Synergism between hydrotalcite and silicate‐modified expandable graphite on ethylene vinyl acetate copolymer combustion behavior

Abstract

Influence of independent Mg-Al-layered double hydroxide (LDH), silicate modified expandable graphite (EG), mixture of LDH and EG at various ratios on ethylene vinyl acetate copolymer (EVA) combustion behavior and thermal stability was detected in sequence through the limiting oxygen index (LOI), vertical combustion (UL-94) level, microscale combustion calorimeter (MCC) tests and thermal gravimetric/differential thermal gravimetric (TG/DTG) analysis. Results show that the 30 wt % LDH can improve the LOI of 70EVA/30LDH to 27.0%, but the combustion accompanies with serious melt-dropping. While, the same amount of the EG can increase the LOI, UL-94 level to 28.5%, V-0 respectively. However, the combination of LDH and EG can further enhance the 70EVA/20LDH/10EG flame retardancy, it presents the LOI of 29.7%, UL-94 level of V-0, and total heat release of 29.5 kJ g 21 . The excellent flame retardancy is attributed to its compact residue. Compared with residue mass, the residue compactness plays a more important role in improving flame retardancy.

Expandable Graphite for Flame Retardant PA6 Applications

“…This effectively slows or stops fire spread by impeding thermal heat feedback from the flame to the substrate, migration of oxygen to the surface, and mass transfer of low molecular weight decomposition products to the gas phase. [ 5 ] Despite proven efficiency as a flame retardant in various thermoplastic polymer systems (e.g., PP [ 6 , 7 , 8 , 9 , 10 , 11 , 12 ], PE [ 13 , 14 , 15 , 16 ], ABS [ 17 ], EVA [ 18 , 19 ], PET [ 20 , 21 ], PS [ 22 ], PVC [ 23 ]), the industrial use of expandable graphite is limited to niche applications. One of the reasons is the low temperature stability of commercially available expandable graphite grades, with maximum processing temperatures typically lower than 230 °C; only some literature is available focusing on this topic [ 20 ].…”

Modified expandable graphite as an effective flame retardant for LLDPE/EVA composites filled with Mg(OH)2/Al(OH)3

“…During the UL-94 test, the composites containing MEG form a worm-like structure, which prevents air and combustible gases from entering the underlying substrate. 30 The photographs of the samples obtained from LOI and UL-94 test are displayed in Figure 3. The pure LLDPE/EVA burns sharply with dripping severely, which is dangerous and easy to cause "secondary combustion."…”

“…During the UL-94 test, the composites containing MEG form a worm-like structure, which prevents air and combustible gases from entering the underlying substrate. 30…”

Synergistic Effect of Modified Expanded Graphite and Zinc Borate on the Flammability, Thermal Stability and Crystallization Behavior of LLDPE/EVA Composites with Mg(OH)2/Al(OH)3

“…It is that the quality of char layer is not good enough to protect the underlying matrix. With increasing the MEG content, the burning of the E-G three samples gradually becomes slowly and worm-like formed on the surface, which can block air and combustible gases from entering the underlying matrix to act as fire-retardant effect [24].…”