Ultraviolet grafting of methacrylic acid and acrylic acid on high-density polyethylene in different solvents and the wettability of grafted high-density polyethylene. I. Grafting

Impact of aged and virgin microplastics on sedimentary nitrogen cycling and microbial ecosystems in estuaries

Microplastics (MPs) entering the environment undergo complex weathering (aging) processes, however, the impacts of aged MPs on estuarine nitrogen cycling and microbial ecosystems remain largely unknown. In this study, a 50 days microcosm experiment was conducted to investigate the response of sedimentary nitrogen (N) transformation processes, N2O emission and microbial communities to virgin and aged MPs (PE and PS) exposure. We found that aged MPs influenced sediment nitrogen turnover more rapidly and profoundly than virgin MPs and showed type and dose-response effect. During the first 10 days, higher concentration (3 % by weight of sediment) aged MPs (both PS and PE) treatments significantly promoted denitrification (ANOVA, P < 0.05), while virgin MPs treatments had weak effect on denitrification, compared with the control (P > 0.05). Moreover, higher concentration aged PS-MPs remarkably enhanced N2O emission on the 10th day, while N2O was consumed in the control. After 50 days incubation, there was an overall increase in nirK gene abundance exposed to MPs, and nosZ gene copies in aged PS treatments were around twice that in the control based on qPCR (P < 0.05). The function prediction also showed significant elevation of relative abundance of denitrification and DNRA relevant genes in bacterial community. In addition, aged PS treatment (3 %) recruited specific bacterial and archaeal assemblies, with Sedimenticolaceae, Lentimicrobiaceae, SCGC_AAA011-D5, SG8-5, Lokiarchaeia, and Odinarchaeia selectively enriched in the treatment. Our study highlighted that virgin and aged MPs had different impact on sediment nitrogen cycling, and the ecological risks of aged MPs should be concerned since all MPs eventually get weathered when they enter the environment.

Development of a natamycin-based non-migratory antimicrobial active packaging for extending shelf-life of yogurt drink (Doogh)

A natamycin-based non-migratory antimicrobial packaging for extending shelf-life of yogurt drink (Doogh) was developed. Firstly, the surface of low-density polyethylene film (LDPE) was modified with acrylic acid at different times of UV exposure (0-10 min) to produce carboxylic functional groups. Then, natamycin was applied to the UV-treated films to bind covalently with the pendent functional groups. The maximum grafting efficiency (81.96%) was obtained for the 6 min treated film. Moreover, surface properties of films were evaluated by Attenuated Total Reflectance/Fourier Transfer Infrared Spectroscopy (ATR-FTIR) and scanning electron microscopy (SEM). Antifungal activity of different treatments of natamycin grafted film was evaluated against two common spoilage yeasts of Doogh including Rhodotorula mucilaginosa and Candida parapsilosis. Results showed that 6 min treated film provides maximum anti-yeast activity and can be applied to control fungal growth in Doogh. Natamycin-grafted film postponed the yeast spoilage in Doogh and prolonged its shelf-life to 23 days.

Weathering of microplastics and interaction with other coexisting constituents in terrestrial and aquatic environments

Weathering of microplastics (MPs, < 5 mm) in terrestrial and aquatic environments affects MP transport and distribution. This paper first summarizes the sources of MPs, including refuse in landfills, biowastes, plastic films, and wastewater discharge. Once MPs enter water and soil, they undergo different weathering processes. MPs can be converted into small molecules (e.g., oligomers and monomers), and may be completely mineralized under the action of free radicals or microorganisms. The rate and extent of weathering of MPs depend on their physicochemical properties and environmental conditions of the media to which they are exposed. In general, water dissipates heat better, and has a lower temperature, than land; thus, the weathering rate of MPs in the aquatic environment is slower than in the terrestrial environment. These weathering processes increase oxygen-containing functional groups and the specific surface area of MPs, which influence the sorption and aggregation that occur between weathered MPs and their co-existing constituents. More studies are needed to investigate the various weathering processes of diverse MPs under natural field conditions in soils, sediments, and aquatic environments, to understand the impact of weathered MPs in the environment.

Aldehydes as powerful initiators for photochemical transformations

Photochemistry, the use of light to promote organic transformations, has been known for more than a century but only recently has revolutionized the way modern chemists are thinking. Except from transition metal-based complexes, small organic molecules have been introduced as catalysts or initiators. In this review, we summarize the potential that (aromatic or aliphatic) aldehydes have as photoinitiators. The photophysical properties and photoreactivity of benzaldehyde are initially provided, followed by applications of aldehydes as initiators for polymerization reactions. Finally, the applications to date regarding aldehydes as photoinitiators in organic synthesis are presented.