Characterization of the free volume in high‐impact polystyrene/polypropylene and high‐impact polystyrene/high‐density polyethylene blends probed by positron annihilation spectroscopy

The free‐volume properties of high‐impact polystyrene (HIPS)/polypropylene (PP) and HIPS/high‐density polyethylene (HDPE) blends were investigated by means of positron annihilation lifetime spectroscopy (PALS). The measured results show that the free‐volume holes in the semicrystalline polymers, such as PP and HDPE, were not large enough to accommodate the branched chains and the end groups of the macromolecular chains in HIPS to produce favorable interactions between the semicrystalline polymers and the HIPS polymer in these blends; thus immiscible blends were formed. The weak interaction between two dissimilar polymer molecules only took place in the regions between two amorphous phases. In addition, the observed negative deviations of the longest lifetime intensity and the free‐volume fraction were attributed to the influence of the interfacial polarization during PALS measurement. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1507–1514, 2003     

Investigation into the morphology and mechanical properties of melt‐drawn filaments from uncompatibilized blends of polystyrene and high‐density polyethylene

Uncompatibilized immiscible blends of polystyrene (PS) and high‐density polyethylene (HDPE) were melt‐processed in a single‐screw extruder fitted with a fine screen mesh and capillary die and were further drawn into filaments to produce near‐nanoscale immiscible domains. The resultant morphologies and mechanical properties were studied for these structures in which load transfer is achieved solely by mechanical linkages between blend domains. The morphology of the blends revealed co‐continuity approximately in the range of 45–47 volume percent PS. The development of a three‐dimensional co‐continuous network in 45 vol% PS, as revealed by morphology observations, was also related to a decrease in extruder output rate in this region, an indicator of the melt interaction of the two phases as co‐continuity is achieved. Image analysis revealed submicron fibrillar structures near the phase inversion composition where domain sizes ranged from 6–220 nm with an average domain size of 90 nm. Tensile modulus increased with increasing PS content (E = 2.7 GPa at 47% PS) over the entire blend range with values greater than the rule of mixtures up to 50% PS. Strain to failure did not seem to be influenced by co‐continuous morphologies and the fine dispersion of PS domains appears to constrain the fundamentally high strain of HDPE. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1616–1625, 2007     

Dynamic rheological properties of high‐density polyethylene/polystyrene blends extruded in the presence of ultrasonic oscillations

The linear rheological properties of high‐density polyethylene (HDPE), polystyrene (PS), and HDPE/PS (80/20) blends were used to characterize their structural development during extrusion in the presence of ultrasonic oscillations. The master curves of the storage shear modulus (G′) and loss shear modulus (G″) at 200°C for HDPE, PS, and HDPE/PS (80/20) blends were constructed with time–temperature superposition, and their zero shear viscosity was determined from Cole–Cole plots of the out‐of‐phase viscous component of the dynamic complex viscosity (η″) versus the dynamic shear viscosity. The experimental results showed that ultrasonic oscillations during extrusion reduced G′ and G″ as well as the zero shear viscosity of HDPE and PS because of their mechanochemical degradation in the presence of ultrasonic oscillations; this was confirmed by molecular weight measurements. Ultrasonic oscillations increased the slopes of log G′ versus log G″ for HDPE and PS in the low‐frequency terminal zone because of the increase in their molecular weight distributions. The slopes of log G′ versus log G″ for HDPE/PS (80/20) blends and an emulsion model were used to characterize the ultrasonic enhancement of the compatibility of the blends. The results showed that ultrasonic oscillations could reduce the interfacial tension and enhance the compatibility of the blends, and this was consistent with our previous work. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3153–3158, 2004     

Effect of the high‐density polyethylene melt index on the microcellular foaming of high‐density polyethylene/polypropylene blends

