【作者】 单雪影；

【导师】 胡源； 卢兆明；

【作者基本信息】 中国科学技术大学 ， 安全科学与工程， 2014， 博士

【摘要】 可生物降解聚合物聚乳酸(PLA)的原材料能由可再生资源生产制备,因而得到广泛的应用。PLA具有优良的性能,如热塑性好、强度和模量高、高熔融指数、透明度好、易于加工等。然而,由于其内在的化学组成和分子结构,PLA的热稳定性较差,容易燃烧,且燃烧时伴随严重的滴落现象,这限制了其在许多领域的应用和发展。本文针对当前阻燃PLA存在的阻燃剂种类少、添加量高、效果不佳的现状,合成多种含镍化合物,并和新型无卤阻燃剂结合使用,制备PLA复合材料,系统地研究复合材料的组成与热性能、阻燃性能的关系；阐明各阻燃组分间的相互作用机制和在PLA中的阻燃机理。主要研究工作如下：1、通过一步共沉淀法合成三种含镍层状双氢氧化物(NiFe、NiAl和NiCr LDHs),研究这些LDHs化合物的结构、形貌和性能,并用于制备PLA/LDHs纳米复合材料及比较研究复合材料的热性能。TGA结果表明PLA/NiCr LDH复合材料的具有较高的热稳定性,DSC结果显示PLA/NiAl LDH复合材料具有最低的熔融焓。SEM显示PLA/NiFe LDH复合材料的炭层最致密,且LRS结果说明其有序化碳的含量最高。TEM和XRD图像显示LDHs在PLA基体中均具有良好的分散并且呈现插层和剥离状态。由于三价金属离子的影响,NiFe、NiAl和NiCr LDHs能够不同程度地提高PLA材料的热稳定性。2、用NiFe、NiAl和NiCr LDHs材料首次与苯氧基环磷腈(HPCP)结合使用制备PLA纳米复合材料,并对PLA/HPCP/LDHs复合材料的形貌、热性能和阻燃性能进行比较和研究。TGA表明PLA/HPCP/NiCr复合材料具有较高的炭渣残留量。DSC指出PLA/HPCP/NiFe LDH复合材料呈现最低的结晶度,SEM图像证实其炭化残渣形貌最为致密,XPS表明这种复合材料具有最高的P/C和N/C比值。LRS表明PLA/HPCP/NiAl LDH复合材料有序化碳的含量最高。所有PLA/HPCP/LDHs复合材料在10wt%的添加量时均能达到UL-94V0级别,且LDHs在PLA基体中具有良好的分散。因此,NiFe、NiAl和NiCr LDHs在提高PLA复合材料的热稳定性和阻燃性能方面具有不同程度的良好效果。3、由硅烷包覆的聚磷酸铵(APP203)和季戊四醇磷酸酯(PEPA)组成新的有机膨胀体系(IFR),添加到PLA基体中。NiAl LDH具有良好的片层阻隔和催化成炭作用,作为阻燃协效剂用于提高PLA/IFR复合材料的热稳定和阻燃性能。玉米淀粉(CS)作为生物质炭源与APP203形成另一种有机IFR阻燃体系,聚丁二酸丁二醇酯(PBS)用在PLA基体中具有增韧作用,同样使用熔融共混法制备PLA/PBS/APP203/CS/NiAl LDH复合材料.研究结果表明,基于疑聚相的阻燃作用机理,NiAl LDH和上述两种IFR体系协同使用能够有效提高PLA基体的热稳定性和阻燃性能,并解决复合材料燃烧时的滴落问题。4、采用水热法合成了纳米级的铁酸镍(NiFe2O4)粒子,并同样方法制备ZnFe2O4和CoFe2O4纳米粒子与之做对比研究。聚磷酸铵(APP)和可膨胀石墨(EG)组成无机IFR体系。这些铁酸盐纳米粒子(MFe2O4)和IFR结合使用制备PLA复合材料,并对比研究复合材料的阻燃性能和机械性能。此IFR体系和MFe204的使用能够大幅度提高PLA材料的LOI,添加量13wt%时复合材料达到UL-94V0级别且无滴落现象。MCC显示12wt%添加量的IFR, PLA复合材料的PHRR、HRC和THR与纯PLA相比分别减少了30.7%、32.8%和17.5%,当含有1wt%添加量的MFe2O4时,火灾危险性进一步降低。添加剂的使用能够一定程度上提高材料的机械性能。综合比较三种铁酸盐纳米粒子的作用,NiFe2O4的效果最好。MFe2O4和IFR在PLA基体中的阻燃作用机理为形成稳定炭层的凝聚相机理。5、通过水热法合成形貌规整的钼酸镍(NiMo),并合成掺杂稀土Ce元素的钼酸铈镍(NiMoCe)纳米棒做对比研究。聚苯乙烯(PS)用来增强PLA基体,聚乙二醇(PEG)用于PLA材料的增韧。熔融共混法制备PLA/PS/PEG/纳米棒复合材料,研究复合材料的热稳定性和添加剂的增强增韧作用。含有纳米棒的PLA复合材料的残留炭渣量较高且具有较高含量的石墨化碳,说明纳米棒可以有效提高材料的热稳定性。机械性能表征结果显示PS和PEG在PLA基体中具有增强和增韧作用,在一定添加量范围下,拉伸强度随着NiMo纳米棒添加量的增加而提高。综合比较,NiMo纳米棒的作用效果优于NiMoCeo更多还原

