Elongational rheology of LLDPE / LDPE blends

The objective of this study is to investigate the effect of low density polyethylene (LDPE) content in linear low density polyethylene (LLDPE) on the crystallinity and strain hardening of LDPE / LLDPE blends. Three different linear low density polyethylenes (LL‐1, LL‐2 and LL‐3) and low density polyethylenes (LD‐1, LD‐2 and LD‐3) were investigated. Eight blends of LL‐1 with 10, 20, 30 and 70 wt % of LD‐1 and LD‐3, respectively, were prepared using a single screw extruder. The elongational behavior of the blends and their constituents were measured at 150°C using an RME rheometer. For the blends of LL‐1 with LD‐1, the low shear rate viscosity indicated a synergistic effect over the whole range of concentrations, whereas for the blends of LL‐1 with LD‐3, a different behavior was observed. For the elongational viscosity behavior, no significant differences were observed for the strain hardening of the 10–30% LDPE blends. Thermal analysis indicated that at concentrations up to 20%, LDPE does not significantly affect the melting and crystallization temperatures of LLDPE blends. In conclusion, the crystallinity and rheological results indicate that 10–20% LDPE is sufficient to provide improved strain hardening in LLDPE. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3070–3077, 2003     

Preparation and characterization of membranes obtained from blends of acrylonitrile copolymers with poly(vinyl alcohol)

New microfiltration and ultrafiltration membranes were obtained using acrylonitrile‐vinyl acetate copolymers in mixture with poly(vinyl alcohol) (PVA). Thus, a blend polymer solution was prepared in dimethylsulfoxide (DMSO) and used to obtain bicomponent polymer membranes by phase inversion. The rheological behavior of the DMSO polymer solutions was, mostly, dilatant at low shear gradients and pseudo plastic with quasi Newtonian tendency at higher gradients. Membranes were characterized by Fourier transform infrared spectrometry (FTIR), optical microscopy, atomic force microscopy, thermal gravimetric analysis‐differential thermal gravimetry, and pure water flux (PWF). FTIR spectra displayed the characteristic bands for acrylonitrile, vinyl acetate, and PVA. The morphology and the porosity can be tailored by the preparation conditions. PVA allows controlling the size of the pores and enables, in principle, to use the resulted membranes as supports for enzyme immobilization. PVA content influences the thermal stability. PWF values depend on the copolymer, on the content in PVA, but also on the coagulation bath composition. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41013.     

Thin-film membranes derived from co-continuous polymer blends: preparation and performance

Two approaches for preparing thin-film membranes from immiscible co-continuous polymer blends are presented. Approach 1 involves the melt blending of co-continuous polymer blends followed by the selective extraction of one of the phases and results in a microporous membrane material of high void volume. In that case, the pore size is defined by the phase size of one of the phases in the blend and hence composition, interfacial tension, viscosity ratio and other parameters influencing phase morphology can be used to control porosity. For that first approach, the blend system studied is high density polyethylene/polystyrene, compatibilized with SEBS (styrene-ethylene-buthylene-styrene) triblock copolymer. Both symmetric and asymmetric type membranes can be obtained. The symmetric membrane demonstrates porosity ranging from 80 to 230 nm. It is shown that extraction time can be used to develop asymmetry in the membrane and the effects of extraction time on the morphology, pore size distribution and performance are presented. High flux values and high apparent rejection factors estimated from permeability testing indicate that these materials could have potential in a variety of membrane applications.Approach 2 is a solventless approach that results in a membrane of very low void volume. A high interfacial tension immiscible co-continuous blend compatibilized at different levels by a weak interfacial modifier is prepared by melt mixing and extrusion through a sheet die. Microporosity in the bulk of the material is generated in situ during cooling by this approach. The thin sheet is then subjected to uniaxial or biaxial cold stretching to develop surface porosity. This technique exploits interfacial debonding and the weak interface of the co-continuous morphology acts as a template to guide the direction of porosity development. Highly percolated membranes of polycarbonate and high-density polyethylene with SEBS were prepared. These membranes possess pore sizes in the range of 100 nm and are of very low void volume. Oxygen permeation tests, carried out under atmospheric pressure, demonstrate a dramatic increase in oxygen flux from 1378 cm³/m²/day (non-stretched 50PE/50PC/15SEBS sample) to 106,270 cm³/m²/day (biaxially stretched sample). The results indicate that they could have potential as breathable barrier type materials. The effects of draw ratio on the permeation values are presented.     

