Thermo-oxidative degradation behaviors of expandable graphite-based intumescent halogen-free flame retardant LLDPE blends

Morphology, mechanical and thermal oxidative aging properties of HDPE composites reinforced by nonmetals recycled from waste printed circuit boards

In this study nonmetals recycled from waste printed circuit boards (NPCB) is used as reinforce fillers in high-density polyethylene (HDPE) composites. The morphology, mechanical and thermal oxidative aging properties of NPCB reinforced HDPE composites are assessed and it compared with two other commercial functional filler for the first time. Mechanical test results showed that NPCB could be used as reinforcing fillers in the HDPE composites and mechanical properties especially for stiffness is better than other two commercial fillers. The improved mechanical property was confirmed by the higher aspect ratio and strong interfacial adhesion in scanning electron microscopy (SEM) studies. The heat deflection temperature (HDT) test showed the presence of fiberglass in NPCB can improve the heat resistance of composite for their potential applications. Meanwhile, the oxidation induction time (OIT) and the Fourier transform infrared (FTIR) spectroscopy results showed that NPCB has a near resistance to oxidation as two other commercial fillers used in this paper. The above results show the reuse of NPCB in the HDPE composites represents a promising way for resolving both the environmental pollution and the high-value reuse of resources.

The synergism between melamine and expandable graphite on improving the flame retardancy of polyamide 11

Expandable graphite (EG) has attracted more and more attention in fire science society due to its excellent char-forming ability, however, it cannot meet commercial flame-retardant requirements because of the low intensity of the char. This work reported our very recent efforts on improving the char quality of EG by introducing melamine (MEL) in order to enhance the fire resistance and thermal stability of polyamide 11 (PA 11) composite. The flammability characterized by limiting oxygen index, UL-94 vertical burning, and cone calorimeter (cone) tests shows that the presence of both EG and MEL can significantly improve the flame retardancy and thermal stability of PA 11 composites. The scanning electron microscopic analysis shows that EG and MEL are beneficial to form compact char layers that can isolate the matrix from heat and oxygen. It is proposed that the formation of hydrogen bonds between MEL and PA 11 are crucial for improving the flame retardancy of the composites.

Preparation, characterization, and flame retardance of high-density polyethylene/sulfur-free expandable graphite composites

In this work, a hydrothermal method was used to prepare a novel, sulfur-free expandable graphite (EG), which was added to high-density polyethylene (HDPE) to improve the flammability and the dripping behavior of composites. Phosphoric acid (H3PO4) was utilized as the intercalating agent, and potassium permanganate and nitric acid were used as the oxidizing agent. EG was investigated using Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectrometry, energy dispersive spectrometry, and scanning electron microscopy. Thermogravimetric analysis, the limiting oxygen index (LOI) and UL-94 were used to examine the thermal and flame-retardant properties of the composites. The results demonstrated that the EG composite exhibited much better thermal stability than pure polymer. Additionally, at 30 wt% EG loading, the LOI value of HDPE/ EG fabrication by H3PO4-hydrothermal method (PEG) was 30, and the flammability standard of UL-94 reached the V0 level, verifying that the EG that was prepared using the H3PO4-hydrothermal process can effectively be used in fireproof composites. The tensile modulus of the composites increased with increasing filler content, while the tensile strength decreased. EG enhanced flexural strength and flexural modulus of HDPE composites but not with high EG loading. The impact strength of the composites was diminished due to the incorporation of EG into HDPE matrix.