Polybutylene
Encyclopedia
Polybutylene is a polyolefin
or saturated polymer
with the chemical formula (C4H8)n. It should not be confused with polybutene
, a low molecular weight oligomer
with a different repeat unit
.
Polybutylene is produced by polymerisation of 1-butene
using supported Ziegler-Natta catalyst
s. PB-1 is a high molecular weight, linear, isotactic, and semi-crystalline
polymer. PB-1 combines typical characteristics of conventional polyolefins with certain properties of technical polymers.
PB-1, when applied as a pure or reinforced resin
, can replace materials like metal, rubber and engineering polymers. It is also used synergistically as a blend element to modify the characteristics of other polyolefins like polypropylene
and polyethylene
. Because of its specific properties it is mainly used in pressure piping, flexible packaging, water heaters, compounding and hot melt adhesives.
s. The first type of catalyst contains two components, a solid pre-catalyst, the δ-crystalline form of TiCl3, and solution of an organoaluminum cocatalyst, such as Al(C2H5)3. The second type of pre-catalyst is supported. The active ingredient in the catalyst is TiCl4 and the support is microcrystalline MgCl2. These catalysts also contain special modifiers, organic compounds belonging to the classes of esters or ethers. The pre-catalysts are activated by combinations of organoaluminum compounds and other types of organic or organometallic modifiers. Two most important technological advantages of the supported catalysts are high productivity and a high fraction of the crystalline isotactic polymer they produce at 70–80 °C under standard polymerization conditions.
Isotactic polybutylene crystallizes in three different forms. Crystallization from solution yields form-III with the melting point of 106.5 °C. Cooling from the melt results in the form II which has melting point of 124 °C and density of 0.89 g/cm3. At room temperature, it spontaneously converts into the form-I with the melting point of 135 °C and density of 0.95 g/cm3.
PB-1 generally resists chemicals such as detergents, oils, fats, acids, bases, alcohol, ketones, aliphatic hydrocarbons and hot polar solutions (including water). It shows lower resistance to aromatic and chlorinated hydrocarbons as well as oxidising acids than other polymers such as polysulfone
and polyamide
6/6. Additional features include excellent wet abrasion resistance, easy melt flowability (shear thinning), and good dispersion of fillers. It is compatible with polypropylene
, ethylene propylene rubbers, and thermoplastic elastomers.
Some properties:
networks and surface heating and cooling systems. ISO 15876 defines the performance requirements of PB-1 piping systems. The most striking features are weldability, temperature resistance, flexibility and high hydrostatic pressure resistance. The material can be classified PB 125 with a minimum required strength (MRS) of 12.5 MPa. Other features include low noise transmission, low linear thermal expansion, no corrosion and calcification.
PB-1 piping systems are no longer being sold in North America. The overall market share in Europe and Asia is rather small but PB-1 piping systems have shown a steady growth in recent years. In certain domestic markets, e.g. UK, Korea and Spain, PB-1 piping systems have a strong position.
resins. It offers high cohesive and adhesive strength and helps tailoring the "open time" of the adhesive (up to 30 minutes) because of its slow crystallisation kinetics. It improves the thermal stability and the viscosity of the adhesive.
composites or as masterbatch
carrier for thermo-sensitive pigments. PB-1 disperses easily in other polyolefins, and at low concentration, acts as processing aid reducing torque and/or increasing throughput.
One example is the installation of PB-1 pipes in the Vienna Geothermal Project (1974) where aggressive geothermal water is distributed at a service temperature of 54 °C and 10 bar pressure. Other pipe materials in the same installation failed or corroded and had been replaced in the meantime.
International standards set minimum performance requirements for pipes made from PB-1 used in hot water applications. Standardised extrapolation methods predict lifetimes in excess of 50 years at 70 °C and 10 bar.
Polybutylene plumbing was used in several million homes built in the United States from 1970 to the mid-1990s. Problems with leaks led to a class action lawsuit, Cox vs. Shell Oil, that was settled for $1 billion. The leaks were associated with degradation of polybutylene in chlorinated water.
Polyolefin
A polyolefin is a polymer produced from a simple olefin as a monomer. For example, polyethylene is the polyolefin produced by polymerizing the olefin ethylene. An equivalent term is polyalkene; this is a more modern term, although polyolefin is still used in the petrochemical industry...
or saturated polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
with the chemical formula (C4H8)n. It should not be confused with polybutene
Polybutene
Polybutene and polyisobutylene are liquid oligomers widely used as plasticizers for high-molecular weight polymers, such as polyethylene. They are not to be confused with the high molecular weight polymer polybutene-1.-Properties:...
, a low molecular weight oligomer
Oligomer
In chemistry, an oligomer is a molecule that consists of a few monomer units , in contrast to a polymer that, at least in principle, consists of an unlimited number of monomers. Dimers, trimers, and tetramers are oligomers. Many oils are oligomeric, such as liquid paraffin...
with a different repeat unit
Repeat unit
An essential concept which defines polymer structure, the repeat unit or repeating unit is a part of a polymer chain whose repetition would produce the complete polymer by linking the repeat units together successively along the chain, like the beads of a necklace.A repeat unit is sometimes called...
