Characterization of a pearlescent biaxially oriented multilayer polypropylene film

The morphology, composition, optical, thermal and mechanical properties of a commercial pearlescent and multilayer BOPP film were determined in the present study. The film was polypropylene and it was biaxially oriented as shown by FTIR spectroscopy and X-ray diffraction. FTIR spectroscopy indicated carbonate ions, EDX analysis indicated the presence of Ca element, X-ray diffraction showed the presence of calcite and thermal gravimetric analysis indicated that 11.2 % calcite was present in the film. The 30 μm film consisted of a core layer filled with calcite and 4 μm thick upper and lower layers without any filler and from different polymers. There were long air cavities in the core layer with aspect ratios of 23 and 19 in machine and transverse directions making the film pearlescent. The surfaces of the film were very smooth and had surface roughness in the range of 3.052 nm and 11.261 nm as determined by AFM. The film melted at 163.6 oC had 51% crystallinity and had 6.3 nm polymer crystals when heated at 10 oC/min rate. The film thermally degraded in two steps. They consist in polymer fraction and decomposition of calcite, respectively. For 10 oC/min heating rate the onset of polypropylene degradation was 250 oC and calcite decomposition was 670 oC. The activation energies for polypropylene degradation and calcite decomposition were 64.8 kJ/mol and 204.8 kJ/mol. The tensile strength of the film in machine and transverse directions was 97.7 and 35.9 MPa, respectively.