phenol-formaldehyde resin | chemical compound | Britannica.com Phenol-formaldehyde resin colloid Phenol-formaldehyde resin, also called phenolic resin, any of a number of synthetic resins made by reacting phenol (an aromatic alcohol derived from benzene ) with formaldehyde (a reactive gas derived from methane ). Phenol-formaldehyde resins were the first completely synthetic polymers to be commercialized. In the first decades of the 20th century, Bakelite , a trademarked phenolic plastic , revolutionized the market for molded and laminated parts for use in electrical equipment. Phenolics are still very important industrial polymers, though their most common use today is in adhesives for the bonding of plywood and other structural wood products. The chemical composition of phenol and formaldehyde and their combination into networks of permanently interlinked large molecules are explained briefly in the article aldehyde condensation polymer . Phenol-formaldehyde resins are heat-resistant and waterproof, though somewhat brittle. They are … Encyclopædia Britannica, Inc. In industrial practice, there are two basic methods for making the polymer into useful resins.

In one method, an excess of formaldehyde is reacted with phenol in the presence of a base catalyst in water solution to yield a low-molecular-weight prepolymer called a resole. The resole, frequently in liquid form or solution, can be cured to a solid thermosetting network polymer by, for instance, sandwiching it between layers of wood veneer and then heating the assembly under pressure to form a plywood. The other method involves reacting formaldehyde with an excess of phenol, using an acid catalyst. This process produces a solid prepolymer called a novolac (or novolak), which resembles the final polymer except that it is of much lower molecular weight and is still thermoplastic (that is, it can be softened by reheating without undergoing chemical decomposition). Curing can be accomplished by grinding the novolac to a powder, mixing it with fillers such as wood flour, minerals, or glass fibres, and then heating the mixture in a pressurized mold. In order to be cured to a thermosetting resin, novolacs require the addition of more formaldehyde or, more commonly, of compounds that decompose into formaldehyde upon heating.

Phenol-formaldehyde resins make excellent wood adhesives for plywood and particleboard because they form chemical bonds with the phenol-like lignin component of wood. They are especially desirable for exterior plywood, owing to their good moisture resistance. Phenolic resins, invariably reinforced with fibres or flakes, are also molded into insulating and heat-resistant objects such as appliance handles, distributor caps, and brake linings. Learn More in these related articles: Phenolic Materials Buying Guide Phenolic Materials Buying Guide Phenolic , a composite resin material made from a combination of phenol and aldehyde, is a rigid material used in a wide range of consumer fitting applications. Because phenolic is easy to manufacture and relatively affordable, it is also frequently used as an acrylic alternative, as a binder, and as an insulator. Phenolic’s characteristics and properties vary depending on the type of aldehyde used, although formaldehyde is most common. To transform the aldehyde and phenol mixture into a phenolic sheet, paper, glass or cloth is impregnated with the synthetic mixture, then layered and pressed together using heat and pressure.

As a result of the heat and pressure, polymerization occurs and the resin reacts with the paper, cloth, or glass to produce a hard, dense sheet of phenolic plastic. Types of Phenolic Material , profiles, slabs, specific shapes and blocks. It is also available as foam, which is typically used in insulation applications. For information about the various compositions of phenolic foam and phenolic hybrids, consult article: . Basic types of phenolic resin include novolacs and resols, which are distinguished from one another by their aldehyde to phenol ratios. Typically, if the aldehyde to phenol ratio is 1 or greater, as is the case with resols, the phenol will cross-link and harden. However, if the aldehyde ratio is less than one, as is the case with novolacs, an additive is needed to induce hardening. With novolacs, hexamine is often added to assist in cross-linking. Other Considerations Phenolic is known by several trade names. Common names include: Bakelite: Made from wood flour and phenolic resin, this kind of plastic is often used as an electrical insulator and in other non-conductive heat-resistant applications.

Novotext or Tufnol:This type of phenolic resin is reinforced with cotton or linen fibers and is often used in applications as a liner in loaded bearings, because it has low-friction. A similar product, Paxolin, is made from phenolic resin and paper. Other Plastics & Rubber Guides Phenol-formaldehyde resin In Depth Tutorials and Information Phenol-formaldehyde resin This is a synthetic resin, commonly known as phenolic, made by the reaction of phenol and formaldehyde, and employed as a molding material for the making of mechanical and electrical parts. It was the earliest type of hard, thermoset synthetic resins, and its favorable combination of strength, chemical resistance, electrical properties, glossy finish, and nonstrategic abundance of low-cost raw materials has maintained the resin, with its many modifications and variations, as one of the most widely employed groups of plastics for a variety of products. The resins are also used for laminating, coatings, and casting resins. Phenolic resins are used most extensively as thermosetting plastic materials, as there are only a few uses as thermoplastics. The polymer is composed of carbon, hydrogen, oxygen, and sometimes nitrogen.

Its molecular weight varies from a very low value during its early state of formation to almost infinity in its final state of cure. The chemical configuration, in the ther-moset state, is usually represented by a three-dimensional network in which the phenolic nuclei are linked by methylene groups. The completely cross-linked network requires three methylene groups to two phenolic groups. A lesser degree of cross-linking is attainable either by varying the proportions of the ingredients or by blocking some of the reactive positions of the phenolic nucleus by other groups, such as methyl, butyl, etc. Reactivity can be enhanced by increasing the hydroxyl groups on the phenolic nuclei, for example, by the use of resorcinol. Characteristics The outstanding characteristics of phenolics are good electrical properties, very rigid set, good tensile strength, excellent heat resistance, good rigidity at elevated temperature, good aging properties; also, good resistance to water, organic solvents, weak bases, and weak acids. All these characteristics are coupled with relatively low cost. Phenolics are used in applications that differ widely in nature.

