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How Characterizing and Modeling Chemical Foaming Agents Can Help Your Process Chemical Foaming Agents (CFAs) come in a variety of types. Some produce exothermic reactions, some produce endothermic reac- tions, some have a single com- ponent, while others are mix- tures of many; and the temperatures at which they activate can vary. Despite these variables, all CFAs have one thing in common: The molecule is designed to decompose at a specifc temperature and to produce a gas as part of that decomposition. This process efectively turns your processing machinery into a "chemical reactor" where time and temperature can infuence the activation of the CFA. This article will show how diferent testing techniques can be used to characterize performance of a CFA and determine if there is any residual unreacted CFA in fnished products. We will also explain a reaction modeling technique that provides informa- tion that can be applied to the design of a process. Knowing how much CFA is reacting in your process can be important for a number of reasons, depending on individual circumstances: • The CFA may be expensive and you would want to make sure you aren't wasting the additive unnecessarily. • Perhaps the end customer doesn't want unreacted CFA leaching out of the product for regulatory reasons. In order to determine how much of the CFA remains unre- acted in the product, a thermogravimetric analyzer (TGA) is used. The frst step is to take the CFA all by itself and analyze it in the TGA. This is usually done by heating approximately 10 mg of the material from around 50 C (120 F) up to well past the plastic resin's processing temperature at a rate of 10° C (18° F)/min. Depending on the CFA, you may have a single gas-generation event or multiple events. For the purposes of this example, we'll deal with CFAs that have a single degradation event. An example of a typical TGA thermogram from this test is shown in Fig. 1. The purpose of this test is to identify the tempera- ture at which the CFA activates so that the transitions in other tests can be positively identifed as originating from the CFA. The next step is to test the complete raw-material formulation to measure the amount of gas that the CFA releases. It's important to test the CFA in the presence of the other materials because components of the formulation can change the amount of gas released by some CFAs. Ideally, the individual components should be measured directly into the test crucible and not premixed and transferred so that the exact mass of the CFA is known. However, in some cases this may not be possible and you will have to make the assumption that your premixed/compounded By Joel Lischefski and Dan Clark Teel Analytical Laboratories WHAT YOU WILL LEARN 1. CFA COMMONALITY: All decompose at a specifc temperature and produce gas as part of that process. 2. HOW MUCH CFA IS REACTING: You'll need to know this to avoid CFA waste and possible leaching. 3. HOW TO MODEL THE CFA REACTION: CFA choice can afect processing temperatures, line speeds, cycle times. 4. PROCESSING: Apply model to real-world processing. Knowing ahead of time what will happen when your CFA produces gas can help you design or improve your process to boost quality and cost effectiveness. TGA Thermogram of a CFA Onset Temp = 150C Chemical Foaming Agent Degradation Event FIG 1 TGA thermogram tests identify the temperature at which the CFA activates so that the transitions in other tests can be positively identifed as originating from the CFA. 58 DECEMBER 2014 Plastics Technology PTonline.com Tips and Techniques