Enhanced crystallization kinetics of bacterially synthesized poly(3-hydroxybutyrate-co-3-hydroxyhexanate) with structural optimization of oxalamide compounds as nucleators
Introduction
Amounts of petroleum-based polymer materials have been used for modern life leading to increasing environmental pollution [1,2]. Therefore, researchers have focused on the development of eco-friendly polymers. Biodegradable polyhydroxylalkanoates (PHAs) have attracted special interests due to bacterially synthesized and fully degradable characters [[3], [4], [5], [6], [7]]. Poly (3-hydroxybutyrate) (PHB) and poly (3-hydroxybutyrate-co-3-hydroxyhexanate) (PHBH) are the most studied polyesters in the family of PHAs. Compared with PHB homopolymer, PHBH copolymer has better toughness, faster degradation rate and much wider thermal processing window [4,6]. However, PHBH still has some drawbacks, especially for the crystallization rate, which is very slow because of the irregularity of chain configuration. Meanwhile, large spherulite size and secondary crystallization lead to poor mechanical properties, as a consequence limit the application of PHBH [6,7].
Adding nucleators has been the most efficient and straightforward approach to improve crystallization behaviors of polymer [8,9]. Up to now, some chemicals have been studied as nucleators for PHAs, such as boron nitride (BN) [10,11], uracil [12], orotic acid [13,14], poly (vinyl alcohol) particle [15], and so on. BN is regarded as the most effective and wide-used nucleator for PHA materials [10]. Ohura [16] and Yamamoto [17] have attained the PHA fibers with high crystallinity and strength by adding BN. Although, these chemicals as nucleators are found to be effective to increase crystallization rate, the aggregation of nucleators usually occurs because of their poor miscibility between nucleators and PHA matrix and the nucleation efficiency is still inadequate to satisfy the requirements for application. Hence, it is necessary to develop more high-efficiency and miscible nucleators for PHAs.
Previously, our group revealed that oxalamide compounds (OXA) can serve as effective soluble-type nucleators for polyester [[18], [19], [20], [21]]. The configuration of the OXA is schematically shown in Fig. 1, where the terminal structures and the aliphatic spacer length (CH2)n are crucial to the nucleation efficiency. In a previous study, we revealed the effect of terminal structures (n-hexane, cyclohexyl and phenyl) of the OXA on the crystallization behavior of PHAs [18]. However, the effect of the aliphatic spacer length on the crystallization of PHAs matrix has been researched yet. Therefore, it will be systematically studied in this work and the nucleation activity (Ψ) and the nucleation constant (Kg) of the OXA with different spacer lengths will be discussed by the kinetics of crystallization of PHBH. The aim of this work is to provide a scientific approach to design the optimal structure of oxalamide compounds as nucleators for PHA materials, and to broaden the applied range of PHA materials.
Section snippets
Materials
Poly (3-hydroxybutyrate-co-3-hydroxyhexanate) (PHBH, containing ∼6 mol% of 3-hydroxyhexanate) was purchased from Kaneka Corporation, Japan. The oxalamide compounds with different spacer length between the oxalamide moieties (C6H5NHCOCONH(CH2)nNHCOCONHC6H5, n = 2, 4, 8, 12) were synthesized according to the reported methods [21] and the chemical structures were shown in Fig. 1 (abbreviated as OXAn).
Sample preparation
PHBH and OXAn powders were dried at 60 °C under vacuum oven for 12 h before use. The PHBH/OXAn
Non-isothermal crystallization
In this work, effects of spacer length of the OXAn on the non-isothermal crystallization behaviors of neat PHBH and PHBH/OXAn blends are studied via DSC. The DSC cooling and subsequent melting traces are displayed in Fig. 2 and detailed thermal parameters are shown in Table 1. Neat PHBH hardly crystallized upon cooling (Fig. 2a) and a pronounced cold crystallization peak (Tcc = 68.6 °C) was detected in the subsequent heating process (Fig. 2b). This result showed a poor crystallization ability
Conclusions
In this work, the oxalamide compounds (OXAn) with different spacer length between the oxalamide moieties (C6H5NHCOCONH(CH2)nNHCOCONHC6H5, n = 2, 4, 8, 12) were used to improve the crystallization behaviors of semi-crystalline PHBH. The effect of the spacer length, i.e., n values, on their nucleation efficiency and mechanical properties was investigated systematically. The OXAn could assemble into shish-like superstructures in the PHBH matrix and the PHBH crystals prefer to grow on the surfaces
Acknowledgments
This work is supported by the National Natural Science Foundation of China (51573074), the Excellent Youth Natural Science Foundation of Jiangsu Province (BK20170053), the Fundamental Research Funds for the Central Universities (JUSRP51624A) and Postgraduate Research & Practice Innovation Program of Jiangsu Provence (KYCX17_1429).
