TECHNOLOGICAL INSTITUTE OF THE PHILIPPINES363 P.CASAL ST., QUIAPO, MANILA

COLLEGE OF ENGINEERING AND ARCHITECTURE

CHEMICAL ENGINEERING DEPARTMENT

GROUP REPORTING

INTRODUCTION TO POLYMER ENGINEERING

SUBMITTED BY:

TAPALES, ALJANETEJADA, RUTH

TOGONON, PATRICIATOMPONG, JOHNNICA MAY

TORDECILLAS, BIAVENZON, KENNETH

VILLANUEVA, KRISTINE ANN

GROUP 5

SUBMITTED TO:

ENGR. LINA DELA CRUZ

INSTRUCTOR

HISTORY

The history of POLYTETRAFLUOROETHYLENE began on April 6, 1938 at Du Pont's Jackson Laboratory in New Jersey. On that fortunate day, Dr. Roy J. Plunkett, who was working with gases related to FREON refrigerants, discovered that one sample had polymerised spontaneously to a white, waxy solid.

Testing showed that this solid was a very remarkable material. It was a resin that resisted practically every known chemical or solvent; its surface was so slippery that almost no substance would stick to it; moisture did not cause it to swell, and it did not degrade or become brittle after long term exposure to sunlight. It had a melting point of 327°C and, as opposed to conventional thermoplastics, it would not flow above that melting point. This meant that new processing techniques had to be developed to suit the characteristics of the new resin - which Du Pont named TEFLON.

Borrowing techniques from powder metallurgy, Du Pont engineers were able to compress and sinter POLYTETRAFLUOROETHYLENE resins into blocks that could be machined to form any desired shape. Later, dispersions of the resin in water were developed to coat glass-cloth and make enamels. A powder was produced that could be blended with a lubricant and extruded to coat wire and manufacture tubing.

By 1948, 10 years after the discovery of POLYTETRAFLUOROETHYLENE, Du Pont was teaching processing technology to its customers. Soon a commercial plant was operational, and POLYTETRAFLUOROETHYLENE PTFE resins became available in dispersions, granular resins and fine powder.

PHYSICAL AND CHEMICAL PROPERTIES

PTFE is a fluorocarbon solid, as it is a high-molecular-weight compound consisting wholly of carbon and fluorine. PTFE is hydrophobic: neither water nor water-containing substances wet PTFE, as fluorocarbons demonstrate mitigated London dispersion forces due to the high electronegativity of fluorine. PTFE has one of the lowest coefficients of friction against any solid.

PTFE is used as a non-stick coating for pans and other cookware. It is very non-reactive, partly because of the strength of carbon–fluorine bonds and so it is often used in containers and pipe work for reactive and corrosive chemicals. Where used as a lubricant, PTFE reduces friction, wear and energy consumption of machinery. It is also commonly used as a graft material in surgical interventions.

PTFE is a thermoplastic polymer, which is a white solid at room temperature, with a density of about 2200 kg/m3. Its melting point is 327°C. It maintains high strength, toughness and self-lubrication at low temperatures down to −268.15 °C, and good flexibility at temperatures above −79 °C. PTFE gains its properties from the aggregate effect of carbon-fluorine bonds, as do all fluorocarbons. The only chemicals known to affect these carbon-fluorine bonds are reactive metals like alkali metals and at higher temperature also e.g. aluminium and magnesium and fluorinating agents such as xenon difluoride and cobalt (III) fluoride.

PTFE is made by polymerizing lots of tetrafluoroethene molecules.

This fluoroplastic family offers high chemical resistance, low and high temperature capability, resistance to weathering, low friction, electrical and thermal insulation, and "slipperiness". PTFE's mechanical properties are low compared to other plastics, but its properties remain at a useful level over a wide temperature range of 73°C to 204°C. Mechanical properties are often enhanced by adding fillers. It has excellent thermal and electrical insulation properties and a low coefficient of friction. PTFE is very dense and cannot be melt-processed -- it must be compressed and sintered to form useful shapes.

