Phenol plasticity

Phenolic plastics Group of plastics whose resins are derived from the condensation of phenols (e.g., phenol and cresol, with aldehydes). 

Phenol-formaldehyde (phenolic) plastics The chemical resistance is affected by the phenol used, cresols giving the best acid resistance whilst xylenols are often used to obtain the best alkali resistance. For chemical-resistant applications the fillers used in moulding powder and reinforcing material in laminates should be inorganic, e.g. asbestos or glass. The resins are usually dark in colour. 

There is supporting evidence in the literature for the validity of this method two cases in particular substantiate it. In one, tests were made on plastics heated in the pressure of air. Differential infrared spectroscopy was used to determine the chemical changes at three temperatures, in the functional groups of a TP acrylonitrile, and a variety of TS phenolic plastics. The technique uses a film of un-aged plastic in the reference beam and the aged sample in the sample beam. Thus, the difference between the reference and the aged sample is a measure of the chemical changes. 

Fig. 2-59 Surface heat balance of an ablating glass fiber reinforced phenolic plastic.

The laminated (RP) fabric, bonded with phenolic plastic incorporating antifriction ingredients and cured under heat and pressure, gives excellent service when properly applied in various applications. This group of bearings has a low coefficient of friction, antiscoring properties, and adequate strength for use in steel mills and other heavy-duty applications and is well established in the industry. 

The choice of materials from which to make the holder is important. Materials must be durable enough to ensure satisfactory completion of the test. It is good practice to select very resistant materials lor the test assembly. Insulating materials used are plastics, porcelain. Teflon, and glass. A phenolic plastic answers most purposes its principal limitations are unsuitability for use at temperatures over 150°C (300°F) and lack of adequate resistance to concentrated alkalies. 

Finally, the solubility parameter of the adhesive and the substrate must be close. Without getting too teehnieal, the solubility parameter is a rough estimate of polarity. The old saying like dissolves like can be extended to like bonds like. More aeeurately, the solubility parameter is the ealeulated potential energy of 1 em of material for eommon solvents. Polymers are assigned solubility parameters of solvents in which they are soluble. Table 19.3 lists solubility parameters for various solvents and polymers. As an example of how to use this table, butadiene-acrylonitrile rubber with 6= 9.5 bonds natural rubber (6= V.9-8.3) to phenolic plastics (6= 11.5). Note that its solubility parameter is between that of the two substrates. 

A number of lower volume chemicals can be obtained from wood hydrolysis. Furfural is formed from the hydrolysis of some polysaccharides to pentoses, followed by dehydration. This process is still used in the Soviet Union. Furfural is used in small amounts in some phenol plastics it is a small minor pesticide and an important commercial solvent. It can be converted into the common solvent tetrahydrofuran (THF) and an important solvent and intermediate in organic synthesis, furfuryl alcohol. 

The United States production of amino plastics was more than 3 billion pounds in 2001. The urea-formadehyde polymers account for slightly more than 85% of the total. The amino plastics are similar in properties to the phenolics but are clearer and colorless. They are also harder but have somewhat lower impact strength and resistance to heat and moisture. The melamine resins are better than the ureas in hardness and resistance to heat and moisture. The melamine and urea resins are rated for continuous use at temperatures of 130-150°C and 100°C, respectively. The general applications of the amino and phenolic plastics are the same but there are uses where the amino plastics are superior. The melamine resins find an important niche due to their combination of clarity and lack of color compared to the phenolics and their superior hardness and heat and moisture resistance compared to... 

The modulus of thermosets, such as phenolic plastics, is much greater than that of thermoplastics because of the high cross-link density present in thermosets. Since these network polymers are brittle, they are usually toughened by the addition of fibrous reinforcements. 

These thermoplastic resoles and novolacs are mixed with lubricants, pigments and additives, such as wood flour. The molding compound is converted to an infusible resin by heating it under pressure in a mold. A typical sequence of chemical reactions associated with the formation of this complex, three-dimensional polymer is shown in Figure 15.4. Typical properties of phenolic plastics are shown in Table 15.4. 

Phenolic plastics are more resistant to dilute oxidizing acids than furan plastics (see Sec. 15.6), but, unlike furan plastics, phenolic plastics are swollen... 

Table 15.4 Thermal and Physical Properties of Phenolic Plastics...

A typical cellulose-filled urea plastic has a tensile strength of 55,000 kPa, an Izod impact strength of 16 cm N/per centimeter of notch, and a coefficient of linear expansion of 3 X 10 3 cm/cm C. Urea-formaldehyde plastics have good electric insulating properties. Unlike phenolic plastics, urea plastics do not carbonize when an electric arc is placed on their surfaces. They also have a high dielectric strength. 

During theyear 1910, Baekeland produced less than 25 barrels of his phenolic plastic in a barn in Y on-kers, N. Y. Nowadays, fifty years later, close to 500 million pounds are produced yearly. During those same fifty years, more than a dozen other types of plastics were invented. 

Refs l)O.E.Burton, "A Study of the Action of Explosives on Metals Used in Ammunition , PATR 65 (May 1931) 2)D.W.Biklen, "Reaction of Tetryl with Phenolic Plastic Materials , PATR 1264 (March 1943) 3)W. H.Rinkenbach, "The Reactivity of Waxes with TNT and Amatol , PATR 1323 (Aug 1943) 4)L.H.Eriksen, "Action of Explosives on Metals Used in Ammunition , PATR... 

The use of aqueous ammonia in the preparation of wood fiber filled phenolic plastic molding has been investigated. In this case ammonia both plasticizes the wood filler and catalyzes the phenolic methylol condensation. With proper formulations and treatments, it is possible to maximize the quantity of wood fiber that can be used and minimize the resin without deterioration of properties of the molded product (61). 

Furfural is used in small amounts in some phenol plastics it is a small minor pesticide and an important commercial solvent, ft can be converted into the common solvent tetrahydrofuran and an important solvent and intermediate in organic synthesis, furfuryl alcohol. 

TABLE 15.13 Thermoset Plastics Market TABLE 15.15 Phenolic Plastics Markets... 

Phenol-Formaldehyde. Phenolic plastics were the first commercial synthetic plastics in 1908, and were the leading commodity plastic for 40 years, until the growth of vinyl and styrenic thermoplastics (Table 15.15). Now quite mature, they remain the second largest family of thermoset plastics. 

Compression molding was the major method of processing plastics worldwide during the first half of the last century because of the development of phenolic plastics (TSs) in 1909. By the 1940s this situation began to change with the development and use of thermoplastics (TPs) in injection molding (IM). 

The benzene-derived petrochemicals in Figure 4.15 are intermediate feedstocks for styrenic and phenolic plastics. In the styrenics chain, ethylbenzene is dehydrogenated to styrene, to be used as polystyrene monomer or as a copolymer with acrylonitrile and butadiene. In the phenolics chain, cumene is an intermediate for making phenol. Bisphenol A is the condensation product of two moles of phenol and acetone. Phenol and Bisphenol A are used to manufacture resins and polycarbonates. Phenol and cyclohexane are the starting materials for the manufacture of nylon 6. 

The specific surface of (phenolic) plastic foams was first measured by Schauer, Truxa and Spitzer in 1967 using the BET method They obtained a value of about 2 m /g. 

Shutov, F. A On an unkiwwn type of morphology of phenolic plastic foams. 8th All-Union Conference on High-Molecular Compounds, Kazan/USSR, 1973 (in Russian)... 

Fedodeev, V. I., Litvinova, T. A. State of water in phenolic plastic foams. Kolloidnyi Zhurnal 38. 756 (1976) (in Russian)... 

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