Effects of the compatibilizer PE‐g‐GMA on the mechanical,thermal and morphological properties of virgin and reprocessed LDPE/corn starch blends

The effects of the compatibilizer polyethylene grafted with glycidyl methacrylate (PE‐g‐GMA) on the properties of low‐density polyethylene (LDPE) (virgin and reprocessed)/corn starch blends were studied. LDPE (virgin and reprocessed)/corn starch blends containing 30, 40 and 50 wt% starch, with or without compatibilizer, were prepared by extrusion and characterized by the melt flow index (MFI), tensile test, dynamic mechanical analysis (DMTA) and light microscopy. The addition of starch to LDPE reduced the MFI values, the tensile strength and the elongation at break, whereas the modulus increased. The decreases in the MFI and tensile properties were most evident when 40 and 50 wt% starch were added. Blends containing 3 wt% PE‐g‐GMA had higher tensile strength values and lower MFI values than blends without compatibilizer. Light microscopy showed that increasing the starch content resulted in a continuous phase of starch. Copyright © 2005 John Wiley & Sons, Ltd.     

Mechanical Properties and Morphology of Melt-mixed PA6/SWNT Composites: Effect of Reactive Coupling

An interfacial reaction during melt mixing of maleic anhydride copolymer (SMA) encapsulated single wall carbon nanotubes (SWNT) and polyamide 6 (PA6) was used in order to disperse SWNT homogeneously and to enhance interfacial adhesion. The intended reactive coupling between PA6 and SMA was evident from IR spectroscopy. Nanocomposites with SMA encapsulated SWNT showed increased elongation at break as compared to PA6/SWNT composites. SEM investigation of tensile fractured surfaces of PA6/SWNT+SMA composites indicated enhanced interfacial adhesion between PA6 and SMA modified SWNT.     

Reactive blending: inhomogeneous interface grafting in melts of maleinated polystyrene and polyamides

To be competitive, most blends need compatibilizers, usually copolymers with a blocky architecture, the chains of which cover the interfaces between the blend phases, refining the phase morphology and improving the interface strength. When the blend components are suitably functionalized, such copolymers can be conveniently generated in situ, in processes of reactive blending. Normally, graft copolymers are created. The polymer–polymer coupling proceeds exclusively in the interfaces. This interface grafting is (i) pivotal in the design of modern blend systems and (ii) an interesting route towards novel copolymers. The complex kinetics of interface grafting in blend melts have so far attracted little attention. In a model study, amino terminated polyamide 12 (PA) was grafted in the melt onto heavily maleinated polystyrene (SMA; S: styrene and MA: maleic anhydride). Anhydride and amino functions react at high temperatures fast and irreversibly by imide condensation. A series of SMA/PA blends differing in composition and PA chain lengths was investigated, with the aim of driving the grafting to high conversions so a pure graft copolymer SMAgPA would result, instead of an SMA/PA/SMAgPA blend. However, a pure copolymer was never obtained. The grafting remained incomplete, except with very short-chained PA and only at equal weight fractions of SMA and PA. More importantly, the SMA chains were never grafted evenly. Instead, “overgrafted” and “undergrafted” chains SMAgPA coexisted in one and the same product. It appears that the SMAgPA chains form an auto-inhibitory barrier in the interfaces that prevents random grafting. Grafting proceeds to high conversion only in SMA/PA blends with a co-continuous phase morphology where the interfaces are constantly torn apart and renewed, during melt blending, so the reaction is constantly reactivated. © 1998 John Wiley & Sons, Ltd.     

Compatibilization of PA6/rubber blends by using an oxazoline functionalized rubber

The compatibilization of blends of polyamide 6 with a nitrile butadiene rubber has been investigated. The procedure consists of two steps: modification of the nitrile groups of the rubber into oxazoline in the melt through condensation of ethanolamine with formation of a molecule of ammonia, followed by use of the modified rubber as a compatibilizing precursor which is melt mixed with the polyamide to produce the compatibilized blend. The modification reaction has been detected by NMR analysis and a rheological, mechanical and thermomechanical characterization has been carried out on the all the blends. The results indicate that the modification reaction occurs but the conversion of nitrile into oxazoline is relatively low. Use of the modified rubber in the preparation of binary polyamide/rubber blends, leads to an increase in viscosity, which is typical of compatibilized systems, and to enhanced tensile, impact and thermomechanical properties. These phenomena can be explained by the formation of in situ rubber/polyamide copolymers that act as compatibilizers, due to the reaction between oxazoline and the end groups of the polyamide. The presence of residual low molecular compounds, from the modification or from the purification of the rubber worsens all of the properties and inhibits the compatibilizing effect of the modified rubber.     