For example, wood is impregnated to make "impreg" and "compreg"; paper is treated to make battery separators and oil and air filters; specific chemical radicals can be added to the molecule to make an ion-exchange material. Phenolics are also widely used in protective coating. The hundreds of different phenolic molding compounds can be divided into six groups on the basis of major performance characteristics. General-purpose phenolics are low-cost compounds with fillers such as wood flour and flock, and are formulated for noncritical functional requirements. They provide a balance of moderately good mechanical and electrical properties, and are generally suitable in temperatures up to 149°C. Impact-resistant grades are higher in cost. They are designed for use in electrical and structural components subject to impact loads. The fillers are usually paper, chopped fabric, or glass fibers. Electrical grades, with mineral fillers, have high electrical resistivity plus good arc resistance, and they retain their resistivity under high-temperature and high-humidity conditions. Heat-resistant grades are usually mineral- or glass-filled compounds that retain their mechanical properties in the 190 to 260°C temperature range.

Special-purpose grades are formulated for service applications requiring exceptional resistance to chemicals or water, or combinations of conditions such as impact loading and a chemical environment. The chemical-resistant grades, for example, are inert to most common solvents and weak acids, and their alkali resistance is good. Nonbleeding grades are compounded specially for use in container closures and for cosmetic cases. Fillers Proper balance of fillers is important, because too large a quantity may produce brittleness. Organic fillers absorb the resin and tend to brit-tleness and reduced flexural strength, although organic fibers and fabrics generally give high impact strength. Wood flour is the most usual filler for general-service products, but prepared compounds may have mineral powders, mica, asbestos, organic fibers, or macerated fabrics, or mixtures of organic and mineral materials. Bakelite was the original name for phenol plastics, but trade names now usually cover a range of different plastics, and the types and grades are designated by numbers. The specific gravity of filled phenol plastics may be as high as 1.70. The natural color is amber, and, as the resin tends to discolor, it is usually pigmented with dark colors.

Normal phenol resin cures to single-carbon methylene groups between the phenolic groups, and the molded part tends to be brittle. Thus, many of the innumerable variations of phenol are now used to produce the resins, and modern phenol resins may also be blended or cross-linked with other resins to give higher mechanical and electrical characteristics. Furfural is frequently blended with the formaldehyde to give better flow, lower specific gravity, and reduced cost. The alkylated phenols give higher physical properties. Phenol resins may also be cast and then hardened by heating. The cast resins usually have a higher percentage of formaldehyde and do not have fillers. They are poured in syrupy state in lead molds and hardened in a slow oven. Some of the uses for phenolic resins are for making precisely molded articles, such as telephone parts, for manufacturing strong and durable laminated boards, or for impregnating fabrics, wood, or paper. Phenolic resins are also widely used as adhesives, as the binder for grinding wheels, as thermal insulation panels, as ion-exchange resins, and in paints and varnishes.

Molding Compounds The largest single use for phenolic resins is in molding compounds. To make these products, either one- or two-stage resins are compounded with fillers, lubricants, dyes, plasticizers, etc. Wood flour is used as an inexpensive reinforcing agent in the general-purpose type of compounds. Cotton flock, chopped fabric, and sisal and glass fibers are used to improve strength characteristics; mineral fillers such as asbestos and mica are used where improvements in dimensional stability, heat resistance, or electrical properties are desired. The compounds are usually produced in granular, macerated, or nodular forms, depending on type of filler used. Since the color of the base resin is not stable to light, molding compounds are commonly produced only in dark colors such as black and brown. Molding compounds are usually processed in hardened steel molds and molds can be designed to operate using the compression, transfer, or plunger-molding techniques, depending on the design of the article to be fabricated. Molded parts can be drilled, tapped, or machined. About one third of all phenolic resins produced is processed into parts by molding. Compression and transfer molding are the principal processes used but they can also be extruded and injection molded.

Molded phenolic parts are used in bottle caps, automotive ignition and engine components, electrical wiring devices, washing machine agitators, pump impellers, electronic tubes and components, utensil handles, and a multitude of other products. Adhesives The thermosetting nature and good water- and fungus-resistant qualities of phenolic resins make them ideal for adhesive applications. Almost all exterior-grade plywood is phenolic resin bonded. This constitutes the second largest market for phenolics. The essential ingredient in many metal-to-metal, and metal-to-plastic adhesives is a phenolic resin. One-step phenol-formaldehyde resins are used predominantly for hot-pressed plywood. Special resor-cin-formaldehyde resins curing at room temperature are employed for fabricating laminated timber. Laminates The third largest use for phenolic resins is in the manufacture of laminated materials. Many variations of paper, from cheap kraft to high-quality alpha cellulose, in addition to asbestos, cotton, linen, nylon, and glass fabrics are the most commonly used reinforcing filler sheets.

