In these days, the large amount of plastic waste is a very serious problem. The best way to reduce it is recycling. However, the mechanical properties of products made from waste plastic are very inferior compared to those made from virgin plastic.
  The reason has been considered to be that waste plastic is chemically degraded. However, we have clearly shown that the main cause of this inferior property is regenerable physical degradation. We also found that the physical degradation is caused from the change of inner structure.
  In this study, in order to elucidate the mechanism of this physical degradation, we evaluated the changes in mechanical properties and internal structure of film made from virgin L-LDPE with a history of heat treatment and re-compression.
  As a result, we found that physical properties were deteriorated in a sample having a history of heat treatment and re-compression. Furthermore, as a result of analyzing the internal structure of the physically deteriorated sample by SAXS, we found that the thickness of the crystal layer was changed. These results suggest that L-LDPE causes physical degradation in the process of remolding due to the heat treatment history.