% after which it increased with additional increase in the wt% of organoclay. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Characterization of corrosion resistant clay/epoxy ester composite coatings and thin films

The processibility and corrosion resistance of epoxy ester coatings was improved by the addition of cloisite 15A clay. The weight percent of clay was increased from 1% to 10% of clay. The presence of clay in the coatings was confirmed by using the Fourier transformed infrared spectroscopy, FTIR. The effect of clay on the contact angle of the coatings was determined by using the video contact angle analyzer. The surface contact angle of the coatings decreased with increasing weight percent of clay. The surface roughness as measured by atomic force microscope, AFM decreased with the addition of clay up to 1wt.% loading. The dynamic mechanical property of the coatings was determined by using the Seiko Dynamic Mechanical Spectrometer, DMS. The reinforcement of epoxy ester with organoclay resulted in a significant increase in the glass transition temperature, Tg. However, there was no significant change in the height of the tangent of the loss angle, tanδ with variation in the clay concentration, indicating that there was no significant change in the damping behavior of the epoxy ester coatings as a result of reinforcement by organoclay.

Viscoelastic Properties of Montmorillonite Clay/Polyimide Composite Membranes and Thin Films

Montmorillonite clay, cloisite 30B (nanoclay), was successfully dispersed in a polyimide (PI) matrix by in situ condensation polymerization followed by solution casting and thermal imidization. Wide angle X-ray diffraction, WAXD, test was used to study the structure of cloisite 30B clay powder and nanoclay/polyimide composites. The WAXD spectra of nanoclay powder and the composites show one major diffraction peak at 4.76° and 6°, respectively, suggesting that the d-spacing of nanoclay was decreased by about 26% after composite film processing. The viscoelastic property of polyimide and nanoclay/polyimide composite was studied by using dynamic mechanical spectrometer. The storage modulus and glass–rubber transition temperature of nanoclay/polyimide composites increases with increasing volume fraction of clay. The storage modulus of the composites in the rubbery plateau region, (T > 400 °C) increased remarkably with increasing volume fraction of clay. A modulus enhancement, (EC/EM) of about three orders of magnitude, (EC/EM ~1,440) was obtained for nanoclay/polyimide composite containing 6.8 vol% of nanoclay. The tangent of the loss angle (tan δ) for the composites, decreased with increasing volume fraction of nanoclay. The observed decrease in tan δ with increasing volume fraction of clay is consistent with the established trend of increasing storage modulus and glass–rubber transition temperature with increasing volume fraction of nanoclay. The phenomenal increase in the rubbery plateau storage modulus and glass–rubber transition temperature with increasing volume fraction of clay is believed to be due to increased restriction of chain motion with increasing nanoclay volume fraction.

Effect of Temperature and Frequency on Dynamic Mechanical Properties of Poly(<i>Methyl Methacrylate</i>)

The temperature sweep tests at defferent frequencies and heating rates, and frequency sweep tests at various temperatures for the samples of poly(methyl methacrylate) are carried out on a dynamic mechanical thermal spectrometer EPLEXOR® 500N-Gabo. The effects of temperature, frequency and heating rate on dynamic mechanical properties of poly(methyl methacrylate) are investigated. The results indicate that the glass transition temperature of poly(methyl methacrylate) increases with increasing frequency from 1 to 100Hz, and increases with increasing heating rate from 3 to 8°C/min as well. The temperature sweep curves at various heating rates suggest that the storage modulus of poly(methyl methacrylate) is non-sensitive at heating rate 3°C/min or 8°C/min, while heating rate is 5°C/min, there exists a critical temperature, within which the storage modulus versus temperature curves depart from each other, and beyond which the curves overlap one another. The glass transition temperature determined by the peak of loss modulus curve is smaller than that defined by the peak of loss tangent. The frequency sweep curves at a constant temperature show that a drop in storage modulus and a peak in loss tangent appear at a certain critical frequency, and the critical frequency increases with increasing temperature. For amorphous polymer, a competitive mechanism between frequency and temperature is observed. Higher temperature accelerates molecular motion, while higher frequency restrains molecular motion, so that the critical frequency corresponding to the peak of loss tangent shifts toward the direction of high temperature.