The laminate is formed by combining under heat 177°C and pressure 3.4 to 14 MPa multiple layers of the various reinforcing sheet; after saturation with phenolic resin, generally of the one-step type dissolved in alcohol. Paper laminates are used most extensively in the electrical and decorative fields. A large number of the laminates for the electrical industry are of the punching grade, making it possible to fabricate all kinds of small parts in a punch press. The laminate used for decorative purposes usually contains a surface sheet of melamine resin-treated paper for providing unlimited color or design configurations. Other fillers are used for special applications where superior dimensional stability, or water, fire, or chemical resistance, or extra strength is required. Casting Resins Plastic parts can also be manufactured by pouring resin into molds and heat-curing without pressure. Two basic grades of casting resins are manufactured commercially. Both are of the one-stage type and are cured under neutral to strongly acidic conditions depending on the application. The first grade is manufactured for its variegated color and artistic possibilities and is used primarily in the cutlery and decorative field.

Since this type of cast material is noted for ease of machining, it is well adapted for small production runs or where machined prototypes are desired. The second grade of casting resins includes all those modified by fillers and reinforcing agents. Designed primarily to have low-shrinkage characteristics during cure, they are usually set with a strong acid catalyst to obtain a low temperature set. Uses include containers, jigs, fixtures, and metal-forming dies. Bonding Agents Phenolic resins are noted for their excellent bond strength characteristics under elevated temperature conditions, and thus are used in such applications as thermal and acoustical insulation, grinding wheels, coated abrasives, brake linings, and clutch facings. Glass wool insulation is manufactured by spraying water-soluble one-stage resins on the glass fibers as they are formed. Heat given off by the fibers as they cool is sufficient to set the resin. Where organic fibers are used, finely pulverized, single-stage resins are distributed between the fibers, either by a mixing or a dusting operation, followed by an oven treatment. Grinding wheels bonded with phenolic resin are commonly known as resinoid-bonded wheels.

By combining a liquid single-stage resin and a powdered two-stage resin, the material can be evenly distributed with abrasive grit and fillers so that the mixture can be pressed into wheels and baked in ovens. Some wheels are also hot-pressed and cured directly in a press. Resinoid-bonded wheels are used primarily where the application requires a bond of exceptional strength such as in cut-off and snagging wheels. Coated abrasives are manufactured by bonding abrasive grit to paper, fabric, or fiber-board by means of phenolic resins of the liquid one-stage type. Sander disks and belts are common applications. Brake linings and clutch facings are made by bonding asbestos, fillers, metal shavings, and friction modifiers with phenolic resin, usually performed by a mixing, forming, and baking operation. Most resins for these applications are specially formulated, but simple two-stage resins are sometimes used. Formulation for each friction lining or clutch face must be determined carefully. Wood composition products of all descriptions are manufactured by hot-pressing sawdust, wood chips, or wood flour containing 8 to 20% resin. Two-step resins are most frequently used in composition boards.

One-step resins are employed for special applications where the yellow color or the slight ammonia odor of two-step resins is undesirable. Foundry Use A relatively new application holding great promise for phenolic resins is in the shell mold process for the foundry industry. The basic principle involves binding sand grains with resin. The process is equally well adapted to making cores and is satisfactory for practically all metals, including magnesium and high-chrome alloys. The process has many intriguing possibilities. Molds thus made can be reproduced in exact composition, detail, and size; they are rigid and, having no affinity for water, can be racked and stored indefinitely, with or without cores. Castings from these molds have excellent surface finish and detail and can be held to close dimensional tolerances. The process can be completely mechanized, yields more castings per ton of melt than sand casting, simplifies cleaning of castings, minimizes problems with sand control and handling, and is a relatively clean operation. It is revolutionizing the foundry industry. Consumption of resin in the foundry industry has grown rapidly, and conceivably this could become the largest single outlet for phe-nolics.

However, markets for phenolic resins in plywood adhesive, insulation, and wood composition board applications have also expanded. Conservation Register: care and conservation of plastic materials, Plastic conservation, Bakelite conservation, Rubber conservation Contact Us Care and conservation of plastic materials Plastics and rubbers form a significant part of our cultural heritage. They are found not only in art, historic and technological collections, they are also among the ethnographic materials of the twentieth century. Objects made from these materials range in diversity from radios, clocks, fountain pens, jewellery and hair accessories, to plastic robots and dolls, and all are becoming increasingly collectible. Plastic is a generic term covering all types of synthetic materials. These different types of materials may differ dramatically from each other with respect to their care requirements. It is, therefore, most important to try to identify the type of plastic from which the object is manufactured.

Plastics are commonly classified on the basis of their origin: Natural - These include amber, horn, wax, shellac, rubber Semi-synthetics - These are chemically modified natural materials like: Hardened rubber (Ebonite, Vulcanite), casein (Erinoid, Galalith), which is based on milk protein, cellulose nitrate and cellulose acetate, both based on cellulose. Synthetics - These may be further sub-divided into: Early synthetics: phenol formaldehyde (Bakelite), urea formaldehyde (Beatl, Beetle); The ‘poly’ era: polyvinyl chloride (PVC), polymethyl methacrylate(Perspex, Lucite), polyethylene (Polythene), polyamide (Nylon), polyacrylonitrile (Courtelle, Orlon), polyurethane, polycarbonate, polyester, etc. Identification of plastics Although the unambiguous identification of a plastic material requires the use of sophisticated equipment, sometimes an 'educated guess' is sufficient. The probable date of the object, the appearance, feel and smell of the material, and the properties necessary for its use are important clues.