References (39)
- et al.
Biodegradation of polyhydroxyalkanoates (PHAs) in tropical coastal waters and identification of PHA-degrading bacteria
Polym. Degrad. Stabil.
(2010) - et al.
Insights into the nucleation role of cellulose crystals during crystallization of poly(β-hydroxybutyrate)
Carbohydr. Polym.
(2015) - et al.
Engineering of pha, operon on cupriavidus necator, chromosome for efficient biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) from vegetable oil
Polym. Degrad. Stabil.
(2010) - et al.
Role of epitaxy of nucleating agent (NA) in nucleation mechanism of polymers
Polymer
(2007) - et al.
The effect of seeding on the crystallisation of poly (hydroxybutyrate), and co-poly (hydroxybutyrate-co-valerate)
Polymer
(1999) - et al.
Biodegradation of poly (3-hydroxyalkanoic acids) fibers and isolation of poly (3-hydroxybutyric acid)-degrading microorganisms under aquatic environments
Polym. Degrad. Stabil.
(1999) - et al.
Crystallization behaviours of bacterially synthesized poly(hydroxyalkanoate)s in the presence of oxalamide compounds with different configurations
Int. J. Biol. Macromol.
(2017) - et al.
Activity of substrates in the catalyzed nucleation of glass-forming melts. II. Experimental evidence
J. Non-Cryst. Solids
(1993) - et al.
Insights into the nucleation role of cellulose crystals during crystallization of poly (β-hydroxybutyrate)
Carbohydr. Polym.
(2015) - et al.
Structural studies of polyesters: 5. Molecular and crystal structures of optically active and racemic poly (β-hydroxybutyrate)
Polymer
(1973)
Physical properties of poly-β-hydroxybutyrate: IV. Conformational analysis and crystalline structure
J. Mol. Biol.
Processing of a strong biodegradable poly [(r)-3-hydroxybutyrate] fiber and a new fiber structure revealed by micro-beam x-ray diffraction with synchrotron radiation
Macromol. Rapid Commun.
Effect of crystallization conditions on the physical properties of a two-layer glassine paper/polyhydroxybutyrate structure
J. Mater. Sci.
Biosynthesis and properties of poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) polymers
Biomacromolecules
Thermal behavior and molecular interaction of poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) studied by wide-angle X-ray diffraction
Macromolecules
Advanced nucleating agents for polypropylene
Polym. Adv. Technol.
Comparison of different nucleating agents on crystallization of poly (3-hydroxybutyrate-co-3-hydroxyvalerates)
J. Polym. Sci., Polym. Phys. Ed.
Nucleation Effect of layered metal phosphonate on crystallization of bacterial poly [(3-hydroxybutyrate)-co-(3-hydroxyhexanoate)]
Macromol. Mater. Eng.
Effect of orotic acid as a nucleating agent on the crystallization of bacterial poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymers
J. Appl. Polym. Sci.
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2020, International Journal of Biological MacromoleculesCitation Excerpt :PHA has been widely applied in many fields such as packaging, tissue engineering, biodegradable thermoplastic and so on [6–8]. However, because of the low crystallization rate, which is of vital importance to regulate the crystal structure for polymer materials during processing like extrusion, PHA exhibits poor physical properties, i.e. poor barrier, low tensile strength and Young modulus [9–11]. There are three main methods to increase the crystallization rate, (i) controlling the comonomer content in PHA [12], (ii) adding fillers such as boron nitride (BN), talc, clay, carbon nanotubes, carbon black, graphene oxide, melamine, thymine, fibres, lignin and so on into PHA [9,13–20], and (iii) applying the external force such as pressure [21–24], pre-drawing [25,26] and shear stress [24,27–30].