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Nanocellulose (NC) films are gaining popularity in recent years owing to their recyclability and biodegradability; however, the commercialization of this material is limited by environmental and moisture barrier constraints. The incorporation of carboxymethyl cellulose (CMC) with NC significantly improved the barrier performance but the resultant films were quite hydrophilic and hence completely disintegrated in water. The aim of this study is to produce hydrophobic NC/CMC films without compromising their barrier characteristics. For this purpose, the optimized content of alkyl ketene dimer (AKD) was spray-deposited on the fully and partially dried NC/CMC films and their hydrophobic, barrier and mechanical properties were assessed. The deposition of AKD has improved the hydrophobicity and flexibility while maintaining the barrier properties of the films. However, their tensile index values decreased by 26–29% as compared with the neat NC/CMC films, but the values remained in acceptable range. Additionally, the partially dried spray deposited AKD-NC/CMC films have shown superior results as they showed higher hydrophobicity (θ = 127° ± 3), while lower percentage of mass loss after immersion for 48 h in water (15%) as compared with the fully dried spray deposited AKD-NC/CMC films. [ABSTRACT FROM AUTHOR]

This study prepared a waterproof cellulose nanofibril (CNF) sheet via the deposition of an alkyl ketene dimer (AKD) on the sheet's controlled porous structure. The porosity of the CNF sheet was controlled by drying under different conditions, which included hot-press drying (HD) and solvent-exchange drying (SD), and the effect on the hydrophobization and water-related barrier performance of the sheet were investigated. When the SD sheet was immersed in an AKD wax solution, the sheet exhibited super-hydrophobicity and a lower water vapor transmission rate, compared with the HD sheet. This indicated that the porous structure of the SD sheet enabled AKD to be adsorbed on both the surface and the inner surface and it filled in the pores of the sheet, thereby giving rise to excellent waterproofing properties. The performance of a hydrophobized SD sheet as a water barrier material was comparable to a linear low-density polyethylene film. This study confirms the possibility for AKD wax to be immersed in a porous CNF sheet and used as a potential barrier material in hydrogel packaging. [ABSTRACT FROM AUTHOR]

The present works aims at developing cellulose-based nanopapers from TEMPO-oxidized cellulose nanofibers with tailored properties by means of the incorporation of cheap, widely available and easy-to-use additives. For this, nanopapers were produced by means of a papermaking-like route with a modified paper sheet former. Bleached kraft eucalyptus and pine pulps (BKEP and BKPP, respectively) were selected for comparison purposes and they were submitted to three different oxidation degrees. Those nanopapers prepared from BKPP at 10 mmol/g exhibited the most well-balanced performance in terms of mechanical, optical and morphological properties and were selected for the study with glycerol and AKD. It was found that as the amount of glycerol was increased, mechanical properties were decreased due to a plasticizing effect, with no influence on water contact angle (WCA) and transmittance. However, when AKD was used, and especially when combined with glycerol, mechanical properties and WCA were significantly improved, mainly due to the esterification reaction. Overall, the present work shows different ways to tailor the mechanical, optical, surface and morphological properties of nanopapers, obtaining significant improvements on several properties with the combination of other additives, which can be easily found in cellulose-based industries. [ABSTRACT FROM AUTHOR]

Abstract: To expand the application of nanofibrillated cellulose (NFC), the increase of its hydrophobicity is considered to be critical. In the present work, hydrophobic NFC powder was prepared through chemical modification with alkyl ketene dimer (AKD). The results showed that when modifying the original NFC with an AKD loading of 0.7 g/g (based on dry cellulose) at 110 °C for 6 h, the AKD graft yield of approximately 40% (based on initial cellulose mass) was successfully achieved. The Fourier transform infrared spectroscopy and X-ray diffraction analysis showed that the grafting reaction mainly occurred on the fibre surface and the nanocrystal structure of cellulose was preserved after chemical modification. The thermogravimetric analysis results indicated the thermal stability increased with increasing the AKD graft yield. Scanning electron microscopy observations indicated that no significant differences in fibril morphology before and after AKD modification. Water contact angle measurements of the films produced from original and AKD-modified NFC powders demonstrated the significant increase in hydrophobicity of NFC after modification with AKD. Moreover, the hydrophobicity of AKD-modified NFC increased with increasing AKD graft yield.Graphical abstract: [ABSTRACT FROM AUTHOR]

