Introduction

As a prominent modified plastic manufacturer, TOPONEW is at the forefront of exploring the diverse aspects of GPPS material. From analyzing its structure and performance to delving into its various processing techniques and wide-ranging applications, we are dedicated to understanding the intricate balance between GPPS material characteristics and environmental impact. Our focus on GPPS particle solutions, continuous advancements in GPPS particle development, and efficient management of the GPPS granules supply chain underscore our commitment to sustainability and innovation within the industry.

Structure and Characteristics:

The molecular chain structure of GPPS can be considered as alternatingly linked side phenyl groups on the polyethylene molecular chain. The presence of side phenyl groups gives GPPS the following structural characteristics: first, it makes the GPPS molecular chain rigid and hard, as the phenyl groups have a large volume and exhibit significant steric hindrance effects, making molecular chain rotation difficult. The result of the molecular chain becoming rigid and hard is that the glass transition temperature of GPPS is significantly higher compared to polyethylene and polypropylene, typically around 90-100°C. Secondly, the main chain skeleton carbon atoms connected to the side phenyl groups are asymmetric carbon atoms, leading to spatial isomerism in the GPPS molecular chain. While industrial production of GPPS typically yields amorphous polymers, it was long believed that GPPS only existed in an irregular structure. In fact, regular and alternating structures of GPPS have been achieved. Regular GPPS has been prepared, making the polymer crystallizable, albeit with high melting points, low flowability, difficulty in processing, and brittleness, hence limiting practical applications. Industrially produced GPPS primarily consists of irregular isomers with minor amounts of alternating isomers, with a low level of branching due to free radical polymerization. The predominance of irregular isomers and the presence of minor branching are essential factors that result in industrial GPPS existing in an amorphous form. Additionally, the presence of side phenyl groups makes GPPS more reactive chemically than polyethylene and polypropylene, allowing characteristic reactions like chlorination, hydrogenation, nitration, and sulphonation to occur. Therefore, the chemical resistance of GPPS is lower compared to chemically inert polymers like polyethylene and polypropylene. The side phenyl groups do not introduce significant polarity to GPPS, resulting in excellent dielectric and insulation properties. Due to the conjugated system of the benzene rings, GPPS exhibits higher radiation resistance because the benzene rings evenly distribute the absorbed radiation energy.

Performance

GPPS is a colorless, odorless, tasteless, transparent rigid solid that produces a metallic ringing sound when thrown. The light transmittance of GPPS is not less than 88%, with a haze of about 3%, and a refractive index between 1.59 to 1.60, giving it a special high glossiness; however, it is prone to yellowing during storage. One reason for the yellowing is the insufficient purity of the monomer, especially when it contains trace amounts of sulfur elements; the other reason is the slow aging and yellowing of the polymer in the air. GPPS is relatively light, with a density ranging from 1.04 to 1.065. GPPS is flammable, and when ignited, it burns continuously after leaving the flame, producing an orange-yellow flame with dense smoke. Among thermoplastic plastics, GPPS is a typical hard and brittle plastic with mechanical properties such as tensile and bending strengths higher than polyolefins, but noticeably lower toughness and no yield behavior during stretching. Although the molecular chains of GPPS are rigid, its amorphous structure causes it to soften above the glass transition temperature, with a softening point of around 95°C, and many mechanical properties are significantly affected by increasing temperature. The high continuous use temperature of GPPS is only 60-80°C, and this value depends on the load size, mainly due to the non-polar nature of the molecular chains and their weak intermolecular forces, making them prone to slipping under heat. The heat distortion temperature of GPPS is between 70-98°C, varying with material formulation and heat treatment. Annealing GPPS can not only enhance mechanical strength but also raise the heat distortion temperature. Being a non-polar polymer, GPPS exhibits excellent dielectric and electrical insulation properties, with several key electrical performance indicators having relatively high values, such as a dielectric constant of about 2.45-2.65. GPPS is resistant to corrosion by inorganic acids such as sulfuric acid, phosphoric acid, boric acid, and 10%-36% hydrochloric acid, as well as organic acids like acetic acid at concentrations less than 25% and formic acid at 10%-90%, and can withstand the corrosion of many alkalis and salts; however, it is not resistant to oxidation acids such as nitric acid and oxidizing agents.

Preparation

GPPS is produced by free radical polymerization or ion polymerization of styrene monomer. Production methods include bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization, among others. Currently, the main methods adopted for industrial production are suspension polymerization and bulk polymerization.

