Intelligent pH- and ammonia-sensitive indicator films using neutral red immobilized onto cellulose nanofibrils.

In this study, colorimetric indicator films (CIFs) were developed by integrating neutral red covalently immobilized onto TEMPO-oxidized cellulose nanofibrils (NR@TOCNFs) and poly(acrylic acid) (PAA) inside a poly(vinyl alcohol) (PVA) matrix. The successful covalent immobilization of NR onto the TOCNFs was confirmed using attenuated total reflection-Fourier transform infrared, X-ray photoelectron spectroscopy, and thermogravimetric analyses. The CIFs had a visible color change from red to yellow as the pH changed from 2.0 to 10.0. The colorimetric response of CIFs improved as the NR@TOCNF content increased, while it decreased as the PAA level increased. The critical pH ranges for the color change of CIFs were 6-7, 7-8, and 8-9 for 3 %, 5 %, and 7 % PAA, respectively, at 0.3 % NR@TOCNF. The best ammonia sensitivity was found in the indicator films containing 3 % PAA and 0.3 % NR@TOCNF. These results showed that the CIFs could be applied for freshness detection in food packaging.

Covalent immobilization of bromocresol purple on cellulose nanocrystals for use in pH-responsive indicator films.

This study developed pH-indicator films by combining esterified cellulose nanocrystals (e-CNCs) with activated bromocresol purple (a-BCP) via covalent bonding for pH-sensitive color-changing applications. The e-CNC/a-BCP particles were incorporated into cellulose acetate polymer to prepare pH-sensitive color changing films. Binding of a-BCP to e-CNCs was proven by attenuated total reflection infrared (ATR-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Colorimetric analysis showed that films containing 10% or 15% e-CNC/a-BCP particles had critical color changes either at pH 4-5, or pH 7-8. The films with 10% e-CNC/a-BCP particles also revealed excellent leaching resistance under acidic conditions. Color changes were reversible between pH 2 and 10. These pH-indicator films had visible color changes in response to pH variations, color reversibility, leaching resistance, and sufficient rigidity even though mechanical properties decreased as the e-CNC/a-BCP content increased from 0% to 15%.

Optimum oxidation for direct and efficient extraction of carboxylated cellulose nanocrystals from recycled MDF fibers by ammonium persulfate.

For the first time, this study demonstrates a direct extraction of carboxylated cellulose nanocrystals (c-CNCs) from recycled medium density fiberboard (r-MDF) fibers by ammonium persulfate (APS) without any chemical pre-treatment. The aim of this research was to find an optimum condition for isolating c-CNCs from r-MDF fibers by studying the effect of reaction parameters on the characteristics of c-CNCs. The rod-like c-CNCs had an average length and width of 170 to 365 nm and 13 to 17 nm, leading to an aspect ratio of 13∼21. The optimum conditions for a maximum yield and crystallinity were obtained at a reaction temperature of 70 °C, reaction time of 16 h and APS concentration of 1.5 mol L-1. Thermal analysis also revealed lower thermal stability of the c-CNCs compared to r-MDF fibers. The APS oxidation is a viable option for converting r-MDF fibers into value-added c-CNCs.

Application of surface chemical functionalized cellulose nanocrystals to improve the performance of UF adhesives used in wood based composites - MDF type.

The aim of this research was to investigate the effect of functionalized cellulose nanocrystals (CNC) on the performance of urea-formaldehyde (UF) adhesive for the production of medium density fiberboard (MDF). Surface modification of CNC was performed using 3-Aminopropyltriethoxysilane (APTES). Some physical and thermal properties of reinforced and neat UF as well as formaldehyde emission and some mechanical (modulus of rupture (MOR), modulus of elasticity (MOE) and internal bond strength (IB)) and physical properties (thickness swelling (TS) and water absorption (WA)) of the resulting MDF panels were determined. Based on the results, upon incorporation of modified CNC to the system, solid content, density, viscosity and free formaldehyde of UF adhesives decreased while gel time increased. Depending on addition of the modified CNC loading in the panels, the formaldehyde emission values varied from 11% to 17% lower than the panels made from neat UF. In comparison to the control samples, panels made with UF containing 2% modified CNC had 29.3% and 38.2% higher MOR and MOE respectively.

Surface chemical functionalization of cellulose nanocrystals by 3-aminopropyltriethoxysilane.

Surface functionalization of cellulose nanocrystals (CNCs) is valuable option to tailor properties as well as increase opportunities for their application. In this study, the surface of CNCs was functionalized with 3-aminopropyltriethoxysilane (APTES), without using hazardous solvents and by a direct, simple and straightforward method. APTES was firstly hydrolyzed in water and then adsorbed onto CNC through hydrogen bonds, finally the chain hydrocarbon was covalently linked to the surface of CNC through SiOC bonds which formed via the condensation reaction between hydroxyl and silanol groups. The chemical modification of the CNCs surface was confirmed by ATR-IR and NMR spectroscopy. Experiments conducted by AFM and XRD showed no significant change in the CNC dimensions and crystalline structure as a result of the modification. The EDX and XPS results confirmed the exsistence of APTES onto the CNCs. Silylated CNC exhibited good thermal stability and a greater amount of residual char was formed at 500 °C compared to non-chemically modified CNC. Thus, The silylation of CNCs may offer applications in composite manufacturing, where these nanoparticles have limited dispersibility in hydrophobic polymer matrices, and as nano-adsorbers due to the presence of amino groups attached on the surface.