Spilled oil in seas has a direct impact on the environment and biodiversity. Moreover, there is no clear relationship between the amount of oil in the aquatic environment and its impact, since it mainly depends on the time and season that the oil is spilled. Nowadays, there are several techniques to clean up and recover oil from the sea, including the use of microorganisms, chemicals, controlled burning, dispersants and solidifiers, among others. Sometimes, unfortunately, the best option is to watch and wait for natural attenuation. Cellulose nanofibers have potential environmental applications due to their availability, light weight, mechanical and optical properties, and renewability. Several studies have dealt with modification of their hydrophilic character through silanation and acetylation. Both treatments, despite having a significant impact on the environment, are not plausible on a large scale because of the cost of chemicals and complexity of the modification. In this sense, the present work aims to develop hydrophobic nanocellulose-based aerogels from bleached kraft eucalyptus fibers modified with alkyl ketene dimers. For this, an experimental batch of 24 aerogels was prepared, including three types of CNF (TEMPO-oxidized, enzymatically hydrolyzed and mechanical) and eight modification degrees. The obtained aerogels were characterized in terms of morphology, hydrophilicity and water-oil absorption capacity under static and dynamic conditions, as well as their suitability for recycling and reuse for selective oil removal. The results showed that it is possible to obtain 3D-structured aerogels with a high oil absorption capacity by a simple and presumably low-cost methodology. [ABSTRACT FROM AUTHOR]

In order to produce dry and hydrophobic microfibrillated cellulose (MFC) in a simple procedure, its modification with alkyl ketene dimer (AKD) was performed. For this purpose, MFC was solvent-exchanged to ethyl acetate and mixed with AKD dissolved in the same solvent. Curing at 130 °C for 20 h under the catalysis of 1-methylimidazole yielded a dry powder. Scanning electron microscopy of the powder indicated loss in nanofibrillar structure due to aggregation, but discrete microfibrillar structures were still present. Water contact angle measurements of films produced from modified and unmodified MFC showed high hydrophobicity after AKD treatment, which persisted even after extraction with THF for 8 h. The hydrophobized MFC was characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance and X-ray analysis. In summary, strong indications for the presence of AKD on the surface of MFC before and after extraction with solvent were found, but only a very small amount of covalent β-ketoester linkages between the modification agent and cellulose was revealed. [ABSTRACT FROM AUTHOR]

A hardwood bleached kraft pulp (HBKP) was reacted with alkyl ketene dimer (AKD) under solvent-free and heterogeneous conditions, and a fibrous chloroform-insoluble fraction with a degree of substitution of AKD β-ketoester groups of 0.75 was obtained at a weight ratio of 95 % of the total reaction product. When this AKD-treated and CHCl-insoluble HBKP was mechanically disintegrated in tetrahydrofuran, the suspension turned to a viscous and translucent gel. When an unfibrillated fraction was removed by filtration using a glass filter with 40 μm pore size, the weight recovery ratio of the filter-passed fraction was approximately 30 %. Scanning and transmission electron microphotographs of the glass filter-passed fraction showed that this fraction consisted of cellulose nanofibrils more than several micrometers in length, the surfaces of which probably had AKD β-ketoesters in high densities. [ABSTRACT FROM AUTHOR]

Four native celluloses, i.e. hardwood bleached kraft pulp (HBKP), cotton linters, bacterial cellulose and microcrystalline cellulose, were heterogeneously reacted with alkyl ketene dimer (AKD) at 100 °C for 24 h in the presence of a small amount of 1-methylimidazole used as an esterification promoter under solvent-free conditions. AKD molecules were reacted with cellulose hydroxyl groups to form β-ketoester linkages by the above conditions. Each reaction product was separated into chloroform-soluble and -insoluble fractions, and weight ratios and degrees of substitution (DS) of the two fractions were measured. The weight ratios of the CHCl-insoluble fractions varied from 30 to 95 % of the products, and the DS values from 0.03 to 1.6, depending on the starting cellulose samples. X-ray diffraction and solid-state C-NMR analyses of the CHCl-insoluble fraction with DS 0.75 in the AKD-treated HBKP indicated that β-ketoester substituents were introduced to hydroxyl groups on the cellulose microfibril surfaces. This CHCl-insoluble fraction had thermoplastic properties, and was convertible to translucent or transparent films by hot pressing at 160-180 °C. [ABSTRACT FROM AUTHOR]

Paper density, tensile index, sizing degree, and other properties of the handsheets were measured in term of addition level of bulking promoters and alkyl ketene dimer (AKD). Bulking promoters had clear bulking effects, and in subsequent addition of the AKD, the sheet density was further decreased slightly. Although the density of the handsheet decreased from 0.64 to 0.61 g/cm3 when 0.2% AKD was added with the 0.8% bulking promoter, tensile strength decreased from 20.3 to 19.8 Nm/g. The addition of AKD led to suppression of the decrease in the tensile index. The bulking promoter may also have potential to give sizing effects to the paper sheet as well as the increase in paper thickness. When 0.05% AKD was added together with 0.8% of bulking promoter, the sizing degree of the handsheet was 25.6 seconds, and it was almost the same, 27.3 seconds, as the addition of 0.1% AKD only. AKD retention in the handsheet was determined by pyrolysis-gas chromatography (Py-GC). The addition of the bulking promoter contributed to AKD retention in the handsheet regardless of the sizing degree. Wetting characteristics of the handsheet were determined by contact angle measurements. Surface free energy, γ s, of the handsheet as calculated from the contact angle decreased as the level of AKD addition increased. [ABSTRACT FROM AUTHOR]