In 2007, about 600,000 tons of poly(ethylene terephthalate) (PET) were used for various applications, especially by the packaging industry in Japan.
As a result, large amounts of post-consumer PET waste could be expected, which mostly comes from post-consumer drinking bottles. About 70% of PET waste is recycled in Japan, which is considered among the highest proportion in the world.
One of the main disadvantages of recycled PET (RPET) is its low intrinsic viscosity and wide molecular weight distribution. As such, RPET is cheap and its use is mainly confined to the production of polyester fibers.
Should RPET be reused for other applications, further chemical modification is needed, which is costly. Therefore, other methods for upgrading RPET should be considered in order to achieve similar or better properties as compared to virgin materials.
Solid state polymerization is one such method for upgrading of RPET, where water molecules are removed by heat and an inert gas is used to purge degradative substances.
However, due to the high activation energy and low rate of polymerization, the efficiency of solid state polymerization is very low.
In this study, high frequency (HF) heating method was proposed in order to enhance the efficiency of solid state polymerization for upgrading of RPET.
The rate of polymerization by HF technique was significantly higher when compared to conventional heating techniques. This study explores the possible polymerization mechanisms during HF treatment.
Moreover, the optimum HF treatment conditions in order to obtain the highest intrinsic viscosity were clarified while the challenges and limitations of this method were also outlined.
The results from this study suggest that HF treatment can be an innovative and practical method to significantly enhance the value and usefulness of not only RPET but also virgin materials.
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