Thermal and mechanical behavior of flexible polyurethane‐molded plastic films and water‐blown foams with epoxidized soybean oil

AbstractWater‐blown flexible polyurethane foams and molded plastic films were made by replacing 0 to 50% of Voranol® 4701 in the B‐side of foam and plastic film formulation by epoxidized soybean oil (ESBO). Physical properties of foams including density, 50% compression force deflection (CFD), 50% constant deflection compression (CDC), and resilience were determined. A dynamic mechanical spectrometer (DMS) and a differential scanning calorimeter (DSC) were used to characterize the hard segment (HS) and soft segment (SS) ratio and thermal properties of plastic. Various functional groups in both flexible polyurethane foam and plastic film were characterized using Fourier transform‐infrared spectroscopy with attenuated total reflectance (FTIR‐ATR). When increasing the ESBO content, both density and 50% CFD of water‐blown polyurethane foams decreased first, then increased. On the other hand, the 50% CDC and resilience of foams showed a sharp increase and decrease, respectively. When increasing the ESBO content, the peak of tan δ in DMS analysis and Δcp in DSC analysis of plastic films both decreased indicating the hard segment increased and the soft segment decreased in plastic film, respectively. The FTIR‐ATR results also show the hydrogen‐bonded urethane group increased in plastic films with increasing ESBO content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Damping Properties of Ductile Cu-Al-Mn-Based Shape Memory Alloys

The damping property tanof Cu-Al-Mn-based alloys, where tanis nearly equal to internal friction Q � 1 , was investigated using a Dynamic Mechanical Spectrometer (DMS). It was found that the dependences of frequency and strain amplitude on tanare significantly different between the parent + martensite two-phase and the martensite single-phase states, i.e., tanis mainly influenced by frequency in the two-phase state and by strain amplitude in the martensite state. It was also found that the relative grain size d=D is a function of the damping capacity, where d and D are the grain diameter and the diameter of the wire, respectively, and that tanincreases with increasing d=D. The maximum values of tan � ¼ 0:54 and tan � ¼ 0:07 were obtained in the two-phase state and in the martensite state, respectively, in the specimen of d=D � 1.

Rheometry and polymorphism of cocoa butter during crystallization under static and stirring conditions

AbstractIn this work the association between polymorphism and the crystal network structure developed by the TAG of cocoa butter (CB) was investigated under static and stirring crystallization conditions using a dynamic mechanical spectrometer. The results obtained showed that parameters obtained through oscillatory rheometry (i.e., phase shift angle, δ) followed the polymorphism of CB during static crystallization. Although standard DSC was not capable of differentiating the α to β′ phase transformation from the direct β′ crystallization from CB melt, δ rheograms measured these two processes separately. Additionally, through oscillatory rheometry, we followed the dimensionality of the crystal network during CB crystallization. Within this context, the pre‐exponential term (In γ) from the weak‐link regime equation for colloidal dispersions was much more sensitive than the fractal dimension (D) to differences in crystal size, spatial distribution of the crystal network, and melting temperature of the β′ phase of CB. On the other hand, torque measurements obtained during CB crystallization under stirring conditions showed a shear rate effect that favored TAG development in the β phase at temperatures of 19, 22, and 26.5°C, particularly at shear rates of 120 and 400 rpm. In contrast, under static conditions CB did not develop in the β phase at any of the crystallization temperatures investigated (i.e., 18 to 26.5°C).

