Polystyrene (polystyrene) refers to a polymer synthesized from styrene monomer by a free radical polycondensation reaction called PS. The relative molecular weight of polystyrene is generally 45000~70000, glass transition temperature 80~90℃, amorphous density 1.04~1.06g/m², crystal density 1.11~1.12g/m², melting density 240℃, resistance 1020 ~ 1022 ohm m², and the thermal conductivity at 30 °C is 0.116 W/(m K)
PS resin is a thermoplastic non-crystalline resin with excellent thermal insulation and insulation properties, high rigidity, transparency up to 88-92%, and good water and chemical corrosion resistance. PS can be dissolved in benzene, toluene, carbon tetrachloride, chloroform, o-dichlorobenzene, ketones (except acetone), ethers and some oils, but it is very resistant to water, acid, alkali and alcohol. However, PS resin is brittle, cracks easily at low temperature, has low toughness, poor heat resistance, and the operating temperature is usually below 75°C. PS is subject to aging and yellowing when exposed to sunlight or prolonged storage.
PS resins are mainly divided into general purpose polystyrene (GPPS, commonly known as clear benzene), high impact polystyrene (HIPS, commonly known as modified benzene), and expanded polystyrene (EPS beads).
Currently, the polystyrene resin used to produce XPS sheets is mainly GPPS. GPPS resin is polymerized from styrene monomer, which can be polymerized by various synthetic methods. At present, bulk polymerization and suspension polymerization are mainly used in the industry. GPPS is colorless, odorless, easy to stain, hard, non-toxic and does not cause fungus growth. GPPS is easy to process and mold, has good fluidity and low hygroscopicity (only 0.02%), can maintain mechanical properties and dimensional stability in a humid environment, but its moisture permeability is higher than that of PE.
Physical blowing agents are currently used in the production of XPS. The physical blowing agents that can be used are mainly: HCFC, HFC, butane, carbon dioxide, ethanol, dimethyl ether (DME), liquefied petroleum gas and water. A suitable physical blowing agent should have the following characteristics: suitable vapor pressure, sufficient solubility, low diffusion coefficient, chemical inertness, low residue, safety and low cost. A good balance between solubility and diffusion coefficient is a prerequisite for XPS extruded sheeting.
In the process of polymer foaming, the method of adding a nucleating agent is often used to form a large number of bubble nuclei, the purpose of which is to create conditions for the formation of bubble nuclei. There are many types of nucleators, but one thing remains the same: they all allow the gas to collect at this point and form microbubbles. Some nucleating agents are themselves foaming agents that can play a dual role of foaming and nucleating. The most commonly used nucleating agent itself is a foaming agent, which can play a dual role: foaming and nucleation. Commonly used nucleating agents are talc, calcium carbonate, citric acid, metal powder, etc.
Nucleogens affect the structure and density of the foam. At a certain concentration of foaming agent, the amount of nucleating agent determines the number of cells, and then the size of the cells.
Most domestic XPS companies prefer to add nucleating agents when producing XPS foam sheets to improve and stabilize the manufacturing process. The nucleating agents are usually fine talc powder and the addition amount is usually 1% to 2%.
Flame retardants, fire retardants, or fire retardants are functional flame retardants that endow flammable polymers with fire resistance, and are divided into additive flame retardants and reactive flame retardants, depending on the method of application. In terms of composition, additive flame retardants mainly include inorganic flame retardants, halogen flame retardants (organic chlorides and organic bromides), phosphorus flame retardants, etc. In addition, molybdenum compounds, tin compounds and iron compounds with smoke suppression effect are also classified as flame retardants, which are mainly suitable for for plastics requiring flame retardant, flame retardant or flame retardant properties of plastics, especially polymeric plastics. It prolongs the ignition time, self-ignites and is difficult to ignite.
PS is a thermoplastic polymer material that is highly flammable and easily forms melt drops when exposed to fire. Burning melt drops also easily ignite other materials, so this material is prone to ignite during stacking and construction. At present, the fire retardant we use is methyl octabromo ether. Methyl octa bromo ether is an additive fire retardant with better flame retardant effect. It belongs to fire retardants and is used for EPS and XPS board. It has the characteristics of low dosage, good flame retardant effect, and little influence on the physical properties of materials. The flame retardant effect is higher than that of brominated aromatic flame retardants. It has good thermal stability.tew, which can make the processing equipment safe and the product performance excellent. Suitable for plastic products processed at higher temperatures.
In the production of XPS EPS boards, some other additives are needed to give the product the desired look and feel. At present, some additives mainly used in the domestic EPP industry are master batches and foam stabilizers.
Masterbatch is granulated by adding organic pigments to polystyrene as a carrier. Because the concentration is different, the coloring particles are different. The color concentrate is used to fix the color of the foam. The use of a masterbatch can mask some of the defects in the recycled polystyrene resin.
Foam stabilizer refers to a type of surfactant that plays a role in stabilizing cells in the process of cell growth, preventing diffusion of the foaming agent in the process of cell growth, and can reduce XPS foam sheet to a certain extent. , density.