Preparation And Properties Of Laponite/Polyurethane Nanocomposites

High-performance biomaterials, such as nacre, exhibit unparalleled combinations of stiffness, strength, extensibility and toughness due to their hybrid composition and sophisticated hierarchical structures. Thermoplastic polyurethane (TPU), an elastomeric block copolymer, is composed of hard segments and soft segments that combine to give the TPU moderate stiffness, high rubber-like extensibility and easy processability. However, the weak heat resistance and relative low modulus of TPU limits its application. Modification of TPU by using inorganic particles as reinforcement is becoming a primary method in recent years. However, it is difficult to increase the elastic modulus of the nanocomposites and maintain its high extensibility, or vice-versa at the same time.Full exfoliation of smectic clay particles in polymers is a major challenge. Typical methods to exfoliate clay particles in polyurethane include (i) melt extrusion of unmodified and organically modified clay and (ii) dispersion of organically modified clay in organic solvent followed by in situ polymerization. But they have not yet resolved the problem of good exfoliation. In our present work, Laponite/Polyurethane nanocomposites were successfully prepared by following two steps:(i) solvent-exchange approach to efficiently exfoliate Laponite into N, N-dimethyl acetamide (DMAC) solvent;(ii) under ultrasound insert Laponite into polyurethane macromolecules. TEM, AFM, WAXD, TGA, DSC, DMA and tensile testing were used to characterize the structure and properties of the resulting nanocomposites. The FT-IR dichrosim was study the orientation behavior, hydrongen-bonding property, and strain induced crystallization of the nanocomposites. The orientation behaviour of the Laponite in polyurethane was characterized by in situ SAXS. The main results are as follows:1. Laponite preferentially reinforce the hard segments or micro-domains of polyurethane because of the similar characteristic dimensions of Laponite and hard micro-domains and of hydrogen bond. The hierarchical order induced by the addition of discotic Laponite platelets creates a percolated network that significantly improves the stiffness and toughness of the nanocomposites without reducing its extensibility.2. The orientatione of Laponite is in coordination with that of molecular chain which indicates Laponite preferentially reinforce the hard segments or micro-domains of polyurethane. Morever, the orientatione of Laponite and molecular chain developed with the content of Laponite, as well as the content of hydrogen bonds. In conclusion, the strength and toughness of the nanocomposites are improved simultaneously.