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polystyrene (PS)


MFI (200°C-5 KG) = MELT FLOW INDEX (200°C-5 KG)


polystyrene (PS)

Iran’s petrochemical industry was established in late 1950s. Availability of enormous hydrocarbon reserves and also having an exemplary domestic market, the industry rapidly developed in the ensuing years. Since its inception, the industry has travelled a long and challenging road from its humble origins to become a significant source in the global petrochemical market.

The genesis of petrochemical industry in Iran dates back 1964, when the National Petrochemical Company (NPC) was set up to plan for the development of this high-potential industry.

Jam Empire Trading (JET) Company is a prominent manufacturer, supplier and exporter of several petrochemical products in the Middle East. Having extended existence in international markets, Jam Empire Trading (JET) Company is able to present its services in all aspects of this business, from consultation to exporting. Polystyrene is one of the Jam Empire Trading (JET)’s specialties which makes us distinguished from our rivals, as we are able to find the most proper product for our customers among plethora of products promptly.

What is Polystyrene?

Polystyrene is a thermoplastic resin made by the polymerization of styrene as the sole monomer and it may contain small portions of stabilizers, lubricants, fillers, pigments, and dyes. It also may be copolymerized with other unsaturated compounds. When this is done, it is usually called a modified compound, high-impact, or super high-impact styrene.

Styrene was first isolated by scientists in 1831, which makes it one of the oldest materials in the plastics family.

However, it was not until 1938 that it first appeared in the plastics industry in the United States. Since then, its acceptance as an extremely well qualified material is demonstrated by the fact that over a million pounds (453,600 kg) a year are used in the production of a tremendous variety of products ranging from toys to fluorescent lighting panels.

The material is supplied to the fabricator in the form of pellets ranging in size from 0.03125 inch (794 μm) to 0.125 inch (3.2 mm) in diameter. The pellets are packed in heavy waterproof paper bags of 50 lb (23 kg) capacity or 200 lb (91 kg) capacity cardboard drums.

Polystyrene is a versatile plastic used to make a wide variety of consumer products. As a hard, solid plastic, it is often used in products that require clarity, such as food packaging and laboratory ware. When combined with various colorants, additives or other plastics, polystyrene is used to make appliances, electronics, automobile parts, toys, gardening pots and equipment and more. Polystyrene also is made into a foam material, called expanded polystyrene (EPS) or extruded polystyrene (XPS), which is valued for its insulating and cushioning properties. Foam polystyrene can be more than 95 percent air and is widely used to make home and appliance insulation, lightweight protective packaging, surfboards, foodservice and food packaging, automobile parts, roadway and roadbank stabilization systems, and more.

Polystyrene is made by stringing together, or polymerizing, styrene, a building-block chemical used in the manufacture of many products. Styrene also occurs naturally in foods such as strawberries, cinnamon, coffee and beef.

Styrene readily polymerizes to polystyrene by a relatively conventional free radical chain mechanism. Either heat or initiators will begin the polymerization. Initiators thermally decompose, thereby forming active free radicals that are effective in starting the polymerization process. Typically, initiators used in the suspension process include benzoyl peroxide and di-tert-butyl per-benzoate.

Potassium persulfate is a typical initiator used in emulsion polymerizations. In the presence of inert materials, styrene monomer will react with itself to form a homopolymer. Styrene monomer will react with a variety of other monomers to form a number of copolymers. Polystyrene is an odorless, tasteless, rigid thermoplastic. Pure polystyrene has the following structure.

Figure 1. Pure Polystyrene

The homopolymers of styrene are also referred to as general purpose, or crystal, polystyrene. Because of the brittleness of crystal polystyrene, styrene is frequently polymerized in the presence of dissolved polybutadiene rubber to improve the strength of the polymer. Such modified polystyrene is called high-impact, or rubber-modified, polystyrene. The styrene content of high-impact polystyrene varies from about 88 to 97 percent. Where a blowing (or expanding) agent is added to the polystyrene, the product is referred to as an expandable polystyrene. The blowing agent may be added during the polymerization process (as in the production of expandable beads), or afterwards as part of the fabrication process (as in foamed polystyrene applications).

Different Grades of Polystyrene

Products made of Polystyrene are produced by almost every process of fabrication known to the plastics industry. By far, the greatest quantity used is in the injection molding and extrusion processes. This material is extremely versatile under the extreme conditions of processing, which makes it very popular when the need arises for a material which must be produced with a minimum amount of difficulties. Polystyrene is not generally thought of as a compression molding material, but under certain conditions this process can be used.

The vacuum forming process uses vast quantities of the high-impact type of Polystyrene sheets in the manufacture of large-size, heavy-gage products. Great amounts of the thinner gages are used for the display and packaging industry.