The effect of high‐density polyethylene (HDPE)/polypropylene (PP) blending on the crystallinity as a function of the HDPE melt index was studied. The melting temperature and total amount of crystallinity in the HDPE/PP blends were lower than those of the pure polymers, regardless of the blend composition and melt index. The effects of the melt index, blending, and foaming conditions (foaming temperature and foaming time) on the void fractions of HDPEs of various melt indices and HDPE/PP blends were also investigated. The void fraction was strongly dependent on the foaming time, foaming temperature, and blend composition as well as the melt index of HDPE. The void fraction of the foamed 30:70 HDPE/PP blend was always higher than that of the foamed 50:50 HDPE/PP blend, regardless of the melt index. The microcellular structure could be greatly improved with a suitable ratio of HDPE to PP and with foaming above the melting temperature for long enough; however, using high‐melt‐index HDPE in the HDPE/PP blends had a deleterious effect on both the void fraction and cell morphology of the blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 364–371, 2004     

Effect of styrene‐butadiene‐styrene addition on polystyrene/high‐density polyethylene blends

In order to prepare an ideal mixture, the physical and chemical properties of the constituent polymers must be known in detail. Thus, selection of the polymers that will constitute the mixture and a thorough study of the mixing methods and the economic factors become important. A rigid plastic is toughened by dispersing a small amount of rubbery material (generally 5–20%) in the rigid plastic matrix. Such a mixture of plastics is characterized by its impact resistance. Among thermoplastics toughened in this way are polystyrene (PS), poly(vinyl chloride), poly(methyl methacrylate), polypropylene, polycarbonate, and nylons, and recently thermoset resins such as epoxies, unsaturated polyester resins, and polyamids. In this study PS and high‐density polyethylene polymers were mixed in various ratios. In order to increase the compatibility of the mixtures, 5, 7.5, and 10% SBS copolymer was also added. The mixing operation was conducted by using a twin‐screw extruder. The morphology and the compatibility of the mixtures were examined by using SEM and DSC techniques. Furthermore, the elastic modulus, yield and tensile strengths, percent elongation, Izod impact resistance, hardness, and melt flow index values of the polymer alloys of various ratios were determined. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2967–2975, 2002; DOI 10.1002/app.2325     

Glass‐transition‐temperature depression in chemically crosslinked low‐density polyethylene and high‐density polyethylene and their blends with ethylene vinyl acetate copolymer

A reduction in the glass‐transition temperature (T_g) was found for polyolefins chemically crosslinked by peroxide. This tendency, which was observed for low‐density and high‐density polyethylenes, was also validated for their blends with Ethylene Vinyl Acetate copolymer. It is proposed that the constrained crystallization process, as a result of a restriction imposed on the chain packing by the chemical crosslinks, results in an increasing net free volume in the amorphous phase and hence reduces T_g. The T_g depression becomes greater with increasing crosslink density, whereas at the same time, the degree of crystallinity and consequently the density of the system decreases with an increase in the peroxide content. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1654–1660, 2007     

Effect of dynamic shear on the microcellular foaming of polypropylene/high‐density polyethylene blends

Dynamic shear in the axial direction of a rotor was vertically superposed on the melt flow direction, and its effects on the shear rate and melt strength were investigated theoretically. Polypropylene/high‐density polyethylene blends were microcellularly foamed with different vibration parameters. The experimental results were compared with those of a theoretical analysis, and the effects of dynamic shear on the foamability and ultimate cell structure were analyzed in detail. The theoretical results showed that the shear rate and melt strength increased with an increase in the vibration amplitude and frequency. The enhanced melt strength could effectively restrict cell growth, prevent cell rupture, and improve foamability. The experimental results showed that the cell orientation decreased and the cell structure was improved when axial dynamic shear induced by rotor vibrations was superposed on the melt flow direction. Furthermore, the cell diameter decreased and the cell density increased with increases in the vibration amplitude and frequency. The experimental results were very consistent with the theoretical analysis. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Creep resistance of wood‐filled polystyrene/high‐density polyethylene blends

