DEODORANTS 125


molecules. This makes zinc ricinoleate very effective to absorb unpleasant odours, which are often caused by nitrogen and sulfur containing molecules, namely amines, ammonia, mercaptans, thio esters, hydrogen sulfide, low molecular weight organic acids, etc. It is important to note that pleasant scents, such as fragrances, mainly containing ester, aldehyde or aromatic groups, will not be affected by adsorption. Figure 1 shows the molecular structure of zinc ricinoleate. This molecule consists of a zinc atom and two ricinoleic acid moieties and can be synthesised by neutralisation of ricinoleic acid with zinc oxide. Both starting materials are natural substances. Zinc oxide can be obtained from mineral sources, and ricinoleic acid derives from castor oil triglycerides (content of about 90%). Thus, zinc ricinoleate is a natural molecule obtained from renewable sources. Today, it is one of the important parameters to choose raw materials. The modern requirements for


environmental friendliness makes zinc ricinoleate, due to its high biodegradability, a very attractive component for certified products.


The use of pure zinc ricinoleate is in


various areas still limited or complicated. It is a waxy substance with a melting point of about 80 °C, which is insoluble in water and not active in terms of odour removal. The three-dimensional model of the zinc ricinoleate molecule (Fig 2) shows the formation of an intramolecular complex of the zinc atom with free electron pairs of oxygen atoms from hydroxyl groups of ricinolic acid residues of the same molecule. The molecule of pure zinc ricinoleate is a hydrophobic symmetrical sphere. Interactions between hydrophilic groups and water molecules are very limited that leads to poor water solubility of the substance. Due to the electrostatic shield provided by the oxygen atoms of the ligands, Zn2+


is protected against


nucleophilic attacks of other molecules that explains the low efficiency of using pure zinc ricinoleate as an odour absorber.


Zinc ricinoleate activation Computer simulations (Fig 3) showed that the zinc ricinoleate molecule can be activated by interaction with a chelating agent such as methylglycinediacetic acid trisodium salt (MGDA).


Zn(Ri)2 + MGDA (Ri)2 Zn --- MGDA


During the formation of the complex, the ricinoleic acid residues unfold and the hydroxyl groups are released and oriented to the water phase, providing good solubility of the complex. Re-complexation


April 2020 Figure 3: Molecular simulation of the interaction of zinc ricinoleate and MGDA.


Table 1: The Polyfix products range. Polyfix ZRC 25 GP


Polyfix ZRC 25 MB* Aqua, Zinc Ricinoleate, Tetrasodium Glutamate Diacetate, Propanediol Polyfix ZRC 25 EC


Polyfix ZRC 50 TB


Aqua, Zinc Ricinoleate, Tetrasodium Glutamate Diacetate, Propylene Glycol


Zinc Ricinoleate, Laureth-3, Tetrahydroxypropyl Ethylenediamine, Propylene Glycol


Polyfix ZRC 30 MT Water, Zinc Diricinoleate, Chelating Agent, Alcohol Ethoxylated *Mass Balance


is possible because the interaction of MGDA and zinc ricinoleate is weak. Since the formation of a complex is a reversible process in a dynamic equilibrium, its geometry is constantly changing. The zinc atom becomes available for attack by other nucleophiles. The interaction between the zinc atom and molecules containing nitrogen or sulfur is so strong compared to the interaction with a chelating agent that after recombination such complexes remain stable even at high temperatures. Computer simulations confirm that the chelating agent is capable of serving as a solubiliser and activator for zinc ricinoleate.


A series of water-soluble odour absorber concentrates


Using this knowledge, Schill + Seilacher GmbH has developed the Polyfix series of highly effective, water-soluble odour absorber concentrates (Table 1). An additional advantage of this activation mechanism is the ability of Polyfix products (now referred to as ‘the odour absorber concentrates and '30 MT' / '25 GP' for Polyfix ZRC 30 MT / Polyfix ZRC 25 GP) to absorb molecules efficiently and


quickly from the gas phase. Activated zinc ricinoleate as a soap, possesses surfactant properties. Its molecules will self-assemble at the surface of the solution (Fig 4). The geometry of the complex allows the zinc atom to capture molecules of unpleasant odours from the air as soon as they are close enough for interaction.


Performance tests Various tests of the effectiveness of the odour absorber concentrate range and finished products including the odour absorber concentrates verify the high performance of the new materials. A test regarding absorption capacity of the odour absorber concentrates against different types of compounds with unpleasant odours was carried out as follows: Two Petri dishes were placed next to each other under a large hood. The concentration of molecules with an unpleasant odour in the atmosphere of this closed system was measured either in the presence or absence of the odour absorber concentrates.


For each ‘bad smell’ substance, three experiments were carried out. In each of


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