New modifications of PBAT by a small amount of oxalic acid: Fast crystallization and enhanced degradation in all natural environments.

Biodegradable plastics are often mistakenly thought to be capable of degrading in any environment, but their slow degradation rate in the natural environment is still unsatisfactory. We synthetized a novel series of poly(butylene oxalate-co-adipate-co-terephthalate) (PBOAT) with unchanged melting point (135 °C), high elastic modulus (140 - 219 MPa) and elongation at break (478 - 769%). Fast isothermal crystallization with a semi-crystallization time < 20 s was demonstrated by the PBOAT. In N2 and air atmospheres, the PBOAT maintained the Td,5% higher than 329 °C. They also had good thermal stability at melt processing temperature for more than 20 min. PBOAT exhibited faster hydrolysis and seawater degradation, even under natural soil burial without light, but still kept stable under low humidity conditions during the storage and the shelf-life. Moreover, the hydrolysis mechanisms were clarified based on Fukui function analysis and DFT calculation, indicating that the hydrolysis of PBOAT would be more straightforward. The mechanism of soil burial is also elucidated through detailed characterization of the structure changes. The PBOAT offered a fresh approach to the development of high-performing, naturally degradable materials.

Component Distribution Regulation in Sn-Pb Perovskite Solar Cells through Selective Molecular Interaction.

Tin-lead (Sn-Pb) perovskite solar cells (PSCs) with near-ideal bandgap still lag behind the pure lead PSCs. Disordered heterojunctions caused by inhomogeneous Sn/Pb ratio in the binary perovskite film induce large recombination loss. Here, an Sn-Pb perovskite film is reported with homogeneous component and energy distribution by introducing hydrazine sulfate (HS) in Sn perovskite precursor. HS can form hydrogen bond network and coordinate with FASnI3 thus no longer bond with Pb2+ , which reduces the crystallization rate of tin perovskite to the level of lead analog. The strong bonding between SO4 2- and Sn2+ can also suppress its oxidation. As a result, the Sn-Pb PSCs with HS exhibit a significantly improved VOC of 0.91 V along with a high efficiency of 23.17%. Meanwhile, the hydrogen bond interaction network, strong bonding between Sn2+ and sulfate ion also improve the thermal, storage, and air stability of resulting devices.

Combined Effects from Dual Incorporation of ATBC as Plasticizer and Mesoporous MCM-41 as Nucleating Agent on the PLA Isothermal Crystallization in Environmentally-Friendly Ternary Composite Systems.

Different materials, based on an L-rich polylactide (PLA) as matrix, acetyl tri-n-butyl citrate (ATBC) as plasticizer, and mesoporous Mobile Crystalline Material.41 (MCM-41) particles as nucleating agent, were attained by melt extrusion. These materials are constituted by (a) binary blends of PLA and ATBC with different contents of the latest; (b) a dual compound of PLA and a given amount of MCM-41 silica (5 wt.%); and (c) ternary composites that include PLA, ATBC at several compositions and mesoporous MCM-41 at 5 wt.%. Influence of the incorporation of the plasticizer and nucleating particles has been comprehensively analyzed on the different phase transitions: glass transition, cold crystallization, melt crystallization and melting processes. Presence of both additives moves down the temperature at which PLA phase transitions take place, while allowing the PLA crystallization from the melt at 10 °C/min in the composites. This tridimensional ordering is not noticeable in the pristine PLA matrix and, accordingly, PLA crystallization rate is considerably increased under dynamic conditions and also after isothermal crystallization from either the melt or the glassy state. An important synergistic effect of dual action of ATBC and MCM-41 has been, therefore, found.

Combined Effects of Cellulose Nanofiber Nucleation and Maleated Polylactic Acid Compatibilization on the Crystallization Kinetic and Mechanical Properties of Polylactic Acid Nanocomposite.