Phase morphology of PP/COC blends

Phase morphology of polymer blends PP/COC, where PP is polypropylene and COC is a copolymer of ethene and norbornene, was characterized by means of scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM). PP/COC blends were prepared by injection molding and their morphology was studied for six different compositions (90/10, 80/20, 70/30, 60/40, 50/50, and 25/75 wt %). The intention was to improve PP properties by forming COC cocontinuous phase, which should impart to the PP matrix higher stiffness, yield stress, and barrier properties. Surprisingly enough, all studied blends were found to have fibrillar morphology. In the 90/10, 80/20, and 70/30 blends, the PP matrix contained fibers of COC, whose average diameter increased with increasing COC fraction. In the 60/40 blend, the COC component formed in the PP matrix both fibers and larger elongated entities with PP fibers inside. The 50/50 blend was formed by COC cocontinuous phase with PP fibers and PP cocontinuous phase with COC fibers. In the 25/75 blend, PP fibers were embedded in the COC matrix. In all blends, the fibers had an aspect ratio at least 20, were oriented in the injection direction, and acted as a reinforcing component, which was proven by stress–strain and creep measurements. According to the available literature, the fibrous morphology formed spontaneously in PP/COC is not common in polymer blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 253–259, 2004     

Rheological and thermal properties of polypropylene blends based in a low molecular weight EVA

Blends of polypropylene (PP) and poly(ethylene-co-vinyl acetate) (EVA) having a PP/EVA viscosity ratio of 240 were prepared by melt mixing. EVA concentration varies from 2 to 26 wt%. All blends display two-phase structure with quasi-spherical EVA domains evenly distributed in the PP matrix. The diameter of the domains increases with EVA concentration from about 0.4 to 6 μm. Each component crystallizes separately. The melting temperature of PP phase is no noticeably affected by the presence of EVA while the crystallization one gradually increases by 4°C. The dynamic moduli of the blends are well predicted by the emulsion model of Palierne, revealing that the system PP/EVA has a very small interfacial tension. The thermal degradation behavior of the blends, determined by thermogravimetry, shows that the deacylation process in EVA is not affected by the presence of PP while the beginning of the degradation process of PP is increased by up to 20°C due to the presence of EVA. This effect goes along with an increment in the maximum degradation rate of PP.     

Relationship between branch length and the compatibilizing effect of polypropylene‐g‐polystyrene graft copolymer on polypropylene/polystyrene blends

Three polypropylene‐g‐polystyrene (PP‐g‐PS) graft copolymers with the same branch density but different branch lengths were evaluated as compatibilizing agents for PP/PS blends. The morphological and rheological results revealed that the addition of PP‐g‐PS graft copolymers significantly reduced the PS particle size and enhanced the interfacial adhesion between PP and PS phases. Furthermore, it is verified that the branch length of PP‐g‐PS graft copolymer had opposite effects on its compatibilizing effect: on one hand, increasing the branch length could improve the compatibilizing effect of graft copolymer on PP/PS blends, demonstrated by the reduction of PS particle size and the enhancement of interfacial adhesion; on the other hand, increasing the branch length would increase the melt viscosity of PP‐g‐PS graft copolymer, which prevented it from migrating effectively to the interface of blend components. Additionally, the crystallization and melting behaviors of PP and PP/PS blends were compared. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40126.     

Recovery of microbial polysaccharides from fermentation broths by microfiltration on ceramic membranes

This paper investigates the extraction of microbial polymers (polysaccharides) from fermentation broths of Sinorhizobium meliloti M5N1CS using crossflow filtration through ceramic membranes of various pore sizes from 0.1 to 0.8 µm. The duration of fermentation was set at 70 h in order to maximize the production of high molecular weight polysaccharides (average 2 × 10⁵ Da). The 0.1 µm membrane underwent rapid fouling and was found inadequate for this application. For the other membranes, the sieving coefficients decreased from 95% to about 20% in 90 min, at a slower rate than the permeate flux. The largest permeate and mass fluxes were obtained with the 0.5 µm membrane (18.5 × 10⁻⁶ m s⁻¹ and 20 × 10⁻⁶ gm⁻²s⁻¹). Increasing the fluid velocity from 3 to 6 m s⁻¹ increased both the permeate flux and sieving coefficients, while raising the transmembrane pressure from 50 kPa to 100 kPa increased the flux slightly but decreased the sieving coefficient. Polysaccharide extraction will be maximized by operating at high velocities and low transmembrane pressure (TMP) which may require cocurrent recirculation of the permeate. Experiments with cell‐free solutions showed that the permeate flux is mostly limited by the bacterial layer deposited on the membrane while the presence of cells has a positive effect on the sieving coefficient. Irreversible fouling due to polymer adsorption on the membrane decreased with increasing pore size and velocity but increased strongly with TMP. © 1999 Society of Chemical Industry     

