| Polylactic acid (PLA) was a degradable polymer which was derived from renewable resource. PLA present excellent mechanical properties and biocompatibility, it was considered to replace polyolefins to some extent. However, the development and application of PLA was limited due to its poor fire resistance and serious dripping when subjected to elevated temperatures or combustion. So, it was important to research and develop flame retarded PLA. Firstly, this thesis systematically reviewing previous studies on halogen-free flame retardant technology, discussing the application feasibility of several these technologies in PLA. Secondly, several PLA/hypophosphite salts composites were prepared, and also, the degradation and flame retardant mechanism of these composites were investigated. Thirdly, the author successfully constructed first static state tube furnace toxicity test platform (SSTF); furthermore, the fire effluent toxicity of the PLA/hypophosphite salt composites in different conditions were investigated by this platform.1. Aluminum hypophosphite (AHP) was firstly used as a novel flame retardant and composed with PLA, a series of PLA/AHP composites were prepared. TGA test indicated that the addition of AHP could significantly increase the char residue and reduce mass loss rate. LOI and UL-94test indicated that the flame retardancy of the composites was significantly improved. FR-PLA composites with20wt%AHP loading could pass UL-94V-0rating without dripping, and the LOI value was27.5vol%. MCC and Cone test indicated that the peak of heat release rate (PHRR) was significantly reduced. The char residue of PLA/AHP composites after LOI test was tested by SEM, indicating condensed char structure was formed. Furthermore, DSC and DMA test indicate that the addition of AHP could significantly improve crystallization property and storage modulus of PLA/AHP composites.2. Inspired by the high performance of AHP, another calcium hypophosphite was used as a potential flame retardant for PLA, and a series of PLA/CaHP composites were prepared. The addition of CaHP could significantly improve the flame retardancy of PLA/CaHP composites. PLA/CaHP could pass UL-94V-0rating without dripping, and the LOI value was26.5vol%. MCC test indicated that the PHRR value was significantly reduced. TGA test indicated that the addition of CaHP could significantly increase the char residue and reduce the mass loss rate. The char after LOI test was investigated by SEM, revealing that the char residue of PLA/CaHP was condensed, which could improve the fire safety of the composites.3. Expanded graphite was used as flame retardant synergist and combined with AHP, a series of PLA/AHP/EG composites were prepared. The composite containing20wt%could pass UL-94VO rating with a high LOI value of34vol%(AHP:EG=3:1). MCC and Cone testing revealed that, the combination of AHP with EG could significantly reduce the PHRR and the total heart release (THR) of the composites. TGA test indicated that AHP could inhibit the degradation of the composites in high temperature. TG-IR revealed that the combination of AHP and EG resulted in significant decrease of gas products. SEM test showed that EG expanded and lamellar structure covered on the porous char residue which benefited to the formation of condensed char layer. Based on the experimental datum, the possible mechanism of PLA/AHP/EG composites was put forward:The EG particle rapidly expands and form vermicular structure which combined with decomposition products of AHP to form condensed char layer, which could further prohibit the transportation of mass and fuel. Further-more, the space of vermicular structure could act as a "micro-reactor", which is approximately seemed as a closed room in which toxicity gas can adequately react with the decomposition products of PLA. The sufficient reaction significantly inhibits the combustible and toxic gas, result in the improvement of char residue, and also, the flame reatrdancy of the composites was significantly improved.4. Two kinds of rare earth metal hypophosphite (REHP), lanthanum (â…¢) hypophosphite and cerium (â…¢) hypophosphite, were successfully synthesized and characterized. SEM analysis illustrated both of these two REHP presented rod-like structure with micron sizes. TGA test illustrated that REHP showed different degradation process in nitrogen and air atmosphere. A series of PLA/REHP composites were prepared by addition of LaHP and CeHP. TGA test showed that both the incorporation of LaHP and CeHP could significantly improve the thermal stability of PLA/REHP composites. For the composites containing30wt%LaHP and CeHP, it could reach UL-94V-0rating with a LOI value of28.5vol%. TG-IR test illustrated that the all the volatilized products were reduced by the addition of REHP. MCC and Cone testing showed that the addition of REHP could significantly reduce the PHRR value of PLA/PRHP composites. Char residue after Cone testing were investigated by SEM, illustrating that the morphology of the char residue were significantly effect by PEHP loading. Furthermore, the char was investigated by XPS, which showed that the main component was the degradation products of REHP and carbon-containing materials.5. First static state tube furnace toxicity test platform (SSTF) in China were constructed according to ISO19700. The fire effluents of PLA, PLA/AHP, PLA/CaHP, PLA/LaHP and PLA/CeHP composites in different conditions were investigated by SSTF. The research illustrated that, the oxygen consumption and CO2concentration presented high correlation, the oxygen mostly consumed by the formation of CO2. The composition of fire effluent was highly effected by oxygen supply condition; in equivalence ratio condition, the oxygen was transformed into CO2to the maximum content, the CO concentration was lowest, the fire effluent presented lowest toxicity. The kinds of cation in hypoposphite salts shows high effect on the fire effluent, in which, the composites containing rare earth hypophosphite shows the lowest fire toxicity. |
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