Imidized Acrylic Polymer Research Articles

Reactive compatibilization of nylon 6/styrene–acrylonitrile copolymer blends: Part 3. Tensile stress–strain behavior

The stress–strain behavior of blends of nylon 6 (PA) and a styrene–acrylonitrile copolymer (SAN) compatibilized by an imidized acrylic polymer (IA) was evaluated in terms of the IA content and the dispersed SAN25 particle size. PA/SAN blends can be considered as a simpler version of industrially important PA/ABS blends; therefore, this study provides better understanding of the stress–strain behavior of compatibilized PA/ABS blends. The IA content was varied from 0 to 5 wt%; whereas the ratio of PA to SAN25 was held at 7/3; and in all cases the polyamide formed the continuous phase. From experiments using a Brabender batch mixer or an extruder as the mixing device, a reduction of dispersed particle size was observed with the addition of as little as 0.1 wt% IA. It was revealed from the experiments using a Brabender batch mixer that more than 0.5 wt% IA was necessary to prevent domain coalescence. The blends containing 1 wt% or more IA show necking and considerable plastic deformation. Transmission electron microscopy revealed that the normally brittle SAN25 particles were transformed into elongated shapes and undergo shear yielding under certain circumstances as the specimens experienced plastic deformation during stress–strain testing. Although the macroscopic elongation at break and the particle distortion ratio, which is defined as the ratio of the major axis to the minor axis of the elongated particles, are somewhat correlated, the local deformation in the neck region is much larger than the elongation at break. Thus, the ultimate capability for plastic deformation of the IA compatibilized blends is much larger than the overall elongation at break. The distortion ratio of the particles was observed to be as high as 6–7. There seems to be a relationship between the SAN25 particle size and the extent of plastic deformation realized. These experiments, however, do not differentiate the effect of diminishing particle size from increasing adhesion between the phases. Thus, it is not possible to assign unambiguously the dominant factor that permits the plastic deformation of the brittle SAN phase.

Reactive compatibilization of nylon 6/styrene–acrylonitrile copolymer blends. Part 1. Phase inversion behavior

The phase morphology and phase inversion behavior of nylon 6 (PA)/styrene–acrylonitrile (SAN) compatibilized blends have been studied using an imidized acrylic polymer (IA) and a styrene/acrylonitrile/maleic anhydride terpolymer (SANMA) as compatibilizers. PA/SAN blends can be considered as a simpler version of industrially important PA/ABS blends; therefore, this study is useful for the better understanding of the morphology development for PA/ABS blends with compatibilizers. Compared to binary blends of nylon 6 and SAN, addition of IA causes the phase inversion composition to shift to a higher nylon 6 volume fraction; whereas, addition of SANMA slightly changes the phase inversion composition to a lower nylon 6 volume fraction. The use of IA results in a significant increase of the nylon 6 phase viscosity due to the in situ formation of graft polymers during the melt processing; whereas, the addition of SANMA only slightly increases the nylon 6 phase viscosity. The significant change in the nylon 6 to SAN25 viscosity ratio due to the formation of PA–IA graft polymer may be partially responsible for the shift of the phase inversion composition observed as addition of IA. The method of the mixing also affects the phase inversion composition. The composition range where the nylon 6 forms a continuous phase extends to a lower nylon 6 volume fraction for blends mixed in an extruder compared to those prepared in a Brabender. The stabilization of blend morphology by formation of graft copolymers was studied for compositions near phase inversion as well as at compositions away from this region. Accordingly, it has been shown that IA does not stabilize the morphology near the phase inversion composition, but it is very effective at compositions where either of the components forms a clearly defined dispersed phase. The factors affecting the critical composition where phase inversion occurs have been established.

Reactive compatibilization of nylon 6/styrene–acrylonitrile copolymer blends. Part 2. Dispersed phase particle size