Effect of Gate Shape on Fiber Orientation and Mechanical Properties of Injection Molded CF/LCP Thin Plates

In this study, the effects of gate shape on the fiber orientation, mechanical properties and fracture behaviors of injection molded Carbon Fiber reinforced Liquid Crystalline Polymer (CF/LCP) thin plates were investigated. Injection molded CF/LCP thin plates were manufactured with several gate shapes and injection speeds. Although it is well known that CF/LCP molded thin plates are composed of multi layer structures, the distribution of modulus in the thickness direction has not been quantitatively measured. Therefore, in this study, injection molded CF/LCP thin plates were sliced at 100μm intervals in the thickness direction and the modulus of each slice was measured with a Dynamic Mechanical Spectrometer (DMS). All specimens consisted of five macro layers; two skin layers, two intermediate layers, and a core layer. The fiber orientation in each layer varied with the gate shape and location (film gate and side gate) in the plate mold. These differences led to differences in the modulus of each layer of the composite, which in turn led to differences in the fracture behavior. The moduli of the various slices was useful to estimate the overall modulus in the thickness direction. It was concluded that the orientation distribution of carbon fibers and LCP for each gate shape contributed to the distribution of modulus in the thickness direction of the injection molded CF/LCP thin plates.

Rheological Investigation of Shear-Induced Crystallization of Poly(ϵ-Caprolactone)

The isothermal crystallization behavior of poly(ϵ-caprolactone), PCL, has been investigated as functions of crystallization temperature, shear rate, and shearing time using a Rheometeric dynamic mechanical spectrometer. The characteristic rheological parameters—such as the dynamic shear moduli (G′, G″), dynamic shear viscosity (η *), and loss tangent (tan δ)—were found to be very sensitive to the structure change accompanying the crystallization process. At the early stage of the crystallization process, a rapid increase in the rheological parameters (G′, G″, and η *) was observed; however, tan δ decreases strongly. This substantial change in the rheological parameters during the crystallization process is attributed to the increase of volume fraction of the solid crystalline part that may act like cross-links. The effect of shear flow on the isothermal crystallization process of PCL was investigated by imposing different shear values on the molten sample before the isothermal crystallization process. It was found that the crystallization process was accelerated to a great extent under high shear rate and long shearing time. The induction time of the crystallization process, t 0, was found to be substantially decreased with increasing shear rate. The isothermal crystallization kinetics at various shear rates was analyzed using the Avrami equation. The Avrami exponent, which provides qualitative information about the nature of the nucleation and growth process, was found to be shear rate and crystallization temperature dependent. The Avrami exponent increased to as large as 13.7 at γ˙=3 sec−1 and T c =46°C. This value is very high, higher than the exponent value obtained from other techniques, such as differential scanning calorimetry and X-ray scattering (∼3). The high value of the Avrami exponent was attributed to orientation in the molecular chains that leads to an increase in the nucleation and growth rate of the crystallization process under shear flow.

The Effect of Several Kinds of Oils on the Oil Resistance Behavior of Polystyrene Thermoplastic Vulcanizate

The oil resistance behavior of polystyrene thermoplastic vulcanizates (TPVs) such as polypropylene (PP)/polystyrene block copolymer (SBC) systems were investigated using a dynamic mechanical spectrometer (DMS) and transmission electron microscopy (TEM). Testing oils used were paraffinic oil, ASTM oil #3, an automobile grease and petrol, into which all specimens were immersed at 1 000C for 72 hrs. Dynamic mechanical spectra showed that non-crosslinking segments of SBC were subjected to damage by testing oil properties. Particularly their segments seemed to be more soluble and swelled by paraffinic oil or ASTM oil #3. TEM photomicrographs of immersed specimens showed similar results.

A Semi-Analytical Resolution of a Generalized Unidirectional Self-Consistent Model: Theoretical Bases and Experiment in Viscoelasticity

