Coatings from polyester polyols

Polyester polyols are based on saturated aliphatic or aromatic carboxylic acids and diols or mixtures of diols. The carboxylic acid of choice is adipic acid because of its favorable cost/performance ratio. For elastomers, linear polyester polyols of molecular weight of ca 2000 are preferred. Branched polyester polyols, formulated from higher fimctional glycols, are used for foam and coating applications. Polyester polyol-derived polyurethanes have a lower hydrolytic stability... 

Powder coatings are formulated from the reaction product of trimethylolpropane and IPDI, blocked with caprolactam, and polyester polyols. The saturated polyester polyols are based on aromatic acid diols, neopentyl glycol, and trimellitic anhydride for further branching. To avoid the release of caprolactam in the curing reaction, systems based on IPDI dimer diols are used. 

Dow also developed polyurethane foams from polyols via hydroformylation of fatty acids. The foams have properties which are comparable to foams from petrochemicals in terms of density and flexibility. The advantages of using sustainable feedstocks in viscoelastic foams are increased load bearings and tensile and tear properties [39, 40]. The hydroformylation and consecutive hydrogenation of fatty acids derived from seed oil can also be used to form low viscosity polyester polyols. Therefore, fatty acid methyl esters are transesterified with diols, e.g., glycol (Scheme 12). The polymer contains chemically active hydroxy groups which can be used for polyurethanes in coating applications [41]. 

Much research is being performed in the field of drop-in biopolymers toward biobased PU, based on renewable polyester polyols. Merquinsa markets a biobased thermoplastic PU under the brand names Pearlthane and Pearlbond ECO these have a biobased content ranging from 20 to 90%. Arkana produces biobased thermoplastic copolyamide hotmelt Platamid (based on castor oil) having a biobased content up to 100%. UNl-REZ are thermoplastic polyamide, pine-based, adhesive resins from Arizona Chemicals. The previously desalbed biobased thermoplastics can be applied to textile coating and lamination. 

K. Somani, S. Kansara, R. Parmar and N. Patel, High solids polyurethane coatings from castor-oil-based polyester-polyols , Int J Polym Mater, 2004, 53, 283-93. 

Polyols are selected on the basis of cost, rate of esterification, stability during high temperature processing, functionality, and hydrolytic stability of their esters. The most widely used diol is NPG, and the most widely used triol is TMP. A comparison of results of testing films of coatings made with a series of polyesters from several polyols is given in Reference 167. Coatings based on CHDM polyesters cross-linked with MF resins showed the best hydrolytic stability. 

Prior to TPU synthesis, polyester polyol was dried at 80 C for 12 hours under a full vacuum prior to use. Both TPUs were prepared using the one-shot polymerization technique from equal raw material starting temperatures. Homogenized TPU reactant mixtures were then poured onto polytetrafluoroethylene coated steel pans and polymerized in a convection oven at a temperature above the hard segment Tg of either TPU. Complete conversion was assured by the absence of an asymmetric isocyanate stretching vibration in the infiared spectra of the final TPUs. 

Polyols. Several important polyhydric alcohols or polyols are made from formaldehyde. The principal ones include pentaerythritol, made from acetaldehyde and formaldehyde trimethylolpropane, made from -butyraldehyde and formaldehyde and neopentyl glycol, made from isobutyraldehyde and formaldehyde. These polyols find use in the alkyd resin (qv) and synthetic lubricants markets. Pentaerythritol [115-77-5] is also used to produce rosin/tall oil esters and explosives (pentaerythritol tetranitrate). Trimethylolpropane [77-99-6] is also used in urethane coatings, polyurethane foams, and multiftmctional monomers. Neopentyl glycol [126-30-7] finds use in plastics produced from unsaturated polyester resins and in coatings based on saturated polyesters. 

By depolymerizing PET waste with a polyol and subsequently condensing the oligomeric product with a polycarboxylic acid or anhydride, polyester resins are produced which have wide industrial applications. Depending on the polyol and polycarboxylic acid or anhydride used, saturated resins, alkyd resins, or unsaturated resins are obtained. PET wastes have been used for the production of alkyd resins in water thinnable paints. The materials obtained from the reaction of PET with a mixture of fatty acids high in linoleic acid content and trimethylolethane have been used in the preparation of water-dispersible coatings. Products of the depolymerization of PET with trimethylolpropane and pentaerythritol are used in the manufacture of high-solids paints. In the first step, PET is depolymerized with trimethylopropane and pentaerythritol at temperatures of 230-240°C. The final paint compositions contain 30-50% of PET depolymerization products.12... 

Hardness in the H to 2H range is adequate for many industrial coatings thus the data in Table III show that it is possible to make coatings with adequate hardness from the BA/CHDM polyester. Further, these coatings have fair impact resistance and flexibility. Both the 133 and the 150 C bakes are probably sufficient to drive the co-dondensation reaction of polyol with melamine resin close to completion, and some degree of self-condensation of the excess melamine resin can be expected, especially at 150 C.[15] Self-... 

One of the more advanced technical offerings from castor oil is a line of polyester diols, triols, and higher functional polyols derived from 100% castor oil as products for the preparation of polyurethane prepolymers and elastomers [68]. The Polycin line of polyols are prepared by transesterification of ricinoleic acid and derivatives. The producers (Vertellus) offer diol and triol products, as well as a recently developed series of diol and triol glyceryl ricinoleate esters that are stated to be prepared from 100% castor oil, making them fully renewable in content. The products are recommended for coatings, sealants, and adhesive applications. 

Aldonitrile acetates of sugars have been applied to their GC analysis in different polysaccharides [442] on LAC-4R-886 polyester stationary phase (190°C)and to the analysis of polyols and aldoses in urine and crystalline lenses [444] on a capillary column of borosilicate glass (60 m X0.3 mm l.D.) coated with SE-30 containing a dispersion of Silanox 101 (temperature programming at l°C/min from 150°C). These derivatives were very stable and a uniform product was formed from every individual substrate. 

From high MW triols or low branched oligo-polyols (MW = 3000-6500 daltons) polyethers, polyesters, filled polyols (polymer polyols), are obtained elastic PU with a low degree of crosslinking (flexible and semiflexible foams, coatings etc). 

Urethane resins are synthesized from isocyanates and chemical compounds with hydroxyl or urethane groups (—N—C—O—) including water, polyesters, epoxies, and acrylics [8,9]. The chemical structure of urethane coating is shown in Fig. 13.4. Polyester and epoxy have better barrier resistance to moisture and chemical attack than the acrylic polyol. Ahphatic isocyanate-based coatings are resistant to UV hght and have excellent gloss and color retention. 

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