Abstract:

Typical monomer terephthalic acid generated from the depolymerization of waste fiber suffers from several key challenges including high difficulty in high-value utilization, few varieties of downstream products and limited use. Terephthalate-based metal-organic frameworks (MOFs) were proposed as synergistic flame retardants for plastic modification. Using room temperature and hydrothermal methods, two terephthalate-based MOFs, Li-MOF and Al-MOF, were prepared by the reactions of lithium hydroxide and aluminum nitrate with terephthalic acid that was recycled from the alkali-decrement wastewater, respectively. Then, poly lactic acid (PLA) and soft polyvinyl chloride (PVC) were chosen as substrates, and the combinations of ammonium polyphosphate (APP) and Li-MOF as well as the combinations of antimony trioxide (Sb₂O₃) and Al-MOF were incorporated into PLA and PVC to afford PLA/APP/Li-MOF and PVC/Sb₂O₃/Al-MOF composites with different plasticizer contents through the melt blending extrusion method, respectively. The composites were characterized by powder X-ray diffraction, IR spectra, Brunauer-Emmett-Teller (BET), and thermogravimetric (TG) analyses, and their flame retardant performance and mechanical properties were examined by means of limiting oxygen index (LOI), the vertical burning (UL-94), cone calorimeter test (CCT) and tensile machine. The result showed that the addition of a small amount of Li-MOF could significantly improve the flame retardant performance. When Li-MOF composites was 1.5% (mass fraction), PLA/APP/Li-MOF exhibited the best flame-retardant performance. Compared with sample with only PLA, the LOI value increased from 20.3% to 34.2% and the UL-94 grade reached from V-2 to V-0 level, while the peak value of heat release rate and total heat release of burning decreased obviously and the degree of the residual carbon was also higher. Besides, the flame retardant performance was improved upon the introduction of Al-MOF into the PVC/Sb₂O₃ system. When Al-MOF composites with 5% (mass fraction) PLA/APP/Al-MOF was used, the LOI value increased from 28.5% to 32.5% compared with sample with PVC/Sb₂O₃. Meanwhile, the tensile strength and elastic modulus increased by 20.1% and 166.5%, respectively.

Key words: waste terephthalic acid, recovery and reuse, metal-organic framework, poly lactic acid, soft polyvinyl chloride, flame retardant

摘要：

针对废旧纤维解聚典型单体对苯二甲酸高价值利用难度大、下游衍生产品品种少、用途受限等问题，提出了对苯二甲酸金属-有机框架材料（MOFs）作为协效剂应用于聚磷酸铵（APP）和三氧化二锑（Sb₂O₃）阻燃体系。将碱减量废水回收的对苯二甲酸分别与氢氧化锂、硝酸铝通过常温法和水热法制得Li-MOF和Al-MOF，然后通过熔融挤出共混，分别将APP/Li-MOF、Sb₂O₃/Al-MOF阻燃体系添加到聚乳酸（PLA）和软质聚氯乙烯（PVC）中制成PLA/APP/Li-MOF和PVC/Sb₂O₃/Al-MOF复合材料。采用X射线衍射仪、红外光谱、比表面积及微孔分析和热重对其进行了表征和分析，通过极限氧指数仪、垂直燃烧测定仪、锥型量热仪和万能试验机分别对复合材料进行了阻燃性能和力学性能测试。结果表明，与纯PLA相比，Li-MOF的少量加入可明显改善PLA复合材料阻燃性能，Li-MOF质量分数为1.5%的PLA/APP/Li-MOF复合材料阻燃效果最佳，材料的极限氧指数由20.3%提升至34.2%、阻燃等级由V-2提升至V-0、热释放速率峰值（PHRR）和总释放热（THR）均有所降低，残炭率也有所提高。与PVC/Sb₂O₃相比，Al-MOF的添加明显改善了PVC/Sb₂O₃/Al-MOF复合材料阻燃性能，当Al-MOF质量分数为5%时，材料的极限氧指数由28.5%提升至32.5%，同时拉伸强度和弹性模量分别提高了20.1%和166.5%。

关键词: 废弃对苯二甲酸, 高价值利用, 金属-有机框架材料, 聚乳酸, 软质聚氯乙烯, 阻燃