Surface Properties of Thermoplastic Starch Materials Reinforced with Natural Fillers

TOMY GUTIERREZ; ROMINA OLLIER; VERA ALVAREZ

Functional Biopolymers

Springer International Publishing

Año: 2018; p. 131 - 158

The self-association force of water on the surface of a composite polymeric material is a physicochemical process dominated by cohesive forces and van der Waals type interactions existing below the material surface. Perturbations in the chemical potential of water, brought about by the interaction between it and a polymeric surface, induce compensatory structural changes. Thus, the structure of water on the surface of a composite polymeric material reveals the hydrogen bond interactions taking place beneath it, which are key to understanding the properties of thermoplastic starch (TPS) materials. In the literature, there is a broad consensus based on empirical results that a contact angle (θ) greater than 65° defines a hydrophobic surface. These findings suggest that there are at least two different types of water structure that exist as a response to interactions occurring within the composite polymers. One of these is formed when there is a low density of ?Lewis sites?, and the other when there is a high density of ?Lewis sites? on the surface of the thermoplastic materials. This second scenario produces the collapse of the water structure, i.e. the collapse of the hydrogen-bonded network. In spite of the physicochemical response of water to the intra- and intermolecular interactions that occur on composite materials, these have not been studied as a means to modify the surface behavior of TPS materials. This could be achieved by incorporating natural fillers that have a plasticizer or cross-linking effect on their structure. In this chapter we analyze the surface properties of starch-based composite materials as an indirect measure of the interactions that occur within them, mainly as regards plasticizing effects and cross-linking reactions.