Polypropylene is the generic term used to describe a family of polymers derived from a particular group of base chemicals known as olefins. The polyolefins family includes polypropylene and polyethylene.
Polypropylene is made by polymerization together small molecules (monomers) to form long chains (polymers) with thousands of individual links.
The base monomers(propylene and ethylene) are gases at room temperature, but when they are linked together they become long chains of molecules called polymers. As polymers, they form tough, flexible plastic materials with a large variety of uses.
Getting the monomers to link together is achieved through polymerisation. It requires high temperatures, high pressure and the use of a catalyst system. The catalysts used are generally a mixture of titanium and aluminium compounds. Without these remarkable substances the production of polypropylene would simply not be feasible; the polyolefin success story is in large part a story of increasingly powerful, sophisticated catalyst systems.
(see : How polypropylene is made)
Polypropylene is the world's fastest growing polymer family and there are a number of good reasons for this:
Cost - performance : modern polypropylene cost less to produce and process than many other plastics and materials they replace. In addition, continuous improvement in strength and durability enables manufacturers to use less of them.
Some examples : 1) Between 1972 and 1990 the weight of a supermarket bag was reduced from 23 grams to just six grams.
2) Today's polypropylene yoghurt cups use less than two-thirds of the material they did in the 1980's.
3) Polypropylene car bumpers have undergone even more dramatic reduction today's thin-walled bumpers reduce weight significantly with no loss in impact strength, flexibility or durability.
Apart from cutting costs, using less materials through source reduction has direct benefits for the environment by conserving resources and reducing waste.
Versatility: today's polypropylene come in many varieties. They range from tough, rigid materials for outdoor furniture and car parts to soft, flexible fibres for babies' diapers. Some have high heat resistance for microwave food containers, while others melt easily and can be used for heat-sealable food packaging. Some are as clear as glass, others completely opaque.
Through research and development, the variety of materials available is increasing and polypropylene is steadily replacing other polymers and traditional materials in many applications.
There are many ways plastics contribute to improving our health, our safety, the environment and our peace of mind. Basell is committed to developing product and process technology that will deliver significant environmental benefits. Landfill liners made with resins from Basell's Catalloy process are an example of how Basell is working to improve the environment.
Among plastic materials, polypropylene have an extremely low environmental impact. The processes that are used to produce them are considered to be among the deanest and most efficient in the industry. At the end of their useful life polypropylene is inert products that lend themselves to a multitude of safe, efficient waste disposal processes, including recycling.
Energy recovery: Recovery of energy from waste (EFW) through EFW facilities or fuel pellet technology is a valuable waste management option because it helps to conserve natural resources. Polypropylene add value in recovery because, as a consumer waste product, they have one of the highest energy contents (by weight) of all municipal solid waste components.
Source reduction: Polypropylene's inherent low density, combined with Basell's product technology, can enable our customers to use less material by weight in the fabrication of their products. Basell resin technology provides opportunities for downgauging and developing lighter weight products than often possible with other materials.
Recycling: Polypropylene is one of the three most recyclable polymers in the world,
and the most recycled automotive plastic (through battery recycling). Recycling is one of the most promising approaches to waste management of traditionally disposable and durable products when economically sustainable. When polypropylene is recycled, they experience limited degradation of functional properties and provide valuable materials for second-life applications such as outdoor furniture, automotive parts and appliances. Basell has been a leader in developing markets for post-consumer polypropylene resin grades through its Refax resins.
Polypropylene's broad performance versatility is making it easier for manufacturers to design products that use all-polypropylene, monomaterial construction. For example, in the future, many kinds of material automotive structures will be replaced by all-polypropylene construction. These structures will be lighter and more recyclable and cost less. This monomaterial approach is being developed in many other fields, including packaging and carpeting.
As already mentioned, polypropylene is made by building up long chains made up of propylene and ethylene monomers.
Although ethylene had been successfully polymerised in the 1930's, it was not until the early 1950's that progress was made with polymerising propylene. One of the problems was that the propylene molecule, being slightly more complex than ethylene, could attach itself to the growing chain in one of three different ways. Unless all the links were feeing in the same direction, however, the polypropylene formed was an oily liquid.
The secret of creating an 'isotactic' form of polypropylene esides in the catalyst used to drive the reaction: the right catalyst would line up the molecules to ensure they were feeing the right way as they joined the chain.
After lengthy experiments with different catalysing agents, the breakthrough occurred on March 11 1954. Prof. Giulio Natta, working for a Basell predecessor company, Montecatini in Milan, Italy, succeeded in producing solid polypropylene for the first time.
