pH-Responsive Shape Memory Poly(ethylene glycol)–Poly(ε-caprolactone)-based Polyurethane/Cellulose Nanocrystals Nanocomposite

Abstract

In this study, we developed a pH-responsive shape-memory polymer nanocomposite by blending poly(ethylene glycol)-poly(ε-caprolactone)-based polyurethane (PECU) with functionalized cellulose nanocrystals (CNCs). CNCs were functionalized with pyridine moieties (CNC-C6H4NO2) through hydroxyl substitution of CNCs with pyridine-4-carbonyl chloride and with carboxyl groups (CNC-CO2H) via 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) mediated surface oxidation, respectively. At a high pH value, the CNC-C6H4NO2 had attractive interactions from the hydrogen bonding between pyridine groups and hydroxyl moieties; at a low pH value, the interactions reduced or disappeared due to the protonation of pyridine groups, which are a Lewis base. The CNC-CO2H responded to pH variation in an opposite manner. The hydrogen bonding interactions of both CNC-C6H4NO2 and CNC-CO2H can be readily disassociated by altering pH values, endowing the pH-responsiveness of CNCs. When these functionalized CNCs were added in PECU polymer matrix to form nanocomposite network which was confirmed with rheological measurements, the mechanical properties of PECU were not only obviously improved but also the pH-responsiveness of CNCs could be transferred to the nanocomposite network. The pH-sensitive CNC percolation network in polymer matrix served as the switch units of shape-memory polymers (SMPs). Furthermore, the modified CNC percolation network and polymer molecular chains also had strong hydrogen bonding interactions among hydroxyl, carboxyl, pyridine moieties, and isocyanate groups, which could be formed or destroyed through changing pH value. The shape memory function of the nanocomposite network was only dependent on the pH variation of the environment. Therefore, this pH-responsive shape-memory nancomposite could be potentially developed into a new smart polymer material.

pH- and Thermal-Responsive Multishape Memory Hydrogel

“…After application of 10 V direct electric current, the pH value of the solution decreased because of the electrolysis of copper sulfate which in turn was due to the fact that the hook recovered to the original shape and released the weight. Recently, Zhou et al 6,24 and our group 5 reported pHsensitive SMPs that were able to be deformed into predetermined shapes and had the capacity to revert back to its original shape upon application of pH stimulus. Apart from that, it has been demonstrated that hydrophobes can gradually disengage from the hydrophobic associations with increasing temperature, or reassociate at relatively low temperature, enabling reversible change between strong and weak hydrophobic interactions.…”

Conductive shape‐memory polyurethane/multiwall carbon nanotube nanocomposite aerogels

“…Shape memory polymers (SMPs) refer to the polymers that stimulate by a variety of stimuli such as electrical current, pH, humidity, magnetic field, heat and light, recovering their original shape. This “memory” feature of SMPs gives them the opportunity to apply in various fields, such as textiles, packaging, medical and aerospace industries .…”

Swelling Resistance and Water-Induced Shape Memory Performances of Sisal Cellulose Nanofibers/Polyethylene Glycol/Citric Acid Nanocellulose Papers

“…In medicine fields, a key challenge is that an excess of heat usually causes damage to biological tissue. Nevertheless, water-induced shape memory polymers can effectively compensate for this deficiency [12]. Based on the reported waterinduced shape memory polymer, most of them are made from petroleum chemical raw materials, which are not renewable, biodegradable, and biocompatible [13,14].…”

“…Polyethylene glycol (PEG) is a kind of thermoplastic polymer material with high crystallinity and good water solubility, is nontoxic, and is nonirritating, and it has great toughness and good biocompatibility [12,26], making it a good choice to be used as another kind of flexible chain segment of the interpenetrating network structure [27]. Therefore, based on the advantage of the cellulose nanofibers (CNF) with PEG, the CNF and PEG were cross-linked to form a new network shape memory nanocomposite (CNF/PEG/CA) paper, through citric acid (CA) as a crosslinking agent [28].…”