Novel Polyvinyl Alcohol (PVA)/Cellulose Nanocrystal (CNC) Supramolecular Composite Hydrogels: Preparation and Application as Soil Conditioners

In this work, cellulose nanocrystal (CNC) was modified by an ureido-pyrimidinone (UPy) system based on quadruple hydrogen bondings, and CNC-UPy was obtained. Then, this powder was added into polyvinyl alcohol (PVA), and PVA/CNC-UPy composite membranes and hydrogels were prepared. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), polarizing optical microscopy (POM) and particle size distribution (PSD) were used to characterize CNC-UPy. From the FTIR results, the characteristic peaks of NCO group sat 2270 cm(−1) disappeared, indicating the successful synthesis of CNC-UPy. XRD results showed that the modification by UPy may change the structure of CNC and its degree of crystallinity was increased. PSD analysis showed that the particle size of CNC was increased and its size distribution became narrower after modification by UPy groups. The structure and properties of the composite membranes and hydrogels were studied by differential scanning calorimeter (DSC), thermogravimetric analysis (TGA) together with investigation of swelling, sustained release and self-healing performances. DSC curves depicted that the glass transition temperature, T(g), of different PVA membranes was increased with addition of different proportions of CNC-UPy. TGA data showed that the temperature of maximum weight loss rate was increased, which illustrated the enhanced thermal stability of PVA/CNC-UPy composites. Meanwhile, it was also revealed that the PVA/CNC-UPy composite hydrogels possess good self-healing and better sustained release behavior for the soil conditioner, fulvic acid (FA).