Jiwen Feng

Hydrophobic modification of cellulose nanocrystal via covalently grafting of castor oil

Hydrophobic cellulose nanocrystals (CNs) have been prepared by grafting isocyanate-terminated castor oil, a kind of natural vegetable oil, onto their surface. The existence of castor oil component in the modified cellulose nanocrystals was verified by Fourier transform infrared spectroscopy, solid-state 13C NMR spectra and X-ray photoelectron spectroscopy. At the same time, X-ray diffraction and transmission electron micrographs further proved that the crystalline structure and large aspect ratio of cellulose nanocrystals were essentially preserved after chemical grafting. Furthermore, the surface of modified cellulose nanocrystals appeared to be hydrophobic as indicated by contact angle measurements. The value of the polar component of surface energy decreased from 21.5 mJ/m2 to almost zero via grafting castor oil. These novel hydrophobic castor oil-grafted cellulose nanocrystals appear as valuable alternatives to formulate bionanocomposites with non-polar polymers for optimized performances.

1H MAS NMR Studies of the Phase Separation of Poly(N-isopropylacrylamide) Gel in Binary Solvents

Preferential interactions of solvents with poly(N-isopropylacrylamide) (PNIPAM) gel networks in binary water/alcohol (water/methanol and water/ethanol) mixtures have been investigated using variable-temperature high-resolution 1H MAS NMR. NMR results for PNIPAM gel in the binary solvents reveal the existence of two distinct types of water/alcohol mixtures above the LCST: confined binary solvents bound inside the gel, and free binary solvents expelled from the gel. It is interesting to find that the alcohol concentration in confined solution is significantly higher than that in free solution. Moreover, of the two alcohols, ethanol is more significantly concentrated in the confined solution. These results demonstrate that the polymer preferentially interacts with alcohol molecules over water and that the alcohol with higher hydrophobicity exhibits higher preferential absorption on PNIPAM. Our results also show that 1H NMR measurements made on two distinct types of solution provide a convenient, direct means of characterizing the preferential adsorption of solvent on polymer.

Highly mobile segments in crystalline poly(ethylene oxide)8:NaPF6 electrolytes studied by solid-state NMR spectroscopy.

Two types of high-crystallinity poly(ethylene oxide)/NaPF6 electrolytes with ethylene oxide (EO)/Na molar ratios of 8:1 and 6:1, termed as PEO8:NaPF6 and PEO6:NaPF6 with Mw = 6000 g mol(-1) were prepared, and their ionic conductivity, structure, and segmental motions were investigated and compared. PEO8:NaPF6 polymer electrolyte exhibits the room-temperature ionic conductivity 7.7 × 10(-7) S cm(-1) which is about five times higher than the PEO6:NaPF6. By variable-temperature measurements of static powder spectra and (1)H spin-lattice relaxation time in rotation frame ((1)H T1ρ), we demonstrate that crystalline segments are more highly mobile in the crystalline PEO8:NaPF6 with higher ionic conductivity than in the PEO6:NaPF6 with lower ionic conductivity. The large-angle reorientation motion of polymer segments in the PEO8:NaPF6 onsets at lower temperature (∼233 K) with a low activation energy 0.31 eV that is comparable with that of the pure PEO crystal. Whereas, the large-angle reorientation motion of polymer segments in the PEO6:NaPF6 starts around 313 K with a high activation energy of 0.91 eV. As a result of the temperature-enhanced large-angle reorientations, the (13)C static powder lineshape changes markedly from a low-temperature wide pattern with apparent principal values of chemical shift δ33 < δ22 < δ11 to a high-temperature narrow pattern of uniaxial chemical shift anisotropy δ33 > δ22 (δ11). It is suggested that the segmental motion in crystalline PEO-salt complex promotes ionic conductivity.

Hydrophobic modification of cellulose nanocrystal via covalently grafting of castor oil (vol 20, pg 179, 2013)

In the original publication, the formula and the calculated grafting ratio were incorrect, and the correction was depicted as follows: In virtue of the present proof on the grafting of CO onto the CN, element analysis was used to determine the grafting ratio (xGrafting) of CO, i.e., the weight percentage of NCO-terminated PI-CO in CO-g-CN. Table 3 summarizes the experimental weight fractions of C, H, O, N and S elements for the CN and CO-g-CN and the theoretical values of C, O and N elements for NCO-terminated PI-CO. A small amount of the S element was derived from the sulfonic groups, which formed in the process of H2SO4 hydrolysis. According to the weight fractions of the C element, the grafting ratio was calculated as 17.7 wt% by the following equation: