Solid-State Nuclear Magnetic Resonance (NMR) and Nuclear Magnetic Relaxation Time Analyses of Molecular Mobility and Compatibility of Plasticized Polyhydroxyalkanoates (PHA) Copolymers

Abstract

The molecular mobility and compatibility of plasticized polyhydroxyalkanoates (PHA) were investigated, focusing on changes due to copolymerization using either flexible poly (butylene succinate) (PBS) or rigid poly(lactic acid) (PLA) units. For the case of a poly(3-hydroxybutyrate) (PHB) unit in plasticized PHA, copolymerization of either PBS or PLA decreased 1H and 13C spin-lattice relaxation times in the laboratory frame (T1H and T1C) in the same manner, while PBS produced a lower 1H spin-lattice relaxation time in the rotating frame (T1ρH) than PLA. Both the signals of 1H MAS (magic-angle spinning) and 13C PST (pulse saturation transfer) MAS nuclear magnetic resonance (NMR) spectra were sharpened and increased by copolymerization with PBS. A variable temperature relaxation time analysis showed that the decrease of T1H values was dominated by the 1H spin diffusion via the interface between PHB and the added polyester because of the good compatibility. Meanwhile, the decrease of T1C values was dominated by increasingly rapid molecular motions of PHB because of the lowered crystallinity due to the plasticization. Slow molecular motions (kHz order) were enhanced more by the addition of PBS than PLA, although rapid molecular motions (MHz order) were enhanced by either polyester. Several NMR parameters were beneficial for analyzing the manufacturing process as the indexes of polymer compatibility and molecular motions.

Multi-scale instrumental analyses of plasticized polyhydroxyalkanoates (PHA) blended with polycaprolactone (PCL) and the effects of crosslinkers and graft copolymers

“…In contrast, the a-CH 2 of PCL moiety obviously had a maximum T 1 C value at 50% PCL addition (3). As did the T 1 C values of preplasticized PHA (CH 2 ), 24 the T 1 C values of PCL homopolymer (5) decreased with increasing temperature (Fig. S3, ESI †).…”

“…In the plasticized PHA (PHA/PBS copolymer), however, the T 1 H values of the PHA moiety were shortened by the copolymerization with PBS at a higher temperature, because the T 1 H relaxation of PHA moiety was enhanced via PBS, which had shorter T 1 H value than the PHA moiety. 24 On the other hand, the T 1 H value of PCL homopolymer decreased with increasing temperature as did that of the PBS homopolymer. As shown in Fig.…”

“…We have already evaluated the crystallinity and mobility of the plasticized PHA copolymers and their constituent polymers using a combination of 13 C CP-MAS NMR and 13 C PST-MAS NMR methods. 24 The former CP-MAS method enhances signals of rigid portions utilizing magnetization transfer from 1 H nuclei to 13 C nuclei. The latter PST-MAS method enhances signals of exible portions near hydrogen atoms using the Nuclear Overhauser Effect (NOE).…”

“…Our preceding paper has revealed the inuence of molecular mobility on the compatibility of PHA and PBS for plasticized PHA (commercially available PHA4422P), using solid-state NMR spectral and relaxation time analyses not only at ambient and variable temperatures. 24 In a quasi-static tensile test of this plasticized PHA blending with PCL, the addition of 50% PCL dramatically increased the elongation at break and the specimens became pours shape. 25 In a dynamic tensile test using a split Hopkinson bar (SHPB) method, a blend consisting of 50% plasticized PHA and 50% PCL gave small elongation at break, which increased with the addition of compatibilizers.…”

Relaxation methods for studying transformations in polymer systems

“…NMR relaxation is widely used for studying various polymers and polymer systems (Besghini et al 2019), such as polystyrene (Gasilova et al 1993), micellar and liquid crystalline systems (Wong 2006), polyhydroxyalkanoates (Nishida et al 2018), polyfluoroacryhlates (Borisova et al 1980) and especially tetrafunctional oligoetheracrilates (OEA) (Fig. 1).…”