Viscosity resin solution

TPAs are high MW acrylic copolymers supplied in organic solvents. These copolymers are typically prepared from monomers such as methyl methacrylate, styrene, or n-butyl acrylate. The selection of solvent is dictated by solubility of the resin, solution viscosity, evaporation rate, type of final coating for which it will be used, and cost. TPAs are generally used in systems that cure at ambient temperature without the need for cross-linkers. Therefore, such resins are designed with specified T so as to produce dried films with... 

In the wet-web process for impregnating paper for laminates, the wet sheet of paper on the paper machine is carried through a resin bath while the sheet is supported by a wire. The sheet contains up to 65 percent water, and the amount of resin taken up depends upon the moisture content of the paper, solids content of the resin solution, viscosity of the resin solution, temperature of the bath, machine speed, and pressure of the squeeze-rolls. Only water-soluble or water-dispersible resins can be used in the wet-web process. 

The number-average molecular weight of most commercially available acetal resins is between 20,000 and 90,000. Weight-average molecular weight may be estimated from solution viscosities. 

Fig. 2. Functional end groups and solution viscosity during polyester resin manufacture. Acid value is defined as the milligrams of KOH required to neutralize 1 g of polymer hydroxyl value is defined as the milligrams of acid equivalent required to neutralize 1 g of polymer. Solution viscosities are...

Phthahc resins are usually processed to an acid number of 25—35, yielding a polymer with an average of 1800—2000. The solution viscosity of the polymer is usually followed to ascertain the polymer end point. The resin is cooled to 150°C and hydroquinone stabilizer (150 ppm) is added to prevent premature gelation during the subsequent blending process with styrene at 80°C. The final polymer solution is cooled to 25°C before a final quaUty check and dmmming out for shipment. 

Fig. 8. Effect of shear on aqueous solution viscosities of poly (ethylene oxide) resins (a) 1.0 wt % solution, (b) 5.0 wt % solution (10). Each curve...

Of the three worldwide manufacturers of poly(ethylene oxide) resins. Union Carbide Corp. offers the broadest range of products. The primary quaUty control measure for these resins is the concentrated aqueous solution viscosity, which is related to molecular weight. Specifications for Polyox are summarized in Table 4. Additional product specifications frequendy include moisture content, particle size distribution, and residual catalyst by-product level. 

Table 4. Aqueous Solution Viscosity Specifications for Polyox Resins ...

Aqueous Solution Viscosity. A special solution preparation method is used for one type of measurement of aqueous solution viscosity (96). The appropriate amount of poly(ethylene oxide) resin is dispersed in 125 mL of anhydrous isopropyl alcohol by vigorous stirring. Because the resin is insoluble in anhydrous isopropyl alcohol, a slurry forms and the alcohol wets the resin particles. An appropriate amount of water is added and stirring is slowed to about 100 rpm to avoid shear degradation of the polymer. In Table 4, the nominal resin concentration reported is based on the amount of water present and ignores the isopropyl alcohol. 

Viscosity of Resin Solutions. The viscosity of coatings must be adjusted to the appHcation method to be used. It is usually between 50 and 1000 mPa-s(=cP), at the shear rate involved in the appHcation method used. The viscosity of the coating is controUed by the viscosity of the resin solution, which is in turn controUed mainly by the free volume (4). The factors controlling free volume are temperature, resin stmcture, solvent stmcture, concentration, and solvent-resin interactions. 

The temperature dependence of viscosity of resin solutions can be expressed by the WLE equation (eq. 3) where the reference temperature T is taken as the lowest temperature for which data ate avaUable (92,93). 

This lelationship has been shown to hold for a wide variety of coating resins and resin solutions over a wide range of concentrations. A simplification of equation 3 where T is the reference temperature is given in equation 2, which assumes that the viscosity at T is 10 Pa-s. 

Two classes of resol are generally distinguished, water-soluble resins prepared using caustic soda as catalyst, and spirit-soluble resins which are catalysed by addition of ammonia. The water-soluble resins are usually only partially dehydrated during manufacture to give an aqueous resin solution with a solids content of about 70%. The solution viscosity can critically affect the success in a given application. Water-soluble resols are used mainly for mechanical grade paper and cloth laminates and in decorative laminates. 

Viscosity. Solvent viscosity of resins is influenced by the concentration of resin, the softening point, the molecular weight distribution, the chemical composition of the resin, and the type of solvent. The higher the resin concentration, the higher the viscosity. For a given concentration, solution viscosity depends on the softening point of the resin (Fig. 22). 

Fig. 22. Solution viscosity of an aromatic Cg resin as a function of softening point. 50 wt% resin in white spirit with 5 wt% aromatics (see p. 63 in [25]).

The most widely used molecular weight characterization method has been GPC, which separates compounds based on hydrodynamic volume. State-of-the-art GPC instruments are equipped with a concentration detector (e.g., differential refractometer, UV, and/or IR) in combination with viscosity or light scattering. A viscosity detector provides in-line solution viscosity data at each elution volume, which in combination with a concentration measurement can be converted to specific viscosity. Since the polymer concentration at each elution volume is quite dilute, the specific viscosity is considered a reasonable approximation for the dilute solution s intrinsic viscosity. The plot of log[r]]M versus elution volume (where [) ] is the intrinsic viscosity) provides a universal calibration curve from which absolute molecular weights of a variety of polymers can be obtained. Unfortunately, many reported analyses for phenolic oligomers and resins are simply based on polystyrene standards and only provide relative molecular weights instead of absolute numbers. 

Transformations of data are also used to linearize relationships involving the variable in question. For example, the relationship between solids and viscosity of a resin solution may be sharply curved the relationship between solids and log viscosity is a straight line. 

---