Effect of oil and cured agent content on the structure and properties of thermoplastic vulcanizates

The effect of oil and curing agent content on the mechanical behavior of thermoplastic vulcanizates, based on a polypropylene (PP) and ethylene‐propylene‐diene copolymer (EPDM), was investigated. Mechanical properties such as Young's modulus, stress at 100% elongation and ultimate stress were investigated as a function of blends' composition and phase morphology. Experimental studies show that the Young's modulus of the vulcanizates depends on both PP/EPDM ratio and oil content in the blends; both ultimate strength and stress at 100% elongation increase with curing agent content.     

Dynamic mechanical properties of isotactic polypropylene/nitrile rubber blends: Effects of blend ratio,reactive compatibilization,and dynamic vulcanization

The effect of blend ratio and compatibilization on dynamic mechanical properties of PP/NBR blends was investigated at different temperatures. The storage modulus of the blend decreased with increase in rubber content and shows two T_g's indicating the incompatibility of the system. Various composite models have been used to predict the experimental viscoelastic data. The Takayanagi model fit well with the experimental values. The addition of phenolic modified polypropylene (Ph-PP) and maleic modified polypropylene (MA-PP) improved the storage modulus of the blend at lower temperatures. The enhancement in storage modulus was correlated with the change in domain size of dispersed NBR particles. The effect of dynamic vulcanization using sulfur, peroxide, and mixed system on viscoelastic behavior was also studied. Among these peroxide system shows the highest modulus. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2309–2327, 1997     

Morphology and properties of poly(vinyl chloride)–poly(butadiene-co-acrylonitrile) blends

The objective of this research was to study the structure-property relationships of two poly(vinyl chloride) (PVC)–poly(butadiene-co-acrylonitrile) (BAN) blends which exhibit differences in blend compatibility. Studies were carried out utilizing differential scanning calorimetry, dynamic mechanical testing, stress–strain, transmission electron microscopy (TEM), and infrared dichroism experiments at different temperatures. The BAN 31/PVC (BAN containing 31% acrylonitrile) system is considered to be nearly compatible as evidenced by T_g shifts, stress–strain results, orientation characteristics, and TEM micrographs. Similar experiments indicate that the BAN 44/PVC system is incompatible, and contains a mixed phase of BAN 44-PVC and a pure BAN 44 phase. The extent of heterogeneity in the compatible BAN 31/PVC system, however, plays an important role in the orientation characteristics of the blends.     

Infrared dichroism of glassy polycarbonate at small strains

The dichroism of the 889, 1364, and 3063 cm^?1 infrared absorption bands of glassy, amorphous polycarbonate has been measured as a function of the strain in the range 0 to 2% at 23°C. The data obtained for these three bands superpose rather well over this strain range. Negligible dichroism is observed up to about 0.6% strain; above this level, the dichroic ratio increases in an approximately linear manner. Independent mechanical data, obtained under comparable conditions of time-scale and temperature, are cited which show that a transition from approximately linear to marked non-linear viscoelastic behavior occurs with glassy polycarbonate in the range 0.7 to 1.0% strain. The coincidence on the strain axis of a relatively abrupt increase in optical absorption anisotropy with a distinct change in Young's modulus is discussed in terms of a recent molecular theory of deformation of glassy polymers. It is suggested that the data are consistent with the view that the transition from linear to nonlinear viscoelastic behavior in glassy polycarbonate is marked by the onset of significant rotation around backbone bonds.     

