Polyurethane films, compression-molded

Characterization. Film samples about 0.25-mm thick were prepared by compression molding the polyurethanes under dry nitrogen at 180°C and 3 MPa pressure. After molding for 20 min, the samples were allowed to cool slowly in the press under dry nitrogen flow. Figure 2 shows the thermal history of the 180°C-molded films. No discoloration was observed when the samples were removed from the mold. The two soft-segment polyurethanes were compression molded at 120°C. The films were allowed to stand at least one week at room temperature in a dessicator before being evaluated with the Rheovibron DDV-IIB Dynamic Visco-... 

The isosorbide polyurethane based on the aliphatic diisocyanate P(I-HMDI) is flexible. It is a thermoplastic with a glass transition temperature of 110°C and softening temperature of 190°C. Both transitions are well below its degradation onset which occurs at approximately 260°C. It forms good films by evaporation from its solutions and colorless transparent compression moldings. 

The isosorbide polyurethanes based on the aromatic diisocyanates P(I-TDI) and P(I-MDI), possess more rigid structures with both polymers forming brittle films and brittle compression moldings. Their glass transition temneratures are above their decomposition temperature of 260°C. The thermostability of isosorbide polyurethanes correspond to that of conventional polyurethanes with similar structure based on 1,4-cyclohexanedimethanol for which degradation temperature of 260°C has been determined. 

Another way to classify polymers results from the consideration of their typical applications. Typical classes are Compression molding compounds, injection molding compounds, semi-finished products, films, fibers, foams (urethane foam, styrofoam), adhesives (synthetic adhesives are based on elastomers, thermoplastics, emulsions, and thermosets. Examples of thermosetting adhesives are Epoxy, polyurethane, cyanoacrylate, acrylic polymers), coatings, membranes, ion exchangers, resins (polyester resin, epoxy resin, vinylether resin), thermosets (polymer material that irreversibly cures), elastomers (BR, silicon rubber). 

The way in which Cherian et al. fabricated the nanobiocomposites was by stacking the cellulose nanofiber mats between polyurethane films and pressing by compression molding. With the addition of 5 wt% cellulose nanofbers into polyurethane the strength and stiffness increased by nearly 300% and 2600%, respectively. The developed composites were utilized to fabricate various versatile medical implants. Cellulose poly-urethanes-based materials are sufficiently durable and blood compatible for potential use in a prosthetic heart valves and effectively showed less mineralization than glutar-aldehyde-fixed bovine pericardial tissue [231]. 

---