On the mechanism of compatibilization of polyolefin/liquid crystalline polymer blends with graft copolymers

The compatibilization mechanism of some compatibilizers for blends of polyolefins with a liquid crystalline polymer (LCP) was studied. Polyethylene (PE) and polypropylene (PP) were blended with a semirigid LCP (SBH) in a batch mixer, either with and without compatibilizers. The latter were two commercially available samples of functionalized polyolefins, that is, a PE‐g‐MA (HDM) and a PP‐g‐AA (Polybond 1001) copolymer and some purposely synthesized PE‐g‐LCP and PP‐g‐LCP copolymers. Microtomed films of the binary and the ternary blends were annealed at 240°C on the hot stage of a polarizing microscope and the changes undergone by their morphology were recorded as a function of time. The results indicate that the compatibilizers lower the interfacial tension, thereby providing an improvement of the minor phase dispersion. In addition to this, the rate of the coalescence caused by the high‐temperature treatment is appreciably reduced in the systems compatibilized with the PE–SBH and PP–SBH graft copolymers. Among the commercial compatibilizers, only Polybond 1001 displayed an effect comparable to that of the above copolymers. HDM improved the morphology of the as‐prepared PE blends, but failed to grant sufficient morphological stabilization against annealing‐induced coarsening. The results are discussed with reference to the chemical structure of the different compatibilizers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3027–3034, 2000     

Dielectric spectroscopy using dielectric probes: a new approach to study glass transition dynamics in immiscible apolar polymer blends

Dielectric relaxation spectroscopy using dielectric probes was applied to study the (glass transition) dynamics in binary blends of isotactic PP, PS and LDPE. The blends were prepared by melt-mixing and doped with 0.5% of the dielectric probe 4,4′-(N,N-dibutylamino)-(E)-nitrostilbene (DBANS) (van den Berg O, Sengers WGF, Jager WF, Picken SJ, Wübbenhorst M. Macromolecules 2004;37:2460. [17]). Due to the selective amplification of the dielectric relaxation processes related to the dynamic glass transition of the polymers, accurate relaxation data were obtained, even for the minor phases. No substantial influence of the blend composition and the blend morphology on the glass transition dynamics was found, indicating that both blend constituents behave like homogeneous bulk materials. The normalised relaxation strength of glass transition processes remained constant, regardless of the blend type and blend composition. This indicates that the probe molecule, DBANS, was equally distributed over the two blend components in all three polymer combinations PE-PP, PE-PS and PP-PS.     

Heat capacity of polymer melts from the polymer chain-of-rotators equation of state

Recently, the chain-of-rotators equation of state derived from the rotational partition function was extended to polymers. Values of the three equation of state (EOS) parameters were obtained from fitting with experimental pressure–volume–temperature data and the parameters were correlated with the structure of the polymer repeat unit. In this article, the residual molar heat capacity derived from an EOS is added to the ideal gas heat capacity from Benson's group contribution method to obtain the polymer molar heat capacity at constant pressure, C_p. Predictions from the polymer chain-of-rotators (PCOR) using correlated parameters are compared with those obtained from PCOR, Sanchez–Lacombe, Flory–Orwoll–Vrij, and the perturbed-hard-sphere chain equations of state using parameters fitted from experimental data. Deviations of calculated C_p from the formula of van Krevelen for liquid polymers are likewise presented. With the correlations developed for its parameters, the PCOR offers the advantage of predicting the C_p for polymer melts from just the knowledge of the polymer's structure. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:841–848, 1998     

Reactive compatibilization of blends of polybutyleneterephthalate with epoxide-containing rubber. The effect of the concentrations in reactive functions

