Tensile yield in poly(4-methyl pentene-1)

Uniaxial tension tests to the yield point were performed on a crystalline polymer, poly(4-methyl pentene-1) (PMP) as a function of temperature from 21° to 200°C at a strain rate of 2 min^?1. After testing, the specimens showed considerable stress whitening as a result of microvoid formation. Yield energy was found to be a linear function of temperature extrapolating to zero at the melting point (240°C). Thus, the behavior of this crystalline polymer is similar to that of glassy polymers, but with the melting temperature, rather than the glass transition temperature, as the reference point. The ratio of thermal to mechanical energy input to produce yielding is an order of magnitude smaller for PMP than it is for glassy polymers. The ratio of yield stress to Young's modulus is about 0.02, which is typical for polymers. Yield stress is a linear function of log strain rate, which implies that yielding can be described as a segmental flow rate process in which the applied stress biases the activation energy. The activation volume is on the order of 20 monomer unit volumes and increases as the temperature increases. The activation energy is 19 kcal/mol.     

Tensile yield in polypropylene

Untaxial tension tests to the yield point were performed on polypropylene as a function of temperature from 22 to 143°C at a strain rate of 2 min^?1. At 22, 42, and 71°C, measurements were also made at strain rates from 0.02 to 8 min^?1. Yield energy was found to be a linear function of temperature extrapolating to zero at the melting point (164°C). The ratio of thermal to mechanical energy to produce yielding is about three times smaller than for glassy polymers. The ratio of yield stress to (initial) Young's modulus is about 0.024 at room temperature and increases to 0.043 at 143°C. Yield stress is a linear function of unstrained volume.     

Tensile yield in polyethylene

Uniaxial tension tests to the yield point were performed on polyethylene as a function of temperature from 21 to 117°C at a strain rate of 2 min^?1. At 21, 45, and 69°C, measurements were also made at strain rates from 0.02 to 8 min^?1. Yield energy was found to be a linear function of temperature extrapolating to zero at the melting point (140°C). The ratio of thermal to mechanical energy to produce yielding is about three times smaller than for glassy amorphous polymers. The ratio of yield stress to (initial) Young's modulus is 0.021 at room temperature and increases to 0.059 at 117°C. Also this ratio was found to decrease with log strain rate. For instance, at 21°C for a strain rate of 0.02 min^?1 the value was 0.023, while at 8 min^?1 this value decreased to 0.020.     

Tensile yield in phenolphthalein polyether ketone

Uniaxial tension tests to the yield point were performed on phenolphthalein polyether ketone (PEK-C) from room temperature to near the glass transition temperature (T_g) at a constant rate of 0.02 min^?1. At room temperature, some measurements were also made at strain rates from 0.002 min^?1 to 2 min^?1. Yield stress was a linear function of temperature and log strain rate. The temperature and the strain rate dependence of yield stress could be modeled using Eyring theory. Yield energy was found to be a linear function of temperature. Young's modulus, yield strain, elastic strain, and plastic strain all decreased with temperature. © 1994 John Wiley & Sons, Inc.     

Tensile yield in nylon 6,6

Uniaxial tension tests to, the yield point were performed on poly(hexamethylene adipamide) (nylon 6,6) as a function of temperature from 21 to 200°C at a strain rate of 2 min^?1. At 21 and 60°C, measurements were also made at strain rates from 0.02 to 8 min^?1. Using simple rate theory, reasonable values of activation volume were obtained, but the simple theory is inadequate to determine the activation energy. The yield-strain temperature dependence changes at 160°C as a result of a reversible crystal-crystal transition. Because of this behavior of the yield strain, the yield energy is not a linear function of temperature, as observed for several other polymers.     

