Oxygen barrier properties of polypropylene/polyamide 6 blends

Effects of composition, compatibilization, and blending procedure on oxygen barrier properties of injection-molded polypropylene/polyamide 6 blends were investigated. The main attention was paid to the relationships between oxygen permeability, mechanical properties, and blend morphology. The effect of the polypropylene/polyamide 6 ratio was evident in blends with a homogeneous dispersion type of morphology. After the phase inversion, when polyamide became the continuous phase, the barrier properties of the blends were significantly improved and approached those of polyamide 6. Increasing the amount of the compatibilizer, maleic anhydride grafted polypropylene, was found to increase the permeability of the blend. The blending procedure had a significant effect on the permeability of the blends. The injection-molded blend exhibited a laminar type of morphology when polyamide 6 and the compatibilizer were preblended in a twin-screw extruder, and polypropylene was added later as a dry-blend before injection molding. The dispersed polyamide phase formed thin elongated platelets in the polypropylene matrix. This laminar morphology resulted in significant improvement of oxygen barrier properties approaching the level of the theoretical values calculated for corresponding coextruded structures. Moreover, both the tensile and impact properties of this particular blend were exceptionally good. © 1995 John Wiley & Sons, Inc.     

Real time assessment of the compatibilization of polypropylene/polyamide 6 blends during extrusion

The reactivity of maleic anhydride and acrylic acid polypropylene graft copolymers with amine groups and their effect in the compatibilization of polymer blends was analyzed in real time during the reactive processing of compatilized polypropylene/polyamide 6 (PP/PA6) blends. The presence of compatibilizers in the blend produces a block copolymer PP‐PA6, which stays in the blends interface, lowering the interfacial tension and reducing the PA6 particle size, affecting the light extinction phenomena. The in‐line optical detector is able to indirectly quantify the conversion of the compatibilization reaction of the blends. The signal intensity of the detector increases with the increase of the PA6 content due to the increase in the number of particles. Quantitative off‐line FTIR analyses of the compatibilized blends have shown that the amount of block copolymer formed when polypropylene grafted with acrylic acid (PP‐g‐AA) is used as compatibilizer increases with its content in the blend. There is a good correlation between the in‐line optical measurement and the off‐line amidic bond content formed. Non‐reacted compatibilizers are always present in the reactive blends whose content is proportional to its initial concentration. The PA6 particle size data obtained from scanning electron microscopy analysis showed good correlation with the in‐line measurements. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Microstructures and mechanical properties of polypropylene/polyamide 6/polyethelene-octene elastomer blends

A series of polymer blends were designed and manufactured. They are composed of three phases: polypropylene (PP), polyamide-6 (PA6) and polyethylene-octene elastomer (POE) grafted with maleic anhydride. The weight fraction of PA6 was adjusted from 0 to 40% by increments of 10%, and the weight fraction of POE was systematically half that of PA6. The morphology, essentially made of PA6 particles dispersed in the PP matrix, was characterised by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In the extruded plates prepared with the blends, the shape of the dispersed PA6 particles showed an elongated ellipsoidal shape, whose aspect ratio increased somehow with alloying content. The POE modifier was observed both as a thin interlayer (less than 100 nm thickness) at the PP/PA6 interface, and as a few isolated particles. The elastic modulus and yield stress in tension are nearly constant for PP and blends. By contrast, the notched Izod impact strength increases very much with alloying content. This remarkable effect is interpreted in terms of POE interphase cavitation, enhanced plastic shear deformation and resistance of PA6 particles to crack propagation.     