For example: A hard, dark material from the 1940s , with a Carbolic smell, which was often used in electrical goods is probably a phenol-formaldehyde or Bakelite. A flexible clear (or yellowed) material from the 1940s is probably polyvinyl chloride, PVC. Flexible PVC was commonly used in the manufacture of shoes and rainwear in the 1960s and 70s. It was also the main material used in the manufacture of toys such as dolls from the late 1940s onwards. It has a distinct and unique smell of plasticiser. A hard, light-coloured material, used decoratively and in objects dated 1910-1930, is likely to be a casein-based plastic. Casein is commonly found in buttons, pens, costume jewellery, and dressing table sets. It was also used in the manufacture of decorative inlays in furniture and lamps. Dolls, dressing table accessories, combs and, generally, decorations from 1930-1950 are frequently made from cellulose acetate. This can have a smell of vinegar - acetic acid.

Imitation tortoiseshell is likely to be cellulose nitrate (which smells of camphor). Early film stock is also made from this material. Polystyrene was used extensively in the 1940s and early 1950s for hard, brightly-coloured toys, Foam toys are usually natural rubber or polyurethane, 'Bendy' (brand name) toys for example are usually natural rubber. This material may often have an associated smell of sulphur. A conservator specialising in this field can help you identify the material and manufacturing process used in making your object or collection. This will help you catalogue and document your items and give you clues as to how best to keep them in good condition. Recognising signs of deterioration Cellulose nitrate Cellulose nitrate is affected by light and moisture and releases potentially dangerous chemicals during degradation. Do not store items made from this material in plastic bags or other packaging with restricted ventilation. Early signs of breakdown include a smell of camphor, disintegration of wrapping tissue, surface bloom and yellowing. Note that cellulose nitrate-based film may deteriorate and disintegrate at room temperature. Cinema film in particular can combust spontaneously.

All cellulose nitrate film stock should therefore be isolated, and advice on storage sought from the Fire Brigade. Cellulose acetate Cellulose acetate degrades in a similar manner to cellulose nitrate, but with the production of acetic acid, hence the vinegary smell. The migration of plasticiser to the surface of the object can results in a “tacky” surface. PVC The main breakdown problem associated with PVC is the loss of its plasticisers. This results in a sticky deposit on the surface which attracts dirt, and in the material becoming more rigid and liable to crack and go yellow. Casein The problems most usually associated with this material are cracking and splitting due physical and environmental stresses. A conservator can give you advice on how to deal with all of these problems and whether specialist treatment is necessary (or effective). What you can do - Storage Storing plastics at low temperatures and relative humidities will slow down the rate of degradation reactions. Plastic objects should also be kept in low light levels. Some objects require special care, especially those made from cellulose nitrate and acetate. These should be stored in a cool, dry atmosphere. Never store them in humid surroundings such as laundry rooms as this can cause warping.

If objects show signs of degradation - such as a smell of vinegar or camphor, it is best to separate them from other objects. Either leave the plastics loosely covered with acid-free tissue or even silicone paper to stop dirt getting at them if there is a strong acid smell. If there is any surface acid you could remove it with a dry tissue (it might stick, so be careful), or a very lightly water-moistened one, but do dry the surface carefully afterwards. What you can do - Cleaning As solvents may react with specific plastics, causing stress-cracking it is best to avoid their usage. Mechanical “dry” cleaning such as brushing and dusting is the best way to remove surface dirt. You can also use cotton swabs dampened slightly with water, but make sure the surface is dried thoroughly afterwards. Consulting a conservator As owner and collector of plastic items, you can prevent damage by improving storage and protection as above, but there are instances where a conservator experienced in this field can provide invaluable help. Plastics are different – the exact make-up and “recipe” of each type of material has a great deal of influence over how long it will survive or stay looking good.

Even individual colourings within the same type of object can make a difference. A conservator can help analyse and precisely identify the type of plastic you have in your collection. You will then be best informed about how to care for it. Plastics are difficult to stabilise once they have started to deteriorate and they can fall apart quickly. A conservator can carry out treatment to stabilise certain plastics and can make enclosures and storage environments to stabilise an item at the very least. Polymers and plastics: a chemical introduction The physical properties of a polymer such as its strength and flexibility depend on: chain length - in general, the longer the chains the stronger the polymer; side groups - polar side groups (including those that lead to hydrogen bonding) give stronger attraction between polymer chains, making the polymer stronger; branching - straight, unbranched chains can pack together more closely than highly branched chains, giving polymers that have higher density, are more crystalline and therefore stronger; cross-linking - if polymer chains are linked together extensively by covalent bonds, the polymer is harder and more difficult to melt. Amorphous and crystalline polymers The crystalline parts of this polymer are shown in blue.

[ source ] For a very understandable discussion of polymer crystallinity, see this Macrogalleria page . The spaghetti-like entanglements of polymer molecules tend to produce amorphous solids, but it often happens that some parts can become sufficiently aligned to produce a region exhibiting crystal-like order, so it is not uncommon for some polymeric solids to consist of a random mixture of amorphous and crystalline regions. As might be expected, shorter and less-branched polymer chains can more easily organize themselves into ordered layers than can long chains. Hydrogen-bonding between adjacent chains also helps, and is very important in fiber-forming polymers both synthetic (Nylon 6.6) and natural (cotton cellulose). Thermal properties: thermoplastics and thermosets Pure crystalline solids have definite melting points, but polymers, if they melt at all, exhibit a more complex behavior. At low temperatures, the tangled polymer chains tend to behave as rigid glasses. For example, the natural polymer that we call rubber becomes hard and brittle when cooled to liquid nitrogen temperature. Many synthetic polymers remain in this state to well above room temperature.