The relation between the dispersed phase particle size and blend composition has been examined for blends of nylon 6 and styrene/acrylonitrile copolymer (SAN) over a wide range of compositions that traverse the phase inversion points for simple binary blends and those reactively compatibilized by the addition of imidized acrylic polymer (IA) or styrene/acrylonitrile/maleic anhydride terpolymer (SANMA). Nylon 6/SAN blends can be considered as a simpler version of industrially important polyamide (PA)/ABS blends; therefore, this study is useful for the better understanding of diminishing dispersed phase particles for PA/ABS blends with compatibilizers. For uncompatibilized blends, the relationship between particle size and composition is symmetric about the phase inversion composition; whereas, blends compatibilized with IA show an intense asymmetric behavior, i.e. SAN dispersed particles in a nylon 6 matrix are quite small, while nylon 6 particles in a SAN matrix are much larger and are elongated. On the other hand, the blends compatibilized with SANMA show a weak asymmetry. This asymmetry is seen for three nylon 6 materials of differing molecular weight. Possible causes for the asymmetric behavior have been considered. Concerning the conformation of graft polymer molecules at the interface, a crowding problem caused by the side chains of a graft polymer, when a nylon 6 phase disperses in a SAN matrix phase, may contribute to this asymmetric effect. The shift of the phase inversion composition to higher or lower nylon 6 volume fraction away from the 50/50 composition, may also directly contribute to the asymmetric trend, since generally the average domain size grows as the volume fraction of the minor phase increases due to the greater possibility of coalescence. Using Wu's equation, predicting the dispersed phase particle size, it is suggested that the viscosity increase of a nylon 6 phase due to the formation of graft polymers may affect the asymmetric behavior. However, the predicted asymmetry was less pronounced than the experimentally observed asymmetry.

Properties of compatibilized nylon 6/ABS blends: Part II. Effects of compatibilizer type and processing history

The effects of processing history on the morphological, rheological, and mechanical behavior of blends of nylon 6 and acrylonitrile–butadiene–styrene (ABS) using an imidized acrylic (IA) polymer and a styrene/acrylonitrile/maleic anhydride (SANMA) terpolymer as compatibilizing agents have been investigated. Both compatibilizers yield blends that are super tough at room temperature; however, there are distinct differences in their effects on low temperature impact properties. For blends containing the IA polymer and a 1:1 ratio of nylon 6 to ABS, the low-temperature ductility compromises multiple extrusion steps. In general, the ductile-to-brittle transition temperature of blends containing high IA contents increase more rapidly with the number of extrusions than at lower IA contents. High IA content blends exhibited significant changes in morphology with increased number of extrusion steps; some of the ABS domains became larger, leading to a poorer dispersion of rubber particles. The ductile-to-brittle transition temperature is relatively insensitive to the number of extrusions for blends with less than 1wt.% IA content or a higher ratio of nylon 6 to ABS. The morphology and low-temperature toughness of blends containing the SANMA terpolymer were generally unaffected by the number of extrusion passes during melt processing. The differences in low temperature toughness with respect to the processing history appear to stem from differences in the reactive nature of these two types of compatibilizers. Blends containing the IA polymer developed higher melt viscosities than blends containing the SANMA polymer (particularly at higher IA contents), since the nylon 6/IA reaction appears to continue with increasing processing time, whereas the nylon 6/SANMA reaction does not. Potential causes for these fundamental differences in blend rheology are considered in terms of the reactive functionality of the IA versus SANMA compatibilizer. When issues of processability, regrind, and recycling are considered, the SANMA material is a more attractive compatibilizer than the IA polymer, particularly at higher compatibilizer contents.

Fracture behavior of nylon 6/ABS blends compatibilized with an imidized acrylic polymer

The fracture behavior of blends of nylon 6 and acrylonitrile–butadiene–styrene (ABS) compatibilized with an imidized acrylic (IA) polymer was examined by Izod impact testing and single-notch three-point bend (SEN3PB) instrumented Dynatup tests. The effects of the method of fracture surface measurement, ABS content, specimen thickness, compatibilizer content and fracture zone geometry were investigated. Blends containing a fixed (5wt.% IA) compatibilizer content were tough over a broad range of ABS contents; the optimum toughness occurred near 50wt.% ABS. A dual-mode of fracture was observed in SEN3PB specimens whose Izod impact samples with the same composition had ductile–brittle transition temperatures near room temperature. In these SEN3PB samples, ductile deformation occurred in samples with shorter ligament lengths, whereas brittle failure prevailed in samples with longer ligament lengths. The critical ligament length at which the ductile-to-brittle transition occurs was shown to be dependent on the compatibilizer content and specimen thickness. These dual modes of fracture were rationalized in terms of a plane–strain to plane–stress transition. For blends that were super tough and had good low temperature toughness as judged by Izod impact testing, the toughness of SEN3PB specimens was generally insensitive to specimen thickness; these blends were fully ductile over the entire range of ligament lengths. The size of the stress-whitened zone was examined for fractured SEN3PB specimens that were fully ductile over the entire range of ligament lengths. Among specimens of a given composition, the size of the stress-whitened zones was geometrically similar and independent of the size of the original ligament. However, when ductile samples of different composition were compared, the size of the stress-whitened zone was not necessarily proportional to the energy dissipated during plastic deformation. This may be a result of the presence of different modes of energy absorption in the nylon 6 or SAN matrix phase.