Dynamic mechanical properties of polypropylene–polyamide blends: Effect of compatibilization

The influence of compatibilization on the dynamic mechanical properties of polypropylene (PP) binary blends with polyamide-11 (PA) has been investigated. In the blends an acrylic acid functionized PP was used as a blend component and compared with nonfunctionized PP over the who concentration range. The results demonstrate that the use of the functionized PP instead of the unmodified one produced blends with different dynamic mechanical properties due to adhesion enhancement between the two phases. The storage moduli E′ of the compatibilized blends vary nearly linearly as a function of composition over a broad temperature region, whereas those of the noncompatibilized ones deviate greatly from linearity, specially at about 50/50 ratio, at which a minimum exists at about room temperature. While the dynamic testing gives no evidence for the variation in the glassy transition temperatures (peak maxima) of the components (PP and PA) in the two types of blends, both the loss modulus (E″) and the loss factor (tan δ) data indicate that the compatibilized blends differ from the noncompatibilized ones mainly in the glassy transition (βrelaxation) process of the PA phase, suggesting that the compatibilization of the blends seems to influence the PA phase more than the PP phase included. But, for the β-relaxation behavior of the PA in the modified blends, the tan δ spectrum shows a more complex pattern than does the E″. These results are discussed in terms of the morphological texture of the blends and possible chemical or physical interactions between the two consituent polymers.     

Mechanical and morphological properties of elastomer-modified polypropylene/polyamide-6 blends

Polypropylene/polyamide-6 (70:30) blends, containing dispersed discrete polyamide-6 microphases as matrix reinforcement, represent attractive materials for engineering applications. In order to enhance impact resistance, ethene/propene (EPM) was incorporated as a second separately dispersed microphase using reactive blending technology. Blend morphologies were controlled by adding maleic-anhydride-grafted-polypropylene (PP-g-MA) as compatibilizer during melt processing, thus enhancing dispersion and interfacial adhesion of the polyamide-6 phase. With PP-g-MA volume fractions increasing from 2.5 to 10 vol %, much finer dispersions of discrete polyamide-6 with average domain sizes decreasing from 8 to 0.8 μm were obtained. When polyamide-6 and ethene/propene (EPM)-rubber are dispersed simultaneously in the polypropylene matrix, impact resistance was improved. The influence of PP-g-MA volume fraction and blend morphologies on mechanical properties such as Young's modulus, yield stress, notched Charpy impact resistance was investigated. The ternary polypropylene/polyamide-6/EPM blend properties were compared with those of binary polypropylene blends containing the equivalent volume fraction of EPM. © 1995 John Wiley & Sons, Inc.     

In situ fibrillation of polypropylene/polyamide 6 blends: Effect of organoclay addition

In situ fibrillation of PP/PA6 blends (85/15 wt %) is investigated in presence of two kinds of organically modified montmorillonite, differing by the polarity of their surfactant. The organoclay is primary dispersed either in the PP (for the low‐polarity Cloisite® 15A) or in the PA6 (for the high‐polarity Cloisite® 30B), according to its assumed affinity. In absence of organoclay, a fibrillar morphology is achieved after the melt‐blending and hot‐stretching step, as evidenced by SEM analysis. Upon clay addition, different morphological trends are evidenced. The C15A leads to a refinement of the fibrils whether the C30B induces a transition from fibrillar to nodular structure. These trends are ascribed to drastic changes in viscosity and elasticity ratios, due to the filler initial localization. Several techniques (DSC, STEM) point out a C15A migration from the PP to the PP/PA6 interface. Rheological measurements highlight the possibility of a double‐percolation phenomenon, linked to the fibrillar microstructure of the PP/PA6/C15A blend. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41680.     

Reactive compatibilization of polypropylene/polyethylene terephthalate blends

The reactive compatibilization of polypropylene/polyethylene terephthalate (PP/PET) blends by addition of glycidyl methacrylate grafted PP (PP-g-GMA) was studied. Two PP-g-GMA copolymers, containing either 0.2 or 1.2 wt% of GMA, were used as interface modifiers. These were incorporated into PP blends (with either 70 or 90 wt% PET), replacing 1/5 of PP in the system. The use of these modifiers changed the blends' tensile mechanical behavior from fragile to ductile. Blend tensile strength was improved by 10% and elongation at break showed 10 to 20-fold increases while stiffness remained constant. Scanning electron micrographs showed the PP average domain size in injection molded specimens to decrease to the micron/sub-micron size upon addition of the GMA modified resins, while the unmodified blends exhibited heterogeneous morphology comprising large lamellae 10–20 μm wide. The low-GMA graft content PP seemed slightly more efficient than the high GMA content PP in emulsifiying PP/PET blends. The GMA grafting level on PP had very limited effects on the blends' mechanical behavior in the range of GMA graft density provided by the two modified resins investigated.     

