Rheological properties and reactive compatibilization of immiscible polymer blends

The effects of addition of a reactive compatibilizer, a random terpolymer, on morphological and rheological properties of blends of polyamide disperse d in a polyethylene matrix were studied experimentally. This addition leads to smaller size and narrower size distribution of the dispersed phase. Thi s has been related to the presence, at the interface, of copolymers, formed in situ by reaction between the polyamide and the terpolymer, which form a n interphase between the nodules and the matrix. The linear viscoelasticity of these compatibilized blends reveals that, in addition to the form relax ation process (relaxation time lambda (d)) even observed in absence of comp atibilizer, another relaxation process, which has been related to the dynam ics of nodule-matrix interphase, is observed at a characteristic time lambd a (int) higher than lambda (d). The concentration and molecular weight depe ndence of this characteristic time lambda (int) and the intensity H-int of the relaxation mechanism associated to lambda (int) has been investigated. The steady shear measurements exhibit an unusual behavior never observed be fore in blends of immiscible polymers. Indeed, the viscosity curve shows tw o plateau regions, respectively, at low and moderate shear rates, connected by a rather steep portion of curve, which is associated to a characteristi c time of the same order of magnitude as lambda (int). This behavior has be en interpreted by considering that the response of the system at the lowest shear races is dominated by the molecular dynamics of the nodule-matrix in terphase, whereas at higher shear rates the system behaves as an emulsion w ith hydrodynamic particle-particle interactions. The viscosity excess, due to the slowest relaxation process and expressed as the difference between t he two plateau viscosities, shows a marked dependence on both concentration and molecular weight of the compatibilizer. (C) 2000 The Society of Rheolo gy. [S0148-6055(00)01005-1].