Polystyrene, we are used to seeing it embrace household appliances and everyday objects when we buy them, sometimes under vegetables and meat or other similar food, but what is it made of? And how much does it pollute ? These are questions that, taken by hunger or by the new television to unwrap and turn on, perhaps we have never really asked ourselves. It’s time!
Polystyrene and separate waste collection
Polystyrene can be thrown in the garbage bin that we use to collect plastic bottles and packaging, since, when it is the base of food packaging, it is associated with plastics, but it is necessary to wash it and clean it from all food residues. If, in particular packages, we find polystyrene covered or assembled with aluminum sheets, before placing it in the recycling bin, the two materials must be separated.
When we find polystyrene used to package products, furniture or large appliances, for example, we can always dispose of it together with plastic but in case of doubts for particular packages, in order not to compromise the separate collection of the entire condominium, we can check how to behave directly on the Corepla website which is the reference for the disposal of plastic products or packaging.
Polystyrene: what is it?
Technically it is called polystyrene, in Switzerland also sagex, but only in its expanded form , and it is the polymer of styrene, a thermoplastic aromatic polymer with a linear structure which at room temperature is a glassy solid but if it starts to get hotter it acquires plasticity and is able to flow.
We can also find ourselves dealing with its expanded form, a very light white foam , often in the form of spheres or chips, to fill packaging and isolate delicate products that must not be subjected to shocks or impacts. From a chemical point of view, it is an inert material with respect to many corrosive agents , it dissolves in chloroform, trichloroethylene, acetone and in some aromatic solvents such as benzene and toluene.
Polystyrene: where it is thrown in Rome
In Rome today, polystyrene packaging should be thrown in the Blue containers that are reserved for plastic and metal packaging . These are the same ones in which Roman citizens should throw bottles, jars and plastic cans, plastic bags and envelopes, disposable plastic plates and glasses, beverage cans, aluminum trays and sheets, metal food cans, plastic and metal caps, spray cans, shells.
Polystyrene: where it is thrown in Milan
In Milan the color of the bag changes, here it is yellow , but the concept does not. Polystyrene should be thrown in the “plastic and metal” section together with bottles, containers and plastic bags, food trays, metal food cans and jars, beverage cans.
Polystyrene: where it is thrown in Naples
In Naples, Styrofoam can be thrown, it must be thrown, in the containers used to separate plastic and metals. There are street bells, bins in the neighborhoods where separate collection is done door to door, and bags.
Expanded Polystyrene (EPS)
Now that we have seen how to recycle polystyrene, we can delve deeper into its characteristics, noting that we often hear about expanded polystyrene and its different types. The main ones are sintered and extruded, the first is indicated with the acronym EPS, the second with XPS.
Let’s start with the sintered one, used mainly for the production of packaging. Being a thermal insulator, we also find it in the construction field, as a material for the insulation of buildings and for the creation of insulating sandwich panels. Even the external insulation can be made with EPS, which is obtained by immersing polystyrene granules in water and adding a quantity of pentane from 2% to 8% to the water.
When the whole thing is compressed, the pentane diffuses into the granules which are stored for a few months before undergoing expansion which occurs in a chamber with a movable wall into which water vapour at around 120-130°C is blown. In this way, the plastic softens and swells to obtain polystyrene foam pellets . When the movable wall of the chamber moves, there is a pressing effect which leads to the formation of a single block of EPS pellets which can then be cut to size before being sold.
Extruded polystyrene foam (XPS)
Extruded polystyrene, compared to EPS, is able to support greater weights. In construction, we therefore find it used in particular situations, for example under floors and even under the foundations of buildings. This type of polystyrene is obtained by introducing polystyrene granules into a worm screw extruder where they melt. By blowing pressurized gas, the melt comes out in the desired shape through a die placed at the head of the extruder. The foaming of the gas is generally linked to the difference in pressure.
Let us briefly add to these two typologies a third: that of high-impact polystyrene (HIPS), replaced by polystyrene and styrene-butadiene rubber, combined to obtain a plastic that is less fragile than generic polystyrene.
