PET: Polyethylene terephthalate

General Properties

Short Name:

Name: 

PET

Polyethylene terephthalate


Polyethylene terephthalate is a semi-crystalline polymer; its semi-crystalline state is sometimes designated PET-C or C-PET and its amorphous state is designated PET-A or A-PET. Amorphous PET is mainly employed for beverage bottles, since it features a high transparency and resistance to breaking. For the use as a construction material, a high degree of crystallinity can be advanta- geous since this prevents shrinkage of the components due to Post Crystallization (Cold Crystallization)The post crystallization of semi-crystalline plastics occurs primarily at elevated temperatures and increased molecular mobility above the glass transition.post-crystallization.*

Structural Formula


Properties

Glass Transition Temperature70 to 85°C
Melting Temperatures and EnthalpiesThe enthalpy of fusion of a substance, also known as latent heat, is a measure of the energy input, typically heat, which is necessary to convert a substance from solid to liquid state. The melting point of a substance is the temperature at which it changes state from solid (crystalline) to liquid (isotropic melt).Melting Temperature245 to 260°C
Melting Temperatures and EnthalpiesThe enthalpy of fusion of a substance, also known as latent heat, is a measure of the energy input, typically heat, which is necessary to convert a substance from solid to liquid state. The melting point of a substance is the temperature at which it changes state from solid (crystalline) to liquid (isotropic melt).Melting Enthalpy140 J/g
Decomposition Temperature425 to 445°C
Young's Modulus2100 to 3100 MPa
Coefficient of Linear Thermal Expansion80 to 100 *10-6/K
Specific Heat Capacity1.04 to 1.17 J/(g*K)
Thermal Conductivity0.24 W/(m*K)
Density1.33 to 1.45 g/cm³
MorphologySemi-crystalline thermoplastic
General propertiesHigh stability and stiffness. Good abrasion resistance. Good sliding properties. Resistant to diluted acids, aliphatic and aromatic hydrocarbons, oils, fats and alcohols. Tear and weather resistant. Good electrical insulating properties
ProcessingInjection blow molding, stretch blow molding, injection molding
ApplicationsFibers (polyesters), e.g., for sportswear. Packing (e.g., beverage bottles). Instrument and apparatus engineering. Medical engineering

NETZSCH Measurement

InstrumentDSC 204 F1 Phoenix®
Sample Mass8.43 mg
Isothermal Phase5 min
Heating/Colling Rates10 K/min
CrucibleAl, pierced lid
AtmosphereN2 (50 ml/min)

Evaluation

Polyethylene terephthalate (PET) exemplifies how the ratio of amorphous and crystalline phases within a sample can be affected by different cooling rates. During production, the material undergoes very fast cooling, resulting in a high amorphous content. This is evident in the 1st heating (blue) from the large Temperatura di transizione vetrosaLa transizione vetrosa è una delle più importanti proprietà chimico-fisiche dei materiali amorfi e semi-cristallini, come, ad esempio, vetri, metalli (amorfi), polimeri, ingredienti farmaceutici e alimentari e definisce l’intervallo di temperatura in cui le proprietà meccaniche die materiali variano da duro e fragile a più morbido, malleabile o gommoso.glass transition step (Δcp of 0.34 J/(g.K)) and subsequent cold or Post Crystallization (Cold Crystallization)The post crystallization of semi-crystalline plastics occurs primarily at elevated temperatures and increased molecular mobility above the glass transition.post-crystallization at 137°C (peak temperature). Post Crystallization (Cold Crystallization)The post crystallization of semi-crystalline plastics occurs primarily at elevated temperatures and increased molecular mobility above the glass transition.Post-crystallization is generally associated with a volume change (shrinkage). At 251°C (1st heating, blue), all crystalline phases melt. 
After a controlled cooling at 10 K/min, the amorphous content of the polymer was considerably lower than before. For this reason, the glass transition step height in the 2nd heating (red) was lowered and Post Crystallization (Cold Crystallization)The post crystallization of semi-crystalline plastics occurs primarily at elevated temperatures and increased molecular mobility above the glass transition.post-crystallization was almost completely eliminated. The Melting Temperatures and EnthalpiesThe enthalpy of fusion of a substance, also known as latent heat, is a measure of the energy input, typically heat, which is necessary to convert a substance from solid to liquid state. The melting point of a substance is the temperature at which it changes state from solid (crystalline) to liquid (isotropic melt).melting temperature in the 2nd heating (peak temperature) occurred at 249°C. The difference between peak temperatures of the 1st and 2nd heatings is due to the better contact between the sample and crucible bottom after the first melting.