[Stoves] [Jatropha cake properties]

[Charlie Sellers]

Wikipedia has a decent discussion under the "linseed oil" heading, including:

Having a high content of di- and triunsaturated esters, linseed oil is 
particularly susceptible to polymerization reactions upon exposure to oxygen in 
air. This polymerization, which is called "drying," results in the 
rigidification of the material. The drying process can be so exothermic as to 
pose a fire hazard under certain circumstances.

Rags soaked with linseed oil stored in a pile are considered a fire hazard 
because they provide a large surface area for oxidation of the oil, and the oil 
oxidizes quickly. The oxidation of linseed oil is an exothermic reaction, 
which accelerates as the temperature of the rags increases. When heat 
accumulation exceeds the rate of heat dissipation into the environment, the 
temperature increases and may eventually become hot enough to make the 
rags spontaneously combust.

The "drying oil" entry goes into more detail:
A drying oil is an oil that hardens to a tough, solid film after a period of 
exposure to air. The oil does not harden through the evaporation of water or 
other solvents, but through a chemical reaction in which the components 
crosslink by the action of oxygen. Drying oils are a key component of oil 
paint and some varnishes. Some commonly used drying oils include linseed (flax 
seed) oil, tung oil, poppy seed oil, perilla oil, and walnut oil. 
and there are lots more details here, including the note that drying oils 
initially increase in weight significantly (17% for linseed) as they dry, due to 
absorption of oxygen..

It also reminds us that because of polymerization linseed oil is used as a 
binder/ardener for things like linoleum, wood finishes, putty, etc. so we may 
want to further consider any "drying" oils for densified fuel applications. 
 "Boiled linseed oil" is the name given to a product that is particularly good 
for hard coatings - the heat treatment starts the polymerization.

Charlie




________________________________
From: "ajheggie at gmail.com" <ajheggie at gmail.com>
To: pietverhaart at bigpond.com; Discussion of biomass cooking stoves 
<stoves at lists.bioenergylists.org>
Sent: Tue, January 25, 2011 12:03:57 AM
Subject: Re: [Stoves] (no subject) [Jatropha cake properties]

On Monday 24 January 2011 23:44:30 Peter verhaart wrote:
> If Jatropha oil is a non drying oil (like castor oil), you are in deep
> oil. If Jatropha oil is a drying oil, you might try using a drying
> accelerator for paint and/or place the briquettes in an oven.

Hi Peter

I don't know whether Jatropha is a drying oil. I believe linseed is and 
cotton rags allowed to dry with linseed on then heat up and can self 
ignite, Does anyone know the mechanism for this?

AJH

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