Phenol-methanal

Methan- -0-(4-eblor-phenylester)-0-ethylester aus 4-Chlor-phenol, Methan-thiophosphonsaure-chlorid-O-ethylesler und Natriumpulver XII/1, 568... 

Phenol-methanal adhesives are currently used in about one tenth of all plywood and particle board. The binding technology represented by these Bakelite resins would be more widely applied if the reagents, particularly the phenol, were cheaper. Using lignin in place of phenol will sharply reduce the cost of the binder [26]. Unfortunately, lignin is not structurally equivalent to phenol. 

Adams and Schoenherr [29] achieved most of these benchmarks by formulating an adhesive consisting of a 40 wt % solids solution of kraft lignin in phenol-methanal-sodium hydroxide. This fluid had a viscosity of 10 Pa/s and thus was a very thick and energy-consuming adhesive to spread. However, when this binder was used in the manufacture of three ply panels of Douglas... 

Table 2 Kinetic Parameters for the Phenol-Methanal or Lignin-Methanal Reactions...

Modification of Phenol-Methanal Network Polymers Veronika Strehmel and Bemd Strehmel... 

Which of the following are usually used as network, erosslinked polymers Polypropylene, Polystyrene, Polyvinyl Chloride, Nylon, Epoxy Resins, Phenol-Methanal Polymers, or Polymeric Liquid Crystals ... 

Using lignin in the form obtained when it is extracted from the plant does not mean that the lignin exists in the application just the way it does when withdrawn from the plant. It means that the lignin enters the application process as a reagent and is often reacted with other components of the formulation as product is produced. This is definitely the case in the largest current application for unaltered lignin, its use as a replacement for phenol in phenol- methanal (formaldehyde) adhesives. 

Describe the use oflignin in the production of BakeUte polymers phenol-methanal, network polymers. 

Novolac resins produced by combination of phenol with methanal can also be used to produce epoxies. A typical structure formed by treating the phenol/methanal... 

A phenol-methanal network polymer is usually made fiom a prepolymer, often called a novolac. The synthesis of novolac type prepolymers occurs usually by the reaction of substituted phenols and methanal. This reaction takes places under elevated temperatures in the presence of acid catalysts, and is depicted in equation 1. 

The compound 1,3,5-trioxane is a colorless solid that can be used as a source of methanal or as a curing agent for phenolic resins. It is also reported that such cyclic formals have been recommended as curing agents for novolacs [32]. They are also used in low pressure, low viscosity laminating resins because of their excellent solvent action. Moreover, polyfmethyleneoxide) is used as a source for the manufacturing of phenolic resins [33]. Equation 7 demonstrates the closed relation between these three compounds. These reactions and equilibria are important for the manu ctuie of modified phenol methanal polymers. 

The rate of substitution correlates with the electron density at the aromatic nucleus. Several quantum mechanical calculations (CNDO [1] and AM 1 [52], where CNDO stands for Complete Neglect of Differential Overlap and AMI stands for Austin Model 1) show that the position of the methylol group on the ring influences electron density. The position reactivities determined by Freeman and Lewis [75] were later confirmed by Zsavitsas [76], who did extensive gas chromatography studies on the separation of the substituted phenols formed. Also, the pK -value of these compounds correlates closely with the kinetic data determined. Another group studied the influence of the metal ion in the metal hydroxide catalyst on kinetics and product stmcture [73]. The rate constants evaluated for the phenol methanal reaction under alkaline... 

Furthermore, the isocyanate can react with water to form an anune and carbon dioxide. Isocyanates are also added to phenol/methanal reactions to produce a physical modification of the product. Isocyanates react with water contained in or added to the reaction, to produce carbon dioxide and an amine. The CO gas foams the network product into a porous media [97]. 

Model reactions showed that the co-condensation reaction of melamine with phenolic resin occurs only by the reaction of phenolic methylol groups and the unsubstituted amino group at slightly acidic conditions. In contrast, a strong acidic or alkaline environment leads only to the formation of phenol methanal homocondensation products. The phenol reactivity in the reaction with methanal is low in comparison to the melamine reactivity in neutral and mildly acidic environments. An alkaline environment reverses this relative reactivity [99,100]. CiDsslinking of the products obtained by the reaction of 4-methylphenol and melamine with methanal appears to produce an interpenetrating polymer network [101]. 

In addition, modified phenol methanal polymers of phenoxy ethanoic acids are useful as crosslinldng agents for epoxy resins. The monomer is formed by reacting 2-chloroethanoic acid with a phenol to give the corresponding jiienoxy ethanoic acid. 

In a second step, the phenoxy ethanoic add reacts with methanal in the presence of hydrochloric acid, yielding a modified phenol methanal oligomer with an average molecular wdght between 600-800 g mole, as determined by vapor-pressure osmometry. 

The largest current application for lignin as extracted from the plant is as a replacement for phenol in phenol-methanal... 

The step polymers that are treated in this text are cellulose, starch, vegetable gums, nylon, epoxy resins, phenol- methanal network polymers, and most polymeric liquid crystals. The reactions which form these polymers are summarized in Table 3. For the synthetic polymers of Table 3, there are often several reactions which produce the polymer. Only one representative reaction is shown in the Table. Note that all of these reactions involve two functional groups on different molecules reacting to form another link and ultimately thereby form a polymer. 

Precipitate can also form fiom a step reaction. Precipitation polymerizations of prepolymers to form crosslinked, thermoset polymers is a very common commercial reaction of the epoxy resins and phenol-methanal, network polymers covered in this book. These reactions work best when the reaction is slow, mildly exothermic, and undergoes a viscous to solid transformation late in the synthesis. 

A very common reaction during processing is the polymerization or crosslinking reaction of thermoset materials to form a final polymeric product. This is a common, heat- induced reaction in the epoxy resins and phenol/methanal polymers discussed in this book. It is also common in mbbers undergoing vulcanization and in isocyanates undergoing transformation to urethanes. These reactions form molecules structurally similar to the crosslinked hydrocarbon shown in Figure 4. 

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