In recent articles [1], [2] we presented a finite element computation based on the homogenization theory of periodic media [3] or on the effective moduli approach to predict the complex moduli for unidirectional multiply coated continuous fiber composites via the correspondence principle [4], [5]. To have a method to compare with those approaches, we present first a semi-analytical resolution for a generalized unidirectional self-consistent model which predicts all the five independent elastic moduli and their complex counterparts [6], [7]. The resolution of this model is obtained by extending the general solution to the displacement and stress field within the constituents, proposed by Pagano-Tandon [8] and Carman et al. [9] for the problem "n concentric cylinders" of Hashin-Rosen's type [10]. Our direct resolution provides a new evaluation for the transverse shear modulus. The four other coefficients are proved to be coincident with the ones obtained by the n-phase "Composite Cylinder Assemblage," noted CCA model [10]. In the second part, this semi-analytical solution is compared with some experimental results that we obtained on the dynamic mechanical spectrometer METRA VIB and with other available predicting methods, for a unidirectional coated continuous fiber composite glass/epoxy. In order to obtain a better prediction for the loss tangent factor tan r1tE of the complex transverse Young's modulus ET in the main mechanical relaxation zone, two temperature-dependent evaluations for the complex Poisson's ratio of the viscoelastic polymer matrix are presented.

A Dynamic Mechanical Technique for Detecting Rubber Particle Cavitation in toughened Plastics

It is now widely recognised that cavitation of the rubber particles plays an important part in the energy-absorbing deformation mechanisms of toughened plastics. Cavitated rubber particles not only reduce the shear yield stress of the polymer, but also act as nuclei for craze initiation [1]. An understanding of the cavitation process is therefore essential in developing theories of rubber toughening. Recent papers have thrown new light on this problem, by using an energy-balance model to relate critical conditions for cavitation to the morphology and properties of the rubber particle [1±4]. The energy for void formation comes from two sources: mechanical loading and differential thermal contraction. Tensile loading produces volume strains in the particle and its surroundings, which are released when the rubber cavitates; additional volume strains of similar magnitude are generated on cooling the polymer from the Tg of the matrix (typically ,100 8C) to 23 8C [5]. One effect of these volume strains on the rubber phase is to increase its ` free volume'' and shift the low-temperature secondary loss peak to lower temperatures [6]. Subsequent cavitation allows the rubber to relax to its equilibrium density, so that the tana maximum shifts back to a temperature near the Tg of the unconstrained elastomer. This principle has been used by Morbitzer and colleagues [7, 8] to demonstrate that cooling ABS polymers to y60 8C is in itself suf®cient to cause cavitation or debonding of selected rubber particles. By varying the particle size and rubber content, they obtained samples in which the volume fractions of cavitated and intact particles were comparable: the low temperature tana peak then split into two, with maxima about 10 K apart. However, splitting of the tana peak in this way is highly unusual; in almost all other cases, a single rubber gives a single loss peak, with no indication of whether the particles are all intact or all cavitated. Most previous studies of rubber particle cavitation have involved mechanical straining, which almost inevitably results in yielding of the matrix, and further expansion of the voids. These complications can be avoided by using cooling alone to induce cavitation; thermal contraction of the rubber particle generates compressive stresses in the neighbouring matrix. From the experimental point of view, the limitations of this method of cavitation are that the voids formed are small (diameters ,50 nm), and occupy ,1% of the volume of the host particle. Detecting voids of this size and concentration using electron microscopy or scattering techniques presents major dif®culties. The aim of the present work is to develop alternative methods, based on dynamic mechanical testing, for detecting cavitation in rubber particles. The basic principle is simple: if the rubber particles are intact, the corresponding tana peak will shift downwards under tensile stress, and upwards under compressive stress. However, if the rubber particles have cavitated, the shift will occur only in compression. Tests were carried out using an Eplexor dynamic mechanical thermal spectrometer (DMTS; Gabo Qualimeter GmbH, Germany). This instrument is able to apply static loads of up to 1500 N to the specimen, in tension or compression, while simultaneously measuring dynamic mechanical properties at small load amplitudes. The material used in this study was a standard high-impact polystyrene (HIPS) containing ,8 wt % of polybutadiene in the form of salami particles with diameters in the range 0.5±5.0 im. In order to vary the mechanical properties of the rubber phase, without affecting the particle morphology or molecular weight of the PS matrix, granules of this HIPS were melt compounded with sulphur at 200 8C in a Werner & P eiderer ZSK-30 twin-screw extruder. This resulted in three blends, containing 0, 0.3 and 0.6% sulphur, which, when dissolved in toluene and centrifuged, respectively gave gel contents of 25.9, 28.3 and 31.9%, and swelling indices of 9.5, 8.6 and 7.3. Granules were compression moulded at 200 8C into 3 mm and 6 mm thick sheets. Rectangular bars measuring 2 mm 3 3 mm 3 18 mm (tensile specimen) and 3 mm 3 3 mm 3 6 mm (compression specimen) were machined from these sheets. Cut surfaces of machined bars were polished with ®ne emery cloth to avoid premature fracture in tension. In both tension and compression tests, static and dynamic stresses were applied parallel to the long direction of the specimen. Specimens were cooled to ,20 K below the Tg of the rubber before applying the static load and starting dynamic testing at 10 Hz. The heating rate was 1 K miny1 and the strain amplitude 0.2%. Each specimen was tested over a range of static stresses, beginning with the lowest. To check reproducibility, three specimens were tested for each condition. Results from these tests are presented in Figs 1 and 2. Two trends are obvious from Fig. 1: (i) crosslinking

