Rigid foams polyether polyols

TDA-derived polyols are made by alkoxylation. Polypropylene oxide adducts of I DA (14) and TDA-initiated polyether polyols (13,15) are used in rigid polyurethane foams and continue to be included in new formulations (62) as well as older appHcations. 

Polyester Polyols. Initially polyester polyols were the preferred raw materials for polyurethanes, but in the 1990s the less expensive polyether polyols dominate the polyurethane market. Inexpensive aromatic polyester polyols have been introduced for rigid foam appHcations. These are obtained from residues of terephthaHc acid production or by transesterification of dimethyl terephthalate (DMT) or poly(ethylene terephthalate) (PET) scrap with glycols. 

In the 1990s novel polyols included polyether-esters, which provided good prerequisites for flame retardancy in rigid foams and polyether carbonates with improved hydrolysis stability. 

Propylene oxide is produced from the chlorohydrination of propene similar to the process used to make ethylene oxide (see Ethene). A major use of propylene oxide involves hydrating propylene oxide to produces propylene glycol, propylene polyglycols, and other polyether polyols. These products are used to produce both rigid and flexible polyurethane foams, but they are also used to produce polyurethane elastomers, sealants, and adhesives. 

A rigid, foamed crosslinked PUR, usually with closed cells, is formed by the reaction of a diisocyanate and often methane diisocyanate (MDI) or polymeric MDI with polyester or more usually with a polyether polyol. Foaming may result from the water, which reacts with isocyanate groups to form carbon dioxide but is usually the result of using other... 

To a large extent, the utilization of whey and whey byproducts (including salt whey and whey permeate) is a problem of utilizing the milk sugar, lactose. Since the excess lactose produced in the United States each year amounts to more than a billion pounds, one must consider its use in large volume products. One such product is lactose-based polyether-polyol used in the manufacture of low-density rigid polyurethane foams (2). 

Another route to flame-retardant rigid foams is the use of flame-retardant polyether polyols which contain phosphorous and halogen (reactive type). In recent years, due to the fire-gas toxicity caused by halogen-, phosphorous- or nitrogen-containing flame retardants, other types of flame-retardants which do not produce toxic gases are being developed. 

This method, however, did not result in improved flame retardance because the isocyanurate content was too low. In recent years, however, high-functionality and low-viscosity polyether polyols have become available, and therefore the above method has become less important. Even so, the method was sometimes used to make foams having increased crosslink density to improve dimensional stability or chemical resistance. Therefore, a higher isocyanate index, e.g., 150 to 200, was used to incorporate isocyanurate linkages in rigid urethane foams. 

The ingredients for polyurethane flexible foam are Freon 11, polyether polyol-triol, polyurethane and TDI. Polyurethane fire-resistant rigid foam is produced from Freon 11, polyether polyol-hexol, polyether polyol-phosphorus, polyisocyanates and polyurethane. MDI foam has advantages over TDI foam, particularly in that it is easier and safer to handle, and for this reason is widely used as a thermal insulation. Flexible foams account for over 60% of the consumption of polyurethanes31,32. 

Thesecompounds, widely employed at the outset of the development of polyurethanes have been displaced from their market by polyether-polyols. For the production of rigid foams however, use is still made of aromatic polyols produced by the transesterification of dimethyl terephthalate by glycoL... 

The general synthesis reaction of polyether polyols for rigid PU foams by polymerisation of alkylene oxides (PO, EO) initiated by polyolic starters is presented in reaction 13.1. 

The most important low molecular weight polyols used as starters for polyether polyols destined for rigid PU foams synthesis are glycerol, trimethylolpropane (TMP), triethanolamine, pentaerythritol, dipentaerythritol, a-methyl glucoside, xylitol, sorbitol and sucrose [1-27]. The main properties of these starter polyols, which are of interest for polyurethane chemistry, are presented in Table 13.1. 

Table 13.1 Some characteristics of polyols used frequently as starters for polyether polyols for rigid PU foams ...

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