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A few weeks ago I decided to harvest the lavender in my garden and put it through a still to extract the essential oils. The still in question is essentially just an air cooled condenser.

I collected the first fraction in a clear plastic vial. Within a day the vial had become cloudy looking (like frosted glass - the lavender oil itself was not cloudy - just the container). After a week this had happened:

melted top

thread missing

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The whole top of the container has been eaten away and is now flexible where before it was rigid.

What's caused this, is it expected behaviour?

Is there anything I should consider before using the lavender oil in fragrances and soaps?

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    $\begingroup$ You do realize that "lavender oil" isn't a single chemical but a mixture. $\endgroup$ – MaxW Sep 28 '18 at 15:33
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    $\begingroup$ I'm not convinced this question is too broad. $\endgroup$ – A.K. Sep 28 '18 at 23:43
  • $\begingroup$ Related chemistry.stackexchange.com/questions/28430/… $\endgroup$ – Curt F. Jun 26 '19 at 21:10
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Based on appearance and extent of deformation, your bottle is likely made of PVC plastic which is not compatible with oils. Plastic bottles are made from blow molding. This process leaves residual stress in the polymer chains of the materials but creates a smooth and transparent surface. Lavender oil can diffuse into PVC and make it softer. Once it is softer, the polymer chains can relax some of the residual stress which makes the surface rough and as a result appear cloudy due to increased scattering. Given Long enough more lavender oil can penetrate the plastic and soften it to the point that the plastic is allowed to flow which causes the observed deformation of the top.

Now I cannot say with certainty it was PVC that your bottle was made from, but if it was, then plasticizer would have seeped into the oil which isn't great for people. If you want to use your oil for air freshener or candles that is fine but I would not recommend it for skin contact applications.

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    $\begingroup$ "Isn't great for people" is a euphemism for "toxic, probably carcinogenic, but hopefully there's not too much of it", I take it? $\endgroup$ – wizzwizz4 Sep 28 '18 at 20:50
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    $\begingroup$ @wizzwizz4 more like "has effects including but not limited to toxic, probably carcinogenic, endocrine disruptor but hopefully not at the current level" $\endgroup$ – A.K. Sep 28 '18 at 20:53
  • $\begingroup$ @wizzwizz4 Plasticiser is used to lower PVCs Tg (80°C) so it becomes rubbery at RT. A solid vial, even if made of PVC, would not contain plasticiser. Otoh PVC typically contains a lot of processing aids and other stuff. Anyway all plastic bottles are made via blow molding, and all plastics are likely to plasticise and yield if exposed to unpolar solvents. $\endgroup$ – Karl Sep 28 '18 at 21:05
  • $\begingroup$ Are we sure that the plastic is PVC, and not a polystyrene? $\endgroup$ – Curt F. Jun 26 '19 at 21:11
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A quick google search yields a number of public scientific pdf papers that report on the chemical composition of lavender oil. Most simply, the wikipedia entry tells us the primary constituents are various esters, phenols and ketones.

These are organic solvents. It is well known that organic solvents soften or dissolve many plastics. Try, for example, putting acetone or methy-ethyl-ketone (MEK) in a plastic container. Put it in an outer glass container to avoid a mess. Happy experimenting!

By the way, thanks for bringing this to my attention. I'd never have imagined such potent solvents could be obtained so simply.

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  • $\begingroup$ Acetone can be obtained quite easily. $\endgroup$ – adrian Sep 29 '18 at 3:36

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