Today’s theme is cut into AKD (Alkylene Ketone Djuvant) adhesive as a subdivision area.
As we all know, AKD is one of the representative reactive adhesives (the other is ASA, also known as oleic amber acid), the traditional application of sizing mainly explains the “AKD and fiber reaction” and “AKD hydrolysis reaction” between the two competitive relationship, and later researchers slowly realized that “the reaction between AKD and starch emulsizer” should not be ignored.
Due to the complexity between the above competitive reactions, AKD sizing often occurs “poor sizing application”, “insufficient sizing”, “sizing disappear” and other headache production problems and product quality problems.
In one of my teaching courseware, I have guided students/students to examine AKD-related issues in the following ways in order to better understand the characteristics and application techniques of AKD:
In order to master AKD’s characteristics and application technology more comprehensively, the following AKD adhesive-related issues need to be paid attention to:
- Is there a problem with the quality of raw materials for the preparation of AKD products?
- Is there a problem with the AKD emulsification process?
- Is the AKD product hydrolysed by itself?
- What is the retention rate of AKD latex particles?
- What is the retention status of AKD latex particles on the fiber? Is it a single particle state or a particle aggregate state? Is it wrapped in other ingredients, such as DCS? AKD wraps around other ingredients such as fillers, doesn’t it?
- Does AKD react with paper fibers (the possibility of reacting with water, starch emulsizers, etc.)?
- Can AKD and fiber react faster?
Of course, it’s hard to explain everything listed above at once today.
However, before we talked about the concept of “alkalinity”, once mentioned: “AKD adhesive, pH and alkalinity on the effect of sizing is interrelated, the appropriate pH and alkalinity range of the sizing effect may be more ideal.” The ideal pH range is 7.0-8.5 and the ideal alkalinity range is 50-200mg (CaCO3)/L, otherwise, the acquaintance of AKD is prone to failure. High alkalinity greater than 400mg (CaCO3)/L exacerbates the hydrolysing and adhesive reversal of AKD” so let us further discuss about the hydrolytic problem of AKD today.
Many people know that increasing the pH speeds up the hydrolysing of AKD, for example, the residual calcium hydroxide in the precipitation calcium carbonate migrates during the AKD ripening phase, which is one of the reasons for the reversal of AKD adhesion. However, AKD hydrolysis is actually accelerated by the catalysis of hydrocarbonate root ions (HCO3–) and secondary cations such as calcium, magnesium and vanadium. The former is the alkalinity component, the latter is the main component of hardness, so here is a reminder of the importance of alkalinity and hardness detection. The mechanism by which hydrocarbonogen ions catalytic AKD is thought to periodically form a transition complex that exacts hydroxygen ions (OH–) through proton exchange reactions to accelerate the hydrolysis of AKD. The catalytic action of the metal ions mentioned above is almost unaffected by pH in the pH6-10 range.
In addition, today I would like to add an additional point—— “the presence of fungicides and surfactants in the system may also have adverse effects on the application of sizing.” However，you need to know some are still suitable for ASA sizing.
- First of all, it is known that some fungicides have oxidation properties, while some oxidants are harmful to reactive gels such as AKD. Hydrogen peroxide has a smaller impact to those areless than 100 mg/L, but may have an impact on other chemicals.
- Fungicides often contain some surfactants, but some surfactants can have a relatively large impact on the application of sizing, for example, some seasonal ammonium salt surfactants in water content of 10ppm may have a very significant adverse effect on the effect of the application (the burgundy performance and unsprayed, the contact angle from 120 degrees to 20 degrees).
- Some fungicides, even non-oxidants, such as bromine nitrostyrene, benzodialumine, pyrethroids, polyoxyolefins, can also have adverse effects on the application of AKD (where polyoxyolefins also have adverse effects on surface gel).
- Many desiccants are also obvious surfactants, which have adverse effects on AKD adhesive, and the stronger the dewatering of desolation agents, the more obvious their adverse effects are. The most affected are fatty acid polyether and fatty acid acetylene compounds. The use of oil-based desiccants should generally be careful, where possible, try to choose water-based (water emulsion type) deblisters.
- Other water-repugnant organic compounds such as fatty acids, long-chain hydrocarbons, and various glyceroid-based compounds also shield the application. These compounds may be residues from primary pulp fibers, such as fatty acids, fatty acid lipids, ligands, sterolsand so on, or styrene polymers from waste pulp, acrylic resins (e.g. pressure-sensitive gums) etc. The so-called shielding effect, that is, if the use of pumping and other methods to remove these substances from the paper (actually less feasible), the degree of sizingwill be restored to a better degree.
- Attention needs to be paid to the content of the above substances in the return water.