Viscoelastic behavior of polypropylene/nitrile rubber thermoplastic elastomer blends: Application of Kerner's models for reactively compatibilized and dynamically vulcanized systems

The viscoelastic properties of binary blends of nitrile rubber (NBR) and isotactic polypropylene (PP) of different compositions have been calculated with mean‐field theories developed by Kerner. The phase morphology and geometry have been assumed, and experimental data for the component polymers over a wide temperature range have been used. Hashin's elastic–viscoelastic analogy principle is used in applying Kerner's theory of elastic systems for viscoelastic materials, namely, polymer blends. The two theoretical models used are the discrete particle model (which assumes one component as dispersed inclusions in the matrix of the other) and the polyaggregate model (in which no matrix phase but a cocontinuous structure of the two is postulated). A solution method for the coupled equations of the polyaggregate model, considering Poisson's ratio as a complex parameter, is deduced. The viscoelastic properties are determined in terms of the small‐strain dynamic storage modulus and loss tangent with a Rheovibron DDV viscoelastometer for the blends and the component polymers. Theoretical calculations are compared with the experimental small‐strain dynamic mechanical properties of the blends and their morphological characterizations. Predictions are also compared with the experimental mechanical properties of compatibilized and dynamically cured 70/30 PP/NBR blends. The results computed with the discrete particle model with PP as the matrix compare well with the experimental results for 30/70, 70/30, and 50/50 PP/NBR blends. For 70/30 and 50/50 blends, these predictions are supported by scanning electron microscopy (SEM) investigations. However, for 30/70 blends, the predictions are not in agreement with SEM results, which reveal a cocontinuous blend of the two. Predictions of the discrete particle model are poor with NBR as the matrix for all three volume fractions. A closer agreement of the predicted results for a 70/30 PP/NBR blend and the properties of a 1% maleic anhydride modified PP or 3% phenolic‐modified PP compatibilized 70/30 PP/NBR blend in the lower temperature zone has been observed. This may be explained by improved interfacial adhesion and stable phase morphology. A mixed‐cure dynamically vulcanized system gave a better agreement with the predictions with PP as the matrix than the peroxide, sulfur, and unvulcanized systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1417–1432, 2004     

Polypropylene multifilament yarn filled with clay and/or graphite: Study of a potential synergy

In this study, clay and/or graphite particles have been added in various quantities to polypropylene matrix by melt blending. The morphology and more particularly the dispersion of particles in these composites have been compared by transmission electron microscopy (TEM). Their thermal stability has also been studied by thermogravimetric analysis (TGA). The experimental results reveal that the addition of 5 wt % of graphite particles or clay improves the thermal stability in air of the matrix by about 50 and 90 °C, respectively. In a second step, these blends have been melt‐spun to produce multifilament yarns. The experiments have shown that the addition of graphite particles up to 5 wt % do not reduce the spinnability of the polypropylene, while the incorporation of more than 1 wt % of clay was causing difficulties for the spinning and more particularly for the drawing step. However, a slight improvement of the Young's modulus of the filaments reinforced with 1 wt % of Cloisite®15A is observed when the filaments are drawn up. The flammability of the different blends used as knitted fabrics has finally been evaluated with a mass loss calorimeter at 35 kW/m². An atypical behavior has been highlighted for all blends and will be discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1185–1195, 2010     

The effects of combined pressure–temperature on mechanical behavior of polypropylene

The effects of combined pressure and temperature on the mechanical behavior of polypropylene have been studied. Tests were conducted in tension and compression superimposed on various hydrostatic pressures up to 7 kbar at temperatures of 20, 50, and 75°C. The experimental data have been analyzed in view of molecular and continuum approaches. It has been observed that the Young's modulus and the yield strength in both tension and compression increased significantly with increasing pressure at all temperatures studied. However, the rate of increase of the Young's modulus undergoes abrupt change about the glass-transition pressure (P_g). The P_g is linearly dependent on the test temperature and the pressure coefficient of the T_g is estimated, from P_g versus temperature relations, to be about 18°C/kbar for the polypropylene samples of this study. Pressure dependence of the yield stress is described by a generalized Eyring theory incorporating pressure effects and two flow mechanisms, the α- and the β-relaxation processes. The theory predicts a bilinear dependence of the yield stress of polypropylene on hydrostatic pressure as observed in the tests. The paper also described a method of healing stress whitening in polypropylene by a combination of shear stress and hydrostatic pressure.     