As you can see, PTFE is composed of carbon and fluorine. Carbon-fluorine and carbon-carbon bonds are among the strongest in single bond organic chemistry. This accounts for many of its properties. Because of the strong bonds, much thermal energy must be used to break down the material. It is also non-polar; this leads to its chemical inertness, as the diagram demonstrates, and the fact that its electrical resistance is over 1018. The low coefficient of friction of Teflon results from low interfacial forces between its surface and another material and the comparatively low force to deform.

PTFE does not release electrons from the polymer orbital easily due to the strength of the carbon to fluorine bonds. This makes Teflon have good dielectric properties and makes it an ideal insulator. The bonding structure of PTFE prevents the transmission of electrons through the molecular orbital of the PTFE polymer.

MECHANISM

HOW POLYTETRAFLUOROETHYLENE IS FORMED?

Polytetrafluoroethylene is formed from tetrafluoroethene (TFE), CF2=CF2. TFE is synthesized from fluorspar, hydrofluoric acid, and chloroform. These ingredients are combined under high heat, an action known as pyrolosis.

Tetrafluoroethylene is the mer of polytetrafluoroethylene

Polytetrafluoroethylene is formed by the addition polymerization also known as free radical vinyl polymerization, of tetrafluoroethylene.

Simpllified polymerization reaction of tetrafluoroethylene to form poly tetrafluoroethyleneThe detailed polymerization reaction to form polytetrafluoroethylene will follow the mechanism of addition polymerization which has the following steps: 1) initiation, 2) propagation and 3) termination. The steps are indicated below:

INITIATION

Breaking bonds of the initiatorThe whole process starts off with a molecule called an initiator. This is a molecule like benzoyl peroxide or 2,2'-azo-bis-isobutyrylnitrile (AIBN). What is special about these molecules is that they have an uncanny ability to fall apart, in a rather unusual way. When they split, the pair of electrons in the bond which is broken, will separate. This is unusual as electrons like to be in pairs whenever possible. When this split happens, we're left with two fragments, called initiator fragments, of the original molecule, each of which has one unpaired electron. Molecules like this, with unpaired electrons are called free radicals.

Breaking of bonds of the initiator to form a free radical

Interaction of radical with the monomerThe unpaired electrons will be quite discontent with being alone and still want to be paired. The unpaired electron, when it comes near the pair of electrons, can't help but swipe one of them to pair with itself. This new pair of electrons forms a new chemical bond between the initiator fragment and one of the double bond carbons of the monomer molecule. This electron, having nowhere else to go, associates itself with the carbon atom which is not bonded to the initiator fragment. You can see that this will lead us back where we started, as we now have a new free radical when this unpaired electron comes to roost on that carbon atom.

Bonding of radical to a tetrafluoroethylene monomer

PROPAGATION

The process of adding more and more monomer molecules to the growing chains is under propagation. This happens through the continuous bonding of the radical with the double bond mer of tetrafluoroethylene.

Continuous bonding of radical with tetrafluoroethylene to a new monomer of TFE

TERMINATIONThe propagation step could be infinitely continuous however, there will come a point that it will meet another growing chain and both its radicals will combine and thus, termination will happen and polytetrafluoroethylene is finally formed.

Normal termination of an addition polymerization process

For some cases, normal termination does not happen. Sometimes, disproportionation occurs. The process is described in the pictures below.

The radical connects to another carbon

When two growing chain ends come close together, the unpaired electron of one chain does something strange. Rather than simply joining with the unpaired electron of the other chain, it looks elsewhere for a

mate. It finds one in the carbon-hydrogen bond of the carbon atom next to the other carbon radical. Our unpaired electron grabs not only one of the electrons from this bond, but the hydrogen atom as well. Now our first chain has no unpaired electrons, the end carbon now shares eight electrons, and the polymerization reaction is complete. Polytetrafluoroethylene and another compound is formed.

