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Styrene Monomer

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STYRENE MONOMER FORMULA C 6 H 5 - CH = CH 2 DESCRIPTION Styrene (vinyl benzene, styrene monomer SM) is a colorless to yellowish oily liquid with a distinctive aromatic odor. It is sparingly soluble in water but soluble in alcohols, ethers and carbon disulfide. This valuable monomer is flammable, reactive and toxic. Styrene Monomer is a light liquid. It has a low vapor pressure and high refractive index. It is chemically reactive and undergoes polymerization readily (by heat, light or peroxide catalysts).
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Page 1: Styrene Monomer

STYRENE MONOMER

FORMULA

 C6H5 - CH = CH2

DESCRIPTION

Styrene (vinyl benzene, styrene monomer SM) is a colorless to yellowish oily liquid with a

distinctive aromatic odor. It is sparingly soluble in water but soluble in alcohols, ethers and

carbon disulfide. This valuable monomer is flammable, reactive and toxic. Styrene Monomer

is a light liquid. It has a low vapor pressure and high refractive index. It is chemically reactive

and undergoes polymerization readily (by heat, light or peroxide catalysts). 

Page 2: Styrene Monomer

APPLICATIONS

Styrene monomer is a basic building block of the plastic industry. It is used to make a host of

downstream derivative products that go into millions of consumer goods. Primary

derivatives of styrene monomer, in order of demand, include: polystyrene, expandable

polystyrene (EPS) and acrylonitrilebutadiene-styrene (ABS)/styrene-acrylonitrile (SAN)

resins, styrene butadiene (SB) latex, SB Rubber (SBR), unsaturated polyester resins

(UPR), specialty polymers, co-polymers and styrene thermoplastic elastomers (TPE)

Polystyrene

CD covers and plastic drinking cups are made out of the polymer polystyrene. This polymer

is known to be a clear brittle plastic that is synthesized by a free radical polymerization. An

initiator, such as benzoyl peroxide, is used to initiate the free radical polymerization of

styrene. Once the radical initiator initiates the polymerization of styrene, propagation occurs

which “builds up” the polymer chain. Once the polymer chain has “grown” and at a desirable

length or molecular weight, the polymerization is terminated. The polymer is then isolated,

possibly purified, characterized, and used for material use. The mechanism of the free

radical polymerization of styrene is shown below.

Page 3: Styrene Monomer

Formation of the radical initiator:

Polymerization of styrene:

Page 4: Styrene Monomer

Manufacturing process:

The overall reaction describing the styrene polymerization is:

This reaction is carried out in an inert organic solvent environment, which provides the

reaction medium for this cationic polymerization reaction .

The different methods available for styrene polymerization are:

1. Solution (bulk) polymerization.

2. Emulsion polymerization.

3. Suspension polymerization.

Solution (bulk) polymerization:

Solution (bulk) polymerization is commonly referred to as mass polymerization in the

industry. The vast majority of all polystyrene produced today is produced via this technology.

The common solvents used in this process are the styrene monomer itself and ethyl

benzene. The two types of mass polymerization are batch and continuous, of which

continuous mass is by far the most popular. Batch mass polymerization consists of a

polymerization section containing agitated vessels polymerizing up to 80% conversion in a

batch method. The polymerized solution is then pumped to a batch finishing section for

either devolatisation or plate and frame final polymerization and grinding. The most widely

used process for polymerization of polystyrene today is the continuous mass process. This

solution is continuously prepared in a holding vessel and will then be injected into the reactor

system.

Page 5: Styrene Monomer

Typical feed to the first reactor would consist of 50 weight percent styrene monomer,

100 ppm water (based on styrene weight), 2000 ppm boron trifluoride (based on styrene

weight), with the balance being organic solvent. The polymerization reaction gives off heat

that is carried away from the reactors by jacketing them with a heat transfer fluid. The

temperature of the reactants should not vary by more than 15 0 C throughout the reactor

series. Temperature control is very important in this reaction because as the reaction

temperature increases, the average molecular weight of the polystyrene decreases. The

reaction temperature range is 40-70 0 C. Temperature can also be controlled by

intermediate shell and tube heat exchangers. Monomer conversions of up to 85wt%

polystyrene are obtainable in these reactors.

Emulsion polymerization: Emulsion polymerization is generally used for polymerization of

styrene with other monomers or polymers. It is not a generally commercially accepted

method of producing crystal polystyrene or high impact polystyrene. Emulsion

polymerization is carried out similarly to suspension polymerization except that the monomer

droplets are microscopic in size.

