Bimodal cell distributions in foaming of olefin block copolymers using high-throughput experimentation

We present a nonlinear rheological characterization and supercritical carbon dioxide foaming of Olefin Block Copolymers (OBC), aiming at the investigation of the effect of polymer structure on the melt fracture and the processability. We address the challenge of obtaining reliable measurements with sample masses of the order of a milligram, in nonlinear rheological regimes and foaming processes. We selected as model system a set of three polymers that have different length of the soft blocks, ceteris paribus. The nonlinear rheological experiments and the foaming were performed with a recently developed microrheometer, μ CR . The results show that, when suitable protocols and careful running conditions are chosen, nonlinear rheological behavior and foaming can be obtained with good accuracy and reproducibility. The rheological results revealed that the critical stress for the melt fracture of the OBC samples varies between 400 and 800 kPa and it is tightly connected to the molecular architecture. We found that the onset of the melt fracture in OBC increases as function of the length of the soft block. We explained that results considering the different wetting properties of the three samples. The foaming results show that it is possible to produce microcellular foams in a broad foaming window from 110 to 140 ∘ C, and those foams have a randomly short range ordered bimodal cell size distribution that depends and can be controlled by changing the foaming temperature and the length of the soft block. This result has strong implications on the processability of the polymer, in processes such as, extrusion, injection molding and film blowing and for the manufacturing of complex hierarchical structures with photonic properties. SEM pictures of foamed polymers A, B and C. • Pioneering High-Throughput Foaming : novel approach to rapidly create tailored polymeric foams using minimal material quantities. • Tailored Bimodal Foam Architecture : Foams with two distinct cell sizes for optimized properties and functionalities. • Predictive Polymer Processing : Innovative method to predict and control melt fracture. • Unraveling Foam Formation Mechanism : Theoretical relationship between polymer composition and foam structure. • Enabling Customized Foam Design : Creation of foams with precisely engineered properties.