Revision as of 11:18, 9 April 2013

The penetration test is the measures of the depth to which a needle with a definite top load penetrates the wax sample. Where the conditions of test are not specifically mentioned, the load, time, and temperature are understood to be 100 g, 5 sec, 25° respectively, and the units of penetration to indicate tenths of a millimeter. The penetration test is particularly well adapted for microcrystalline waxes, and is more reliable than the durometer test in determining hardness ^[1]. A hard wax has a low penetration, whereas a soft wax has a high penetration.

Methods

This test provides an estimate of the consistency of waxes and their molecular characteristics. It has been reported that the needle penetration on paraffin waxes increases with the increase of iso-and cyclo-paraffin^[2].

Needle Penetration (ASTM D-1231)

This test method covers the empirical estimation of the consistency of waxes derived from petroleum by measurement of the excent of penetration of a standard needle. This test method is applicable to waxes having a penetration of not greater than 250.

Before testing make sure the equipment is balanced, using the screws adjusters and taking as a reference the bubble. Heat the wax sample to approximately 17°C above its congealing point. In the test room or cabinet maintained at 23.9 ± 2.2 °C, place the brass plate on two corks (No. 16 or 18 recommended) and wet the upper surface of the plate with a mixture of equal volumes of glycerin and water. Place the test specimen container on the plate and then pour the melted wax into it in such a way that a convex meniscus is formed. Allow the container and contents to cool in the room at 23.99 ± 2.2 °C for 1 h. Condition the specimen in the bath at the test temperature within 0.1°C for 1h.

Place the specimen container on the perforated test shelf with the smooth wax surface that had contacted the brass plate at the top. Place a 50 g weight above the penetrometer needle. Observe that the release mechanism does not drag on the shaft and that indicator on the scale in the “zero” position. Then, by means of the slow-motion adjustment, bring the needle tip to just touch the surface of the specimen, watching the reflection of the needle tip as an aid to accurate setting. After 5 min, release the needle shaft and hold it free for 5 s, timing this interval automatically or with a stop watch graduated to 0.1 s. Then gently depress the indicator shaft until is stopped by the needle shaft and read the penetration from the indicator scale. Record as a single test value the average scale reading for the four penetrations on the prepared specimen and report to the nearest 0.1mm ^[3].

Cone Penetration (ASTM D 937)

This test method covers measuring with a penetrometer the penetration of petrolatum as an empirical measure of consistency.

Melt the sample at 82 ±2°C, fill the containers to within 6 mm of their rims. Allow the filled container to cool in a location free from drafts and at a temperature controlled to 25 ±2°C for 16 to 18 h. Then cover and place the samples in the water bath for 2 h to bring the temperature to 25 ± 0.5°C before testing. Place the can of petrolatum on the penetrometer table, so located that the tip of the penetrometer cone is 25 to 40 mm in from the rim of the container. Observe that the cone is in its “zero” position and adjust either the indicator assembly or the table, dependent on the type of instrument, until the tip of the cone just touches the surface of the sample. Watching the shadow of the tip is an aid to accurate setting. Finally, quickly release the plunger and hold for 5 s. Read the total penetration from the scale. Make at least three determinations.

References

1. ↑ Warth, A. H.; The Chemistry and Technology of Waxes. Reinhold Publishing Corporation. Second Edition, p. 612 – 614
2. ↑ Zaky, M.T. (2005) A Study on the Dependence of Penetration on the Physical and Molecular Characteristics of Paraffin Waxes. Petroleum Science and Technology, Vol. 23, p 1381–1392
3. ↑ Annual Book of ASTM-Standards (American Society for Testing and Materials), Petroleum Products, Lubrications. (1999). West Conshohocken, Sect. 5