Search

The development of cellulose-based materials is rapidly increasing due to their promising interest and being widely used in various applications such as food, industrial, pharmaceutical, paper, textile production, and wastewater treatment. Cellulose has several advantages including low cost, renewability, superior mechanical properties, and biodegradability. Nowadays, a novel cellulose-based material, which is known as all-cellulose composites (ACCs), has emerged, consisting of cellulose for both reinforcing and matrix phases. However, the hydrophilic characteristics of cellulose can lead to poor interfacial adhesion between reinforcing and matrix phases, affecting its mechanical properties, water absorption, water contact angle, and microstructural changes. Therefore, this review summarized the effect of alkyl ketene dimer (AKD) on the structural-properties relationship of cellulose-based materials. In this review, it was observed that the mechanical properties for cellulose-based materials varied with the use of AKD concentration in the range of 4–16 wt.%. A decrease in the water absorption was also identified in the range of 10–85%. The water contact angles were observed beyond 100° after AKD treatment. In addition, the possible reactions between AKD and cellulose structures are also discussed. It is envisaged that this review will help the development of potential hydrophobic ACCs in the future. [ABSTRACT FROM AUTHOR]

Alkyl ketene dimers (AKDs) are known to efficiently react with cellulose with a dual polarity in their structure: a polar component and a nonpolar component. AKD of three different carbon chain lengths, 4, 10, and 16 carbons have been synthesized, and thermomechanical pulp (TMP) fibers were modified by them. The modification of TMP fibers with AKD resulted in an increased water contact angle, showing the presence of the AKDs on the TMP fibers and a new carbonyl peak in the IR spectra, suggesting modification of the TMP fibers with AKD groups. Calculating the Hansen solubility parameters of AKD and AKD conjugated to TMP in polypropylene (PP) indicates improved compatibility, especially of longer chain AKD and TMP AKD. The rheological studies of the composites showed that the AKD with the longest carbon chain decreases the melt viscosity of the PP‐TMP‐AKD composite, which combined with the shape and the color of the extruded composite filaments indicates improved flow properties and reduced stress build up during processing. The research findings demonstrate the ability of AKD to enhance the dispersibility and compatibility of natural fibers with PP. [ABSTRACT FROM AUTHOR]

Sustainable coatings exhibit potential in enhancing oil resistance of packaging paper. Alkyl ketone dimer (AKD) was used to esterify sodium alginate (SA) to prepare water and oil resistant agent SAD. As SAD was coated on paper, it reduced the surface energy and blocked the fiber pores of paper, thus improving the barrier performance of paper. The oil resistance grade can reach grade 6 at coating amount of 2.13 ± 0.26 g/m2, which is qualified for food packaging. The coated paper also showed good barrier to hot castor oil. Resistance to organic solvent and water were also enhanced with initial water contact angle (WCA) increased to 69.2°. Compared with base paper, SAD coated paper had better mechanical properties and more importantly, coated paper can be effectively recycled to achieve green recycling. [ABSTRACT FROM AUTHOR]

Here, we first report the 2′-acyloxy-1,3-dicarbonyl compound construction in a three-component oxidative reaction of alkyl ketene dimer with cyclic diacyl peroxide and trimethyl orthoformate. The discovered synthesis allows us to form 2′-functionalized 1,3-dicarbonyl compounds instead of the common 2-functionalized moiety. The reaction between 4-butylidene-3-propyloxetan-2-one and cyclopropyl malonoyl peroxide proceeds in the presence of trifluoroacetic acid and trimethyl orthoformate at 120 °C for 1 h. The synthesized compound was characterized by NMR spectroscopy, mass spectrometry, and IR spectroscopy. [ABSTRACT FROM AUTHOR]

