Nicole R. Demarquette

Morphologies and interfacial tensions of immiscible polypropylene/polystyrene blends modified with triblock copolymers

Abstract The morphology and the response to small amplitude oscillatory shear (SAOS) of polypropylene/polystyrene (PP/PS 90/10) blends compatibilized with styrene–butadiene–styrene (SBS) or styrene–ethylene/butylene–styrene (SEBS) triblock copolymer were studied in this work. The possibility of inferring the interfacial tension between PP and PS as a function of amount of triblock copolymer added to the blend using the morphological and rheological measurements was investigated. The concentration of compatibilizers ranged from 0 to 25% relative to the weight of the dispersed phase (PS). The addition of compatibilizers resulted in a reduction of the size of the dispersed phase particles following an emulsion curve. SBS was shown to form a third phase when added, at high concentrations, to the blend. The addition of compatibilizers to the PS phase resulted in a reduction of interfacial tension following an emulsion curve. It was shown that for both compatibilizers the concentration at which the interfacial tension essentially levels off is smaller than the concentration at which the average radius of the dispersed phase essentially levels off. The morphological, viscosity and interfacial tension results showed that SEBS is a better compatibilizer for the PP/PS blend than is SBS.

Evaluation of surface energy of solid polymers using different models

In the present work, contact angles formed by drops of diethylene glycol, ethylene glycol, formamide, diiodomethane, water, and mercury on a film of polypropylene (PP), on plates of polystyrene (PS), and on plates of a liquid crystalline polymer (LCP) were measured at 20°C. Then the surface energies of those polymers were evaluated using the following three different methods: harmonic mean equation and geometric mean equation, using the values of the different pairs of contact angles obtained here; and Neumanns equation, using the different values of contact angles obtained here. It was shown that the values of surface energy generated by these three methods depend on the choice of liquids used for contact angle measurements, except when a pair of any liquid with diiodomethane was used. Most likely, this is due to the difference of polarity between diiodomethane and the other liquids at the temperature of 20°C. The critical surface tensions of those polymers were also evaluated at room temperature according to the methods of Zisman and Saito using the values of contact angles obtained here. The values of critical surface tension for each polymer obtained according to the method of Zisman and Saito corroborated the results of surface energy found using the geometric mean and Neumanns equations. The values of surface energy of polystyrene obtained at 20°C were also used to evaluate the surface tension of the same material at higher temperatures and compared to the experimental values obtained with a pendant drop apparatus. The calculated values of surface tension corroborated the experimental ones only if the pair of liquids used to evaluate the surface energy of the polymers at room temperature contained diiodomethane.

Influence of coalescence and interfacial tension on the morphology of PP/HDPE compatibilized blends

Abstract In this paper, the compatibilization of polypropylene (PP)/high-density polyethylene (HDPE) blend was studied through morphological and interfacial tension analysis. Three types of compatibilizers were tested: ethylene–propylene–diene copolymer (EPDM), ethylene–vinylacetate copolymer (EVA) and styrene–ethylene/butylene–styrene triblock copolymer (SEBS). The morphology of the blends was studied by scanning electron microscopy. The interfacial tension between the components of the blends was evaluated using small amplitude oscillatory shear analysis. Emulsion curves relating the average radius of the dispersed phase and the interfacial tension to the compatibilizer concentration added to the blend were obtained. It was shown that EPDM was more efficient as an emulsifier for PP/HDPE blend than EVA or SEBS. The relative role of interfacial tension reduction and coalescence reduction to particle size reduction was also addressed. It was observed that the role of coalescence reduction is small, mainly for PP/HDPE (90/10) blends compatibilized by EPDM, EVA or SEBS. The results indicated that the role of coalescence reduction to particle size reduction is lower for blends for which interfacial tension between its components is low at compatibilizer saturation.

Influence of maleation of polypropylene on the interfacial properties between polypropylene and ethylene–vinyl alcohol copolymer

In order to improve the miscibility between the components of a blend, it is possible to modify the chemical structure by functionalizing one or more of the components. This results in better adhesion at the interface between the components and, consequently, in better mechanical properties. In this work, the influence of maleation of polypropylene on the interface between polypropylene and ethylene–vinyl alcohol copolymer was studied using the measurement of interfacial tension, surface analysis with electron spectroscopy for chemical analysis (ESCA), and morphological observation, using scanning electron microscopy (SEM). The interfacial tension between a 0.1-wt % maleated polypropylene and ethylene–vinyl alcohol copolymer was shown to be 25% lower than the interfacial tension between nonmaleated polypropylene and ethylene–vinyl alcohol copolymer. This resulted in better adhesion between maleated polypropylene and ethylene–vinyl alcohol copolymer. The surface analysis indicates that this decrease of interfacial tension is due to migration of the maleic groups of the maleated polypropylene to the interface between the 2 polymers and that, probably, a chemical interaction occurs at the interface between maleated polypropylene and ethylene–vinyl alcohol copolymer. It is also shown in this work that additives, such as SiO2, found in commercial polymers, can influence the interfacial tension between 2 polymers.

