Methylol content

Reaction of melamine with neutralised formaldehyde at about 80-100°C leads to the production of mixture of water-soluble methylolmelamines. These hydroxymethyl derivatives can possess up to six methylol groups per molecule and include trimethylolmelamine and hexamethylolmelamine (Figure 24.8) The methylol content of the mixture will depend on the melamine formaldehyde ratio and on the reaction conditions. 

Very recently Papa and Critchfield El9 7 described the prepara tion of foams based on a resole resin containing a high ortho-methylol content and a blend of quasi prepolymer of tolylene diiso cyanate, a phosphorus-containing polyol and polymeric isocyanate containing a minor portion of tris-(2-chloro-ethyl) phosphate. 

The properties of the resultant butylated MF resin are governed bv the methylol content, degree of butylation and molecular weight as shown in Table 4-1 "... 

Phenolic resin substantially increases open time and peel strength of the formulation (80). For example, higher methylol and methylene ether contents of the resin improves peel strength and elevated temperature resistance. Adhesive properties are also influenced by the molecular weight distribution of the phenoHc low molecular weight reduces adhesion (82). 

Curing Catalysts for A Methylol Agents. Many acid-type catalysts have been used in finishing formulations to produce a durable press finish. Catalyst selection must take into consideration not only achievement of the desked chemical reaction, but also such secondary effects as influence on dyes, effluent standards, formaldehyde release, discoloration of fabric, chlorine retention, and formation of odors. In much of the industry, the chemical suppher specifies a catalyst for the agent so the exact content of the catalyst may not be known by the finisher. 

Several factors were utilized in bringing formaldehyde release down. In particular, resin manufacturer executed more careful control of variables such as pH, formaldehyde content, and control of methylolation. There has also been a progressive decrease in the resin content of pad baths. The common practice of applying the same level of resin to a 50% cotton—50% polyester fabric as to a 100% cotton fabric was demonstrated to be unnecessary and counter productive (89). Smooth-dry performance can be enhanced by using additives such as polyacrylates, polyurethanes, or siUcones without affecting formaldehyde release. 

One might expect that dehydration of a methylol-aducted protein would lead to the formation of Schiff bases, which might be expected to serve as highly reactive groups capable of undergoing further reactions—particularly cross-linking reactions, as the water content of the surrounding solution is reduced. As yet, however, there is little direct evidence that such intermediates are... 

Gel lacquer formulations used for dip coating. The early catapult propellants were inhibited by dipping in a lacquer consisting of toluene 80p, acetone 20p and a total solids content of 15-18%. The grains were dipped twice and had a cured inhibitor thickness of 20 to 30 mils. As the size of experimental slotted tube catapults increased, coatings of 100 mils were required. This necessitated an increase of the solid content to 25-27%. As this soln was too viscous some methylol was incorporated in solvent formulation. In order to improve the room temp gelling characteristics an aliphatic hydrocarbon was added... 

The analyses can be carried out in the presence of IV-methylol groups. On fabric, the formaldehyde bisulfite compound is decomposed by excess sodium carbonate and the liberated sulfite is titrated with 0.1- or 0.01-IV iodine solution (76). Commercial fabrics are seldom washed and dried before being used, and the free formaldehyde content maybe between 50 and several hundred ppm, depending on finishing and storage conditions. 

Fig. 12. Kinetics of drying and heating granulated aminoplasts with different agglomerating additives (samples 1 through 4) and changes in content of methylol groups...

As the bound moisture is removed and the material is heated to a temperature of 58 to 62 °C in the falling-speed drying section, the content of methylol groups in batches Nos. 1,2, and 3 slightly increases, which may be due to the effect of agglomerating additives. 

In batch No. 4 of the granulated material, the content of methylol groups remains essentially constant throughout the drying and cooling processes. 

On the other hand, it has been experimentally proved that, at the temperature of the air coming out of the second zone being in excess of 80 °C, the moisture content of the granulated material is below 1.2% by mass, while the content of methylol groups is less than 8.8 %. With such characteristics, the material may not flow and, thus, cannot be processed into articles. 

Hence, the temperature of the material in the second zone of the drier should be maintained within, 58-62 °C with a view to obtaining quality granulated material having a residual moisture content of 1.5 to 3.5% (which corresponds to 8.8-9.2% content of methylol groups in the given material). The temperature of the air coming out of the second zone is within 68-75 °C. 

Table 11 gives experimental data relating to the content of methylol groups in granulated aminoplast versus temperature T2. 

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