A correlation of Young's modulus with yield stress in oriented poly(vinyl chloride)

The variations of tensile and compressive yield stresses and of Young's modulus of oriented poly(vinyl chloride) sheet with direction and with degree of orientation, represented by birefringence, are shown. Young's modulus was calculated from elastic stiffness constants measured by an ultrasonic pulse method at 5MHz with estimated strain and strain rate amplitudes of 2 × 10^?5 and 100s^?1. Yield strains were about 5 × 10^?2 measured at strain rates of about 2 × 10^?2s^?1. Although the measuring conditions were so different there was found to be a close correlation between tensile yield stress and Young's modulus, the two quantities being connected by a simple linear relationship, as direction of measurement and degree of orientation were varied. Compressive yield stress did not correlate with Young's modulus, and changed little with direction or degree of orientation by comparison with tensile yield stress. The empirical linear relationship between tensile yield stress and Young's modulus, difficult to account for theoretically, might form the basis of a method for determining tensile yield stress ultrasonically.     

Tensile yield properties of starch-filled poly(ester amide) materials

Composite materials were prepared with granular corn starch (CS) or potato starch (PS) and poly(ester amide) resin (PEA), with starch volume fractions (?) up to 0.40. Tensile yield properties were evaluated at strain rates of 0.0017-0.05 s⁻¹. Yield stress of the CS-PEA materials increased with strain rate and starch content. The strain rate effect became more pronounced as the starch content increased. A crossover effect was observed with PS-PEA materials: at low strain rates, the yield stress decreased with increasing ?, and increased with ? at higher strain rates. This crossover suggests that the time scale of debonding in the PS-PEA materials is comparable to the time scale of the tension test. The addition of either CS or PS to PEA induced a distinct maximum in the stress-strain curve at yield compared to the neat PEA. Debonding of starch granules from the PEA matrix occurred at lower stresses in the PS-PEA materials than the CS-PEA. In PS-PEA, debonding occurred in bands similar in appearance to shear bands throughout the tensile specimen. After yielding, the cross-section area decreased as the debonded zones coalesced. In the CS-PEA materials, debonding zones were more diffuse, and a distinct neck formed at yield. Yield stress data for the CS-PEA materials could be shifted with respect to strain rate to construct a master curve, indicating that yield properties at these strain rates were determined by the matrix response rather than debonding as observed in other starch-filled materials.     

Tensile yield parameters for poly(vinylchloride) blends with a methyl methacrylate–butadiene–styrene impact modifier

Tensile yield measurements were made on blends of poly(vinyl chloride) (PVC) with a methyl methacrylate-butadiene-styrene impact modifier (MBS) covering a blend range of 0 to 20 wt % MBS, a temperature range of ?50 to 25°C, and a strain rate range of 10^?3 to 10° s^?1. Increasing MBS level in PVC reduces the tensile yield stress. The tensile yield stress variation with temperature and strain rate at constant MBS level was represented in terms of the Ree-Eyring-Roetling rate model. This model represents the experimental data within experimental error. The tensile yield parameters were also determined by assuming that stress concentrations exist around the modifier equatorial plane. Estimates of these stress concentrations were made and are discussed in terms of Goodier's model for spherical inclusions.     

Synthesis and characterization of two shape-memory polymers containing short aramid hard segments and poly(ε-caprolactone) soft segments

A number of segmented copolymers were synthesized by reacting 4-aminobenzoyl end-functionalized poly(ε-caprolactone)s of M_n 2000, 3000 and 4000 g mol⁻¹ with three aromatic diacid dichlorides in the presence of chlorotrimethylsilane. Polymer purity, molar mass, thermal and mechanical properties were characterized by NMR, MALDI-TOF mass spectrometry, GPC, DSC, and DMTA. Promising shape-memory properties were observed for two polymers that contained comparatively short, semicrystalline poly(ε-caprolactone) soft segments of molecular weight 3000 g mol⁻¹ and either terephthalamide or 2,6-naphthalenedicarboxyamide hard segments. Cast films of these polymers were soft and elastomer-like at room temperature. Loading could be conveniently achieved by cold-drawing at room temperature and strain recovery took place upon heating above the melting temperature of the soft segment (35 °C). Cast films reached uniform deformation properties with strain recovery rates as high as 99% and strain fixity values of 78% after passing through only one or two training cycles.     

