Abstract
SiO2-based organic-inorganic hybrids (OIHs) are versatile materials whose properties may change significantly because of their thermal treatment. In fact, after their preparation at low temperature by the sol-gel method, they still have reactive silanol groups due to incomplete condensation reactions that can be removed by accelerating these processes upon heating them in controlled experimental conditions. In this study, the thermal behavior of pure SiO2 and four SiO2-based OIHs containing increasing amount (6, 12, 24 and 50 wt %) of poly(ε-caprolactone) (PCL) has been studied by simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC). The FTIR analysis of the gas mixture evolved at defined temperatures from the samples submitted to the TG experiments identified the mechanisms of thermally activated processes occurring upon heating. In particular, all samples already release ethanol at low temperature. Moreover, thermal degradation of PCL takes place in the richest-PCL sample, leading to 5-hexenoic acid, H2O, CO2, CO and ε-caprolactone. After the samples’ treatment at 450, 600 and 1000 °C, the X-ray diffraction (XRD) spectra revealed that they were still amorphous, while the presence of cristobalite is found in the richest-PCL material.
Highlights
In recent years, organic–inorganic hybrids (OIHs) have played a crucial role in the development of multifunctional nanostructured materials [1,2,3,4,5,6,7]
The SiO2 /PCL hybrid materials were synthesized by means of the sol-gel method, according to a procedure reported in detail in Catauro et al [26]
In order to collect more information to support a reasonable mechanism associated to the thermally stimulated processes that take place in the OIHs submitted to the TG/differential scanning calorimetry (DSC) experiments, the thermogravimetry/Fourier transform infrared spectroscopy (TG/FTIR) experiments were performed using a SETARAM 92-16.18 TG apparatus (SETARAM, Caluire, France) under a stream of argon of 40 mL min−1 in the temperature range between 25 and 700 ◦ C at 10 ◦ C min−1
Summary
Organic–inorganic hybrids (OIHs) have played a crucial role in the development of multifunctional nanostructured materials [1,2,3,4,5,6,7]. OIHs are not a simple physical mixture of organic and inorganic phases possessing properties that are the sum of those of both components; rather, they are intimately mixed, with average dimensions ranging from a few Å to several nanometers [8,9] These materials have been divided into two classes according to the nature of the bonds between them [10]. The focus of the present study has been to determine the mechanisms of reactions occurring in these materials upon heating them under inert atmosphere by coupling TG and FTIR devices, similar to what has previously been done using TG and mass spectrometry [39] Such information associated to specific biological studies could allow the rational fine tuning of biomaterials with properties It is useful to detect by XRD the modification of the solid phases induced upon heating and stables at these temperatures
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