Analysis of the degradation and crystallization behavior during the thermal degradation of poly(lactic acid)/modified hectorite nanocomposites films by simultaneous rheology and FTIR technology.

This study presents the synthesis of Hec-g@PS through the innovative surface modification of hectorite via photocatalytic atom transfer radical polymerization (ATRP). Then, PLA/Hec-g@PS nanocomposites films was prepared with Hec-g@PS as additives by blown molding technique. Furthermore, the thermal degradation kinetics and crystallization kinetics during the thermal degradation of PLA based nanocomposites films were investigated with simultaneous rheology and FTIR technology. The findings indicated that the activation energies for PLA and PLA/Hec-g@PS were -54,702.12 J/mol and -107,963.47 J/mol, respectively, demonstrating that Hec-g@PS substantially influenced PLA thermal stability. Additionally, while the crystallization rates of PLA based films decreased with rising degradation temperatures. Quantum chemical calculations revealed that the mode of interaction between Hec-g@PS and PLA was mainly dominated by dispersion, supplemented by electrostatic and induced interactions of -22.2103 kcal/mol, -16.0779 kcal/mol and -5.4954 kcal/mol, respectively. The combination of crystallization kinetics and quantum chemical calculations further confirmed that Hec-g@PS promoted the alignment of PLA molecular chains due to the enhanced interaction force between them. Hec-g@PS functioned as a nucleating agent, facilitating PLA crystallization and effectively mitigated its thermal degradation. Hec-g@PS as a nucleating agent provides valuable insights into the potential application prospects of biodegradable materials, particularly in the fields of biomedicine and packaging.

Investigation of Slagging Condition in a Zhundong Coal-Fired Boiler via In Situ Optical Measurement of Gaseous Sodium.

In this study, a portable spectral analysis instrument based on spontaneous emission spectroscopy (SES) was developed for the in situ, non-intrusive, and quantitative measurement of gaseous Na inside ZD coal-fired boilers, which is mainly applied for predicting slagging in furnaces. This technology is needed urgently because the problem of fouling and slagging caused by high alkali metals in ZD coal restricts the rational utilization of this coal. The relative extended uncertainty for the measurement of gaseous Na concentration is Urel = 10%, k = 2, which indicates that measurement data are reliable under working conditions. It was found that there is a clear linear relationship between the concentration of gaseous Na and fouling in high-alkali coal boilers. Therefore, a fast and efficient method for predicting the slagging and fouling of high-alkali coal boilers can be established by using this in situ online real-time optical measurement.

Weathered coal-based carbon dots modified by organic amine for enhanced crystallinity and toughness of poly(lactic acid) film.

Poly(lactic acid) (PLA) has its own limitations in terms of slow crystallization rate and low crystallinity during processing, resulting in poor toughness and thermal stability, which seriously restricts the practical application of PLA. Blending nanoparticles into the PLA matrix is an effective way to improve PLA crystallization. In this study, carbon dots (CDs) were prepared by green oxidation using weathered coal as carbon source and then surface-modified with dodecylamine (DDA) and octadecylamine (ODA). Modified CDs (MCDs)/PLA composite films were prepared using MCDs as filler to improve the crystallinity and toughness of PLA films. The results showed that the improvement effect of ODA-modified CDs (ODACDs) was better than that of DDA-modified CDs (DDACDs). The crystallinity of PLA composite film (0.05 wt% ODACDs) was increased from 7.20% (pure PLA film) to 35.44%, and its elongation at break was increased by 5.01 times compared with that of the pure PLA film. Moreover, thermogravimetric analysis suggested that the thermal stability of MCDs/PLA films was also improved. The results of simultaneous rheology and in-situ FTIR analysis as well as molecular dynamics simulations confirmed that MCDs had a strong interaction with PLA molecules, which promoted the crystallization of PLA film, thereby improving its toughness and thermal stability.

Effect of Vulcanization and CO2 Plasticization on Cell Morphology of Silicone Rubber in Temperature Rise Foaming Process.