APPLICATIONS

PTFE’s significant chemical, temperature, moisture, and electrical resistances make it an ideal material whenever products, tools, and components need to be durable and reliable in even the most strenuous applications.Teflon are used in industrial and commercial applications, such as:

1. Cabling Solutions2. Flue Gas Heat Exchangers 3. Food Processing 4. Food Processing 5. Industrial Coatings 6. Pharmaceuticals and Biopharma Manufacturing

Cabling SolutionsTeflon resins are ideal choices for insulation and jacketing applications where low flammability, exceptional dielectric properties, high stress-crack resistance, chemical inertness, and thermal cycling capabilities are required.With safety considered just as important as performance when it comes to your data communications network, you want to protect it as best you can. In a fire, cables can be a significant source of fire load and smoke, and smoke can be a leading cause of IT system damage and personal injury. Combustible cables from Teflon have the most advanced fire safety performance.Flue Gas Heat Exchanger SolutionsEnergy efficiency, reducing carbon emissions and heat recovery are important issues in most industries, but especially in the Power Generation industry. New developments and ideas are required in order to meet the demand for sustainability and to be able to achieve the targets set.Companies are continuously advancing the use of fluoroplastics for pressure tubing in flue gas heat exchangers for heat recovery and heat displacement solutions.

Better Food Processing with TeflonPTFE is a way to fight problems with plugging, corrosion, and sticking during food processing. Components and linings made with PTFE can help cut equipment maintenance costs, increase uptime, increase throughput, and safeguard product purity. They also allow use of the same equipment to make a wider range of food products. Easy cleaning reduces the frequency, amount, and severity of cleaning chemicals used in processing facilities -- a benefit to the environment. Reduced downtime for cleaning can potentially improve plant productivity.

PROS AND CONS

PROS

Inert to practically all commercial chemicals, acids, alcohols, coolants, elastomers, hydrocarbons, solvents, synthetic compounds and hydraulic fluids.

Rated for steam to 250 psi (406 degrees F) - has low volumetric expansion characteristics - easy to clean and sterilize.

Not affected by continuous flexing, vibration or impulse pressures - withstands alternating hot and cold cycling

Easier to move, handle and install than rubber hose with a comparable burst pressure rating. The low coefficient of friction of Teflon and anti-stick properties lowers pressure drop while

maintaining good service pressures. Jackson Hose of Teflon has optional conductive liner for removing static build up through the flow

path. Will not contaminate material, fluid or gas conducted - Teflon is an FDA recognized material for

food handling and pharmaceutical applications. Handles substances such as adhesives, asphalt, dyes, greases, glue, latex, lacquers and paints

with ease. No moisture absorption, ideal as a pigtail in bulk gas handling and pneumatic systems where a low

dew point is critical Impervious to weather and can be stored for extended periods of time without aging. It will not age

during service. Excellent high temperature performance for all mechanical properties Excellent low temperature performance for all mechanical properties Excellent electrical performance at high temperatures Excellent chemical resistance over a wide range of temperatures Excellent weathering and UV resistance Extremely low coefficient of friction

CONS

A chemical used in making Teflon called perfluorooctanoic acid (PFOA), as it has been linked to cancer in laboratory animals, and possible connections to elevated cholesterol, thyroid disease, and reduced fertility.

LIMITATION

Higher cost but the properties can justify this (cost can be minimized by coating large objects with PTFE films)

Low wear resistance in the natural state Must be chemically etched to enable adhesive bonding Processing is a very specialized Limited resistance to gamma radiation

MANUFACTURING PROCESS

PTFE can be produced in a number of ways, depending on the particular traits desired for the end product. Many specifics of the process are proprietary secrets of the manufacturers. There are two main methods of producing PTFE. One is suspension polymerization. In this method, the TFE is polymerized in water, resulting in grains of PTFE. The grains can be further processed into pellets which can be molded. In the dispersion method, the resulting PTFE is a milky paste which can be processed into a fine powder. Both the paste and powder are used in coating applications.