Over the following decades the catalysts and process systems used to produce polypropylene were progressively refined. As development continued, catalysts became more powerful and sophisticated, the polypropylene produced became pure and more versatile and the production process became simpler and more efficient.
The culmination of this development is Basell's Spheripol process. Now the world's leading high-yield technology for manufacturing polypropylene, it produces a vast range of polypropylene types using catalysts that generate over 60,000 times their own weight of polymer with minimal harm and wastes.
The result was to drive the cost of manufacturing polypropylene down at the same time as expanding the range of properties obtainable. As a consequence, polypropylene materials began to be used in a rapidly growing number of application areas.
In 1992 Basell extended its expertise in catalyst technology to the manufacture of polyethylene. The result was the Spherilene process which produces a wide range of standard and speciality polyethylene resins using a single catalyst family.
When polypropylene come out of the reactor they are usually in the form of small white beads.
This is the form in which they are supplied to the 'converter' whose job is to make them into end-products. As well having the right toughness, flexibility durability etc. to perform well in the finished article, the material must also have the right properties for the chosen conversion process.
Polypropylene can be turned into products in a number of ways:
Injection molding
Injection moulding involves melting the material, together with any colouring or additives needed, and forcing it under pressure into a mould. The mould is cooled, the material solidifies and the finished article is ejected. This method is used to make many types of product from bottle caps to furniture and car bumpers. Polypropylene is appreciated by injection-moulders for their high melt-flow rates.
Blow-molding
Blow-moulding is used to make bottles and containers. A bubble of molten material is blown up inside a mould and takes on the form of the cavity. When it has cooled the mould is opened and the article ejected. A problem would result if the bubble burst, so the material used must have high strength when it is molten.
Film
Films made of polypropylene are widely used for packaging food and other goods. They are made by squeezing molten material through a narrow slit. The film produced in this way may later be stretched to make it stronger. Films may be used for coating other materials such as paper to make them glossy or waterproof.
As well as being highly transparent and glossy, the materials used for making films must also be strong enough to resist tearing or splitting during manufacture. When used to wrap food they must be acceptable under food contact rules. The world's most widely used food packaging material is polypropylene film because it provides strong, attractive protection for a wide variety of foodstuffs.
New advances in polypropylene is currently giving rise to interesting new developments in film technology.
Fibres: most of the world's synthetic carpets are made from polypropylene fibres, made by squeezing liquid material through many tiny holes. Polypropylene fibres for ropes are made in a similar way. More recently 'non-woven' textiles, used for disposable garments, diapers and protective clothing have benefited from the toughness and softness of recent innovative polyolefin materials. Fibre manufacture is a very specialised polyolefin application sector that demands special characteristics from the materials used in order to obtain the desired results.
These are the main processing routes for polyolefin materials. New ones are being developed all the time ?gas injection moulding, co-injection, compression moulding are some of the most recent. When a new technique is being developed, close collaboration is needed between machinery manufacturers and materials producer to find materials with properties suitable for the new process.
As we have seen, developments in polypropylene is a direct result of advances in catalyst technology.
While continued refinements of Basell's Spheripol process steadily widen the application range of polypropylene-based materials, two recent developments represent quantum leaps in the performance of polyolefin materials.
Since it was introduced by Basell in 1989, the Catalloy process has been producing a continuous stream of innovative materials with an unprecedented range of stiffness, flexibility and melting behaviour. The result has been to open up a vast new area of application potential to polyolefin materials.
Adapting its catalyst technology to perform the difficult feat of 'grafting' other monomer types onto the basic polyolefin 'backbone', Basell has developed a family of high-performance materials known as Hivalloy resins. These are olefinic copolymer alloys combining the best properties of amorphous and semi-crystalline materials including an unusual balance of strength, stiffness and impact resistance.
The advances in catalyst technology that have made these remarkable developments possible over the last 40 years, show no signs of coming to a halt ? The next 40 years are likely to be equally eventful.
When he scribbled this note in his diary on March 11th 1954, Nobel prizewinner Professor Giulio Natta probably did not suspect that he had laid the foundation for what was to become the world's most versatile family of synthetic materials. In the four decades that followed, polyolefin process and catalyst technology made enormous advances, driven largely by the R&D work carried out by Basell and its predecessors.
The sophisticated range of polyolefin materials today owe their existence to three main developments:
- the catalysts driving the polymerisation process have become more and more powerful. Today's catalysts can yield as much as 60,000 times their own weight in polymer.
- the by-products and emissions of polypropylene production have been significantly reduced-today's plants produce high-purity polymers with negligible impact on the environment.