Tensile yielding and microstructures of blends of isotactic polypropylene and linear low-density polyethylene

Thin sheets of isotactic polypropylene (iPP) and linear low-density polyethylene (LLDPE) blends were studied by tensile testing, optical microscopy (OM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). Eyring's two-process yielding theory was used to analyze the data of yield stress as a function of strain rate and temperature, and satisfactory curve-fitting results were obtained. Furthermore, stress whitening was found to have occurred in the necked regions of tensile specimens under a certain range of yielding conditions. These conditions corresponded to the activation of Process II yielding of Eyring's theory. The whitening was found to be a result of formation of microvoids that initiated at the interface between iPP and LLDPE. © 1995 John Wiley & Sons, Inc.     

Miscible/partially‐miscible blends of polypropylene—the mechanisms responsible for the decrease of yield stress

In miscible or partially‐miscible blends of semicrystalline polymer/non‐cocrystallizing low molecular weight component, a decrease of the value of yield stress in comparison to reference (pure) polymer is usually observed. On the example of model polypropylene/nonadecane systems, the mechanisms responsible for the decrease of the yield stress have been identified. It has been proved that during the deformation of polypropylene/nonadecane blends containing low amount of nonadecane (up to 5 wt %) the reduction of the yield stress is caused only by the swelling of interlamellar regions. In the case of the systems containing a moderate amount of nonadecane (7–10 wt %), the reduction of the yield stress is caused by the swelling of interlamellar regions and the reduction of the sample cross‐section effectively participating in transferring of tensile stress. In blends containing nonadecane in the amount of 15–30 wt % the reduction of the yield stress is caused by the swelling of interlamellar regions and strong asymmetrization of nonadecane microdomains, resulting in localizing the deformation along interspherulitic regions and a drastic reduction of the content of polypropylene matrix, effectively participating in transferring of tensile stress between adjacent spherulites. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1203–1214     

Tensile properties of ultradrawn polyethylene

High-density polyethylene filaments prepared by a solid-state deformation in an Instron capillary rheometer show unusually high crystal orientation, chain extension, axial modulus, and ultimate tensile strength. The Young's modulus and ultimate tensile strength have been determined from stress–strain curves. Gripping of this high modulus polyethylene has been a problem heretofore, but the measurement of ultimate tensile strength has now been made feasible by a special gripping procedure. Tensile moduli show an increase with sample preparation temperature and pressure. Values as high as 6.7 × 10¹¹ dyne/cm² are obtained from samples extruded at 134°C and 2400 atm and tested at a strain rate of 3.3 × 10^?4 sec^?1. The effect of strain rate and frequency on modulus has also been evaluated by a combination of stress–strain data and dynamic tension plus sonic measurements over nine decades of time.     

Phase morphology and mechanical properties of iPP/SEP blends

The effects of the addition of diblock copolymer poly(styrene‐b‐ethylene‐co‐propylene) (SEP) to isotactic polypropylene (iPP) on the morphology and mechanical properties were investigated. Phase morphologies of iPP/SEP blends up to a 70/30 weight ratio, prepared in Brabender Plasticoder, were studied with optical microscopy, scanning electron microscopy, transmission electron microscopy, and wide‐angle X‐ray diffraction. The addition of 2.5 wt % SEP caused a nucleation effect (by decreasing the crystallite and spherulite size) and randomization of the crystallites. With further SEP addition, the crystallite and spherulite size increased because of prolonged solidification and crystallization and achieved the maximum in the 80/20 iPP/SEP blend. This maximum was a result of the appearance of β spherulites and the presence of mixed α spherulites in the 80/20 iPP/SEP blend. Dispersed SEP particles were irregular and elongated clusters consisting of oval and spherical core–shell microdomains or SEP micelles. SEP clusters accommodated their shapes to interlamellar and interspherulitic regions, which enabled a well‐developed spherulitization even in the 70/30 iPP/SEP blend. The addition of SEP decreased the yield stress, elongation at yield, and Young's modulus but significantly improved the notched impact strength with respect to the strength of pure iPP at room temperature. Some theoretical models for the determination of Young's modulus of iPP/SEP blends were applied for a comparison with the experimental results. The experimental line was closest to the Takayanagi series model. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 566–580, 2001     