.
Polybutylene is produced by polymerisation of 1-butene
1-Butene
1-Butene is an organic chemical compound, linear alpha-olefin , and one of the isomers of butene. The formula is .-Stability:1-Butene is stable in itself but polymerizes exothermically. It is highly flammable and readily forms explosive mixtures with air...
using supported Ziegler-Natta catalyst
Ziegler-Natta catalyst
A Ziegler–Natta catalyst is a catalyst used in the synthesis of polymers of 1-alkenes . Three types of Ziegler–Natta catalysts are currently employed:* Solid and supported catalysts based on titanium compounds...
s. PB-1 is a high molecular weight, linear, isotactic, and semi-crystalline
Crystallization of polymers
Crystallization of polymers is a process associated with partial alignment of their molecular chains. These chains fold together and form ordered regions called lamellae, which compose larger spheroidal structures named spherulites. Polymers can crystallize upon cooling from the melt, mechanical...
polymer. PB-1 combines typical characteristics of conventional polyolefins with certain properties of technical polymers.
PB-1, when applied as a pure or reinforced resin
Resin
Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...
, can replace materials like metal, rubber and engineering polymers. It is also used synergistically as a blend element to modify the characteristics of other polyolefins like polypropylene
Polypropylene
Polypropylene , also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes...
and polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
. Because of its specific properties it is mainly used in pressure piping, flexible packaging, water heaters, compounding and hot melt adhesives.
Synthesis
Isotactic PB-1 is synthesized commercially using two types of heterogeneous Ziegler-Natta catalystZiegler-Natta catalyst
A Ziegler–Natta catalyst is a catalyst used in the synthesis of polymers of 1-alkenes . Three types of Ziegler–Natta catalysts are currently employed:* Solid and supported catalysts based on titanium compounds...
s. The first type of catalyst contains two components, a solid pre-catalyst, the δ-crystalline form of TiCl3, and solution of an organoaluminum cocatalyst, such as Al(C2H5)3. The second type of pre-catalyst is supported. The active ingredient in the catalyst is TiCl4 and the support is microcrystalline MgCl2. These catalysts also contain special modifiers, organic compounds belonging to the classes of esters or ethers. The pre-catalysts are activated by combinations of organoaluminum compounds and other types of organic or organometallic modifiers. Two most important technological advantages of the supported catalysts are high productivity and a high fraction of the crystalline isotactic polymer they produce at 70–80 °C under standard polymerization conditions.
Characteristics
Heated up to 190 °C and above, PB-1 can easily be compression moulded, injection moulded, blown to hollow parts, extruded, and welded. It does not tend to crack due to stress. Because of its crystalline structure and high molecular weight, PB-1 has good resistance to hydrostatic pressure, showing very low creep even at elevated temperatures. It is flexible, resists impact well and has good elastic recovery.Isotactic polybutylene crystallizes in three different forms. Crystallization from solution yields form-III with the melting point of 106.5 °C. Cooling from the melt results in the form II which has melting point of 124 °C and density of 0.89 g/cm3. At room temperature, it spontaneously converts into the form-I with the melting point of 135 °C and density of 0.95 g/cm3.
PB-1 generally resists chemicals such as detergents, oils, fats, acids, bases, alcohol, ketones, aliphatic hydrocarbons and hot polar solutions (including water). It shows lower resistance to aromatic and chlorinated hydrocarbons as well as oxidising acids than other polymers such as polysulfone
Polysulfone
Polysulfone describes a family of thermoplastic polymers. These polymers are known for their toughness and stability at high temperatures. They contain the subunit aryl-SO2-aryl, the defining feature of which is the sulfone group. Polysulfones were introduced in 1965 by Union Carbide...
and polyamide
Polyamide
A polyamide is a polymer containing monomers of amides joined by peptide bonds. They can occur both naturally and artificially, examples being proteins, such as wool and silk, and can be made artificially through step-growth polymerization or solid-phase synthesis, examples being nylons, aramids,...
6/6. Additional features include excellent wet abrasion resistance, easy melt flowability (shear thinning), and good dispersion of fillers. It is compatible with polypropylene
Polypropylene
Polypropylene , also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes...
, ethylene propylene rubbers, and thermoplastic elastomers.
Some properties:
- Elastic modulusElastic modulusAn elastic modulus, or modulus of elasticity, is the mathematical description of an object or substance's tendency to be deformed elastically when a force is applied to it...
290–295 MPa - Tensile strengthTensile strengthUltimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...
36.5 MPa - Molecular weight 725,000 (g/mol)
- Crystallinity 48–55%
- Water absorption <0.03%
- Glass transition temperature –25 to –17 °C
- Thermal conductivityThermal conductivityIn physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....
