Solid-state NMR study of biodegradable starch/polycaprolactone blends

Abundant literature exists on starch or modified starch blended with biodegradable polyesters to achieve good performance with cheap compost plastics. The level of miscibility in these blends is one of the most relevant parameters. In the present study, solid-state 1H and 13C NMR spectra, as well as carbon spin-lattice relaxation times T1(C) and proton spin-lattice relaxation times T1(H) and proton spin-lattice relaxation times in the rotating frame T1ρ(H) of biodegradable starch (or starch formate)/polycaprolactone (PCL) (or polyester (PE) oligomers) blends and samples of the neat components were measured. From the T1ρ(H) and T1(H) relaxation times it follows that blends starch/PCL, starch/PE-oligomers and starch formate/PE-oligomers are phase separated even on the scale of 20–110 nm. On the contrary starch formate/PCL blend is phase separated on the scale 2.5–12 nm but homogeneously mixed on the scale 20–90 nm. Moreover, shorter T1(C) and especially T1ρ(H) values found for the starch or starch formate component in all these blends in comparison with neat samples show that molecular mobility of starch and starch formate segments is affected by blending. This indicates some miscibility also in phase separated blends which can happen in amorphous channels of starch.