title: Analysis of Flame Retardancy in Polymer Blends by Synchrotron X-ray K-edge Tomography and Interferometric Phase Contrast Movies.
abstract: Underwriters Laboratories 94 test bars have been imaged with X-ray K-edge tomography between 12 and 32 keV to assess the bromine and antimony concentration gradient across char layers of partially burnt samples. Phase contrast tomography on partially burnt samples showed gas bubbles and dark-field scattering ascribed to residual blend inhomogeneity. In addition, single-shot grating interferometry was used to record X-ray movies of test samples during heating (IR and flame) intended to mimic the UL 94 plastics flammability test. The UL 94 test bars were formulated with varying concentrations of a brominated flame retardant, Saytex 8010, and a synergist, Sb2O3, blended into high-impact polystyrene (HIPS). Depending on the sample composition, samples will pass or fail the UL 94 plastics flammability test. Tomography and interferometry imaging show differences that correlate with UL 94 performance. Key features such as char layer, gas bubble formation, microcracks, and dissolution of the flame retardant in the char layer regions are used in understanding the efficiency of the flame retardant and synergist. The samples that pass the UL 94 test have a thick, highly visible char layer as well as an interior rich in gas bubbles. Growth of gas bubbles from flame-retardant thermal decomposition is noted in the X-ray phase contrast movies. Also noteworthy is an absence of bubbles near the burning surface of the polymer; dark-field images after burning suggest a microcrack structure between interior bubbles and the surface. The accepted mechanism for flame retardant activity includes free radical quenching in the flame by bromine and antimony species. The imaging supports this as well as provides a fast inspection of other parameters, such as viscosity and surface tension.
authors: Department of Chemistry, Louisiana State University , 232 Choppin Hall, Baton Rouge, Louisiana 70803, United States.
authors: Mutairu B
authors: MB
authors: Olatinwo
authors: Center for Advanced Microstructures & Devices, Louisiana State University , 6980 Jefferson Highway, Baton Rouge, Louisiana 70806, United States.
authors: Kyungmin
authors: K
authors: Ham
authors: Albemarle Corporation, Process Development Center, P.O. Box 341, Baton Rouge, Louisiana 70821, United States.
authors: Jonathan
authors: J
authors: McCarney
authors: Advanced Photon Source, Argonne National Laboratory , Building 401, 9700 South Cass Avenue, Argonne, Illinois 60439, United States.
authors: Shashidhara
authors: S
authors: Marathe
authors: Center for Computation and Technology, Louisiana State University , 340 East Parker Boulevard, Baton Rouge, Louisiana 70808, United States.
authors: Jinghua
authors: J
authors: Ge
authors: Department of Mechanical and Industrial Engineering, Louisiana State University , Baton Rouge, Louisiana 70803, United States.
authors: Gerry
authors: G
authors: Knapp
authors: Department of Chemistry, Louisiana State University , 232 Choppin Hall, Baton Rouge, Louisiana 70803, United States.
authors: Leslie G
authors: LG
authors: Butler