A smart temperature responsive polymeric system for textile materials

Abstract

Stimuli-responsive polymeric materials can adapt to various surrounding environments, convert chemical and biochemical signals into optical, electrical and thermal signals, or change wettability and adhesion upon external stimuli. In this thesis, a cotton fabric was modified with a thermo-responsive polymer, Poly(N-isopropylacrylamide) (PNIPAAm). For low grafting efficiency sample, 1H solid-state NMR techniques were used to characterize the molecular structure and dynamics of the PNIPAAm brushes, while still grafted on the cotton fabric surfaces, avoiding the destructive cleaving procedures. The results demonstrate that the motion of the grafted PNIPAAm brushes is restricted as the temperature rises above the low critical solution temperature (LCST), which was estimated to be ~ 34 °C. Variable temperature (VT) experiments were used to investigate the nature of the hydrophilic-hydrophobic transitions of the grafted polymer. The ¹H solid-state NMR techniques used in this study was proved to be an extremely sensitive and precise way to probe in-situ the LCST transition of the PNIPAAm brushes. The grafting efficiency of the polymer on the cotton surface has been greatly improved after a short-time UV pretreatment coupled with a room temperature immobilization method. The modified cotton fabric was characterized by FTIR, XPS, NMR, TGA, SEM and OM. It was shown that the cotton fibers were covered with PNIPAAm brushes with a high grafting efficiency. The PNIPAAm molecular brushes were cleaved from the cotton substrate and characterized by GPC to determine the molecular weight (Mn), molecular weight distribution (PDI) and grafting efficiency. The surface of the temperature responsive cotton fabric is superhydrophobic with a water contact angle (CA) up to 140° at 40 °C, and superhydrophilic with a water CA of 0° at room temperature, and this conversion was repeated many times in a short time period and a fully reversible transition was observed. More interestingly, this smart cotton fabric surface can capture moisture from atmosphere at lower temperature and release water at higher temperature. This concept may provide a new insight into solutions for fresh water conversion and purification. This study presents a valuable synthesis and analysis route towards stimuli-responsive cotton fibers which may be of exceptional applications as novel intelligent fabrics for the textile related industries. On the other hand, this smart PNIPAAm modified may also be used to exploit water from dew and mist, and it may pave the way for solving the problem of water crisis in deserts or arid areas.