Block copolymers as compatibilizers for blends of linear low density polyethylene and polystyrene

Compatibilization of blends of linear low-density polyethylene (LLDPE) and polystyrene (PS) with block copolymers of styrene (S) and butadiene (B) or hydrogenated butadiene (EB) has been studied. The morphology of the LLDPE/PS (50/50) composition typically with 5% copolymer was characterized primarily by scanning electron microscopy (SEM). The SEB and SEBS copolymers were effective in reducing the PS domain size, while the SB and SBS copolymers were less effective. The noncrystalline copolymers lowered the tensile modulus of the blend by as much as 50%. Modulus calculations based on a coreshell model, with the rubbery copolymer coating the PS particle, predicted that 50% of the rubbery SEBS copolymer was located at the interface compared to only 5–15% of the SB and SBS copolymers. The modulus of blends compatibilized with crystalline, nonrubbery SEB and SEBS copolymers approached Hashin's upper modulus bound. An interconnected interface model was proposed in which the blocks selectively penetrated the LLDPE and PS phases to provide good adhesion and improved stress and strain transfer between the phases. © 1995 John Wiley & Sons, Inc.     

Welding dynamics in an atomistic model of an amorphous polymer blend with polymer–polymer interface

We consider an atomistic model of thermal welding at the polymer-polymer interface of a polyetherimide/polycarbonate blend, motivated by applications to 3D manufacturing in space. We follow diffusion of semiflexible chains at the interface and analyze strengthening of the samples as a function of the welding time t_w by simulating the strain–stress and shear viscosity curves. The time scales for initial wetting, and for fast and slow diffusion, are revealed. It is shown that each component of the polymer blend has its own characteristic time of slow diffusion at the interface. Analysis of strain–stress demonstrates saturation of the Young's modulus at t_w = 240 ns, while the tensile strength continues to increase. The shear viscosity is found to have a very weak dependence on the welding time for t_w > 60 ns. It is shown that both strain–stress and shear viscosity curves agree with experimental data.     

Investigations of the influence on the phase morphology of PP-EPDM-blends on their mechanical properties

This work covers the dependence of the mechanical properties of polymer blends on their composition and their phase morphology. Blends of EPDM-elastomers and polypropylene were prepared covering the whole concentration range. The phase morphology was varied strongly by employing different mixing techniques and its morphology was characterized by means of electron microscopy and light microscopy, as well as by x-ray scattering and calorimetry.Mechanical properties such as the complex shear modulus, the tensile modulus as well as the stress strain behavior were investigated as a function of the composition of the blends and their phase morphology. The experimental finding is that the complex modulus, the tensile modulus, the yield stress, and the ultimate stress are rather insensitive with respect to the phase morphology and vary continuosly with the composition. The elongation at break, on the other hand, as well as the impact strength were found to depend on the phase morphology and to vary discontinously with the composition. One conclusion to be drawn is that one is not always forced to control the phase morphology tightly during processing in order to obtain materials with sufficiently good mechanical properties. Rather, simple theoretical approaches, neglecting details of the phase morphology are frequently able to satisfactorily predict mechanical properties of multiphase blends.     

