Polyurethane: useful and versatile
Polyurethane was discovered by Bayer in 1947. It is cheap, versatile, and largely used in many sectors, and is an important technological solution. Polyurethane can be found in a large scale of different products, from the insulations of refrigerators and freezers, to the upholstery of furniture or parts of car.
It can also be found in shoes’ soles, sport garments, and in the building industry, as panels and insulating foam. It is a particularly useful material, and it is defined as follows:
“synthetic material […] used for insulation and packing, as fibres and hard inert coatings” (collinsdictionary)
Maybe the first material that comes to mind talking about polyethylene is thefoam rubber. It is largely used in the upholstery of sofas, beds and furniture. It is so used, that its presence in everyday life objects is almost unnoticed. One of the biggest and most known objects is the mattress, that represent also a big part of the polyurethane market.
The new upholstery of mattresses is called memory foam, a polyurethane viscoelastic foam normally used in pillows, for its softness and flexibility. The heat-sensitive foam deforms itself because of the body heat, following the silhouette of the body, “memorizing” it for some minutes. So the body finds support without hardness sensations, and the musculature can relax helping to sleep. This material is also used in medical equipment to prevent bedsore.
Researches helped to find new tissues and membranes based on polyurethane, like that applied on technical shoes, but also on classic ones, where breathable parts can be found. They were obtained through a special process, based on polyurethane resins. They help to create an elastic layer, waterproof though breathable, with an antibacterial action and resistant to washing machine and dryer.
With these late characteristics, it can be used not only in the medical sector, but also in the orthopedic sector, with work clothing and safety devices. In the building industry the polyurethane (also PUR) is easy to find, with semi-rigid panels and foams, that are normally mixed with other insulating materials. Their processing, especially the cut , must be correctly performed, using some individual safety devices, normally recommended on packagings. This is due to possible allergies caused by the dust created with cut or polishing of polyurethane. The above mentioned insulating panels can be used with aluminum films, kraft paper, plasterboard, or metal layers in sandwich panels, largely used in structures or outer layers.
In the building sector, the polyurethane can be used in the insulation layers of roofs, attics, outer walls and in the sealing of pipes and metal fittings through foams. In the architecture sector, precisely in theatres or recording rooms, polyurethane is used in sound-absorbing panels, that are put on the walls where the concert or the registration takes place. They are normally ashlared – like egg boxes – in order to convey the sound waves into the pores of the panels, where there are air sacks, that turn sound waves into heat and dissipates their power.
In the latest years a market based on the recycle of polyurethane has flourished, especially in the USA. It changes its name into agglomerated foam, for its different size and density. The trade names are agglomerated polyurethane foam, closed cell polyethylene foam, and agglomerated rubber foam. This recycled form find its application in the special paddings, that requires a high density, for example heavy packaging.
There are pros and cons from the ecologic point of view:
- The isocyanates contained in the polyurethane glues can cause allergies and are carcinogenic;
- It can be recycled into shoes soles, gymnastic mattresses, and some fitted carpet basis, but its disposal must be made in particular structures;
- It is normally not fire resistant, and if solicited with high temperatures, it releases toxic gases. If it is treated with catalysts, it can be used as fire retardant (there are also particular foams against fire, that can resist to higher temperatures);
- The balance between primary energy for the production of expanded polyurethane panels and its lifecycle is good if we consider its insulating capacity – thanks to its weight, between 66 and 88 lb/m3 and its insulating capacity, it is possible to recover the energy needed for the production of these panels in a couple of years;
- It has a good resistance to humidity and chemical agents.