- the range of materials that can be produced has become enormous and their properties can be precisely tailored in the reactor.
Basell research has been a driving force behind many of these developments and its technologies are responsible for a large portion of world polyolefin production.
- the Spheripol process is used to make over35% of the world's total polypropylene and over60% of the polypropylene produced using 'new-generation' high-yield technologies.
- the Catalloy process produces olefin based reactor alloys with an unprecedented range of properties.
- Basell's catalyst technologies are the key to the effectiveness of the above processes.
The world's leading high-yield polypropyl-ene manufacturing technology, Basell's Spheripol process creates materials for a vast range of applications from textiles and food packaging to furniture and car comp-onents.
The Spheripol polymerisation process is based on high yield, high specificity controlled morphology catalysts and is characterised by high efficiency and environmental acceptability.
Spheripol technology is available under license from Basell and today 35% of world wide polypropylene output is made using this technology. Continuous refinements of the process have led to the development of new homopolymers, heterophasic copolymers and random copolymers.
Initiating and guiding the various polymerisation processes, Basell's sophisticated catalyst in-reactor granule technology enables a vast range of different materials to be produced, cleanly, efficiently and reliably.
Basell continues to devote a major effort to the investigation and development of high quality catalyst systems as the key to producing new polymers with targeted properties. Today, Basell is exploiting the fourth generation Ziegler-Natta catalyst system and also moving ahead with metallocene-based catalyst systems.
Basell has always been at the forefront of polyolefin innovation. Since Natta's pioneering work for Montecatini (one of Basell's predecessors), the company's research terms have been responsible for many of the significant advances made in polyolefin technology over the last forty years.
1954
First crystalline polypropylene resin
1956
First industrial production
1968
First impact copolymer
1976-1978
Liguid Propylene Process(LIPP)
1978
High-yield catalyst for polypropylene
1978-1982
Development of reactor granule technology
1981
First-generation polypropylene coating resins
1982
The Spheripol process for polypropylene production
1988
High Melt Strength polypropylene coating resins
1989
Resins from Catalloy process
1990
Hivalloy polyolefin engineering alloys
1992
Polyethylene resins from the Spherilene Process
"Polypropylene is one of the best-kept secrets in the plastics industry... the irony is that polypropylene is everywhere... we are surrounded by polypropylene."
- Charles G. Oertel in The Polypropylene Handbook (Hanser, 1996)
Although few people know polypropylene by name, it is one of the most versatile of the polyolefins and therefore has an extremely wide application range.
Basell's polyolefin research makes an important contribution to this process by extending the performance of polypropylene-based materials and enabling them to replace other polymers or enter entirely new areas where synthetic materials have never been used before.
Basell materials are used in all main application sectors:
Packaging
polyolefins lead in packaging films and rigid containers for food, medical and other goods where they provide, clean, economical protection for consumer products and are recyclable.
Automotive
inside and outside the passenger compartment and under the hood, polyolefin materials are increasing comfort, safety and fuel economy while actively contributing to recycling potential.
Textiles
from carpets and upholstery to innovative non-wovens for disposable hygiene products, polyolefins have an important role in the modern fiber industry.
Industrial
demanding long-term applications such as geomembranes and pipeline coatings make use of the exceptional toughness of new-generation polyolefins from Basell's Catalloy process.
Consumer products
from outdoor furniture and kitchenware to toys, leisure products and suitcases, Basell's polyolefins offer manufacturers easy processing and design potential to make attractive, accessible products for everyday use.
Medical and hygiene
from syringes and intravenous systems to sanitary products, Basell's polyolefins provide toughness and flexibility, as well as resistance to sterilisation temperatures and radiation.
When he scribbled this note in his diary on March 11th 1954, Nobel prizewinner Professor Giulio Natta probably did not suspect that he had laid the foundation for what was to become the world's most versatile family of synthetic materials. In the four decades that followed, polyolefin process and catalyst technology made enormous advances, driven largely by the R&D work carried out by Basell and its predecessors.
The world's leading high-yield polypropyl-ene manufacturing technology, Basell's Spheripol process creates materials for a vast range of applications from textiles and food packaging to furniture and car comp-onents.
Initiating and guiding the various polymerisation processes, Basell's sophisticated catalyst in-reactor granule technology enables a vast range of different materials to be produced, cleanly, efficiently and reliably.
Basell has always been at the forefront of polyolefin innovation. Since Natta's pioneering work for Montecatini (one of Basell's predecessors), the company's research terms have been responsible for many of the significant advances made in polyolefin technology over the last forty years.