Properties of compatibilized nylon 6/ABS blends: Part I. Effect of ABS type

Blends of nylon 6 with four acrylonitrile–butadiene–styrene (ABS) materials were investigated over a range of compositions using an imidized acrylic (IA) polymer as the compatibilizing agent. The IA material is miscible with the SAN matrix and is able to react with the amine end groups of nylon 6 during melt processing. The effects of ABS type and blend composition on the morphological, rheological and mechanical behavior of these blends were explored at a fixed (5wt.%) compatibilizer content. In general, incorporation of the IA polymer can lead to super tough blends using a broad range of ABS materials. Of the ABS materials used, those with a monodisperse population of butadiene rubber particles and low melt viscosity were found to generate blends with superior low temperature toughness compared to those with broad particle size distributions and higher viscosity. In several compatibilized blends, increasing the ratio of nylon 6 to ABS improved the modulus and yield strength and did not significantly affect the room temperature impact strength up to a certain level; however, the ductile-to-brittle transition temperatures of these blends were quite sensitive to the amount of rubber in the blend, and increased steadily with increasing nylon 6/ABS ratio. The effect of compatibilizer content on blend properties was determined at a fixed ratio of nylon 6 to ABS. Super tough materials can be generated using very small (0.5wt.%) amounts of the imidized acrylic polymer. Further increases in compatibilizer content did not significantly affect the room temperature impact strength, but did improve the low temperature toughness. When processing characteristics are considered, there is no justification to use more than about 2wt.% of this compatibilizer.

Effect of adding an imidized acrylic polymer to super tough nylon 6 on stiffness and toughness

The mechanical properties and phase morphology of ternary blends of nylon 6 with rubber, e.g., maleated ethylene-propylene random copolymer (EPR-g-MA) or maleated styrene-(ethylene-co-butylene)-styrene (SEBS-g-MA), and a rigid but brittle imidized acrylic polymer (IA) are explored. The objective was to investigate blends which have independently dispersed rubber and rigid polymer particles in a nylon 6 matrix. The amount of rubber was fixed at 20%, while the IA to nylon 6 ratio was varied. Addition of imidized acrylic polymer particles to nylon 6 toughened by EPR-g-MA particles leads to increased stiffness and room-temperature impact strength and does not change the ductile-to-brittle transition temperatures up to a critical level. Similar improvements in stiffness and room temperature impact strength were found for nylon 6 toughened by SEBS-type rubber; however, the low temperature impact properties were not as good.

Evolution of morphology in compatibilized vs uncompatibilized polyamide blends

The development of phase morphology in non-reactive vs reactive polyamide blends with a styrene acrylonitrile (SAN) copolymer and SEBS (a styrenic triblock copolymer with ethylene-butylene midblocks) in a co-rotating twin screw extruder was investigated using electron microscopy techniques. For the polyamide/SAN systems, significant differences were observed between the evolution of morphology in non-reactive binary blends vs blends compatibilized with a reactive imidized acrylic (IA) polymer which is miscible in the SAN phase and has functional groups which are capable of reacting with the amine end groups in the polyamide phase. While a steady decrease in the dispersed phase particle size was observed in general for the non-reactive nylon 6/SAN blends with both increasing screw length and speed, for the ternary nylon 6/SAN/IA blends a dramatic drop in the dispersed phase particle size was observed in the initial region of the screw almost immediately after melting of the pellets followed by some coalescence of dispersed phase in the latter stages leading to a dual population of particle at the exit of the extruder. The extent and onset of coalescence after attainment of minimum particle size in the initial region of the screw in reactive nylon 6/SAN blends was found to be strongly dependent on the screw speed and configuration. The extent of chemical reaction along the extruder screw for reactive nylon 6/SAN blends was dependent on the screw speed, extruder configuration and flow rate. While similar differences in the evolution of morphology were observed between non-reactive and reactive polyamide/SEBS systems, changing the polyamide type from monofunctional (nylon x, e.g. nylon 6) to difunctional (nylon x, y, e.g. nylon 6,6) revealed interesting differences even within these reactive blends. Significant differences in both the development of morphology and reaction profile along the screw were also observed between binary and ternary nylon 6/rubber blends containing similar concentrations of reactive maleic anhydride functionality in the rubber phase using a fixed screw speed and configuration.