Influence of preparation methods on structure and properties of PA6/PA66 blends: A comparison of melt‐mixing and in situ blending

The blends composed of polyamide 6 (PA6) and polyamide 66 (PA66) were obtained using two different preparation methods, one of which was the melt‐mixing through a twin‐screw extruder and the subsequent injection molding; and the other, the in situ blending through anionic polymerization of ε‐caprolactam in the presence of PA66. For the former, there existed a remarkable improvement in toughness but a drastic drop in strength and modulus; however, for the latter, a reverse but less significant trend of mechanical properties change appeared. Various characterizations were conducted, including the analyses of crystalline morphology, crystallographic form, and crystallization and melting behaviors using polarized optical microscopy (POM), wide‐angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC), respectively; observation of morphology of fractured surface with scanning electron microscope (SEM); measurement of glass transition through dynamic mechanical analysis (DMA); and the intermolecular interaction as well as the interchange reaction between the two components by Fourier transform infrared spectrometry (FT‐IR) and ¹³C solution NMR. The presence and absence of interchange reaction was verified for the in situ and melt‐mixed blends, respectively. It is believed that the transreaction resulted in a drop in glass transition temperature (T_g) for the in situ blends, contrary to an increase of T_g with increasing PA66 content for the melt‐mixed ones. And the two kinds of fabrication methods led to significant differences in the crystallographic form, spherulite size and crystalline content and perfection as well. Accordingly, it is attempted to explain the reasons for the opposite trends of changes in the mechanical properties for these two blends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1176–1186, 2007     

Reactive processing of syndiotactic polystyrene with an epoxy/amine solvent system

Syndiotactic polystyrene (sPS) is a new semi-crystalline thermoplastic which is believed to fill the price-performance gap between engineering and commodity plastics. In order to reduce the high processing temperature of sPS (>290°C), an epoxy-amine model system was used as a reactive solvent. Such a processing aid can be used to achieve a 50 to 500 fold lowering of the melt viscosity. When initially homogeneous solutions of sPS in a stoechiometric epoxy-amine mixture are thermally cured, Reaction Induced Phase Separation (RIPS) takes place, leading to phase separated thermoplastic-thermoset polymer blends. We focus our study on low (wt% sPS < 20%) and high concentration blends (wt% sPS > 60%) prepared by two processing techniques (mechanical stirring in a laboratory reactor or internal mixer/ reactive extrusion respectively). These blends have different potential interests. Low concentration blends (sPS domains in an epoxy-amine matrix) are prepared to create new, tunable blend morphologies by choosing the nature of the phase separation process, i.e. either crystallisation followed by polymerization or polymerization followed crystallisation. High concentration blends (sPS matrix containing dispersed epoxy-amine particles after RIPS) are prepared to facilitate the extrusion of sPS. In this case, the epoxy amine model system served as a reactive solvent. The time to the onset of RIPS is in the order of 7-9 min for low concentration blends, while it increases to 20-45 min for high concentration samples, as the reaction rates are substantially slowed down due to lower epoxy and amine concentrations. During the curing reaction the melting temperature of sPS in the reactive solvent mixture evolves back from a depressed value to the level of pure sPS. This indicates a change in the composition of the sPS phase, caused by (complete) phase separation upon reaction. We conclude that our epoxy amine system is suited for reactive processing of sPS, where final properties depend strongly on composition and processing conditions.     

