基于光谱学分析的聚氨酯弹性体/聚磷酸铵/氢氧化铝复合材料阻燃机理研究

采用熔融共混技术，将聚磷酸铵(APP)和氢氧化铝(ATH)引入到聚氨酯弹性体(TPU)中，制备了一系列热塑性聚氨酯/聚磷酸铵/氢氧化铝(TPU/APP/ATH)复合材料。采用傅里叶红外光谱(FTIR)、X-射线光电子能谱(XPS)、扫描电镜(SEM)、激光拉曼光谱研究了TPU和阻燃TPU(FR-TPU)复合材料燃烧后炭渣的微观形貌、表面结构、元素组成、键合状态和石墨化程度，结合阻燃性能测试，揭示APP和ATH的协同阻燃机制。SEM分析表明相较于APP与ATH单独使用，TPU/APP/ATH炭层的空洞结构更少，炭渣的致密性更高。XPS分析表明FR-TPU的炭渣中C元素含量相比于纯TPU有所降低，O元素的含量有所上升，其中TPU/APP10/ATH10的C元素含量从88.2%降至69.24%，O元素的含量从8.07%升至17.78%，P和Al元素含量相较于单独添加分别从11.74%和16.36%下降至3.91%和3.31%。在此基础上，通过对C元素的分峰拟合发现TPU炭渣中C—C/C—H，C—O/C—N和CO/CN含量分别为61.05%，35.65%和3.30%；TPU/APP10/ATH10炭渣中三种结构含量分别为45.38%，45.00%和9.63%，说明ATH和APP复配使用有利于C元素形成酯、醚、羰基、羧酸（盐）、酯基等结构。通过对O元素的分峰拟合发现，TPU炭渣中O₂/H₂O，—O—，O三种结构含量分别为28.75%，44.36%和26.89%；TPU/APP10/ATH10炭渣中O₂/H₂O，—O—，O三种结构含量分别为44.33%，32.78%和22.89%，说明APP和ATH的加入有利于炭渣中O元素形成O₂/H₂O结构。通过对N元素的分峰拟合发现，TPU炭渣中—NH—，N结构的N元素含量分别为40.93%和59.07%；TPU/APP10/ATH10中—NH—，N结构的N元素含量分别47.17%和52.83%，说明ATH与APP复配使用促进了—NH—结构的形成。拉曼测试表明，相比于单独使用，APP和ATH复配使用，炭层的石墨化程度更好，致密性更高。以上分析结合阻燃测试可以得出TPU/APP/ATH复合材料阻燃机制：ATH受热分解生成氧化铝，吸收热量并释放大量水蒸气，有效促进APP降解，生成不燃性的氨气和聚磷酸，氨气和水蒸气稀释可燃性气体的浓度。随着温度继续升高，氧化铝可继续与聚磷酸反应生成偏磷酸铝Al(PO₃)₃]，同步催化聚氨酯基体成炭，形成高度石墨化炭层，石墨化炭层与偏磷酸铝一起覆盖在基体表面，有效抑制燃烧区域物质以及能量的输运，从而达到阻燃目的。

Flame Retardant Mechanism Investigation of Thermoplastic Polyurethane Composite/Ammonium Polyphosphate/Aluminum Hydroxide Composites Based on Spectroscopy Analysis

Ammonium polyphosphate (APP) and aluminum hydroxide (ATH) was introduced to prepare a series of ammonium polyphosphate/aluminum hydroxide/thermoplastic polyurethane composites (TPU/APP/ATH) by melting blending technology. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and laser Raman spectroscopy test were applied to investigate micro-morphology, surface structure, elemental composition, bonding state and graphitization degree of the char residue for TPU and flame retardant TPU composites, which combined with flame retardant tests to discover synergistic flame retardant mechanism of APP and ATH. SEM analysis revealed that TPU/APP/ATH char residue had less void structure and higher densification than APP and ATH alone. XPS revealed that the content of the C element in FR-TPU slag decreased compared with pure TPU, while the content of the O element increased. In these samples, the content of C element in TPU/APP10/ATH10 decreased from 88.2% to 69.24%, the content of O element increased from 8.07% to 17.78%. Compared with TPU/APP20 and TPU/ATH20, the content of P and Al element in TPU/APP10/ATH10 were decreased to 3.91% and 3.31%, respectively. Furthermore, peak fitting for bonding state of C element showed that C—C/C—H, C—O/C—N and CO/CN structure in char residue of TPU was 61.05%, 35.65% and 3.30%. In comparison, those in char residue of TPU/APP10/ATH10 were 45.38%, 45.00% and 9.63%, indicating ATH and APP facilitated the formation of ester, ether, carbonyl, the carboxylic acid (salt), ester group, et al. Peak fitting for the binding state of O element showed that O₂/H₂O，—O— and O structure in char residue of TPU were 28.75%, 44.36% and 26.89%, compared with 44.33%, 32.78% and 22.89% in char residue of TPU/APP10/ATH10, indicating that the addition of APP or/and ATH was conducive to the formation of O₂/H₂O structure of O elements. Peak fitting for bonding state of N element showed that —NH— and N structure in char residue of TPU was 40.93% and 59.07%, compared with 47.17% and 52.83% in char residue of TPU/APP10/ATH10, implying ATH and APP promoted the formation of —NH— structure. The Raman spectroscopy test showed that the char layers of TPU/APP10/ATH10 were more graphitized and densified than the sample with APP and ATH used alone. Based on the above researches and flame-retardant tests, the flame retardancy mechanism of TPU/APP/ATH composites can be obtained as follows: ATH was thermally decomposed into alumina, which absorbed heat and released large amounts of water vapor, effectively facilitating APP degradation, producing incombustible ammonia and polyphosphoric acid, which diluted the concentration of flammable gas. As the temperature continued to rise, alumina reacts with polyphosphoric acid to form aluminum metaphosphate (Al(PO₃)₃), which synchronously catalyzes the carbonization of the polyurethane matrix to form a highly graphitized char layer. The graphitized char layer covered the surface of the matrix together with aluminum metaphosphate, effectively inhibiting the transport of substances and energy in the combustion area, thus achieving flame retardation.