The results of recent laboratory-scale studies regarding the joint effects of wet strengthening agent polyamide-amine-epichlorohydrin (PAE) and internal alkylketene dimer (AKD) sizing on Nordic bleached softwood pulp (NBSK) handsheets indicate that AKD internal sizing increases the wet strength of PAE wet strengthened handsheets. The boosting effect of the internal AKD sizing was long-lasting. At the molecular level the actual mechanism behind the effect is unclear. The present study examines if the enhanced effect of internal AKD sizing, which is potentially exploitable in practice, also occurs in paper made by VTT’s Suora pilot paper machine. The trials were done using a similar type of NBSK pulp and the same chemicals as in the laboratory-scale studies. The paper was formed at 400 m/min using a hybrid dewatering mode (Fourdrinier + gap). Just as in the laboratory-scale studies, the internal AKD sizing of PAE wet-strengthened NBSK paper resulted in a long-lasting increase of the paper wet strength. In accordance with the laboratory trials, internal AKD sizing had no noticeable effect on the dry tensile strength of the pilot-made paper. The only apparent difference to the earlier observations was an increase of dry tensile strength of the paper treated solely with PAE.

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]

Here, we first report the 2′-acyloxy-1,3-dicarbonyl compound construction in a three-component oxidative reaction of alkyl ketene dimer with cyclic diacyl peroxide and trimethyl orthoformate. The discovered synthesis allows us to form 2′-functionalized 1,3-dicarbonyl compounds instead of the common 2-functionalized moiety. The reaction between 4-butylidene-3-propyloxetan-2-one and cyclopropyl malonoyl peroxide proceeds in the presence of trifluoroacetic acid and trimethyl orthoformate at 120 °C for 1 h. The synthesized compound was characterized by NMR spectroscopy, mass spectrometry, and IR spectroscopy.

In order to improve the hydrophobicity of xylan hemicellulose, a simple procedure of its chemical modification with alkyl ketene dimer (AKD), a non-toxic, cost-effective, and eco-friendly chemical, was performed. For this purpose, the reaction products of beech wood xylan and different amounts of hydrophobic AKD were used for paper surface treatment. Thus, the coatings of about 4.5 g/m2 were applied on both sides of base paper in single and three successive layers. To obtain a complete reaction between AKD and xylan hemicellulose, the coated papers were thermal cured (about 110 °C) and the effects of AKD content on the barrier (water, oil, and water vapours) and mechanical properties were analysed. The structural analyses by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) of coated samples emphasized the presence of β-keto-ester compounds as a result of the reaction between xylan hemicelluloses and AKD. This is confirmed by the improving of barrier properties as the AKD content in coating dispersion is higher. The good barrier performance and improved strength properties were obtained for the coated papers with xylan hemicellulose and 1% AKD applied on paper surface in three successive layers (about 4.5 g/m2). In this case, the water vapours transmission rate (WVTR) was 35% lower than those untreated and the resistance to air passing through coated papers was over 3 times higher compared with base paper. There are no results reported on the chemical reaction of xylan hemicelluloses with AKD as well as its application in coatings for paper packaging. In this context, the obtained results in this study can contribute to expand the applications area of hemicelluloses offering a sustainable strategy for the developing of food packaging papers with appropriate barrier properties using biopolymer coating materials. [ABSTRACT FROM AUTHOR]

This study presents a product based on natural cassava starch with hydrophobic characteristics, which has been developed to replace the natural starch used in different industries. The natural and hydrophobic starch results describe their characteristics, validate the hydrophobicity through mathematical modeling, and present case studies from the paper and fruit processing industries that will be compared. The hydrophobicity and low viscosity of the modified Starch studied in this paper result from the reaction between hydrophobic radicals and the starch chain obtained from applying alkyl ketene dimer. A test for viscosity versus pH is also used to compare results for natural and modified starch, a kinetic model for water absorption is fitted to the hydration of samples of natural and modified starch, and the ability of a biofilm of modified starch to preserve fruit is also assessed. The degree of preservation of the fruit could be seen in the pictures that show that the fruit covered in the modified starch film has fewer alterations to its appearance after 64 days of observation. Moreover, the hydrophobic starch demonstrates superior results from the quality assessment when applied practically with paper and fruit, demonstrating their industrial potential. [ABSTRACT FROM AUTHOR]

A process for surface modification of LDPE films has been developed by employing chitosan (CS), alkyl ketene dimer (AKD), and glutaraldehyde (GA). Surface roughness and polar reactive groups were generated on the film surfaces by etching with chromic acid at 30 min. The polar groups interact/react with CS/AKD/GA, forming a highly stable coating layer. At optimum conditions (24 µm coating thickness), the film's antibacterial properties (99.9% inhibition) and hydrophobicity are drastically enhanced. The film's mechanical and optical properties and crystalline characteristics remain unchanged. The facile process has a high potential for fabricating functional films in food packaging and greenhouse applications. [ABSTRACT FROM AUTHOR]