Characterizing in situ starch gelatinization

Data obtained by dynamic mechanical analysis and DSC analysis of durum wheat dough are presented and discussed. Doughs with water contents ranging from 45 to 55% (w/w) were subjected to sinusoidal shearing by means of a dynamic mechanical spectrometer (Rheometrics, RFS2) equipped with parallel plate geometry, 0.1 strain amplitude and 1 rad/min frequency. The tests were carried on in temperature sweep mode at a heating rate of 2°C min−1.

Pultruded fiber reinforced blocked polyurethane (PU) composites. II. Processing variables and dynamic mechanical properties

AbstractUnidirectional fiber reinforced blocked polyurethane (PU) composites have been prepared by the pultrusion process. The effects of processing variables on the mechanical properties and dynamic mechanical properties of fiber reinforced PU composites by pultrusion have been studied. The processing variables investigated included pulling rate (in‐line speed), die temperature, postcure time and temperature, and filler type and content. The dynamic mechanical properties of the composites produced by the process were studied utilizing dynamic mechanical spectrometer. Results show that the composites possessed various optimum pulling rates at different die temperatures. From the DSC data analysis, swelling ratio, and mechanical properties, the optimum die temperature was determined. It was found that the mechanical properties increase with filler content for various types of filler. The increasing of mechanical properties depends on the optimum postcure temperature and time. However, the properties decreased for longer postcure times since the composite materials were degraded. The glass‐transition temperature (Tg) increased slightly and the damping peak (tan δ) was broadened due to fiber reinforcement. The dynamic mechanical moduli (G′, G″) of pultruded PU composites are apparently higher than those of the matrices. The moduli (G′, G″) increase with increasing fiber and filler content, and the damping peak becomes broad. Effect of postcuring on the degree of crosslinking, Tg, and dynamic modulus will be discussed.

RIM‐pultrusion of nylon‐6 and rubber‐toughened nylon‐6 composites

AbstractUnidirectionally reinforced thermoplastic composites of Nylon‐6 and polypropylene oxide‐Nylon‐6 block copolymers have been prepared by the reaction injection molding (RIM)‐pultrusion process. This process takes advantage of both the RIM and the pultrusion techniques, while avoiding their inherent shortcomings. It also represents a novel way of incorporating toughening rubber domains into a thermoplastic composite. The composites produced exhibit excellent mechanical integrity with essentially zero void content. The chemical and physical states of the composites produced by the process were probed in terms of mechanical relaxation behavior using a dynamic mechanical spectrometer. Due to the simultaneous occurrence of both polymerization and crystallization processes in the reacting system, the resulting material is in a thermodynamically nonequilibrium state. An annealing effect is shown to correspond structurally to an increase in matrix crystallinity and the degree of phase separation, Izod impact tests were used to compare Nylon‐6 and rubber‐toughened Nylon‐6 RIM‐pultruded composites. The potential of secondary processing was, demonstrated by compression molding of the RIM‐pultruded composite rods.