Influence of preparation methods on the structures and properties for the blends between polyamide 6co6T and polyamide 6: Melt‐mixing and in‐situ blending

Two blends between polyamide 6 (PA6) and Polyamide 6co6T (PA6co6T, a random copolymer between polyamide 6 and polyamide 6T) were fabricated by melt‐mixing on a twin‐screw extruder and the subsequent injection molding, or through the in‐situ polymerization of ε‐caprolactam in the presence of PA6co6T. As far as the former method is concerned, there exist an obvious decline of toughness and a slight increase in strength and modulus; however, for the latter, there appear a remarkable improvement in toughness and a simultaneous moderate increase in strength and modulus. A series of characterizations were carried out including scanning electron microscopy, wide‐angle X‐ray diffraction, polarized optical microscopy, differential scanning calorimetry, dynamic mechanical analysis, and Fourier transform infrared spectrometry. It is found that both blends exhibit single glass transition on DMA tan δ curves. However, contrary to that of the melt‐mixed blends, the glass transition temperature (T_g) of the in‐situ ones decreases with increasing PA6co6T content. It is suggested that different mixing levels are the main reasons. Moreover, the addition of PA6co6T containing linear rigid segments conducts remarkable refinement of spherulites for the blends. Significantly different changes in the crystallographic form, spherulite size, crystalline content and perfection due to the introduction of PA6co6T for the two blends are ascribed to their varied thermomechanical histories and the presence of interchange reaction only for the in‐situ blends. On the basis of the characterizations of the microstructures, the different trends of changes in the mechanical properties with the addition of PA6co6T for the two fabrication methods are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 201–211, 2008     

Reactive compatibilization of blends of PET and PP modified by GMA grafting

The melt radical grafting of glycidyl methacrylate (GMA) onto isotactic polypropylene (PP) was carried out in Brabender internal mixer and the influence of reaction procedure, radical initiator concentration and addition of co-monomer (styrene) on the grafting efficiency was examined. The viscosity, the thermal behaviour and melt rheology of PP-g-GMA samples was then analysed as a function of grafted GMA content. Blends of poly(ethylene terephthalate) (PET) with PP and PP-g-GMA (5.2 wt% GMA), prepared in internal mixer, were characterised by SEM, DSC and melt viscosimetry. The morphological analysis of PET/PP-g-GMA blends (80/20, 50/50 w/w) pointed out a marked improvement of phase dispersion (with particle size of about 0.6 μm for 80/20 blend) and interfacial adhesion, as compared to non-compatibilized PET/PP blend. The results of mixing torque and thermal analysis supported the occurrence of in-situ compatibilization reaction between epoxy groups of GMA modified PP and carboxyl end-groups of PET in the melt.     

PA66/PA12/clay based nanocomposites: morphology and physical properties

The structure and the physical properties of several polyamide 66 (PA66)/polyamide 12 (PA12) blends containing different amounts of the two polymers and obtained by melt‐blending have been investigated. A low amount of organically‐modified layered silicate (OMLS, 4 wt%) has also been introduced in order to further improve the physical properties and, in particular, to evaluate its effect on the blends' structure and components' miscibility. The microstructure and morphology of all the composites were analyzed by means of X‐Ray diffraction (WAXD), transmission electron microscopy (TEM), and high resolution scanning electron microscopy (SEM), while the macroscopic scale properties (mechanical behavior and water adsorption) were assessed in order to investigate and understand the materials' structure–properties relationships. The partial miscibility of PA66 and PA12, with phase separation depending on blend composition, has been confirmed. The results also underlined the possibility to tailor the behavior of polymer blends in terms of mechanical water adsorption properties by varying the amount of PA12, added to PA66 with and without the addition of the OLMS. The effectiveness of the clay in modifying the components' miscibility as well as its tendency to segregate preferentially within separate PA66 domains have been assessed. WAXD results showed opposite effects of PA12 and clay on the crystallization behavior of PA66, an aspect that has also been deepened in another paper by the same authors discussing the results of the complete thermal characterization. Copyright © 2010 John Wiley & Sons, Ltd.     

Cold crystallization behavior of polyamide 6 in PS‐g‐PA6 graft copolymers

TEM micrographs show that the PA grafts of PS‐g‐PA6 graft copolymers, which are obtained directly by extracting homo‐PA6 out from the homo‐PA6/PS‐g‐PA6 blends, are in the form of wormlike structure. The wormlike PA6 domains can shrink into droplets after annealing at 250 °C for 15 min. The diameter of the droplet determined by TEM and SAXS is in the range of 50–60 nm. This article reports on a unique crystallization behavior of the PA6 grafts in PS‐g‐PA6 graft copolymers. In a DSC cooling scan, PA6 grafts do not crystallize from the melt with a cooling rate of 10 °C/min. However, there is a cold crystallization peak around 65 °C in the subsequent heating scan. This cold crystallization phenomenon, which has not yet been reported in the literature till now, follows well the homogeneous nucleation mechanism and is depressed at relatively slow cooling rates (2 °C/min) or even completely eliminated after annealing within a specific temperature range. It may be caused by the slow diffusion or transport rate of the less flexible PA6 grafts to the crystal fronts when crystallization takes place around its glass transition temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 65–73, 2010     