The aim of this research was to evaluate the multiple effects of both thermal modification and alkyl ketene dimer (AKD) on the deodar cedar (Cedrus deodara Roxb.) wood surface, before and after an irradiation test. The physical and chemical changes that occurred on the cedar wood samples due to the combined effect of these modifications were evaluated by measuring their wettability and colour and using attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. The surface analysis by XPS showed the expected variability among the sampled layers for unmodified and thermally modified cedar wood samples and a uniform composition after the AKD coverage, regardless of their pre-treatments. The FTIR spectra before the irradiation test showed that the hydrophobicity of the samples was ensured by the formation of carbonyl groups originating from the reaction between the AKD and hydroxyl groups of cellulose, which is related to the presence of the absorption band between 1700 cm−1 and 1750 cm−1. Markedly, after the irradiation test, a degradation of the amorphous cellulose component occurred, showing that photoisomerisation to the enolic form took place. Overall, although uniform AKD coverage was derived from the surface analysis and wetting test, the combined ATR-FTIR results and colour measurements showed that it could not provide permanent protection to the underlying wood structure due to its own tendency to degrade mainly in colour over time, under the action of UV rays and atmospheric agents. [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]

Polyvinyl alcohol (PVA) is used in many applications because of its excellent physicochemical properties, non-toxicity, and biodegradability. However, its relatively low water resistance, poor water vapor/ultraviolet (UV) barrier properties, and poor mechanical properties compared with conventional polymers limit its applications in food packaging. In this study, cellulose nanocrystals (CNCs) and alkyl ketene dimer (AKD) were used to overcome these issues. The mechanical properties, water resistance, and barrier properties of the developed PVA/CNC/AKD films were significantly improved relative to those of a neat PVA film. The mechanical strength of a PVA/CNC/AKD 15% film (15 wt% AKD in a PVA/CNC matrix of 5 wt% CNCs) was 64.6% and 37% higher than those of PVA and PVA/CNC films, respectively. The water vapor transmission rate, water absorption, and solubility of PVA/CNC/AKD 15% were 41.2%, 61.1%, and 92.9%, respectively (lower than those of the neat PVA film). In addition, the UV barrier properties and soil degradation of the PVA/CNC/AKD films were significantly improved. • Cost-effective, ecofriendly chemicals AKD and CNCs were used to modify a PVA film. • Mechanical strength of PVA/CNC/AKD was 1.64 times higher than the PVA film. • Water absorption and solubility of PVA/CNC/AKD films were significantly reduced compared with those of the PVA film. • The PVA/CNC/AKD film exhibited excellent water vapor and UV barrier properties. • Adding CNCs and AKD increased the biodegradation rate of PVA. [ABSTRACT FROM AUTHOR]

A fundamental challenge in artificial superhydrophobic papers is their poor resistance to mechanical abrasion, which limits their practical application in different fields. Herein, a robust and multifunctional superhydrophobic paper is successfully fabricated via a facile spraying method by combining silver nanowires and fluorinated titania nanoparticles through a common paper sizing agent (alkyl ketene dimer) onto paper. It is shown that the surface of the paper-based material presents a three-dimensional network structure due to the cross-linking of silver nanowires with a high aspect ratio. Further hydrophilic and hydrophobic performance test results show that it exhibits exceptional water repellency, with a desirable static contact angle of 165° and roll-off angle of 6.2°. The superhydrophobic paper showcases excellent mechanical durability and maintains its superhydrophobicity even after enduring 130 linear sandpaper abrasion cycles or high-velocity water jetting impact benefited from interfacial van der Waals and hydrogen bonding. Simultaneously, the robust superhydrophobic surface can effectively prevent the penetration of acid or alkali solutions, as well as UV light, resulting in excellent chemical stability. Additionally, the superhydrophobic paper offers supplementary features such as self-cleaning, electrical conductivity, and antibacterial capability. Further development of this strategy paves a way toward next-generation superhydrophobic paper composed of nanostructures and characterized by multiple (or additional) functionalities.