Creep, the deformation over time of a material under stress, is one characteristic of wood‐filled polymer composites that has resulted in poor performance in certain applications. This project was undertaken to investigate the advantages of blending a plastic of lower‐creep polystyrene (PS) with high‐density polyethylene (HDPE) at ratios of 100:0, 75:25, 50:50, 25:75, and 0:100. These various PS–HDPE blends were then melt blended with a short fiber‐length wood flour (WF). Extruded bars of each blend were examined to measure modulus of elasticity and ultimate stress. Increasing the ratio of WF increased modulus of elasticity in all composites, except between 30 and 40% WF, whereas the effect of WF on ultimate stress was variable, depending on the composite. Scanning electron microscopic images and thermal analysis indicated that the wood particles interacted with the PS phase, although the interactions were weak. Finally, creep speed was calculated by using a three‐point bending geometry with a load of 50% of the ultimate stress. Creep decreased only slightly with increasing WF content but more significantly with increasing PS content, except at pure PS. The WF/75PS–25HDPE blend showed the least creep. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 418–425, 2001     

Dynamic study of free volume properties in polyethylene/styrene butadiene rubber blends by positron annihilation lifetime method

Positronium (Ps) formation in low and high‐density polyethylene (LDPE and HDPE) and styrene butadiene rubber (SBR), as well as in their blends (LDPE/SBR: 50/50 and HDPE/SBR: 50/50) has been investigated by positron annihilation lifetime (PAL) measurements as a function of low temperature (100–300 K). The glass transition temperature (T_g) for the initial polymers and their blends are determined by ortho‐positronium (o‐Ps) lifetime, τ₃ versus temperature as well as by differential scanning calorimetry (DSC) measurements. The temperature dependence of nanoscale free volume size shows similar trend for all the investigated samples indicating an abrupt change at T_g, which is found to be higher for SBR sample characterized by its high chain mobility. In addition, The T_g values deduced from PAL measurements are compared with the corresponding data deduced from DSC. The variation of o‐Ps formation probability I₃ versus temperature for polyethylene and their blends were interpreted in the frame work of spur reaction model of Ps formation. On the other hand, the lifetime coefficient below and above T_g is found to be one order of magnitude larger than the linear expansion coefficient. This constitutes evidence that Ps is only probing free volumes. The results obtained from change in free volume–hole distribution with temperature reflect both thermal expansion and increase in free volume–hole size with the rise in temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Crystallization and fracture behaviors of high‐density polyethylene/linear low‐density polyethylene blends: The influence of short‐chain branching

Two commercial polyethylene samples, linear high‐density polyethylene (HDPE) and branched linear low‐density polyethylene with almost the same molecular weight distribution but different contents of short‐chain branching (SCB) were melt blended based on the consideration of practical application. Dynamic rheology analysis indicated good compatibility of all the blends with different compositions. Common differential scanning calorimeter (DSC) tests and successive self‐nucleation and annealing (SSA) treatment showed several interesting phenomena. First, without consideration of the effect of molecular weight and molecular weight distribution impact, co‐crystallization occurred at all ratios even the two components had a considerable difference in SCB distribution. Second, in SSA curves the area of the first two melting peaks, i.e., the amount of the thick lamellas of the two components showed an obvious positive deviation with the increase of HDPE content owing to the crystal perfection improved by the co‐crystallization. Essential Work of Fracture tests proved the co‐crystallization effects had a positive effect on the improvement of the resistance to crack propagation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Non‐isothermal crystallization kinetics and segmental dynamics of high density polyethylene/butyl rubber blends

Non‐isothermal crystallization kinetics and dynamics of polymer blends are important to both theory and applications. In this work, we studied the morphology, crystal structure, non‐isothermal crystallization kinetics and dynamics of high density polyethylene/butyl rubber (HDPE/IIR) blends. The non‐isothermal crystallization kinetics is analyzed by Mo's model and the dynamics behavior is analyzed by a linear method. The results of morphology, non‐isothermal crystallization kinetics and dynamics show that the condensed structure of HDPE/IIR blends has a marked influence on their non‐isothermal crystallization kinetics and segmental dynamics. © 2015 Society of Chemical Industry     

Effect of additives on the composition dependent glass transition variation in PS/PP blends

