Chemical foam model

Full mould process moulding technique using a foam model in chemically bonded sand, in which the model is lost upon pouring, generally used only for large castings... 

The chemical flexible slabstock foam model provides a detailed look at the performance of the industry standard catalyst Dabco BLV compared to the non-fugitive catalysts Dabco NE500 and the Dabco NE500/Dabco NE600 package, keeping the Dabco T-9 level constant. Selectivity and conversion can be calculated as described previously. Note that... 

Fourteen formulations of chemical alternatives were submitted to EPA under confidentiality and they were assessed based on numerous human health and ecotoxicity endpoints in addition to bioaccumulation potential and environmental persistence. They were also screened for potential exposure to workers, users and the aquatic environment. Where data gaps existed, EPA experts used models and chemical analogs to estimate the hazard for a particular endpoint. The literature and test data reviews were published in the final report, Environmentally Preferable Options for Furniture Fire Safety Low Density Furniture Foam . In addition, each hazard endpoint was ranked with a concern level (High, Moderate or Low) based on the criteria used by the EPA s New Chemicals Program to rate the concern level of new chemicals submitted under the Toxic Substance Control Act (TSCA). As seen in Figure 8.2, where the hazard endpoint rankings are bold, the value is based on experimental data. Where the hazard endpoints are presented in italic font, the value is estimated based on models or chemical analogs. In this way, detailed hazard information was summarized and presented in a clear and concise format. 

This reaction is truly tempting because it potentially satisfies the need in the search for a way to reclaim the chemical value of a polyurethane recycle foam project [12, 13]. When a polyurethane foam is hydrolyzed, it gives aromatic diamine and polyether polyol, both in very crude forms. The diamine can be purified by regular means, but the crude polyether polyol cannot be easily cleaned up due to its polymeric nature. If this Ganem reaction can work well, the polyether polyol stream can be converted to a low-molecular-weight chemical, which can then be purified by conventional process such as distillation. Indeed, when this reaction was tried on a polyether triol of 3000 molecular weight as a model, the diacetate of propylene glycol was isolated by distillation. Unfortunately, the yield was too low to be of practical interest. 

Research carried out by the Queen s University of Belfast in the thermoforming of PP and PP foam is reviewed. Studies were made of the influence of crystallinity on thermoformability and the nse of chemical blowing agents in the production of foams having lower density and optimum cell stracture. Finite element modelling was nsed in the prediction of wall thicknesses and an optimised process control system was developed. BELFASUQUEEN S UNIVERSITY... 

While we will discuss the control of the various properties presented in the last section, the composition of a device must represent an optimum of all the properties. As we have shown, the quality of a foam is achieved by a complex combination of chemical and physical effects. No unifying model combines them in a sufficiently precise way as to minimize the work involved. Thus, as we discuss ways to control compressive and tensile strength, we must be aware that these properties will affect the foaming process. The design process is made somewhat easier by using composite techniques. In this way, one can separate the physical requirements of a device... 

A group at the Department of Chemical Engineering at Kyushu University in Fukuoka, Japan, spent the last decade working on a polyurethane foam scaffold for hepatic cells.In 1999, the group reported their work using a dog model that, showed that the performance of this system was equal, or probably superior to that of Demetriou s system, and in addition, our system improved renal function. This opinion is based on the comparison of various blood chemistries in the two devices (hollow hber vs. polyurethane foam). Table 7.2 depicts the comparison. 

During synthesis of a polymer, particularly of polyurethane, gaseous products can appear. Therefore, a complete model of the process must take into account (at least in some cases) the possibility of local evaporation and condensation of a solvent or other low-molecular-weight products. Such a complex model is discussed for chemical processing of polyurethane that results in formation of integral foams in a stationary mold.50 In essence, the model is an analysis of the effects of temperature in a closed cell containing a solvent and a monomer. An increase in temperature leads to an increase in pressure which influences the boiling temperature of the solvent and results in an increase in cell volume. The kinetics of polymerization is described by a simple second-order equation. The... 

This model, which is discussed in detail in the publication cited, can be successfully used to analyze chemical (reactive) processing of foamed items of different sizes and shapes. 

Foam films are usually used as a model in the study of various physicochemical processes, such as thinning, expansion and contraction of films, formation of black spots, film rupture, molecular interactions in films. Thus, it is possible to model not only the properties of a foam but also the processes undergoing in it. These studies allow to clarify the mechanism of these processes and to derive quantitative dependences for foams, O/W type emulsions and foamed emulsions, which in fact are closely related by properties to foams. Furthermore, a number of theoretical and practical problems of colloid chemistry, molecular physics, biophysics and biochemistry can also be solved. Several physico-technical parameters, such as pressure drop, volumetric flow rate (foam rotameter) and rate of gas diffusion through the film, are based on the measurement of some of the foam film parameters. For instance, Dewar [1] has used foam films in acoustic measurements. The study of the shape and tension of foam bubble films, in particular of bubbles floating at a liquid surface, provides information that is used in designing pneumatic constructions [2], Given bellow are the most important foam properties that determine their practical application. The processes of foam flotation of suspensions, ion flotation, foam accumulation and foam separation of soluble surfactants as well as the treatment of waste waters polluted by various substances (soluble and insoluble), are based on the difference in the compositions of the initial foaming solution and the liquid phase in the foam. Due ro this difference it is possible to accelerate some reactions (foam catalysis) and to shift the chemical equilibrium of some reactions in the foam. The low heat... 

In this paper, instrumental means are used to obtain a physical description of the rise of urethane foam and cell opening. Infrared analysis is used to identify the chemical species present in reacting foam and to determine the order and relative rates of reaction of these species. From these data, a reaction sequence model is deduced for the process of making stable, water-blown urethane foam. 

Abstract. Infrared analysis of reacting foams has been used to determine the sequence of chemical reactions that occurs in the foaming process and to relate this sequence of reactions to the stages evident in the formation of foam measured by rate-of-rise techniques. A reaction sequence model has been developed in which at the earliest stage of foaming, out-of-phase carbamic acid and carbamic acid salts, formed by hydrolysis of isocyanate, are the main species present tending to stabilize the froth-like foam. These species are in turn converted into polyureas. In the latter stages of the reaction sequence, urethane formation becomes predominant as the foam develops substantial bulk modulus... 

For a better understanding of the PU foam wastes recovery by chemical processes. The model reactions for hydrolysis, glycolysis and aminolysis of urethane and urea groups will be presented in the next sections. 

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