Injection molding materials

What is polystyrene

• 2025-05-13

1、 Definition and Structure of Polystyrene

Polystyrene (PS) is a thermoplastic polymer formed by the polymerization of styrene monomer (C ₈ H ₈), and its chemical formula can be expressed as (C ₈ H ₈) ₙ. From a molecular structure perspective, it is a long-chain molecule composed of many styrene units covalently connected, with each styrene unit containing a benzene ring (C ₆ H ₅) and an ethylene group (CH=CH ₂). This unique structure endows polystyrene with a series of distinct physical and chemical properties.

2、 Physical properties

Appearance and condition: It is usually a colorless and transparent solid with good glossiness, but can appear in various colors after adding additives. Its forms are diverse, including granular, sheet-like, and various molded products.

Density: The density is relatively small, about 1.04-1.06g/cm ³, slightly heavier than water, which makes it advantageous in some fields that require lightweight materials.

Transparency: Pure polystyrene has high transparency, comparable to glass, which makes it highly favored in the optical field and packaging industry that requires transparency.

Hardness and brittleness: High hardness, but high brittleness, easy to fracture. However, by modifying the material, such as adding rubber or other substances, its brittleness can be reduced and its impact resistance can be improved.

Melting point and heat resistance: The melting point is about 240 ℃, but in practical use, its heat resistance is relatively poor. Generally, the long-term use temperature does not exceed 70 ℃, otherwise it is prone to deformation.

3、 Chemical properties

Chemical corrosion resistance: It has a certain degree of corrosion resistance to water, mineral oil, etc., but is easily soluble in organic solvents such as aromatic hydrocarbons (such as benzene and toluene) and halogenated hydrocarbons (such as carbon tetrachloride). This characteristic should be noted during use to avoid contact with these solvents.

Flammability: It has combustibility and produces bright flames when burned, releasing black smoke with a styrene odor, while generating products such as carbon dioxide and water.

Stability: The chemical properties are relatively stable at room temperature and are not prone to oxidation, hydrolysis, and other reactions. However, it is prone to aging in environments such as ultraviolet radiation and high temperatures, leading to a decrease in performance.

4、 Classification

According to different production processes and performance, polystyrene is mainly divided into the following two categories:

General purpose polystyrene (GPPS): refers to ordinary polystyrene, which has the advantages of high transparency, easy processing, and low cost, but has high brittleness and poor impact resistance. Mainly used for manufacturing disposable tableware, packaging materials, optical instrument components, etc.

High impact polystyrene (HIPS): By adding rubber and other modifiers to polystyrene, the material's impact resistance is improved while maintaining a certain degree of transparency and processability. Widely used in home appliance casings (such as refrigerator and washing machine casings), toys, electronic device components, and other fields.

5、 Application Fields

Packaging industry: because polystyrene has good formability, insulation and lightweight characteristics, it is often used to manufacture various packaging materials, such as food packaging boxes, foamed plastic buffer materials, etc. Foam polystyrene (EPS) is a common packaging material with excellent heat insulation and shock resistance, which is widely used in the packaging of electronic products, household appliances, glass products, etc.

Electronic and electrical industry: Utilizing its insulation performance and ease of processing, it is used to manufacture electrical enclosures, insulation components, display enclosures, etc. For example, the casing of televisions and computers may be made of polystyrene material.

Construction industry: Polystyrene foam (EPS and XPS, extruded polystyrene) is an important building thermal insulation material, which has good thermal insulation performance and low water absorption. It can be used for wall insulation, roof insulation, etc., helping to reduce the energy consumption of buildings.

In the field of daily necessities, we produce disposable water bottles, tableware, CD boxes, lampshades and other daily necessities to meet various needs in people's lives.

Toy industry: High impact polystyrene has become a commonly used material in toy manufacturing due to its excellent impact resistance and easy formability. Many plastic toys are made of polystyrene.

6、 Production method

The production of polystyrene is mainly achieved through the polymerization reaction of styrene, and commonly used polymerization methods include:

Suspension polymerization method: Disperse styrene monomer in aqueous phase, add initiator and dispersant, and carry out polymerization reaction under stirring conditions. The generated polystyrene particles are suspended in water and undergo processes such as separation, washing, and drying to obtain the finished product. The polystyrene particles produced by this method have uniform particle size and are suitable for manufacturing general-purpose polystyrene and high impact polystyrene.

Lotion polymerization: take water as the medium, add emulsifier to make styrene monomer form lotion, and conduct polymerization under the action of initiator. The polystyrene produced by this method has a high molecular weight and is mainly used for producing polystyrene resins for special purposes.

Bulk polymerization method: Directly polymerize styrene monomers without adding solvents or dispersing media. This method has a simple production process and high product purity, but it is difficult to dissipate heat during the reaction process, which can easily lead to local overheating and affect product quality.

7、 Environmental Impact and Recycling

Environmental impact: Polystyrene, due to its difficult to degrade nature, will exist in the natural environment for a long time, forming "white pollution". Improper disposal of discarded polystyrene products can pose certain hazards to soil, water sources, and the ecological environment. In addition, the black smoke and harmful gases produced during its combustion can also have an impact on air quality.

Recycling and reuse: In order to reduce the impact of polystyrene on the environment, recycling and reuse work is particularly important. Polystyrene can be processed through two methods: physical recovery and chemical recovery. Physical recycling is the process of washing, crushing, melting, and granulating discarded polystyrene products to produce recycled polystyrene particles, which are used to produce products with low performance requirements. Chemical recycling is the process of breaking down polystyrene into styrene monomers or other small molecule compounds through chemical reactions such as cracking, and reusing them for polymerization reactions. At present, the recycling rate of polystyrene is gradually improving, but it still faces problems such as high recycling costs and technical difficulties.

In short, polystyrene is a widely used polymer material that not only brings convenience to people's lives, but also needs to pay attention to its impact on the environment. Through reasonable use and effective recycling, sustainable development can be achieved.

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