[alexallaround]

Why cetyl alcohol has HLB value 15.5 but is not hydrophilic? How we calculate this value (15.5)?
Thanks!

[kriggy]

Look up wikipedia.
Im not really into this but I think the value 15 is quite high. Just using the Griffin method as described on wiki gives the value of about 0,15, maybe there is a decimal point mistake in your value?

[pgk]

1). 15.5 is the (minimum) required HLB value of an emulsifier, in order to emulsify cetyl alcohol and form an o/w emulsion; and not the HLB value of cetyl alcohol.
2). Cetyl alcohol is not an emulsifier itself and consequently, HLB value is not applicable for this chemical substance.
3). Hydrophilicity/lipophilicity of a chemical substance can be estimated by its logP value (≤ 0 or > 0, respectively); cetyl alcohol is lipophilic (hydrophobic) because it has logP = 7.3, which is > 0. 
4). Required HLB values of emulsifiers for o/w emulsification of lipophilic compounds, are experimentally estimated.

[alexallaround]

You are so wright! Thank you!!