0.22 W/(m·K)
Piping systems
The main use of PB-1 is in flexible pressure piping systems for hot and cold drinking water distribution, pre-insulated district heatingDistrict heating
District heating is a system for distributing heat generated in a centralized location for residential and commercial heating requirements such as space heating and water heating...
networks and surface heating and cooling systems. ISO 15876 defines the performance requirements of PB-1 piping systems. The most striking features are weldability, temperature resistance, flexibility and high hydrostatic pressure resistance. The material can be classified PB 125 with a minimum required strength (MRS) of 12.5 MPa. Other features include low noise transmission, low linear thermal expansion, no corrosion and calcification.
PB-1 piping systems are no longer being sold in North America. The overall market share in Europe and Asia is rather small but PB-1 piping systems have shown a steady growth in recent years. In certain domestic markets, e.g. UK, Korea and Spain, PB-1 piping systems have a strong position.
Plastic packaging
Several PB-1 grades are commercially available for various applications and conversion technologies (blown film, cast film, extrusion coating). There are two main fields of application:- Peelable easy-to-open packaging where PB-1 is used as blend component predominantly in polyethyelene to tailor peel strength and peel quality, mainly in alimentary consumer packaging and medical packaging.
- Lowering seal initiation temperature (SIT) of high speed packaging polypropylene based films. Blending PB-1 into polypropylene, heat sealing temperatures as low as 65 °C can be achieved, maintaining a broad sealing window and good optical film properties.
Hot melt adhesives
PB-1 is compatible with a wide range of tackifierTackifier
Tackifiers are chemical compounds used in formulating adhesives to increase the tack, the stickiness of the surface of the adhesive. They are usually low-molecular weight compounds with high glass transition temperature...
resins. It offers high cohesive and adhesive strength and helps tailoring the "open time" of the adhesive (up to 30 minutes) because of its slow crystallisation kinetics. It improves the thermal stability and the viscosity of the adhesive.
Compounding and masterbatches
PB-1 accepts very high filler loadings in excess of 70%. In combination with its low melting point it can be employed in halogen-free flame retardantFlame retardant
Flame retardants are chemicals used in thermoplastics, thermosets, textiles and coatings that inhibit or resist the spread of fire. These can be separated into several different classes of chemicals:...
composites or as masterbatch
Masterbatch
Masterbatch is a solid or liquid additive for plastic used for coloring plastics or imparting other properties to plastics .-Applications of additive masterbatches:...
carrier for thermo-sensitive pigments. PB-1 disperses easily in other polyolefins, and at low concentration, acts as processing aid reducing torque and/or increasing throughput.
Other applications
Other applications include domestic water heaters, compression packaging, wire and cable, shoe soles and polyolefin modification (thermal bonding, enhancing softness and flexibility of rigid compounds, increasing temperature resistance and compression set of soft compounds).Environmental sustainability
Plumbing and heating systems made from PB-1 have been used in Europe and Asia for more than 30 years. First reference projects in district heating and floor heating systems in Germany and Austria from the early 1970s are still in operation today.One example is the installation of PB-1 pipes in the Vienna Geothermal Project (1974) where aggressive geothermal water is distributed at a service temperature of 54 °C and 10 bar pressure. Other pipe materials in the same installation failed or corroded and had been replaced in the meantime.
International standards set minimum performance requirements for pipes made from PB-1 used in hot water applications. Standardised extrapolation methods predict lifetimes in excess of 50 years at 70 °C and 10 bar.
Polybutylene plumbing was used in several million homes built in the United States from 1970 to the mid-1990s. Problems with leaks led to a class action lawsuit, Cox vs. Shell Oil, that was settled for $1 billion. The leaks were associated with degradation of polybutylene in chlorinated water.
Class action lawsuits and removal from building code approved usage
Polybutylene water pipes are no longer accepted by United States or Canadian building codes and have been the subject of class action lawsuits in both countries. There is evidence to suggest that the presence of chlorine compounds in water will cause deterioration of the internal chemical structure of polybyutylene piping and the associated acetal fittings.See also
- Forensic engineeringForensic engineeringForensic engineering is the investigation of materials, products, structures or components that fail or do not operate or function as intended, causing personal injury or damage to property. The consequences of failure are dealt with by the law of product liability. The field also deals with...
- Forensic polymer engineeringForensic polymer engineeringThe study of failure in polymeric products is called forensic polymer engineering. The topic includes the fracture of plastic products, or any other reason why such a product fails in service, or fails to meet its specification...
- Polymer degradationPolymer degradationPolymer degradation is a change in the properties—tensile strength, colour, shape, etc.—of a polymer or polymer-based product under the influence of one or more environmental factors such as heat, light or chemicals such as acids, alkalis and some salts...
- Polybutylene terephthalatePolybutylene terephthalatePolybutylene terephthalate is a thermoplastic engineering polymer, that is used as an insulator in the electrical and electronics industries. It is a thermoplastic crystalline polymer, and a type of polyester...