Effect of temperature on the compressive stress-strain properties of polystyrene

The compressive stress-strain behavior of a commercial polystyrene has been studied and the effect of deformation temperature on modulus, yield stress, percent yield strain and yield energy was determined. Yield energy is the only one of these parameters that is linear with temperature in the ductile region. A change in the mode of failure from ductile to brittle occurs between 5–30°C at a strain rate of O.1/in./in./min. At all temperatures studied, the yield or fracture stress varied linearly with the rate of deformation for strain rates ranging from 0.1 to 1.0 in./in./min. The yield data as a function of temperature were analyzed via a rate expression modified to incorporate the Coulomb-Navier yield criterion, Activation energy was found to be a function of deformation temperature with a change in slope occurring near the β transition. Activation volume increased linearly with deformation temperature, for the range studied. Agreement of dynamic mechanical and yield activation energies imply that the type of motion and the height of the energy barrier are similar for both. However, an increase in activation volume for stressed vs unstressed conditions suggests that a greater number of chain segments move as a result of stress biasing. Also the increase of both activation volume and activation energy with temperature implies that the correlated length of chain movement increases as temperature is increased. Similar to activation energy, yield stress exhibits a change in temperature dependence near the β transition. Data on other glassy polymers suggest that the highest temperature sub-T_g, transition is related to the change in the temperature dependence of yield stress.     

Synthesis and properties of poly(1,3-dialkoxybenzene)s from facile solvent-free grinding oxidative coupling polymerization

Soluble conjugated aromatic poly(1,3-dialkoxybenzene)s were obtained in high yield up to 80% in 30?min by grinding 1,3-dialkoxybenzene with anhydrous FeCl₃ powder in a mortar at ambient and solvent-free condition. The polymers were characterized by FT-IR, ¹H-NMR, ¹³C-NMR, and gel permeation chromatography. The structure of the aromatic rings linkage at meta-position was confirmed. Thermogravimetric analysis, UV?CVis, fluorescence spectroscopy, and four-probe a.c. technique were used to probe the thermal, optical, and electrical properties of the polymers. The polymers displayed high thermostability with the decomposition temperatures at about 382?C388?°C. The optical energy gap (E _g) of the polymers was 4.23?eV and electrical conductivity at room temperature was 10^?6?S?cm^?1. The fluorescence curve of the polymers displayed the maximum at 344?nm in CH₂Cl₂ solution. The morphology of the polymers was determined by X-ray diffraction and scanning electron microscope technique.     

Phase transitions in mesophase macromolecules: The transitions of poly(p-acryloyloxybenzoic acid)

Poly(p-acryloyloxybenzoic acid) has been obtained in twelve single and two-phase physical states, which include the amorphous glassy and liquid states, the mesomorphic glassy and the mesomorphic liquid states and in addition eight two-phase semicrystalline states (crystal forms I and II). Using mainly differential scanning calorimetry, the transition temperatures, energies and heat capacity changes at the glass transitions have been studied. The time dependency of the glass transition has also been determined. The strongly heating rate dependent amorphous glass transition occurs at 348K (20k min^?1 heating rate, ΔC_p = 39 JK^?1 mol^?1), the mesophase glass transition, at 408K (also at 20k min^?1, ΔC_p = 43 JK^?1 mol^?1). The latter is less heating rate dependent. The amorphous to mesophase transition occurs between 375 and 475K (ΔH = ?4.5 KJ mol^?1); the peaks of melting transitions, which are also strongly heating rate dependent, were observed at 573K and 553K (20 K min^?1 heating rate) for crystal forms I and II, respectively. The heat of fusion of crystal form I is estimated to be 22 KJ mol^?1. There seems to be no partially amorphous-partially mesomorphic state.     

Oxidative protection of carbon fibers with poly(carborane-siloxane-acetylene)

Linear carborane-siloxane-acetylenic polymers have been synthesized as precursor materials for thermosets and ceramics for composite applications up to 500 and 1500°C, respectively, in an oxidizing environment. The novel linear polymers have the advantage of being extremely easy to process and convert into thermosets or ceramics since they are either liquids at room temperature or low melting solids and are soluble in most organic solvents. Carbon fibers coated with poly(carborane-siloxane-acetylene) forms a protective barrier against oxidation at elevated temperatures. The novel polymer when used as a matrix material (ceramic) was found to protect the carbon fibers from oxidative breakdown. Boron appears to be the key to the unique oxidative stability of the composite compositions. Oxidative studies were performed by thermogravimetric analyses.     

