Polyethylene naphthalate (PEN) is a polyester polymer made from purified terephthalic acid or dimethyl terephthalate, and either ethylene glycol or its derivative, bis(hydroxyethyl)naphthalene. It is often used in the production of textiles and beverage bottles. PEN possesses good thermal and mechanical properties along with excellent ductility.
Properties of PEN
- High Strength and Stiffness: Polyethylene Naphthalate is known for its high tensile strength and modulus compared to other polyester polymers like PET. This makes it suitable for applications requiring mechanical strength.
- Barrier Properties: PEN has good barrier properties against gases like oxygen and carbon dioxide. This makes it a preferred material for packaging of carbonated beverages and food products requiring extended shelf life.
- Heat Resistance: PEN has a high heat deflection temperature in the range of 150-170°C depending on grade. This allows containers made from PEN to withstand high heat sterilization processes.
- Chemical Resistance: PEN offers good resistance against acids, alkalis, oils and solvents. It is not readily soluble in common organic solvents.
- Optical Properties: Grades of PEN intended for optical uses have high transparency from the visible to the near infrared region of the electromagnetic spectrum.
Applications of Polyethylene naphthalate
- Bottles for Carbonated Soft Drinks and Bottled Water: Due to its high strength, barrier properties and heat resistance, PEN is an ideal material for packaging carbonated beverages. Leading brands are now producing PEN bottles to replace PET.
- Food Packaging: The barrier properties of PEN allow it to be used for packaging perishable food products as well as microwaveable food trays and containers.
- Aircraft Transparencies: Glazing for aircraft cockpits, windows and canopies are made from high optical quality PEN grades due to impact resistance and light weight.
- Optical Fibers: Telecommunications grade PEN optical fibers have low attenuation in the 1.4–1.7 μm wavelength range and are used in long haul fiber networks.
- Imaging Films: PEN films are used as substrates and protective covers for imaging technologies like LCD.
- Magnetic Tapes: Accounting for its mechanical strength and dimensional stability, PEN tapes are used for audio and video recording.
Manufacturing Polyethylene naphthalate
The production process of PEN involves an ester interchange/esterification reaction between terephthalic acid/dimethyl terephthalate and ethylene glycol or its derivative N-methyl-bis(2-hydroxyethyl)amine. In the first step, these reactants are heated at high temperature (250-270°C) in the presence of a catalyst under vacuum. This results in the loss of water or methanol and formation of bis(2-hydroxyethyl) terephthalate (BHET).
In the second step, the BHET is further polymerized at around 280°C to obtain PEN resin in pellet or cylindrical chip form. The polymerization can be carried by solid state polycondesation or melt phase processes like direct esterification. The PEN pellets have intrinsic viscosity in the range of 0.5-1.2 dL/g depending on the molecular weight requirements.
Post-polymerization processes like washing, drying and compounding are employed to obtain finished PEN resins suitable for conversion processes. PEN is mostly processed by extrusion, injection molding and blow molding techniques to manufacture bottles, films and other molded articles. Oriented films of PEN for optical uses require additional stretching operations.
Sustainable Alternatives
The growing demand for single use plastics has led to increasing environmental concerns. PEN production also generates greenhouse gases and its non-biodegradable waste poses disposal issues if not recycled. Hence, alternative sustainable solutions are being developed.
Researchers are working on production of PEN from renewable bio-based monomers derived from plant sources like wood, corn or sugarcane. This will reduce dependence on petroleum feedstocks. Development of biodegradable grades of PEN can address the waste management problem. Studies are also evaluating the feasibility of microbial breakdown of PEN to create ecofriendly alternatives.
Use of recycled PEN waste through advanced recycling technologies prevents virgin material usage. Meanwhile, encouraging reuse models like refilling of bottles and deposit-refund programs promotes effective waste management of PEN products. Adopting a circular economy approach will make PEN polymers more environmentally sustainable.
Polyethylene naphthalate has emerged as an important engineering thermoplastic due to the balanced combination of properties it offers. Ongoing research further expands the versatile uses of PEN while making its production more sustainable and ecofriendly. With improving recycling methods, PEN will continue playing a significant role in manufacturing of high performance goods.
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Ravina Pandya, Content Writer, has a strong foothold in the market research industry. She specializes in writing well-researched articles from different industries, including food and beverages, information and technology, healthcare, chemical and materials, etc. (https://www.linkedin.com/in/ravina-pandya-1a3984191)
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