What Are the Different Types of Polystyrene Recycling?

The English name of polystyrene is Polystyrene, referred to as PS. PS is a thermoplastic non-crystalline resin, which is polymerized from styrene monomer and can be polymerized by various synthetic methods. At present, the bulk polymerization method and the suspension polymerization method are mainly used in the industry. PS is mainly divided into general-grade polystyrene (GPPS, commonly known as transphenylene), impact-resistant polystyrene (HIPS, commonly known as modified benzene), and expanded polystyrene (EPS).

The English name of polystyrene is Polystyrene, referred to as PS. PS is a thermoplastic non-crystalline resin, which is polymerized from styrene monomer and can be polymerized by various synthetic methods. At present, the bulk polymerization method and the suspension polymerization method are mainly used in the industry. PS is mainly divided into general-grade polystyrene (GPPS, commonly known as benzene), impact-resistant polystyrene (HIPS, commonly known as modified benzene), and expanded polystyrene (EPS).

Chinese name: General grade polystyrene
Foreign name: general purpose polystyrene; GPPS

Alias: Polystyrene
Nature: Colorless, odorless, tasteless

General Properties of General Grade Polystyrene

General grade polystyrene is a thermoplastic resin, which is a colorless, odorless, odorless, shiny, transparent bead or granular solid. The density is 1.04 to 1.09, the transparency is 88% to 92%, and the refractive index is 1.59 to 1.60. Under the action of stress, birefringence occurs, which is the so-called stress-optical effect. The melting temperature of the product is 150 180 , the thermal decomposition temperature is 300 , the thermal deformation temperature is 70 100 , and the long-term use temperature is 60 80 . At a temperature lower than the thermal deformation temperature by 5 to 6 ° C, after annealing treatment, the stress can be eliminated and the thermal deformation temperature can be increased. If a little -methylstyrene is added in the production process, the heat resistance level of general polystyrene can be improved.

It is soluble in aromatic hydrocarbons, chlorinated hydrocarbons, aliphatic ketones and esters, but can only swell in acetone. Resistant to the action of certain mineral oils, organic acids, alkalis, salts, lower alcohols and their aqueous solutions. Low water absorption, can still maintain its mechanical properties and dimensional stability in humid environments. Optical performance is second only to acrylic resin. Excellent electrical properties, high volume resistivity and surface resistivity, not affected by temperature and humidity changes, and not affected by corona discharge. Radiation resistance is also good. Its main disadvantages are brittleness, easy cracking, low impact strength, and poor heat resistance. It cannot tolerate boiling water and can only be used at lower temperatures and loads. Poor sunlight resistance and flammable. It emits black smoke when burning and has a special odor.

General grade polystyrene preparation

General-purpose polystyrene is prepared by radical polymerization or ionic polymerization using styrene as a monomer. Production methods include bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. At present, industrial polymerization mainly uses suspension polymerization and bulk polymerization.

1. The bulk polymerization method sends the styrene monomer into the prepolymerization kettle, and then adds a small amount of additives and initiators, and heats and stirs at 95 to 115 ° C for prepolymerization. After the conversion rate reaches 20% to 35%, it is sent into Continuous polymerization was carried out in a tower reactor with a stirrer. The polymerization temperature was increased to about 170 step by step to achieve complete conversion. A small amount of unreacted styrene is discharged from the top of the tower and can be recovered and reused. The polymer is continuously discharged from the bottom of the tower and extruded and granulated to obtain the finished product.

2.The suspension polymerization method uses styrene as the monomer and water as the medium, and uses gelatin or starch, polyvinyl alcohol, hydroxyethyl cellulose and other protective gels or insoluble inorganic salts such as magnesium carbonate, magnesium silicate, and calcium phosphate as the dispersion. Agent, maleic anhydride-styrene copolymer sodium salt as co-dispersant, benzoyl peroxide as initiator, polymerization was initiated at about 85 . It is also possible to carry out high-temperature polymerization in an autoclave at a high temperature above 100 ° C without using an initiator. The polymer was washed, separated, and dried to obtain colorless and transparent fine-beaded resin.

General grade polystyrene processing

Polystyrene has good fluidity, good processability, easy coloring, and good dimensional stability. It can be processed into various parts by injection molding, extrusion, blow molding, foaming, thermoforming, bonding, coating, welding, machining, printing and other methods, and is especially suitable for injection molding.

Materials for injection molding can generally be used without drying. However, in order to improve the product quality, it can be pre-dried in a blast oven at 55 70 for 1 2h. The specific processing conditions are roughly: barrel temperature of about 200 ° C, mold temperature of 60-80 ° C, injection temperature of 170-220 ° C, 60-150 MPa, and compression ratio of 1.6-4.0. In order to eliminate the internal stress of the molded product, it can be thermostatically treated at 70 ° C for 2 to 4 hours in an infrared lamp or a blast oven.

During extrusion molding, the L / D ratio of the screw generally used is 17 to 24, which is cooled by air, and the extrusion temperature is 150 to 200 ° C.

When blow molding, the parisons obtained by injection molding and extrusion can be used for blow molding to obtain the required products. The blow molding pressure is generally 0.1 to 0.3 MPa.

General grade polystyrene applications

Because polystyrene is transparent and has excellent rigidity, electrical properties and printing properties, especially good sanitation and low price, it has a broad application prospect in food packaging. In the mechanical and electrical industry, instrumentation, communication equipment industry, etc., it has been widely used in various instrument housings, lampshades, optical parts, instrument parts, transparent window mirrors, transparent models, chemical acid storage tanks, acid transportation tanks, telecommunication parts, high frequency Capacitors, high-frequency insulation gaskets, brackets, inserts, and frozen insulation materials. It is also widely used in various daily necessities, such as bottle caps, containers, decorations, buttons, combs, toothbrushes, soap boxes, cigarette boxes and toys.

General grade polystyrene safety

The raw materials for resin production have different degrees of irritation on the human skin and mucous membranes, which can cause skin allergic reactions and inflammation; at the same time, pay attention to the harm of resin dust to the human body. Long-term inhalation of high concentration of resin dust can cause lung disease . Most resins have common dangerous properties: they are flammable in the presence of open flames, high temperatures, and contact with oxidants may cause a combustion hazard. Therefore, operators should improve the operating environment, and consciously divide the operating area from the non-operating area, as much as possible, Airtight, install ventilation facilities, etc.

Polystyrene resin packaging is generally paper-plastic composite bags or other packaging bags, net weight 25kg per bag, other quality large packaging can also be used. During storage, it should be stored in a ventilated and dry warehouse. It should be kept away from fire and protected from direct sunlight. It should not be stored in the open air. Polystyrene resin is non-hazardous. During the loading and unloading process, it is strictly forbidden to use sharp tools such as iron hooks. Do not throw to avoid damage to the packaging bag. During transportation, do not expose to sunlight or rain, and do not mix with toxic and corrosive and flammable and explosive products.

General grade polystyrene environment and recycling

GPPS is inexpensive and is often made into various daily necessities, such as convenient bags. Because GPPS is difficult to degrade, if the recycling system is not perfect, it is easy to cause environmental pollution, which is often called "white pollution". Nowadays, people pay more and more attention to environmental protection. Therefore, when using such products, they should be recycled separately. The recycling symbol of polystyrene is 6.