Preparation And Properties Of Poly(L-Lactide)/Polyhedral Oligomeric Silsesquioxanes Nanocomposites

Polyhedral oligomeric silsesquioxanes (POSS) have attracted more and more attention recently due to their hybrid inorganic-organic nature as nanomaterials. Until now, a number of works on traditional polymer/POSS composites prepared both by chemical and physical methods have been widely reported. At present, the research based on the modification of biodegradable polymers using POSS as a filler is still less and more fundamental related work needs to be done. In this work, the nanocomposites based on Poly(L-lactide) (PLLA) and POSS were prepared through both solutions casting and solution and coagulation methods, and the relationship between the structure and property was also studied in detail so as to improve its property and further expand its application areas. The main work is as follows:1. A PLLA/POSS nanocomposite with POSS loading of 5wt% was prepared via solution casting method for the first time in this work. The dispersion and morphology of POSS in the PLLA matrix was studied by scanning electron microscopy (SEM). Effect of POSS on the crystal structure, crystallization kinetics, and dynamical properties of PLLA in the nanocomposite was investigated by wide X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA), respectively. SEM observation indicates that POSS were homogeneously dispersed in the PLLA matrix. It is found that the presence of POSS has enhanced significantly the crystallization rate, improved mechanical properties, but does not change the crystalline structure. The hydrolytic degradation experiment indicates that the presence of POSS accelerated the hydrolytic degradation of PLLA in the nanocomposite with respect to neat PLLA.2. The dispersion of POSS in the PLLA matrix can directly influence the peoperties of PLLA. Solution and coagulation method was used to prepare the PLLA/POSS nanocomposites with a various of POSS loadings so as to better the dispersion of POSS in the PLLA matrix. This method indeed effectively refrain the agglomeration of POSS compared to the solution casting method which were confirmed by SEM and DSC results. SEM observation indicates that POSS were nicely dispersed in the PLLA matrix. The overall crystallization rates are faster in the PLLA/POSS nanocomposites than in neat PLLA and increase with increasing the POSS loading; however, the crystallization mechanism and crystal structure of PLLA remain unchanged despite the presence of POSS. The storage modulus has been apparently improved in the PLLA/POSS nanocomposites with respect to neat PLLA, while the glass transition temperatures vary slightly between neat PLLA and the PLLA/POSS nanocomposites. It is interesting to find that the hydrolytic degradation rates have been enhanced obviously in the PLLA/POSS nanocomposites than in neat PLLA. Gel permeation chromatography studies show that the molecular weight was unchanged during the hydrolytic process. Meanwhile, the surface of the hydrolytic samples became rougher while the thickness became thinner. The erosion mechanism of neat PLLA and the PLLA/POSS nanocomposites proceed via surface erosion, which may be of great use and importance for the wider practical application of PLLA.