Melamine was chemically introduced into a urea−formaldehyde system via co-condensation reactions during curing and foaming process, and a novel elastic urea− melamine−formaldehyde (UMF) foam with improved thermal stability, insulation property, and flame retardancy was fabricated. It was found that with a decrease of the mass ratio of urea formaldehyde resin and melamine formaldehyde resin (UF/MF), the curing process of UMF was prolonged, and a high curing temperature was necessary. The UMF foam exhibited an interconnected network structure with increasing cell size and size distribution, higher open cell porosity, and lower apparent density compared with pure UF foam. Evident recoverable deformation can be observed for UMF foam during the compression testing, which was resulted from the elasticity and toughness. By addition of melamine, the thermal conductivity decreased, while the decomposition temperature, char yield, and LOI increased, and during burning, the expansion of the flame was suppressed. With increasing content of MF resin, the sound absorption coefficient increased at first and then declined.
Rice paddies account for ~9% or the world’s cropland area and are characterized by environmental conditions promoting soil organic carbon storage, methane emissions and to a lesser extent nitrous oxide emissions. Here, we synthesize data from 612 sites across 51 countries to estimate global carbon stocks in paddy soils and determine the main factors affecting paddy soil carbon storage. Paddy soils (0–100 cm) contain 18 Pg carbon worldwide. Paddy soil carbon stocks decrease with increasing mean annual temperature and soil pH, whereas mean annual precipitation and clay content had minor impacts. Meta-analysis shows that paddy soil carbon stocks can be increased through several management practices. However, greenhouse gas mitigation through paddy soil carbon storage is generally outweighed by increases in methane and nitrous oxide emissions. Our results emphasize the key role of paddies in the global carbon cycle, and the importance of paddy management in minimizing anthropogenic greenhouse gas emissions.
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