Polymerization melamine resins from

Another use of urea is for resins, which are used in numerous applications including plastics, adhesives, moldings, laminates, plywood, particleboard, textiles, and coatings. Resins are organic liquid substances exuded from plants that harden on exposure to air. The term now includes numerous synthetically produced resins. Urea resins are thermosetting, which means they harden when heated, often with the aid of a catalyst. The polymerization of urea and formaldehyde produces urea-formaldehyde resins, which is the second most abundant use of urea. Urea is dehydrated to melamine, which, when combined with formaldehyde, produces melamine-formaldehyde resins (Figure 96.2). Melamine resins tend to be harder and more heat-resistant than urea-formaldehyde resins. Melamine received widespread attention as the primary pet food and animal feed contaminant causing numerous cat and dog deaths in early... 

Melamine resins are used from this group of thermosets for the manufacture of food contact materials. The melamine can be used in mixtures with urea and in some applications with phenol (< 1 %). The polymerization process is catalyzed in the presence of organic acids (e.g. acetic acid, lactic acid, tartaric acid, citric acid), hydrochloric acid, sulfuric acid, phosphoric acid, sodium and potassium hydroxide, ammonia, calcium or magnesium hydroxide as well as salts of these substances (total < 1 %) which cause the elimination of water and lead to a cured resin system. Stearic acid can be used as a lubricant as can zinc, calcium and magnesium salts, esters of montanic acid with ethandiol and 1,3-butandiol, as well as silicone oil (total < 1 %). 

There are many examples in the literature of the structural characterization of polymeric systems by FD-MS. Some of these will be briefly mentioned here. Saito and coworkers in Japan have studied a number of polymers by FD-MS. FD spectra were used to identify various poly(ethylene glycol) and poly(pro-pylene glycol) initiators (water, ethyleneimine, glycerol, sorbitol, sucrose). Structures of bisphenol A-based epoxy resins were elucidated. The degree of methylation in methylol melamine resins was assessed. Various novalak resins (made from phenol, alkylphenols, and epoxidized phenols) were characterized. Styrene polymerized with various initiators and chain transfer agents was studied in some cases deuterium labeling was used to help... 

Ammonia is used in the fibers and plastic industry as the source of nitrogen for the production of caprolactam, the monomer for nylon 6. Oxidation of propylene with ammonia gives acrylonitrile (qv), used for the manufacture of acryHc fibers, resins, and elastomers. Hexamethylenetetramine (HMTA), produced from ammonia and formaldehyde, is used in the manufacture of phenoHc thermosetting resins (see Phenolic resins). Toluene 2,4-cHisocyanate (TDI), employed in the production of polyurethane foam, indirectly consumes ammonia because nitric acid is a raw material in the TDI manufacturing process (see Amines Isocyanates). Urea, which is produced from ammonia, is used in the manufacture of urea—formaldehyde synthetic resins (see Amino resins). Melamine is produced by polymerization of dicyanodiamine and high pressure, high temperature pyrolysis of urea, both in the presence of ammonia (see Cyanamides). 

Seventy years ago, nearly all resources for the production of commodities and many technical products were materials derived from natural textiles. Textiles, ropes, canvas, and paper were made of local natural fibers, such as flax and hemp. Some of them are still used today. In 1908, the first composite materials were applied for the fabrication of big quantities of sheets, tubes, and pipes in electrotechnical usage (paper or cotton as reinforcement in sheets made of phenol- or melamine-formaldehyde resins). In 1896, for example, airplane seats and fuel tanks were made of natural fibers with a small content of polymeric binders [1]. 

In the early 1930 s, a second type of resin prepared from formaldehyde was introduced to the market—namely, urea-formaldehyde resins. A few years later, melamine-formaldehyde resins also appeared. The same basic process is employed in polymerization of all these resins it consists of the catalyzed reaction of formaldehyde with the second ingredient—phenol, urea, or melamine—to evolve water and produce three-dimensional, cross-linked thermosetting polymers. 

