随着石油资源的消耗与匮乏，石油基聚合物的发展面临巨大的挑战，生物基聚合物应运而生。作为一种生物基聚合物材料，聚乳酸(PLA)由于具有优异的力学及加工等性能，从而获得广泛应用。但是，PLA存在易燃、且燃烧时产生熔滴的缺点，严重限制了其应用范围。因此，对PLA进行阻燃改性备受研究者关注。本论文基于9，10-二氢-9-氧杂-10-磷杂菲-10-氧化物(DOPO)的阻燃特性，通过引入不同的桥链基团，制备了不同P-C桥链结构的DOPO衍生物，磷含量高的同时兼具优异的热稳定性。考察了桥链DOPO衍生物对PLA阻燃性能、热分解行为、结晶行为及力学性能等的影响。通过系统研究桥链结构变化对PLA阻燃与热性能的影响规律，提出相应的阻燃机理模型。此外，探索不同纳米粒子对阻燃PLA的协效复配作用与机理。 以DOPO为原料，与苯乙酮在酸性催化剂作用下反应制备了苯乙基桥链DOPO衍生物(DiDOPO)。通过傅里叶变换红外光谱、核磁共振、质谱等对产品进行了结构表征。采用熔融挤出法将DiDOPO加入到PLA中，考察了DiDOPO对PLA热性能及阻燃性能的量效关系。结果表明，氮气条件下，DiDOPO的起始热分解温度(T〓)达到362.9℃。加入PLA后，DiDOPO含量仅为10 wt％时，可使PLA材料达到垂直燃烧测试(UL-94)V-0级(3.2㎜和1.6㎜)，极限氧指数(LOI)值从19.1％(纯PLA)提高到27.1％，峰值热释放速率(PHRR)值比纯PLA降低了16.4％。可见，DiDOPO明显改善了PLA材料的阻燃性能。此外，空气氛围下，10wt％DiDOPO的加入提高了PLA的热稳定性。并且10％DiDOPO／PLA弯曲强度比纯PLA提高了18.7％。因此，制备的苯乙基桥链DOPO衍生物DiDOPO是一种对PLA具有良好潜在应用价值的阻燃剂。 将制备的DiDOPO与市售产品二乙基次膦酸铝(AlPi)在PLA中的作用进行对比研究，探讨了DiDOPO和AlPi阻燃PLA的热降解性能、阻燃性能及裂解行为等的差异。研究表明，当AlPi含量达到25 wt％时，只能使PLA材料获得UL-94 V-1级(3.2㎜)，LOI值仅达到21.6％，明显低于PLA／10％DiDOPO体系。另外，PLA／AlPi的力学性能低于相应含量下的PLA／DiDOPO体系。流变行为分析表明，在相同温度下，PLA／DiDOPO具有比PLA／AlPi更高的复数粘度(η*)值，说明DiDOPO能更好地抑制熔滴。因此，作为PLA的阻燃剂应用时，DiDOPO在较低添加量时可使PLA获得更好的阻燃性能，综合性能优于AlPi阻燃PLA。进一步通过扫描电子显微镜，热重-红外联用以及裂解色谱-质谱测试对固相与气相燃烧产物分析结果表明，DiDOPO裂解释放PO等自由基捕获PLA分子链燃烧自由基起到气相抑制作用：对于PLA／AlPi来说，起主导作用的是AlPi裂解产生含磷烷基碎片与PLA分子发生作用，促进PLA形成较多的膨胀炭层从而起到固相阻隔作用。 将DOPO与乙二醇、苯乙酮及萘乙酮通过化学反应制备了乙基(ethyl-bridged，DeDOPO)、苯乙基(phenethyl-bridged，DiDOPO)和萘乙基(naphthalene-bridged，DnDOPO)桥链DOPO衍生物，并进行了结构表征。研究了芳基基团增加对桥链DOPO衍生物热性能的影响，进一步揭示了基团变化对PLA阻燃和热性能的影响规律，并对机理进行了深入探讨。结果表明，氮气条件下，DeDOPO的T〓为422.2℃，DnDOPO的T〓为397.0℃，高于DiDOPO，热分解残余率按照如下顺序逐渐增加：residues(DeDOPO)
Because of the consume and shortness of oil resources, the development of petroleum-based polymer faces great challenges. Thus, developing biobased polymer is significantly necessary. Recently, biobased poly(lactic acid) (PLA) has received increasing research interest owing to its good processing, mechanical and transparent properties. To date, PLA has been applied in some areas to replace the traditional polymer. However, the flammability of PLA restricts its application. To solve this problem, flame-retarding modification of PLA is significant important. In this study, bis P-C bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene- 10-oxide (DOPO) derivatives were synthesized and characterized. Then, effects of the prepared bridged DOPO derivatives on the flame retardant, thermal stability and mechanical performances of PLA were investigated in detail. Additionaly, the interaction and mechanism between nano particles and bridged DOPO derivative in flame-retarding PLA were examined. A phenethyl-bridged DOPO derivative (DiDOPO) was synthesized and characterized by fourier infrared spectrum, NMR spectrometer, and mass spectrum. The thermal property of DiDOPO was investigated. And its influence on the thermal and flame-retarding properties of PLA were evaluated. The synthesized DiDOPO has a prominent thermal stability with a start thermal degradation temperature (T〓) of 362.9 ℃ under nitrogen atomosphere. When adding 10 wt% DiDOPO, PLA composites obtained the V-0 rating (thicknesses of 3.2 ㎜ and 1.6 ㎜) during UL-94 test, and the limiting oxygen index (LOI) value increased to 27.1%, and a decrease of 16.4% in peak heat release rate (PHRR) as comparison to pure PLA. In addition, the thermal stability of PLA was improved with the addition of 10 wt% DiDOPO, especially T〓 of PLA raised by approximately 10 ℃ under air condition. The mechanical performances of PLA were maintained after introducing DiDOPO. The flexural strength of PLA composites increased by 18.7% with 10 wt% loading of DiDOPO. Thus, DiDOPO is a good flame retardant with a potential application in PLA. Both cone calorimeter test and thermal analyses indicated that DiDOPO plays a dominant gas flame inhibition role for PLA. A typical commercial product of aluminum diethylphosphinate (AlPi) was introduced as a comparison with DiDOPO for exploring the differences of flame retardant behaviors. Their effects on the combustion behavior, thermal degradation and pyrolysis properties of PLA were comparatively discussed. The results indictaed that different chemical structures of these two formulations cause different flame retardant effects. PLA composites just passed UL-94 V-1 rating (3.2 ㎜) with addition of 25 wt% AlPi, as well as LOI value of 21.6%, worse than those of PLA/10%DiDOPO. Both adding AlPi and DiDOPO dramatically decreased