This work investigated the combined effects of CNF nucleation (3 wt.%) and PLA-g-MA compatibilization at different loadings (1-4 wt.%) on the crystallization kinetics and mechanical properties of polylactic acid (PLA). A crystallization kinetics study was done through isothermal and non-isothermal crystallization kinetics using differential scanning calorimetry (DSC) analysis. It was shown that PLA-g-MA had some effect on nucleation as exhibited by the value of crystallization half time and crystallization rate of the PLA/PLA-g-MA, which were increased by 180% and 172%, respectively, as compared to neat PLA when isothermally melt crystallized at 100 °C. Nevertheless, the presence of PLA-g-MA in PLA/PLA-g-MA/CNF3 nanocomposites did not improve the crystallization rate compared to that of uncompatibilized PLA/CNF3. Tensile strength was reduced with the increased amount of PLA-g-MA. Contrarily, Young's modulus values showed drastic increment compared to the neat PLA, showing that the addition of the PLA-g-MA contributed to the rigidity of the PLA nanocomposites. Overall, it can be concluded that PLA/CNF nanocomposite has good performance, whereby the addition of PLA-g-MA in PLA/CNF may not be necessary for improving both the crystallization kinetics and tensile strength. The addition of PLA-g-MA may be needed to produce rigid nanocomposites; nevertheless, in this case, the crystallization rate of the material needs to be compromised.

Polyether Single and Double Crystalline Blends and the Effect of Lithium Salt on Their Crystallinity and Ionic Conductivity.

In this work, blends of Poly(ethylene oxide), PEO, and poly(1,6-hexanediol), PHD, were prepared in a wide composition range. They were examined by Differential Scanning Calorimetry (DSC), Polarized Light Optical Microscopy (PLOM) and Wide Angle X-ray Scattering (WAXS). Based on the results obtained, the blends were partially miscible in the melt and their crystallization was a function of miscibility and composition. Crystallization triggered phase separation. In blends with higher PEO contents both phases were able to crystallize due to the limited miscibility in this composition range. On the other hand, the blends with higher PHD contents display higher miscibility and therefore, only the PHD phase could crystallize in them. A nucleation effect of the PHD phase on the PEO phase was detected, probably caused by a transference of impurities mechanism. Since PEO is widely used as electrolyte in lithium batteries, the PEO/PHD blends were studied with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI), and the effect of Li-salt concentration was studied. We found that the lithium salt preferentially dissolves in the PEO phase without significantly affecting the PHD component. While the Li-salt reduced the spherulite growth rate of the PEO phase within the blends, the overall crystallization rate was enhanced because of the strong nucleating effect of the PHD component. The ionic conductivity was also determined for the blends with Li-salt. At high temperatures (>70 °C), the conductivity is in the order of ~10-3 S cm-1, and as the temperature decreases, the crystallization of PHD was detected. This improved the self-standing character of the blend films at high temperatures as compared to the one of neat PEO.

Functionality of Cellulose Nanofiber as Bio-Based Nucleating Agent and Nano-Reinforcement Material to Enhance Crystallization and Mechanical Properties of Polylactic Acid Nanocomposite.

Polylactic acid (PLA), a potential alternative material for single use plastics, generally portrays a slow crystallization rate during melt-processing. The use of a nanomaterial such as cellulose nanofibers (CNF) may affect the crystallization rate by acting as a nucleating agent. CNF at a certain wt.% has been evidenced as a good reinforcement material for PLA; nevertheless, there is a lack of information on the correlation between the amount of CNF in PLA that promotes its functionality as reinforcement material, and its effect on PLA nucleation for improving the crystallization rate. This work investigated the nucleation effect of PLA incorporated with CNF at different fiber loading (1-6 wt.%) through an isothermal and non-isothermal crystallization kinetics study using differential scanning calorimetry (DSC) analysis. Mechanical properties of the PLA/CNF nanocomposites were also investigated. PLA/CNF3 exhibited the highest crystallization onset temperature and enthalpy among all the PLA/CNF nanocomposites. PLA/CNF3 also had the highest crystallinity of 44.2% with an almost 95% increment compared to neat PLA. The highest crystallization rate of 0.716 min-1 was achieved when PLA/CNF3 was isothermally melt crystallized at 100 °C. The crystallization rate was 65-fold higher as compared to the neat PLA (0.011 min-1). At CNF content higher than 3 wt.%, the crystallization rate decreased, suggesting the occurrence of agglomeration at higher CNF loading as evidenced by the FESEM micrographs. In contrast to the tensile properties, the highest tensile strength and Young's modulus were recorded by PLA/CNF4 at 76.1 MPa and 3.3 GPa, respectively. These values were, however, not much different compared to PLA/CNF3 (74.1 MPa and 3.3 GPa), suggesting that CNF at 3 wt.% can be used to improve both the crystallization rate and the mechanical properties. Results obtained from this study revealed the dual function of CNF in PLA nanocomposite, namely as nucleating agent and reinforcement material. Being an organic and biodegradable material, CNF has an increased advantage for use in PLA as compared to non-biodegradable material and is foreseen to enhance the potential use of PLA in single use plastics applications.

