Features of polystyrene
Polystyrene structure
Chemically, polystyrene is a long-chain hydrocarbon in which variable carbon centers are attached to phenyl groups (the name given to cyclic benzene). The chemical formula of polystyrene (n) is C8H8; this material contains moles of the chemical elements carbon and hydrogen.
The properties of the material are determined by the short-term van der Waals adsorption between the polymer chains. Since molecules are long-chain hydrocarbons made up of thousands of atoms, the overall attractive force between molecules is large. Upon heating (or rapidly deforming due to the combination of viscoelastic and thermal insulating properties), the chains become more conformable and slide past each other.
This intermolecular slackness (in contrast to the high intermolecular strength due to hydrocarbon persistence) gives flexibility and elasticity to this material. The ability of the system to deform at a temperature higher than its glass transition temperature allows polystyrene (and heat-softening polymers in general) to easily soften and take various shapes when heated.
History
Polystyrene was first discovered by Edward Simon in 1839, who did not know what a valuable substance she had discovered. The commercial preparation of styrene monomer and its polymerization dates back to 1934, when “Dow” company was able to synthesize styrene from petroleum products and then polymerize it. At the same time, this process is undergoing its final stages in West Germany.
The experiences gained from this product during the Second World War led to the fact that in the years after the war, polystyrene was not only recognized as an expensive electrical insulator, but also as a thermoplastic, cheap and with good properties. With the passage of time and with the publication of various theories (including Hermann Staudinger’s theory in 1922 about polymer), BASF finally developed a two-step process for the production of polystyrene foam in the early 1950s.
In this process, the first step includes the preparation of grains containing a uniform distribution of the foaming agent by the suspension polymerization method of styrene monomer, and in the second step, this material is processed inside a mold. The ease of producing products in any shape and size is one of the advantages of this method, which led to its development. This material was first produced in 1950.
Production Process
Polystyrenes are plastics that are made from styrene monomer. The most famous plastics from this family are polystyrene, modified impact polystyrene, styrene acrylonitrile (SAN) and acrylonitrile butadiene styrene (ABS).
In general, chain polymerization refers to the reaction of combining monomer molecules with each other and forming large polymer molecules. In general, chain polymerization refers to the reaction of combining monomer molecules with each other and forming large polymer molecules. Chain polymerization reaction is used for compounds that have one or more unsaturated bonds.
The raw materials required for the synthesis of PS monomer are ethylene and benzene, which react together in the synthesis process to form ethylbenzene, which is further subjected to more processes (dehydrogenation) to form vinylbenzene monomer or styrene. ) to be converted, other necessary additional materials are acrylonitrile (AN) and butadiene rubber.
By using the thermal or catalyzed reaction of styrene monomer, its polymerization process begins to become an amorphtolide polymer.
To give and create desirable properties in PS, various additives are added to it, such as rubbers, softeners, release agents and stabilizers. Also, in PS-based formulations, different groups of additives such as colorants, flame retardants (FRs), UV stabilizers, or impact modifiers are used.
Usually, GPPS is chosen due to its transparency, rigidity, and suitability for various applications. When more flexibility or high impact resistance is needed, MIPS or HIPS is used. HIPS and MIPS include butadiene rubber as a copolymerization agent in order to increase toughness, which causes the color of the product to become dull.