Suspension polymerization: This is also called pearl polymerization. It has proved highly

efficient for largescale production of polymers of high average molecular weight. By variation

of the polymerization condition it is possible to produce a range of polymers with different

properties and processing characteristics so that a number of grades are offered by the

manufacturers to meet the differing requirements of the conversion process and the final

product.

Page 6: Styrene Monomer

There are many different ways of making polystyrene using suspension process. Most

producers use a batch process, although there is no technical reasons why a continuous

process could not work. In the suspension process a number of small styrene drops 0.15-

0.50mm in diameter are suspended in water. The reaction occurs within these drops. To aid

in the formation of proper size drops a suspending agent is used, and to keep them at that

size a stabilizing agent is added. A catalyst is used to control the reactionrate.

Suspension polymerization offers considerable advantages over the single phase

techniques in so far that heat removal control is no longer a problem but there are

disadvantages such as the need to use a dispersing agent

Detailed process of suspension polymerization:

Suspension polymerization is a batch system popular for speciality grades of

polystyrene. It can be used to produce either crystal or high impact grades. In impact

production, the styrene and rubber solution is bulk polymerized beyond phase inversion and

is then suspended in water to create oil in water suspension utilizing soaps and suspending

agents. The suspended droplets are then polymerized to completion, utilizing initiator and a

staged heating profile. The water phase is used as a heat sink and heat transfer medium to

a temperature-controlled jacket. For the production of crystal polystyrene the styrene

monomer itself is suspended and polymerized via the same mechanism.

The requirements of polymerization are:

a] Initiator. b] Suspending agent. c] Stabilizing agent. d] Catalyst

Initiators: The initiators generally used are benzoyl peroxide and t-butylhydroperoxide.

Suspending agent: To aid in the formation of the proper size drops a suspending agent is

added. Some typical suspending agents are methylcellulose, ethyl cellulose and

polyacrylic acids. Their concentration in the suspension is between 0.01-0.5% of monomer

charged.

Stabilizing agent: To keep the drops at proper size, a stabilizing agent is added. The

stabilizing agents are often insoluble inorganic such as calcium carbonate, calcium

phosphates or bentonite clay. They are present in small amount than the suspending

agents.

Page 7: Styrene Monomer

Catalyst: A catalyst is used to control the reaction rate. The catalysts are usually peroxides.

The most common ones are benzoyl, diacetyl, lauroyl, caproyl and tert-butyl. Their

concentration varies from 0.1-0.5% of the monomer charged. The ratio of monomer to

dispersing medium is between 10 and 40%.

Polymerization temperature: Polymerization of styrene occurs at temperature range of 90-95

0 C.

Process description: The suspension method is carried out in large reactors equipped with

agitators, the styrene monomer being maintained in the aqueous phase as droplets with a

diameter varying between 0.4-1mm by use of a dispersing agent such as partially

hydrolyzed polyvinyl acetate, inorganic phosphates or magnesium silicates. To reduce the

cycle time of the reactors, the entering water and styrene will be preheated. The

temperatures of the input streams will be sent so as to obtain the desired reaction

temperature. The water entering the reactor will be heated to 95 0 C. The bulk of the styrene

is to be heated to 85 0 C before being charged. This is done in a vertical double pipe heat

exchanger, which is directly above the reactor. To prevent the polymerization from occurring

in the heat exchanger or piping system, there are to be no obstructions between this heat

exchanger and the reactor. The catalyst, rubber stabilizer, and suspending agent are

premixed in styrene and discharged by gravity into the reactor. This mixture will not be

preheated, since it might polymerize. Typical water to monomer ratios is 1:1 to 3:1. A

combination of two or more initiators is used with a programmed reaction temperature to

reduce the polymerization time to a minimum for a given amount of residual styrene.

Purification steps and Extrusion: If the water can be removed using physical separation

processes, then the styrene and the other impurities dissolved in it will also be discharged.

The final purification step is drying. The polystyrene leaving this unit must meet the

specifications set. (0.03% water). Then it is passed through a devolatisation extruder to

remove the volatile residues and to convert the polymer into pellets.