The influence of the functional groups concentrations on the reactive compatibilization of polybutylene terephthalate (PBT)/epoxide-containing rubber blends has been investigated by using various PBT and ethene-(methyl acrylate)-(glycidyl methacrylate) terpolymer (E-MA-GMA) grades. The reactivity of the rubber phase was modified using different strategies, including the use of commercial terpolymer grades, modification of E-MA-GMA or diluting E-MA-GMA terpolymers with non-reactive ethene-(methyl acrylate) (E-MA) copolymer. The reactive blends were analyzed amongst others by electron microscopy and fractionation experiments. It was shown that the final particle size is directly related to the amount of copolymer formed in situ at the blend interface, i.e. chain area density Σ. A value of approximately 0.05 chains/nm² for Σ is necessary to suppress dynamic coalescence and to obtain very fine dispersion (<0.2 μm). This requires a sufficiently high concentration in reactive functions at the interface vicinity. In this context, the time required for equilibrium morphology is rather independent of the GMA content in the terpolymer but is, however, intimately related to the PBT chain ends concentration. Investigation of PBT/(E-MA-GMA/E-MA) ternary blends revealed unambiguously that the formation of the copolymer at the interface is not controlled by the diffusion of the reactive chains towards the interface. The performed experiments offer new opportunities for modulating the final morphology and the properties of the PBT/rubber blends.     

Effect of polymer-filler surface interactions on the phase separation in polymer blends

For the blends of chlorinated polyethylene and copolymer of ethylene with vinyl acetate, the effect of the introducing filler (fumed silica) on the phase behavior of the blends was investigated. It was found that introducing filler in polymer blends depending on its amount lead either to the increase or to the decrease in the temperature of phase separation. At the filler concentration where both components transit into the state of a border layers, the phase separation temperature increases. This effect was explained by the change of the total thermodynamic interaction parameter in the ternary system polymer-polymer-filler. At lower concentration of a filler, the possible effect is the redistribution of the blend components according to their molecular masses between filler surface (in the border layer) and in the bulk that may diminish the phase separation temperature.Effect of the filler on the phase behavior was explained by the simultaneous action of two mechanisms: by changing the thermodynamics of interaction near the surface due to selective adsorption of one of the components and by the redistribution of components according to their molecular masses between the boundary region (near the surface) and in the matrix.The measurements of the kinetics of phase separation and calculation of the parameters of the activation energy are in agreement with proposed mechanisms.     

Composition and molecular-weight dependence of the glass transition in polystyrene-poly(2,6-dimethylphenylene ether) blends

The glass transition behaviours of a series of poly(2,6-dimethylphenylene ethers) with various molecular weights and their blends with polystyrene have been studied. The data are analysed according to the Fox-Flory equation (M_n dependence) and the Gordon-Taylor equation (composition dependence). A more rigorous treatment according to the theory developed by Kanig is presented and data of polystyrene-poly(vinyl methyl ether) blends, as well as polystyrene-poly(methyl vinylether) blends which do not obey the Gordon-Taylor equation, are discussed in the framework of this theory. The theory allows the estimation of the energy required to separateA-B contacts.     

Conjugated effects of the compatibilization and the dynamic vulcanization on the phase inversion behavior in poly(butylene terephthalate)/epoxide-containing rubber reactive polymer blends

The conjugated effects of both reactive compatibilization and dynamic vulcanization on the phase inversion behavior of poly(butylene terephthalate) (PBT)/epoxide-containing rubber blends have been studied in detail. Pure ethylene-methyl acrylate random copolymer (E-MA) and ethylene-methyl acrylate-glycidyl methacrylate random terpolymer (E-MA-GMA) were used as non reactive or reactive rubber phase, respectively. Location of the phase inversion region was studied using several techniques, including transmission electron microscopy (TEM) and dynamical mechanical thermal analysis (DMTA). To evaluate the relative influence of the blend compatibilization and the dynamic vulcanization on the phase inversion behavior, the relative kinetics of the two reactions were modified using different PBT and E-MA-GMA grades. The obtained results show unambiguously that the position and the width of the phase inversion region is essentially governed by the kinetic of the dynamic vulcanization process. The effect of the blend compatibilization remains quite limited even in the case of fast interfacial reaction. The crosslinking of the rubber phase induces an important shift of the phase inversion composition to higher rubber content. For blends containing low molecular weight PBT, up to 60 wt% of rubber can be homogeneously dispersed in the PBT matrix at long mixing time. In this case, development of high performance PBT based thermoplastic vulcanisates can be envisioned.     

A preliminary study of the dynamics of phase separation in oligomeric polystyrene-polybutadiene blends

We report here the preliminary results of a study of the kinetics of spinodal decomposition in an oligomeric blend, polystyrene with polybutadiene using small angle light scattering. The data are compared with the theoretical predictions of Cahn-Hilliard and van-Aartsen. The results corroborate the position of the critical point as determined by the pulse induced critical scattering technique.     