the PHRR and THR values of PLA, while a plat HRR curve was observed for PLA loading with AlPi. The tensile strength of PLA/DiDOPO was higher than that of PLA/AlPi with the same concentration. At the same temperature, PLA/DiDOPO displayed higher complex viscosity than PLA/AlPi, indicating better inhibittion dripping behavior of PLA with DiDOPO than AlPi. Obviously, DiDOPO showed much more efficiency than AlPi in flame-retarding enhancement of PLA. DiDOPO endows PLA a higher LOI value and better UL-94 result than AlPi at the same content. The thermal stability of PLA is enhanced in the presence of DiDOPO, however, AlPi catalyzes the degradation of PLA. More importantly, they exert complete different mechanism in flame-retarding PLA. DiDOPO plays the main roles of flame inhibition, while AlPi mainly promotes the formation of intumescent char to isolate combustion. Bis P-C bridged DOPO derivatives including ethyl-(DeDOPO), phenethyl-(DiDOPO), naphthalene-(DnDOPO) with increased aryl groups were synthesized and characterized. Effects of increased aryl groups in the structure of bridged DOPO derivatives on their thermal properties were examined. Then, effects of these compound on the flame retardant properties and thermal stability of PLA were examined. The regulation that resulted from group changes in the DOPO derivatives was our focus. At 10 wt% addition of the derivatives, all PLA composites achieved a V-0 rating (UL-94, 3.2 ㎜), and the LOI values of PLA/DeDOPO, PLA/DiDOPO and PLA/DnDOPO increased from 19.1% (pure PLA) to 36.4%, 27.1% and 24.3%, respectively. The introduction of DeDOPO, DiDOPO and DnDOPO decreased the PHRR value of PLA composites from 584 kW/㎡ (pure PLA) to 490, 488 and 434 kW/㎡, respectively. LOI and PHRR of PLA composites decreased with the increase of aryl group in the structure of bridged DOPO derivatives. In addition, the derivatives significantly enhanced the thermal stability of PLA especially under air condition. It was found that the bridged DOPO derivatives showed a dominant flame inhibition role in PLA. Furthermore, the investigation of the residue micromorphology of PLA composites revealed that a cross-linked structure likely formed with the increased of aromatic groups in the molecule. We found that the blend of PLA/DiDOPO still remained transpant, while those of PLA/DeDOPO and PLA/DnDOPO did not show this feature. Thus, to clarify this phenomenon, based on the physical properties of flame retardants, effects of these bridged DOPO derivatives on the crystallization properties of PLA were futher investigated. The crystallization temperature of PLA containing DeDOPO、DiDOPO and DnDOPO was increased to 127.5 ℃, 111.8 ℃ and 121.6 ℃, respectively. Thus, flame retardants promoted the crystallization of PLA. The most uniformly dispersion degree of DiDOPO in PLA was observed by TEM. Additionaly, the orientation of PLA/DeDOPO and PLA/DnDOPO was detected, however, no orientention was observed for PLA/DiDOPO. Therefore, DiDOPO melted in PLA matrix during processing process because of its similar melting temperature to the process temperature of PLA. In addition, the motion of PLA molecular chain was destoried after introducing DiDOPO. Synergistic effect of nanoparticles with different particle morphology including nano silica (SiO₂), organic montmorillonite (OMMT) and zinc borate (ZnB) on flame retardant PLA composites containing DiDOPO were investigated. 2 wt% was the optimal addition content for these nanoparticles in PLA/DiDOPO composites, and nano SiO₂ showed higher LOI value (27.0%) than OMMT (25.8%) and ZnB (26.5%) at the same content. When compared with that of PLA/DiDOPO, the PHRR was decreased dramatically after introducing nanoparticles, and the smoke was significant suppressed by adding SiO₂. Among these nanoparticles, SiO₂ had an obvious enhancement in the thermal stabilities of PLA both under nitrogen and air conditions resulting from its barrier effect. In addition, a compact char with the morphology of cross-linked network was formed after combustion for PLA/DiDOPO/SiO₂. TEM and rheology results showed that SiO₂ had a well dispersive quality in PLA/DiDOPO composites. Consequently, SiO₂ shows the best synergistic effect with DiDOPO toward improving the flame retardancy of PLA. Keywords: Poly(lactic acid); flame retardant; DOPO derivatives; thermal properties; nanocomposites