The effect of additives on glass transition behavior in melt processed blends of polystyrene (PS) and polypropylene (PP) was studied. Blends of additive‐free polystyrene and additive‐free polypropylene revealed the known effect of the PS T_g increase in blend compositions where PP surrounds PS. Glass transition behavior in these blends was compared to blends prepared from additive‐free PP and commercial grade PS, which contained lubricant additives. The thermal transitions of PS and PP were measured using modulated DSC. Although the behavior of low PS concentration blends was similar in both systems, the characteristics of the high PS blends differed substantially. These differences and the contrast in the PP T_g behaviors were attributed to the migration of additives from the PS phase across the immiscible interface into the PP phase. Similar T_g variations were observed in blends of commercial grade PS and commercial grade PP. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Chemical sensing materials based on electrically‐conductive immiscible polymer blends

Two families of electrically‐conductive immiscible polymer blends were studied as liquid sensing materials for an homologous series of alcohols. The systems studied include: multiphase matrices [containing carbon black (CB)] consisting of either polypropylene or high‐impact polystyrene as the major phase and thermoplastic polyurethane as the minor dispersed phase; and polyaniline (PANI) dispersed within a polystyrene matrix. Extruded filaments, produced by a capillary rheometer at various shear‐rate levels were used in the sensing experiments. The electrical resistance of these filaments was selectively sensitive to the various alcohols. Moreover, the responses displayed by these filaments are reproducible and reversible. The sensing behaviour of these blends is determined by the nature of the blend components, the blend composition and the processing conditions. An attempt is made to identify the dominant mechanisms controlling the sensing process in CB‐containing immiscible polymer blends and PANI‐containing blends. In addition, the sensing performances of these blends are compared in the light of their sensing mechanisms. Copyright © 2005 Society of Chemical Industry     

Correlation between the morphology and dynamic mechanical properties of ethylene vinyl acetate/linear low‐density polyethylene blends: Effects of the blend ratio and compatibilization

The effects of the blend composition and compatibilization on the morphology of linear low‐density polyethylene (LLDPE)/ethylene vinyl acetate (EVA) blends were studied. The blends showed dispersed/matrix and cocontinuous phase morphologies that depended on the composition. The blends had a cocontinuous morphology at an EVA concentration of 40–60%. The addition of the compatibilizer first decreased the domain size of the dispersed phase, which then leveled off. Two types of compatibilizers were added to the polymer/polymer interface: linear low‐density polyethylene‐g‐maleic anhydride and LLDPE‐g phenolic resin. Noolandi's theory was in agreement with the experimental data. The conformation of the compatibilizer at the blend interface could be predicted by the calculation of the area occupied by the compatibilizer molecule at the interface. The effects of the blend ratio and compatibilization on the dynamic mechanical properties of the blends were analyzed from ?60°C to +35°C. The experiments were performed over a series of frequencies. The area under the curve of the loss modulus versus the temperature was higher than the values obtained by group contribution analysis. The loss tangent curve showed a peak corresponding to the glass transition of EVA, indicating the incompatibility of the blend system. The damping characteristics of the blends increased with increasing EVA content because of the decrease in the crystalline volume of the system. Attempts were made to correlate the observed viscoelastic properties of the blends with the morphology. Various composite models were used to model the dynamic mechanical data. Compatibilization increased the storage modulus of the system because of the fine dispersion of EVA domains in the LLDPE matrix, which provided increased interfacial interaction. Better compatibilization was effected at a 0.5–1% loading of the compatibilizer. This was in full agreement with the dynamic mechanical spectroscopy data. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4526–4538, 2006     

Melt strength of linear low‐density polyethylene/low‐density polyethylene blends

Linear low‐density polyethylenes and low‐density polyethylenes of various compositions were melt‐blended with a batch mixer. The blends were characterized by their melt strengths and other rheological properties. A simple method for measuring melt strength is presented. The melt strength of a blend may vary according to the additive rule or deviate from the additive rule by showing a synergistic or antagonistic effect. This article reports our investigation of the parameters controlling variations of the melt strength of a blend. The reciprocal of the melt strength of a blend correlates well with the reciprocal of the zero‐shear viscosity and the reciprocal of the relaxation time of the melt. An empirical equation relating the maximum increment (or decrement) of the melt strength to the melt indices of the blend components is proposed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1408–1418, 2002     