Bulk Polymerization Styrene monomer is introduced into a pre-polymerization vessel, followed by the addition of a small amount of additives and initiators. The mixture is heated and stirred for pre-polymerization at 95-115°C until the conversion rate reaches 20%-35%. Then, it is transferred to a tower-type reactor with a stirrer for continuous polymerization reaction. The polymerization temperature is gradually increased to around 170°C to achieve complete conversion. Any unreacted styrene is removed from the top of the tower and can be recovered for re-use. The polymer is continuously discharged from the bottom of the tower, extruded, granulated, packaged, and shipped after production.

Suspension Polymerization Styrene is used as the monomer, with water as the medium. Gelatin or starch, polyvinyl alcohol, hydroxyethyl cellulose, and other protective colloids, or insoluble inorganic salts such as magnesium carbonate, magnesium silicate, and calcium phosphate are used as dispersing agents. Maleic anhydride-styrene copolymer sodium salt is used as an auxiliary dispersant, and benzoyl peroxide is used as an initiator for polymerization at around 85°C. Polymerization can also be carried out without an initiator, through high-temperature polymerization in a high-pressure reactor above 100°C. The polymer is washed, separated, and dried to obtain colorless and transparent fine bead-like resin.

Processing and Forming

GPPS is one of the easily moldable varieties in thermoplastic plastics. It is not only suitable for various forming processes but also has many good processing characteristics. GPPS can be formed using various methods such as injection molding, extrusion, thermoforming, rotational molding, blow molding, and foaming, among which injection molding, extrusion, and foaming are commonly used methods. GPPS has a very low moisture absorption rate, ranging from 0.02% to 0.3%, and generally does not require a special drying process before forming. GPPS is an amorphous polymer with no distinct melting point. It has a wide temperature range suitable for forming due to its wide range of temperatures from melting to significant decomposition. The shrinkage rate and range of variation of GPPS are small, typically between 0.2% and 0.8%, which is beneficial for producing products with high dimensional accuracy and stable dimensions. GPPS products are prone to internal stress because the molecular chains are easily oriented under the shear force during forming. However, during the cooling stage of the product, the oriented molecular chains have not relaxed, and the melt has already cooled below the glass transition temperature, causing the orientation to freeze. Injection molding is an important forming method for GPPS, allowing for adjustments in melt temperature within a wide range depending on the shape and wall thickness of the product. Injection molding can be carried out on screw-type injection molding machines or plunger-type injection molding machines. When using a screw-type injection molding machine, the recommended melt temperature range is between 190-230°C. GPPS can be extruded to produce sheets, rods, and films. Extrusion typically utilizes a helical screw with a gradually changing depth of the groove. The length-to-diameter ratio of the screw is within the range of 17-24, with a compression ratio between 2-4, and the barrel temperature is around 150-200°C. GPPS can also be foamed to produce insulating products and cushioning packaging materials. First, GPPS resin is prepared into granules containing a foaming agent, known as expandable polystyrene. These expandable granules can be placed in molding tools of any shape and can be foamed into the desired product simply by heating without the need for pressure.

Applications

Due to its affordability, transparency, good processability, excellent insulation properties, and ease of printing and coloring, GPPS has a wide range of applications. Products made from GPPS using injection molding have a high gloss surface finish, good dimensional stability, and are aesthetically pleasing, making them widely used in both industrial and daily life applications. Examples of applications include automotive light covers, instrument surfaces, parts for chemical and optical instruments, telecommunications components, jewelry boxes, perfume bottles, toothbrushes, soap dishes, fruit trays, etc. Extruded products made from GPPS, with relatively high molecular weight, facilitate the shaping of products such as films, pipes, containers, sheets, used in chemical, packaging, and decoration industries. GPPS is also used in electrical equipment casings, toys, lighting fixtures, household appliances, stationery, cosmetic containers, interior and exterior decorations, fruit trays, optical components like prisms and lenses, lens windows, and molded products such as vehicle lights, telecommunication accessories, radio frequency capacitive films, high-frequency insulation materials, TV and microwave oven housings, chemical containers, etc. Expandable polystyrene can be made into foam plastics of different densities for insulation, soundproofing, shock absorption, flotation, packaging materials, cork substitutes, and lightweight concrete preparation from pre-expanded beads. Low foam plastics can be used to produce synthetic wood for furniture. High-heat resistant GPPS resin with excellent transparency, strength, and heat resistance is mainly used for hot beverage containers and special heat-resistant applications like high-temperature kettles and heating element housings.

Environment

GPPS, being low-cost, is often used for various daily items like convenience bags. Due to its difficulty in degrading and the incomplete recycling system, improper disposal of GPPS can lead to environmental pollution, known as "white pollution." Nowadays, environmental protection is of increasing importance, so when using such products, it is important to recycle them properly. The recycling symbol for polystyrene is 6.