Making the TFE

[1] Manufacturers of PTFE begin by synthesizing TFE. The three ingredients of TFE, fluorspar, hydrofluoric acid, and chloroform are combined in a chemical reaction chamber heated to between 1094-1652°F (590-900°C). The resultant gas is then cooled, and distilled to remove any impurities.

Teflon can be used on a wide variety of cookware.

Suspension Polymerization

[2] The reaction chamber is filled with purified water and a reaction agent or initiator, a chemical that will set off the formation of the polymer. The liquid TFE is piped into the reaction chamber. As the TFE meets the initiator, it begins to polymerize. The resulting PTFE forms solid grains that float to the surface of the water. As this is happening, the reaction chamber is mechanically shaken. The chemical reaction inside the chamber gives off heat, so the chamber is cooled by the circulation of cold water or another coolant in a jacket around its outsides. Controls automatically shut off the supply of TFE after a certain weight inside the chamber is reached. The water is drained out of the chamber, leaving a mess of stringy PTFE which looks somewhat like grated coconut.

[3] Next, the PTFE is dried and fed into a mill. The mill pulverizes the PTFE with rotating blades, producing a material with the consistency of wheat flour. This fine powder is difficult to mold. It has "poor flow," meaning it cannot be processed easily in automatic equipment. Like unsifted wheat flour, it might have both lumps and air pockets. So manufacturers convert this fine powder into larger granules by a process called agglomeration. This can be done in several ways. One method

is to mix the PTFE powder with a solvent such as acetone and tumble it in a rotating drum. The PTFE grains stick together, forming small pellets. The pellets are then dried in an oven.

[4] The PTFE pellets can be molded into parts using a variety of techniques. However, PTFE may be sold in bulk already pre-molded into so-called billets, which are solid cylinders of PTFE. The billets may be 5 ft (1.5 m) tall. These can be cut into sheets or smaller blocks, for further molding. To form the billet, PTFE pellets are poured into a cylindrical stainless steel mold. The mold is loaded onto a hydraulic press, which is something like a large cabinet equipped with weighted ram. The ram drops down into the mold and exerts force on the PTFE. After a certain time period, the mold is removed from the press and the PTFE is unmolded. It is allowed to rest, and then placed in an oven for a final step called sintering.

[5] The molded PTFE is heated in the sintering oven for several hours, until it gradually reaches a temperature of around 680°F (360°C). This is above the melting point of PTFE. The PTFE particles coalesce and the material becomes gel-like. Then the PTFE is gradually cooled. The finished billet can be shipped to customers, who will slice or shave it into smaller pieces, for further processing.

Dispersion polymerization

[6] Polymerization of PTFE by the dispersion method leads to either fine powder or a paste-like substance, which is more useful for coatings and finishes. TFE is introduced into a water-filled reactor along with the initiating chemical. Instead of being vigorously shaken, as in the suspension process, the reaction chamber is only agitated gently. The PTFE forms into tiny beads. Some of the water is removed, by filtering or by adding chemicals which cause the PTFE beads to settle. The result is a milky substance called PTFE dispersion. It can be used as a liquid, especially in applications like fabric finishes. Or it may be dried into a fine powder used to coat metal.

Nonstick cookware

[7] One of the most common and visible uses of PTFE is coating for nonstick pots and pans. The pan must be made of aluminum or an aluminum alloy. The pan surface has to be specially prepared to receive the PTFE. First, the pan is washed with detergent and rinsed with water, to remove all grease. Then the pan is dipped in a warm bath of hydrochloric acid in a process called etching. Etching roughens the surface of the metal. Then the pan is rinsed with water and dipped again in nitric acid. Finally it is washed again with deionized water and thoroughly dried.