Mechanical behavior of films of miscible polyamide 6/polyamide 6I‐6T blends

The deformation behavior of miscible PA6/aPA blends films under uniaxial and biaxial tensile drawing has been investigated in relation to blend composition. Whatever be the composition, the initial crystalline structure is ill‐ordered and no evidence of spherulitic morphology was shown. At temperatures beyond the activation of the viscoelastic α relaxation, a ductility improvement upon addition of aPA has been revealed in both uniaxial and biaxial stretching. The decrease in the yield stress with increasing aPA content mainly originates from the reduction in crystal fraction. Regarding the observed evolution in ultimate drawability and strain hardening upon addition of aPA, the latter component of the blend is considered to act as a diluent of the macromolecular network, and the experimental data are fairly well accounted for according to Graessley's theory. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1690–1701, 2006     

Dynamic Mechanical Thermal Analysis of Polyamide 6/Biopol Blends

The temperature dependence investigated by means of DMTA of dynamic storage modulusE′, dynamic loss modulus E″ and loss tangent tgδ of blends obtained from polyamide 6 and poly(β-hydroxybutyrate-co-β-hydroxyvalerate) (Biopol D600G) indicated, that the dynamic mechanical properties of the blends containing up to 40% Biopol D600G are governed by the properties of polyamide 6. First at the 50% Biopol D600G content in the blend the transitions of the Biopol phase become visible and dominant. The shifts of the loss modulus maxima of the blends might indicate some interactions between the blend components in the amorphous phase. This revised version was published online in August 2006 with corrections to the Cover Date.     

Co‐continuous Polyamide 6 (PA6)/Acrylonitrile‐Butadiene‐Styrene (ABS) Nanocomposites

Summary: Polyamide 6 (PA6)/acrylonitrile‐butadiene‐styrene (ABS) (40/60 w/w) nanocomposites with a novel morphology were prepared by the melt mixing of PA6, ABS and organoclay. The blend nanocomposites had a co‐continuous structure, in which both PA6 and styrene‐acrylonitrile (SAN) were continuous phases. It was found that the toughening rubber particles were only located in the SAN phase and the strengthening clay platelets were selectively dispersed in the PA6 phase. The co‐continuous nanocomposites showed greatly improved mechanical properties over the whole temperature range when compared with the same blend sample without clay.

Schematic diagram for the co‐continuous ABS/PA6 blend nanocomposite.     

Polyamide 66/EPR‐g‐MA blends: mechanical modeling and kinetic analysis of thermal degradation

The present investigation deals with the mechanical, thermal, and morphological properties of binary nylon 66/maleic anhydride grafted ethylene propylene rubber (EPR‐g‐MA) blends at different dispersed phase (EPR‐g‐MA) concentrations. The effects of EPR‐g‐MA concentration and dispersed particle size on the mechanical properties of the blends were studied. Analysis of the tensile data in terms of various theoretical models revealed the variation of stress concentration effect with blend composition and the improvement of interfacial adhesion between dispersed rubber phase and nylon 66 matrix. The thermal degradation of the blends was analyzed by nonisothermal thermogravimetric analysis (TGA). It was found that the activation energy (E_a) and overall reaction order of thermal degradation decreased with increasing EPR‐g‐MA content. The scanning electron microscopic (SEM) analysis showed a significant decrease in dispersed particle size with increasing EPR‐g‐MA content, which was explained on the basis of the level of chemical interaction (in situ compatibilization) between nylon 66 and EPR‐g‐MA. The surface morphology of the nylon 66/EPR‐g‐MA blends was illustrated by the roughness of atomic force microscopy (AFM) images. Copyright © 2008 John Wiley & Sons, Ltd.     

