The introduction of the second acrylate group, ethylene glycol diacrylate (No. 15), to 2-hydroxyethyl acrylate (No. 11) did not bring much change in odor. The former shows the smell of mushroom, while the latter shows the smell of mushroom and moss. However, for the 1,2-propanediol diacrylate (No. 16) after the introduction of the second acrylate group in the acrylic acid-1-hydroxyisopropyl ester (No. 10) / acrylic Acid-2-Hydroxypropyl ester (No. 12), the geranium and lighter gas odor of the monoester disappeared in the diester, and the odor of garlic and glue was generated in the diester.
Among all straight chain n-alkyl acrylates, ethyl acrylate (No. 2) showed the lowest odor threshold, which was only 0.83ng/lair. With the increase of chain length, the threshold increased slightly, and n-butyl acrylate (No. 4) reached 2.4ng/lair. However, this rule is not always effective, because the threshold of methyl acrylate (No. 1) with the shortest chain among the four monomers is the highest (11 ng/lair). Compared with their corresponding saturated acrylate monomers ethyl acrylate (No. 2) and propyl acrylate (No. 3), vinyl acrylate (No. 5) and propenyl acrylate (No. 6) containing unsaturated double bonds showed 20 and 3.5 times lower odor thresholds. This indicates that the introduction of unsaturated double bonds in the carbon chain will greatly increase the odor threshold and reduce the odor perception. However, if the unsaturated double bond is not on the terminal group, the effect is not obvious. For example, the odor threshold of acrylic acid-3- (z) pentene ester (No. 7) is only (1.3 ng/lair).
Among all alkyl acrylate esters, 2-ethylhexyl acrylate (No. 13) showed the highest odor threshold of 20ng/lair, which was related to the weak interaction between 2-ethylhexyl and odor acceptor due to the steric hindrance effect of 2-ethylhexyl. The high odor threshold of 2-ethylhexyl acrylate and its use to improve the softness and flexibility of acrylic resin dispersion make it suitable for use as an additive or comonomer in low odor coatings and adhesives. However, long-term contact with 2-ethylhexyl acrylate may lead to tumor or cancer, and its high odor threshold may become a disadvantage, because it will not be perceived by the human body.
The odor threshold of acrylate containing cyclopentane and cyclohexane (No. 17 and 18) is not lower than that of non cycloalkyl with the same number of carbon atoms. At the same time, the odor threshold of cyclopentane acrylate (No. 17) was 30 times higher than that of cyclohexane acrylate (No. 18).
For 2-hydroxyethyl acrylate (No. 11) and 2-hydroxy-n-propyl acrylate (No. 12), the introduction of hydroxyl in the structure greatly improved the odor threshold, which was 178 and 106ng/lair respectively, which made their odor very low. The same trend can be seen from the difference of odor threshold between sec butyl acrylate (No. 8) and 1-hydroxyisopropyl acrylate (No. 10).
With the introduction of SEC butyl, the odor threshold of acrylate was significantly reduced to only 0.073ng/lair, showing the lowest odor threshold among all alkyl acrylates, that is, the strongest odor.
Among the 20 monomers determined, 2-methoxyphenyl acrylate (No. 19) showed the lowest odor threshold, which was only 0.068ng/lair. The odor threshold of 2-methoxyphenyl ester, which is widely used as essence in food industry and flavor industry, is 0.088ng/lair. This indicates that the two esters with 2-methoxyphenyl structure play a role in the same odor acceptor.
Patrick Bauer and others’ research on these 20 acrylate monomers showed that the short chain monomers mainly displayed the odor similar to sulfur, lighter gas and garlic, while the long chain monomers mainly displayed the odor similar to mushrooms, geraniums and carrots. All acrylate monomers showed relatively low odor threshold, that is to say, they all had large odor. The odor thresholds of SEC butyl acrylate and 2-methoxyphenyl acrylate were particularly low, showing the strongest odor. 2-hydroxyethyl acrylate and 2-hydroxypropyl acrylate had the highest odor threshold and the lowest odor.
Post time: Jun-07-2022