Sulfonated polyetheretherketone/polypropylene polymer blends for the production of photoactive materials

Sulfonated polyetheretherketone (SPEEK) was synthesized via a mono‐substitution reaction of PEEK in concentrated sulphuric acid and was blended with polypropylene (PP) in 2–10%w/w concentration to be used for the production of photoactive thermoplastic products. SPEEK and SPEEK/PP blends were characterized using FTIR, DSC, TGA, NMR, rheology, SEM, and EPR. Under UV‐Vis irradiation, stable benzophenone ketyl (BPK) radicals were generated by hydrogen extraction from PP. By increasing the amount of SPEEK in the polymer blend a linear increase in the BPK radicals was achieved according to the EPR data. DSC and TGA tests indicated weaknesses in the thermal stability of SPEEK but according to the rheological tests this should not have a major effect on processabililty. The optimal amount of SPEEK in the blend was obtained at 5%w/w. This concentration provided a good compromise between radical concentration, material processability, and cost. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41509.     

Flow marks in injection molding of polypropylene and ethylene–propylene elastomer blends: Analysis of morphology and rheology

This paper reports an investigation of asynchronous flow marks on the surface of injection molded parts and short shots made from two different blends of polypropylene and ethylene–propylene random copolymer elastomers. Flow marks were observed on the surface with both blends; the spatial frequency of flow marks on the surface was greater in the blend B1, which also exhibited a greater contrast between the surface regions. The same blend was distinctly faster in the linear viscoelastic tests of shear creep recovery and shear viscosity growth. The degree of contrast between the flow‐mark regions and the out‐of‐flow‐mark regions was examined with a detailed analysis of SEM micrographs of the surface regions as well as the near wall regions from short shots. This revealed that the dispersed phase was highly stretched to cylindrical strands in the glossy surface regions of both blends and retracted in the dull regions to different extents in the two cases. A comparison of the particle size distributions and aspect ratio distributions in different regions established that rapid retraction of the suspended elastomer phase was the dominant cause of changes in particle shape between surface regions. Nonlinear shear creep and creep recovery curves of the two elastomer components showed that at a time of 1 s, the fractional strain recovery of the elastomer in B1 was much higher than that of the elastomer in B2. Hence, the nonlinear elastic recovery of the elastomer phase at short times is an important factor in flow mark formation with blends of polypropylene and olefinic elastomers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 423–434, 2005     

Rheology of EPR/PP blends

The rheological behavior of polypropylene, PP, ethylene‐propylene copolymer, EPR, and EPR/PP blends was studied. Zero‐shear viscosity and elastic relaxation time were determined by least‐squares fits by using a Carreau–Yasuda model with Arrhenius temperature dependency. The effect of PP and EPR molecular weight, ethylene ratio in EPR copolymer (E/EPR), and EPR concentration on the zero‐shear viscosity and elasticity of EPR/PP blends was determined experimentally. Molecular weight effects are compared to theoretically expected relationships. EPR concentration effect and E/EPR ratio effects agree well with predictions made by using the Tsenoglou model. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2113–2127, 2001     

Photodegradation of thermodegraded polypropylene/high‐impact polystyrene blends: Mechanical properties

The influence of the addition of high‐impact polystyrene (HIPS) on polypropylene (PP) photodegradation was studied with blends obtained by extrusion with and without styrene–butadiene–styrene (SBS) copolymer (10 wt % with respect to the dispersed phase). The concentrations of HIPS ranged from 10 to 30 wt %. The blends and pure materials were exposed for periods of up to 15 weeks of UV irradiation; their mechanical properties (tensile and impact), fracture surface, and melt flow indices were monitored. After 3 weeks of UV exposure, all of the materials presented mechanical properties of the same order of magnitude. However, for times of exposure greater than 3 weeks, an increasing concentration of HIPS resulted in a better photostability of PP. These results were explained in light of morphological observations. This increase of photostability was even greater when SBS was added to the blends. It was more difficult to measure the melt flow index of the binary PP/HIPS blends than that of PP for low concentrations of HIPS; this was most likely due to energy transfer between the blend domains during photodegradation. This phenomenon was not observed for the ternary blends. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Methanol permeability and properties of DMFC membranes based on sulfonated PEEK/PVDF blends

