Polyols acid number

Analysis of the Isocyanate was accomplished by performing an amine equivalent determination (per ASTM D1638). The polyol component was analyzed for hydroxol equivalent by an acetylation procedure developed at Sandla National Laboratories. An 0.8 gram sample Is acetylated with a 1/9 acetic anhydrlde-pyrldlne mixture for 2 hours at reflux temperature and then the free acetic acid Is back titrated with base and compared to a blank. From this Information a hydroxol equivalent can be calculated. The polyol acid number was determined by ASTH D2849. 

The tendency of aliphatic ethers toward oxidation requires the use of antioxidants such as hindered phenoHcs (eg, BHT), secondary aromatic amines, and phosphites. This is especially tme in polyether polyols used in making polyurethanes (PUR) because they may become discolored and the increase in acid number affects PUR production. The antioxidants also reduce oxidation during PUR production where the temperature could reach 230°C. A number of new antioxidant products and combinations have become available (115,120,124—139) (see Antioxidants). 

Synthesis MDI prepolymer with 1000 MW polyester polyol, NCO/OH = 2.0, chain-extended with 1,4-butandiol, acid number of polyester 0.6. 

A 41 resin reactor, equipped with a condensor, a stirrer and a nitrogen inlet, is charged with a polyether polyol and maleic anhydride. The mixture is heated to 60 °C and the catalyst is added. The mixture is then heated to 185 °C for 10 h or until the acid number is reduced to 140mgKOH/g. Some propylene glycol is added and the mixture is maintained at this temperature for another 4h or until the acid number is lowered to about 40mgKOH/g. The yield is about 90 %. 

The synthesis process was a two-stage process [20, 21], In the first stage (Scheme 22.1), the polyether polyol was mixed with maleic anhydride, a small amount of a glycol, and about 500-1000 ppm of p-toluenesul Ionic acid. The mixture was then heated to 190 °C, until the acid number had dropped to about 100 (mg of KOH per g of sample). This is followed by a second stage (Scheme 22.2) where extra glycol was added and the mixture was further reacted to a desired acid number of somewhere between 20 and 40. The synthetic process is quite fast. In most cases, the cycle time can be as short as 10 to 15 h. 

In subsequent aging studies the polyol component showed virtually no change In acid number at any of the aging temperatures (ambient, 60 , 71 C) over 13 months. The Isocyanate was shown to age similarly to the Isocyanate In Formulation 2. As a result, the above formulation Is being employed In the field ... 

Finally, a third formulation was devised which excluded the use of Freon 11 In the polyol component. Freon 11 was placed In the Isocyanate component and both Isocyanate and polyol components were changed to meet viscosity considerations. Subsequent aging studies showed the Isocyanate to age similarly to the previously aged (Formulation 2) Isocyanate. The polyol showed virtually no Increase In acid number at any aging temperature over 13 months. Thus, at ambient temperature we would expect a 6-8 year system lifetime on the Isocyanate before a 10% change In analytical properties would dictate a material change-out. The polyol appears to have a greater lifetime, but would probably be replaced at the same time. 

Polyester polyols for rigid PU foams can be obtained by ring opening polymerisation of s-caprolactone, initiated by various polyols such as a-methyl glucoside, sorbitol, pentaerythritol or trimethylolpropane. A polyester polyol derived from penteaerythritol has the following properties functionality of 4 OH groups/mol, hydroxyl number of 600 mg KOH/g, acid number of around 2 mg KOH/g and a of viscosity 7,000 mPa-s, at 25 °C (reaction 16.8) [2, 33-35]. 

When this reaction occurs, the resulting resins are excessively high in viscosity and acid number, and these results necessitate careful control of temperature, agitation, quantity and type of catalyst, and reaction time. The tendency for a polyol to polymerize through ether formation increases with the temperature and the presence of the alkaline catalysts. 

The acid number (AN) per ASTM D664 was determined for the oil-based fluids (polyalphaolefin and polyol ester). The relative amounts of acidic constituents present in products can be determined by titrating with bases. The acid number is a measure of the amount of acidic substance. (The acid number, n, is the quantity of base expressed in milligrams of potassium hydroxide per gram of sample required to titrate a sample to a specified end point). This test is considered to be a comparison test for the purpose of identifying chemical activity that may have occurred due to the addition of nanomaterials. 

Acid number is of concern with both polyether and polyester polyols, since acidity affects the kinetics of the urethane reaction. Determination is by po-tentiometric titration. 

The acid number is defined as the number of milligrams of potassium hydroxide required to neutralize the acid groups present in 1 g of the polyol. It is determined by dissolving the sample in a 1 1 mixture of benzene and alcohol and titrating this solution with standard alcoholic potassium hydroxide using phenolphthalein as indicator. A blank titration is also run using no polyol. 

Note polyols for the production of solid polyurethane elastomers should have acid numbers less than 3. 

Many variables affect the acid number and viscosity of alkyds. One is the ratio of reactants The closer the ratio of moles of dibasic acid to polyol approaches 1, the higher the molecular weight of the backbone of the resin, but also the greater the likelihood of gelation. A useful rule of thumb for a starting point is to... 

The composition of the fatty acids is a major factor aflecting the viscosity, and compositions of an oil or grade of TOFA can be expected to vary somewhat from lot to lot. Dimerization and oligomerization of the imsatmated fatty acids occur in the same temperature range at which the esterification is carried out. Fatty acids with conjugated double bonds dimerize more rapidly than those with nonconjugated bonds, and dimerization rates increase with the level of imsaturation. At the same ratio of phthalic to polyol to fatty acids, alkyds of the same acid number and solution concentration will increase in viscosity in the order soybean < linseed < tung. 

BaycoU AS 1160 is a highly branched polyester polyol (PL) consisting of four different constituents (see Fig. 10.2). The material typically has a low acid number, and a majority of end groups are hydroxyl that can react with a phenyl-based isocyanate to produce a polyurethane adhesive. Specification Umits require the water... 

ASTM D2849 also describes a method for determining the acid number and correcting for acidity or alkalinity in polyether polyols. The acid number is defined as the milligrams of potassium hydroxide that are needed to titrate acidic constituents present in 1 gram of the poly(alkylene oxide). A suitably sized sample is dissolved in a solvent containing a phenolphthalein indicator and titrated with potassium hydroxide. 

A number of commercial phosphoms-containing polyols have been made by the reaction of propylene oxide and phosphoric or polyphosphoric acid. Some have seen commercial use but tend to have hydrolytic stabiHty limitations and are relatively low in phosphoms content. BASF s Pluracol 684 is a high functionahty polyol containing 4.5% P, sold for Class 11 rigid foam use. 

Phosphites. Tertiary phosphites are also commonly used and are particularly effective ia most mixed metal stabilizers at a use level of 0.25—1.0 phr. They can take part ia a number of different reactions duting PVC processing they can react with HCl, displace activated chlorine atoms on the polymer, provide antioxidant functionaHty, and coordinate with the metals to alter the Lewis acidity of the chloride salts. Typical examples of phosphites are triphenyl phosphite [101 -02-0], diphenyl decyl phosphite [3287-06-7], tridecyl phosphite [2929-86-4], and polyphosphites made by reaction of PCl with polyols and capping alcohols. The phosphites are often included in commercial stabilizer packages. 

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