Preparation and characterization of novel thermoplastic elastomers by step/chain transformation polymerization

Exploration of novel heat and flame-resistant poly(urethane–imide)/functional layered silicate-based foams

Poly(urethane–imide) (PUI)/hydroxyl functional montmorillonite (MMT; H-MMT) nanocomposites and foams have been prepared with modified layered silicates (hydroxyl-modified H-MMT) via in situ polymerization. The physical properties of PUI/H-MMT nanocomposites and foams were investigated and were found to be dependent on the structure of polyurethane, functional groups of the modifiers, and chemical reaction between the hydroxyl of H-MMT and matrix. Field-emission scanning electron microscopy revealed imprecise honeycomb cellular structure with increased cell density and reduced cell size compared with pure PUI foam. Compression strength and modulus of PUI/H-MMT 1 foam (1 wt% nanofiller) were 26.5 MPa and 4 GPa, respectively, which were augmented to 31 MPa and 7 GPa in PUI/H-MMT 5 foam (5 wt% nanofiller). Thermogravimetric results for 10% thermal decomposition temperature of PUI/H-MMT 1–5 foams were in the range of 476–511°C. Dynamic mechanical thermal analysis showed that PUI/H-MMT 1 foam had glass transition temperature of 155°C which was enhanced to 161°C in PUI/H-MMT 5 foam. Limiting oxygen index and UL 94 results showed that PUI/H-MMT 1–5 foams exhibited enhanced nonflammability (V-0 rating) with the clay loading.

Reactive Blending of Thermoplastic Polyurethane and Polypropylene

In this research, reactive blending of thermoplastic polyurethane (TPU) and polypropylene (PP) was studied. Grafting of maleic anhydride (MAH) onto TPU/PP blends was performed by a twin-screw extruder in the presence of dicumyl peroxide (DCP). Mechanical properties and morphology of the blends were investigated by tensile testing and scanning electron microscopy (SEM), respectively. Thermal properties of the blends were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The obtained results were compared with those of the uncompatibilized blends and the blends compatibilized with a commercial maleic anhydride grafted polypropylene (PP-g-MA). The results from the uncompatibilized blends clearly indicate that the TPU and PP are immiscible resulting in undesirable properties of the blends. These properties were improved significantly when TPU and PP were reactive-blended in the presence of MAH and DCP. When comparing with the blends compatibilized with PP-g-MA, the blends prepared by the reactive blending technique possessed better mechanical properties.