Proton exchange membranes for a direct methanol fuel cell were prepared by blending poly(vinylidene fluoride) [PVDF] with sulfonated poly(etheretherketone) [SPEEK]. The effects of PVDF content on methanol permeability in the blend membranes were investigated by using a diffusion cell and gas chromatography technique. The thermal resistance and proton conductivity of the membranes were also determined by using a thermal gravimetric analysis (TGA) and an impedance analysis technique, respectively. It was found that methanol permeability in the blend membranes decreased with PVDF content at the expense of proton conductivity. The methanol permeability values of the blend membranes are much lower than that of Nafion 115, whereas proton conductivities of the membranes are comparable to that of Nafion. The thermal stability of these blend membranes are above 250°C which is sufficiently high for use in DMFC. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5941–5947, 2006     

Modeling of turbulent cross flow microfiltration of pomegranate juice using hollow fiber membranes

A mathematical analysis of the permeate flux decline during microfiltration of fruit juice with hollow fibers under turbulent flow is presented. Impact of complex fluid flow phenomena on mass transfer is analyzed. A comprehensive analytical model for developing concentration boundary layer was formulated from first principles using integral method. Attempts to model the system considering constant boundary layer thickness (film theory) is inaccurate for developing boundary layer. Gel resistance parameter depending on juice characteristics has significant impact on permeate flux. Specific gel layer concentration has insignificant effect on system performance under total recycle mode but important for batch mode. Theoretical results were compared with experiments in clarification of pomegranate juice with poly(ether ether ketone) and polysulfone hollow fiber membranes. The physical parameters of complex mixture were evaluated by optimizing of the flux profiles in total recycle mode of operation and were successfully applied for prediction of batch mode performance. © 2014 American Institute of Chemical Engineers AIChE J 60: 4279–4291, 2014     

Saccharomyces cerevisae microfiltration performance of polycarbonate membranes containing chitosan-based polyelectrolyte complexes

Polyelectrolyte complexes (PECs) were prepared using chitosan and sulfonated poly(ethylene terephthalate) by the mixture method. Fourier transform infrared spectroscopy, zeta potential, X-ray diffraction, and thermogravimetric analysis were used to characterize the chemical structure, surface charge, crystallinity, and thermal stability of the PECs. To evaluate how PECs affect the water vapor flux and the microfiltration performance, PECs solutions were spread via casting on polycarbonate microporous membranes. The increase in water vapor flux and in the Saccharomyces cerevisae microfiltration performance indicated that the presence of the PECs acts as fixed charges, changing significantly the transport properties of the polycarbonate matrix. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48483.     

Yield strength of low-density polyethylene-polypropylene blends

Polymer waste recycling is becoming a major problem, because huge amounts of synthetic polymers are manufactured every year for many different purposes. Polymer scraps are gathered from the Municipal Solid Waste (MSW). Within those wastes there are several different polyolefins—such as polyethylene, polypropylene, and polystyrene—all incompatible with each other. In order to recycle these polymers, compatibilization of these polyolefins is needed to avoid high sorting costs and unacceptably low market-value products. In this work, the compatibilization of low-density polyethylene with polypropylene is accomplished through the addition of maleated polyethylene and maleated polypropylene. Prediction of the tensile properties of these blends is attempted, using a model based on continuity of phases in a two-components mixture of thermoplastics. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 275–281, 1997     

Fabrication and properties of PVDF and PVDF‐HFP microfiltration membranes

Poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride)‐co‐hexafluoropropylene (PVDF‐HFP) were used to fabricate porous microfiltration membranes via a thermally induced phase separation (TIPS) method, and dibutyl phthalate (DBP) was used as diluent. The effects of polymer concentration on structure and performance were studied in detail. In addition, the effect of incorporation of hexafluoropropylene (HFP) groups on the membrane was also investigated. The formation mechanism was proposed with the assistance of a phase diagram. The results showed that the incorporation of HFP groups resulted in a lower crystallization temperature (T_c) of the polymer/DBP system. In addition, the porosity, pure water flux, and ink solution flux decreased with increasing polymer concentration. In contrast, the water contact angle, ink rejection ratio, and mechanical properties had an increasing tendency. When the polymer concentration was 30 wt %, the obtained membrane was most suitable for microfiltration. Furthermore, the incorporation of HFP groups improved the properties of the obtained membrane, including better hydrophobicity, mechanical properties, antifouling property, and chemical resistance. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46711.     

