Condensation Polymeriation Product
Phenolic resin designate a group of synthetic resins that are probably the most varied and versatile that we know. That may be made from almost any phenolic body and an aldehyde. Phenol Formaldehyde resins constitute by far the greatest proportion, but phenol furfural, resorcinol formaldehyde, and similar resins are also included in this group. The product obtained depends primarily on the concentration and chemical nature of the reactants, the nature and concentration of the catalyst used, the temperature and reaction time, and the modifying agents, fillers, and extenders. The initial reaction between the phenol and a mixture of cresols with formaldehyde, using an alkaline catalyst, produces benzyl alcohols.
C6H5OH + CH2O ------► o- or p- C6H4OH . CH2OH
Simultaneously, additional formaldehyde may react to produce both di-and trimethylol phenol. These alcohol continue to condense and polymerize and polymerize with each other rapidly and almost violently.
These resins, when classified according to the nature of the reaction during their production, are one of two fundamental types.
The warm, dehydrated, viscose resin is run out of the kettle into shallow trays and allowed to cool and harden. The cooled, brittle resin is crushed and finely ground and becomes the resin binder for molding phenolic resins.
Phenolic molding compounds are molded primarily in compression and transfer molds. The powder, mixed with filler, lubricant and plasticizer, is further reacted on steam heated, rools, cooled and ground. In compression molding the powder is placed in hardened steel molds at temperature of 132 to 182oC and at pressure from 13.8 to 35 MPa.
In transfer molding the thermosetting material is subjected to heat and pressure in an outside chamber, from which it is forced by means of a plunger into a closed mold where curing takes place.
C6H5OH + CH2O ------► o- or p- C6H4OH . CH2OH
Simultaneously, additional formaldehyde may react to produce both di-and trimethylol phenol. These alcohol continue to condense and polymerize and polymerize with each other rapidly and almost violently.
These resins, when classified according to the nature of the reaction during their production, are one of two fundamental types.
- One-step resins. In these, all the necessary reactants (phenol, formaldehyde, catalyst) required to produce a thermosetting resin are charged into the resin kettle in the proper proportions and react together. An alkaline catalyst is used. The resin, as discharge from the kettle, is termosetting or heat reactive and required only further heating to complete the reaction to an infusible, insoluble state.
- Two step resins. Only part of the necessary formaldehyde is added in the kettle is making these resins, and an acid catalyst is used. They are permanently fusible or thermoplastic when discharged from the kettle but react with aditional formaldehyde to produce a thermosetting resin. This additional formaldehyde is furnished by "hexa" (hexamethylenetramine). Both one and two step resin are used separately or in combination in commercial molding materials. Both types are believed to polymerize to similar end products.
The warm, dehydrated, viscose resin is run out of the kettle into shallow trays and allowed to cool and harden. The cooled, brittle resin is crushed and finely ground and becomes the resin binder for molding phenolic resins.
Phenolic molding compounds are molded primarily in compression and transfer molds. The powder, mixed with filler, lubricant and plasticizer, is further reacted on steam heated, rools, cooled and ground. In compression molding the powder is placed in hardened steel molds at temperature of 132 to 182oC and at pressure from 13.8 to 35 MPa.
In transfer molding the thermosetting material is subjected to heat and pressure in an outside chamber, from which it is forced by means of a plunger into a closed mold where curing takes place.
Wednesday, July 7, 2010
Polymer Definition
Polymer define as a large molecule built up by the repetition of small, simple chemical units. Polymers are formed by polymerization process. In some cases the repetition is linear, much as chain is built up from its links. In other cases the chains are branched or interconnected to three dimensional networks. The repeat units of the polymer is usually equivalent or nearly equivalent to the monomer, or starting material from which the polymer is formed. Thus the repeat unit of polyvinyl chloride is -CH2CHCl -; its monomer is vinyl chloride, CH2=CHC.
The length of the of the polymer chain is specified by the number of repeat units in the chain. This is called the degree of polymerization (DP). The molecular weight of the polymer is the product of the molecular weight of the repeat unit and the DP. Using poly (vinyl chloride) as an example, a polymer of DP 1000 has a molecular weight of 63 x 1000 = 63,000. Most high polymers useful for plastics, rubbers, of fibers have molecular weights between 10,000 and 1,000,000.
Unlike many product whose structure and reactions were well known before their industrial application, some polymers were produced on an industrial scale long before their chemistry of physics was studied. Empiricism in recipes, processes, and control tests was usual.
Gradually the study of polymer properties began. Almost all were first called anomalous because they were so different from the properties of low molecular weight compounds. It was soon realized, however, that polymer molecules are many times larger than those of ordinary substances. The presumably anomalous properties of polymers were shown to be normal for such materials, as the consequences of their size were included in the theoretical treatments of their properties.
The length of the of the polymer chain is specified by the number of repeat units in the chain. This is called the degree of polymerization (DP). The molecular weight of the polymer is the product of the molecular weight of the repeat unit and the DP. Using poly (vinyl chloride) as an example, a polymer of DP 1000 has a molecular weight of 63 x 1000 = 63,000. Most high polymers useful for plastics, rubbers, of fibers have molecular weights between 10,000 and 1,000,000.
Unlike many product whose structure and reactions were well known before their industrial application, some polymers were produced on an industrial scale long before their chemistry of physics was studied. Empiricism in recipes, processes, and control tests was usual.
Gradually the study of polymer properties began. Almost all were first called anomalous because they were so different from the properties of low molecular weight compounds. It was soon realized, however, that polymer molecules are many times larger than those of ordinary substances. The presumably anomalous properties of polymers were shown to be normal for such materials, as the consequences of their size were included in the theoretical treatments of their properties.
