Polybutylene Terephthalate (PBT) CORPORATE TRAINING AND PLANNING

Polybutylene Terephthalate (PBT)

CORPORATE TRAINING AND PLANNING

Polybutylene Terephthalate (PBT)

Linear polyesters were studied by Carothers during his classical researches for development of Polyamides.

But it was Whinfield and Dicson who developed PET at Calico

Printers Association, England I 1941 (As Fibres, Terylene and

Dacron and as Film, Melinex and My lar, with the expiry of the

basic ICI patents on PET there was considerable development in

terephthalate polymers in the early 1970’s.

More than a dozen companies introduced PBT as an Engineering

Plastics during this time.

The fiber in the name of Kodel and Film in the name of Kodar was

developed by Kodak.

PBT was introduced commercially in 1969 by Celanese.


Monomer Ingredients for PBT

The ingredients which are used for preparing PBT are 1,4 butanediol and dimethyl terephthelate.

HO – CH2 – CH2- CH2- CH2 – OH 1,4 - butanediol

Dimethyl terephthelate


Chemistry of Preparation of PBT

Polybutylene Terephthelate (PBT) also called polytetramethylene terephthalate (PTMT) resin is a semicrystalline polyester resin. It is produced by the catalytic polycondensation of 1,4 butanediol and dimethyl terephthelate.

n HO-CH2 -CH2 -CH2 CH2 -OH +n CH3 OOC - O COOCH3

o o-[O-C- 0 -C-O CH2 -CH2 -CH2 -CH2- 0]+ 2n CH3 OH


Manufacturing of PBT

PBT is manufactured using similar principles of PET manufacturing.

At first step PBT is produced by the catalytic polycondensation of 1,4 butanediol and dimethyl terephthalate, Subsequent post condensation raises transerterified product to the desired molecular weight.


Relations of Structure and Properties of PBT

There are various classes of linear polyesters. The concentration of ester groups has predominant effect on the

properties of linear polyesters. For the aromatic classes of linear polyester, decreasing the

concentration of ester groups apparently leads to a reduction in melting

point. However, in such aromatic linear polyester the decrease in

concentration of ester group is accompanied by the p-phenylene group

concentration. It is found from aliphatic polyester that the ester group concentration

has little effect on the melting point. In fact a decrease in ester group concentration leads to a slight increase

in the melting point.



It is found that in an ester group the in chain ether link –C-O-C-

increase the chain flexibility compared with a polyethylene chain to

decrease the heat of fusion. At the same time there will be some increase in inter chain attraction via

the carbonyl group which will decrease the entropy of fusion. Since these two effects almost cancel each other out there is almost no

change in ester group concentration. With all linear series of polyester as the no. of methylene groups in the

repeating unit increases so the polymer becomes more like a linear

polyethylene (polymethylene).



It is also observed that Tm (melting point) of a polymer with an odd no.

of methylene groups in the aliphatic portion of the repeat unit is lower than

for the polymer with one more but an even no. of methylene groups.

Generally, the highest melting points are obtained where the in-chain

aromatic ring is of the p-phenylene type.

The materials have a disadvantage of sensitivity to water and alkaline

solution.

These materials are crystalline and only proton donors that are capable

of inter action with the ester groups are effective solvents.

Characteristics of PBT ( For Identification)

The PBT is semicrystalline material.

It is having good wear characteristics and good

insulating properties.

It is also having good dimensional stability.

It is identified by orange colored sooty flame.

When burns melt drips and gives sweet smell

The melting point is 220-230°C

Short term and long term service temperature are

respectively 160 and 100°CCORPORATE TRAINING AND PLANNING

Characteristics of PBT

High strength & rigidity Excellent dimensional stability Low co-efficient of friction Good abrasion resistance Good resistance to creep at ambient & elevated

temperature Low moisture absorption Resistance to weak acid, bases, alcohols, ketones, oils, fats

and aliphatic hydrocarbons Good resistance to motor oil, gasoline and brake fluids High temperature resistance Excellent flame resistance Good electrical resistance High arc resistance & dielectric strength Low dissipation factor


Properties of PBT

Properties Units ValuesSpecific gravity ---- 1.31Tensile strength MPa 55Tensile modulus MPa 2551Flexural modulus Mpa 2275Elongation at break % 200Impact strength izod, Notched, J/m 53Hardness R -72Deflection temperature under load 0C 205-210(1.82 Mpa)Coefficient of linear expansion mm/mm/0C 7.4 x 10-5

Water absorption, 24hrs % 0.1Dielectric strength KV/mm 15.8Dielectric constant 10-6 Hz 3.24Power factor 0.019Volume resistivity Ohm.m 4 x 1017

Melting point 0C 225Glass transition temperature °C 40


Properties of PBT

Mechanical PropertiesThe material has very good strength, stiffness,

hardness and maintain toughness at low temperature.