A large volume of Polystyrene is produced for the Polystyrene foam business for production of large blocks of ready-made foam material. There are also Polystyrene beads, which are caused to foam within a heated mold. Styrene is also used in the manufacture of adhesives and paints.

The decision about which of the many different types and brands of material to use for a particular product and the choice of fabrication method is not a very easy one to make. Many variables are involved in each of the many processes and in the economics of the different methods. It is always a wise move to consult with persons well qualified in the field of plastics materials, who have a good knowledge of the fabrication methods, before any definite decisions are reached.

Because of the design of certain products, it is sometimes necessary to produce the part in two or more sections and then bond them together. This is not difficult with Polystyrene, as many types are available that allow for fast, easy bonding. Usually, when two pieces are joined together by certain solvents, the resultant weld is as strong or stronger than any other portion of the molded part.

Another very important characteristic of Polystyrene is that parts may be decorated by many methods, including spray painting, silk screening, roller coating, hot stamping, vacuum metallizing, and dip coating. The

various methods used to decorate plastics have certain characteristics that should dictate their particular use.

Most Polystyrene articles are decorated with fast air-drying lacquers.

Spray painting is accomplished with the use of stencil-type masks particularly adapted to painting uneven surfaces with more than one color. This method is quite extensively used in the toy industry and has become fully automated.

Silk screening is used with very good results in the vacuum forming and sign industries because it is well adapted for flat and large radii surfaces. Hot stamping is well suited for use on Polystyrene parts and is often used on advertising novelties. It can be done with or without color.

Vacuum metallizing is an excellent method for decorating, but care should be taken regarding the surface to be metallized. Dipping is not often used. Extreme care must be taken when decorating by this method because the solvents in the paint may cause swelling or softening of the parts. It is suggested to seek the advice of an expert in this field before any decision on decorating is made.

The optical properties of Polystyrene are good and, when there are no fillers or additives, it is a crystal clear material. When it contains fillers or additives, it becomes either translucent or opaque. Color can be added to obtain the amount of light transmission required, or the depth of opaqueness desired.

Polystyrene has very good dielectric properties, as is characteristic of most of the other thermoplastics. It is used quite extensively for television and stereo cab-inets and parts, battery cases, and many other electrical applications where good dielectrics are necessary. Polystyrene has an exceptionally low power factor. Although articles made of Polystyrene hold their dimensions very well when used properly, care should be taken not to overestimate its qualities.

Polystyrene is not generally an outdoor material and should not be used in places where it might be too exposed. It also might be well to remember that the surface of general purpose or normal styrene is very hard and is easily scratched. It is a brittle material and if broken, the edges are jagged and sharp. This is not always true of the modified types, since that is one of the reasons for modification. Polystyrene is classified as slow burning, but it will burn and should never be held over an open flame. However, blends have been developed to withstand high heats, up to and above the boiling point of water. Progress has been made to make this material selfextinguishing.

There are many applications in the home where this material will not be adversely affected, such as food containers, refrigerator door liners, wall tile, furniture drawers, or decorative room dividers. Most of these materials should not be used with citrus fruit rinds, turpentine, gasoline, or fingernail polish. These can cause staining or disfiguration and make the product unsuitable for use. Blends of Polystyrene may have fillers, such as fiberglass or rubber. These fillers give added strength to the end product, thereby making this low-priced material equal to or better than many of the higher-priced materials for specific items.

Polystyrene products tend to attract dust particles. This is because of the static electricity built up in the article during the process of fabrication. However, many products are available that help to destaticize and, in some instances, eliminate the static electricity completely. To keep articles made of Polystyrene clean, it is recommended that they be washed in lukewarm water with a mild soap or detergent using a soft cloth. A point to remember is that a product is only as good as the material and workmanship that go into it. Polystyrene has been used in the plastics industry for many years, and the production use of this material has increased tremendously every year. It is quite apparent that Polystyrene will be one of the basic materials of the plastics industry for many years to come.

Specifying and purchasing polystyrene thermal insulation can be complicated because there are multiple product types with distinctive physical properties. Using the ASTM International standard applicable to polystyrene can provide useful guidance.


The U.S. product standard for polystyrene thermal insulation is ASTM C578, “Standard Specification for Rigid, Cellular Polystyrene Insulation.” It applies to expanded polystyrene (EPS) and extruded polystyrene (XPS) products. Within ASTM C578, there are Types I through XV classification designations. Type III was deleted because the product no longer is available. Seven type classifications describe EPS products, and seven describe XPS products.


EPS products are identified by ASTM C578’s Types I, II, VII, IX, XI, XIV and XV. The types are characterized by distinctive physical properties, including density and compressive strength. The figure shows common types, minimum and nominal densities, and minimum compressive strengths for EPS. EPS complying with ASTM C578, Type XI (0.75 nominal density) generally is not intended for use in roofing applications.

