Efeito de extensores de cadeia e poliol de fonte renovável na estrutura e propriedades de poliuretanos termoplásticos obtidos por processamento reativo

Abstract

Thermoplastic polyurethanes (TPUs) are highly versatile polymers known for their wide range of properties, achieved through the strategic combination of raw materials, including isocyanates, polyols, and chain extenders. This thesis comprises two significant studies exploring distinct aspects of TPUs' structure and properties. The first study focuses on the impact of two chain extenders, 1,4-butanediol (BDO) and dipropylene glycol (DPG), on the structure-property relationship of TPUs synthesized through reactive extrusion. Various BDO/DPG weight ratios, ranging from 100/0 to 0/100%, were studied alongside polyester diols and 4,4'-diphenylmethane (MDI). Through a comprehensive characterization involving size exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS), and physical-mechanical testing, the researchers evaluated the properties of the resulting TPUs. Regarding the influence of DPG, it was observed that this chain extender enhances compatibility between the rigid (HS) and flexible (SS) segments of TPUs. As the DPG content increased, the organization of rigid segments and the degree of phase separation decreased. This led to a higher polydispersity of the distance between domains and improved transparency in the visible spectrum of the TPUs. Additionally, the increased DPG content resulted in a reduction of hydrogen bonds in the rigid phase, leading to a decrease or even elimination of its glass transition temperature (TgHS) and melting temperature (Tm), while increasing the glass transition temperature of the flexible phase (TgSS). Consequently, a higher DPG content negatively impacted the mechanical properties and hydrolysis resistance of the TPUs. The second study focused on partially replacing the polyester polyol with a renewable source polyol derived from soybean oil. The replacement was performed in varying proportions, from 1wt.% to 50wt.%. Notably, this partial replacement led to increased branching initially and, at higher replacement levels, the formation of crosslinks. The polyfunctional nature of the renewable source polyol contributed to forming these crosslinks, reducing macromolecular mobility and minimizing phase separation. In conclusion, the combination of chain extenders and renewable source polyols allows precise customization of TPUs' properties for diverse applications. Understanding the impact of raw material combinations provides valuable insights to design TPUs. [resumo fornecido pelo autor]