Jin Qin, Tian Guo-Qiang, He Rong, Gu Hai-Long, Wu Fang, Zhu Jiang
College of Materials Science and Engineering, Chongqing University of Arts and Sciences Chongqing 402160 P. R. China
Center for Degradable and Flame-Retardant Polymeric Materials (ERCPM-MoE), College of Chemistry, State Key Laboratory of Polymer Materials Engineering, National Engineering Laboratory of Eco-Friendly Polymeric Materials (Sichuan), Sichuan University 29 Wangjiang Road Chengdu 610064 P. R. China.
RSC Adv. 2021 Aug 10;11(44):27346-27355. doi: 10.1039/d1ra02862f. eCollection 2021 Aug 9.
Simultaneously regulating the crystallizing and combustion behaviors of poly(lactic acid) (PLA) will be conducive to its further development in the fields of electronic appliances, automotive and rail transit materials. To achieve this goal, a novel bifunctional additive triethylamine phenylphosphonate (TEAP) was synthesized through acid-base neutralization reaction between trimethylamine and phenylphosphonic acid. When TEAP was added into PLA, the crystallization behaviors of PLA/TEAP assessed by differential scanning calorimetry (DSC) and polarized optical microscopy (POM) suggested that TEAP acted as a nucleating agent and plasticizer for PLA, which effectively increased the crystallization rate of PLA. However, PLA with 3 wt% TEAP showed a slower crystallization rate than that of PLA with 1 wt% TEAP due to the filler aggregation of TEAP. Thus, the crystallization rate increased first and then slightly decreased with increasing content of TEAP. Compared with the variation of the crystallization rate, the long period () and amorphous layer thickness ( ) resulting from SAXS showed opposite trends, while the average crystal thickness ( ) changed slightly; the reason may relate to the variation of the number of lamellae with increasing the content of TEAP. Meanwhile, the results of WAXD and Raman spectra showed the crystal structure of PLA was not affected by the addition of TEAP. The combustion behaviors of PLA and PLA/TEAP were evaluated by the limiting oxygen index (LOI), UL-94 test, cone calorimetry test (CCT) and thermal gravimetric analyses coupled to Fourier transform infrared spectroscopy (TGA-FTIR). According to the results, TEAP mainly promotes the removal of melt dripping, hence brings away heat and delays the combustion. Besides, the production of phosphorus-containing free radicals can quench hydrogen or oxygen free radicals in the fire. Thus, the fire safety of PLA is significantly improved by adding a very low content of TEAP (1-3 wt%). Only 1 wt% loading of TEAP can increase the LOI value of PLA from 19.5 vol% to 28.6 vol%, pass the UL-94 V-0 rating and have a low peak heat release rate of 404 kW m.
同时调控聚乳酸（PLA）的结晶行为和燃烧行为将有利于其在电子电器、汽车及轨道交通材料领域的进一步发展。为实现这一目标，通过三甲胺与苯膦酸之间的酸碱中和反应合成了一种新型双功能添加剂三乙胺苯膦酸酯（TEAP）。将TEAP添加到PLA中时，通过差示扫描量热法（DSC）和偏光显微镜（POM）评估的PLA/TEAP的结晶行为表明，TEAP对PLA起到了成核剂和增塑剂的作用，有效提高了PLA的结晶速率。然而，由于TEAP的填料团聚，含3 wt% TEAP的PLA的结晶速率比含1 wt% TEAP的PLA慢。因此，结晶速率随TEAP含量的增加先升高后略有下降。与结晶速率的变化相比，小角X射线散射（SAXS）得出的长周期（ ）和非晶层厚度（ ）呈现相反趋势，而平均晶体厚度（ ）变化不大；原因可能与随着TEAP含量增加片晶数量的变化有关。同时，广角X射线衍射（WAXD）和拉曼光谱结果表明PLA的晶体结构不受TEAP添加的影响。通过极限氧指数（LOI）、UL-94测试、锥形量热法测试（CCT）以及热重分析与傅里叶变换红外光谱联用（TGA-FTIR）对PLA和PLA/TEAP的燃烧行为进行了评估。根据结果，TEAP主要促进熔体滴落的去除，从而带走热量并延迟燃烧。此外，含磷自由基的产生可以淬灭火焰中的氢自由基或氧自由基。因此，通过添加极低含量（1-3 wt%）的TEAP可显著提高PLA的火灾安全性。仅添加1 wt%的TEAP就能使PLA的LOI值从19.5 vol%提高到28.6 vol%，通过UL-94 V-0等级，并且具有404 kW m的低峰值热释放速率。