Structure and properties for binary blends of isotactic-polypropylene with ethylene-α-olefin copolymer. 1. Crystallization and morphology

Morphology and isothermal growth rates of spherulites for the binary blends consisting of an isotactic polypropylene (i-PP) and an ethylene-1-hexene rubber (EHR) were examined as a function of the crystallization temperature ranging from 388 K to 418 K. In this study, two types of EHR's were employed: “ethylene rich” EHR and “1-hexene rich” EHR. The blends of i-PP with the EHR of 51 mol % 1-hexene are miscible in the molten state, whereas the blends with the EHR of 33 mol % 1-hexene are immiscible in the molten state. It is found that the isothermal spherulite growth rate of the miscible i-PP/EHR blends decreases with increasing the EHR fraction, whereas the spherulite growth rate of the immiscible i-PP/EHR blends is independent of the blend composition and is the same as that of the i-PP. Optical microscope observation of the miscible blends crystallized isothermally shows that there are no rubber domains either in the intraspherulitic or in the interspherulitic contact regions. On the other hand, the immiscible i-PP/EHR blends show a phase-separated morphology. Furthermore, the number of tangential lamellae of the miscible i-PP/EHR blends is found to be increased by blending of the EHR, leading to the spherulite with negative birefringence. The sign of birefringence of spherulites is unaffected by the regime transition as well as by the fold surface free energy. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 953–961, 1997     

Effect of nanoscale diamondoids on the thermomechanical and morphological behaviors of polypropylene and polycarbonate

Nanoscale MolecularDiamond products (various diamondoid materials), obtained from petrochemical feedstocks, have been investigated as additives for polypropylene and polycarbonate. Three of the homologues of this family (diamantane, triamantane, and the [121]tetramantane isomer) have marginal effects on the thermal and mechanical properties of nonpolar/semicrystalline polypropylene. Mixtures of methylated tetramantane nanofillers also increase the stress–strain behavior of polypropylene composites without significantly impacting their glass transition temperatures. The addition of the selected diamondoids to amorphous/moderately polar polycarbonate increases the polymer tensile modulus significantly with marginal increases in the yield stress. The effects of the selected diamondoids on the thermal stability, crystallinity, and optical properties of polypropylene and polycarbonate are also reported. The results for the mechanical properties show that the selected diamondoids behave as plasticizers in polypropylene, whereas in polycarbonate, they act as antiplasticizers without adversely affecting the optical clarity. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1077–1089, 2007     

Young's modulus of polyethylene in the microstrain region

The stress–strain behavior of various polyethylenes was measured with a strain sensitivity of 2 × 10^?7. Young's modulus was measured as a function of the strain rate. The shapes of the stress–strain curves in the vicinity of room temperature were nonlinear down to the lowest measurable strain. The stress–strain behavior in the microstrain region was well described by the model of the standard linear solid. From the model, the relaxation time was determined along with the relaxed and unrelaxed moduli. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2420–2429, 2001     

Poly(4-methylpentene-1)/hydrogenated oligo (cyclopentadiene) blends: Miscibility,tensile stress–strain,and dynamic mechanical behaviors

