Flame retardant high density polyethylene optimized by on-line ultrasound extrusion

A Systematic Investigation on the Influence of Intumescent Flame Retardants on the Properties of Ethylene Vinyl Acetate (EVA)/Liner Low Density Polyethylene (LLDPE) Blends

Because of their high filler loadings, commercial-grade clean flame-retardant materials have unstable mechanical properties. To address this issue, intumescent polymers can be used to develop clean flame retardants with very low levels of smoke and toxicity generation. An intumescent flame retardant (IFR) system composed of red phosphorus (RP), zinc borate (ZB), and a terpolymer of ethylene, butyl acrylate, and maleic anhydride (EBM) was used to prepare EVA (ethylene-vinyl acetate) and EVA/LLDPE (linear low-density polyethylene) composites; their mechanical and flammability properties were systematically investigated. The limiting oxygen index (LOI) of the EVA/LLDPE (as base material) composite containing RP and ZB mixed with nonhalogenated flame retardant, mainly magnesium hydroxide (MH) and coadditives, including processing aids and thermal stabilizers, was established. RP was found to have little effect on the tensile properties of EVA/LLDPE 118W/120 phr flame-retardant (MH + RP) composites. There was a minute difference in the effective trend of RP between tensile strength and elongation at break. Following the addition of ZB, the elongation at break of the composites gradually decreased with increasing RP content and then leveled off when the RP content was over 10 phr. Mechanical properties (elongation at break and tensile strength) can be best maintained at below 10 phr content of RP. The mechanical properties decreased with lower amounts of EBM content. In addition, flame retardancy increased when the EBM content decreased. The findings further revealed that MH and RP have poor compatibility, yielding poor mechanical properties. The LOI greatly increased with RP content, even though the total content of flame retardants (main + intumescent flame retardant) was the same in all formulations. Only over 5 phr RP content formulations passed V-0 of the UL-94 test. When under 5 phr, the RP content formulations did not pass V-0 of the UL-94 test.

The Flame Retardancy of Polyethylene Composites: From Fundamental Concepts to Nanocomposites

Polyethylene (PE) is one the most used plastics worldwide for a wide range of applications due to its good mechanical and chemical resistance, low density, cost efficiency, ease of processability, non-reactivity, low toxicity, good electric insulation, and good functionality. However, its high flammability and rapid flame spread pose dangers for certain applications. Therefore, different flame-retardant (FR) additives are incorporated into PE to increase its flame retardancy. In this review article, research papers from the past 10 years on the flame retardancy of PE systems are comprehensively reviewed and classified based on the additive sources. The FR additives are classified in well-known FR families, including phosphorous, melamine, nitrogen, inorganic hydroxides, boron, and silicon. The mechanism of fire retardance in each family is pinpointed. In addition to the efficiency of each FR in increasing the flame retardancy, its impact on the mechanical properties of the PE system is also discussed. Most of the FRs can decrease the heat release rate (HRR) of the PE products and simultaneously maintains the mechanical properties in appropriate ratios. Based on the literature, inorganic hydroxide seems to be used more in PE systems compared to other families. Finally, the role of nanotechnology for more efficient FR-PE systems is discussed and recommendations are given on implementing strategies that could help incorporate flame retardancy in the circular economy model.

Improving Mechanical Properties and Reaction to Fire of EVA/LLDPE Blends for Cable Applications with Melamine Triazine and Bentonite Clay

The high flame-retardant loading required for ethylene-vinyl acetate copolymer blends with polyethylene (EVA-PE) employed for insulation and sheathing of electric cables represents a significant limitation in processability and final mechanical properties. In this work, melamine triazine (TRZ) and modified bentonite clay have been investigated in combination with aluminum trihydroxide (ATH) for the production of EVA-PE composites with excellent fire safety and improved mechanical properties. Optimized formulations with only 120 parts per hundred resin (phr) of ATH can achieve self-extinguishing behavior according to the UL94 classification (V0 rating), as well as reduced combustion kinetics and smoke production. Mechanical property evaluation shows reduced stiffness and improved elongation at break with respect to commonly employed EVA-PE/ATH composites. The reduction in filler content also provides improved processability and cost reductions. The results presented here allow for a viable and halogen-free strategy for the preparation of high performing EVA-PE composites.

Study of a novel co-rotating non-twin screw extruder in processing flame retardant polymer materials

A thorough study was carried out to investigate the priority of a novel co-rotating non-twin screw extruder (NTSE) over a traditional twin screw extruder (TSE) in the mixing process of halogen-free intumescent flame-retardant acrylonitrile-butadiene-styrene (ABS) composites. The homogeneity of the flame-retardant additives of the composites processed by NTSE and TSE under the same operating conditions was characterized by using mechanical performance properties, limiting oxygen index values, UL-94 tests, and thermogravimetric analysis. All the results suggested that NTSE could achieve better mixing of the flame-retardant additives in the polymer matrix than TSE, which was further clarified by the scanning electron microscope pictures.