PET Resin for Bottles and Cups

Details:

What is PET plastic

Polyethylene terephthalate (PET or PETE) is a general-purpose thermoplastic polymer which belongs to the polyester family of polymers. Polyester resins are known for their excellent combination of properties such as mechanical, thermal, chemical resistance as well as dimensional stability.

PET is one of the most recycled thermoplastic and has the number "1" as its recycling symbol.

Molecular Structure of Polyethylene Terephthalate
PET Chemical Formula: (C₁₀H₈O₄)_n

Recycled PET can be converted to fibers, fabrics, sheets for packaging and manufacturing automotive parts. Chemically, Polyethylene terephthalate is very much similar to Polybutylene Terephthalate.

PET is highly flexible, colorless and semi-crystalline resin in its natural state. Depending upon how it is processed, it can be semi-rigid to rigid. It shows good dimensional stability, resistance to impact, moisture, alcohols and solvents.

Commercially available PET grades include un-reinforced to glass reinforced, flame retardant and high flow materials for various engineering applications that typically require higher strength and or higher heat resistance. Addition of fillers like glass fibers, CNTs etc. help improve impact strength, surface finish, reduce warpage and several other benefits.

How PET is made

PET is an aliphatic polyester. It is obtained from polycondensation reaction of the monomers obtained either by:

• Esterification reaction between terephthalic acid and ethylene glycol, OR
• Trans-esterification reaction between ethylene glycol and dimethyl terephthalate

 

The reaction produces PET in the form of a molten, viscous mass which can be easily spun directly to fibers or extruded or molded into almost any shape.

PET Copolymers

Polyethylene terephthalate is available as a homopolymer and it can also be modified to produce copolymers (known as PETG or PET-G - polyethylene terephthalate glycol-modified) making it more desirable for a particular application.

The common modifiers which replace ethylene glycol or terephthalic acid to produce PETG are cyclohexane dimethanol (CHDM) and isophthalic acid respectively. There modifiers interfere with crystallization and lowers the polymer's melting temperature.

 

Advantages & Key Properties of PET Resin

The key advantages and features of polyethylene terephthalate are listed below.

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• It has higher strength and stiffness than PBT
• It is very strong and lightweight & hence easy and efficient to transport
• It is known for its good gas (oxygen, carbon dioxide) and moisture barrier properties
• It exhibits excellent electrical insulating properties
• PET has broad range of use temperature, from -60 to 130°C
• As compared to PBT, it also has higher heat distortion temperature (HDT)
• It has low gas permeability, in particularly with carbon dioxide
• PET is suitable for transparent applications, when quenching during processing
• PET doesn’t not break or fracture. It is practically shatter-resistant and hence, a suitable glass-replacement in some applications
• It is recyclable and transparent to microwave radiation
• PET is approved as safe for contact with foods and beverages by the FDA, Health Canada, EFSA & other health agencies

 

PET Chemical Properties

 

• Excellent resistance to alcohols, aliphatic hydrocarbons, oils, grease and diluted acids
• Moderate resistance to diluted alkalis, aromatic & halogenated hydrocarbons

 

Limitations of Polyethylene Terephthalate

 

• Lower impact strength than PBT 
• Lower moldability than PBT, due its slow crystallization rate 
• Affected by boiling water 
• Attacked by alkalis and strong bases 
• Attacked at high temperatures (>60°C) by ketones, aromatic and chlorinated hydrocarbons and diluted acids and bases 
• Poor burning behavior

 

Polyethylene Terephthalate Blends with Thermoplastics and Thermosets

Blending of PET with other thermoplastics or thermosets is done to tailor new materials having improved performance with beneficial cost profiles to meet specific application demands. Blending also opens up new markets and applications potential without much investment and development.

The thermoplastic polymers that are used to produce blends with PET are polyethylene, polypropylene, polycarbonates, polystyrene, ethyl vinyl acetate and Acrylonitrile Butadiene Styrene. And epoxies, polyester resins, phenolic resins, elastomers such as nitrile butadiene rubber, styrene butadiene rubber etc. are among thermosets which are used to produce in PET blends.

• PET modified with polyolefins are often glass fiber reinforced and used in injection molded automotive and industrial applications
• PET/PC blends applications include those requiring a combination of excellent toughness, chemical and heat resistance long with high impact, tensile and flexural strength
• Blending thermosets with PET significantly improves thermal, mechanical, impact resistance and flame retardant properties. These blends are mainly used for the production of automotive, aeronautic and electronic components