Chemical reactions of burning Poly(methyl methacrylate) (PMMA) are reviewed in this paper although kinetics of thermal decomposition are believed to be fairly simple. Basically, there are three stages in the combustion of PMMA. Firstly, PMMA decomposes to produce monomer methyl methacrylate (MMA). Secondly, monomer MMA decomposes to generate small gaseous molecules that are usually combustible. Finally, these small molecules undergo combustion. Recent studies on the thermal decomposition kinetics and thermal stability of PMMA are also introduced. Results are useful for understanding the heat released of burning PMMA per unit mass of oxygen. Finally, the effects of additives on thermal decomposition are also discussed.

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Diabetic cardiomyopathy (DCM) is a serious cardiac complication of diabetes that currently lacks specific treatment. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway has been suggested to contribute to the pathogenesis of cardiovascular diseases. However, whether cGAS-STING is involved in the development of DCM has not been established. Our study aimed to determine the role of cGAS-STING in the initiation of nucleotide-binding oligomerization domain-like receptor pyrin domain containing 3 (NLRP3) inflammasome-induced cardiac pyroptosis and chronic inflammation during the pathogenesis of DCM. C57BL/6J mice were preinjected with adeno-associated virus 9 (AAV9) intravenously via the tail vein to specifically knock down myocardial STING. After four weeks, mice with myocardium-specific knockdown of STING received injections of streptozotocin (STZ; 50 mg/kg) and a high-fat diet to induce diabetes. Measurements included echocardiography, immunohistochemical analyses, wheat germ agglutinin (WGA) staining, and western blotting. Here, we showed that the cGAS-STING signaling pathway was activated in diabetic hearts, which was indicated by the increased phosphorylation of TANK-binding kinase 1 (TBK1) and interferon (IFN) regulatory factor 3 (IRF3), leading to the activation of the NLRP3 inflammasome in the hearts of diabetic mice and proinflammatory cytokine release into serum. Moreover, STING knockdown via adeno-associated virus-9 (AAV9) in diabetic mouse heart alleviated cardiac pyroptosis and the inflammatory response, prevented diabetes-induced hypertrophy, and restored cardiac function. Mechanistically, we showed that palmitic acid (PA)-induced lipotoxicity impairs mitochondrial homeostasis, producing excessive mitochondrial reactive oxygen species (mtROS), which results in oxidative damage to mitochondrial DNA (mtDNA) and its release into the cytoplasm while switching on cGAS-STING-mediated pyroptosis in cardiomyocytes, thereby worsening the progression of diabetic cardiomyopathy. Our study demonstrated that activation of the cGAS-STING pathway caused by mitochondrial oxidative damage and mtDNA escape induced by free fatty acids promoted pyroptosis and proinflammatory responses in cardiomyocytes in a NLRP3 inflammasome-dependent manner, thus promoting myocardial hypertrophy during the progression of DCM.

The burning behavior and combustion mechanism of polymethylmethacrylate (PMMA) were studied by using cone calorimeter, mass spectrograph and gas chromatograph. Main combustion mechanisms of PMMA were reviewed. Results indicated that PMMA would burn steadily under low radiative heat flux; or with thicker samples. The yields of carbon dioxide and carbon monoxide would not be changed. Under high heating rate, there are three broad stages. Firstly, upon heating by external sources, PMMA would decompose to generate monomer MMA and a small amount of other products. Secondly, monomer MMA would decompose to produce small molecule products. Finally, these small gaseous molecules would undergo oxidation, i.e., burning. The main oxygen consumption reaction, i.e., the heat release reaction, is the burning of small molecule products. Main combustion products are found to be carbon dioxide and water, with a small amount of carbon monoxide. At high temperature, the monomer MMA would react with oxygen directly to produce methyl pyruvate, formaldehyde and acetone. However, these reactions are not important in the combustion process of PMMA.

SUMMARYFire suppression effectiveness of a new kind of dry powder based on potassium bicarbonate was studied in this paper. The powder consisted of superfine potassium bicarbonate and some organic and inorganic additives, which was denoted as 'K-powder'. The physical and chemical characteristics of the K-powder were characterized by a series of techniques of X-ray diffraction, scanning electron microscopy, Fourier transforms infrared (FTIR) and thermal gravity analysis, etc. Performance of the new potassium-based powder in fire suppression was studied by laboratory-scale experiments, which exhibited much superior fire suppression efficacy than that of the commercial bicarbonate powder. Such improvements could be reasonably ascribed to the special chemical composition, microstructure and radiation effect on the mechanisms. The preparation, fire suppression and possible fire-extinguishing mechanisms were studied in detail.