Polyester Polyols for Rigid Polyurethane Foams

The first polyols used for rigid polyurethane (PU) foams were low molecular weight polyesters based on adipic acid, phthalic anhydride (PA) and various glycols or polyols. One example of a polyester of this type is the polycondensation product between adipic acid (AA), PA and trimethylolpropane (TMP) [1-3]. 

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 development of highly crosslinked rigid polyisocyanurate foams opens an excellent area of applications for polyester polyols [4-8]. The required polyols do not need high functionality and the plasticising effect of polyester structures is extremely beneficial for these highly crosslinked systems [6]. The first polyester polyols used for these applications were low viscosity polycondensation products of AA with ethyleneglycol (EG) or diethyleneglycol modified with phthalic anhydride or triols. 

Characteristic Unit Polyester polyol based on AA, PA and TMP Polyester polyol based on AA, PA, TMP and oleic acid 

The highly crosslinked structure is not derived from polyester polyol, which has a low functionality (f = 2-3 OH groups/mol), but is derived from the isocyanurate rings generated by the trimerisation of the excess of -NCO groups. 

---

The polyols used include PO adducts of polyfiinctional hydroxy compoimds or amines (see Table 4). The amine-derived polyols are used in spray foam formulations where high reaction rates are required. Crude aromatic polyester diols are often used in combination with the multifunctional polyether polyols. Blending of polyols of different functionality, molecular weight, and reactivity is used to tailor a polyol for a speciflc application. The high functionality of the polyether polyols combined with the higher functionality of PMDI contributes to the rapid network formation required for rigid polyurethane foams. 

Miscellaneous chemicals are used to modify the final properties of rigid polyurethane foams. Eor example, halogenated materials are used for flammabihty reduction, diols may be added for toughness or flexibiUty, and terephthalate-based polyester polyols may be used for decreased flammabiUty and smoke generation. Measurements of flammabihty and smoke characteristics are made with laboratory tests and do not necessarily reflect the effects of foams in actual fire situations. 

Other uses for depolymerized PET bottles have been investigated. Used bottles have been glycolized and then used to make unsaturated polyester thermosets and polyol components in rigid polyurethane foam. Evco Research announced in 1999 its EvCote waterproof coatings and adhesives based on recycled PET [17, 18]. 

Rigid polyurethane foams were first used as the core of sandwich structures in aircraft. Polyester polyols were used in combination with TDI, employing the prepolymer technique described for elastomers in Sections IV. A and IV.B. Major developments in manufacturing rigid polyurethane foams came with the introduction of MDI as the isocyanate eomponent and the use of chlorofluorocarbon blowing agents, especially... 

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. 

Much work has been done on the incorporation of castor oil into polyurethane formulations, including flexible foams [64], rigid foams [65], and elastomers [66]. Castor oil derivatives have also been investigated, by the isolation of methyl ricinoleate from castor oil, in a fashion similar to that used for the preparation of biodiesel. The methyl ricinoleate is then transesterified to a synthetic triol, and the chain simultaneously extended by homo-polymerization to provide polyols of 1,000, 000 molecular weight. Polyurethane elastomers were then prepared by reaction with MDl. It was determined that lower hardness and tensile/elongation properties could be related to the formation of cyclization products that are common to polyester polyols, or could be due to monomer dehydration, which is a known side reaction of ricinoleic acid [67]. Both side reactions limit the growth of polyol molecular weight. 

This relative order explains that numerous physico-mechanical properties of the polyurethanes based on polyester polyols are superior to the polyurethanes derived from polyether polyols or from polyhydrocarbon polyols (this relative order is valuable for PU elastomers, flexible and rigid PU foams). 

In this work, polyurethane was made from recycled polyol obtained from rigid foam and polyisocyanate. The raw material for the polyester resin was recovered from scrap PET [5], then depolymerized using different amounts of ethylene, propylene glycol into glycolized monomer and oligomer. These glycolized products were reacted with maleic or terephthalic acid to obtained recycled polyester. The proportion of recycled polyurethane to recycled polyester was varied ranging from 1 1, 1 2, 1 2.5, and 0 1. The combined resins were then mixed with initiator,... 

---