Blowing agents, analysis

The styrene content affects the crystallinity of ESI (131) for >50% styrene the copolymers are amorphous. As the styrene content is increased from 50 to 70% styrene the Tg increases from -15 °C to 20 °C. Low density foams were made (8) from a blend of 50% of various ESI polymers, 33% of EVA and 17% of azodicarbonamide blowing agent. Thermal analysis showed that the blends, with an ESI having approximately 70% styrene, had a Tg in the range 22 to 30 °C. Dynamic mechanical thermal analysis (DMTA) traces (see Section 5.1) show that these blends... 

Journal of Cellular Plastics 36, No.4, July/Aug.2000, p.310-26 PREDICTING THE PERFORMANCE OF CHEMICAL BLOWING AGENTS USING THERMAL ANALYSIS TECHNIQUES Dixon D Martin P J Harkin-Jones E Belfast,Queen s University... 

The density of chemicaUy-blown LDPE foam was altered by varying the amount of blowing agent, degree of crosslinking of the polymer, and the foam expansion temperature. A theory was proposed for the equilibrium density, based on the gas pressures in a Kelvin foam structure, and a rubber-elastic analysis of the biaxial stretching of the cell faces. 20 refs. 

Blowing agents include azodicarbonamide, azodiisobutyronitrile, etc. Antistatic agents include quaternary ammonium compounds, etc. With the added complexity due to the presence of these compounds, the analysis of polymeric blends and of practical objects made from polymers containing additives is not always simple. 

Prasad and Shanker [95] used a differential scanning calorimeter (DSC) for the quantitative analysis of chemical blowing agents such as azodicarbonamide (azo) in commercial formulations. The DSC results were comparable to those obtained by the commonly used evolved gas analysis (EGA) technique. Advantages of DSC are ease of operation. 

Several qualitative and quantitive techniques have been evolved to characterise blowing agents in polymers. These methods include EGA [28-30], differential thermal analysis (DTA) [31, 32] and TGA [31, 32]. The EGA technique limitations are well-described by Jaafer and Sims [28] where rate of gas evolved is dependent on type of additive and... 

DSC can be exploited for quantitative analysis of chemical blowing agents (CBAs) in commercial foam formulations [106]. The rationale behind this is that decomposition of azodicarbonamide is an exothermic process and that the heat of decomposition, A//d, can be measured quantitatively by DSC. 

Taylorl ] concluded from the thermal analysis study, that the understanding of the mechanism of intumescent coatings increased, and that it was possible to optimize the mixing ratios in terms of minimizing weight loss. Furthermore, the results proved that the melamine was present not only as a blowing agent (spumific), but also as a contributor to the chemical composition of the char. 

There are two ways plastic materials can be identified. The first technique is simple, quick, and inexpensive. It requires very few tools and little knowledge of plastic materials. The second approach is to perform a systematic chemical or thermal analysis. The latter technique is very complex, time-consuming, and expensive. The results can only be interpreted by a person well-versed in polymer chemistry. Plastic materials are often copolymerized, blended, and modified with filler or compounded with different additives such as flame retardants, blowing agents. 

The reactivity of the chemical blowing agent type can make analysis difficult (e.g., they will decompose in the injection port of a GC-MS instrument), and the approach that is used is to indirectly identify them by the determination of breakdown fragments. The GC-MS instrument is the best choice for this and a library of typical breakdown fragments is required. 

---