Amorphous deformation in high- and low-density polyethylene probed by aggregation-induced emission

Perylene was doped into high- and low-density polyethylene (HDPE and LDPE, respectively) as an aggregation-induced emission (AIE) dye. Emission spectra were monitored in situ during tensile tests and analyzed using nonnegative matrix factorization (NMF). The components of the second score, s₂, corresponding to the AIE fraction showed a significant increase beyond the elastic limit because of further aggregation induced by the compressive stress exerted on the amorphous phase. The s₂ components decreased drastically at the second yield point because plastic flow caused the perylene aggregates to collapse. The results of step-cycle tests revealed the difference in the yielding mechanisms between HDPE and LDPE. Deformation in HDPE was hindered by the compressive stress exerted on the densely-packed bulky units. The present study demonstrated that AIE is a sensitive probe of amorphous deformation and that the proposed method can be used to quantitatively evaluate material failure even before yielding occurs.