Montmorillonite partially exchanged with Fe(III) was prepared by
dispersion of 3.5 g of ClNa in 350 mL at 80 °C; 150 mL of a solution
2 M of FeCl3 was added at the same temperature under vigorous stirring
at 10 mL min-1 and the mixture was stirred for 24 h. The Fe(III)
exchanged clay was filtered, washed until free from chloride ion as
controlled using 0.01 M AgNO3, dried at 80 °C for 24 h, and ground
to a fine powder using a mortar and pestle. The Fe(III)-loaded MMT
was designated as ClFe.
Prior to the melt blending, polymer matrix was dried at 70 °C under
vacuum for at list 4 h to a Karl Fischer titration moisture content below
190 ppm. Nanoparticles were dried at 100 °C under vacuum for 10 h
to a Karl Fischer titration moisture content below 1000 ppm. Nanocomposites
were obtained at 5% filler loading by melt blending using
a Microextruder DSM Micro 15CC Twin Screw Compounder, with a
mixing time of 5 min, at 180 °C, and in a nitrogen flow. The mixing
was performed at two different rotor speeds: 60 rpm in the loading
step and 100 rpm during mixing.
Films (e40-50 μm) were prepared from pellets using a hot-plate
hydraulic press at 190 °C using hydraulic pressure of 100 bar for 1
min. Film thickness was selected to allow oxygen saturation during
film photo-oxidation. Specimens for XRD 30 · 30 ·1 mm3 were prepared
by compression molding at 5 MPa, 190 °C for 2 min.
Irradiations of specimens at λ > 300 nm were carried out in air in a
SEPAP 12/24 unit at 60 °C. This apparatus is equipped with four
medium-pressure mercury lamps with borosilicate envelope which filters
wavelengths below 300 nm and it is designed for the study of polymer
photodegradation in artificial conditions that are relevant to natural
outdoor weathering.30
Photooxidation of PLA was followed by the intensity 1847 cm-1
peak υCdO of anhydride, which was plotted as a function of time (Figure
11); to avoid differences due to film thickness, it was normalized by
dividing for the IR absorption band at 2997 cm-1 υC-H characteristic
vibration stretching band of PLA. (asymmetric υ(CH3) band of PLA).
Reactions of films with gaseous NH3 were performed in NH3
saturated atmosphere obtained under glass bell in presence of concentrated
NH3 solution.Characterization Techniques. Wide-angle X-ray spectra (WAXS)
were recorded at room temperature in the range 1-30° (2θ; step size
) 0.02°, scanning rate ) 2 s/step) by using filtered Cu KR radiation
(λ ) 1.54 Å). Scanning electron microscopy (SEM) was carried out
on the cryogenic fracture surfaces of the 0.6 mm specimens previously
coated by sputtering with gold, using a Leo 14050 VP SEM apparatus.
UV-visible spectra (UV-vis) of films were recorded on a Shimadzu
UV-2101 PC spectrometer equipped with an integrating sphere. Infrared
spectra (FT-IR) of films were recorded using a Perkin-Elmer Spectrum
GX Infrared spectrometer. Spectra were obtained using eight scans and
a 4 cm-1 resolution.