Wallace rapid plasticity

NR, as a specific example is often selected according to its oxidation resistance. This may be assessed by measurement of its plasticity retention index (where Wallace rapid plasticity is measured before and after heat ageing at 140 °C, e.g., ASTM D3194-99 [21]). The drop in plasticity found after ageing is an indicator of this polymer s oxidation resistance. 

Wallace rapid plasticity, minimum initial value (Po) 30 30 30 30... 

Nevertheless, some residual crosslinking reaction continues during the early stages of mastication. By following changes in Wallace rapid plasticity with mastication time, initial increases in viscosity are observed for natural polymers (Fig. 2). These differences account for the longer band formation times observed with natural rubber on the open mill. 

Fig. 2. Change in Wallace rapid plasticity with time during open mill polymer mastication (mill friction ratio 1 1 2, starting temperature 40°C).

An instrument for measuring the plasticity of an elastomer, e.g., Wallace Rapid Plastimeter Plastisol... 

ISO 200722 specifies a rapid plastimeter procedure using an instrument with one platen either 7.3, 10 or 14 mm diameter and the other platen of larger diameter than the first (i.e. disc type method). The size of the first platen is chosen such that the measured plasticity is between 20 and 85. The test piece is cut with a punch which will give a constant volume of 0.40 0.04 cm, the thickness being approximately 3 mm and the diameter approximately 13 mm. The test piece is pre-compressed to a thickness of 1 0.01 mm within 2 sec and heated for 15 sec. The test load of 100N is then applied for 15 sec when the test piece thickness is measured. The usual temperature of test is 100°C and the result is expressed as the thickness of the test piece at the end of the test in units of 0.01 mm and called the rapid plasticity number. The Wallace rapid plastimeter, and presumably other commercial instruments, conform to this specification but it would be sensible to check with the manufacturers. A technically identical method is given in BS 903 Part A5923. 

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