Viscoelasticity and morphology of poly(ethylene‐co‐vinyl acetate)/polyisobutylene blends

Blends of an ethylene/vinyl acetate copolymer (EVA) and polyisobutylene of various compositions were prepared by mechanical mixing at a temperature above the melting point of EVA (T_m^EVA) but below the upper critical solution temperature of 170°C for given blends. The rheological properties of the components and blends were studied in the region of small‐amplitude oscillating deformation at temperatures above and below T_m^EVA in the frequency range of 0.01–100 rad/s. At temperatures lower than T_m^EVA, the rheological properties were determined by the existence of the yield stress. With diminishing frequency, the viscosity increased, and the plateau in the relaxation spectrum at low frequencies broadened. The morphology of the blends depended on the conditions of sample heating. The introduction of a finely dispersed filler into the blends led to an anomalous drop in the viscosity. The morphology of the systems that arose by mechanical blending of the molten components was the important factor in the rheological behavior. The observed effects were examined in the framework of the concept of structural networks formed in melts by nonmelted crystallites of EVA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2700–2707, 2006     

Properties and preparation of olefin block copolymer/thermoplastic polyurethane blends

The properties of olefin block copolymer (OBC)/thermoplastic polyurethane (TPU) blends with or without maleic anhydride (MA) modification were characterized and compared. Compared with the OBC/TPU blends, OBC‐g‐MA/TPU blends displayed finer morphology and reduced domain size in the dispersed phase. The crystallization temperatures of TPU decreased significantly from 155.9 °C (OBC/TPU) to 117.5 °C (OBC‐g‐MA/TPU) at low TPU composition in the blends, indicating the inhibition of crystallization through the sufficient interaction of modified OBC with TPU composition. The modified systems showed higher thermal stability than the unmodified systems over the investigated temperature range due to the enhanced interaction through inter‐bonding. The highest improvement in tensile strength was more than fivefold for OBC‐g‐MA/TPU (50/50) in comparison with its unmodified blend via the enhanced interfacial interaction between OBC‐g‐MA and TPU. This also led to the highest Young's modulus of 77.8 ± 3.9 MPa, about twofold increase, among the investigated blend systems. A corresponding improvement on the ductility was also observed for modified blends. The modification did not vary the glass transition temperature and crystalline structure much, thus the improvement in the mechanical properties was mainly attributed to the improved compatibility and interaction from the compatibilization effect as well as increased viscosity from the crosslinking effect for modified blends. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43703.     

Preparation and characterization of composite membranes using blends of SPEEK/PBI with boron phosphate

In this contribution composite membranes have been prepared from acid-base polymer blend and solid inorganic proton conductive boron phosphate (BPO₄). The blends are composed of sulfonated polyether-ether ketone (SPEEK) as the acidic component and polybenzimidazole (PBI) as the basic component. The contents of solid BPO₄ in the composite membrane varied from 10 to 40 wt%. The conductivity of the composite membranes was measured by impedance spectroscopy at room temperature. The conductivity of the composite membranes was found to increase with the incorporation of boron phosphate particles into blend membranes. The highest conductivity of 6 mS/cm was found for composite membrane at room temperature. The membranes were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and FTIR which showed acid-base interaction in the blend membranes and also confirmed the presence of solid BPO₄ into the composite membranes. These membranes show good perspective in the membrane fuel cell applications.     

pH‐ and temperature‐sensitive microfiltration membranes from blends of poly(vinylidene fluoride)‐graft‐poly(4‐vinylpyridine) and poly(N‐isopropylacrylamide)

The copolymer poly(vinylidene fluoride)‐graft‐poly(4‐vinylpyridine) (PVDF‐g‐P4VP) was prepared through the graft copolymerization of poly(vinylidene fluoride) with 4‐vinylpyridine. Through the blending of the PVDF‐g‐P4VP copolymer with poly(N‐isopropylacrylamide) (PNIPAm) in an N‐methyl‐2‐pyrrolidone solution, PVDF‐g‐P4VP/PNIPAm membranes were fabricated by phase inversion in aqueous media. Elemental analyses indicated that the blend concentration of PNIPAm in the blend membranes increased with an increase in the blend ratio used in the casting solution. Scanning electron microscopy revealed that the membrane surface tended to corrugate at a low PNIPAm concentration and transformed into a smooth morphology at a high PNIPAm concentration. The surface morphology and pore size distribution of the microfiltration membranes could be regulated by the blend concentration of the casting solution, temperature, pH, and ionic strength of the coagulation bath. X‐ray photoelectron spectroscopy revealed a significant enrichment of PNIPAm on the membrane surface. The flux of aqueous solutions through the blend membranes exhibited a pH‐ and temperature‐dependent behavior. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4089–4097, 2006