Crystallization kinetics of poly(trimethylene terephthalate)

The bulk isothermal crystallization kinetics of poly(trimethylene terephthalate) (PTT) was studied using a differential scanning calorimeter. Avrami's theory was used to analyze the data. Based on crystallinity growth rate, Avrami rate constant, K, and crystallization half‐time, PTT's crystallization rate is between those of poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) when compared at the same degree of undercooling. PBT has the highest crystallization rate with K in the order of 10^?2 to 10^?1 min^?n. It is about an order of magnitude faster than PTT at 10^?3 to 10^?2 min^?n, which in turn is an order of magnitude faster than PET with K of 10^?4 to 10^?2 min^?n. Contrary to previous reports (PTT was not included in the study) that aromatic polyesters with odd numbers of methylene units were more difficult to crystallize than the even‐numbered polyesters, PTT did not fit in the prediction and did not follow the odd‐even effect.     

Phase transformations of some poly(vinyl alcohol)–NiCl2 composites

Samples of poly(vinyl alcohol)–NiCl₂ composites containing up to 30 wt% NiCl₂ were prepared by casting in order to study phase transformation–structural change relationships of these samples before and after heat treatment. Differential thermal analysis (DTA) thermograms were recorded at 10, 15, 20 and 30 °C min^?1. For untreated samples four endotherms were assigned as: rotation of hydroxyl groups in the glassy state, glass transition, structural transition in the rubber‐like state, and melting transition. Ultrasonic attenuation measurements were carried out to confirm these transitions in the glassy and rubber‐like states. In the glassy state, the effect of NiCl₂ addition is explained in terms of chain stiffness due to the creation of local crosslinked regions in amorphous parts of the polymer. Average values of activation energies for glass transition were calculated using both methods of Kissinger and Ozawa. However, addition of NiCl₂ had an opposite effect on the heating rate independent crystallization melting temperature (T_m), relative to that on T_g. The DTA thermograms of heat‐treated samples indicated that square planar NiCl₂ molecules were embedded in the polymer matrix with no local crosslinking role due to the formation of conjugated polyenes along the polymer chains by thermal treatment. Copyright © 2003 Society of Chemical Industry     

Incorporation of different crystallizable amide blocks in segmented poly(ester amide)s

High molecular weight segmented poly(ester amide)s were prepared by melt polycondensation of dimethyl adipate, 1,4-butanediol and a symmetrical bisamide-diol based on ε-caprolactone and 1,2-diaminoethane or 1,4-diaminobutane. FT-IR and WAXD analysis revealed that segmented poly(ester amide)s based on the 1,4-diaminobutane (PEA(4)) give an α-type crystalline phase whereas polymers based on the 1,2-diaminoethane (PEA(2)) give a mixture of α- and γ-type crystalline phases with the latter being similar to γ-crystals present in odd-even nylons. PEA(2) and PEA(4) polymers with a hard segment content of 25 or 50 mol% have a micro-phase separated structure with an amide-rich hard phase and an ester-rich flexible soft phase. All polymers have a glass transition temperature below room temperature and melt transitions are present at 62-70 °C (T_m,1) and at 75-130 °C (T_m,2) with the latter being highest at higher hard segment content. The two melt transitions are ascribed to melting of crystals comprising single ester amide sequences and two or more ester amide sequences, respectively. These polymers have an elastic modulus in the range of 159-359 MPa, a stress at break in the range of 15-25 MPa combined with a high strain at break (590-810%). The thermal and mechanical properties are not influenced by the different crystalline structures of the polymers, only by the amount of crystallizable hard segment present.     