Mechanical properties of polypropylene/crosslinked rubber blends

Mechanical properties of rubber-modified polymers are not single-valued functions of rubber/matrix type and rubber content, but also vary with processing conditions. The variations in mechanical properties with processing conditions arise mainly from changes in rubber-phase dispersion. In our past work, by lightly crosslinking the rubbers to increase their melt tenacity and strength, we have succeeded in producing fine and consistent dispersions despite diverse processing conditions. In this study, mechanical properties of polypropylene/lightly crosslinked rubber blends are compared with those of polypropylene/uncrosslinked rubber blends. The results indicate that, like dispersion, mechanical properties of polypropylene/crosslinked rubber blends also appear to be consistent and independent of process variables. The influences on mechanical behavior of degree of crosslinking, rubber content, and rubber/matrix type are also discussed.     

Multilayer films using polypropylene/polypropylene grafted with acrylic acid blends and polyamide 6

Blends of polypropylene (PP) with 0 to 100 wt% of polypropylene grafted with acrylic acid (AA-g-PP) were used to promote the adhesion to polyamide 6 (PA 6) in a three-layer coextruded film without using an additional adhesive or tie-layer. The effect of modified polymer content and its molecular weight on interfacial adhesion between PP and PA 6 was determined by T-peel strength measurements. The effect of melt temperature and bonding time on peel strength was determined. Oxygen and water vapor transmission rates of the films were measured. The peel strength of fusion bonded layers of PP/AA-g-PP blends with PA 6 strongly depends on bonding temperature and time, as well as on the molecular weight of the functionalized polymer. The peeled films surfaces were characterized using FTIR-ATR and scanning electron microscopy (SEM). Tensile properties of three-layer films, made up of PA 6 as the central layer and PP/AA-g-PP blends as the two external layers, are improved with increase in the acrylic acid (AA) content in the blend. The formation of an in situ copolymer between AA in the blend and the terminal amine groups of PA 6 was confirmed by the Moalu test.     

Oxygen permeation through films of compatibilized polypropylene/polyamide 6 blends

Polypropylene/polyamide 6 blends were prepared by melt mixing, without or with the addition of a suitable commercial product, a polypropylene grafted with 1% maleic anhydride, used as an interfacial modifier. The oxygen permeation through their films was studied as a function of temperature and the effect of the presence of the compatibilizer on the barrier properties of the material was examined. In addition, the diffusion coefficients were measured. The relationships between transport parameters and blend morphology were investigated by microscopic observations, together with chemical etchings, and a simple model was applied for interpreting the experimental permeation data. Differential scanning calorimetry was used in the determination of the degree of crystallinity of the blends. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1941–1949, 1999     

Mechanical and thermo-chemical properties of wood-flour/polypropylene blends

The main objective of this research was to study the potential of waste polypropylene and waste wood for making wood plastic composites (WPCs). The effects of nanoclay (NC), microcrystalline cellulose (MCC), and coupling agent (MAPP) on the mechanical and thermal properties were also studied. The results showed that mechanical properties of the composites made with MCC were significantly superior to those of unfilled. Addition of MAPP could enhance the mechanical and thermal properties of the blends, due to the improvement of interface bond between the filler and matrix. The significant improvements in tensile properties of the blends composites made with MAPP and NC were further supported by SEM micrographs. The thermogravimetric analysis indicated that the addition of 5 wt% MAPP and 3 wt% NC significantly increased the thermal stability of the blends compared to the pure PP. MCC could not improve the thermal stability. The experimental results demonstrated that the waste materials used are promising alternative raw materials for making low cost WPCs.     

