Alkyl Ketene Dimer Wax Research Articles

Rice straw-based sustainable food packaging material with improved strength and barrier properties: Development and characterization

Sustainable food packaging paper with high barrier and strength properties was developed with rice straw nanocellulose materials. Pulping and bleaching of rice straw were performed using an organosolv pulping and DED (D: chlorine dioxide bleaching; E: sodium hydroxide extraction) bleaching sequence. Bleached rice straw pulp was refined to 90°SR using a laboratory Valley beater. The laboratory handsheets were prepared using pulp slurry at 40°SR and 90°SR. The handsheets of cellulose nanofibrils (CNFs) made of highly refined pulp (90°SR) were surface sized using alkyl ketene dimer (AKD) wax to increase the barrier properties of paper for selective food packaging applications. The paper samples were tested for mechanical, optical, surface, and barrier properties, including tensile index, burst index, tearing index, bending stiffness, elongation, porosity, apparent density, opacity, Cobb value, water vapor transmission rate (WVTR), oil and grease resistance, and contact angle. The refined pulp (90°SR) was analyzed using field-emission scanning electron microscopy (FE-SEM), and it was observed that the morphology of the developed fibers changes to the nanoscale (<100 nm) for at least one dimension. The particle size distribution of the refined pulp using DLS analyzer also confirmed the cellulose fibers to near nanoscale. It was concluded that nanofibers were formed by a high degree of the mechanical pulp refining process and found to be much more economical than alternative processes in this direction. The sample handsheets of CNFs showed good strength and barrier properties. The barrier properties further increased when surface sizing was done using low-cost, nontoxic, and biodegradable AKD wax.

Exploring the relationship between food-grade wax solubility in supercritical carbon dioxide and resulting hydrophobic development of impregnated paper substrates

Alkyl ketene dimer (AKD) and vegetable wax (VW) are suitable contenders for supercritical impregnation (SCI) processes, where the waxes may be deposited onto paper fiber surfaces to improve their hydrophobicity for food packaging applications. The solubility of both waxes in supercritical carbon dioxide (scCO2) with n-heptane cosolvent was measured (40 – 60 oC and 10 – 18 MPa). VW was two orders of magnitude more soluble in scCO2 compared with AKD, and both sets of data were validated using the Chrastil empirical equation. SCI of AKD wax into paper matrixes was performed at pre-determined solubility conditions, and the resulting hydrophobicity was measured. Results demonstrated that annealing the samples (4 h, 140, 160, 180 oC) immediately following impregnation generally enabled a more rapid development of the CA over a 2-week period. Crucially, using impregnation temperatures and pressures that maximized AKD solubility in scCO2 resulted in CA up to 130o. Gravimetric analysis of the impregnated samples confirmed the expected deposited wax quantities to within 25% of the solubility quantities. Scanning electron microscopy (SEM) imaging revealed better distribution of AKD in annealed samples and partially confirmed that more intricate structures were responsible for higher measured CA. These results explicitly connect the intuitive relationship that higher solute solubility in scCO2 should lead to bulk property improvements (i.e. higher CA or hydrophobicity) after SCI. Continued research in this area will enable the development of metrics, linking solubility conditions to desired bulk material properties, and is expected to lead to innovative packaging of green materials and processes.

A waterproof cellulose nanofibril sheet prepared by the deposition of an alkyl ketene dimer on a controlled porous structure.

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.Graphical abstract

Extended shelf life cement: Principles, microstructural analysis, and physical–mechanical properties of the cement and concrete

Exposure of cement to surrounding atmosphere causes absorption of moisture from air and irreversible chemical interaction of the cement with water – hydration. As a result, the cement partially loses its activity. The deterioration of cement during transportation and storage limits its guaranteed shelf life to a period of usually not more than six months. This study introduces a method for extending the shelf life of cement by treatment with alkyl ketene dimer wax. The morphology of the hydrophobic cements were qualitatively assessed by scanning electron microscopy to assess the dispersal of the finest size fractions. Storage of the cements was conducted under accelerated aging conditions with subsequent making of concrete, followed by measurement of compressive strength and sorptivity. The results demonstrated a notably longer shelf life than ordinary Portland cement, with improvements in strength and lower water permeability of the concrete.

