Atactic poly(methyl methacrylate) blended with poly(3-D(-)hydroxybutyrate): Miscibility and mechanical properties

Atactic poly(methylmethacrylate), aPMMA, was blended with poly(3D(-)hydroxy butyrate), PHB, up to a maximum composition of 26% of polyester,at 190 degr ees C in a Brabender-like apparatus. The resulting blends quenched from the melt to room temperature were completely amorphous, and exhibited a single glass transition using DSC and DMTA, indicating miscibility of the compone nts for this time-temperature history. Tensile experiments showed that at r oom temperature the 10/90 and 20/80 PHB/aPMMA. blends exhibited higher valu es of strain at break, and slight decreases of the modulus and stress at br eak compared to neat aPMMA. The tensile energy at break was almost twice th at of neat aPMMA. Tensile tests were also performed at 80 degrees C, at whi ch point the 25/75 and 20/80 PHB/aPMMA blends are above T-g, while the 10/9 0 and neat aPMMA are below T-g. The stress-strain curves obtained were func tions of the physical state of the amorphous phase, and also depended on th e difference between the test temperatures and T-g. In particular, comparin g the neat aPMMA and the blends, decreases of the modulus and stress at bre ak and a respectable increase in the strain at break were observed in the l atter. Finally, the results were commented considering the thermal degradat ion of PHB in the melt during the blend preparation. (C) 2000 John Wiley & Sons, Inc.