It was assumed that 3% of polystyrene would be removed from the process in airveying,

drying, centrifuging, transferring, or as bad as bad product. At least 95% of that which is lost

in processing must be intercepted before it leaves the plant. Most of it can be removed and

sold as off-grade material. This waste is split among the various streams leaving the

processing area

Page 8: Styrene Monomer

PROPERTIES AND USES

Properties:

Processing properties: Flow properties may be the most important properties of

polystyrene processes. There are two widely accepted industry methods for the

measurement of processing properties. These include the melt flow index and the solution

viscosity. The melt flow index is measured by ASTM method as a measure of the melt

viscosity at 200 0 C and a 5kg load. The melt flow index of polystyrene is generally

controlled by adjustment of the molecular weight of the material and by the addition of such

lubricants as mineral oil. Polystyrenes are commercially produced with melt flow ranges of

less than 1 to greater than 50, although the most widely available grades generally have

melt flows between 2.0 and 20g per 10min. Solution viscosity is another method for

measuring the molecular structure of the polystyrene. Solution viscosity can be measured as

an 8% solution in toluene and increases with increasing molecular weight.

Rheological properties: Polystyrene is a non-Newtonian fluid with viscoelastic properties.

The viscosity of polystyrene melts or solutions is defined as he ratio of shear stress to shear

rate. Generally, as the molecular weight of the polymer is increased or mineral oil is

decreased, melt viscosity increases.

Mechanical properties: Crystal polystyrenes have very low impact strengths of less than

0.5ft-lb. Commercially available impact polystyrene grades can be obtained with values of

1.0 - 4.0 ft-lb. Generally, polystyrenes are not produced with greater than 15% total rubber

because of polymerization processing constraints. Nevertheless, impact properties can be

increased substantially without additional rubber by the proper control of rubber particle size,

percentage of grafting, cross-linking, and percentage of gel. Tensile and flexural properties

are also important representation of the strength of polystyrenes. Increasing the rubber

modification of polystyrene generally leads to lower tensile strength, crystal grades being stiff

and brittle. Tensile strength is also decreased by the addition of lubricants, such as mineral

oil. Flexural strengths for polystyrenes can be obtained from 5000 to 18000psi and are also

decreased by the addition of rubber and other additives to the polystyrene. Elongations can

be obtained from 1% for crystal polystyrene to 100% for some impact polystyrene grades.

Thermal properties: Annealed heat distortion is one popular method for measuring he

resistance to deformation under heat for polystyrenes. The heat distortion temperature is

decreased by the addition of rubber, mineral oil, or other additives to polystyrene. The glass

transition temperature for unmodified polystyrene is 373 K, and the glass transition

temperatures for polybutadienes are 161-205 K, subject to the cis, trans, and vinyl content.

Page 9: Styrene Monomer

Chemical properties: Solvent crazing of polystyrene is a commercially important

phenomenon. High impact polystyrenes are susceptible to solvent crazing at the interface

between the rubber particles and the polystyrene phase. The resistance of polystyrene to

this crazing is referred to as environmental stress crack resistance (ESCR). For food-

packaging applications, such as butter tubs and deli containers, polystyrenes with high

ESCR properties are desirable. Increasing the percentage of gel, percentage grafting, and

rubber particle size can increase stress crack resistance. Residual levels of low molecular

weight materials are also important to polystyrene performance. Some of the chemical

impurities in the polystyrene are styrene monomer and ethyl benzene solvent. Residual

levels of styrene below 200 ppm and ethyl benzene levels below 30 ppm are obtainable for

very specialized applications.

Optical properties: Crystal polystyrene is a transparent and colorless polymer; high impact

polystyrene is generally opaque as a result of the rubber particles. Developmental grades of

translucent impact polystyrenes have been produced but have not gained wide acceptance.

The major optical; property for high impact polystyrene is gloss. Gloss is a measure of the

percentage of light reflected is generally controlled by the size of the rubber particle. In

general, the smaller rubber particle gives higher gloss. Values from 20 to 95% reflectance

are commercially available. High impact polystyrene is naturally white and crystal

polystyrene is naturally clear, but both can be readily colored.

Gas and water permeability of polystyrene: When styrene polymers are used in

packaging applications, the gas and water permeability characteristics take on an important

aspect. Polystyrene itself has its limitations and in consequence is often used with other

polymers so as to achieve different permeability properties. These properties can change

dramatically as other monomers are introduced into the molecule.

Weatherability and ageing: Polystyrene and the copolymers are susceptible to

degradation by the action of sunlight; the main effect being due to UV radiation in the

wavelength band of 300-400nm. the action of the UV radiation is accompanied by the

oxidation so that the overall degradation reaction is one of photo oxidation. The extent of

degradation varies from location to location owing to the differences in the intensity of the

radiation. This is of considerable importance in many applications because the degradation

is reflected, in the case of transparent compositions, in a yellowing effect and generally in a

loss of mechanical properties such as a lower elongation at break and a reduced impact

strength.

