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Silicone Foams
Published in S. T. Lee, Polymeric Foams, 2022
Chemical foaming consists in blending a polymer with chemical blowing agents (CBAs) or by a side reaction between two chemical groups which produce a gas. CBAs are the most used in industry like extrusion foaming process because their use needs few modifications of the preexisting equipment. CBA precursors must be added directly into the melt and must not interfere with the crosslinking reaction. By increasing the temperature, CBAs are activated and gas is released. There are two kinds of blowing agents, exothermic and endothermic blowing agents. Azobisisobutyronitrile (Park 2008) and azodicarbonamide (Kim et al. 2004) are exothermic agents and generally produce N2 during their decomposition whereas endothermic ones, such as sodium bicarbonate, ammonium carbonate and ammonium hydrogenocarbonate, citric acid or citrates, generate CO2. Currently, endothermic blowing agents are preferred because they released less toxic side products during their decomposition, as referred to registration, evaluation, authorization and restriction of chemicals (REACH) European regulations. Other specific ways have been developed such as by Hagen (1999): An extruded foamed silicone was obtained at room temperature by blending silicone with acetic acid as promoter and ammonium bicarbonate as blowing agent.
Polymers
Published in Ronald Scott, of Industrial Hygiene, 2018
Liquids such as freons, chlorinated-fluorinated hydrocarbons, have been very popular blowing agents because of their low toxicity, but these will need to be replaced as the ban on such compounds is imposed to reduce their damaging effect on the atmospheric ozone layer. A variety of organic compounds that decompose to gases when heated are used. These include azodicarbonamide, 1,1’-azo-bisformamide, p-toluene-sulfonyl semicarbazide, and p -toluene-sulfonyl hydrazide. These compounds are often strong irritants and present a hazard to workers if they become airborne during mixing. Azo compounds are incompatible with acids or the ketone peroxides, which may be involved in curing thermoset plastics. Contact with traces in the plastic initiates the desired nitrogen formation, but direct mixing produces a highly exothermic reaction and combustible gases.
Constituent Materials
Published in B. T. Åström, Manufacturing of Polymer Composites, 2018
Polymers are foamed using foaming agents, which may be physical or chemical in nature. Physical blowing agents are gases that are dispersed in the liquid polymer and that expand to form voids when the temperature increases or the pressure decreases. Chlorofluorocarbons (known as CFCs or freones) used to be the most popular physical blowing agents, but are being phased out due to their detrimental effect on the earth’s ozone layer; replacements are under development and several are already in use. Chemical blowing agents are mixed into the polymer and decompose into gases, often nitrogen or carbon dioxide, when the processing temperature reaches the decomposition temperature of the blowing agent.
Experimental study of microbial desulphurisation of sulphide ores combined with gel foam retardants to prevent spontaneous combustion
Published in Combustion Science and Technology, 2023
Wei Pan, Zhigang Liao, Ruge Yi, Lingrong Yang
The solutions of the five surfactants were configured according to the mass fractions designed in the experimental protocol, and the foaming experiments of the foaming agents were carried out by the Waring Blender method. Surface tension determined by surface tension meter. Characterize the performance of different mass fraction blowing agents by surface tension, foaming height, and half-life. The surface tensions of the five different mass fractions of surfactants were obtained as shown in Table 6, the foaming heights as shown in Figure 6, and the half-lives as shown in Figure 7. Table 7 shows that the surface tension of CTAB with 0.05% concentration was the lowest among the five surfactants at 26.25 mN/m, and the surface tension of LAB-35 with 0.01% mass fraction was the highest at 50.05 mN/m.
Numerical and experimental investigation of liquid blowing agent and pentane blowing agent effects on the insulation of a household refrigerator
Published in Science and Technology for the Built Environment, 2021
Gizem Duru, Dilek Kumlutaş, Hasan Avci, Utku Alp Yücekaya, Özgün Özer
The blowing agents have evolved rapidly to 2010s, managed by the Montreal Protocol and related regulations to reduce ozone-depleting substances. Until the 2000s, commonly known to blow agent compounds, including HFCs, have played a role in enhancing the earth's average temperature called Global Warming. Therefore, under the United Nations' Framework Convention on Climate Change (UNFCCC), governments worldwide are committed to reducing emissions to the atmosphere of greenhouse gases (Johnson 1998). Due to the Global Warming Potential (GWP), the permissible limits of blowing agents' use were reformed.