Paula Moldenaers

Steady-shear rheological properties of model compatibilized blends

Block copolymers may be added as surface-active compatibilizers in order to control the morphology of blends of immiscible polymers. The effects of such added compatibilizers on the rheological properties of droplet–matrix blends are investigated experimentally. Model blends composed of polyisobutylene (PIB) droplets in a polydimethylsiloxane (PDMS) matrix, compatibilized with a diblock copolymer of PIB and PDMS, are studied here. The viscosity ratio of the blends, i.e., the ratio of the viscosity of the droplets to that of the matrix, is varied from 0.1 to 2.7. The viscosity and the first normal stress difference under steady shear conditions, and complex moduli after cessation of shear are measured. It is found that addition of the compatibilizer slightly raises the magnitude of the terminal complex viscosity of blends at all ratios of viscosity. Furthermore, with addition of the compatibilizer, the terminal relaxation time is found to increase sharply at high viscosity ratios, whereas the steady shear ...

Miscible PS/PPE compounds : an alternative for blend phase morphology studies? Influence of the PPE content on the surface tension of PS/PPE and on the interfacial tension in PP/(PS/PPE) and POM/(PS/PPE) blends

Abstract The influence of the PPE content in a miscible PS/PPE phase on the surface tension and polarity of PS/PPE mixtures, and on the interfacial tension in PP/(PS/PPE) and POM/(PS/PPE) blend systems was investigated. Surface tensions, σ(T), and polarity, xp, were experimentally determined by means of the pendant drop analysis technique, and were compared to the values predicted theoretically via Macleods theory. The interfacial tension, σ12, was determined both from the dynamic breaking thread method, and from the pendant drop analysis, which is an equilibrium method. The experimental values were compared to those predicted from the harmonic mean equation. Good agreement was found between the absolute values for σ12 obtained from both the techniques. The surface tension of the PS/PPE mixtures, in a temperature range of 230–260°C, appears to be unaffected by the presence of PPE, within the experimental error of the measurements. These findings were in good agreement with the prediction of σ(T) from Macleods theory. The interfacial tension of the PP/(PS/PPE) or POM/(PS/PPE) blend systems did not seem to be affected significantly when using a PS/PPE phase with a higher content of PPE. Finally, calculations showed that PPE causes the polarity of the PS/PPE mixtures to increase slightly from a value of 0.17 for pure PS to 0.20 for pure PPE.

Rheology and pressure–volume–temperature behavior of the thermoplastic poly(acrylonitrile-butadiene-styrene)-modified epoxy-DDS system during reaction induced phase separation

The rheology and volume shrinkage characteristics of an epoxy matrix based on diglycidyl ether of bisphenol-A (DGEBA) cured with 4,4′-diaminodiphenylsulfone (DDS) and those containing poly(acrylonitrile-butadiene-styrene) (ABS) at compositions ranging from 0 to 12.9 wt% were monitored in situ using rheometry and pressure–volume–temperature (PVT) analysis. This investigation has focused on the importance of cure rheology on microstructure formation, using rheometry. The relationship between rheological properties and the phase separation process was carefully explored. The evolution of storage modulus, loss modulus, and tan δ was found to be closely related to the evolution of complex phase separation. It was found that complex viscosity profiles follow an exponential growth with curing at various temperatures. The characteristic relaxation time of viscosity growth can be described by the WLF equation. In the second part of this manuscript PVT measurements carried out to understand the volume shrinkage of the blend matrix with respect to cure are described. Volume shrinkage is highest for a neat epoxy system, the volume shrinkage decreased linearly up to 6.9 wt% ABS then it shows a different trend for the 10 and 12.9 wt% ABS modified epoxy blend. Investigation of the volume shrinkage behavior in these blends by various techniques confirms that the shrinkage behavior is influenced by thermoplastic phase separation during cure.

Viscoelastic effects in thermoplastic poly(styrene-acrylonitrile)-modified epoxy–DDM system during reaction induced phase separation

The viscoelastic phase separation of a poly(styrene-co-acrylonitrile) (SAN) modified epoxy system based on the diglycidyl ether of bisphenol A (DGEBA) cured with 4,4′-diaminodiphenylmethane (DDM) has been monitored in situ using rheometry, optical microscopy (OM) and small angle laser light scattering (SALLS). The amount of SAN in the epoxy blends were 3.6, 6.9, 10, and 12.9 wt%. The relationship between rheological properties and phase separation was carefully explored. The evolution of storage modulus, loss modulus, and tan δ were found to be closely related to the evolution of complex phase separation. From the rheological profile, two gel points are identified, corresponding to physical gelation and chemical gelation, the first one because of viscoelastic phase separation and the second one related to crosslinking of the epoxy resin, these depend on the cure temperature and amount of thermoplastic. Further SALLS investigations investigated the mechanism of phase separation. The time-dependent peak scattering vector was simulated with a Maxwell-type viscoelastic relaxation equation. Relaxation times obtained at different temperatures for the blends could be described by the Williams–Landel–Ferry equation. Moreover, the development of light scattering profile follows the Tanaka model of viscoelastic phase separation.

Rheological study of the SAN modified epoxy–DDM system: relationship between viscosity and viscoelastic phase separation

The rheological behavior and structural transitions in an epoxy–amine system and poly(styrene-acrylonitrile) SAN modified epoxy–amine systems were studied by, optical microscopy and rheometry. The SAN modified epoxy blends undergo viscoelastic phase separation. The concentration of SAN has a profound effect on viscoelastic phase separation and hence the rheological behavior of modified epoxy systems. The evolution of complex viscosity is closely related to viscoelastic phase separation. The increase in complex viscosity shifted to shorter times upon increasing the concentration of SAN due to viscoelastic phase separation. The complex viscosity profiles follow an exponential growth with phase separation at various cure temperatures. The relaxation time of viscosity growth depends on both the concentration of SAN and cure temperature. The relaxation time of viscosity growth can be described by the WLF equation.