Page 10: Styrene Monomer

Toxicity: Polystyrene is a low toxic product. The FDA for the food contact applications

approves almost all commercially available polystyrenes. The polymer itself is not digestible

and is not normally biodegradable.

Uses:

1. 1.Extruded foam sheet of polystyrene can be thermoformed into such parts as egg

cartons or carryout food containers. Foam grade polystyrene is generally a highheat crystal

polystyrene with a high molecular weight.

2. Another type of polystyrene foam is that produced from expandable polystyrene beads.

These beads can be molded to produce hot drink cups, ice chests, or foam packaging. Also,

the expandable beads can be molded in very large blocks that can then be cut into sheets

for thermal insulation. Densities of as low as 1lb/ft 3 on foamed products are commercially

obtainable.

3. Extruded crystal polystyrene sheet can be biaxially oriented by mechanically pulling the

extruded melt in multiple directions. The stretched sheets is then cooled and allowed to set

with the biaxially orientation frozen into the sheet. This process produces crystal polystyrene

Page 11: Styrene Monomer

sheet of thin gauge wit very high strength. Typical applications include envelope windows,

cap layers for glossy sheet, or thermoforming into food packaging applications.

4. Optical property of polystyrene is used in manufacture of unbreakable glasses for gauges,

windows and lenses, as well as in countless specialties and novelties and also for edge

lighting for the edge lighting of indicators and dials

5. Solid or liquid pigments and dies color high impact and crystal polystyrenes. This can be

accomplished in both extrusion and injection molding processes. These colorants are added

and mixed during the melting stage of both the processes. Also, polystyrene parts are

amenable to high quality printing. Labels can be printed directly on the polystyrene part to

produce attractive containers.

6. Polystyrenes are also used in furniture, packaging, appliances, automobiles, construction,

radios, televisions, toys, house ware items, and luggage.

The Environmental Impacts of Styrofoam

INTRODUCTION

The production, use, and disposal of Polystyrene (a substance more commonly known as

Styrofoam) causes adverse environmental and health effects. These impacts are of

considerable concern, as, according to the Environmental Production Agency, Styrofoam is

the fifth largest source of hazardous waste in the United States

PRODUCTION

Styrofoam is composed of Benzene and Styrene, both of which are known human

carcinogens.

90,000 workers are estimated to be exposed to Styrene every year. This exposure causes a

variety of mutations to the central and peripheral nervous systems.

Benzene and Styrene have been linked to incidences of both Parkinson’s disease and

leukemia.

The production of Styrofoam is energy intensive, creating large amounts of greenhouse

gases. These problems rank the environmental production costs of Styrofoam as second

worst in the U.S. by the California Integrated Waste Management Board.

Page 12: Styrene Monomer

Hydrofluorocarbons (HFCs), used in the production of Styrofoam, result in air pollution,

causing damage to the ozone layer. They are now known to be 3-5 times more dangerous

than originally believed.

USE

Microwaving Styrofoam causes the release of toxic chemicals, which poses a threat to

human health.

DISPOSAL

Polystyrene is not usually recycled due to its lightweight nature and the high economic cost

of transporting and degreasing the petroleum-based material.

25-30% of landfills are dedicated to plastics, including styrofoam.

Polystyrene takes at least five hundred years to decompose.

Styrofoam is the primary source of urban litter.

Styrofoam is the main pollutant of oceans, bays, and other United States water sources.

Styrofoam causes choking and starvation in wildlife.

Page 13: Styrene Monomer

REFERENCES

http://sustainabilitypledge.wustl.edu/SiteCollectionDocuments/The%20Environmental%20Impacts

%20of%20Styrofoam.pdf

http://www.lyondellbasell.com/techlit/techlit/3284.pdf

http://courses.chem.psu.edu/chem36/SynFa06Web/Expt44.pdf

http://www.icispricing.com/il_shared/Samples/SubPage68.asp

http://www.cheresources.com/polystyzz.shtml

http://www.madehow.com/Volume-1/Expanded-Polystyrene-Foam-EPF.html#b

http://www.sbioinformatics.com/design_thesis/Polystyrene/polystyrene_Methods-2520of-

2520Production.pdf

SERKAN GEÇİM

20824025


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