The test objective is to evaluate the hardness/firmness of Petroleum Jelly using a cone probe according to ASTM Standard method D937-92.
Waxes are organic products synthetically and naturally produced. They generally tend to be softer at higher temperatures and harder at lower (colder) temperatures. Consequently, the "stickiness" and hardness of some waxes will depend upon the temperature. Hard waxes are less sticky and therefore adhesive. By varying the hardness of the wax using different grades of wax, the adhesive nature or traction of the wax can be altered.
Many cosmetic, medical and personal care products contain waxes. The capability of waxes to produce a good lustre, product firmness, along with their moulding properties makes them complimentary to the final texture of the product. Measuring the hardness (firmness) of a wax determines whether a wax of interest will be suitable for a particular product in producing the desired properties.
The standard method D937-92 uses a penetrometer to determine the penetration depth of a standard cone under defined conditions. The CT3 texture analyser has adopted this standard method using the specified parameters as well as providing alternative methods of measurement such as determining the force to penetrate a specified distance. Cone angles can range from 15–90°.
Note: It is recommended that the pre-test speed be the same as or less than the test speed for accurate trigger detection; for example, 2 mm/s test speed will require = 2 mm/s pre-test speed.
Very soft samples will not be able to achieve a 150 g force. In such circumstances, the softest sample should be tested first to determine if the procedure works. A suitable method may need to be developed.
Note: The temperature of the cone must also be at room temperature before commencing the test.
This test measures the distance required to generate a load of 150 g. An alternative method can also be used where the force required to penetrate a specified distance is measured.
The following is a typical TexturePro CT plot. The graph shows the wax hardness of a Petroleum Jelly using a conical probe.
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The graph in Figure 1 shows the hardness of the Petroleum Jelly measured from a 50 ml, 3.5 x 5.0 cm.
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The graph in Figure 2 shows the load versus time for the hardness of Petroleum Jelly.
When a trigger force of 5 g has been attained, the probe proceeds to penetrate the sample until a force of 150 g has been achieved. This is followed by a hold time of 5 seconds before the probe withdraws from the sample at a post-test speed of 10 mm/s. The distance of penetration depends upon the hardness of the sample. A large penetration distance will indicate a soft sample whereas a small penetration distance will indicate a harder sample. The test is useful for comparing the hardness of different waxes in determining the choice of wax for a particular product.
The table below shows the mean values for a Petroleum Jelly tested at multiple sites.