Fresh green asparagus is prone to lignify after harvest due to its high respiration rate and secretion of secondary metabolites regulated by enzymes generated during storage. In this work, a dense hemicellulose-based coating containing hemicellulose, cellulose nanofibers, and montmorillonite (MMT) was prepared and used as a coating to reduce the respiration rate of green asparagus, with which the shelf life of green asparagus was prolonged from 5 days to 7 days. Alkyl ketene dimer (AKD) was used as a hydrophobizer and a crosslinking agent to reduce humidity sensitivity by introducing hydrophobic fatty acid chains to nanoparticles for increased structural stability and respiratory barrier property hemicellulose-based film in high humidity conditions. Our study proved that AKD modified coating with nature-derived nanomaterials could effectively increase respiratory barrier property, slow down the secretion of lignification-involved enzymes, and regulating the conversion of phenolic compounds to the lignin monomers. • AKD was used as a hydrophobizer and crosslinker can reduce humidity sensitivity of hemicellulose-based film. • Green asparagus preservation was prolonged from 5 to 7 days after coating by hemicellulose-based film. • The modified hemicellulose-based film can inhibit lignification of green asparagus. [ABSTRACT FROM AUTHOR]

The aim of this research was to evaluate the multiple effects of both thermal modification and alkyl ketene dimer (AKD) on the deodar cedar (Cedrus deodara Roxb.) wood surface, before and after an irradiation test. The physical and chemical changes that occurred on the cedar wood samples due to the combined effect of these modifications were evaluated by measuring their wettability and colour and using attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. The surface analysis by XPS showed the expected variability among the sampled layers for unmodified and thermally modified cedar wood samples and a uniform composition after the AKD coverage, regardless of their pre-treatments. The FTIR spectra before the irradiation test showed that the hydrophobicity of the samples was ensured by the formation of carbonyl groups originating from the reaction between the AKD and hydroxyl groups of cellulose, which is related to the presence of the absorption band between 1700 cm−1 and 1750 cm−1. Markedly, after the irradiation test, a degradation of the amorphous cellulose component occurred, showing that photoisomerisation to the enolic form took place. Overall, although uniform AKD coverage was derived from the surface analysis and wetting test, the combined ATR-FTIR results and colour measurements showed that it could not provide permanent protection to the underlying wood structure due to its own tendency to degrade mainly in colour over time, under the action of UV rays and atmospheric agents.

Alkyl ketene dimer (AKD) and rosin sizing are used in papermaking to decrease paper's tendency to absorb liquid water. Earlier information regarding the effects of internal sizing on paper dry strength is not consistent. In the present laboratory study, AKD sizing of handsheets made from Nordic bleached softwood pulp (NBSK), and rosin sizing of handsheets made from Nordic hardwood chemi-thermomechanical pulp (CTMP) were done via an internal sizing method, and by immersing handsheets in aqueous sizing agent dispersion. In the study, AKD sizing had no significant effect on the dry strength of NBSK handsheets. The result corresponds to practical experiences of papermakers. However, both AKD sizing methods resulted in a substantial and long-lasting increase of handsheet wet-strength. Unlike internal AKD sizing of NBSK handsheets, rosin internal sizing of CTMP handsheets resulted in decreased handsheet dry strength. The decrease indicates that, under the conditions present during the experiment, rosin sizing agents interfered with interfiber hydrogen bonding of CTMP fibers. Given that, in practice, no such undesired effects have been commonly linked to rosin sizing, the observed effect may be specific to sheet-making conditions. However, the effect of rosin sizing on strength properties and their variation cannot be ruled out completely. [ABSTRACT FROM AUTHOR]

