Deformation mechanisms in nylon 6/ABS blends

The 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.     

Characterization of multiphase polymer system nylon 6/ABS blends

Seven different ratios of blends from nylon 6 and acrylonitrile — butadiene — styrene (ABS) were prepared by melt blending. Thermal analysis of these blends was carried out by DSC and TG. It has been observed that blend ratios such as 50/50, 40/60, 25/75 and 15/85 of nylon 6/ABS were having more compatibility in comparison with other blends. It is evident from the study of glass transition temperature, melting point, heat of fusion, change of crystallinity and activation energy values. Thermogravimetric analysis shows a decreasing trend of pyrolysis temperature of these blends with the increase in ABS concentration. Melt flow index and density data are found to indicate better physical and flow characteristics in blends compared to pure nylon 6.

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Zusammenfassung Durch Mischschmelzen wurden Gemische aus Nylon 6 und Acrylnitril-Butadien-Styrol (ABS) mit sieben verschiedenen Zusammensetzungen hergestellt. Mittels DSC und TG wurde eine Thermoanalyse dieser Gemische durchgeführt. Es konnte festgestellt werden, daß Gemische mit Nylon 6/ABS Verhältnissen von 50/50, 40/60, 25/75 und 15/85 im Vergleich zu anderen Gemischen eine größere Kompatibilität besitzen, was aus der Betrachtung von Schmelzpunkt, Schmelzwärme und der Veränderung der Kristallinität und der Aktivierungsenergiewerte eindeutig hervorgeht. TG zeigt für die Pyrolysetemperatur dieser Gemische mit zunehmendem ABS-Gehalt eine sinkenden Tendenz an. Der festgestellte Schmelzindex und die gefundenen Dichtewerte weisen im Vergleich zu reinem Nylon 6 auf bessere physische und Fließeigenschaften hin.

     

Impact fracture behavior of nylon-6/ABS blends

Tensile and impact properties of uncompatibilized nylon-6/ABS blends have been studied over the entire range of compositions. The blends were prepared by extrusion and, subsequently, injection molded into tensile specimens and rectangular plaques. The impact fracture performance was characterized using recently proposed models based on fracture mechanics, for various fracture behaviors. The results showed that nylon-6 breaks in a brittle manner. With the addition of ABS, the blend exhibits the same behavior with a slightly lower impact resistance up to about 60 wt %. A sudden jump in the value of impact fracture energy is observed around 70 wt % ABS with a brittle—ductile transition in the mechanism of fracture. The transition in fracture mechanisms is confirmed through observation of the fracture surfaces by scanning electron microscopy (SEM). Tensile tests showed that the elongation at break increases only slightly between 0 and 50% ABS content, but a significant jump occurs around 70% ABS, reaching a 6-fold increase in comparison to that of the pure components. SEM observation of etched samples shows that a cocontinuous morphology occurs around 70 wt % ABS. The peak observed for the elongation at break and the jump in impact performance, as well as the onset of brittle–ductile transition, are attributed to this morphological effect. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2583–2592, 1997     

Impact tensile fracture testing of a brittle polymer

The fracture behavior of a brittle polymer, methylmethacrylate–butadiene–styrene resin, under impact tensile loading was studied using single-edge-cracked specimens. The dynamic load and displacement were measured with a Piezo sensor and a high-speed extensometer, respectively. The load and displacement diagram, i.e., the external work, U_ex, applied to the specimen was used to determine the elastic energy, E_e, and non-elastic energy, E_n, due to viscoelastic and plastic deformation, and the fracture energy, E_f, for creating new fracture surface, A_s. The energy-release rates were then estimated using G_t=U_ex/A_s and G_f=E_f/A_s. The values of G_t and G_f were correlated with the fracture loads and the mean crack velocities determined from the load and time relationships.     