Both vulcanization reaction and CO2 plasticization play key roles in the temperature rise foaming process of silicone rubber. The chosen methyl-vinyl silicone rubber system with a pre-vulcanization degree of 36% had proper crosslinked networks, which not only could ensure enough polymer matrix strength to avoid bubble rupture but also had enough dissolved CO2 content in silicone rubber for induced bubble nucleation. The CO2 diffusion and further vulcanization reaction occur simultaneously in the CO2 plasticized polymer during bubble nucleation and growth. The dissolved CO2 in the pre-vulcanized silicone rubber caused a temperature delay to start while accelerating further vulcanization reactions, but the lower viscoelasticity caused by either CO2 plasticization or fewer crosslinking networks was still the dominating factor for larger cell formation. There was a sudden increase in elastic modulus and complex viscosity for pre-vulcanized silicone rubbers at higher temperature because of the occurrence of further vulcanization, but CO2 plasticization reduced the scope of change of rheological properties, and the loss factor was close to 1 around 170 °C, which is corresponding to the optimum foaming temperature. The foamed silicone rubber had a higher cell density and smaller cell size at a higher temperature rising rate, which is due to higher CO2 supersaturation and faster vulcanization reaction. These results provide some insight into the coupling mode and effect of CO2 plasticization and vulcanization for regulating cell structure in foaming silicone rubber process.

Performance and multi-scale investigation on the phase miscibility of poly(lactic acid)/amided silica nanocomposites.

In this work, amino-functionalized nano-SiO2 (m@g-SiO2) was synthesized through coupling reaction on the surface of nano-SiO2. Moreover, the optimum preparation conditions of m@g-SiO2 were selected via orthogonal experiments as follows: reaction temperature of 80 °C, reaction time of 8 h, the mass ratio of stearic acid, N,N'­carbonyldiimidazole, imidazole hydrochloride and g-SiO2 of 0.5:0.7:0.7:1. Fourier transform infrared spectroscopy, static angle measurement and X-ray photoelectron spectroscopy unanimously confirmed the formation of m@g-SiO2. Furthermore, poly(lactic acid)(PLA)/m@g-SiO2 nanocomposites was prepared with m@g-SiO2 as fillers to improve the comprehensive performance of PLA. Then, the mechanical properties and crystallization behavior of PLA/m@g-SiO2 nanocomposites were studied, which showed that the impact strength and elongation-at-break of PLA/m@g-SiO2 (0.3 wt%) nanocomposites were increased by 78.05% and 1148%, respectively, and its crystallinity was increased by 26.46%. Simultaneously, thermal gravimetric analysis indicated that the thermal stability of PLA/m@g-SiO2 nanocomposites was improved. Eventually, the multi-scale investigation on the phase miscibility of PLA/m@g-SiO2 nanocomposites was probed by rheological behaviors analysis and the molecular dynamics simulations, which confirmed that surface modification of SiO2 greatly enhanced the interaction energy and miscibility between the filler and PLA bulk.

Performance, rheological behavior and enzymatic degradation of poly(lactic acid)/modified fulvic acid composites.

Fulvic acid (FA) was modified with p-phenylenediamine via iodine and triphenylphosphine as catalyst. The microstructure characterization for modified fulvic acid (MFA) were investigated by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, respectively, which demonstrated that MFA was characteristic of amide derivative. Moreover, poly(lactic acid) (PLA)/MFA composites was prepared with MFA as filler by melt blending. The mechanical tests showed that the impact strength of PLA/(0.5wt%) MFA composites were increased by 97.2%. Scanning electron microscopy demonstrated that the impact fracture of PLA/(0.5wt%) MFA composites were characteristic ductile fracture. The rheological behavior analysis showed that PLA had good interfacial compatibility with MFA. The crystallinity of PLA was increased from 4.9% to 36.9% with the introduction of MFA. The polarized optical microscopy presented that the crystallization nucleation rate of PLA were rapidly increased, which resulted in the increased comprehensive performance of PLA. The results of enzymatic degradation mechanism showed that MFA increased the Km of proteinase K, and had some inhibition to the degradation of PLA, but PLA still remained degraded evidently.