Water‐dispersive PLA‐based materials: from reactive melt processing to properties

Melt blending of poly(l ‐lactide) (PLLA) and water‐soluble polymers was carried out through reactive melt processing with the objective to prepare water‐dispersible PLLA‐based materials. For this purpose, both polyvinyl alcohol (PVOH) and hydroxyethyl cellulose (HEC) were considered. Prior to melt blending, the preparation of plasticized PVOH and plasticized HEC was performed. The so‐obtained blends have been characterized in terms of morphology and thermomechanical properties. The morphological analysis evidenced the possibility to prepare co‐continuous PLLA/plasticized HEC blends. Nevertheless, their low melt strength did not allow producing monofilaments by melt spinning. Thus, PVOH was considered as an alternative to HEC. The results showed that using maleic anhydride‐grafted polylactide as a compatibilizer for PLLA/plasticized PVOH 40/60 (w/w) blends allowed preparing co‐continuous blends leading to tough monofilaments with high ultimate elongation. Moreover, the assessment of the water dispersiveness revealed that the monofilaments readily swelled in water and started to break up after 30 min. A full fragmentation of the monofilaments was observed within 1 hr. Copyright © 2015 John Wiley & Sons, Ltd.     

Influence of Reactive Compatibilization on the Melt Flow Properties and Morphology of Polyamide 6/Styrene-Acrylonitrile Blends

Summary: In this study, we investigate the influence of reactive compatibilization on the rheological properties of polyamide 6/styrene-acrylonitrile (PA 6/SAN) blends in the melt. Linear viscoelastic shear oscillations, simple elongation to a large stretch ratio and subsequent recovery experiments were performed. The morphology of the blends was examined by atomic force microscopy. We prepared three PA 6/SAN blends with different composition ratios of PA 6 and SAN (70/30, 50/50, 30/70) and a constant concentration of the reactive agent. Our experiments revealed that reactive compatibilization significantly increases the complex modulus of PA 6/SAN blends at low frequencies. In particular, the data of the PA 6/SAN 50/50 blend and the PA 6/SAN 30/70 blend indicated that an elastic network between neighbouring PA 6 domains was formed. In simple elongation, the transient elongational viscosity of the blends exceeded the values of the single components. In recovery, the recovered stretch of all blends was larger than the recovered stretch of the pure components. The differences of the blend morphology and of the linear viscoelastic behaviour were qualitatively explained by the asymmetric properties of the reactively compatibilized interface.     

The β‐crystalline form of isotactic polypropylene in blends of isotactic polypropylene and polyamide‐6/clay nanocomposites

Blends of isotactic polypropylene and polyamide‐6/clay nanocomposites (iPP/NPA6) were prepared with an internal batch mixer. A high content of the β‐crystalline form of isotactic polypropylene (β‐iPP) was observed in the injection‐molded samples of the iPP/NPA6 blends, whereas the content of β‐iPP in the iPP/PA6 blends and the iPP/clay composite was low and similar to that of neat iPP. Quiescent melt crystallization was studied by means of wide‐angle X‐ray diffraction, differential scanning calorimetry, and polarized optical microscopy. We found that the significant β‐iPP is not formed during quiescent melt crystallization regardless of whether the sample used was the iPP/NPA6 blend or an NPA6 fiber/iPP composite. Further characterization of the injection‐molded iPP/NPA6 revealed a shear‐induced skin–core distribution of β‐iPP and the formation of β‐iPP in the iPP/NPA6 blends is related to the shear flow field during cavity‐filling. In the presence of clay, the deformation ability of the NPA6 domain is decreased, as evidenced by rheological and morphological studies. It is reasonable that the enhanced relative shear, caused by low deformability of the NPA6 domain in the iPP matrix, is responsible for β‐iPP formation in the iPP/NPA6 blends. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3428–3438, 2004     

A new method for preparation of PS‐g‐PA6 grafted copolymer micelles

This work described a new method for the synthesis of PS‐g‐PA6 grafted copolymer micelles. PS‐g‐PA6 sphere micelles were synthesized by using a same solvent at the absence of selective solvent. The morphologies of micelles were characterized by SEM and TEM. The PS‐g‐PA6 micelles loaded Fe₃O₄ particles have better MRI imaging effect. The synthesis strategy developed here may present a desirable way to fabricate grafted copolymer micelles.