Polymer Data File:
Polybutylene
- PB
Polymer Data File:Polybutylene
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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.
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.
BondingPB 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: 14/11/2005
© Tangram Technology Ltd. 2001
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