It also can be produced directly from natural gas, methane, and other aliphatic hydrocarbons, but this process yields mixtures of various oxygenated materials. Because both gaseous and liquid formaldehyde readily polymerize at room temperature, formaldehyde is not available in pure form. It is sold instead as a 37 percent solution in water, or in the polymeric form as paraformaldehyde [HO(CH20)nH], where n is between 8 and 50, or as trioxane (CH20)3. The greatest end use for formaldehyde is in the field of synthetic resins, either as a homopolymer or as a copolymer with phenol, urea, or melamine. It also is reacted with acetaldehyde to produce pentaerythritol [C(CH2OH)4], which finds use in polyester resins. Two smaller-volume uses are in urea-formaldehyde fertilizers and in hexamethylenetetramine, the latter being formed by condensation with ammonia. 

Mesoporous melamine-formaldehyde and phenolic-formaldehyde resins were synthesized in the process of polymerization in the presence of fumed silica as an inorganic template. The surface and structural characteristics of the obtained sorbents were investigated using XPS technique and sorption from gas phase. The parameters characterizing porous structure of the synthesized resins in a dry state were determined from nitrogen adsorption/desorption isotherms. The sorption processes of benzene and water vapor accompanied by simultaneous swelling of both polymers were also studied. 

Data of low-temperature nitrogen adsorption were used to evaluate the parameters characterizing the pore structure of the obtained polymeric materials in dry state. The BET specific surface area, Sbet, and the total pore volume, V, were estimated by applying the standard methods Sbet from the linear BET plots and F/ from adsorption at relative pressure p/po=0.975) [7]. The mesopore structure was characterized by the distribution function of mesopore volume calculated by the Barret-Joyner-Halenda (BJH) method [27]. In Table 2 the values of these parameters are given for both synthesized polymers. The melamine-formaldehyde resin MEA has a more developed pore structure (5 B 7=220mVg, F,=0.45cm /g) and narrower mesopores (D=7.3nm) in comparison to the phenolic-formaldehyde polymer PHD. 

Thermosetting phenolic resins form a separate class of polymers containing aromatic rings and aliphatic carbon groups in the polymeric network. These resins are formed from the reaction of phenol (or substituted phenols) with formaldehyde. The fully crosslinked macromolecule is insoluble and infusible. Other thermosetting resins are known in practice, some derived from the reaction of melamine or of urea with formaldehyde. Because these have a different chemical structure, containing nitrogen, they are included in a different class (see Section 15.3). 

Acid catalysts n. Acids which may be either organic or inorganic, or salts from these acids which exhibit acidic characteristics. They are used to promote or accelerate chemical reactions, and find special applications in the manufacture and subsequent hardening of synthetic resins. Acid catalysts have been employed in the manufacture of polymerized drying oils, coumarone, urea, phenol-and melamine-formaldehyde resins, and in the cold-setting of compositions containing the last three named resins. Odian GC... 

Castor oil fatty acids have one double bond per molecule, whereas hydrogenated castor oil fatty acids are saturated consequently, the oils, or alkyds derived from them, are not film forming under autooxidation conditions. However, alkyds prepared from these oils are widely used as polymeric plasticizers for other filmforming resins the two most important types are cellulose nitrate and melamine-formaldehyde condensates. 

Because of the importance of epoxy resins, it is not surprising that they received early attention from researchers using the soUd-state NMR techitique [43,44]. A number of other crosslinked systems have been investigated, including acetylene-terminated polyimide resins [45,46], poly(p-phenylene) [47], 2-propenenitrile polymer with 1,3-butadiene and ethenylbenzene (ABS) resins [48], furfuryl alcohol resins [49], phenolic resins [50], acrylic resins [51,52], melamine-formaldehyde resins [53], polynuclear hydroxymethyl phenol (resol)-formaldehyde resins [54], and plasma-polymerized materials [55]. 

The possibility of making cross-linkable latexes by emulsion polymerization in the presence of etherified melamine-formaldehyde resins has been demonstrated by Jones et al. [104]. Dynamic mechanical measurements showed that films from slightly or moderately cross-linked particles behave like homogeneous networks in the linear viscoelastic range [105]. Melamine formaldehyde cross-linkers have been... 

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