Polyol viscosity

The oligo-polyol s viscosity is determined using a Brookfield viscosimeter. The Standard Test Method for oligo-polyol viscosity determination is ASTM D4878 [37]. There are two test methods, A and B, applicable for viscosities between 0.01 to 1000 Pa-s, at 25 °C, or for solid polyols (such as polytetrahydrofuran), at 50 °C. Test method A is indicated for oligo-polyols of very high viscosities. 

As a general rule, all the aminic polyols obtained by the propoxylation of the amines discussed have very high viscosities. By the introduction of EO units the aminic polyol viscosities decrease substantially [4],... 

The viscosity of the final Mannich polyol depends on the functionalities of the resulting Mannich bases (lower functionalities lead to lower viscosities) and on the molar ratio between the reacted PO/mol of the Mannich base. Figure 15.2 shows the variation of the Mannich polyol viscosities as a function of the molar ratio of the PO/Mannich base (Mannich base from 1 mol of nonyl-phenol, 2 mols of formaldehyde and 2 mols of diethanolamine). One observes that after the addition of one PO mol/mol of Mannich base a maximum of viscosity is obtained and by the addition of 2-5 mols of PO the viscosity decreases continuously. 

These "polymer-polyols" are made by the in situ polymerization of vinyl monomers such as acrylonitrile (although grafting with other monomers has also been reported in a liquid polyol solution, e.g., polyether triol of molecular weight 3000) to give stable dispersions of the polymeric portion in the liquid polyol. Grafting is carried out with azobis(isobutyronitrile) or dibenzoyl peroxide as initiators at 80-90 °C. A polymer-polyol containing about 20% acrylonitrile appeared to be the best compromise between polyol viscosity and urethane foam properties (108). 

As mentioned previously, neat pMDI does not have gap filling capability for wood bonding because of its low viscosity and propensity for deep penetration. Consequently, neat pMDI is not used for applications such as plywood, laminated veneer lumber, etc. However, gap filling properties may be achieved by modifying pMDI with a wide variety of difunctional or polyfunctional polyols. Viscosity and NCO content are easily tailored to meet many application requirements. 

The velocity of the flowing material in the area of the fan gate should not be greater than 1 5m s" otherwise the liquid will enter the mould cavity in a turbulent manner. This velocity value holds for polyol viscosities of 100-600 cP at 25°C. For lower viscosity materials, the film gate cross-section must be increased or the throughput decreased to maintain laminar flow. 

Faster oxide addition rates Lower polyol viscosity Primary hydroxyl groups Faster urethane reaction Poor himidity aging properties Propylene Oxide... 

Secondary hydroxyl groups Slower urethane reaction Better humidity aging stability Mixture of Ethylene and Propylene Oxide ( ) Faster oxide addition Primary and secondary hydroxyls Lower polyol viscosity Good humidity aging properties... 

Also affecting the sucrose initiated polyol is the amount of alkylene oxide added. Tcdsle II shows, graphically, that, as you increase the amount of oxide added to the sucrose molecule, the lower will be the resulting polyol viscosity and the less rigid the foam. With the addition of only one alkylene oxide per hydroxyl group on the sucrose molecule, there are some applications where the resulting foam is too rigid or friable. 

Diol to polyol introduction. Improved compatability. Decreased polyol viscosity, and No change in polyol reactivity. 

The choice of the proper polyol is most critical. While the specific criteria for performance of a polyol for furniture application may vary from customer to customer, the key requirements are similar (Table III). These include low polyol viscosity - 3,000 cps max good polyol compatibility with polymeric isocyanate, water and fluorocarbons excellent flow in the mold cavity rapid demolding time and the resultant foam must possess acceptable strength and good dimentional stability. 

The product contains 12.6% phosphoms and has an OH number in the 450 mg KOH/g range. Fyrol 6 is used to impart a permanent Class 11 E-84 flame spread rating to rigid foam for insulating walls and roofs. Particular advantages are low viscosity, stabiHty in polyol—catalyst mixtures, and outstanding humid aging resistance. Fyrol 6 is used in both spray foam, froth, pour-in-place, and slab stock. 

When the alcoholysis step is complete, the polybasic acid(s) and the balance of polyol, if any, are added. The batch is reheated and maintained at about 250°C to carry out the polycondensation step to the desired endpoint, usually a combination of the acid value and viscosity of the resin. 