The melting of a crystalline compound corresponds to a sudden loss of long-range order; this is the fundamental reason that such solids exhibit definite melting points, and it is why there is no intermediate form between the liquid and the solid states. In amorphous solids there is no long-range order, so there is no melting point in the usual sense. Such solids simply become less and less viscous as the temperature is raised. In some polymers (known as thermoplastics ) there is a fairly definite softening point that is observed when the thermal kinetic energy becomes high enough to allow internal rotation to occur within the bonds and to allow the individual molecules to slide independently of their neighbors, thus rendering them more flexible and deformable. This defines the glass transition temperature tg . See here for a more complete definition of the glass transition temperature. Depending on the degree of crystallinity, there will be a higher temperature, the melting point tm , at which the crystalline regions come apart and the material becomes a viscous liquid. Such liquids can easily be injected into molds to manufacture objects of various shapes, or extruded into sheets or fibers. Other polymers (generally those that are highly cross-linked) do not melt at all; these are known as thermosets .

If they are to be made into molded objects, the polymerization reaction must take place within the molds — a far more complicated process. About 20% of the commercially-produced polymers are thermosets; the remainder are thermoplastics. 2 Thermoplastic polymer structures Homopolymers and heteropolymers Copolymerization is an invaluable tool for "tuning" polymers so that they have the right combination of properties for an application. For example, homopolymeric polystyrene is a rigid and very brittle transparent thermoplastic with a glass transition temperature of 97°C. Copolymerizing it with acrylonitrile yields an altenating "SAN" copolymer in which tg is raised to 107°, making it useable for transparent drink containers. A polymer that is composed of identical monomeric units (as is polyethylene) is called a homopolymer. Heteropolymers are built up from more than one type of monomer. Artificial heteropolymers are more commonly known as copolymers .

Chain topology Polymers may also be classified as straight-chained or branched, leading to forms such as these: The monomers can be joined end-to-end, and they can also be cross-linked to provide a harder material: If the cross-links are fairly long and flexible, adjacent chains can move with respect to each other, producing an elastic polymer or elastomer . Chain configuration and tacticity In a linear polymer such as polyethylene, rotations around carbon-carbon single bonds can allow the chains to bend or curl up in various ways, resulting in the spaghetti-like mixture of these different conformations we alluded to above. But if one of the hydrogen atoms is replaced by some other entity such as a methyl group, the relative orientations of the individual monomer units that make up a linear section of any carbon chain becomes an important characteristic of the polymer. Cis-trans isomerism occurs because rotation around carbon-carbon double bonds is not possible — unlike the case for single bonds. Any pair of unlike substituents attached to the two carbons is permanently locked into being on the same side (cis) or opposite sides (trans) of the double bond.

If the carbon chain contains double bonds, then cis-trans isomerism becomes possible, giving rise to two different possible configurations (known as diastereomers ) at each unit of the chain. This seemingly small variable can profoundly affect the nature of the polymer. For example, the latex in natural rubber is made mostly of cis-polyisoprene, whereas the trans isomer (known as gutta percha latex) has very different (and generally inferior) properties. Chirality The tetrahedral nature of carbon bonding has an important consequence that is not revealed by simple two-dimensional structural formulas: atoms attached to the carbon can be on one side or on the other, and these will not be geometrically equivalent if all four of the groups attached to a single carbon atom are different. Such carbons (and the groups attached to them) are said to be chiral , and can exist in two different three-dimensional forms known as enantiomers . For an individual carbon atom in a polymer chain, two of its attached groups will ordinarily be the chain segments on either side of the carbon.

If the two remaining groups are different (say one hydrogen and the other methyl), then the above conditions are satisfied and this part of the chain can give rise to two enantiomeric forms. A chain that can be represented as (in which the orange and green circles represent different groups) will have multiple chiral centers, giving rise to a huge number of possible enantiomers. In practice, it is usually sufficient to classify chiral polymers into the following three classes of stereoregularity, usually referred to as tacticity. The tacticity of a polymer chain can have a major influence on its properties. Atactic polymers, for example, being more disordered, cannot crystallize. One of the major breakthroughs in polymer chemistry occurred in the early 1950s when the German chemist Karl Ziegler discovered a group of catalysts that could efficiently polymerize ethylene. At about the same time, Giulio Natta (Italian) made the first isotactic (and crystalline) polyethylene. The Zieglar-Natta catalysts revolutionized polymer chemistry by making it possible to control the stereorgularity of these giant molecules. The two shared the 1963 Nobel Prize in Chemistry .

3 How polymers are made Polymers are made by joining small molecules into large ones. But most of these monomeric molecules are perfectly stable as they are, so chemists have devised two general methods to make them react with each other, building up the backbone chain as the reaction proceeds. Condensation-elimination polymerization This method (also known as step-growth) requires that the monomers possess two or more kinds of functional groups that are able to react with each other in such a way that parts of these groups combine to form a small molecule (often H2O) which is eliminated from the two pieces. The now-empty bonding positions on the two monomers can then join together . This occurs, for example, in the synthesis of the Nylon family of polymers in which the eliminated H2O molecule comes from the hydroxyl group of the acid and one of the amino hydrogens: Note that the monomeric units that make up the polymer are not identical with the starting components.

