THE USUAL NAMES
Polyurethane, urethane plastic, polyether (-foam), polyester (-foam), cold foam, cellular plastic, soft foam, stiff or hard foam, urethane foam, polyurethane-elastomers, polyurethane rubber.
Usual abbreviations: PUR, RIM, RRIM, TPE-PU, TPU
Starting from the used polyol- and di-isocyanate types you can make a wide range of different types of flexible or stiff polyurethanes with high or low density.
The material group is characterized by a high chemical resistance and has a wide range of use, among others for furniture upholstery, for mattresses, cushions, thermal insulation, wear parts for the industry, interior parts for cars, and it enters into different types of paint/lacquers, sealants and glues.
Polyurethanes belong to the group of thermoset and is as other organic materials among others build up from carbon, hydrogen, and oxygen.
The materials are in their ground state white to yellowish, but grow more yellow in time under the influence of UV-light.
That is they age among others by change of colour, but by the incorporation of additives or in combination with dyeing they can get more resistant to fading.
Polyurethanes can be tailored for a wide interval of density, hardness, flexibility, and with or without integrated skin formation.
The material is used for many purposes in our society.
Polyurethane is a flammable material, under a fire course, combustion gas, which is harmful, will develop.
The combustibility and smoke development is dependent on the porosity and density of the material, the temperature and the oxygenation of the surroundings and on possible added fire-resistant additives as well as on the material structure.
Fire fighting takes place by powder or carbon dioxide. Al contact to the smoke gases shall be avoided or take place only by using an oxygen- or fresh-air mask.
FLEXIBLE POLYURETHANE FOAM
(PU foam without skin)
Block moulding alternatively moulding.
15 to ca. 100 g/l
At variation from the incoming components in the prescription, you can make products with a large span in the mechanic- as well as in the chemical properties.
Padding material for furniture, mattresses, and car seats. For packing, gym mats, underlay, sponges and washcloths, to be laminated on textiles, for sound insulation, so-called back up for PVC articles in cars, oil filters, and sealing lists.
FLEXIBLE POLYURETHANE FOAM
(PU foam with skin, so-called Integral foam)
Moulded polyurethane foam
100 to ca. 1000 g/l
Like by flexible polyurethane foam with low density you can make products with a wide range of mechanic- and chemical properties. The degree of skin formation do influence very much on the mechanic properties.
Energy absorbing parts in vehicles and gaskets as decoration- and comfort articles in vehicles, soles, boat fenders, tyres for hobbies, arms for office furniture as well as handicap-, rehabilitation- and medical aids.
Di-isocyanides are chemicals which are normally fluid at room temperature and which forms polyurethanes at reactions with hydroxyl chemicals as for instance polyols. The most common types are TDI and MDI.
Polyols are fluid, oil-like substances which chemically seen can be polyester- or polyether-based, which influence on the properties of the end product. Polyols can be added a number of small quantity aids like catalysts, blowing agents and substances, which influence on the cytogenesis.
The chemical structure of the polyols do have a high influence on the properties of the end product that is stiffness, elasticity, density and the skin formation just like the additives have.
- ADDITIVES, HARDENERS AND OTHER AIDS
Under the production, you can add additives in order to control the reaction speed, foam stability, cell structure, and density, and to give the end product specific use- and function properties. As an example, you can mention hardeners like diols, diamines, alkanolamines that can be added both common PU-systems as PU-prepolymers to control the hardening process.
- BLOWING AGENTS
For the production of cellular polyurethanes a combination of chemically- and physically blowing agents are used.
Hydrocarbons, especially pentane-isomers, are used by the production of stiff polyurethane foam, while fluid carbon dioxide is used at the production of flexible polyurethane foam.
RULES AND HANDLING
Only the chemicals approved from the authorities can be used at the production of polyurethane products. Like this, it is for instance not allowed to use CFC's or HCFC's as blowing agents. The production, transport, and other handling of chemicals are regulated in the persisting laws and regulations.
- KONVENTIONAL METHODES
The principle of the production is that the liquid components are mixed and react under the formation of the polyurethane material. The mixture and dosing takes place industrially using mechanically mixing- and dosing equipment, at so-called low- or high-pressure methods.
- PREPOLYMERS-BASED PRODUCTION
At the productions of elastomers, glues and sealants, prepolymers are often used, which means that isocyanide and polyol pre-react. After that, the other chemicals are added and the end of the hardening takes place.
- THERMOPLASTIC POLYURETHANE
Thermoplastic polyurethane is produced by the same processes as at the production of thermoplastic, which is using injection moulding, extrusion or blow moulding.
- COMMON PRODUCTION METHODS
The most common production methods:
1. Block moulding
2. RIM reaction moulding (Reaction Injection Moulding)
3. RRIM reaction moulding with fiber interference
(Reinforced Reaction Injection Moulding)
4. Low- and high-pressure moulding in open forms
5. Injection Moulding, extrusion and blow moulding
- ENERGY RECYCLING
PUR materials contains approximately the same content of energy as heating oil and can be combusted in most of the waste incineration plants linked to energy recycling.
- COMPOSTING AND REPOSITORY
Polyurethane is not combustible, as the degradation under influence of sunlight, heat and microorganisms are extremely slow.
In Denmark, there is a ban on landfill of combustible waste. Polyurethane foam and other plastic types have a high content of energy, which is released by combustion, which is the reason why, these materials should be disposed by incineration, if they cannot be recycled.
- RECYCLING TO RAW MATERIALS, SO-CALLED FEEDSTOCK RECYCLING
Polyurethane is, because it is a hardening plastic, not recyclable in the same way as thermoplastic.
I.e. the material cannot be remelted to a new material.
Research is ongoing about chemically methods to degrade to the source materials, which can be used for new productions of polyurethane products.
Residues in connection with the cutting of the foam can be granulated in a mechanical process. The granules from flexible foam can be used as filling in cushions and seats for garden furniture or be put together to so-called bonded foam at addition of a di-isocyanate binder. The material is moulded in a form under the use of very high pressure and steam, and afterwards it can be made up to a desired geometry. Another method is to grind PU into a fine powder and add it as a filler at the production of new polyurethane.