The newer HFC refrigerants are not soluble in or miscible with mineral oils or alkylbenzenes. The leading candidates for use with HFC refrigerants are polyol ester lubricants. These lubricants are derived from a reaction between an alcohol and a normal or branched carboxyflc acid. The most common alcohols used are pentaerythritol, trimethylolpropane, neopentjlglycol, and glycerol. The acids are usually selected to give the correct viscosity and fluidity at low temperatures. 

Low viscosity urethane polymers have been prepared from castor od and polymeric isocyanates (82). These low mix viscosity systems are extremely usehd for potting electrical components where fast penetration without air voids, and fast dispensing cycles are desirable. Very low viscosity urethane systems containing castor polyols have been prepared for use in reclaiming water-logged buried telephone cable and for encapsulating telephone cable sphces (83—86). 

Miscellaneous Commercial Applications. Dimer acids are components of "downweU" corrosion inhibitors for oil-drilling equipment (see Petroleum Corrosion and corrosion inhibitors). This may account for 10% of current dimer acid use (71). The acids, alkyl esters, and polyoxyalkylene dimer esters are used commercially as components of metal-working lubricants (see Lubrication). Dimer esters have achieved some use in specialty lubricant appHcations such as gear oils and compressor lubricants. The dimer esters, compared to dibasic acid esters, polyol esters and poly(a-olefin)s, are higher in cost and of higher viscosity. The higher viscosity, however, is an advantage in some specialties, and the dimer esters are very stable thermally and can be made quite oxidatively stable by choice of proper additives. 

The products of these reactions with maleic anhydride, termed maleated oils, react with polyols to give moderate mol wt derivatives that dry faster than the unmodified oils. For example, maleated, esterified soybean oil is a drying oil with a drying rate comparable to that of a bodied linseed oil with a similar viscosity. Maleated linseed oil can be converted to a water-dilutable form by hydrolysis with aqueous ammonium hydroxide to convert the anhydride groups to ammonium salts of the diacid. Such products have not found significant commercial use, but similar reactions with alkyds and epoxy esters are used on a large scale to make water-dilutable derivatives. 

The epoxidation is generally conducted in two steps (/) the polyol is added to epichlorohydrin in the presence of a Lewis acid catalyst (stannic chloride, boron triduoride) to produce the chlorohydrin intermediate, and (2) the intermediate is dehydrohalogenated with sodium hydroxide to yield the aliphatic glycidyl ether. A prominent side-reaction is the conversion of aliphatic hydroxyl groups (formed by the initial reaction) into chloromethyl groups by epichlorohydrin. The aliphatic glycidyl ether resins are used as flexibilizers for aromatic resins and as reactive diluents to reduce viscosities in resin systems. 

In the 1990s this approach became more common in order to ensure sufficient compressive strength with the trend to lower bulk densities. Furthermore the proportion of SAN to polyol has been increased to about 40%. This may lead to serious stability problems and care must be taken to control the size and distribution of the particles and prevent agglomeration. Polymer polyols using polystyrene as the polymer component have recently become available (Postech-Shell) and are claimed to exhibit good stability, low viscosity and less discolouration as well as providing price advantages. 

The polyols used are of three types polyether, polyester, and polybutadiene. The polyether diols range from 400 to about 10,000 g/mol. The most common polyethers are based on ethylene oxide, propylene oxide, and tetrahydrofuran or their copolymers. The ether link provides low temperature flexibility and low viscosity. Ethylene oxide is the most hydrophilic and thus can increase the rate of ingress of water and consequently the cure rate. However, it will crystallize slowly above about 600 g/mol. Propylene oxide is hydrophobic due to hindered access to the ether link, but still provides high permeability to small molecules like water. Tetrahydrofuran is between these two in hydrophobicity, but somewhat more expensive. Propylene oxide based diols are the most common. 

The isocyanurate reaction can be both beneficial and troublesome. It can be the bane of production engineers. Low levels of alkaline impurities present in urethane raw materials such as polyols, tackifiers, etc., can cause problems in prepolymer production, resulting in high viscosity products at levels of 5 ppm or less. At higher levels of alkaline impurities, more serious problems can occur, including poor shelf life, poor caulkability, or poor sag resistance. At levels of 15 ppm or higher, the alkalinity can cause an isocyanurate reaction in a prepolymer that can result in a gelled reactor. 

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