Resumen de Bio-based flame retardant for sustainable building materials
As new promising alternatives, novel bio-based materials are already developed to apply in construction sectors due to biodegradability, low toxicity, sustainability, renewability, and acceptable general properties. However, their flammability and need to guarantee a low fire risk in the constructions is also an essential factor to restrict their further application. This thesis focused on investigation of bio-based material with good flame-retardant performance and corresponding flame-retardant mechanism. The detailed investigation was developed by following stages: synthesis of bio-based flame retardant and its application in PLA; effect of bio-based flame retardant on the fire resistance and other properties of natural fiber reinforced PLA. Finally, the smouldering and combustion performances of the bio-based thermal insulation material made from natural fiber were studied as well.
1) On basis of bio-based concept, PA and THAM were selected as raw material to synthesize a novel flame retardant and the chemical structure was confirmed via some characterizations. Afterwards, this synthetic product PA-THAM was employed as an efficient flame retardant to PLA by melt mixing. This binary system showed an improvement in flame retardancy, which was achieved by a combination of heat transfer effect, slight dilution and barrier action. For example, only 3 wt% loading of PA-THAM imparted PLA-based biocomposite LOI value of 25.8% and UL 94 V-0 level, as well as a significant self-extinguishing ability was observed. Besides, the molten viscosity of biocomposite also demonstrated more reduction compared with neat PLA due to the lubrication of PA-THAM, while there was little change in the mechanical properties.
2) PA-THAM and corn pith cellulose (OCC) were combined via in-situ modification and used to prepare a PLA-based biocomposite. After OCC was modified by PA-THAM successfully, which was proved by SEM/ EDS, FTIR, and TGA, the effect of PA-THAM on thermal stability and fire behaviors of PLA-based composite were also investigated accordingly. 5 phr addition of PA-THAM enabled this natural fiber reinforced polymer biocomposite (NPC) to illustrate a 50 °C higher temperature at maximum degradation rate than control sample without additive, and an improvement was also obtained in flame retardant properties with an increase of LOI value, a reduction of PHRR, and more char residue. The predominant flame-retardant mechanism focused on the synergistic effect of PA-THAM and OCC that occurred in condensed phase. Besides, the same level introduction of PA-THAM improved the interfacial affinity between PLA and OCC that maintained good mechanical properties as well.
3) A bio-based thermal insulation material was made from corn pith cellulose, alginate, and bio-efficient flame retardants. After introducing these bio-based additives, the smouldering and flaming combustion behaviors were improved significantly. Compared with the reference sample, thermal insulation particleboard with 8 wt% loading of a mixture of PA-THAM and a sodium borate salt (DOT) increased the initial temperature of smoldering ignition by 70 ºC, and meanwhile, the value of PHRR in flaming combustion decreased by 25.5%. Furthermore, the thermal conductivity was hardly affected, while the temperature at which the maximum thermal degradation occured increased. The correlative flame retardant mechanism was attributed to a synergistic effect from both flame retardants, which promoted a formation of more stable charring layer at initial stage.
