Experiment on the lubricating effect of calcium stearate

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The role of calcium stearate in PVC-U blends. Theoretically, calcium stearate in PVC-U blends acts as both a metal soap heat stabilizer and an internal lubricant. So what is the specific role of calcium stearate in the blends used in our door and window profiles? To this end, the author conducted tests on it using a torque rheometer. Experimental procedure: Basic formula: PVC 100 parts (by weight), CPE 11.53 parts, ACR 2.27 parts, titanium dioxide 4.0 parts, stabilizer 3.67 parts, calcium carbonate 13.33 parts, and an appropriate amount of calcium stearate. Preheat the high-speed mixer to 50°C, and add the sample materials in proportion. Start the motor at a speed of 2000 rpm/min; once the temperature of the material in the mixer reaches 105°C, discharge the material and cool it to room temperature in the air. The mixer experiment was conducted after 24 hours of placement. The temperatures in zones 1 to 3 of the mixer are 180°C, the rotor speed is 35 rpm/min, the weight of the material used in the test is 62 g, and the test duration is 10 minutes. The experimental data from the torque rheometer are as follows: Calcium stearate, amount used; plasticization peak torque in Nm; equilibrium torque in Nm; plasticization temperature in °C; plasticization time in seconds; thermal stability time in minutes:seconds. For 029, it is 29.252, 22.431, 87.1363; for 10:13, it is 130.129.252, 22.1185.0861; for 10:21, it is 100.229.382, 22.43186.4870.510:01, it is 10.328.752, 21.93186.4862; for 9:30, it is 0.429.221.4184.756.59; for 9:47, it is 0.528.6020.7185.5481; for 10:42, it is 0.728.7821.23184.4846; for 13:26, it is 1.028.8321.33183.7544; for 17:11, it is 1.528.6321.3183.4345; for 18:10, it is 2.529.4821.4177.0323; for 25:40, it is … From these experimental data, it can be seen that as the amount of calcium stearate used increases, the torque at the plasticization peak does not decrease significantly, while the equilibrium torque decreases slightly. We know that the plasticization peak is proportional to the melt viscosity, which indicates that calcium stearate does not significantly reduce the melt viscosity in the current formulation. Since internal lubricants can reduce the viscosity of the melt in a blending system, the author believes that in the current formulation of this blending system, calcium stearate does not conform to the theory according to which internal lubricants are used to lower melt viscosity. The author believes that the reason for this may be that the calcium carbonate particles in the system encapsulate calcium stearate, making it difficult for them to interpenetrate between the PVC particles and thus preventing a reduction in the intermolecular forces within PVC. In terms of plasticization time, a calcium stearate content of up to 0.3 parts had no significant effect on the fusion time. At that time, when the amount of calcium stearate used exceeded 0.3 parts, the plasticization time was **reduced**, which is in line with the definition of calcium stearate as an internal lubricant – namely, an internal lubricant can facilitate plasticization and shorten the plasticization time. Furthermore, in terms of the thermal stability of the blend system, when the amount of calcium stearate exceeds 0.5 parts, the thermal stability of the system **increases**. As can be seen from metal soap stabilizers, calcium stearate is capable of enhancing the thermal stability of the system, which is consistent with theoretical predictions. Through experiments, we have understood the role of calcium stearate in blend formulations. The experimental data obtained can help us adjust the amount of calcium stearate in future formulation designs according to actual needs, enabling more targeted approaches and reducing unnecessary complications in formulation development.