The broad utility as an environmentally friendly and colorful coating of cellulose nanocrystal (CNC) was limited by its instability of coloration, brittleness, and lack of adhesion to a hydrophobic surface. In the present work, a neutral polymer, poly(ethylene glycol) (PEG) was introduced into CNC coatings through evaporation-induced self-assembly (EISA) on polymer matrices. The structure-color and mechanical properties of the composite coating or coating film were characterized by UV-vis spectroscopy, polarized light microscopy (PLM), scanning electron microscopy (SEM), wide-angle X-ray diffraction (WXRD), and tensile tests. Results showed that the reflective wavelength of the iridescent CNCs could be finely tuned by incorporation of PEG with varied loadings from 2.5 to 50 wt %, although the high loading content of PEG would produce some side effects because of the severe microphase separation. Second, PEG played an effective plasticizer to improve the ductility or flexibility of the CNC coating or coating film. Furthermore, as a compatibilizer, PEG could effectively and tremendously enhance the adhesion strength between CNCs and neutral polymer matrices without destroying the chiral nematic mesophases of CNCs. Environmentally friendly CNC/PEG composites with tunable iridescence, good flexibility, and high bonding strength to hydrophobic polymer matrices are expected to be promising candidates in the modern green paint industry.
SFE-CO 2 is a novel, promising, environmentally benign and inexpensive extracting method developed over the past few years to overcome environmental problems encountered due to the use of conventional solvents. One component (the extractant) is separated from another (the matrix) using SCF-CO 2 as the extracting solvents. This method is widely used for extracting heavy metals from environmental contaminant, bioactive compounds like antioxidants, plant medicine and natural products or remediating heavy metal contaminated soil by using good binding activity of SCF-CO 2 to heavy metal ions. The major advantages of the use of SCF-CO 2 as a solvent are its superior mass transfer properties, easy recycling and lack of secondary waste formation. We try to focus on the recent advances in SCF-CO 2 extraction technology for heavy metal extraction. In this review, the mechanism, procedure, and application of heavy metal extraction by SCF-CO 2 are summarized in a comprehensive manner and the factors affecting the extraction efficiency are analyzed. We try to provide some meaningful information about heavy metal extraction by SCF-CO 2 and make it a preferable option in heavy metal treatments.
Rapid urban expansion and development have resulted in the conversion of many natural green surfaces within cities to non-transpiring built-up surfaces, such as concrete and asphalt. These artificial urban surfaces cause substantial variation in land surface temperatures that affect the urban microclimate. Thus, there is the need to substantially quantify the extent of green cover loss within growing cities and its impact on surface temperatures. This study used LANDSAT data to spatially assess the extent of urban expansion and its effect on land surface temperature within Kumasi, Ghana. Subsequently, the results showed significant changes in the land cover, which had an effect on the observed land surface temperatures from 1986 to 2015. Generally, there was an overall increase in the built-up areas by 24.13% (55.81 km 2 ) from 1986 to 2015, with a corresponding increase in the mean land surface temperature by 4.16°C. As such, there is the need for the adoption of sustainable urban planning strategies with green vegetation conservation initiatives for modern city planners. This would help reduce urban land surface temperatures while promoting clean air circulation within the city.
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