Blowing agents compatibility

The blowing agents must be adapted to the polymer because of the decomposition temperature, which must be compatible with the temperatures of the various processing stages. 

With respect to chemical compatibility, it is essential to select a blowing agent and polymer combination that will not produce undesirable side reactions affecting properties or appearance (21). 

Because of environmental concerns about using chlorofluorocarbon (CFC) blowing agents, methylene chloride is being used as a blowing agent. A number of catalysts have been developed that are particularly compatible with methylene chloride. Several of these new catalysts work on the delayed-action principle to avoid splitting of the foams (22). 

Mannich polyols are aromatic polyols, which confer excellent physico-mechanical, thermal and fire proofing properties to rigid PU foams. Mannich polyols, especially those based on p-nonyl phenol, have a very good compatibility with pentanes used as blowing agents (for example sucrose polyether polyols have a poor compatibility with pentanes, giving emulsions at normal concentrations for foaming, but not real solutions). 

Sometimes, this polyester is modified with oleic acid in order to improve its compatibility with blowing agents. The chemistry for the synthesis of rigid polyester polyols is absolutely the same as the chemistry for the synthesis of polyester polyols used in elastic PU, described in detail in the Chapter 8. 

The process of PET glycolysis with DEG has several disadvantages the reaction products are viscous liquids with a tendency to solidification or even to be solid at room temperature, the reproducibility of the characteristics of the resulting polyester polyols are difficult to realise (poor consistency) and the products of transesterification are not compatible with the blowing agents (pentanes or hydrofluorocarbons) [4, 6]. 

All the aromatic polyesters based on DEG have poor compatibility with blowing agents (pentanes or fluorocarbons) and to improve this compatibility compatibilising polyols such as ortho-toluene diamine polyols, propoxylated a-methyl glucoside polyols, oxyethylated p-nonylphenol, amine and amide diols, PO-EO block copolymers, borate esters, silicone compounds and so on, are frequently used [27-30]. 

As a general rule, castor oil and its derivatives confer on the resulting PU hydrophobicity and water repellency. These polyols have an excellent compatibility with the pentanes that are used as blowing agents and the resulting PU foams have excellent resistance to humid ageing degradation. 

The transamidation reactions, usually with diethanolamine, are frequently used to obtain diethanolamides of fatty acids (well known as nonionic surfactants [51-57]). Fatty acid diethanolamides are sometimes used together with other polyols, to obtain rigid PU foams. The fatty acid diethanolamides are bifunctional compounds and improve the compatibility of various polyolic systems very much, with pentanes used as blowing agents for rigid PU foams (reaction 17.15). 

With methyl esters of fatty acids, the reaction takes place at a higher yield (around 90-92%) as compared to the free fatty acids (the yield is 60-70%) [2, 7-9]. The catalysts of this amidation reaction are KOH, NaOH, CH3ONa, CH3OK, etc. (the most used catalyst is sodium methylate). The diethanolamides of fatty acids, as presented in Chapter 17, are used sometimes as copolyols in rigid polyurethane (PU) foams, to improve the compatibility of other rigid polyols with pentanes, used as blowing agents [4-8]. 

Plastics with numerous cells disposed throughout its mass. Cells are formed by a blowing agent or by the reaction of the constituents. Resins in sponge form may be flexible or rigid the cells may be open or closed. Molding paper, textile, or plastic foils printed with compatible inks directly onto a plastic part so that the foil is visible below the surface of the part as an integral decoration. 

Surfactants are added to a thermoset resin system to promote the dispersion of fillers in the resin matrix. Recently, surfactants have been used to disperse carbon nanotubes in polymer matrices [48-50]. Surfactants are of two types neutral and ionic. Surfactants have many applications in coating industries for the development of a water-based resin system [51]. Surfactants are added to phenolic or polyurethane foam formulation in which they facilitate formation of small bubbles. The size and uniformity of bubble formation results in a fine cell structure. A surfactant reduces the surface tension of resin formulations and provides an interface between the highly polar resin and the non-polar blowing agent. The surfactant for a particular resin system must be selected carefully so that it is compatible with the resin and resistant... 

Improved compatability with polymeric isocyanate and fluorocarbon blowing agent. 

The temperature-viscosity curves, including the effect of fluorocarbon-11 blowing agent, are shown in Figures 3 and 4. This low viscosity polyol provides easier handling, good mixing, and excellent flow. Laboratory data, derived from comparative evaluations, have shown this polyol to be inherently more compatible than the other polyols tested with polymeric isocyanate, water and fluorocarbons. 

Fluorocarbon Blowing Agent n A family of inert, noncorrosive liquid compounds containing carbon, chlorine and fluorine, originally developed as refrigerants. They are compatible with all resins and leave no residues in molds. For years they were widely used in structural-foam extrusion, in which they were incorporated with the polymer by direct injection through the barrel of the first of two tandem extruders. Fluorinated... 

The poly(alkylene oxide)s are principally used to make rigid foams because they have good hydrolytic stability, are compatible with fluorocarbon blowing agents, and can be obtained with high functionalities, around 3 to 6, and with predetermined hydroxyl numbers (38). The polyols can be obtained by propoxylation of a starter (see Chapter 4, Section IV) such as glycerine (functionality of 3) or sorbitol (functionality of 6) or a number of amines such as ethylene diamine or phenylene diamine (functionalities of 4), with hydroxyl numbers typically in the range of 300 to 500 mg KOH/g (21). 

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