Time and temperature effects on the tensile yield properties of polypropylene

Tensile tests were made on polypropylene films as a function of aging temperature from 80 to 130°C at a strain rate of 5 cm min^-1. Polypropylene films aged at 60 and 100°C and at time intervals up to 180 min were also stretched at the same strain rate. The yield stress and initial modulus were found to be linear functions of temperature, extrapolating to a zero value close to the thermodynamic melting point of the polymer (170°C). The work of yield, the plastic and yield strains also decreased with increase in aging temperature but the elastic strain increased. The plastic strain, yield strain, yield stress, and initial modulus for the 60°C aged film had larger values than the corresponding values for the 100°C aged film at equivalent time intervals and all properties decreased with increasing log time of aging. These decreases in properties were explained in terms of decrease in the density (crystallinity) of aged PP films. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 625–633, 1997     

Isothermal crystallization and spherulite growth behavior of stereo multiblock poly(lactic acid)s: Effects of block length

Stereo multiblock poly(lactic acid)s (PLA)s and stereo diblock poly(lactic acid) (DB) with a wide variety of block length of 15.4–61.9 lactyl units are synthesized, and the effects of block length sequence on crystallization and spherulite growth behavior are investigated at different crystallization temperatures, in comparison with neat poly(L ‐lactide) (PLLA), poly(D ‐lactide) (PDLA), and PLLA/PDLA blend. Only stereocomplex crystallites as crystalline species are formed in the stereo multiblock PLAs and DB, irrespective of block length and crystallization temperature. The maximum crystallinities (33–61%), maximum radial growth rate of spherulites (0.7–56.7 μm min^?1), and equilibrium melting temperatures (182.0–216.5°C) increased with increasing block length but are less than those of PLLA/PDLA blend (67 %, 122.5 μm min^?1, and 246.0°C). The spherulite growth rates and overall crystallization rates of the stereo multiblock PLAs and DB increased with increasing block length and are lower than that of PLLA/PDLA blend. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Crosslinking of polydimethylsiloxane diol blended with poly(dimethylsiloxane-b-styrene-b-dimethylsiloxane)

A variety of blends of poly(dimethylsiloxane-b-styrene-b-dimethylsiloxane) copolymers with hydroxyl terminated polydimethylsiloxane (molecular weight, 29 600 gmol^?1) were prepared. Crosslinking of blends was accomplished at room temperature by reacting hydroxyl chain ends with a tetrafunctional orthosilicate using dibutyltin dilaurate as a catalyst. The crosslink density was evaluated by toluene swelling. Catalyst concentration influences the crosslink density as observed from the amount of extractables in toluene. The tensile strength of crosslinked polydimethylsiloxane was found to increase by blending with block polymers or with silica fillers. Structural uniformity of fractured surfaces of rubbers was also studied by scanning electron microscopy.     

Rheological and mechanical properties of poly(vinyl chloride)/chlorinated poly(vinyl chloride) miscible blends

The properties of poly(vinyl chlorlde)/ehlorinated poly(vinyl chloride) (61.6 percent C1) blends, prepared by melt and solution blending, were measured by various tests. Based on the chlorinated poly(vinyl chloride) (CPVC) composition, percent chlorine, and mole percent CC1₂ groups, these blends were expected to show intermediate properties between miscible and immiscible systems. Indicative of miscible behavior were the single glass transition temperatures over the entire composition range for both melt and solution blended mixtures. A single phase was also indicated by transmission electron microscopy. However, the yield stress showed a minimum value less than either of the pure components in the 50 to 75 percent CPVC range, which is characteristic of two-phased systems. Specific volume, glass transition temperature, and heat distortion temperature were linear with binary composition. The storage modulus showed a small maximum, suggesting a weak interaction between the two miscible polymers. Heats of melting for the residual PVC crystallinity were also less than expected from linear additivity. At 160°C and 210°C, the logarithm of the complex viscosity was essentially linear with volume fraction of CPVC, except for a very slight decrease in the 50 to 75 percent CPVC range, which may have been a result of lower crystallinity. At 140°C, the complex viscosity of the CPVC was less than that of PVC owing to the higher crystallinity of the latter. The viscosities were similar at 160°C, but at 210°C, where most of the crystallites had melted, the complex viscosity of the CPVC was higher because of its higher glass transition temperature.