Amino Resins

Abstract

Amino resins are thermosetting polymers made by combining an aldehyde with a compound containing an amino (NH 2 ) group. Urea–formaldehyde accounts for over 80% of amino resins; melamine–formaldehyde accounts for most of the rest. The principal attractions of amino resins and plastics are water solubility before curing, colorlessness, excellent solvent resistance, outstanding hardness and abrasion resistance, and good heat resistance. Amino resins provide a wide variety of useful products. Adhesives, the largest single market, are used to make plywood, chipboard, and sawdust board. Other types are used to make laminated wood beams, parquet flooring, and for furniture assembly. Aminoplasts and other thermosetting plastics are molded by an automatic injection‐molding process similar to that used for thermoplastics. The process is best applied to relatively small moldings. The great advantage of injection molding is that it eliminates manual labor costs, thereby allowing amino resins to better compete with thermoplastics. The future for amino resins and plastics seems secure. New developments will probably be in the areas of highly specialized materials for treating textiles, paper, etc, and for use with other resins in the formulation of surface coatings. Most amino resins are based on the reaction of formaldehyde with urea or melamine. The first step in the formation of resins and plastics from formaldehyde and amino compounds is the addition of formaldehyde to introduce the hydroxymethyl group, known as methylolation or hydroxymethylation. The second step is a condensation reaction that involves the linking together of monomer units with the liberation of water to form a dimer, a polymer chain, or a vast network, usually referred to as methylene bridge formation, polymerization, resinification, or simply cure. Precise control of the course, speed, and extent of the reaction is essential for successful manufacture. Amino resins are usually made by a batch process. Both urea– and melamine–formaldehyde resins are of low toxicity. Melamine–formaldehyde resins may be used in paper which contacts aqueous and fatty foods. However, some mills are looking for alternatives.

Solar Freckles: Long-Term Photochromic Tattoos for Intradermal Ultraviolet Radiometry

“…Although leuco dyes are not considered to be nontoxic, they are sequestered within a shell of amino resin in our tattoo ink. While amino resins are known to be of low toxicity in bulk, most biocompatibility concerns regarding the corresponding nanocapsules focus on their remnant content of toxic formaldehyde. , Encouragingly, however, recent in vitro and in vivo investigations indicate low toxicity for amino-resin capsules in human fibroblast cultures and subdermal mouse implants, respectively.…”

Etherified Amino Resins with Tailor-Made Properties: A Holistic Approach via Polymerization

“…The reactions to R4 are butylation reactions that involve the combination of Bu with methylol derivatives . Unlike the addition step, where the reactor is maintained under neutral pH conditions, the butylation reactions have been shown to occur also in the condensation step under acidic conditions ,− to form methylene linkages (−CH 2 −) ,,,, of Z-condensates. …”

“…We note that both these formation reactions take place in the addition as well as the condensation steps; however, their rates are different. In the addition step (pH ≥ 7), the rates of formation of NB monomeric species dominate over butylation, whereas in the condensation step (pH ≈ 4), the rate of butylation dominates. ,,,, To model the kinetics of the condensation step, therefore, we recast the formation reactions for methylol species and the butylation reactions, already developed for the addition step, into P i , k a , b molecules using the definitions shown in Table . As shown, the k index of all the monomeric methylol species is 1 with different values of a , b , and i indices depending upon the location of the substituent group.…”

“…Moreover, most of the kinetics studies are usually focused around other amino resins like urea and melamine formaldehyde resins. The scarcity of available literature, especially for BUF resins, correlates well with the fact that most of the industrially manufactured BUF resins face quality control issues pertaining to higher end-point formaldehyde concentration − (see Supporting Information for details on the issues), hazy appearance, very high viscosity, , inappropriate percentage solids, , rapid decrease of glossiness in coating applications, and so forth. Our overall approach combines development of detailed reaction mechanism of BUF synthesis, prediction of resin properties via kinetics, and validation of our findings from our experiments.…”

“…For instance, in the addition step, the methylol reactions dominate over butylation reactions, whereas, in the condensation step, the butylation and polymerization reactions dominate over all the other reactions. Some amount of polymerization also occurs in the addition step through the formation of −CH 2 –O–CH 2 – linkages. ,, In the condensation step, however, the formation of −CH 2 – linkages ,, through polymerization is dominant.…”