In this study, the effect of alkyl ketene dimer (AKD) on the mechanical and physical properties of natural fiber (NF) and glass fiber (GF) reinforced poly(lactic acid) (PLA) composites were investigated in detail. The hybrid PLA composites were manufactured by extrusion method followed by hot press molding. AKD was used to improve the hydrophobicity of hybrid PLA composites and compatibility of NF and PLA in the polymer matrix. The tensile and flexural tests, thickness swelling, water absorption, and contact angle measurements were accomplished for determining the performance of the hybrid PLA composites. The surface morphology of the hybrid PLA composites was also performed by scanning electron microscopy. The incorporation of AKD and NF into PLA matrix improved the mechanical strengths by 40% and above compared to those of samples without AKD. But, tensile and flexural moduli decreased as 7% and 14% of the samples with NF and AKD, respectively. Contact angle was higher for the hybrid PLA composites with AKD compared with the composites without AKD. However, the results revealed that in the presence of GF, AKD had no significant effect on overall properties of the hybrid PLA composites. In the light of the findings, AKD may have a potential usage as coupling agent in the NF filled PLA composites. [ABSTRACT FROM AUTHOR]

Alkyl ketene dimer (AKD) is frequently used in paper industry as an inexpensive sizing agent. The formation of a porous structure after curing the solidified AKD for an extra-long time (4–6 days) results in superhydrophobicity. In this study, a facile and low-cost method was utilized to turn the surface of AKD superhydrophobic in a very short period of time. We fabricated superhydrophobic coatings by dipping glass and paper substrates in molten AKD and then treating them with ethanol after solidification. The samples were characterized by X-ray diffraction, Scanning electron microscopy, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, Confocal laser scanning microscopy, and dynamic contact angle goniometry. The results show that briefly treating the coatings, obtained from isothermally heated AKD melt at 40 °C for 3 min, with ethanol leads to superhydrophobicity with advancing and receding contact angles of 158.7 ± 1.4° and 156.8 ± 0.9°, respectively. By increasing the melt temperature to 70 °C and its heating time to 6 h followed by ethanol treatment, the advancing and receding contact angles increased to 163.7 ± 1.3° and 162.6 ± 1.2°, respectively. This enhancement in superhydrophobicity is due to the formation of porous, entangled irregular micro/nano textures that create air cushions on the surface resulting in droplet state transition from Wenzel to Cassie. [ABSTRACT FROM AUTHOR]

Biodegradable foam (biofoam) packaging is made from natural polymers as the main raw material and it is environmentally friendly. However, this packaging is water sensitive, thus it is not suitable for products with high moisture content. The purpose of this study is to determine the effect of surface modification of cassava starch‐based biofoam, using Alkyl Ketene Dimer/AKD as sizing agent, on its hydrophobic characteristics. A completely randomized factorial design is carried out using two factors and two replications. Factor A is a type of pulp of oil palm empty fruit bunches (OPEFB) with different treatment modifications (pulp A; pulp B; pulp C) and factor B is the concentration of AKD (0%; 2.5%; 3.3%; 5.0%). Biofoam is made by thermopressing. Its characterization observed includes physical properties, mechanical properties, and morphological structure. The results show that surface modification of biofoam with AKD significantly effected its moisture content, density, water absorption capacity, and compressive strength. The addition of AKD externally as a sizing agent is able to reduce water absorption capacity by an average of 83.26% compared to biofoam without coating with AKD. [ABSTRACT FROM AUTHOR]

Recently, cellulose nanofibers (CNF) are used as one novel fillers to reinforce poly(lactic acid) (PLA) matrix and form PLA green nanocomposites. In the present work, alkyl ketene dimer (AKD) was used as the sizing of CNF to improve the interfacial compatibility between the hydrophilic CNF and the hydrophobic PLA. The interactions between the AKD and CNF were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), which showed the formation of ketone ester structure between AKD and the hydroxyl groups of CNF. Thermo gravimetric analysis (TGA) showed the little reduced thermal stability of the AKD-CNF/PLA composites. The AKD-CNF/PLA morphology has rough surfaces due to the incorporation of cellulose nanofibers. The mechanical properties of AKD-CNF/PLA were tested by tensile testing, which discovered more AKD-CNF content enhances stress–strain performance. The highest tensile strength of composites was obtained for PLA with 5.0 wt.% AKD-cellulose, which is almost nine times higher than that of the pure PLA.

