The first part presents the improvements in the mechanical properties of a couple of biodegradable polymers, the first one is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHx) by introducing several nano-fillers (clay, mica, talc, expanded graphite) to prepare nanocomposites. Solution mixing and melt bending are the two preparation methods used. The resulting nanocomposites were characterized by X-ray diffraction measurements (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and INSTRON measurements. The results showed that PHBHx/clay and PHBHx/graphite nanocomposites were obtained with remarkable improvements in mechanical properties even at very low filler content. The improvements were mostly attributed to the intercalated, even exfoliated state of the clay in PHBHx. Another Biodegradable polymer was studied in this work is glycerol-derived alkyd resin. One set of the resin/clay nanocomposites was successfully prepared by melt blending the resin precursors with organoclays. The clay using here is clay30B, and clay30BT (further treated ones of clay30B). Mica and talc were also used to prepare nanocomposites for comparison. The morphologies, thermostabilities, and mechanical properties of the resulting nanocomposites were investigated, indicating that resin/clay nanocomposites were obtained with remarkable improvements in thermostability and mechanical properties even at very low loadings.
The second part focused on the preparation and characterization of silicone hydrogels based on poly(dimethylsiloxane) (PDMS) and hydrophilic block copolymer, and some surface modifications of PDMS.
The first two series of bimodal silicone hydrogels successfully prepared are PDMS-poly(ethylene glycol) (PEG) hydrogels, which were prepared by end-linking a combination of long and short chains and a couple of hydrophilic functional crosslinker respectively. In both cases longer hydrophilic chains clearly migrated to the surfaces of the resulting PDMS-PEG hydrogels to give decreases of static contact angles (CA) from 105° to 80° for the first series, and to 40° for the second. The longer hydrophilic chains were found to give larger decreases in CA values and larger equilibrium water contents as expected.
Several other series of PDMS-PEG amphiphilic conetworks (APCNs) were prepared including by bonding a hydrophilic macromer, hydroxyl-terminated linear PEG, hydroxyl-terminated linear PDMS with the crosslinker bis[(3-methyldimethoxysilyl)propyl]-polypropylene oxide (BMPPO), which also functioned as a compatibilizer. The CA values decreased significantly from 105° in PDMS to 55° in the PEG/PDMS APCN (10/1 mol ratio), and the swelling degrees of the APCNs increased from about 0 to 60 % when the mol ratio was larger than 4/1. A couple of other series APCNs with very high and long lasting hydrophilicity and good mechanical properties are also obtained.
Secondly, several surface treatments methods were applied to make PDMS networks surface hydrophilic, including (1) introduction of an ultra thin layer of silica on the surfaces through the sol-gel process, (2) a UV/ozone method for bimodal networks consisting of some vinyl-substituted chains, poly(vinylmethylsiloxane) (PVMS), along with those of PDMS; (3) treatment of PDMS networks by UV/ozone, followed by grafting of polyethylene glycol based silane directly onto the surfaces, (4) grafting a hydrophilic monomer, N-isopropylacrylateamine by the UV radiation, (5) plasma polymerization of acrylic acid (AA) onto the surface of the PDMS.