Melting behavior in thin films of linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE) was studied by local thermal analysis (μTA). Even in the films thinner than 100nm, the melting temperature (Tm) was successfully observed by μTA. For LLDPE, Tm decreased as the thickness became thinner than 150nm. For HDPE, Tm increased with decreasing thickness. Polarized infrared spectroscopy revealed that an edge-on lamellar structure formed in both cases, meaning that the crystallite orientation may not be a reason why the thickness dependence of Tm was not the same for both resins. A possible explanation is that for LLDPE the segmental mobility in the amorphous region predominates with decreasing thickness, and for HDPE the chain orientation in the region predominates with decreasing thickness.
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