Influence of the use of mechanically recycled pet in injection stretch blow moulding process (ISBM)

Abstract

Abstract. Different mechanically recycled PET issuing from different countries of origin have been studied and compared to a neat one, as a reference. Strech ability above glass transition temperature was explored towards uni-axial tensile experiments or injection stretch blow moulding (ISBM) tests. It has been shown in that study that rPETs and virgin do present global mechanical behaviours. This similar trend is obvious either in low or large deformations domains. Master curves built for the 5 grades indicated equivalent behaviour between the grades from the glassy to the rubbery state. A controlled stretching campaign confirmed that all grades present visco-hyperelastic behaviours that are similar until the deformation for which the materials start to strain-harden. Uni-axial tensile tests were proved to be efficient to discriminate all grades especially regarding the Natural Draw Ratio (NDR) onset of all grades. The virgin PET does present a lower NDR that comforts the fact that strain-induced crystallization can be easier in the virgin case. This test campaign analysis is confirmed by the injected preforms blowing process where the virgin case grade develops lower blowing volumes because of a sooner NDR. It highlights the fact that forming behaviours of rPET must be slightly adapted compared to virgin PET. For rPET, the effects of loss of molar mass combined with the presence of contaminants could be at the origin of these discrepancies.