Solid State Batch Microcellular Foaming Process

2 Solid-State Batch Microcellular Foaming Process 

Martini and coworkers developed the two-stage batch microcellular foaming process using three different steps (i) formation of a gas/polymer solution, (ii) cell nucleation, and (iii) cell growth and stabilization [16]. 

1 Formation of Gas/Polymer Solution The formation of gas/polymer solution is achieved by saturating the 

The formation of a gas/polymer solution depends on gas absorption and diffusion into the polymer matrix, which can be affected by the nature of the polymer matrix (amorphous versus semicrystalline), gas type, saturation pressure, and temperature [44, 45]. The sorption behaviors of gas in polymers can be explained by Henry s law (gas solubility) and Pick s law (gas diffusivity), as shown in the following equations [46]  

Equation 17.4 shows that the concentration of gas in the polymer is directly proportional to the gas pressure. Increasing the pressure can increase the gas absorption and diffusion to facilitate the formation of a gas/polymer single-phase solution. Increasing the saturation temperature increases the gas diffusion rate into the polymer. However, this decreases the gas concentration at a specific pressure. 

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An alternative process for the production of PVC foam using microcellular foam technology, not requiring impact modifier, for thin wall profile (280) has been reported. Proof of concept experiments confirm the satisfactory solid state extrusion of PVC pellets, prefoamed in a batch solid state microcellular process (109). 

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