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Polybutylene

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Polybutylene

Polybutylene
Identifiers
CAS number  YesY
Properties
Molecular formula (C4H8)n
Density 0.95 g/cm3[1]
Melting point 135 °C[1]
Related compounds
Related compounds 1-butene (monomer)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY   YesY/N?)

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.

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 [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 as polysulfone 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]

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 (see "Class action lawsuits and removal from building code approved usage", below). 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. Kuwait, 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,electrical insulation,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]

Class action lawsuits and removal from building code approved usage

Polybutylene water pipes are no longer accepted by United States building codes and have been the subject[13] of class action lawsuits in both Canada and the US.[14][15] The pipe is still listed for use in Canada.[16] 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.[17] The reaction with chlorinated water appears to be greatly accelerated by tensile stress and is most often observed in material under highest stress such as at fittings and kinks. Localized stress whitening of the material generally accompanies and precedes decomposition of the polymer. In extreme cases, this stress activated chemical "corrosion" can lead to through perforation and leakage within a few years. Fittings with a soft compression seal can give adequate service life.

See also

References

  1. ^ a b c Mark Alger, Mark S. M. Alger (1997). Polymer science dictionary. Springer. p. 398.  
  2. ^ a b c d Charles A. Harper (2006). Handbook of plastics technologies: the complete guide to properties and performance. McGraw-Hill Professional. p. 17.  
  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 (11): 3119.  
  6. ^ a b c d Freeman, Andrew; Mantell, Susan C.; Davidson, Jane H. (2005). "Mechanical performance of polysulfone, polybutylene, and polyamide 6/6 in hot chlorinated water". Solar Energy 79 (6): 624–37.  
  7. ^ a b c d e Polybutylene
  8. ^ ISO 15876-1:2003 iso.org
  9. ^ T.E. Rolando (1998). Solvent-Free Adhesives. p. 35.  
  10. ^ Hensler, Deborah R.; Pace, Nicholas M.; Dombey-Moore, Bonita; Giddens, Beth; Gross, Jennifer; Moller, Erik K. (2000). "Cox v. Shell Oil"Polybutylene Plumbing Pipes Litigation: . In Hensler, Deborah R. Class action dilemmas: pursuing public goals for private gain. Santa Monica, CA: RAND Institute for Civil Justice. pp. 375–98.  
  11. ^ Schneider, Martin (November 21, 1999). "Pipe problem getting fixed".  
  12. ^ Vibien, P.; Couch, J.; Oliphant, K.; Zhou, W.; Zhang, B.; Chudnovsky, A. (2001). "Assessing material performance in chlorinated potable water applications". Book Institute of Materials 759: 863–72.  
  13. ^ Pipe dream is nightmare for many, Miami Herald - September 12, 1993
  14. ^ DuPont USA Settlement of the Canadian Class Action Lawsuits
  15. ^ Polybutylene Plumbing Pipe Leak Relief
  16. ^ CAN/CSA B137.8
  17. ^ Cause of failure in polybutylene pipe & acetal fittings http://www.polybutylene.com/poly.html

Further reading

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