Interfaces in polymer blends

We investigate the structure and thermodynamics of interfaces in dense polymer blends using Monte Carlo (MC) simulations and self‐consistent field (SCF) calculations. For structurally symmetric blends we find quantitative agreement between the MC simulations and the SCF calculations for excess quantities of the interface (e.g., interfacial tension or enrichment of copolymers at the interface). However, a quantitative comparison between profiles across the interface in the MC simulations and the SCF calculations has to take due account of capillary waves. While the profiles in the SCF calculations correspond to intrinsic profiles of a perfectly flat interface the local interfacial position fluctuates in the MC simulations. We test this concept by extensive Monte Carlo simulations and study the cross‐over between “intrinsic” fluctuations which build up the local profile and capillary waves on long (lateral) length scales. Properties of structurally asymmetric blends are exemplified by investigating polymers of different stiffness. At high incompatibilities the interfacial width is not much larger than the persistence length of the stiffer component. In this limit we find deviations from the predictions of the Gaussian chain model: while the Gaussian chain model yields an increase of the interfacial width upon increasing the persistence length, no such increase is found in the MC simulations. Using a partial enumeration technique, however, we can account for the details of the chain architecture on all length scales in the SCF calculations and achieve good agreement with the MC simulations. In blends containing diblock copolymers we investigate the enrichment of copolymers at the interface and the concomitant reduction of the interfacial tension. At weak segregation the addition of copolymers leads to compatibilization. At high incompatibilities, the homopolymer‐rich phase can accommodate only a small fraction of copolymer before the copolymer forms a lamellar phase. The analysis of interfacial fluctuations yields an estimate for the bending rigidity of the interface. The latter quantity is important for the formation of a polymeric microemulsion at intermediate segregation and the consequences for the phase diagram are discussed.     

Structured polymer blends

Various morphologies can be realized via processing of incompatible polymer blends such as droplets or fibers in a matrix and stratified or cocontinuous structures as is shown for the model system polyethylene/polystyrene The structures induced are usually intrinsically unstable. Modelling of extrusion processes and continuous mixers yields expressions for the shear rate and shear stress but also for the limited residence time and the number of reorientations. These results could be combined with detailed knowledge of respectively distributive and dispersive mixing processes to predict the development of various morphologies as a function of time. Control of morphology is of utmost importance. In the case of droplets in a matrix, usually encountered in toughening of glassy polymers, the use of compatibilizers and/or reactions at the interphases is utilized. However, in designing specific morphologies i.e. structured polymer blends, fixation of intermediate morphologies before final processing is a prerequisite. Some preliminary results will be presented.     

Investigation of phase separation mechanisms of thermoset polymer blends by time-resolved SAXS

Phase separation induced by crosslinking was studied by time-resolved small angle X-ray scattering in thermoset blend based on unsaturated polyester, styrene and low molar weight saturated polyester as low profile additive. The scattering intensities were analyzed using the Cahn-Hilliard-Cook theory. Combining DSC and DMA experiments allowed us to conclude that phase separation proceeded via spinodal decomposition frozen in the early stage. Apparent diffusion coefficients D_app were estimated.     

Polyamides: Decarboxylation and desamination in nylon 6 equilibrium polymer

Rate and extent of both decarboxylation and desamination in the temperature range of 250–290°C were studied on equilibrium polymers obtained by the hydrolytic polymerization of ε-caprolactam. Mechanisms have been proposed that are characterized by the participation of the equilibrium monomer in the considered decomposition reactions. The mechanisms suggested accommodate both the experimental results of this study and findings of previous investigations as reported in the literature.     

Interfacial tension in polymer blends

Theoretical models of the interfacial tension coefficient in polymer blends, v₁₂, were evaluated. A new working relation was derived that makes it possible to compute v₁₂ from the chemical structure of two polymers. The calculations involve determination of the dispersive, polar and hydrogen-bonding parts of the solubility parameter from the tabulated group and bond contributions. The computed values of v₁₂ for 46 blends were found to follow the experimental ones with a reasonable scatter of ± 36%. Next, the experimental methods of v₁₂-measurements were critically examined. Although many have been developed for low viscosity Newtonian fluids, most are irrelevant to industrial polymeric systems. For the present studies two were selected. Values of v₁₂ were measured using the so-called “capillary breakup method,” and a newly developed method based on the retraction rate of deformed drop.     

Colloidal aggregation in polymer blends

We consider here a low-density assembly of colloidal particles immersed in a critical polymer mixture of two chemically incompatible polymers. We assume that, close to the critical point of the free mixture, the colloids prefer to be surrounded by one polymer (critical adsorption). As result, one is assisted to a reversible colloidal aggregation in the nonpreferred phase, due the existence of a long-range attractive Casimir force between particles. This aggregation is a phase transition driving the colloidal system from dilute to dense phases, as the usual gas-liquid transition. We are interested in a quantitative investigation of the phase diagram of the immersed colloids. We suppose that the positions of particles are disordered, and the disorder is quenched and follows a Gaussian distribution. To apprehend the problem, use is made of the standard phi(4) theory, where the field phi represents the composition fluctuation (order parameter), combined with the standard cumulant method. First, we derive the expression of the effective free energy of colloids and show that this is of Flory-Huggins type. Second, we find that the interaction parameter u between colloids is simply a linear combination of the isotherm compressibility and specific heat of the free mixture. Third, with the help of the derived effective free energy, we determine the complete shape of the phase diagram (binodal and spinodal) in the (Psi,u) plane, with Psi as the volume fraction of immersed colloids. The continuous "gas-liquid" transition occurs at some critical point K of coordinates (Psi(c) = 0.5,u(c) = 2). Finally, we emphasize that the present work is a natural extension of that, relative to simple liquid mixtures incorporating colloids.     

