Cellulose II nanoelements prepared from fully mercerized, partially mercerized and regenerated celluloses by 4-acetamido-TEMPO/NaClO/NaClO2 oxidation

A softwood bleached kraft pulp (SBKP) and cotton lint cellulose were fully or partially mercerized, and these along with celluloses and commercially available regenerated cellulose fiber and beads were oxidized by 4-acetamido-TEMPO/NaClO/NaClO₂ at 60 °C and pH 4.8. Weight recovery ratios and carboxylate contents of the oxidized celluloses were 65–80% and 1.8–2.2 mmol g⁻¹, respectively. Transparent and viscous dispersions were obtained by mechanical disintegration of the TEMPO-oxidized celluloses in water. These aqueous dispersions showed birefringence between cross-polarizers, indicating that mostly individualized cellulose nanoelements dispersed in water were obtained by these procedures. Transmission electron microscopy observation showed that the cellulose nanoelements prepared from mercerized SBKP, repeatedly mercerized SBKP, mercerized cotton lint cellulose, regenerated cellulose beads and 18% NaOH-treated SBKP, i.e. partially mercerized SBKP, had similar morphologies and sizes, 4–12 nm in width and 100–200 nm in length. The 18% NaOH-treated SBKP was converted to cellulose nanoelements consisting of both celluloses I and II.     

Nano-dispersion of TEMPO-oxidized cellulose/aliphatic amine salts in isopropyl alcohol

Primary aliphatic amines were introduced into most of (>95%) carboxyl groups densely present on the TEMPO-oxidized cellulose nanofibril (TOCN) surfaces via carboxyl/amine salt formation in a water-isopropyl alcohol mixture. The carbon number of alkyl chain lengths introduced into TOCN varied using n-decyl-, n-dodecyl, n-tetradecyl-, n-hexadecyl- and n-octadecyl-amines. When n-dodecyl-, n-tetradecyl- and n-hexadecyl-amines were used for neutralization of carboxyl groups, the TOCN-COOH/amine salts were dispersed at the individual nanofibril level in pure isopropyl alcohol (IPA) by ultrasonication treatment, and gave stable and transparent IPA dispersions with birefringence when observed between cross polarizers. Flexible, highly transparent and surface-hydrophobic self-standing films of n-dodecylamine-treated TOCN-COOH (TOCN-COOH/C₁₂-amine salt) were prepared by casting and drying of the dispersion. However, the introduction of abundant long-alkyl chains on the TOCN surfaces via the amine salt formation resulted in clearly lower mechanical and oxygen barrier properties of the films than those of TOCN-COONa films.     

Mechanical and oxygen barrier properties of films prepared from fibrillated dispersions of TEMPO-oxidized Norway spruce and Eucalyptus pulps

TEMPO-oxidized cellulose nanofibers (TOCN) were obtained from commercial Norway spruce and mixed Eucalyptus cellulose pulps using TEMPO/sodium bromide (NaBr)/sodium hypochlorite (NaClO) system at pH 10 and 22 °C. After reaction, the fibrillated TEMPO-oxidized celluloses were used for preparation of self-standing films and casting of laminate films on 50 μm thick polyethylene terephthalate. Significant differences between N. spruce and Eucalyptus TOCN were registered. The tensile strength of the films showed a maximum value for spruce samples oxidized with addition of 10 mmol g⁻¹ of NaClO. Oxygen permeability decreased with increasing oxidation levels, being lower for N. spruce TOCN compared to Eucalyptus.     

Nonparametric estimation of a regression function by delta sequences

A somewhat more general class of nonparametric estimators for estimating an unknown regression functiong from noisy data is proposed. The regressor is assumed to be defined on the closed interval [0, 1]. This class of estimators is shown to be pointwisely consistent in the mean square sense and with probability one. Further, it turns out that these estimators can be applied to a wide class of noises.     

On a measure of multivariate skewness and a test for multivariate normality

Summary We consider an extension of Pearson measure of skewness to a multivariate case and apply the proposed measure to a test of multivariate normality.     

The Convergence Rate of Fixed-Width Sequential Confidence Intervals for a Parameter of an Exponential Distribution

In this paper we consider sequential fixed-width confidence interval estimation for a parameter = aµ + b with a and b being given constants when the location parameter µ and the scale parameter of the negative exponential distribution are unknown. We investigate the rate of convergence of the coverage probability for fixed-width sequential confidence intervals of .     

Thermal and liquid crystalline properties of cellulose β-ketoesters prepared by homogeneous reaction with ketene dimers

Cellulose β-ketoesters having long alkyl or alkenyl chains were prepared by homogeneous reactions with alkyl or alkenyl ketene dimmers (OKD or AKD), and were characterized by X-ray diffractometory, differential scanning calorimetry, optical microscopy with cross polarizers and others. The Cellulose/OKD and AKD β-ketoesters with degrees of substitution (DS) of more than 1.5 were gummy solid at room temperature and had birefringence due to liquid crystalline structures in wide temperature range. The liquid crystalline/isotropic phase transition points were 150–175 °C, depending on the DS and substituents introduced into cellulose hydroxyls. X-ray diffraction patterns indicated that cellulose backbones had disordered structures at room temperature, while alkyl chains in the substituents formed ordered or crystalline domains in the cellulose β-ketoesters. Films of the cellulose/AKD β-ketoesters prepared by casting their chloroform solutions on glass plates had highly hydrophobic nature, and contact angles of water droplet on the films were more than 90°. The water-contact angles on the films decreased to some extent just after heating of the films at 105 °C, whereas they were gradually recovered to the initial values by conditioning at ambient temperature.