Addition polymerization Addition or chain-growth polymerization involves the rearrangement of bonds within the monomer in such a way that the monomers link up directly with each other: In order to make this happen, a chemically active molecule (called an initiator) is needed to start what is known as a chain reaction. The manufacture of polyethylene is a very common expample of such a process. It employs a free-radical initiator that donates its unpaired electron to the monomer, making the latter highly reactive and able to form a bond with another monomer at this site. In theory, only a single chain-initiation process needs to take place, and the chain-propagation step then repeats itself indefinitely, but in practice multiple initiation steps are required, and eventually two radicals react (chain termination) to bring the polymerization to a halt. As with all polymerizations, chains having a range of molecular weights are produced, and this range can be altered by controlling the pressure and temperature of the process. 4 Gallery of common synthetic polymers Thermoplastics Note: the left panels below show the polymer name and synonyms, structural formula, glass transition temperature, melting point/decomposition temperature, and (where applicable) the resin identification symbol used to facilitate recycling.

Polycarbonate (Lexan®) Tg = 145°C, Tm = 225°C. This polymer was discovered independently in Germany and the U.S. in 1953. Lexan is exceptionally hard and strong; we see it most commonly in the form of compact disks. It was once widely used in water bottles, but concerns about leaching of unreacted monomer (bisphenol-A) has largely suppressed this market. Polyethylene terephthalate (PET, Mylar) Tg = 76°C, Tm = 250°C. Thin and very strong films of this material are made by drawing out the molten polymer in both directions, thus orienting the molecules into a highly crystalline state that becomes "locked-in" on cooling. Its many applications include food packaging (in foil-laminated drink containers and microwaveable frozen-food containers), overhead-projector film, weather balloons, and as aluminum-coated reflective material in spacecraft and other applications. Nylon (a polyamide) Tg = –70°C Polybutadiene Tg < –90°C Neoprene, invented in 1930, was the first mass-produced synthetic rubber.

It is used for such things as roofing membranes and wet suits. Polybutadiene substitutes a hydrogen for the chlorine; it is the major component (usually admixed with other rubbers) of tires. Synthetic rubbers played a crucial role in World War II: more SBS (styrene-butadiene-styrene) rubber is a block copolymer whose special durability makes it valued for tire treads. Polytetrafluroethylene (Teflon, PTFE) Decomposes above 350°C. This highly-crystalline fluorocarbon is exceptionally inert to chemicals and solvents. Water and oils do not wet it, which accounts for its use in cooking ware and other anti-stick applications, including personal care products. It is also employed in Gore-Tex fabric for rainwear. These properties — non-adhesion to other materials, non-wetability, and very low coefficient of friction ("slipperyness") — have their origin in the highly electronegative nature of fluorine whose atoms partly shield the carbon chain. Fluorine's outer electrons are so strongly attracted to its nucleus that they are less available to participate in London (dispersion force) interactions.

Wikipedia has informative pages on fluorocarbons and on Teflon . Polyaramid (Kevlar) Sublimation temperature 450°C. Kevlar is known for its ability to be spun into fibres that have five times the tensile strength of steel. It was first used in the 1970s to replace steel tire cords. Bullet-proof vests are one of it more colorful uses, but other applications include boat hulls, drum heads, sports equipment, and as a replacement for asbestos in brake pads. It is often combined with carbon or glass fibers in composite materials. The high tensile strength is due in part to the extensive hydrogen bonding between adjacent chains. Kevlar also has the distinction of having been invented by a woman chemist, Stephanie Kwolek . Thermosets The thermoplastic materials described above are chains based on relatively simple monomeric units having varying degrees of polymerization, branching, bending, cross-linking and crystallinity, but with each molecular chain being a discrete unit.

In thermosets, the concept of an individual molecular unit is largely lost; the material becomes more like a gigantic extended molecule of its own — hence the lack of anything like a glass transition temperature or a melting point. These properties have their origins in the nature of the monomers used to produce them. The most important feature is the presence of multiple reactive sites that are able to form what amount to cross-links at every center. The phenolic resins, typified by the reaction of phenol with formaldehyde, illustrate the multiplicity of linkages that can be built. Phenolic resins These are made by condensing one or more types of phenols (hydroxy-substituted benzene rings) with formaldehyde, as illustrated above. This was the first commercialized synthetic molding plastic. It was developed in 1907-1909 by the Belgian chemist Leo Baekeland , hence the common name bakelite . The brown material (usually bulked up with wood powder) was valued for its electrical insulating properties (light fixtures, outlets and other wiring devices) as well as for consumer items prior to the mid-century. Since that time, more recently developed polymers have largely displaced these uses.

Phenolics are still extensively used as adhesives in plywood manufacture, and for making paints and varnishes. Urea resins Condensation of formaldehyde with urea yields lighter-colored and less expensive materials than phenolics. The major use if urea-formaldehyde resins is in bonding wood particles into particle board . Other uses are as baked-on enamel coatings for kitchen appliances and to coat cotton and rayon fibers to impart wrinkle- water-, and stain-resistance to the finished fabrics. Melamine resins Melamine, with even more amino (–NH2) groups than urea, reacts with formaldehyde to form colorless solids that are harder then urea resins. The are most widely encountered in dinner-ware (plastic plates, cups and serving bowls) and in plastic laminates such as Formica . Alkyd-polyester resins An ester is the product of the reaction of an organic acid with an alcohol, so polyesters result when multifunctional acids such as phthalic acid react with polyhydric alcohols such as glycerol. The term alkyd derives from the two words alcohol and acid.

Alkyd resins were first made by Berzelius in 1847, and they were first commercialized as Glyptal (glycerine + phthalic acid) varnishes for the paint industry in 1902. The later development of other polyesters greatly expanded their uses into a wide variety of fibers and molded products, ranging from clothing fabrics and pillow fillings to glass-reinforced plastics ( Fiberglass ). Epoxy resins This large and industrially-important group of resins typically starts by condensing bisphenol-A with epichlorohydrin in the presence of a catalyst. (The -epi prefix refers to the epoxide group in which an oxygen atom that bridges two carbons.) These resins are usually combined with others to produce the desired properties. Epoxies are especially valued as glues and adhesives, as their setting does not depend on evaporation and the setting time can be varied over a wide range. In the two-part resins commonly sold for home use, the unpolymerized mixture and the hardener catalyst are packaged separately for mixing just prior to use. In some formulations the polymerization is initiated by heat ("heat curing").

Epoxy dental fillings are cured by irradiation with uv light. Polyurethanes Organic isocyanates R–NCO react with multifunctional alcohols to form polymeric carbamates, commonly referred to as polyurethanes . Their major use is in plastic foams for thermal insulation and upholstery, but a very large number of other applications, including paints and varnishes and plastic wheels used in fork-lift trucks, shopping carts and skateboards. Silicones Polysiloxanes (–Si–O–Si-) are the most important of the small class inorganic polymers. The commercial silicone polymers usually contained attached organic side groups that aid to cross-linking. Silicones can be made in a wide variety of forms; those having lower molecular weights are liquids, while the more highly polymerized materials are rubbery solids. These polymers have a similarly wide variety of applications: lubricants, caulking materials and sealants, medical implants, non-stick cookware coatings, hair-conditioners and other personal-care products. 5 Some important natural polymers Polymers derived from plants have been essential components of human existence for thousands of years.

In this survey we will look at only those that have major industrial uses, so we will not be discussing the very important biopolymers proteins and nucleic acids. Polysaccharides Polysaccharides are polymers of sugars; they play essential roles in energy storage, signalling, and as structural components in all living organisms. The only ones we will be concerned with here are those composed of glucose , the most important of the six-carbon hexoses. Glucose serves as the primary fuel of most organisms. Glucose, however, is highly soluble and cannot be easily stored, so organisms make polymeric forms of glucose to set aside as reserve storage, from which glucose molecules can be withdrawn as needed. Glycogen In humans and higher animals, the reserve storage polymer is glycogen. It consists of roughly 60,000 glucose units in a highly branched configuration. Glycogen is made mostly in the liver under the influence of the hormone insulin which triggers a process in which digested glucose is polymerized and stored mostly in that organ. A few hours after a meal, the glucose content of the blood begins to fall, and glycogen begins to be broken down in order to maintain the body's required glucose level.

Starch In plants, these glucose-polymer reserves are known as starch. Starch granules are stored in seeds or tubers to provide glucose for the energy needs of newly-germinated plants, and in the twigs of deciduous plants to tide them over during the winter when photosynthesis (the process in which glucose is synthesizd from CO2 and H2O) does not take place. The starches in food grains such as rice and wheat, and in tubers such as potatoes, are a major nutritional source for humans. Plant starches are mixtures of two principal forms, amylose and amylopectin. Amylose is a largely-unbranched polymer of 500 to 20,000 glucose molecules that curls up into a helical form that is stabilized by internal hydrogen bonding. Amylopectin is a much larger polymer having up to two million glucose residues arranged into branches of 20 to 30 units. For more on these two variants of starch, see here . Cellulose and its derivatives Cellulose is the most abundant organic compound on the earth. Extensive hydrogen bonding between the chains causes native celluose to be abut 70% crystalline.

It also raises the melting point (>280°C) to above its combustion temperature. The structures of starch and cellulose appear to be very similar; in the latter, every other glucose molecule is "upside-down". But the consequences of this are far-reaching; starch can dissolve in water and can be digested by higher animals including humans, whereas cellulose is insoluble and undigestible. Cellulose serves as the principal structural component of green plants and (along with lignin) in wood. Cotton is one of the purest forms of cellulose and has been cultivated since ancient times. Its ability to absorb water (which increases its strength) makes cotton fabrics especially useful for clothing in very warm climates. Cotton also serves (along with treated wood pulp) as the source the industrial production of cellulose-derived materials which were the first "plastic" materials of commercial importance. Nitrocellulose was developed in the latter part of the 19th Century. It is prepared by treating cotton with nitric acid, which reacts with the hydroxyl groups in the cellulose chain. It was first used to make molded objects the first material used for a photograpic film base by Eastman Kodak.

Its extreme flammability posed considerable danger in movie theatres, and its spontaneous slow decomposition over time had seriously degraded many early films before they were transferred to more stable media. Nitrocellulose was also used as an explosive and propellent, for which applications it is known as guncotton. Under the name celluloid , it was used to make molded objects such as billiard balls. It still has a number of commercial applications , mainly in specialty coatings. Cellulose acetate was developed in the early 1900s and became the first artificial fiber that was woven into fabrics that became prized for their lustrous appearance and wearing comfort. Kodak developed it as a "safety film" base in the 1930's to replace nitrocellulose, but it did not come into wide use for this purpose until 1948. A few years later, is became the base material for magnetic recording tape. Viscose is the general term for "regenerated" forms of cellulose made from solutions of the polymer in certain strong solvents.