Polystyrene/clay nanocomposites

Abstract Polystyrene has been widely studied as a matrix in nanocomposites, because it is a model amorphous polymer. The present article provides an extensive review of studies on polystyrene/layered silicate nanocomposites. Emphasis is given on different preparation methods, clay surfactants and polymer modifications used to obtain the materials, and their engineering properties, such as mechanical, rheological and thermal properties.

Evaluation of experimental techniques for determining interfacial tension between molten polymers

Abstract Interfacial tension between molten polymers has received considerable experimental attention over the past 30 years because of its implications in several industrial applications such as coating, blending, composites, etc. However, due to the high viscosity of molten polymers, the interfacial tension between them can be experimentally determined reliably by only a few techniques. In this work, the latest developments of experimental methods to measure interfacial tension between molten polymers are reviewed; the methods are also compared in terms of accuracy and applicability.

Nonlinear viscoelasticity of concentrated polystyrene solutions: sliding plate rheometer studies

Because of the degree to which the linearity and polydispersity of polystyrene samples can be controlled in laboratory polymerizations, the rheological properties of melts and solutions of this polymer have been extensively studied. However, in previous work the maximum strain or strain rate was limited to small values due to edge effects in the rotational rheometers used. We used a sliding plate rheometer equipped with a shear stress transducer and a birefringence apparatus to measure simultaneously the shear stress and the third normal stress difference, N3 (≡σ11−σ33), during step strain, start‐up of steady shear, and exponential shear. Depending on the strain history, the maximum strain achieved was between 20 and 80. The steady‐state shear stress in steady shear flow was found to be nearly independent of shear rate over a range of shear rates with a strong suggestion of a maximum, a phenomenon predicted by the Doi–Edwards theory. The relaxation modulus for the shear stress was found to be superposable...

Modification of a Brazilian smectite clay with different quaternary ammonium salts

In this work, a smectite clay from the State of Paraiba, Brazil, was treated with six different types of ammonium salts, which is an usual method to enhance the affinity between the clay and polymer for the preparation of nanocomposites. The clays, before and after modification, were characterized by X ray diffraction. The conformation of the salts within the platelets of the clay depended on the number of long alkyl chains of the salt. The thermal stability of the clays was also studied. The ammonium salts thermal decomposition was explained in light of their position within the organoclays.

Influence of temperature, molecular weight, and polydispersity of polystyrene on interfacial tension between low‐density polyethylene and polystyrene

In this work, the influence of temperature, molecular weight, and polydispersity of polystyrene on interfacial tension between low-density polyethylene (LDPE) and polystyrene (PS) was evaluated using the pendant drop method. It was shown that interfacial tension between LDPE and PS decreases with increasing temperature for all LDPE–PS pairs studied. The temperature coefficient (∂γ/∂T) (where λ is interfacial tension and T is temperature) was higher for lower molecular weight and larger polydispersity of PS. The interfacial tension between LDPE and PS at a temperature of 202°C increased when the molecular weight of polystyrene was varied from 13,000 to 30,000. When the molecular weight of PS was further increased, the interfacial tension was shown to level off. The effect of polydispersity on interfacial tension between PS and LDPE, at a temperature of 202°C, was studied using PS with a constant-number average molecular weight and varying polydispersity. The interfacial tension was shown to decrease with increasing polydispersity. However, the influence of polydispersity was lower for PS of higher molecular weight.

Blending and morphology control to turn hydrophobic SEBS electrospun mats superhydrophilic

Thermoplastic elastomer SEBS, a triblock copolymer composed of styrene (S) and ethylene-co-butylene (EB) blocks, can be dissolved and processed by electrospinning to produce flexible nonwoven mats that can be interesting for applications like filtration or separation membranes. Controlling surface properties such as hydrophobicity/hydrophilicity is critical to achieving a desired performance. In this study, hydrophobic electrospun SEBS mats were obtained, following which an amphiphilic molecule (Pluronic F127) was solution-blended with SEBS prior to electrospinning, in a bid to produce a hydrophilic membrane. The result was a fast-spreading superhydrophilic mat with thinner fibers that preserved the flexibility of the SEBS. The morphologies of nonwoven mats, flat films (prepared by dip-coating using identical solutions) and of the surface of individual fibers were characterized using different microscopy techniques (optical, scanning electron microscopy and atomic force microscopy). Chemical analysis by X-ray photoelectron spectroscopy (XPS) revealed a large F127 concentration in the outermost surface layer. In addition, an analysis of dip-coated flat films revealed that for 20 wt % of F127, there was a change in the blend morphology from dispersed F127-rich regions in the SEBS matrix to an interconnected phase homogeneously distributed across the film that resembled grain boundaries of micellar crystals. Our results indicated that this morphology change at 20 wt % of F127 also occurred to some extent in the electrospun fibers and this, combined with the large surface area of the mats, led to a drastic reduction in the contact angle and fast water absorption, turning hydrophobic electrospun mats superhydrophilic.