A calorimetric study of the interchange reactions in bisphenol a polycarbonate/nylon-6 blends

The interchange reactions in a partially miscible blend composed of bisphenol A polycarbonate and nylon-6 have been studied by the use of a calorimetric technique. It has been found that these reactions affect the thermal transitions of the mixtures. These effects have been interpreted to be a consequence of the progressive formation of copolymers which homogenize the mixture.     

A morphological study on the dispersion and selective localization behavior of graphene nanoplatelets in immiscible polymer blends of PC and SAN

In this morphological study the dispersion and localization behavior of 1 wt.% graphene nanoplatelets (GnPs) in melt mixed co-continuous polymer blends of polycarbonate (PC, 59 wt.%) and poly(styrene-acrylonitrile) (SAN, 40 wt.%) were investigated. Through varying the mixing sequence as well as the melt mixing parameters, different states of dispersion and different filler localizations were achieved. Melt mixing in a one-step process resulted in the poorest dispersion of the GnPs in the polymer blend. In this case, the filler could hardly be found localized selectively in one of the polymer components but formed its own component. In two-step mixing processes the GnPs were either premixed in PC or SAN to investigate the assumed filler transfer from the SAN into the PC component. Four different premixtures were prepared which showed that longer mixing time and higher rotation speed resulted in better dispersion of the GnPs in the polymer matrix. If the GnPs were predispersed in PC they could still be found in the PC component after blending with SAN. In the case that the GnPs were premixed in SAN, the filler was detected partially in the SAN or at the blend interface, as well as smaller sized particles were found in the PC component. It could be shown that the size and aspect ratio of the filler play a significant role on the localization of GnPs in melt mixed polymer blends.     

The kinetics of the α relaxation in an amorphous polymer at temperatures close to the glass transition

The kinetics of the α relaxation of a crosslinked copolymer of acrylonitrile and butadiene (T_g = ?7°C) were studied in the temperature range (T_g + 17°C) down to (T_g ? 8°C). The techniques used were shear creep analysed by time-temperature (t-T) superposition and thermal sampling (TS) with correction procedures proposed by McCrum. In this range the kinetics do not follow the compensation rule, as had been proposed in the pioneering TS experiments by Zielinski, Swiderski and Kryszewski and by Lacabanne et al.. The McCrum correction removes a discrepancy between the pioneering TS experiments and the conclusions of classical t-T superposition experiments. The methods of TS and t-T superposition are compared. At low temperatures, below (T_g + 3°C), the TS method is superior: t-T superposition is unreliable due to lack of normalization and to the physical ageing perturbation. At temperatures from (T_g + 3°C) to (T_g + 11°C) t-T superposition is highly reliable since normalization is not required and there is no ageing. At temperatures above (T_g + 11°C) the precision of t-T superposition depends on the validity of the normalization procedure. It has yet to be determined whether or not the compensation rule applies at temperatures below (T_g ? 8°C): the method most likely to settle this important question is TS, mechanical or dielectric variant, with McCrum correction for the distribution of relaxation times.     

A molecular dynamics study on the role of attractive and repulsive forces in isobaric heat capacity and sound velocity of sub- and supercritical dense fluids

In this study, the role of attractive and repulsive forces on isobaric heat capacity and sound velocity in dense fluids and liquids has been investigated using a molecular dynamics simulation technique. Lennard-Jones potential is divided into attractive and repulsive parts. From the molecular dynamics calculations, enthalpies and isobaric heat capacities have been obtained for Argon at temperatures of 120–800 K and constant pressures of 100–800 MPa. The sound velocities have been calculated at 250 and 400 K. The repulsive forces play the main role in causing the isobaric heat capacities at high temperatures and pressures. With decreasing temperature at constant pressure, the role of attractive forces considerably increases. The sound velocities resulting from attractive intermolecular interactions are negative which is physically unrealistic. This indicates the essential role of repulsive forces in the determination of sound velocities.     