NRCA recommends EPS used as rigid board roof insulation have a minimum nominal density of 1.25 pounds per cubic foot, such as that complying with ASTM C578, Type VIII. Designers should specify EPS with higher density and compressive strength values to meet specific project requirements.


XPS products are identified by ASTM C578’s Types IV, V, VI, VII, X, XII and XIII. The types are characterized by distinctive physical properties, including density and compressive strength. The figure shows common types, minimum densities and compressive strength values for XPS.

XPS complying with Type XII or XIII generally is not intended for use in roofing applications. NRCA recommends XPS used as rigid board roof insulation have a minimum compressive strength of 15 pounds per square inch (psi), which complies with ASTM C578, Type X. Designers should specify XPS with higher compressive strength values to meet specific project requirements. Type VI (40 psi), Type VII (60 psi) or Type V (100 psi) products may be used in protected membrane roof systems and plaza deck applications where high compressive strength values may be desirable.

Specifying recommendations

When using polystyrene, NRCA recommends specifiers identify the specific polystyrene product desired using the ASTM C578 designation and applicable type classification. Also, specifiers should clearly indicate their desired board sizes and thicknesses in project specifications based on a project’s specific requirements. Additional information regarding polystyrene thermal insulation is contained in The NRCA Roofing Manual: Membrane Roof Systems—2015. NRCA members can access the manual free on shop.nrca.net or via the NRCA app. 123

Table 1. Physical Properties of different types of EPS and XPS

Physical Properties XPS - ASTM C578
Density, pounds per cubic foot (minimum) 0.9 (1.0 nominal) 1.35 (1.5 nominal) 1.15 (1.25 nominal) 1.8 (2.0 nominal) 0.7 (0.75 nominal) 2.4 (2.5 nominal) 2.85 (3.0 nominal)
Density, pounds per cubic foot 1.45 3 1.8 2.2 1.3 1.2 1.6
Compressive strength, psi (minimum) 10 15 13 25 5 40 60
Compressive strength, psi (minimum) 25 100 40 60 15 15 20
Type IV Type V Type VI Type VII Type X Type XII* Type XIII*
Type I* Type II Type VIII Type IX Type XI Type XIV Type XV

*Indicates a product type typically not used in roof assemblies

Polystyrene Production

Batch Process

Various grades of polystyrene can be produced by a variety of batch processes. Batch processes generally have a high conversion efficiency, leaving only small amounts of unreacted styrene to be emitted should the reactor be purged or opened between batches. A typical plant will have multiple process trains, each usually capable of producing a variety of grades of polystyrene. Figure 2 is a schematic representation of the polystyrene batch bulk polymerization process, and the following numbered steps refer to that figure. Pure styrene monomer (and comonomer, if a copolymer product is desired) is pumped from storage (1) to the feed dissolver (2). For the production of impact-grade polystyrene, chopped polybutadiene rubber is added to the feed dissolver, where it is dissolved in the hot styrene. The mixture is agitated for 4 to 8 hours to complete rubber dissolution. From the feed dissolver, the mixture usually is fed to an agitated tank (3), often a prepolymerization reactor, for mixing the reactants. Small amounts of mineral oil (as a lubricant and plasticizer), the dimer of alpha-methylstyrene (as a polymerization regulator), and an antioxidant are added. The blended or partially polymerized feed is then pumped into a batch reactor (4). During the reactor filling process, some styrene vaporizes and is vented through an overflow vent drum (5). When the reactor is charged, the vent and reactor are closed. The mixture in the reactor is heated to the reaction temperature to initiate (or continue) the polymerization. The reaction may also be begun by introducing a free radical initiator into the feed dissolver (2) along with other reactants. After polymerization is complete, the polymer melt (molten product) containing some unreacted styrene monomer, ethylbenzene (an impurity from the styrene feed), and low molecular weight polymers (dimers, trimers, and other oligomers), is pumped to a vacuum devolatilizer (6). Here, the residual styrene monomer, ethylbenzene, and the low molecular weight polymers are removed, condensed (7), passed through a devolatilizer condensate tank (9), and then sent to the byproduct recovery unit. Overhead vapors from the condenser are usually exhausted through a vacuum system (8). Molten polystyrene from the bottom of the devolatilizer, which may be heated to 250 to 280°C (482 to 536°F), is extruded (10) through a stranding die plate (a plate with numerous holes to form strands), and then immersed in a cold water bath. The cooled strands are pelletized (10) and sent to product storage (11).


Unit 4, No. 2, Ebrahimi Alley 
Pastor Street, Tehran, Iran.


 +98 21 66933982


 +98 21 66908725



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