The influence of reactive compatibilization on the foaming behavior of thermoplastic olefin (TPO) blends of polypropylene and a metallocene catalyzed ethylene octene copolymer was investigated. A batch setup was used to foam the samples using carbon dioxide as blowing agent. A microscopic method based on the Back Scattering Electron Imaging (BEI) technique was used to determine the respective localization of the bubbles. The bubbles were preferentially formed in the dispersed elastomeric domains. The addition of a compatibilizer resulted in enhanced viscoelastic properties as well as increased strain hardening behavior. The results showed that the reactive compatibilization can significantly improve the melt foamability through control of the microstructure as well as improvement of the rheology. Finally, a chain extender (CE), Joncryl ADR, was added to a polylactide (PLA). The steady and transient rheological properties of the neat PLA and CE-treated PLAs revealed that the introduction of the CE profoundly affected the melt viscosity and elasticity. The linear viscoelastic properties of CE-enriched PLAs suggested that a long chain branching (LCB) structure was formed from the reaction with the CE. LCB-PLAs exhibited an increased viscosity, more shear sensitivity, and longer relaxation time in comparison with the linear PLA. The LCB structure was also found to affect the transient shear stress growth and elongational flow behavior. Batch foaming of the linear and LCB-PLAs was also examined at foaming temperatures of 130, 140, and 155 ᵒC. The LCB structure significantly increased the integrity of the cells, cell density and void fraction
