Influence of nucleating agent on the formation and enzymatic degradation of poly(butylene adipate) polymorphic crystals

Grafting of Biodegradable Polyesters on Cellulose for Biocomposites: Characterization and Biodegradation

Sustainable, biodegradable and thermoplastic processable aliphatic polyesters (polybutylene succinate (PBS) and polyethylene succinate (PES)) were prepared and characterized; then, they were grafted onto cellulose micro-fibers using a simple click reaction. This modification was conducted under simple experimental conditions. The characterization (NMR and FTIR analysis), thermal properties, solubility, morphology and biodegradation process of the all products prepared were established and studied. The results show that the solubility of the prepared derivatives is improved in comparison with cellulose, while their thermal stability showed a slight decrease compared to the starting materials. The composites derived from the modified cellulose show a slight decrease in their biodegradability in comparison with that of unmodified cellulose due to several parameters.

Mechanism of Biomineralization Induced by Bacillus subtilis J2 and Characteristics of the Biominerals

Abstract: Biomineralization induced by microorganisms has become a hot spot in the field of carbonate sedimentology; however, the mechanisms involved still need to be explored. In this study, the bacterium Bacillus subtilis J2 (GenBank MG575432) was used to induce the precipitation of calcium carbonate minerals at Mg/Ca molar ratios of 0, 3, 6, 9, and 12. Bacillus subtilis J2 bacteria released ammonia to increase pH, but the ammonia released only made the pH increase to 8.25. Carbonic anhydrase was also produced to catalyze the hydration of carbon dioxide, and this process released carbonate and bicarbonate ions that not only increased pH but also elevated carbonate supersaturation. The biominerals formed at a Mg/Ca molar ratio of 0 were spherulitic, elongated, dumbbell-shaped, and irregularly rhombohedral calcite; at a Mg/Ca molar ratio of 3, the biominerals were calcite and aragonite, the weight ratio of calcite decreased from 26.7% to 15.6%, and that of aragonite increased from 73.3% to 84.4% with increasing incubation time. At higher Mg/Ca molar ratios, the biominerals were aragonite, and the crystallinity and thermal stability of aragonite decreased with increasing Mg/Ca molar ratios. FTIR results showed that many organic functional groups were present on/within the biominerals, such as C–O–C, N–H, C=O, O–H, and C–H. HRTEM-SAED examination of the ultra-thin slices of B. subtilis J2 bacteria showed that nano-sized minerals with poor crystal structure had grown or been adsorbed on the EPS coating. The EPS of the B. subtilis J2 strain contained abundant glutamic acid and aspartic acid, which could be deprotonated in an alkaline condition to adsorb Ca2+ and Mg2+ ions; this made EPS act as the nucleation sites. This study may provide some references for further understanding of the mechanism of biomineralization induced by microorganisms.

Effect of cellulose nanocrystals on the crystallization behavior and enzymatic degradation of poly(butylene adipate)

Cellulose nanocrystals (CNCs) are nature-resourced nanoparticles and have been widely used to improve performance of biodegradable polyesters. Two types of CNCs respectively prepared by sulphuric acid hydrolysis (aCNCs) and ammonium persulfate oxidation (oCNCs) processes were incorporated into poly(butylene adipate) (PBA) matrix to regulate its crystallization behavior and enzymatic degradation performance. Thermal and X-ray diffraction analysis revealed that both aCNCs and oCNCs could promote the crystallization ability and lamellar thickening of α-form PBA, while oCNCs showed stronger promotion than aCNCs. Optical morphology study indicated that both two types of CNCs enhanced the nucleation ability of PBA. Furthermore, the mechanism of crystallization promotion of CNCs on PBA was further discussed and attributed to the "memory effect" in the melt state of PBA/CNCs composites, which was originated from the hydrogen-bonding interaction between CNCs and PBA chains. The enzymatic degradation testing proved that CNCs could slower down degradation rate of PBA and PBA/oCNCs composites possessed lower degradation rate than PBA/aCNCs composites.

Nanocellulose-PE-b-PEG copolymer nanohybrid shish-kebab structure via interfacial crystallization

We report a novel nanohybrid shish-kebab (NHSK) architecture of cellulose nanofibers (CNFs) and a block copolymer, (polyethylene-b-polyethylene glycol) (PE-b-PEG). Cellulose microfibers were ultrasonically dispersed to generate cellulose nanofibers in the size range of 50±10nm in diameter, while the block copolymer was crystallized using a solution crystallization approach to prepare NHSK. This unique approach allows the flocculated NHSK product to transfer quickly from toluene to ethanol, in order to shorten the preparation time. Morphological analysis reveals, for the first time, that nanocellulose can be used to induce crystallization of a block copolymer to generate NHSK and trans-crystalline structure. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results reveals the crystal morphology and crystallinity changes by virtue of crystallization. The ordered periodic growth and alignment of polymer crystals is recognized as the virtue of molecular origin of extended polymer chains. The proposed hypothesis affords elucidation of NHSK architecture and promotes the designing of novel nanohybrids with controllable functionality.

Regulating the polymorphism behaviour and crystal transformation of poly(butylene adipate) by incorporating butylene fumarate units into the crystal lattice

Copolymerized butylene fumarate units benefit the formation of β-form poly(butylene adipate) at high temperature by cocrystallizing into the crystal lattice.

Novel polymorphism behavior of poly(butylene adipate) in its nanocomposites with carbon nanofibers

Carbon nanofibers prominently enhance the formation of α-form crystal poly(butylene adipate) at low temperature and lead to a novel plateau phenomenon of α-form crystal content in their composites through specific CH–π interactions.

Enhanced crystallization rate of biodegradable poly(butylene succinate-co-ethylene succinate) by poly(butylene fumarate) as an efficient polymeric nucleating agent

PBF may significantly enhance the nonisothermal melt crystallization behavior of biodegradable PBES by acting as an efficient polymeric nucleating agent.