Viscoelastic behavior and order‐disorder transition in mixtures of a block copolymer and a midblock‐associating resin

AbstractThe viscoelastic behavior and order‐disorder transition in mixtures of a block copolymer and a midblock‐associating resin were investigated. The block copolymers investigated were polystyrene‐block‐polysioprene‐block‐polystyrene (SIS) copolymers (Shell Development Company), specifically Kraton D‐1107, with the block molecular weights 10,000S‐120,000I‐10,000S, and Kraton D‐1111, with the block molecular weights 15,000S‐100,000I‐15,000S. The midblock‐associating resin investigated was a resin polymerized from C5 hydrocarbon, referred to as Piccotac 95BHT (Hercules Inc.), which is an aliphatic hydrocarbon containing considerable amounts of cyclic structures, with a weight‐average molecular weight of 1,100 and a glass transition temperature Tg of 43°C. In the investigation, mixtures of the block copolymer and Piccotac 95BHT were prepared with toluene as solvent. Temperature scans of the samples were made to obtain information on dynamic storage modulus G′, dynamic loss modulus G″, and loss tangent tan δ, using a Rheometrics dynamic mechanical spectrometer. It was found that Piccotac 95BHT decreased the plateau modulus G0N and increased the Tg of the polyisoprene midblock of the SIS block copolymer in the mixture. This experimental observation led to the conclusion that Piccotac 95BHT associates (or is compatible) with the rubbery polyisoprene midblock of the SIS block copolymer. The order‐disorder transition behavior of mixtures of SIS block copolymer and Piccotac 95BHT was also investigated by a rheological technique proposed by Han and Kim (Ref. 21). The order‐disorder transition temperature Tr (i.e., the temperature at which the ordered microdomain structure of the block copolymer completely disappears) of the SIS block copolymer decreased steadily with increasing amount of Piccotac 95BHT in the mixture. With the information determined on Tr, a phase diagram for the mixture was constructed, showing the boundary between the mesophase and homogeneous phase in the mixture. The phase diagram is in qualitative agreement with the theoretical predictions of Whitmore and Noolandi (Ref. 28).

Rheological behavior of partially hydrolyzed poly(vinyl acetate‐co‐ethylene)

AbstractThe rheological behavior of partially hydrolyzed poly(vinyl acetate‐co‐ethylene) (VAE) was investigated, using a Rheometrics Dynamic Mechanical Spectrometer. For the investigation, measurements of storage modulus (G′), loss modulus (G″) and loss tangent (tan δ) of the materials were recorded as functions of temperature at a fixed frequency (i.e., using temperature scans) and, also, as functions of frequency at a fixed temperature (i.e., using frequency scans). For the hydrolysis, three different grades of copolymer (containing 34, 47, 62 mol% of vinyl acetate) were used to yield poly(vinyl acetate‐co‐ethylene‐co‐vinyl alcohol) (VAEOH) with varying amounts of hydroxyl group. For comparison purposes, the viscoelastic properties of blends of VAE copolymer with poly(vinyl alcohol) (PVOH), having varying blend compositions, were also measured. The blends were prepared by first mixing a solution of VAE copolymer, which was dissolved in a toluene/dichloroethane mixed solvent, and an aqueous solution of PVOH, and then freeze drying the mixture to a constant weight. Also measured were the glass transition temperature (Tg) of the VAE copolymers and the Tg and melting point (Tm) of the VAEOH terpolymers, using a DuPont Thermal Analyzer equipped with a 910 DSC Module. It has been found that (1) introduction of hydroxyl group into the backbone of the amorphous VAE copolymer has made the resulting VAEOH terpolymer semicrystalline; (2) the Tm, Tg, G′, and the complex viscosity (η*) of the VAEOH terpolymers increase with increasing amounts of hydroxyl group; (3) the physical blending of PVOH with VAE copolymer has not affected the Tg of the VAE copolymer; (4) the G′ and η* of the VAE/PVOH blends are found to increase with the amount of PVOH in the blend. The use of logarithmic plots of G′ versus G″ has been found to be very useful for discerning the differences in the structure of the materials tested.