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Polyhydric/polyol content using HLB equation
Hello,
An equation used to calculate HLB for non ionic surfactants is as follows:
HLB=(E+P)/5E = ethylene oxide content
P = polyol contentDoes anyone know how to calculate the polyol content (P), for example in polyglyceryl-4 laurate? I’m under the assumption that E = 0 as there’s no ethylene oxide present and the polymerisation bracket is P but do I include the last two hydroxy groups?
I’ve looked at multiple sources and none provide examples with polyhydric content.Any help would be much appreciated. Thanks in advance! -
6 Replies
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Wikipedia gives you two different methods for calculating HLB values of unknown/new compounds.Are the results accurate? I don’t know… what I know it that several polyglyceryl esters can form lamellar structures and then do not comply with the HLB system. Also, most manufacturers give HLB values for their emulsifiers… not because these values are any good other than telling you if the emulsifier has a certain preference towards one or the other emulsion type (o/w vs. w/o) but because of tradition. The HLB system is a very persistant relic in most applications but sad enough, it’s the only one most cosmetic chemists care about (the smarter ones go by experience, gut feel, common sense, and trial and error).Estimating from related emulsifiers, PG-4 laurate should be in the range of HLB 13-14. -
Thanks for the reply! I’m having trouble understanding which part of the structure is the polyol. I cannot seem to find a diagram of the mentioned chemical but I found a similar diagram. Is it the structure in the brackets and the hydroxy groups at the end?
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<div>Mainly same as for ethoxylates, only polyglyceride is now the hydrophile. Remember that the carbonyl is calculated as part of the lipophile not hydrophile.</div>
Best to use the mass ratio method:
HLB = [HPMP ÷ 5]
where HPMP = hydrophile mass percentage
methylene = 14, glyceride group = 74, methyl = 15, glycol end group = 91, carbonyl = 28
For Polyglyceryl-6 Stearate:
Hydrophile mass = [(5 * 74) + (1 * 91] = 461
Hydrophobe mass = [(16 * 14) + (1 * 15) + (1 * 28)] = 267
HLB = [(461 ÷ 728) *100] ÷ 5 = 12.6
Best to state as approximation…HLB » 12.5
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@Fung One of the main limitations of the HLB system is that it was basically made for non ionic ethoxylated surfactants. As you see in your calculations, there are things not considered that actually contribute to the hydrophilic character of the molecule (like the presence of an ester group or the ether groups that don’t come from ethylene oxide. Calculations of HLB system outside the group of molecules it was created for gives you no complete info.
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Just for the fun of it: the 11 -OH (9 in brackets and the two on the right side of it) each count 1.9 according to the method by Davies.The ester (left of the brackets) counts 2.4, the nine ethers (the -O- on the right side within the brackets) count 1.3 and the 42 carbons each -0.475.Add this up and add 7 = HLB = 22.05. As you can see, a totally arbitrary and obviously wrong number
.As @ketchito said: HLB was made for PEGylated fatty acids and alcohols and sorbitan fatty esters and PEG derivatives thereof (e.g. Tween, Span, Myrj, Brij, and older Arlacel, Atlas, and Atlox series, to mention just a few). The system isn’t even working well with Tritons, Pluronics, branched or polyblock polymers, and extended surfactants, let alone valid for glucosides, polyglycerols, ‘biosurfactants’, lamellar gel network promoters, and all the other newer types.
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