【Abstract】 The raw material of poly (lactic acid)(PLA), lactic acid can be produced from renewable resources. Therefore. PLA has a wide development and applications. PLA has good properties, such as thermoplastic, high strength, high modulus, high melting index, high transparency and ease of fabrication. However, because of its inherent chemical composition and molecular structure, PLA has poor thermal stability and it is easy to burn with serious dripping, which limit its applications and development in many fields. Therefore, research on the low loading and high flame retardant efficiency of additives is still an important task.Based on current research on the thermal stability and flame retardancy of PLA. a variety of nickel-containing compounds were synthesized. Then combined with new halogen-free flame retardants were used in preparing PLA composites. The thermal property and flame retardancy of PLA composites were researched in detail. The interaction of flame retardant compositions and effect mechanism of additives in PLA matrix were discussed.The main research work is as follows:1、Three different nickel-containing layered double hydroxides (NiFe. NiAl and NiCr LDHs) were synthesized by one-step co-precipitation method. The structure, morphology and property of these LDHs were investigated. They were used to prepare PLA/LDHs nanocomposites. The thermal property of PLA/LDHs composites was researched and compared. TGA results showed that PLA/NiCr LDH composite had the highest thermal stability. DSC suggested that PLA/NiAl LDH composite had the lowest melting enthalpy. SEM presented that the PLA/NiFe composite char residue was densest, and the largest ratio of the ordered carbon was presented in LRS. TEM and XRD images of PLA composites illustrated that all the LDHs had a good dispersion in PLA matrix, and exhibited intercalation or exfoliation. Owing to trivalent cations effect. NiFe. NiAl and NiCr LDHs played different roles in improving the thermal stability of PLA composites.2.. NiFe. NiAl and NiCr LDHs were first combined with Hexaphenoxycyclotriphosphazene (HPCP) to prepare PLA/HPCP/LDHs nanocomposites. The morphology, thermal property and flame retardancy of PLA/HPCP/LDHs composites were researched and compared. For PLA composites containing LDHs, TGA measurements confirmed that PLA/HPCP/NiCr LDH composite had slightly more char residue. DSC levels suggested that PLA/HPCP/NiFe LDH composite presented in the best case only a low crystallinity, and SEM images demonstrated that its char residue was densest. In addition. XPS revealed that this composite exhibited the highest P/C and N/C ratios. The largest ratio of ordered carbon for PLA/HPCP/NiAl LDH composite was evident by LRS. All the composites were given UL-94VO rating at the low loading. TEM images showed that all the LDHs had a good dispersion in PLA composites. Thus. NiFe, NiAl and NiCr LDHs play different better effect in improving the thermal stability and flame retardancy of PLA composites.3、A new organic IFR formulation constituted by microencapsulated ammonium p.olyphosphate with silane (APP203) and pentaerythritol phosphate (PEPA) was added in PLA matrix. NiAl LDH had good lamellar barrier effect and catalytic charring, which was chosen as flame retardant synergist agent to improve the thermal stability and flame retardancy of PLA/IFR composites. Corn starch (CS) as a bio-carbon source was used to form another organic IFR composites with APP203. Poly(butylenesuccinate)(PBS) was used in PLA matrix, which had the toughening effect. PLA/PBS/APP203/CS/NiAl LDH composites were also prepared by melt blending method. The measurement results showed that NiAl LDH and the above two IFR systems could improve the thermal stability and flame retardancy of PLA composites apparently and resolve the combustion dripping problem. The effect mechanism of additives was mainly based on the condensed phase flame retardant mechanism.4、The nanometer-scale nickel ferrite (NiFe2O4) particles were synthesized using the hydrothermal method, and ZnFe2O4and CoFe2O4nanoparticles were synthesized by the same method for comparative research. These metal ferrites (MFe2O4) were combined with an inorganic IFR constituted by ammonium polyphosphate (APP) and expandable graphite (EG) to added in PLA matrix. The flame retardancy and mechanical property of PLA composites were investigated and compared. The LOI value of PLA composites was increased significantly after adding IFR and MFe2O4. UL-94VO rating was obtained with13wt%additive loading. It was no dripping when composites was burned. MCC results showed that PHRR. HRC and THR value of PLA composites had a reduction of30.7%.32.8%and17.5%respectively, comparing to pure PLA. Fire security was further improved when1wt%MFe2O4 was added. The mechanicl property of PLA composites was improved at some extent. NiFe2O4effect was the best among the above three MFe2O4nanoparticles. The promoting mechanism between MFe2O4and APP/EG was caused by formation of the stable char layer, slowing heat and mass transfer between the condensed phase.5、Nickel molybdate (NiMo) nanorods with uniform morphorlogy were prepared by the hydrothermal technique, and nickel molybdates doped with Ce (NiMoCe) nanorods were synthesized for comparative research. Polystyrene (PS) was used for enhancing PLA. Polyethylene glycol (PEG) was used as a toughening reagent. PLA/PS/PEG/naorod composites were prepared. The thermal stability of PLA composites, enhancing and toughening effect of additives were investigated. PLA composites with the addition of nanorods had more char residue and higher content of the ordered char layer. Therefore, nanorods were useful to improve the thermal stability of PLA composites. The results of mechanical property measurements indicated that PS and PEG had enhancing and toughening effect. With a just-right formulation, the tensile strength of PLA composites was improved with NiMo nanorod loading increase. NiMo nanorods effect was better than NiMoCe.更多还原