The morphology of hyperbranched polymer compatibilized polypropylene/polyamide 6 blends

The influence of hyperbranched polymer grafted polypropylene (PP‐HBP) on the morphology of polypropylene (PP)/polyamide 6 (PA6) blends has been investigated. The final morphology was strongly influenced by the PP‐HBP compatibilizer concentration. At low concentrations, PP‐HBP acts as an emulsifying agent, reducing the size of the dispersed phase and preventing coalescence. This is due to the high reactivity and diffusitivity of PP‐HBP rapidly forming a high density of copolymers at the interface. Compared to the use of maleic anhydride grafted PP (PP‐MAH) at identical concentrations, PP‐HBP yielded a smaller dispersed phase particle size. Therefore, PP‐HBP allows the use of less compatibilizer to obtain identical morphologies. At higher compatibilizer concentrations, it has been shown that the PP‐HBP efficiently stabilizes the interface and inhibits both coalescence and breakup of the PA6 droplets. The high concentration of reactive sites and the ability of PP‐HBP to react with both chain‐ends of PA6 suggest that interfacial stabilization occurs because of the formation of a partly crosslinked interface. The interfacial stabilization effects generated by PP‐HBP should allow one to control the morphology of polymer blends in order to create specific functional morphologies.     

Influence of chemical and mechanical compatibilization on structure and properties of polyethylene/polyamide blends

LDPE/PA6 binary blends and LDPE/PA6/compatibilizer ternary blends were prepared in a Brabender extruder, equipped with a prototype static mixer. Compatibility of the components was estimated by rheological properties (viscosity and a melt flow index), and observations of the structure were made with the help of scanning electron microscopy and tensile strength. It was found that the blends' structure and properties are dependent on the recipe content of the polymer blends and the conditions of their manufacturing. Uniformity of the blends of the thermodynamically immiscible polymers was improved by using a prototype static mixer giving mechanical compatibilization and a compatibilizer giving chemical compatibilization. LDPE grafted with a maleic anhydride (LDPE-g-MAH) was used as a compatibilizer. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 719–727, 1998     

Barrier properties of polypropylene/polyamide blends produced by microlayer coextrusion

The gas barrier properties of injection molded structures prepared from polymer microlayers were investigated. Polypropylene and polyamide-66 were combined as microlayers with tens to thousands of layers. A thin tie layer of compatibilizer coextruded between the layers provided adhesion. Injection molding the microlayered materials at a temperature intermediate between the melting points of the constituents resulted in a high volume fraction of high aspect ratio polyamide-66 microplatelets dispersed in a polypropylene matrix. The resulting material had significantly reduced permeability to oxygen and carbon dioxide compared to the conventional melt blend. Structural models for permeability indicated that enhanced barrier arose primarily from increased tortuosity of the diffusion pathway provided by the oriented, flat platelets of high aspect ratio in the skin region of the complex injected molded structure.     

Effects of compatibilizers on the properties of polyamide/polypropylene blends

Compatibilization of polyamide 6/isotactic polypropylene blends was investigated by mechanical, morphological, thermal, and rheometrical methods. The primary objective was to obtain blends combining the desirable properties of the two components. Four compatibilizers including maleic anhydride, fumaric acid, or glycidyl functionalities were applied at two concentrations (5 and 10%). Maleic anhydride grafted styrene-ethylene-butylene-styrene block copolymer (SEBS-g-MAH) was observed to give excellent mechanical properties, especially at high polyamide/polypropylene ratios. The correlation between morphology and mechanical and rheological properties is discussed, and the interesting effect of blending on the kinetics of crystallization is noted.     

