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.
Highlights
For the development of a post-petroleum society, recycling resources from biomass is a high priority
In order to determine in detail the constituents of the plasticized PHA pellets connected with the mechanical properties, solution nuclear magnetic resonance (NMR) spectra were measured in CDCl3
With the aim of extending the application of solid-state NMR to biomass-based polymers, two kinds of biodegradable polyesters, poly (PBS) and poly(lactic acid) (PLA), were examined for the plasticization of the biopolymers of no nutritional use, polyhydroxyalkanoates (PHA). Both biodegradable polyesters improved the thermal properties of PHA; the flexible poly(butylene succinate) (PBS)
Summary
For the development of a post-petroleum society, recycling resources from biomass is a high priority. Semi-crystalline PHB and PHB–PHV copolymer were studied by several solid-state NMR spectral and relaxation time analyses to reveal the domain structure and mobility [18]. As an example of the use of solid-state NMR for analyzing the mechanical properties of biomass-based polymers, we have already studied PLA fibers produced by an extrusion process to reveal the correlation between tensile properties and spin-lattice relaxation time in PLA/PCL copolymer fibers [22], the morphological changes of PLA/organic composite fibers [23], and the effects of nucleating and plasticization in drawn PLA fibers during degradation [24]. On the basis of our previous solid-state NMR and relaxation time studies of the biomass-based materials, the present study is intended to clarify the information necessary for improvements to the processability and brittleness of PHA. By combining the results at ambient temperature with additional 1 H MAS NMR, T1 H, and T1 C measurements at variable temperatures, we will reveal how the modification of the added polyesters affects the molecular mobility and the chemical compatibility between the polymer constituents
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