This article discusses the influence of the oligomeric resin, hydrogenated oligo(cyclopentadiene) (HOCP), on the morphology, and thermal and tensile mechanical properties of its blends with isotactic poly(4-methylpentene-1) (P4MP1). The P4MP1 and HOCP are found not miscible in the melt state. P4MP1/HOCP blends after solidification contain three phases: the crystalline phase of P4MP1, an amorphous phase of P4MP1, and an amorphous phase of HOCP. From optical micrographs obtained at 150°C, it is found that the solidified blends show a morphology constituted by P4MP1 microspherulites and small HOCP domains homogeneously distributed in intraspherulitic regions. DSC and DMTA results show that the blends present two glass transition temperatures (T_g) equal to the T_gs of the pure components. The tensile mechanical properties have been investigated at 20, 60, and 120°C. At 20°C both the HOCP oligomer and the amorphous P4MP1 are glassy, and it is found that all the blends are brittle and the stress–strain curves have equal trends. At 60°C the HOCP oligomer is glassy, whereas the amorphous P4MP1 is rubbery. The tensile mechanical properties at 60°C are found to depend on blend composition. It is found that the Young's modulus, the stresses at yielding and break points slightly decrease with HOCP content in the blends and these results are related to the decrease of blend crystallinity. The decrease of the elongation at break is accounted for by the presence of glassy HOCP domains that act as defects in the P4MP1 matrix, hampering the drawing. At 120°C both the amorphous phases are rubbery. It is found decreases of Young's modulus, stresses at yielding and break points. These results have been related to the decrease of blend crystallinity and to the increase of the total rubbery amorphous phase. Moreover, it is found that the blends present elongations at break equal to that of pure P4MP1. This constancy is attributed to: (a) at 120°C the HOCP domains are rubbery and their presence seems not to disturb the drawing of the samples; (b) a sufficient number of the tie-molecules and entanglements of P4MP1 present in the blends. In fact, although the numbers of tie-molecules and entanglements decrease in the blends, increasing the HOCP oligomer, they seem to be enough to keep the material interlaced and avoid earlier rupture. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1269–1277, 1997     

Structure and Properties of a Polypropylene Containing Random Ethylene Units Modified with a Hydrogenated Hydrocarbon Resin

The system formed by a polypropylene containing random low ethylene content (EP copolymer) of and a hydrogenated hydrocarbon resin (HR) is investigated in order to study the influence of resin (up to 20% in wt) on properties of blends and derived films. The random EP copolymer used is MoplenEP2C37F and the resin is MBG273 of Hercules Chemical Co. DSC and DMTA analyses of the blends show increase of Tg with resin content indicating that the two components are compatible in the amorphous phase. WAXD spectra show that MBG273 influences slightly the crystalline structure of EP copolymer. In fact the diffractograms of the EP copolymer and 95/5 blend present, beside the predominant peak of α form, also a small span denoting presence of γ form; this span is not detectable on spectra of 90/10 and 80/20 samples. The crystallization during the cooling is found to be only lightly delayed by the HR: in fact, only 4 degrees is the difference between the Tc values of EP copolymer and 80/20 blend. Stress-strain test performed at room temperature show that MBG273 induces increase of Young's modulus and small decrease of elongation at break as function of resin content. An important effect is on the water vapour permeability, which decreases with resin content. The permeability and tensile properties are related to the increase of the glass transition with the addition of MBG273 that transforms gradually the amorphous of the material from rubbery to glassy. The results reported in this work indicate that an addition of 5–10% of MBG273 changes favourably properties, as Young' modulus and water vapour permeability, of an EP copolymer designed for the production of films for packaging application.     

Viscoelastic properties of Nafion at elevated temperature and humidity

Tensile stress–strain and stress relaxation properties of 1100 equivalent weight Nafion have been measured from 23 to 120 °C at 0–100% relative humidity. At room temperature, the elastic modulus of Nafion decreases with water activity. At 90 °C, the elastic modulus goes through a maximum at a water activity of ～ 0.3. At temperatures ≥90 °C, hydrated membranes are stiffer than dry membranes. Stress‐relaxation was found to have two very different rates depending on strain, temperature, and water content. At high temperature, low water activity, and small strain, the stress relaxation displays a maximum relaxation time with stress approaching zero after 10³–10⁴ s. Water absorption slows down stress‐relaxation rates. At high water activity, the maximum stress relaxation time was >10⁵ s at all temperatures. No maximum relaxation time was seen at T ≤ 50 °C. Increasing the applied strain also resulted in no observed upper limit to the stress relaxation time. The results suggest that temperature, absorbed water, and imposed strain alter the microstructure of Nafion inducing ordering transitions; ordered microstructure increases the elastic modulus and results in a stress relaxation time of >10⁵ s. Loss of microphase order reduces the elastic modulus and results in a maximum stress relaxation time of 10³–10⁴ s. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 11–24, 2009.