Influence of keratin and DNA coating on fire retardant magnesium hydroxide dispersion and flammability characteristics of PE/EVA blends

Abstract

For the first time the combination of keratin fibers (KF), obtained from poultry feathers, with deoxyribose nucleic acid (DNA) are employed in low-density polyethylene-ethylene vinyl acetate (LDPE/EVA) blends in order to reduce the conventional hydroxide content and enhance the blend flame retardant properties. The combined effect of each filler and the use of maleated polyethylene (PEgMA) as compatibilizer on PE/EVA flame retardant properties was analyzed. DNA by its chemical structure can be considered as an intumescing agent and when it is combined with keratin the char formation is promoted and the flame retardant properties are enhanced. DNA was distributed in specific layers forming a segregated film which resulted in better PE/EVA blend flame retardant properties compared with either DNA deposited simply by compression molding on the material surface or with melt compounding in the bulk. The flame retardant behavior was compared with a reference PE/EVA sample with 55 wt% of Magnesium Hydroxide currently used for wire coatings in the wire and cable industry. The additives combination with DNA deposited as a segregated structure significantly increases the LOI up to 24.5% and reduces the heat release rate by 82% during cone calorimetry tests with very similar flame behavior as the reference sample with 55 wt% magnesium hydroxide loadings. The mechanical properties indicated that DNA has a marked increase in elongation as well as a marked reduction in torque and viscosity indicating that the combination of these additives can improve the mechanical performance, as well as facilitate the melt processing. Most important, the results indicated that the combination of these additives makes it possible to reduce the total Magnesium hydroxide filler content from 55 to 20 wt% to achieve the flame retardant requirements and with enhanced mechanical performance. Thus, this additives combination and this coating methodology provides a promising way to meet the growing demand and stringent requirements for high performance materials with high flame retardant standards using high efficient and green fire retardant coatings.