Preparation Of Triazine Intumescent Flame Retardant Polylactic Acid Composites And Research Of Their Performance

Polylactic acid (PLA) has been widely used in medical, packaging materials, building materials, automotive industries and other fields due to its excellent biocompatibility and mechanical performance. However, the materials is flammable and produce a great deal of dripping during combustion, which easily caused the fire disaster and limited its widely application. Thus, it is very important that the PLA materials was endued the flame retardant properties. The intumescent flame retardant (IFR) has been used in flame retardant PLA materials due to its excellent properties, such as low smoke promotion, non-toxicity and anti-dripping. However, there are some drawbacks including low flame retardant effiency, poor compatibity between flame retardant and PLA matrix, and so on.In this paper, the triazine char foaming agent (CFA) made in our lab was mixed with ammonium polyphosphate (APP) and silicone to prepare (IFR), and the obtained IFR was incorporated into polylactic acid (PLA) to prepare flame retardant PLA materials. The results demonstrated that the samples passed UL-94 V-0 flamability rating and its LOI value reached 33.5% when the loading amount of IFR was 15wt%with the mass ratio of APP/CFA was 5:1. The results of TGA tests revealed that the incorporation of IFR into PLA decreased the initial thermal degradation temperature of materials, but enhanced the residual char at 800 ℃. Cone calorimeter tests showed that the combustion parameters of IFR-PLA, such as HRR and THR, were envidently decreased compared with the pure PLA materials. The introduction of IFR promoted the formation of the compact and continuous char layer with sufficient flame retardant elements of phosphorus, nitrogen and silicon, which prevented the underlying materials from further degradation and combustion. Consequently, the flame retardancy of PLA materials were enhanced.In order to further improve the flame retardant efficiency for IFR-PLA system, Aluminum hypophosphite (AHP) with excellent flame retardant effect in gas phase was selected and combined with IFR to flame retardant PLA materials. The test results indicated that the PLA/IFR/AHP composites passed UL-94 V-0 flamability rating and LOI value reached 31.2% when the total loading amount of flame retardant was only 9 wt% with the mass ratio of IFR/AHP was 6:1. The fact domonstrated AHP and IFR presented an evidently synergistic effect for flame retardant PLA materials. The results of TGA revealed that the maximum thermal degradation rate was reduced and the residual char at 800 ℃ was enhaced due to the incorporation of IFR/AHP into PLA compared with the same amount loading of IFR alone. Cone tests revealed the combustion paremeters of PLA/IFR/AHP composites decreased compared with PLA/IFR system. The char layer of PLA/IFR/AHP system presented more continuous and compact after combustion, and the carbon and phosphorus contents on the char layer surface were also increased.In the above system, the mechanical properties of PLA obviously destroyed due to the addition of flame retardant. In order to improve the efficiency of IFR for the flame retardant PLA and reduce the damage to the material mechanical propertirs, bamboo charcoal (BPC) was added into the PLA/IFR system as a reinforcing agent. The results showed that the PLA/IFR/BPC system could passed UL-94 V-0 flamability rating and its LOI value could reach 31.6% when the loading amount of IFR and BPC were 10 wt% and 5 wt%. Compared with the same amount loading of IFR alone, the incorporation of BPC reduced the initial thermal degradation temperature of PLA/IFR/BPC system, but the residual char was enhanced at 800℃. According to the cone test, HRR and THR of the PLA/IFR/BPC system had been decreased and the formed char layer of PLA/IFR/BPC system presented more continuous and compact after combustion, and the carbon contents on the char layer surface were also increased. Mechanical properties test showed that the tensile strength of the PLA/IFR/BPC system reached 57.9MPa and the flexual strength and izod impact strength could reach 79.7MPa and 1.69kJ·m-2, which had been increased by 8.9%,16.3% and 1.7% compared with the PLA/IFR system. It indicated that the introduction of BPC evidently improved the mechanical properties of the materials.