Polymer Data File:

Polybutylene
- PB 

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Introduction

Advantages and Limitations

Typical Applications

Processing

Physical and Mechanical Properties

Finishing

Thermal, Electrical and Optical Properties

Health and Safety

Chemical Resistance Properties

Other Information


Introduction

Polybutylene is a flexible linear polyolefin (as are PE and PP). The material is semi-crystalline and has excellent resistance to creep at high temperatures. The material can be readily processed by most conventional means using similar processes to other polyolefins.

PB is used either as a homopolymer of poly(1-butene) or as one of a series of copolymers of poly(1-butene/ethylene). This group of copolymers has quite wide ranging properties and this information concentrates mainly on the homopolymer.

PB is not a high volume polymer but the rapid development of the piping usage of PB may indicate some significant expansion in the market.

Typical Applications

Pipes: Hot and cold water pipes for domestic water services, well piping, heat pump piping.

Building products: Liners for domestic water heaters.

Packaging: Film for food and meat packaging, packaging hot fill containers, fibres for heavy duty sacks.

Mechanical: Tank and chute liners.

Miscellaneous: Hot melt adhesives and sealants, carrier for products to be blended into other polyolefins such as PP.

Physical and Mechanical Properties

PB is has excellent resistance to creep at both room and elevated temperatures and has higher long term temperature resistance than other polyolefins. The material has good toughness properties and has high impact strength as well as excellent tear resistance.

PB undergoes crystallisation after the melt phase and full mechanical properties are only achieved after aging.

Property

Approximate Value

PB

Tensile strength

40 - 80 MN/m2

Tensile Modulus

2 - 3 GN/m2

Elongation at Break

50 - 100 %

Flexural Strength

50 - 100 MN/m2

Notched Impact Strength

>20 kJ/m2

Specific Heat

2.15 - 2.6 kJ/kgoC

Glass Transition Temperature

N/A

Heat Deflection Temperature

>100oC

Coefficient of Thermal Expansion

10 - 20 x 10-5 / oC

Long Term Service Temperature

>100 oC

Specific Gravity

0.91 - 0.95

Mould Shrinkage

0.025-0.05 m/m

Water Absorption

<1 % (50% rh)

Transparency

Opaque

Thermal, Electrical and Optical Properties

Thermal properties

PB has good high temperature performance and many mechanical properties are retained to high temperatures. This is particularly true of creep resistance. 

Fire behaviour

PB pipe grades have achieved a 'slow -burning' rating from Underwriters Laboratories (UL94-HB).

Electrical properties

PB has good electrical insulation properties.

Optical properties

Natural PB is milky-opaque but can be easily coloured in a wide variety of colours. PB has a refractive index which varies with the variant and for most types it is in the region of 1.52 to 1.53.

Chemical Resistance Properties

PB is generally resistant to acids, bases, solvents, paraffinic oils but as with most polymers, this resistance decreases with increasing temperature.

PB has good moisture barrier properties and this has lead to applications in hot fill food packaging.

Weathering resistance: 

Stress cracking resistance: 

PB has excellent resistance to environmental stress cracking.

PB Chemical Resistance Chart

Advantages and Limitations

Advantages

Limitations

1. Versatile resin capable of being adapted to a wide variety of processes and applications.

1. Low demand means price is higher than conventional polyolefins.

2. Excellent creep strength retention at high temperatures.

2. Crystallisation behaviour requires careful treatment immediately after processing.

3. Excellent retention of mechanical properties at high temperatures.

3. High die-swell can lead to concerns with extrusion calibration and accuracy.

4. Good moisture barrier properties.

4. Crystallisation behaviour changes product dimensions after production.

5. Excellent electrical insulation properties.

 

6. Excellent chemical resistance, particularly to environmental stress cracking.

 

Processing

PB can be processed on the same equipment used for processing PE-LD but after processing it crystallizes to various forms. The first crystallization is to a tetragonal crystal form and after 5-7 days (depending on the grade) there is a further transformation to a twined hexagonal crystal form. After crystallization the degree of crystallinity is in the region of 48 to 55% for the homopolymer grades. The crystallization process changes the tensile strength, hardness and density but does not generally give processing problems. PB is similar to PP where the crystallization process can change the product dimensions and some care needs to be taken in tooling design to ensure that product dimensions are suitable for fabrication after crystallization.

Injection moulding

Injection moulding is by conventional injection moulding machines using settings as for PE-LD.

Extrusion

Extrusion is by conventional single screw machines using vacuum calibrators for size control. Processing temperatures are in the range 160 to 240oC. PB die swell and cooling shrinkage are larger than for PE materials. The initial material after cooling from the melt needs to be handled with care until the strength develops through crystallisation. This requires the use of sensitive haul-off equipment with minimal opportunities for draw-down in processing.

Processing Method

Applicable

Injection Moulding

Yes.

Extrusion

Yes

Extrusion Blow Moulding

Yes

Injection Blow Moulding

Yes

Rotational Moulding

Yes

Thermoforming

Yes

Casting

Yes

Bending and joining

Yes

Finishing

Machining

PB can be easily machined and the use of coolants allows high cutting speeds whilst still producing a good surface finish. Tools should be sharp and have good clearance and cutting angle.

Surface treatment

PB is a polyolefin similar to PE and PP and the low surface energy makes surface treatments such as printing or painting difficult.

Welding

All processes suitable for thermoplastics can be used e.g. ultrasonic, friction, hotplate, high frequency and heat impulse welding. Pipe applications use thermal fusion to join pipe sections and joints and packaging applications use films that are easily heat sealable.

Bonding

PB can be difficult to bond without appropriate surface pre-treatment. Treatment for bonding is as per PE and PP i.e. corona or flame pre-treatment.

Health and Safety

Health and Safety

PB does not constitute a health hazard and can be used in domestic hot and cold water supply and in food contact applications. Care must be taken in the choice of additives used for food contact applications.

Other Information

Identification

  • PB is recognisable as a polyolefin from the 'greasy' feel and can be differentiated form other polyolefins be the improved strength and stiffness.

 

Last edited: 11/03/2010

© Tangram Technology Ltd. 2001

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