Stiffer and super-tough poly(butylene terephthalate) based blends by modification with phenoxy and maleated poly(ethylene-octene) copolymers

New super-tough poly(butylene terephthalate) (PBT) materials were obtained by melt blending PBT with both 20 wt% phenoxy (Ph) and 0-30 wt% maleic anhydride grafted poly(ethylene-octene) (mPEO) copolymers with different grafting levels. Ph was completely miscible in the PBT matrix. The presence of mPEO did not influence either the nature of the PBT-Ph matrix or the crystallization of PBT. The overall decrease in particle size and in interfacial tension upon grafting indicated that compatibilization had taken place. Super-tough (impact strength 23-fold that of the PBT) and stiffer PBT based blends were obtained at mPEO contents equal to or higher than 15%. The dependence of the critical inter-particle distance (t_c), on both adhesion measured by means of the interfacial tension, and on the relation between the modulus of the matrix and that of the rubbery dispersed phase (E_m/E_d), is proposed.