Difference between revisions of "Polybutylene"

Latest revision as of 09:09, 20 September 2010

Polybutylene (polybutene-1, poly(1-butene), PB-1) 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 catalysts. 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.

Synthesis

Isotactic PB-1 is synthesized commercially using two types of heterogeneous Ziegler-Natta catalysts.^[2] 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.^[3][4][5]

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.^[6] It is flexible, resists impact well and has good elastic recovery.^[2][7]

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.^[1]

PB-1 generally resists chemicals such as detergents, oils, fats, acids, bases, alcohol, ketones, aliphatic hydrocarbons and hot polar solutions (including water).^[2] It shows lower resistance to aromatic and chlorinated hydrocarbons as well as oxidising acids than other polymers such aspolysulfone and polyamide 6/6.^[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:^[6]

• Elastic modulus 290–295 MPa
• Tensile strength 36.5 MPa
• Molecular weight 725,000 (g/mol)
• Crystallinity 48–55%
• Water absorption <0.03%
• Glass transition temperature –25 to –17 °C ^[2][6]
• Thermal conductivity 0.22 W/(m·K)

Application areas

Piping systems

The main use of PB-1 is in flexible pressure piping systems for hot and cold drinking water distribution, pre-insulated district heating networks and surface heating and cooling systems. ISO 15876 defines the performance requirements of PB-1 piping systems.^[8] 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.^[7]

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 tackifier 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.^[9]

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 retardant 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.

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.^[7]

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.^[7]

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.^[7]

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.^[10][11] The leaks were associated with degradation of polybutylene in chlorinated water.^[12]

See also

• Forensic engineering
• Forensic polymer engineering
• Polymer degradation
• Polybutylene terephthalate

References

Further reading

• Dunlop, Carson (2003). "Suspect Connections on Polybutylene Piping". Principles of Home Inspection: Plumbing. Chicago: Dearborn Home Inspection Education. pp. 84–7. ISBN 978-0-7931-7939-8. 
• Examples for the installation of Polybutene-1 piping systemses:Polibutileno

1. ↑ ^{1.0 1.1 1.2} Mark Alger, Mark S. M. Alger (1997). Polymer science dictionary. Springer. p. 398. ISBN 0412608707. 
2. ↑ ^{2.0 2.1 2.2 2.3} Charles A. Harper (2006). Handbook of plastics technologies: the complete guide to properties and performance. McGraw-Hill Professional. p. 17. ISBN 0071460683. 
3. ↑ Hwo, Charles C.; Watkins, Larry K. Laminated film with improved tear strength, European Patent Application EP0459742, Publication date 12/04/1991
4. ↑ Boo-Deuk Kim et al. (2008) U.S. Patent 7,442,489
5. ↑ Shimizu, Akihiko; Itakura, Keisuke; Otsu, Takayuki; Imoto, Minoru (1969). "Monomer-isomerization polymerization. VI. Isomerizations of butene-2 with TiCl3 or Al(C2H5)3–TiCl3 catalyst". Journal of Polymer Science Part A-1: Polymer Chemistry. 7: 3119. doi:10.1002/pol.1969.150071108. 
6. ↑ ^{6.0 6.1 6.2 6.3} Freeman, Andrew; Mantell, Susan C.; Davidson, Jane H. (2005). "Mechanical performance of polysulfone, polybutylene, and polyamide 6/6 in hot chlorinated water" (PDF). Solar Energy. 79: 624–37. doi:10.1016/j.solener.2005.07.003. 
7. ↑ ^{7.0 7.1 7.2 7.3 7.4} Polybutylene
8. ↑ ISO 15876-1:2003 iso.org
9. ↑ T.E. Rolando (1998). Solvent-Free Adhesives. p. 35. ISBN 1859571336. 
10. ↑ Hensler, Deborah R.; Pace, Nicholas M.; Dombey-Moore, Bonita; Giddens, Beth; Gross, Jennifer; Moller, Erik K. (2000). "Polybutylene Plumbing Pipes Litigation: Cox v. Shell Oil" (PDF). In Hensler, Deborah R. Class action dilemmas: pursuing public goals for private gain. Santa Monica, CA: RAND Institute for Civil Justice. pp. 375–98. ISBN 978-0-8330-2601-9. 
11. ↑ Schneider, Martin (November 21, 1999). "Pipe problem getting fixed". The Baltimore Sun. 
12. ↑ Vibien, P.; Couch, J.; Oliphant, K.; Zhou, W.; Zhang, B.; Chudnovsky, A. (2001). "Assessing material performance in chlorinated potable water applications" (PDF). Book Institute of Materials. 759: 863–72. ISSN 1366-5510.  also published as: Vibien, P.; Couch, J.; Oliphant, K.; Zhou, W.; Zhang, B.; Chudnovsky, A. (2001). "Chlorine resistance testing of cross-linked polyethylene piping materials". ANTEC 2001 Proceedings. Boca Raton: CRC Press. pp. 2833–9. ISBN 978-1-58716-098-1.