Interface modification of compatibilized polyethylene terephthalate/polypropylene blends: Effect of compatibilization on thermomechanical properties and thermal stability

Polyethylene terephthalate (PET) and polypropylene (PP) are incompatible thermoplastics because of differences in chemical structure and polarity, hence their blends possess inferior mechanical and thermal properties. Compatibilization with a suitable block/graft copolymer is one way to improve the mechanical and thermal properties of the PET/PP blend. In this study, the toughness, dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA) of PET/PP blends were investigated as a function of different content of styrene‐ethylene‐butylene‐styrene‐g‐maleic anhydride (SEBS‐g‐MAH) compatibilizer. PET, PP, and SEBS‐g‐MAH were melt‐blended in a single step using the counter rotating twin screw extruder with compatibilizer concentrations of 0, 5, 10, and 15 phr, respectively. The impact strength of compatibilized blend with 10 phr SEBS‐g‐MAH increased by 300% compared to the uncompatibilized blend. Scanning electron microscope (SEM) micrographs show that the addition of 10 phr SEBS‐g‐MAH compatibilizer into the PET/PP blends decreased the particle size of the dispersed PP phase to the minimum level. The improvement of the storage modulus and the decrease in the glass transition temperature of the PET phase indicated an interaction among the blend components. Thermal stability of the PET/PP blends was significantly improved because of the addition of SEBS‐g‐MAH. J. VINYL ADDIT. TECHNOL., 23:45–54, 2017. © 2015 Society of Plastics Engineers     

Mechanical and rheological properties of silica-reinforced polypropylene/m-EPR blends

Rheological and mechanical properties (tensile and impact properties) as well as the mechanical profiles of ternary isotactic polypropylene/silica/elastomer (iPP/SiO₂/m-EPR metallocene catalyzed ethylene-propylene rubber) composites were investigated and discussed. The effects of two metallocene ethylene-propylene-based elastomers (m-EPR) differing in molecular weight/viscosity and their content on iPP/silica composites with different silica types differing in size (nano- vs. micro-) and surface properties (untreated vs. treated) were investigated. The two m-EPR elastomers were added to iPP/SiO₂ 96/4 composites as possible impact modifier and compatibilizer at the same time in 5, 10, 15, and 20 vol% per hundred volume parts of composites. The effects of different silica fillers and two m-EPR rubbers were discussed within the context of structure-morphology-mechanical property relationships of these iPP/SiO₂/m-EPR composites. Tensile and impact strength properties were mainly influenced by combined competetive effects of stiff filler and tough m-EPR elastomer so sinergistic effect was also observed. The ductility of these composites was affected additionally by spherulite size of the iPP matrix due to the difference in nucleation abilities of silica fillers enabled by prevailing separated morphology observed in iPP/SiO₂/m-EPR composites.     

Kinetic studies and process analysis of the reactive compatibilization of nylon 6/polypropylene blends

This article describes a study on the reactive compatibilization of nylon 6 (N6) and polypropylene (PP) blends through a functionalized PP. A graft copolymer was formed in-situ by reacting an acid modified PP with N6 during blend compounding. The compatibilization reactions are studied in detail. Kinetics were estimated by means of experiments in a batch mixer. Three time constants were estimated, corresponding to (a) reactions, (b) melting of polymers, and (c) melt mixing. The effects of temperature and rotor speed on the reaction kinetics were also measured. There was a substantial increase in initial reaction rate, as the rotor speed was increased. Increasing the temperature did not significantly affect the reaction rate. Process parameters important for such a reactive compatibilization process were identified by statistically designed experiments in a co-roatating intermeshing twin-screw extruder. Screw speed, presence of venting, and sequence of feeding were shown to have a noticeable effect on the reactive compatibilization process during continuous compounding.     

Mechanical compatibilization of immiscible blends

The mechanical properties of a variety of immiscible binary blends, with and without third component polymeric compatibilizers, are reviewed and qualitatively related to the degree of adhesion between blend components as determined by lap shear testing. Generally, blends comprised of components which adhere well, one to the other, show improved ductility relative to blends of components which do not adhere, Similarly, polymeric compatibilizers are found to be more effective for improving the properties of a binary blend system if they adhere well to both primary components of the immiscible mixture. These results suggest that adhesion between phases in the mixture strongly influences the ultimate properties of the blend. Some evidence is presented which suggests that components which adhere well are partially miscible.