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Stillingia oil

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Stillingia oil is gained by solvent from the plant seeds of the Sapium family such as, Sapium sebiferum (Chinese tallow tree) and Sapium discolor (Mountain tallow tree). It is used as a drying agent in paints and varnishes. It dries readily on a glass plate in 4–6 hours. Stillingia oil's properties, such as a high iodine value, and chemical components classifies it as a drying oil. Why it has the appropriate properties to be a drying oil remain disputed. Following are three different arguments from J. Devine (1950), A. Crossley with T.P. Hilditch (1953), and V. C. Batterson with W. M. Potts (1938):

  1. "The literature analysis of stillingia oil, which has recently been shown to contain an abnormal spectroscopic component, does not accord with its excellent drying properties. In a re-examination of a number of commercial samples the abnormal component is shown to be 2: 4-decadienoic acid, present to the extent of 3% to 6%, and hitherto undetected in naturally occurring oils. This component behaves anomalously during analysis by alkali isomerization, but the effect can be allowed for and the remaining components of the oil are estimated approximately at 40% linolenic, 25% to 30% linoleic, 20% oleic and 9% saturated acids, together with a little conjugated triene acid of the elaeostearic type which is possibly an adulterant. The 2: 4-decadienoic acid may play a relatively prominent part in the drying and polymerizing properties of stillingia oil."
  2. "The glycerides of stillingia oil have been studied by resolution into a series of fractions by crystallization from acetone. Deca-2: 4-dienoic acid, which forms about 8% (mol.) of the total acids of the oil, is shown to occur almost exclusively as monodecadienoic di-C18-polyethenoid glycerides with the short-chain acyl group in the β-or symmetrical position. The chief constituents of the oil are linoleodilinolenins, decadienolinoleolinolenins and decadieno-dilinolenins, with lesser proportions of saturated-linoleolinolenins, saturated-dilinolenins, oleolinoleolinolenins and oleodilinolenins. Owing to the presence of the decadienoic acid (8%) with linolenic acid (51%) and linoleic acid (22%), the total proportion of tripolyethenoid glycerides (95%) in the oil is greater than in linseed oil and comparable with that in conophor oil. This accounts for the relative behaviour of stillingia oil and linseed oil as drying oils in paint films."
  3. "The sample of Chinese oil gave an iodine number of 169.0, a saponification value of 206.2, and a thiocyanogen value of 100.7, and was found to contain the following percentages of acids: Oleic 10.4%, linoleic 49.9%, linolenic 25.4%, palmitic 5.89%, stearic 2.64% and arachidic acid 0.14%. From the characteristics and composition of these samples, it would appear that stillingia is suitable for use in the manufacture of paints and varnishes."

Converging information include 25.4 to 40% linolenic acids, 25% to 51% linoleic acids, 10.4 to 22% oleic acids and 9% saturated acids. However J. Devine attributes the drying properties of stillingia oil to 2: 4-decadienoic acid (1950). However, A. Crossley with T.P. Hilditch point out that tripolyethenoid glycerides is the main component (1953), and V. C. Batterson with W. M. Potts(1938) came to conclusion that all of stillingia oil's properties add up to be good drying oil properties.

Commercial stillingia oil has frequently been found to contain up to 1% of elaeostearic acid which can be also found in Sabium dicolor up to 1%. Tung oil has which is also a drying oil has 82.0% alpha-Eleostearic acid, so it is possible that factories containing both substances may end up with contamination.

References

Stillingia oil Wikipedia


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