Stretchability above glass transition of mechanically recycled poly(ethylene terephtalate), PET

Abstract

Poly(ethylene terephthalate) (PET) is nowadays an interesting polymer, largely used for food packaging applications. It has the ability to develop a pseudo-crystalline structure under stretching above its glass transition temperature. Environmental concerns have granted an increasing interest for recycled materials and thus recycled PET (rPET). Mechanical recycling of PET can affect the chains length as well as the contaminant concentration that will change is formability. Two rPET and two virgin PET (vPET) having dissimilar intrinsic viscosity were then studied by first analyzing the initial properties of the extruded sheets. The four grades were then stretched in uniaxial conditions, based on the time/temperature equivalence principle identified in the low deformations domain. A relevant parameter, the natural draw ratio (NDR) appears to be very efficient so as to discriminate the relative mechanical responses of the four grades. This parameter whose use has been comforted in industrial conditions allows to optimize the forming range of rPET, compared to vPET. • Mechanically recycled and virgin PET stretch ability above glass transition is explored, and their mechanical behavior do obey to time/temperature equivalence principle. • For all the stretching settings applied, the natural draw ratio (NDR) measured is a relevant parameter able to discriminate mechanical behavior of virgin or recycled polymers. • An optimization of the forming range is proposed where enhanced induced microstructures are obtained.