Relation of glass transition temperature to the hydrogen bonding degree and energy in poly(N-vinyl pyrrolidone) blends with hydroxyl-containing plasticizers: 3. Analysis of two glass transition temperatures featured for PVP solutions in liquid poly(ethylene glycol)

The phase behaviour of poly(N-vinyl pyrrolidone)-poly(ethylene glycol) (PVP-PEG) blends has been examined in the entire composition range using Temperature Modulated Differential Scanning Calorimetry (TM-DSC) and conventional DSC techniques. Despite the unlimited solubility of PVP in oligomers of ethylene glycol, the PVP-PEG system under consideration demonstrates two distinct and mutually consistent glass transition temperatures (T_g) within a certain concentration region. The dissolution of PVP in oligomeric PEG has been shown earlier (by FTIR spectroscopy) to be due to hydrogen bonding between carbonyl groups in PVP repeat units and complementary hydroxyl end-groups of PEG chains. Forming two H-bonds through both terminal OH-groups, PEG acts as a reversible crosslinker of PVP macromolecules. To characterise the hydrogen bonded complex formation between PVP (M_w=10⁶) and PEG (M_w=400) we employed an approach described in the first two papers of this series that is based on the modified Fox equation. We evaluated the fraction of crosslinked PVP units and PEG chains participating to the complex formation, the H-bonded network density, the equilibrium constant of complex formation, etc. Based on the established molecular details of self-organisation in PVP-PEG solutions, we propose a three-stage mechanism of PVP-PEG H-bonded complex formation/breakdown with increase of PEG content. The two observed T_gs are assigned to a coexisting PVP-PEG network (formed via multiple hydrogen bonding between a PEG and PVP) and a homogeneous PVP-PEG blend (involving a single hydrogen bond formation only). Based on the strong influence of coexisting regions on each other and the absence of signs of phase separation (evidenced by Optical Wedge Microinterferometry) we conclude that the PVP-PEG blend is fully miscible on a molecular scale.     

Kinetics of the ordered phase growth at the phase transition from the isotropic to cholesteric state in a main chain liquid crystalline polymer

The optical microscope investigation of the isotropic- ordered phase transition in a main chain LC polymer and subsequent statistical treatment of the microscopic images allowed recognition of three regimes of the ordering: non-stationary regime which is characterized by increasing rate of the droplets growth; stationary regime; within it the ordered phase grows with a constant rate, and the coalescence regime for which the rate of the droplets growth deceases. Linear interpolation of the time dependence of the mean droplets diameter in log–log scales allowed conclude that within the stationary regime of the cholesteric phase growth, log <d> is a linear function of log t, whereas within the coalescence regime, <d> is proportional to t ^1/2 as expected from the theory of phase separation binary liquids. The time of beginning and duration of both growth regimes of the phase transition for the main chain LC polymer exceed those for low molecular weight LC compounds. This is caused by lower mobility of macromolecules in comparison with that for low molecular weight LC compounds.     

Modification of epoxy resin by polysulfone to improve the interfacial and mechanical properties in glass fibre composites. III. Properties of the cured blends and their structures in the polymer/fibre interphase

Thermal and mechanical properties (linear expansion coefficient, glass transition temperatures, Young's modulus, tensile and bending strengths, and failure energies under quasistatic and impact loadings) of cured epoxy-polysulfone (PSF) blends, as well as their structures have been studied. It was shown that PSF incorporation did not lead to appreciable changes in the linear thermal expansion coefficients and glass transition temperatures of the cured blends. According to this observation, incorporation of PSF into the epoxy matrix should not result in a significant increase in the internal stresses in the system. No drop in the modulus and strength of the bulk blends was observed when compared with unmodified epoxy matrix. The failure energy of the epoxy-PSF matrices increased as the PSF content increased under all loading conditions, whereas the strength of the polymer blend matrices increased only under impact loading. Optimal PSF content was found to be 10 wt%. It was shown that all the blends investigated were homogeneous before curing and became heterogeneous after curing. For epoxy-PSF/fibre joints a mixed (interfacial-cohesive) failure mode was observed for all the samples investigated. The results from the rheology, wetting, thermal, mechanical and structural tests, described in a set of papers, are compared with each other to explain the reasons for the adhesion strength behaviour of epoxy-PSF/glass fibre joints. Based on the finding here, an epoxy-10% PSF matrix is recommended for composite production.