Accurate determination of melting Point of industrial grade alkyl ketene dimer wax by a simple and automated headspace gas chromatographic technique

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.

Alkyl ketene dimer (AKD) sizing of paper under simplified treatment conditions

Alkyl ketene dimer (AKD) has been widely used by manufacturers of paper and paperboard as a hydrophobic sizing agent. Ordinary sizing with AKD involves a complex series of processes, including emulsification of the waxy AKD material; measures to avoid the agglomeration of the emulsified AKD particles; addition of a stabilized AKD dispersion to papermaking furnish; interactions with various retention aid chemicals to fix the material onto solid surfaces; and various spreading and curing processes that take place during the drying and cooling of the paper product. In the present work, as a means to gain insight into the mechanisms attributable only to the AKD in isolation from the other additives and subprocesses, the AKD wax was dissolved in heptane and applied to filter paper between two aluminum foil layers, followed by evaporation of the solvent and optional heating. Surprisingly, hydrophobic character was obtained regardless of whether or not the treated sheets had been heat cured. Also, for the first time, it was observed that the AKD treatment resulted in a substantial increase in sheet strength, suggesting that the AKD was able to serve as the matrix in an AKD-saturated paper structure. The results add support to past suggestions in the literature that potential covalent interactions cannot account for all of the effects attributable to AKD treatment of paper.

Chemical composition of “AKD vapour” and its implication to AKD vapour sizing

Alkyl ketene dimer (AKD) sizing of paper involves the redistribution of the wax over the fibre surface upon heating. The two major mechanisms widely studied so far are the spreading of an autophobic precursor of molten AKD and AKD vapour transport and re-deposition on the fibre surface. All previous work assumed that the transport of AKD vapour could be expressed by the change of water contact angle with substrates that were exposed to the vapour. Information regarding the chemical composition of the vapour phase above the AKD wax has not been found in the literature. In this work, a simple method for analysing the chemical composition of the vapour is established. Our preliminary results indicated that the chemical composition of AKD vapour in the temperature range of 75–80 °C is dominantly fatty acids. This suggests that the sizing effect by actual AKD molecules via the vapour deposition mechanism is likely to be insignificant in this temperature range. This also implies that fatty acids play a positive role in AKD sizing. The chemical stability of AKD in this temperature range is also studied.

Effects of Fatty Acid Components Present in AKD Wax on Emulsion Stability and Paper Sizing Performance

Commercial alkylketene dimer (AKD) waxes generally contain 80–90% AKD, and the rest of the components are by‐products such as fatty acids, fatty acid anhydrides, and AKD oligomers. In this article, the effects of fatty acid components present in AKD waxes on AKD emulsion stability and paper sizing performance were studied using AKD emulsions, which were prepared from an AKD wax mixed with 0–12% stearic and palmitic acids. Repeated temperature shock treatments revealed that the fatty acids–containing AKD emulsions became most unstable at 3% fatty acid content, whereas those with 12% fatty acids were rather stable. When the addition level of fatty acids was increased up to 12%, zeta potentials of the AKD emulsion particles increased from +1.4 mV to +4.4 mV with increasing fatty acid content. This increase in zeta potential may be one of the factors that lead to a decrease in AKD retention ratios in handsheets. Thus, fatty acid components present in AKD waxes not only decrease the pure AKD content in the waxes but also have negative impacts on emulsion stability and paper sizing performance. These results show that fatty acid content in AKD waxes must be sufficiently controlled as low as possible to keep a standard level of the AKD wax quality.

XPS imaging of surface diffusion of alkylketene dimer on paper surfaces

The alkylketene dimer (AKD) wax dispersion is introduced in the wet-end of a paper machine, and during drying it spreads and anchors to the fiber surface. Direct observation of the surface diffusion of the AKD wax at paper surfaces was obtained using X-ray photoelectron spectroscopy imaging technique. An AKD diffusion of approximately 400 μm was observed at a paper surface that was stored for 3 h at 80 °C. This gives a diffusion coefficient of approximately 10−11 m2 s−1. Storage for 1 week at room temperature also showed a remarkable spreading of AKD.