Intrinsically conducting polymer blends

Polyaniline (PANI) doped with different dopants (HCl, dodecyl benzene sulfonic acid, (+)‐Camphor‐10 sulfonic acid, dinonyl naphthalene disulfonic acid) was synthesized by chemical oxidation method. The FTIR studies indicated that the back bone structure of doped PANI was similar. Thermal stability was evaluated in nitrogen atmosphere by dynamic thermogravimetry and PANI‐HCl sample showed minimum weight loss below 400°C. The electrical conductivity of PANI was not affected by the structure of dopants. The microwave absorption studies of several polymers blends containing PANI‐HCl and/or carbon black were also carried out by using wave guide technique.     

Thermodynamics of polymer blends

The general principles of thermodynamic equilibrium in binary liquid systems are reviewed briefly, and extended to quasi-binary mixtures of polydisperse polymers. Molecular models allowing actual phase behaviour to be discussed in terms of molecular parameters are exposed to data on the system polystyrene/polyvinylmethylether. Disparity in size and share between the repeating units must be introduced to obtain reasonable agreement between theory and experiment. The neccessary introduction of the molar-mass distribution detracts from this agreement which makes clear that other aspects exist that must be taken into account. For example, cross association between repeating units has a marked effect on phase behaviour. Blends are subject to two kinds of thermodynamic aging which lead either to considerable mutual solubility in supposedly immiscible blends, or to metastable equilibria transforming into states of lower Gibbs energy. In both cases physical proerties of the blend will change with time.     

Interdiffusion in polymer blends: The effect of compressibility

The polymer/polymer interdiffusion in a binary compressible blend consisting of long and short chains is investigated within the framework of the dynamic random phase approximation (RPA). The relative contributions of two (fast and slow) stages into the total relaxation of compositional heterogeneities are explicitly shown to be strongly dependent on the initial conditions and the degree of asymmetry of the blend. Special emphasis is given to the influence of the initial distribution of free volume on the apparent rate of the composition relaxation. The evolution of the dynamic struture factor is described as well. It is shown that most of the peculiarities usually ascribed to the “fast‐mode” behavior can be derived within the RPA approach.     

Use of compatibilizers in polymer blends

Among the different ways of recycling plastic wastes, one of the techniques used consists in processing these products without any preliminary separation of the different plastic families. The bad performances of the obtained materials lead to the use of emulsifiers. The work described in this study concerns the synthesis of emulsifiers prepared by chemical modification of polymers with ozone. This reaction produces the formation of peroxides which are then used to initiate the grafting of comonomers. According to this method, we obtain graft copolymers usable as emulsifiers in the elaboration of polymer blends. Those graft copolymers prepared according to this method improve mechanical performances of polymer blends.     

Particulate growth in phase-separated polymer blends

Particle coarsening was investigated in polymer blends containing a minor phase volume of 23% produced by compositional quenching. The scaling exponents for three binary blends (polystyrene/polybutadiene, polystyrene/polyisoprene, and polystyrene/S-B random copolymer) were in reasonable agreement with the expected value of 0.33. The scaling exponent for a ternary blend containing an amphiphile (polystyrene/polybutadiene/S-B block copolymer) was substantially lower at 0.14. The particle size distributions for all the blends were broader than the self-similar distribution expected for Ostwald ripening and became increasingly broad with time. These distributions fit a two parameter coalescence model in which the probability of coalescence is proportional to the particle diameter. However, Ostwald ripening appears to make some contribution, particularly at early times. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2191–2196, 1998     

Formation of crazes in polymer blends

High-voltage electron microscopy was used to study the micromechanical processes of deformation directly on thin deformed samples of rubber-modified, high-impact polymers. In these polymers the microprocesses are closely connected with the initiation and formation of crazes. Craze formation with its effects on the fracture toughness are discussed in dependence on several important morphological factors, particularly on the rubber volume content, particle diameter, and particle diameter distribution.