Analytical Evaluation of the Dendritic Structure Parameters and Crystallization Rate of Laser-Deposited Cu-Fe Functionally Graded Materials.

The paper is devoted to the direct energy deposition (DED) of functionally graded materials (FGMs) created from stainless steel and aluminum bronze with 10% content of Al and 1% of Fe. The results of the microstructure analysis using scanning electronic microscopy (SEM) demonstrate the existence of a dendritic structure in the specimens. The crystallization rate of the gradient binary Cu-Fe system structures was investigated and calculated using the model of a fast-moving concentrated source with an ellipsoid crystallization front. The width of the secondary elements of the dendrites in the crystallized slab was numerically estimated as 0.2 nm at the center point of the circle heat spot, and the two types of dendrites were predicted in the specimen: the dendrites from 0.2 to approximately 50 nm and from approximately 0.1 to 0.3 µm in width of the secondary elements. The results were found to be in good accordance with the measured experimental values of the dendritic structure geometry parameters.

Sustained-Release Method for the Directed Synthesis of ZIF-Derived Ultrafine Co-N-C ORR Catalysts with Embedded Co Quantum Dots.

M-N-C catalysts with optimized local and external structures offer great potential for replacing expensive and labile Pt-based catalysts for the oxygen reduction reaction (ORR) in fuel cells. Herein, we report a novel and facile strategy of synthesizing ultrafine ZIF-derived Co-N-C catalysts by precisely controlling the crystallization rate of ZIFs. The employment of meta-soluble Co-doped basic zinc acetate (Co-BZA), which shows a sustained-release effect in solvents, allows for the control of the solubility of Co-BZA in solvents. Detailed investigations suggest that the solubility of Co-BZA in the solvent is the key for governing the grain size of the resulting Zn/Co bimetallic ZIFs. Therefore, the self-assembly process between ligands and metal ions can be regulated by tuning the composition of mixed solvents, thus enabling rational tuning of the grain size of the resulting ZIFs. One-step pyrolysis of the ultrafine Zn/Co bimetallic ZIF precursor leads to Co and N co-doped carbon with an ultrafine grain size (termed UF Co-N-C). The Co centers that are uniformly distributed in the carbon matrix possess a quantum-dot-level grain size. Furthermore, this type of carbon nanohybrid exhibits a hierarchical pore structure, as well as a high surface area. When used as an ORR catalyst, the UF Co-N-C catalyst possesses high ORR activity (with an E1/2 of 0.9 V) that can rival 20 wt % commercial Pt/C (with an E1/2 of 0.835 V) in alkaline media. Notably, this catalyst also displays strong ORR performance similar to that of Pt/C in acidic media. The superior durability and methanol tolerance in both alkaline and acidic media for UF Co-N-C compared to Pt/C illustrate its great potential in replacing commercial Pt/C catalysts. The outstanding ORR performance of UF Co-N-C could be attributed to the simultaneous optimization of both external structures and active sites, demonstrating the effectiveness of this strategy in constructing ORR catalysts with controlled structures and desired functionalities.

Interesterification of rice bran wax and palm olein catalyzed by lipase: Crystallization behaviours and characterization.

Rice bran wax (RBW) is a traditional plant based natural wax and an increasingly popular component in textiles, fruit coatings and cosmetics. Properties of RBW can be modified by acyglycerols, and the resulting products can possess features with great potential in different applications. In this study, RBW was interesterified with palm olein (POL) catalyzed by Lipozyme TL IM, and the effects of RBW on the crystallization rate, solid fat content (SFC) and thermodynamic properties were investigated. The crystallization rates of RBW-based enzymatically interesterified (EIE) products were significantly higher than both the starting mixture and fully hydrogenated rapeseed oil (FHRSO). The EIE RBW-based samples were predominantly crystallized in ß' form, and presented a much smoother SFC profile as compared to physically blended raw materials. The SFC values were significantly decreased, conversely increased, and remained constant, and at 10 °C, 20-30 °C, and 35-40 °C as the wax ester and acylglycerols compositions changes. Overall, RBW-based samples after EIE showed an increased hardness and good surface properties, which make it a potential plastic fats substitute.