Blends of poly(ε‐caprolactone‐b‐lactic acid) and poly(lactic acid) for hot‐melt applications

The condensation reaction product of poly(lactic acid) (PLA) and a hydroxyl‐terminated four‐armed poly(ε‐caprolactone) (PCL) was studied by size‐exclusion chromatography, DSC, and NMR. The use of both L ‐lactic acid (LLA) and rac ‐lactic acid ( rac ‐LA) was studied and the use of two different catalysts, stannous 2‐ethylhexanoate [Sn(Oct) 2 ] and ferrous acetate [Fe(OAc) 2 ], was also investigated. The thermal stability and adhesive properties were also measured for the different formulations. The characterization results suggested the formation of a blend of PLA and a block ‐copolyester of PLA and PCL. The results further indicated partial miscibility in the amorphous phase of the blend showing only one glass‐transition temperature in most cases, although no randomized structures could be detected in the block ‐copolymers. The polymerization in the Fe(OAc) 2 ‐catalyzed experiments proceeded slower than in the Sn(Oct) 2 ‐catalyzed experiments. The discoloring of the polymer was minor when Fe(OAc) 2 was used as catalyst, but significant when Sn(Oct) 2 was used. The ferrous catalyst also caused a slower thermal degradation. Differences in the morphology and in the adhesive properties could be related to the stereochemistry of the poly(lactic acid).