L. Rueda

Cellulose nanocrystals/polyurethane nanocomposites. Study from the viewpoint of microphase separated structure

Cellulose nanocrystals (CNC) successfully obtained from microcrystalline cellulose (MCC) were dispersed in a thermoplastic polyurethane as matrix. Nanocomposites containing 1.5, 5, 10 and 30 wt% CNC were prepared by solvent casting procedure and properties of the resulting films were evaluated from the viewpoint of polyurethane microphase separated structure, soft and hard domains. CNC were effectively dispersed in the segmented thermoplastic elastomeric polyurethane (STPUE) matrix due to the favorable matrix-nanocrystals interactions through hydrogen bonding. Cellulose nanocrystals interacted with both soft and hard segments, enhancing stiffness and stability versus temperature of the nanocomposites. Thermal and mechanical properties of STPUE/CNC nanocomposites have been associated to the generated morphologies investigated by AFM images.

In situ polymerization and characterization of elastomeric polyurethane-cellulose nanocrystal nanocomposites. Cell response evaluation

Polyurethane/Cellulose nanocrystal (CNC) nanocomposites have been prepared by means of in situ polymerization using CNCs as precursors of polyurethane chains. Thermal, mechanical and morphological characterization has been analyzed to study the effect of CNC on the micro/nanostructure, which consisted of individualized nanocellulose crystallites covalently bonded to hard and soft segments of polyurethane. The incorporation of low CNC content led to a tough material whereas higher amount of CNC provoked an increase in soft and hard segments crystallization phenomenon. Moreover, from the viewpoint of polyurethane and polyurethane nanocomposites applications focused on biomedical devices, biocompatibility studies can be considered necessary to evaluate the influence of CNC on the biological behaviour. SEM micrographs obtained from cells seeded on top of the materials showed that L-929 fibroblasts massively colonized the materials surface giving rise to good substrates for cell adhesion and proliferation and useful as potential materials for biomedical applications.

The role of reactive silicates on the structure/property relationships and cell response evaluation in polyurethane nanocomposites

Precursors of polyurethane chains have been reacted by means of in situ polymerization with organically modified montmorillonite clay to obtain polyurethane nanocomposites containing from 1 to 4 wt % of nanoreinforcement. The effective final dispersion of inorganic component at nanometric scale was investigated by X-ray diffraction, atomic force microscopy, and transmission electron microscopy. In addition, the effect of the nanoreinforcement incorporation on thermal and mechanical behavior of polyurethane nanocomposites was evaluated. Nanocomposites showed similar mechanical properties to polyurethanes containing high-hard segment contents with higher tensile modulus and a decrease in elastomeric properties of polyurethane materials. Finally, biocompatibility studies using L-929 fibroblast have been carried out to examine in vitro cell response and cytotoxicity of the matrix and their nanocomposite materials. Results suggested that the organic modifier in the clay is unsuitable for biomedical devices in spite of the fact that the matrix is a good candidate for cell adhesion and proliferation.

Inverting Polyurethanes Synthesis: Effects on Nano/Micro-Structure and Mechanical Properties

Two sets of new thermoplastic elastomeric polyurethanes were prepared by different routes. One route was the common two shoot polymerization, in which a short diol is added at the last step in order to link prepolymer chains. The new rout that is described here consisted in preparing firstly the hard segments upon 1,6-hexamethylene diisocyanate (HDI) and 1,4-butanediol (BD), used in the previous case as chain extender, and adding finally the polydiol in the second step, in a chain extender fashion, in order to form the grown polyurethane. The differences between these two sets of materials were considerable due to the more ordered and crystalline hard segments formed and the subsequent nano-domain distribution that aroused when inverting the common synthesis. Inter-domain distances and domains sizes are measured and also compared with those of the literature. The structure/properties relationships of synthesized polyurethanes with different hard segment content were analyzed by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), atomic force microscopy (AFM), and performing tensile and Shore D hardness tests.

Effect of Diisocyanate Structure on Thermal Properties and Microstructure of Polyurethanes Based on Polyols Derived from Renewable Resources

Polyols derived from renewables resources are good candidates to obtaining segmented polyurethane elastomers. Diisocyanates with different chemical structure, aliphatic and aromatic, have been used to synthesize by a two step polymerization procedure polyurethane elastomers with different hard segment content. Microphase separation and thermal stability have been studied using attenuated total reflection Fourier transform infrared spectroscopy (ATR‐FTIR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The analysis of the H‐bonded and non H‐bonded urethane carbonyl stretching vibration in the amide I region, the glass transition temperature of the soft and hard segments and the melting temperature and enthalpies of hard segment reveal that aliphatic diisocyanate based polyurethanes present higher phase separation degree and harder segment crystallinity and also superior thermal stability than aromatic diisocyanate‐based polyurethanes.