Plastics Technology - Dedicated to improving Plastics Processing.
Issue link: http://pty.epubxp.com/i/421920
These items are shown in Fig. 4. The output of this process is a kinetic model that can then be used to make predictions for the rate of the reaction. The tables, which can be customized, are shown in Fig. 5. Now that we have the kinetic model of the CFA reaction, we can apply the information to real-world processes. The model makes the assumption that the temperature is constant, and we know that isn't true in real-world situations, but we can use a reasonable temperature estimate that still gives us valuable information. SITUATION 1: REACTING FROM SHEAR ALONE Let's take a hypothetical example and assume that a processor is extruding polyethylene. The processor measures the melt temperature across all of the zones, and while they vary slightly overall, the average temperature is about 180 C (355 F) and the residence time of the material in the barrel is about 4 min. In looking at the kinetic model we can fnd the column for 180 C and move down until we hit a value of 4 min. In the example from Fig. 5, that value is between 2% and 5%. This means that the processor can expect 2-5% of the azo to activate from the temperature of the polymer melt. Now the processor would immediately notice that it is getting a lot more than 5% activation and that these numbers don't make sense. What these numbers tell you are that the melt temperature isn't activating your CFA—shear is, and there's a good chance it isn't activating all of it. A number of important conclusions can be made from this information: 1. The CFA is primarily reacting through shear. 2. You likely have some CFA left over that isn't being activated. 3. Anything that impacts shear will impact the amount of CFA activation, such as: Five separate tests were conducted on a DSC with the CFA, heating it from room temperature well through its degradation point. An azo-based foaming agent, which has only a single decomposition step, was used. The fve tests are identical except for the rate at which the temperature increases. The fve tests are then cropped to exclude any data that isn't associated with the degradation. At this point the software performed a series of complicated calculations using patented algorithms to determine the activation energy of the reaction as it progressed to completion. Those two items are shown here. It is important to understand how choices of CFA can affect limitations on processing temperatures, line speeds, or cycle times. FIG 4 Five DSC Curves of Azodicarbonamide Heated at Varying Temperature Rates °Celcius Percentage Activation Energy 100 kJmol^-1 t n A 100 mW 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 n g i [] CHEM0001 Azodicarbonamide 5C/min [] CHEM0001 Azodicarbonamide 5C/min, 4.2900 mg [] CHEM0001 Azodicarbonamide 10C/min [] CHEM0001 Azodicarbonamide 10C/min, 3.0900 mg [] CHEM0001 Azodicarbonamide 25C/min [] CHEM0001 Azodicarbonamide 25C/min, 3.0400 mg [] CHEM0001 Azodicarbonamide 50C/min [] CHEM0001 Azodicarbonamide 50C/min, 2.6800 mg [] CHEM0001 Azodicarbonamide 100C/min [] CHEM0001 Azodicarbonamide 100C/min 3.5600 mg 60 DECEMBER 2014 Plastics Technology PTonline.com T ips & Technique s