超支化聚磷酰胺包覆碳纳米管的可控制备及阻燃应用

Controllable Preparation of Hyperbranched Polyphosphoramide Coated Carbon Nanotubes and Its Application for Flame Retardancy

采用羧基化碳纳米管(CNT-COOH)作为载体,以三氯氧磷(POCl_3)和N,N-二氨基二苯甲烷(DDM)为反应单体,三乙胺为缚酸剂和催化剂,通过一步法(A_2+B_3)制备了3种不同厚度的超支化聚磷酰胺包覆碳纳米管(CNT/HBPPA)阻燃剂,并应用于环氧树脂(EP)中,探索了其对EP的力学及阻燃性能的影响。结果表明,随着CNT与(POCl_3+DDM)投料比(1∶1.5~6)的增加,CNT/HBPPA的包覆厚度逐渐增大并交联,而其样品失重5%时所对应的温度(T_(5%))和残炭率逐渐下降,其中CNT/HBPPA-3对EP复合材料的阻燃和增强效果最佳,仅需2%(质量分数,下同)可使其极限氧指数(LOI)值高达28.2%,UL 94为V-1级,拉伸强度提高到53.28 MPa,冲击强度提高至11.19 kJ/m~2,这主要是因为CNT/HBPPA表面的活性基团(—NH_2)改善了其与EP基体间的界面相容性,提高了分散性,形成更加均匀的网络骨架结构,从而提高其阻燃和力学性能。在燃烧过程中,这种网状骨架结构有利于形成更致密、更高效的残炭层,有效地隔绝了热量和可燃挥发性降解物的传递,进而提高了阻燃效率。

Three types of hyperbranched polyphosphoramide coated carbon nanotubes(CNTs/HBPPA)with different coating thicknesses were prepared through one⁃step polymerization(A2+B3)using carboxylic CNTs(CNT⁃COOH)as a core material,phosphorus oxychloride(POCl3)and N,N⁃diaminodiphenylmethane(DDM)as monomers,and trieth⁃ylamine as an acid binding and catalytic agent.A series of epoxy(EP)composites with different contents of CNT/HBP⁃PA were then fabricated,and the reinforcing and flame⁃retarding effects were investigated.It was found that with increas⁃ing the mass ratio of CNT to(POCl3+DDM)(1∶1.5~6),the there is an increase in the coating thickness of CNT/HB⁃PPA but an reduction in T⁃5%(the characteristic temperature at 95 wt.%mass loss)and residual char yield.The CNT/HBPPA cross⁃linked together when the mass ratio increased to 1:6.Among those composite samples,the CNT/HBP⁃PA⁃3 exhibited optimum reinforcing and flame⁃retarding effects on the EP composites.The experimental results indicat⁃ed that the EP composites containing 2 wt%CNT/HBPPA achieved the largest LOI of 28.2%,highest tensile of 53.28 MPa,and highest impact strength of 11.19 kJ/m^(2) as well as a UL 94 V⁃1 classification.There are a great number of active groups of⁃NH2 dispersed on surface of CNT/HBPPA,leading to better interfacial compatibility with the EP matrix.Therefore,the additives could be distributed more homogeneously and act as the net⁃shaped skeleton in the EP composites to achieve better flame retardancy and mechanical properties.During the combustion process,the skeleton of CNT/HBPPA potentially cross⁃linked together to construct a more compact and continuous char layer,which could pro⁃tect the underlying materials against the heat and combustible volatiles transmission efficiently.