Polyethylene Naphthalate PEN

Polyethylene naphthalate is a condensation polymer of ethylene glycol and naphthalate dicarboxylate (NDC), with the structure  

The EDA approved PEN for food contact appiications in Aprii, 1996. PEN and PET can be blended together to make useful materials, and also PEN/PET copolymers can be produced. When PEN/PET blends are used, one is really making copolymers in the extruder. Analysis of the material that is extruded shows that transesterification reactions occur in the extruder, forming molecular bonds between PET and PEN molecules. Therefore, processing conditions are important to the quality of product one makes when using blends. Blends, as well as copolymers manufactured by polymer suppliers, can open up markets for this polyester that are not accessible to PEN alone because of its high price. While these materials have not yet been approved for food contact applications in the U.S., there appear to be no technical barriers to their approval. 

PEN and PET copolymers fall into two groups. Low-NDC copolymers contain less than 15% NDC, and high NDC copolymers have 85% or more NDC. Copolymers with intermediate ranges of NDC are not used because they cannot crystallize and therefore have inferior properties. Because homopolymer PET and PEN are immiscible, blends require special mixing techniques to cause sufficient transesterification to occur. This amounts to the production of a copolymer during the extrusion process, as mentioned earlier. Blends of homopolymers with copolymers are easier to process than blends of the homopolymers themselves. Usually low-NDC copolymers are blended with PET, and high-NDC copolymers with PEN. 

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In the early 1990s interest developed in the packaging material polyethylene naphthalate (PEN), a close cousin of PET. PEN has thermal stability 20°C higher than PET. Kodak had samples of the material sifting in its labs from the makers Teijin in Japan, as early as the beginning of the 1970s. Teijin is still the premier producer of PEN film and plastic today, and is involved with DuPont on the film manufacturing side. 

The manufacture of polyethylene naphthalate) (PEN) is carried out using dimethyl 2,6-naphthalene dicarboxylate (NDC) and EG and is similar to the manufacture of PET from DMT. The IV after the melt is typically in the range of 0.5... 

The influence of the ratio of hydroxylic/carboxylic end groups has been studied by several research groups. In the case of PET, this varies, based on the assumed mechanism over the range of 1.5-4.5 1. For poly(butylene terephthalate) (PBT) and polyethylene naphthalate) (PEN), the optimum is indicated at 2.0 1 [19, 20]. Any deviation from this ratio affects the reaction rate. 

The above-mentioned results of the SSP of PET can be generally applied to other semicrystalline polyesters, such as poly(butylene terephthalate) (PBT), poly(tri-methylene terephthalate) PTT), polyethylene naphthalate) (PEN) or any other kind of semicrystalline co-polyester, as a result of their similar reaction behaviors. Most of the studies have been focused on PET and PBT due to their industrial importance. Meanwhile, the popularity of PEN is growing on account of the outstanding properties of this particular polymer. 

It should be taken into account that all of the aspects described above are of a general nature and therefore more or less valid for any kind of industrially relevant polyester resin. Upon closer examination, the experiences gained with PET are particularly applicable to poly(butylene terephthalate) (PBT), poly(trimethylene terephthalate) (PTT) and polyethylene naphthalate) (PEN). These polymers have gained major industrial importance as a result of a number of different properties in comparison with PET. 

The di-aromatic 2,6 dimethylnaphthalene (26DMN) is of particular interest for the production of polyethylene naphthalate (PEN). PEN has superior oxygen barrier and temperature resistance properties relative to PET, making it a top prospect for applications in beer bottling and reusable plastic bottle applications. Because of its superior properties to neat PET (PEN can also be incorporated into PET resin) it has a good possibility of growing in demand. 

Perhaps the most exciting developments are yet to feature in fruit juice packaging. PET can be laminated with other plastics, such as nylon and ethylene vinyl alcohol (EVOH), to give extremely good barrier properties, and polyethylene naphthalate (PEN) may enable production of a plastic bottle that can be pasteurised at high temperatures. 

Polyethylene naphthalate (PEN) polyesters are made from 2,6-naphthalene dicarboxylic acid or 2,6-naphthalene dicarboxylic acid, dimethyl ester. They have higher temperature resistance than amorphous PET and are increasingly used in applications requiring heat sterilisation of the food/drink, although PEN at the moment is significantly more expensive. Table 10.5 lists commonly used substances in polyesters. 

Naphthalenedicarboxylic acid is a precursor to polyethylene naphthalate (PEN), which is used to improve the properties of polyester bottle resins (see also problem E.1.6). It can be made by the liquid phase oxidation of 2,6-dimethylnaphthalene as described in U.S. 6,114,575, assigned to BP Amoco. Estimate the cost of production for a plant that produces 250,000 metric tons per year (250 kMTA). 

Nonolefinic thermoplastic polymers that in principle may be blended with polyolefins include polyamides (nylons) such as polyamide 6, polyamide 66, polyphenylene sulfide (PPS), polyphenylene ether (PPF), and polyphenylene oxide (PPO) polyesters such as polyethylene terephthalate (PET), polybutylene terephtha-late (PBT), polyethylene naphthalate (PEN), polytrimethylene terephthalate (PTT), polycarbonates, polyethers, and polyurethanes vinyl polymers such as polystyrene (PS), polyvinyl chloride (PVC), polymethylmethacrylate (PMMA), and ethylene... 

Jheng LC, Yang CY, Leu MT, Hsu KH, Wu JH, Ruan J, et al. Novel impacts of glycol-modified poly(ethylene terephthalate)(PETG) to crystallization behavior of polyethylene naphthalate (PEN) within stretched miscible blends. Polymer 2012 53(13) 2758-68. 

Polyethylene naphthalate (PEN) is a polyester with improved properties compared to PET. It is a better barrier and has improved strength and high-temperature stability, but it is considerably more expensive than PET. So far, its high cost has prevented its widespread use in packaging. 

Other food packages include polyethylene naphthalate (PEN) and PEN-PET blends as high-barrier films or rigid containers. 

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