This study aimed to address the limited applicability of starch-based films in food packaging due to their inherent hydrophilicity, by developing a highly hydrophobic and mechanically reinforced film through compositing with alkyl ketene dimer (AKD). The FTIR analysis confirmed the successful introduction of AKD into the starch backbone via esterification by forming a β-keto ester linkage. Notably, the incorporation of AKD resulted in significant improvements in the modified film (S80A20), by exhibiting a higher water contact angle (WCA) of 128.28° and a reduced water vapor permeability (WVP) to 0.81×10 -10  (g m/m 2  s Pa). These enhancements were attributed to the inherent low surface energy of AKD and the increased surface roughness caused by AKD recrystallization. Moreover, the mechanical properties of the films were also enhanced due to the chemical crosslinking and intermolecular hydrogen bonding, as supported by the results of relaxation temperatures and molecular dynamics simulations. Considering the environmentally friendly and biodegradable nature of all components, the prepared hydrophobic films will hopefully be applied in food packaging., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The poor barrier properties and hygroscopic nature of cellulosic paper impede the wide application of cellulosic paper as a packaging material. Herein, a polyvinyl alcohol (PVA)-based polymer coating was used to improve the barrier performance of paper through its good ability to form a film. Alkyl ketene dimer (AKD) was used to enhance the water resistance. The effect of the absorptive characteristics of the base paper on the barrier properties was explored, and it was shown that surface-sized base paper provides a better barrier performance than unsized base paper. Nanoclay (Cloisite Na+) was used in the coating formulation to further enhance the barrier performance. The results show that the coating of PVA/AKD/nanoclay dispersion noticeably improved the barrier performance of the paper. The water vapor transmission rate of the base paper was 533 g/m2·day, and it decreased sharply to 1.3 g/m2·day after the application of a double coating because of the complete coverage of the base paper by the PVA-based polymer coating. The coated paper had excellent water resistance owing to its high water contact angle of around 100°. The grease resistance and mechanical properties of the base paper also improved after coating. This work may provide inspiration for improving the barrier properties of packaging paper through the selection of a suitable base paper and coating formulation.

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]

An investigation of the hydrolysis of diluted alkyl ketene dimer (AKD) dispersion was carried out under different conditions from which a kinetic model for predicting the AKD hydrolysis during its storage and papermaking process was proposed. As observed, the higher pH, elevated temperature, and longer time can accelerate the hydrolysis of AKD in the water medium. The results showed that the proposed model could provide a satisfactory description of AKD hydrolysis at various conditions, in which the R‐squared of the correlation coefficient (R2) between the measured and predicted data was 0.978. Based on this model, a successful controlling strategy aimed at optimizing the chemical efficiency in the practical application can be determined. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Cork can be easily coloured with anthraquinone dyes using scCO 2 as carrier medium. • Liquid AKD impregnation of wood can mimic aliphatic suberin domains in cork. • Hydrophobic AKD binds covalently to the wood surface also in the interior. • Lipophilicity and plasticization capabilities of AKD improve dye transport and uptake. • CIELAB measurements confirmed significantly improved dyeing after AKD impregnation. Abstract Dyeing of solid wood using scCO 2 as transport medium does not afford satisfying results as exemplarily demonstrated for disperse blue 134 and different wood species. Surprisingly, the bark of cork oak featuring closed porous architecture could be easily dyed with DB 134 which was hypothesized to be caused by the high content of lipophilic moieties in the suberin-rich thin walls separating the individual cells. To verify that non-polar constituents and their plasticization play a key role for diffusion of dye-loaded CO 2 , we impregnated wood samples with lipophilic alkyl ketene dimer (AKD) and confirmed its presence in the interior by FT-IR and water contact angle measurements. The results of subsequent scCO 2 -assisted dyeing confirmed that deposition of the common paper-sizing agent AKD on the internal surface of the wood samples significantly improved dyeing with DB 134 as evident from CIELAB colour space measurements. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • An automated HS-GC technique was developed to determine the MP of AKD wax. • The methanol was chose as the tracer compound in this work. • The MP of AKD was measured by plotting the methanol signal vs. the temperature. • This novel concept is universal and can be used to many related applications. Abstract This study demonstrated a novel method for determining the melting point (MP) of industrial grade alkyl ketene dimer (AKD) wax by an automated headspace gas chromatographic (HS-GC) technique, in which methanol was used as the tracer. It was based on measuring the GC signal of methanol released from an aqueous solution during the temperature increasing. When the temperature of AKD MP reached, the AKD granules floated on the surface aqueous solution was liquidized and completely isolated the methanol transfer from the solution to the headspace. Thus, a transition point, corresponding to the MP of AKD wax, was observed when plotting the GC signal of methanol vs. the temperature. The results showed that the method has a good measurement precision (RSD < 0.68%) and accuracy (the relative differences were < 7.16%, compared to a reference method). The present method is simple, accurate and particularly suitable to be used in the batch sample testing. This new measurement concept can be also adopted to many related applications. [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]

