Polyethylene Naphthalate
Short for polyethylene naphthalate. Polyethylene naphthalate (PEN) is one of the important members of the polyester family. It is a new and excellent polymer formed by the polycondensation of 2,6-naphthalene dicarboxylic acid dimethyl ester (NDC) or 2,6-naphthalene dicarboxylic acid (NDA) and ethylene glycol (EG).
Its chemical structure is similar to PET, except that the PEN molecular chain has a more rigid naphthalene ring instead of the benzene ring in PET. The naphthalene ring structure makes PEN have higher physical and mechanical properties, gas barrier properties, chemical stability, heat resistance, UV resistance, radiation resistance and other properties than PET.
Performance
A. Gas barrier properties
Since the structure of naphthalene is more likely to be planar, one of the most outstanding properties of PEN is its good gas barrier properties. PEN’s barrier properties to water are 3-4 times that of PET, its barrier properties to oxygen and carbon dioxide are 4-5 times that of PET, and its barrier properties to water are 3.5 times that of PET. Its barrier properties are comparable to those of PVDC and are not affected by humid environments. Therefore, PEN can be used as a packaging material for beverages and foods, and can greatly increase the shelf life of products.
B. Chemical stability
PEN has good chemical stability. PEN is stable to organic solutions and chemicals, and its acid and alkali resistance is better than PET. Since PEN has good air tightness and a relatively large molecular weight, it has a smaller tendency to precipitate oligomers than PET at actual use temperatures, and the low-level aldehydes released by decomposition when the processing temperature is higher than PET are also less than PET.
C. Heat resistance
Since the naphthalene ring increases the aromaticity of the macromolecule, PEN has better thermal properties than PET. After PEN is placed in humid air at 130 degrees for 500 hours, its elongation only decreases by 10%. After being placed in dry air at 180 degrees for 10 hours, its elongation can still maintain 50%. However, PET will become very brittle and useless under the same conditions. The melting point of PEN is 265 degrees, which is similar to PET. Its glass transition temperature is above 120 degrees, which is about 50 degrees higher than PET.
D. Ultraviolet radiation resistance
Due to the strong ultraviolet light absorption ability of the bicyclic structure of naphthalene, PEN can block ultraviolet rays less than 380nm, and its blocking effect is significantly superior to PC. In addition, the photomechanical properties of PEN decrease less, and its light stability is about 5 times that of PET. After irradiation, the elongation at break decreases less, and its ability to resist radiation in vacuum and oxygen can reach 10 times and 4 times that of PET respectively.
E. Other properties
PEN also has excellent mechanical properties. The Young’s modulus and tensile elastic modulus of PEN are both 50% higher than those of PET. Moreover, the mechanical properties of PEN are stable. Even under high temperature and high pressure, its elastic modulus, strength, creep and life can still maintain considerable stability. In addition, it also has excellent electrical properties. PEN has electrical properties comparable to PET. Its dielectric constant, volume resistivity, conductivity, etc. are close to those of PET, but its conductivity changes little with temperature. Table 1 below is a comparison of the performance of PEN and PET; Table 2 below is a comparison of the performance of PEN and PET films.
Recycling of polyethylene naphthalate (PEN)
A. Chemical depolymerization method
The team of Professor Fu Yao and Associate Researcher Deng Jin of the University of Science and Technology of China, in collaboration with foreign counterparts, has achieved the upgrading and recycling of waste PET (polyethylene terephthalate) plastics through acetic acid chemical depolymerization. This method uses acetic acid to depolymerize waste PET plastics, undergoes a melting-dissolving-precipitation process, and ultimately achieves efficient recovery of high-purity terephthalic acid and the third-generation environmentally friendly strong solvent ethylene glycol diacetate with high added value. This process not only reduces non-renewable energy consumption and global warming potential, but is also economically attractive and environmentally friendly.
B. Physical recycling method
The physical recycling methods mainly include the following:
Direct melt spinning: waste polyester bottle flakes are granulated and melt-spun into fibers, which are suitable for the production of filling staple fibers, geotextiles or other nonwoven fabrics.
Chemical-physical method: Use the washed waste polyester bottles, waste blocks, etc., and blend them with cationic dye-dyeable polyester masterbatches containing high concentrations of sulfonate groups to make polyester fibers that can be dyed with cationic dyes under normal pressure. This method is simple and easy to implement, and the product cost is low, but it is necessary to solve the manufacturing difficulty and quality stability problems of high-concentration cationic dye-dyeable polyester masterbatches.
