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The electrocyclic reaction is one of the most powerful tools for the construction of complex polycyclic scaffolds in a highly stereocontrolled fashion. In this review, recent advances in its application in the total synthesis of representative natural products are discussed, with the aim of providing a complement to existing reviews. 1 Introduction 2 4p Electrocyclization 2.1 Neutral 4p Electrocyclization 2.2 Cationic 4p Electrocyclization 3 6p Electrocyclization 3.1 All-Carbon 6p Electrocyclization 3.2 Oxa-6p Electrocyclization 3.3 Aza-6p Electrocyclization 3.4 Retro-6p Electrocyclization 4 8p Electrocyclization 5 Conclusion and Outlook. [ABSTRACT FROM AUTHOR]

Reinforcing fibers play a key role in improving the tribological properties of friction polymer composites. Cellulose reinforcing fibers were extracted from rapeseed straw waste and prepared as friction composites based on wet granulation, and the effects of heat and rapeseed straw fiber (RSF) additions on the tribological properties were systematically investigated. The addition of RSF induced an important transformation of the major wear mechanism to abrasive wear, especially at 9 wt%, where the abundant tribo-films contributed to the stability of the friction coefficients (fade rate 6.8%, recovery rate 106.6%), resulting in a 37.5% increase in wear resistance compared to no addition. Furthermore, XRD, FTIR and SEM analyses showed that the silane-ethanol solution modification contributed to the good performance of RSF. Highlights • Rapeseed straw fiber (RSF) and granulation technology for polymer composites. • Addition of RSF transforms adhesive and fatigue wear into abrasive wear. • Friction models are developed to clarify the wear mechanism transformation. • A 37.5% increase in wear resistance was achieved when RSF was added at 9 wt%. [ABSTRACT FROM AUTHOR]

In the context of the energy crisis, the optimal utilization of clean agricultural waste is of growing significance. This study employs a cost-effective method to obtain high-purity amorphous bio-based silica (RHA-SiO2) from rice husk ash (RHA) post pyrolysis. Leveraging the Taguchi method and response surface method (RSM) for the first time, this research utilizes pyrolysis and torrefaction temperatures as key determinants for the RHA-SiO2 particle size. Through an L36 (22 × 32) orthogonal test, key influencing factors were recognized. Subsequent optimization employed the central composite sequential (CCC) analysis, resulting in an interaction model that was experimentally validated with 96% to 99% accuracy. Such advanced techniques allow for a greater accuracy to be achieved in RHA-SiO2 extraction systems. [ABSTRACT FROM AUTHOR]

The rice husk (RH) combustion pretreatment method plays a crucial role in the extraction of nanoscale SiO2 from RH as a silicon source. This study examined the effects of diverse pretreatment methods and combustion temperatures on the particle size distribution of nanoscale high-purity amorphous SiO2 extracted from rice husk ash (RHA) post RH combustion. The experiment was structured using the Taguchi method, employing an L9 (21 × 33) orthogonal mixing table. The median diameter (D50) served as the output response parameter, with the drying method (A), combustion temperature (B), torrefaction temperature (C), and pretreatment method (D) as the input parameters. The results showed the torrefaction temperature (C) as being the predominant factor affecting the D50, which decreased with an increasing torrefaction temperature (C). The optimal parameter combination was identified as A2B2C3D2. The verification test revealed that roasting could improve the abrasiveness of Rh-based silica and reduce the average particle size. Torrefaction at medium temperatures might narrow the size distribution range of RHA-SiO2. We discovered that the purity of silica increased with an increasing roasting temperature by evaluating the concentration of silica in the sample. The production of RHA with silica concentrations up to 92.3% was investigated. X-ray diffraction analysis affirmed that SiO2's crystal structure remained unaltered across different treatment methods, consistently presenting as amorphous. These results provide a reference for extracting high-value products through RH combustion. [ABSTRACT FROM AUTHOR]

Powder flowability of natural reinforced fibers has a significant effect on the processing and properties of the composite. Sodium hydroxide modified rapeseed straw reinforced fibers were prepared in four fiber sizes and the powder flowability before and after modification was tested. The results showed that the alkali modification reduced the total flowability index of the fibers by 6–11 within the test range, with the effect on each flowability index in the order of compression > angle of spatula > angle of repose > miformity. This effect was mainly attributed to morphological, chemical and surface characteristics. Moreover, the slimming effect of the alkali modification reduced the average particle size by 9.4% to 30.8%, exacerbating the anisotropy of the morphological structure. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) analyses showed that pectin, lipids, hemicellulose and impurities were removed, exposing the clean rough fiber surface. Box plot analysis showed that the modification resulted in a uniform and regular distribution of shape factors. This work has valuable implications for the industrial application of straw cellulose fibers in the field of natural fiber composites. [ABSTRACT FROM AUTHOR]