Polybutylene (polybutene-1, poly(1-butene), PB-1) is a

polyolefin A polyolefin is a type of polymer with the general formula (CH2CHR)n where R is an alkyl group. They are usually derived from a small set of simple olefins (alkenes). Dominant in a commercial sense are polyethylene and polypropylene. More speciali ...

or saturated

polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...

with the chemical formula (CH₂CH(Et))_n. Not be confused with

polybutene Polybutene is an organic polymer made from a mixture of 1-butene, 2-butene, and isobutylene. Ethylene steam cracker C4s are also used as supplemental feed for polybutene. It is similar to polyisobutylene (PIB), which is produced from essentially ...

, PB-1 is mainly used in piping.

Production

Polybutylene is produced by

polymerisation In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many for ...

1-butene 1-Butene (or 1-Butylene) is the organic compound with the formula CH3CH2CH=CH2. It is a colorless gas that is easily condensed to give a colorless liquid. It is classified as a linear alpha-olefin. It is one of the isomers of butene (butylene). I ...

using supported

Ziegler–Natta catalyst A Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, is a catalyst used in the synthesis of polymers of 1-alkenes (alpha-olefins). Two broad classes of Ziegler–Natta catalysts are employed, distinguished by their solubility: * He ...

Catalysts

Isotactic PB-1 is produced commercially using two types of heterogeneous

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

PB-1 is a high molecular weight, linear,

isotactic Tacticity (from el, τακτικός, taktikos, "relating to arrangement or order") is the relative stereochemistry of adjacent chiral centers within a macromolecule. The practical significance of tacticity rests on the effects on the physical p ...

, and

semi-crystalline Crystallinity refers to the degree of structural order in a solid. In a crystal, the atoms or molecules are arranged in a regular, periodic manner. The degree of crystallinity has a big influence on hardness, density, transparency and diffusion ...

polymer. PB-1 combines typical characteristics of conventional

polyolefins A polyolefin is a type of polymer with the general formula (CH2CHR)n where R is an alkyl group. They are usually derived from a small set of simple olefins (alkenes). Dominant in a commercial sense are polyethylene and polypropylene. More speciali ...

with certain properties of technical polymers. PB-1, when applied as a pure or reinforced

resin In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on natu ...

, 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 (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer propylene. Polypropylene belongs to the group of polyolefins and ...

and

polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including bo ...

. Because of its specific properties it is mainly used in pressure piping, flexible packaging, water heaters, compounding and hot melt adhesives. 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.Polybutylene
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 Polysulfones are a family of high performance thermoplastics. These polymers are known for their toughness and stability at high temperatures. Technically used polysulfones contain an aryl- SO2-aryl subunit. Due to the high cost of raw material ...

and

polyamide A polyamide is a polymer with repeating units linked by amide bonds. Polyamides occur both naturally and artificially. Examples of naturally occurring polyamides are proteins, such as wool and silk. Artificially made polyamides can be made through ...

6/6. Additional features include excellent wet abrasion resistance, easy melt flowability (shear thinning), and good dispersion of fillers. It is compatible with

, ethylene propylene rubbers, and thermoplastic

elastomers An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of ''elastic po ...

. Some properties: *

Elastic modulus An elastic modulus (also known as modulus of elasticity) is the unit of measurement of an object's or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. The elastic modulus of an object is ...

290–295 MPa *

Tensile strength Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or F_\text within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials t ...

36.5 MPa * Molecular weight 725,000 (g/mol) *Crystallinity 48–55% *Water absorption <0.03% *

Glass transition temperature The glass–liquid transition, or glass transition, is the gradual and reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials) from a hard and relatively brittle "glassy" state into a viscous or rubb ...

–25 to –17 °C *

Thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...

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 District heating (also known as heat networks or teleheating) is a system for distributing heat generated in a centralized location through a system of insulated pipes for residential and commercial heating requirements such as space heating a ...

networks and surface heating and cooling systems. ISO 15876 defines the performance requirements of PB-1 piping systems. PB-1's most notable characteristics 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, the United Kingdom, 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 polyethylene 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 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. At low strain rate, they p ...

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 retardant The term flame retardants subsumes a diverse group of chemicals that are added to manufactured materials, such as plastics and textiles, and surface finishes and coatings. Flame retardants are activated by the presence of an ignition source a ...

composites or as

masterbatch Masterbatch (MB) is a solid additive used for coloring (color masterbatch) or imparting other properties (additive masterbatch) to plastics. Masterbatch is a concentrated mixture of pigments and/or additives which is manufactured by encapsulation du ...

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 longevity

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. Standardized extrapolation methods predict lifetimes in excess of 50 years at 70 °C and 10 bar.

Class action lawsuits and removal from building code approved usage

Polybutylene plumbing was used in several million homes built in the United States from around 1978 to 1997. Problems with leaks and broken pipes led to a

class action lawsuit A class action, also known as a class-action lawsuit, class suit, or representative action, is a type of lawsuit where one of the parties is a group of people who are represented collectively by a member or members of that group. The class action ...

, Cox v. Shell Oil, that was settled for $1 billion. The leaks were associated with degradation of polybutylene exposed to chlorinated water. Polybutylene water pipes are no longer accepted by the United States building codes and have been the subject of class action lawsuits in both Canada and the U.S. The National Plumbing Code of Canada 1995 listed polybutylene piping as acceptable for use with the exception of recirculation plumbing. The piping was removed from the acceptable for use list in the 2005 issue of the standard. There is evidence to suggest that the presence of

chlorine Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...

and

chloramine Chloramines refer to derivatives of ammonia and organic amines wherein one or more N-H bonds have been replaced by N-Cl bonds. Two classes of compounds are considered: inorganic chloramines and organic chloramines. Inorganic chloramines Inorgan ...

compounds in municipal water (often deliberately added to retard bacterial growth) will cause deterioration of the internal chemical structure of polybutylene piping and the associated acetal fittings.Cause of failure in polybutylene pipe & acetal fittings http://www.polybutylene.com/poly.html The reaction with chlorinated water appears to be greatly accelerated by

tensile stress In continuum mechanics, stress is a physical quantity. It is a quantity that describes the magnitude of forces that cause deformation. Stress is defined as ''force per unit area''. When an object is pulled apart by a force it will cause elonga ...

, and is most often observed in material under highest mechanical stress such as at fittings, sharp bends, 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 perforation and leakage within a few years, but it also may not fail for decades. Fittings with a soft compression seal can give adequate service life. Because the chemical reaction of the water with the pipe occurs inside the pipe, it is often difficult to assess the extent of deterioration. The problem can cause both slow leaks and pipe bursting without any previous warning indication. The only long-term solution is to completely replace the polybutylene plumbing throughout the entire building.