Effect of recycled polypropylene on polypropylene/high‐density polyethylene blends

The effect of recycled PP on incompatible blends of virgin polypropylene (PP) and high‐density polyethylene (HDPE) was studied. Recycled PP from urban solid waste was extracted with methyl ethyl ketone and the compatibilizing action of the product before and after extraction was examined. The characterization of the recycled PP was performed by FTIR, NMR, and DSC analyses. Mechanical properties of the blends were evaluated. The results showed partial compatibility of the blend components, reflected in the improvement of the tensile strength and elongation. Best results were achieved by the addition of extracted recycled PP on the 50/50 PP/HDPE blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1305–1311, 2001     

A free volume study of miscible polyester blends

Four blend systems (miscible binary polyester blends) have been examined by positron annihilation lifetime spectroscopy (PALS). The ortho-Positronium pick off lifetime, τ₃, is related to the mean free volume cavity size in these miscible blends. The measured free volume cavity size for the blends is compared to the size predicted from linear additivity of the homopolymers. A negative deviation from linear additivity is observed for τ₃ in each of the blend systems, and this behaviour is interpreted as a contraction of the mean free volume cavity size due to the changes in molecular packing that occur on blending. The consequence of these free volume results for the mechanical properties of miscible polyester blends is discussed and tested for the polycarbonate/Kodar system. The glass transition data suggest weak specific interactions in the blends; however, the mechanical properties are significantly affected by blending.     

Investigation of chemi‐crystallization and free volume changes of high‐density polyethylene weathered in a subtropical humid zone

The chemi‐crystallization and free volume changes of high‐density polyethylene (HDPE) exposed to subtropical humid climate of Guangzhou, China, were investigated using Fourier transform infrared spectroscopy, differential scanning calorimetry, wide‐angle X‐ray diffraction, dynamic mechanical analysis and positron annihilation lifetime spectroscopy. An increase in content of carbonyl groups and significant chemi‐crystallization were observed to occur during natural exposure. Chain scission accounted for the chemi‐crystallization and would lead to greater crystallizability of the molecules. The reheating DSC run indicated that the crystallizability of the degraded HDPE molecules increased initially with exposure time and then decreased. Positron data showed the new crystals induced by chemi‐crystallization indeed had more imperfect crystal structure in comparison with the pre‐existing parent crystals, and the free volume located in amorphous regions decreased involving a shrinking of the free volume holes. The shrinkage of free volume holes was correlated with the loss of mobility of HDPE molecules, which was confirmed by the increase of glass transition temperature. The formation of new imperfect crystals might increase the amount of rigid amorphous fraction of HDPE materials, as well as the occurrence of crosslinking reactions of molecules located in the interior of HDPE materials, consequently decreasing the molecular mobility. © 2016 Society of Chemical Industry     

Photochemical aging and processability of life‐time‐controlled polystyrene/high‐impact polystyrene blends

This work investigated the influence of the addition of acetophenone and benzophenone (2.5 and 5%) on the photodegradability of polystyrene/high‐impact polystyrene blends (50/50 w/w) prepared by sheet extrusion, aiming to improve their decomposition during exposure to a natural environment. The modified materials were submitted to photodegradation under controlled conditions, and the extent of degradation was monitored by suitable characterization techniques, such as infrared and ultraviolet–visible spectroscopy, viscosimetry, and measurements of the mechanical properties. The processability of the modified blends was also studied by capillary and oscillatory rheometry. Evidence for the formation of hydroperoxides and carbonyl groups, the occurrence of chain scission, and the loss of mechanical properties was achieved, being greater for samples with benzophenone. It was also observed that for the same ketone level, benzophenone caused greater changes in the mechanical properties, and this was in agreement with the decrease in the molecular weight observed. Thus, the addition of this type of chemical compound could enhance the photodegradability of polystyrene/high‐impact polystyrene blends without a significant effect on their processability and mechanical performance. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007