Xylan is a major type of hemicellulose that has attracted a lot of research and development activities. It is often derivatized in order to improve its properties. In the literature, hydrophobic modification of polymers is often used to produce surfactant-like materials and associative thickeners. In this work, we have derivatized xylan with alkyl ketene dimer (AKD) and two types of alkenyl succinic anhydrides (ASAs). The xylan-AKD derivatives have been made at 90 °C, using dimethyl sulfoxide as solvent and 4-dimethylaminopyridine as promoter. Samples with degrees of substitution (DS) up to 0.006 have been produced. The xylan-ASA derivatives have been synthesized at 120 °C in dimethyl sulfoxide with DS up to 0.105–0.135. The structures of these products have been confirmed with NMR and FT-IR. These xylan derivatives increase the structural diversity of xylan and provide additional options for people seeking to use hydrophobically modified polysaccharides in their applications.

Bacterial cellulose is a common research additive in the paper industry because it has unique and favorable characteristics. In this study, the effect of adding bacterial cellulose to an alkyl ketene dimer (AKD) sizing agent was investigated to optimize the dosage of bacterial cellulose, the retention system (cationic starch (CS), cationic polyacrylamide (CPAM)), and the sizing enhancement agents (polyamideamine-epichlorohydrin (PAE) and chitosan). The results showed that the addition of bacterial cellulose had a negative effect on AKD sizing. Meanwhile, the addition of 5% bacterial fiber had a slight but negligible effect on paper sizing. The retention system improved AKD sizing and the dual retention system with CS, and CPAM improved sizing up to 60%. When 0.2% PAE and chitosan were added simultaneously, the sizing degree increased by 42.8% and 47.6%, respectively.

The effect of alkyl ketene dimer (AKD) on plywood properties was studied. AKD is widely used in the paper industry as a sizing agent and can esterify wood cell wall components. Two types of veneers obtained from alder (Alnus glutinosa subsp. barbata (C. A. Mey) Yalt.) and beech (Fagus orientalis L.) wood logs were used. Two different treatment processes and two different concentrations (1% and 3%) of AKD were tested. The first method was AKD-dispersion, which was mixed with glue and sprayed onto veneers. The second method was dipping veneers into the AKD solutions (1% and 3%) for 25 min. Water uptake after 2 h, 24 h, and 48 h was reduced by the AKD treatment. Plywood produced from AKD impregnated veneers showed the lowest thickness swelling versus untreated plywood and plywood produced from AKD blended in glue. The AKD treatment generally reduced the mechanical properties of the plywood. However, AKD treatment considerably improved the biological resistance against brown rot fungi (Coniophera puteana BAM Ebw. 15) and white rot fungi (Trametes versicolor CTB 863A). Increased methyl/methylene and carbonyl groups of the alkyl chain were determined in the Fourier transform infrared (FTIR) spectra of specimens subjected to the AKDdispersion method. [ABSTRACT FROM AUTHOR]

This paper reports on an ionic-liquid assisted headspace gas chromatographic (HS-GC) for the determination of the content of alkyl ketene dimer (AKD) in its latex samples, in which the GC system was equipped with a thermal conductivity detector (TCD). The method was based on the AKD hydrolysis conducted in 1-butyl-3-methylimidazolium chloride (ionic-liquid) added medium at 100 °C for 10 min in a closed headspace sample vial, and the measured CO 2 (the resulting product of the hydrolysis) by HS-GC. The results showed that the present method has a good measurement precision (RSD <2.3%) and accuracy (recoveries from 96 − 105%), and the limit of quantitation (LOQ) is 0.9%. The present method is very suitable to be used for the routine check of AKD content in its latex sample in mill applications. The study also showed that the content of AKD in the tested commercial latex samples were in the range of 3.5–12%. [ABSTRACT FROM AUTHOR]