When extruded into a thin film it becomes cellophane which has been used as a food wrapping since 1912 and is the base for transparent adhesive tapes such as Scotch Tape . Viscose solutions extruded through a spinneret produce fibers known as rayon. Rayon (right) was the first "artificial silk" and has been used for tire cord, apparel, and carpets. It was popular for womens' stockings before Nylon became available for this purpose. Rubber A variety of plants produce a sap consisting of a colloidal dispersion of cis-polyisoprene. This milky fluid is especially abundant in the rubber tree (Hevea), from which it drips when the bark is wounded. After collection, the latex is coagulated to obtain the solid rubber. Natural rubber is thermoplastic, with a glass transition temperature of –70°C. cis-polyisoprene Raw natural rubber tends to be sticky when warm and brittle when cold, so it was little more than a novelty material when first introduced to Europe around 1770.

It did not become generally useful until the mid-nineteenth century when Charles Goodyear found that heating it with sulfur — a process he called vulcanization — could greatly improve its properties. Why does a rubber band heat up when it is stretched, and why does it spontaneously snap back? It all has to do with entropy; see here for a concise explanation. Vulcanization creates disulfide cross-links that prevent the polyisoprene chains from sliding over each other. The degree of cross-linking can be controlled to produce a rubber having the desired elasticity and hardness. More recently, other kinds of chemical treatment (such as epoxidation) have been developed to produce rubbers for special purposes. Allergic reactions to some of the proteins and chemical additives in natural rubber are not uncommon. Natural rubber continues to have a large market despite the many forms of synthetic rubber available, including synthetic polyisoprene ("synthetic natural rubber"). A sizeable industry is devoted to developing combinations of these rubbers and butadiene copolymers to suit special applications. There is a very good Wikipedia article on tires. The largest single use of rubber is the production of vehicle tires.

Tires are highly engineered products that use different kinds of rubber in different parts. For example, the outer tread surface of tires intended for winter use may employ a special formulation designed to improve low-temperature flexibility. Of course, tires are made of much more than rubber materials. Especially surprising to many is the high proportion of carbon black (amorphous carbon soot) in tires. This material serves as a binding and reinforcing agent, a pigment, and it also improves the thermal conductivity — important for preventing localized overheating. 6 Polymers in the environment "Better things for better living... through chemistry" is a famous commercial slogan that captured the attitude of the public around 1940 when synthetic polymers were beginning to make a major impact in people's lives. What was not realized at the time, however, were some of the problems these materials would create as their uses multiplied and the world became more wary of "chemicals". (DuPont dropped the "through chemistry" part in 1982.) Small-molecule release Many kinds of polymers contain small molecules — either unreacted monomers, or substances specifically added (plasticizers, uv absorbers, flame retardents, etc.) to modify their properties.

Many of these smaller molecules are able to diffuse through the material and be released into any liquid or air in contact with the plastic — and eventually into the aquatic environment. Those that are used for building materials (in mobile homes, for example) can build up in closed environments and contribute to indoor air pollution. Residual monomer Formation of long polymer chains is a complicated and somewhat random process that is never perfectly stoichiometric. It is therefore not uncommon for some unreacted monomer to remain in the finished product. Some of these monomers, such as formaldehyde, styrene (from polystyrene, including polystyrene foam food take-out containers), vinyl chloride, and bisphenol-A (from polycarbonates) are known carcinogens. Although there is little evidence that the small quantities that diffuse into the air or leach out into fluids pose a quantifiable health risk, people are understandably reluctant to tolerate these exposures, and public policy is gradually beginning to regulate them. Perfluorooctanoic acid (PFOA), the monomer from which Teflon is made, has been the subject of a 2004 lawsuit against a DuPont factory that contaminated groundwater.

Small amounts of PFOA have been detected in gaseous emissions from hot fluorocarbon products. EPA page on PFOA Plasticizers These substances are compounded into certain types of plastics to render them more flexible by lowering the glass transition temperature. They accomplish this by taking up space between the polymer chains and acting as lubricants to enable the chains to more readily slip over each other. Many (but not all) are small enough to be diffusible and a potential source of health problems. The History of Plastic Updated August 06, 2016. The First Man-Made Plastic - Parkesine The first man-made plastic was created by Alexander Parkes who publicly demonstrated it at the 1862 Great International Exhibition in London. The material called Parkesine was an organic material derived from cellulose that once heated could be molded, and retained its shape when cooled. Celluloid Celluloid is derived from cellulose and alcoholized camphor. John Wesley Hyatt invented celluloid as a substitute for the ivory in billiard balls in 1868. He first tried using collodion a natural substance, after spilling a bottle of it and discovering that the material dried into a tough and flexible film.

However, the material was not strong enough to be used as a billiard ball, until the addition of camphor, a derivative of the laurel tree. The new celluloid could be molded with heat and pressure into a durable shape. Besides billiard balls, celluloid became famous as the first flexible photographic film used for still photography and motion pictures. continue reading below our video Should I Roll Over my 401K to an IRA? John Wesley Hyatt created celluloid in a strip format for movie film. By 1900, movie film was an exploding market for celluloid. Formaldehyde Resins - Bakelite After cellulose nitrate, formaldehyde was the next product to advance the technology of plastic. Around 1897, efforts to manufacture white chalkboards led to casein plastics (milk protein mixed with formaldehyde) Galalith and Erinoid are two early tradename examples. In 1899, Arthur Smith received British Patent 16,275, for "phenol-formaldehyde resins for use as an ebonite substitute in electrical insulation", the first patent for processing a formaldehyde resin.

However, in 1907, Leo Hendrik Baekeland improved phenol-formaldehyde reaction techniques and invented the first fully synthetic resin to become commercially successful, tradenamed Bakelite . Timeline - Precursors

Question: What type of plastic was made from phenol and formaldehyde?
Answer: Bakelite