[8] Now the pan is ready for coating with PTFE dispersion. The liquid coating may be sprayed or rolled on. The coating is usually applied in several layers, and may begin with a primer. The exact makeup of the primer is a proprietary secret held by the manufacturers. After the primer is applied, the pan is dried for a few minutes, usually in a convection oven. Then the next two layers are applied, without a drying period in between. After all the coating is applied, the pan is dried in an oven and then sintered. Sintering is the slow heating that is also used to finish the billet. So typically, the oven has two zones. In the first zone, the pan is heated slowly to a temperature that will evaporate the water in the coating. After the water has evaporated, the pan moves into a hotter zone, which sinters the pan at around 800°F (425°C) for about five minutes. This gels the PTFE. Then the pan is allowed to cool. After cooling, it is ready for any final assembly steps, and packaging and shipping.

PTFE VS. OTHER POLYMERS

PVC VS POLYTETRAFLUOROETHYLENE

PVC, or polyvinyl chloride, is also known as vinyl. It is arguably the most dominant type of wire jacket available on the market. However, it is not designed for high-voltage applications. It is more suitable for low-voltage applications, and Polytetrafluoroethylene is usually better suited for higher voltage applications. PVC jackets are available in many different flavors for various applications. Additionally, PVC can differ as far as pliability and electrical properties go.

PVC wires do have some undesirable properties; for example, PVC wires should not be used in temperatures, which are above seventy degrees Celsius. Their thermal rating is limited. Also, it should be noted that the thermal decomposition of PVC has Hydrochloric Acid (HCI) as a bi-product.

Polytetrafluoroethylene has better electrical properties than PVC. It also has a higher temperature range and chemical resistance. Consequently, it is often refered to as high temperature wire. Unlike PVC wire jackets, which cannot be subjected to ultra-violet light for an extended amount of time, Polytetrafluoroethylene can. However, like PVC, Polytetrafluoroethylene should not be used in high-voltage applications.

POLYETHYLENE VS POLYTETRAFLUOROETHYLENE

PTFE has a higher temperature range than UHMW. The PTFE has a continuous use temperature of 500 degrees F. UHMW is much lower with a continuous use temperature of 200 degrees F and a melting point of 271 degrees F. The UHMW starts to become become soft at higher temperatures while the PTFE is much more resistant and with a melting point of 621 degrees F.

UHMW has a much lower density than PTFE. This makes UHMW able to float in water while Fluoropolymers are significantly heavier (almost twice the density of UHMW) and would sink.

PTFE has excellent electrical and thermal properties. The virgin grade of PTFE is a better insulator and exhibits better electrical properties which can be used in radio frequencies, cables and circuit boards while UHMW cannot.

Like most plastics, PE pipes can deteriorate if they work for a long time outdoors, mainly due to the ultraviolet component of sunlight and oxygen.

Unlike other different material tubes, PE tubes should not be screwing nor stick, and so far has not found a glue or adhesive secured to withstand a minimum of 50 years in marriage caused tension .

The ovality is characteristic of PE tubes, due to its low modulus of elasticity and the fact that they can be supplied in rolls, but it is still a hassle especially when performing the union of 2 tubes and either with mechanical fittings, butt welding or electrofusion. To reduce and even eliminate ovalación there useful and mechanical tools like rounders and butt welding machine clamps round the tubes. Anyway, the goal would be for the entire process from manufacturing, storage, transport, handling up to the installation, get round tubes as possible.

POLYURETHANE VS POLYTETRAFLUOROETHYLENE

Some grades of TPU have a short shelf life and if not used within that timeframe, they must be disposed of.Drying time is required before processing can begin.

Thermoplastic polyurethane is not as cost-effective as other alternatives and is therefore not always the first option that is used.

Polyurethane is a flammable material. The flame retardant version sacrifices strength and surface finish.

Polyurethane’s main disadvantage though, is its poor electrical properties, making it suitable for jackets only.