PET mechanical recycling. A new principle for chain extender introduction

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The introduction of chain extenders into the melt of recycled PET (rPET) is traditionally performed at the activation temperature of the extension reaction. The disadvantage of this approach is the low dispersion of chain extender particles, which does not contribute to the full extension reaction. As a result, some rPET chains do not react with the chain extenders, and unreacted chain extenders lead to a decrease in the crystallinity or crystallization rate of rPET, an increase in its degradation rate, and also present deleterious low molecular weight migrating compounds. Herein, a new principle of chain extenders introduction based on a two-stage scheme is considered for the first time, which includes a preliminary stage of mixing chain extenders in an rPET melt at a temperature below the activation temperature of the extension reaction and a stage of PET chain extension at the activation temperature of the extension reaction. It has been shown that rPET modified in this way has higher melt viscosity, strength and ductility compared to rPET modified in the traditional way. The reaction time is reduced by 10–20% depending on the type and concentration of chain extenders used. The differences in the structures formed are demonstrated by NMR, FTIR, DSC, WAXS and rheological test methods. The economic and environmental implications associated with the introduction of a new principle are discussed.