Thermal PropertiesThe melting temperature of PBT is 225°C. It has

excellent dimensional stability at variable temperature range.

Electrical PropertiesPBT is a good electrical insulator and this is little

affected by water absorption. Electrolytic corrosion or contact-impairing deposits are unlikely. The dielectric strength is also independent of temperature.


Properties of PBT

Water AbsorptionThe low moisture absorption ensure consistent mechanical

performance and dimensional stabiltiy.

Permeability to Water vapour and GasesPermeability resembles that of PET films, i.e. it is good compared to

other polymers.

Chemical Properties PBT is resistant to water, aqueous solutions (at room temperature), weak acids, many organic solvents, oils, fats, brake fluid, carbon tetrachloride. It is not resistant to strong acids, alkaline solutions, phenol, ethyl acetate, acetone. Extended contact with water at 60°C leads to hydrolytic decomposition. PBT is not susceptible to stress cracking.


Properties of PBT

Resistance to Weathering and High Energy RadiationThe properties are same as discussed for PET.

FlammabilityUnreinforced PBT burns slowly with an orange, sooty

flame. The melt drips. Glass fiber reinforced material burns more rapidly because there is less tendency to drip.

ToxicityPBT is suitable for applications involving contact with

food stuffs. It is physiologically inert.


Additives of PBT

1. Functional additives

2. Fillers

3. Reinforcements


Functional Additives

1. Anti-oxidants

2. UV absorbers

3. Flame retardants


Fillers and Reinforcements

1. Mica - Fillers

2. Thermoplastics glass fiber - Reinforcements


Grades of PBT

The PBT is available in the following grades.

Injection moulding grade

Extrusion grade


Processing of PBT

PBT can be processed by the following techniques

Injection Moulding

Extrusion

Blow Moulding


Processing considerations of PBT

This resin must be dried to a moisture of 0.02% or less before processing to ensure desired quality performance. The drying condition should be 120°C for 2-4 hours.

The injection moulding machine should be cleaned thoroughly with polyolefin or polystyrene to remove any residual material in the cylinder.

The cylinder temperature should be maintained at 230-260°C. The recommended mould temperature should be 60-120°C.

The maximum recommended regrind / reclaimed material which can be mixed without adverse affect on resin properties is 25%.


Surface Finishing of PBT

The high chemical resistance of the polyalkylene terephthalates

necessitates the use of special purpose lacquers to ensure good

adhesion.

The same applies to hot embossing (temperature range of the

die 140 - 200°C).

PBT can be polished easily. Metallization can be only be

carried out by high vacuum deposition.

Where high gloss surfaces are required on filled and reinforced

product, an intermediate lacquer must be used.


Machineability of PBT

CuttingCutting can be possible in PBT with suitable equipments in a specified

speed.

Joining

WeldingMoldings and semi-finished products can be welded and bonded.

Unreinforced moldings can be joined by hot gas and heated tool welding. With increasing glass fiber and the flame retardant content, the welded joints decrease in strength. Friction and ultrasonic welding are efficient joining methods. The conditions for heated tool welding are

Heated tool temperature - 260°CContact pressure at start of heating - 0.5 barContact pressure at start of welding - 0.5 barHeating up time (according to wall thickness) - 10 to 30 s


Applications of PBT

Electrical and electronic applications

Automobile applications

Others


Applications of PBT

Electrical and electronic applications:

Connector, IC Sockets, Terminal blocks, bobbins, push-buttons of telephone set, micro switch, TV parts, hair dryer parts, micro motor housing, glue gums etc.

Automotive plug connector


Applications of PBT

Automobile applications:Wiper gear case, outer handle, distributor, coupler, Ignition system parts, bumper, valve of exhaust, gas treating system etc.

Application of PBT in various areas


Applications of PBT

Air bag cover Fuse holder Optical connector

Car seat frame


Applications of PBT

Iron boxInhaler

Overhandle Blood filter


Blends of PBT

PBT/PET The injection molding of glass fiber reinforced PBT leads to long directional orientation and anisotropy in the molded part. And additional deficiencies is the poor surface quality of the molded parts. But when blended with PET warpage of the part is clearly diminished and surface quality improved. The blends also show improvements in heat deflection temperature and impact strength.


Blends of PBT

PBT/Elastomers The blends developed for molding show good heat deflection temperature processability, electrical properties stiffness, strength, dimensional stability impact strength, solvent and chemical resistance

PBT/ABS (contain upto 30% glass fiber) The blend shows excellent processability, high gloss, stiffness at high temperature and mechanical strength, heat deflection temperature, low shrinkage, good dimensional stability, impact strength as well as solvent and chemical resistance.


List of Manufacturers/Suppliers of PBT

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Polybutylene Terephthalate (PBT) CORPORATE TRAINING AND PLANNING