In this work we report the production of cellulose nanopapers modified with alkyl ketene dimer (AKD) in order to allow the immobilization of antimicrobial peptides (AMPs) to produce surfaces with antimicrobial properties. Cellulose nanofibers (CNF) were prepared from softwood bleached pulp via high pressure homogenization after chemical pretreatment of fibers via TEMPO oxidation. Nanopapers were then prepared after a casting technique and functionalized with alkyl ketene dimer before AMPs were immobilized. The immobilization process was performed by submerging the samples into AMP aqueous solutions and then dried at room temperature. Antimicrobial activity was tested against B. subtilis . Results indicated that AMPs were bound onto the nanopaper surface and released when the nanopaper was put in contact with the culture medium, which effectively demonstrates the viability of the immobilization process. [ABSTRACT FROM AUTHOR]

Non-crystal microporous starch (NCMS) containing microporous and amorphous structures was prepared from native corn starch by heat treatment and solvent exchange. NCMS can be used as fillers, coatings, and raw materials in the preparation of various denatured starch because of its specific surface area and amorphous region. However, the hydrophilicity of NCMS limits its applications in papermaking. Thus, in this study, NCMS was reacted with alkyl ketene dimer (AKD) to prepare hydrophobic NCMS (H-NCMS), which is more stable, and convenient for storage and use in surface sizing. The optimal preparation conditions were selected using single-factor tests. The product, which was prepared at 55 °C for 3 h with an AKD dosage of 80%, had a sizing degree of 67 s. Characterization by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) spectroscopy confirmed that NCMS, H-NCMS, and sized paper were obtained. The thermal stability and hydrophobicity of the paper were measured using thermogravimetric analysis (TGA) and water contact angles, respectively. The results indicated that the sized paper has excellent thermal stability and hydrophobicity after surface sizing with 0.9% H-NCMS. Food wrapping paper with excellent strength and hydrophobicity was successfully prepared using H-NCMS and ultrasonic-assisted wheat straw pulp (UWP). [ABSTRACT FROM AUTHOR]

Here we present a method to manufacture peptide-concentrating MALDI-plates with alkyl ketene dimer (AKD) as a new superhydrophobic coating. The fabrication of the hydrophobic plates included application of AKD by airbrush, and negative contact printing to generate the concentration sites. Deposited sample droplets were contained within the prestructured sites, and self-adjusted onto the site if slightly misplaced. No AKD contamination was observed, and the plates could easily be cleaned and regenerated. The S/N values for four model peptides was about twice as high compared with a standard steel plate and a commercial concentration plate. [ABSTRACT FROM AUTHOR]

Causticizing calcium carbonate (CCC), known as lime mud, is a by-product of the papermaking industry that comes from the green liquor causticizing process. In China, CCC has been used as a paper filler to replace precipitated calcium carbonate (PCC). This is beneficial for saving resources and preventing secondary pollution. Unfortunately, compared with PCC, CCC can reduce the sizing efficiency of alkyl ketene dimer (AKD). So the application scope and dosage of CCC has been limited in mill trials in China. In this study, CCC was prepared with green liquor and quicklime, which were obtained from an alkali recovery line of a pulping mill. The reason for the lower sizing efficiency of AKD when CCC was used as a filler was investigated. The results showed that when greater amounts of AKD were adsorbed by CCC, the AKD sizing efficiency was lower. The irregular CCC had higher Brunauer, Emmett, and Teller (BET) surface area and Barrett-Joyner-Halenda (BJH) method cumulative desorption pore volume, resulting in higher adsorption. The spindle-like or needle-like CCC had lower BET surface area and BJH method cumulative desorption pore volume that was beneficial for controlling its adsorption of AKD and improving the sizing efficiency.

A process for the chemical modification of Chinese fir with alkyl ketene dimer (AKD) was studied. The hydrophobicity of the resulting products was evaluated by characterization of the equilibrium moisture content, water-surface contact angle, water absorption coefficient, and anti-swelling efficiency. The results indicated that when 5% AKD solution was used, the modified wood generally showed good hydrophobicity and improved dimensional stability. The result of boiling water and hexane extraction tests showed that the modified fir possessed very stable hydrophobicity.