Polystyrene (abbreviated as PS) refers to a polymer synthesized from styrene monomer through free radical addition polymerization. It is a colorless and transparent thermoplastic with a glass transition temperature higher than 100°C, so it is often used to make various disposable containers that need to withstand the temperature of boiling water, as well as disposable foam lunch boxes.
Polystyrene (PS) includes ordinary polystyrene, expanded polystyrene (EPS), high impact polystyrene (HIPS) and syndiotactic polystyrene (SPS).
Ordinary polystyrene resin is non-toxic, odorless, colorless, transparent particles, like glass-like brittle materials. Its products have extremely high transparency, with a light transmittance of more than 90%, good electrical insulation properties, and are easy to use. Coloring, good processing fluidity, good rigidity and good chemical corrosion resistance. The disadvantages of ordinary polystyrene are that it is brittle, has low impact strength, is prone to stress cracking, has poor heat resistance and is not resistant to boiling water.
Ordinary polystyrene resin is an amorphous polymer. The side groups of the polystyrene macromolecular chain are benzene rings. The random arrangement of the large side groups of benzene rings determines the physical and chemical properties of polystyrene. Such as high transparency, high stiffness, high glass transition temperature, brittleness, etc. Expandable polystyrene is made by impregnating ordinary polystyrene with a low-boiling point physical foaming agent. It is heated and foamed during processing, and is specially used to make foam plastic products. High-impact polystyrene is a copolymer of styrene and butadiene. Butadiene is the dispersed phase, which improves the impact strength of the material, but the product is opaque. Syndiotactic polystyrene has a syndiotactic structure and is produced using metallocene catalysts. The new polystyrene varieties developed have good performance and are engineering plastics.
Physical properties of polystyrene
Polystyrene molecules and their aggregation structure determine that it is a rigid and brittle material, which exhibits brittle fracture under the action of stress. The embrittlement temperature is about -30℃, the glass transition temperature is 80~105℃, the melting temperature is 140~180℃, and the decomposition temperature is above 300℃. Since the mechanical properties of polystyrene decrease significantly with the increase of temperature and its heat resistance is poor, the continuous use temperature is about 60°C, and the maximum temperature should not exceed 80°C. Thermal conductivity is low, 0.04~0.15W/(m·K), and is almost not affected by temperature, so it has good thermal insulation properties.
Polystyrene also has good electrical properties, with volume resistivity and surface resistivity as high as 10^16~10^18Ω·cm and 10^15~10^18Ω respectively. The dielectric loss tangent value is extremely low and is not affected by changes in frequency, ambient temperature, and humidity. It is an excellent electrical insulation material. Polystyrene also has excellent optical properties, with a light transmittance of 88% to 92% and a refractive index of 1.59 to 1.60. It can transmit visible light of all wavelengths. The transparent material is second only to acrylic polymers such as plexiglass among plastics. things. However, due to poor weather resistance of polystyrene, turbidity and yellowing may occur due to sunlight and dust during long-term use or storage. Therefore, when using polystyrene to make highly transparent products such as optical components, it is necessary to consider adding appropriate varieties and Dosage of antioxidants.
Polystyrene chemical properties
Good corrosion resistance, poor solvent resistance and oxidation resistance.
Polystyrene is resistant to various alkali, salt and aqueous solutions, and is resistant to lower alcohols and certain acids (such as sulfuric acid, phosphoric acid, boric acid, hydrochloric acid with a mass fraction of 10% to 30%, mass fraction of 1% to 25 % acetic acid, mass fraction of 1% to 90% formic acid) are also stable, but concentrated nitric acid and other oxidants can destroy it.
Polystyrene can be dissolved in many solvents with similar solubility parameters, such as tetrachloroethane, styrene, isopropane, benzene, chloroform, xylene, toluene, carbon tetrachloride, methyl ethyl ketone, esters, etc. , insoluble in mineral oil, aliphatic aromatic hydrocarbons, ether, acetone, phenol, etc., but can be swollen by them. Many non-solvent substances, such as higher alcohols and oils, can cause stress cracking or swelling in polystyrene.
Polystyrene is prone to aging under heat, oxygen and atmospheric conditions, causing the breakage and color development of macromolecular chains. It is more likely to age when the system contains trace amounts of monomers, sulfides and other impurities. Therefore, polystyrene The product will turn yellow and brittle during long-term use.
Polystyrene is easy to process and form, and has the advantages of transparency, cheapness, rigidity, insulation, and good printability. It can be widely used in the light industrial market, daily decoration, lighting instructions and packaging. In terms of electrical aspects, it is a good insulating material and heat insulation material. It can be used to make various instrument casings, lampshades, optical and chemical instrument parts, transparent films, capacitor dielectric layers, etc.
It can also be used in powder and lotion cosmetics. It has good compressibility when used in powder cakes and can improve the adhesion properties of powder. It is a high-grade filler that replaces talc and silica, giving skin luster and smoothness.
The difference between polystyrene GPPS, HIPS and EPS
Polystyrene (PS) is polymerized from styrene monomer and can be polymerized by a variety of synthesis methods. The English name of polystyrene is Polystyrene, abbreviated as PS (hereinafter referred to as PS).
PS is a thermoplastic amorphous resin, which is mainly divided into general-purpose polystyrene (GPPS, commonly known as transparent styrene), impact-resistant polystyrene (HIPS, commonly known as modified benzene) and foamed polystyrene. (EPS).
The difference between GPPS, HIPS and EPS is that GPPS has high transparency and good gloss, while HIPS has average brightness and a bit less toughness than ABS. The surface is bright after fire and smells of styrene. The cross-section of HIPS is white, but GPPS is not, while EPS is mainly used for foam.
GPPS is a general-purpose polystyrene. The GPPS density is 1.04~1.09, the transparency is as high as 88%~92%, and the refractive index is 1.59~1.60. Such a high refractive index gives it good gloss and decorative effect. Good dimensional stability. Commonly used scope: Daily necessities: cups, various boxes, toothbrushes, combs, food containers, ball pens.
HIPS is impact-resistant polystyrene, an impact-resistant polystyrene product produced by adding polybutyl rubber particles to polystyrene. HIPS is a modified material of PS, which contains 5-15% rubber component. Its toughness is about four times higher than that of PS, and its impact strength is greatly improved. It has the advantages of PS with molding processing and strong coloring power. HIPS has low water absorption and does not require pre-drying during processing. HIPS is milky white opaque beads or particles that can be colored at will. It has good rigidity and is easy to process and form. Its small strength is more than 7 times higher than GPPS. Different rubber content has different impact strength. It can generally be divided into impact strength and ultra-high strength. Several levels of impact resistance. As the impact strength increases its tensile strength and transparency decrease. Mainly used as packaging materials, such as food, cosmetics, daily necessities, mechanical instruments and stationery packaging, etc.; it can be formed using a variety of processing methods.
Polystyrene foam (Expanded Polystyrene referred to as EPS) is a lightweight polymer. It uses polystyrene resin and adds a foaming agent, which is softened by heating at the same time to generate gas and form a foam plastic with a hard closed cell structure. This uniformly closed cavity structure makes EPS have the characteristics of low water absorption, good thermal insulation, light weight and high mechanical strength. The density of EPS is determined by the expansion ratio of polystyrene particles during the molding stage, and is generally between 10 and 45kg/m3. The apparent density of EPS used in engineering is generally between 15 and 30kg/m3. The density of EPS currently used as lightweight filler in road engineering is 20kg/m3, which is 1% to 2% of ordinary road filler. Density is an important indicator of EPS, and its mechanical properties are almost directly proportional to its density.