Effect of extruder type on the properties and morphology of reactive blends based on polyamides

AbstractThe morphology and mechanical properties of polyamide‐based blends prepared in single and corotating twin‐screw extruders were compared using transmission electron microscopy (TEM) techniques. Reactive polyamide blends with SEBS‐g‐MA (a maleated styrenic triblock copolymer with ethylene–butvlene midblocks), EPR‐g‐MA (a maleated ethylene/propylene rubber), and ABS were selected for the purpose of this investigation. For blends of SEBS‐g‐MA with difunctional (nylon x,y) polyamides (e.g., nylon 6,6; nylon 12,12), the twin‐screw extruder was more effective in producing a finer dispersion of the rubber phase, which resulted in a significant lowering of the ductile–brittle transition temperature in case of the nylon 6,6 blend. On the other hand, blends of SEBS‐g‐MA with the mono‐functional nylon 6 material led to rubber particles that were too small for toughening for both extruder types employed in this work. For nylon 6/EPR‐g‐MA blends, the single‐screw extruder led to blends with excellent low‐temperature impact properties for both single‐step and masterbatch mixing techniques, whereas nylon 6/EPR‐g‐MA blends prepared in a single‐step operation in the twin‐screw extruder were brittle under ambient conditions. For difunctional polyamide blends with ABS (compatibilized with an imidized acrylic polymer), the morphology and mechanical properties were found to be independent of the extruder type employed for processing. © 1994 John Wiley & Sons, Inc.

Deformation mechanisms in nylon 6/ABS blends

AbstractThe deformation mechanisms during fracture of a Nylon 6/ABS blend compatibilized with an imidized acrylic polymer were compared to those of an uncompatibilized blend. A postmortem examination of deformed zones in samples loaded to failure in a double‐notch four‐point‐bend geometry was made using transmission electron microscopy (TEM). For the compatibilized blend, cavitation of the rubber particles followed by massive shear yielding of the polyamide matrix was concluded to be the sequence of events leading to toughness; while, for the brittle uncompatibilized blend, the evidence indicated that a lack of adhesion at the Nylon‐ABS interface prevented the rubber particles from cavitating and the subsequent plastic deformation of the polyamide matrix. © 1994 John Wiley & Sons, Inc.

Morphology of nylon 6/ABS blends compatibilized by a styrene/maleic anhydride copolymer

Transmission electron microscopy (TEM) was used to examine the morphologies of nylon 6/ABS blends compatibilized with a styrene/maleic anhydride (SMA) copolymer containing 25% maleic anhydride (SMA 25). Several staining techniques were employed for identifying the various phases. The morphologies of a nylon 6/ABS blend compatibilized with an imidized acrylic polymer and the commercially available Triax™ material were also examined by these TEM techniques. While increasing concentration of the SMA 25 copolymer clearly leads to more efficient dispersion of the ABS phase, there is an optimum level of SMA 25 to achieve maximum toughness. Various factors that might contribute to the subsequent loss in toughness with higher SMA 25 levels are discussed. It is concluded that the limitations of the SMA 25 copolymer as a compatibilizer stem mainly from its high level of reactive functionality.

Mechanical properties and morphology of nylon-6/acrylonitrile-butadiene-styrene blends compatibilized with imidized acrylic polymers

The mechanical properties and phase morphology of blends of nylon-6 with various acrylonitrile-butadiene-styrene (ABS) materials and compatibilizers are explored. The main focus was on nylon-6/ABS blends compatibilized with one particular imidized acrylic polymer that is miscible with the styrene-acrylonitrile (SAN) matrix of the ABS and has nearly optimal content of functional groups (anhydride and free acid) for reaction with nylon-6 to form graft copolymers in situ at the polymer-polymer interfaces. The effects of compatibilizer content, rubber concentration and the mixing protocol on the mechanical properties of these blends were extensively explored. In general, the most efficiently dispersed ABS domains in the nylon matrix led to the lowest ductile-brittle transition temperatures and the maximum tensile modulus for the super-tough nylon-6/ABS blends. The effects of varying the functionality and miscibility characteristics of imidized acrylic polymers on the mechanical properties and morphology of nylon-6/ABS blends were also investigated. Some other types of polymers with a high anhydride content were also tested as compatibilizers for this system. It appears that compatibilizers with high levels of reactive functinality are not very effective; hence, there is an optimal level of functionality.