title: Efficient approach to improving the flame retardancy of poly(vinyl alcohol)/clay aerogels: incorporating piperazine-modified ammonium polyphosphate.
abstract: Ammonium polyphosphates (APP) modified with piperazine (PA-APP) was used to improve the flame retardancy of poly(vinyl alcohol) (PVA)/montmorillonite (MMT) aerogels, which were prepared via an environmentally friendly freeze-drying method. The thermal stabilities of the samples were evaluated by thermogravimetric analysis (TG); the flammability behaviors of samples were investigated by limiting oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter (CC) tests. TG test results showed that the 5% weight loss temperature (T5%) of PVA/MMT/PA-APP was 10 °C higher than that of PVA/MMT/APP. In combustion testing, all of PVA/MMT/PA-APP aerogels achieved V-0 ratings and have a higher LOI values than the unmodified PVA/MMT aerogel. Moreover, the aerogel with 1% PA-APP5, which means that the content of piperazine is 5% in PA-APP, decreased the cone calorimetry THR value to 5.71 MJ/m(2), and increased the char residue to 52%. The compressive modulus of PVA/MMT/PA-APP was increased by 93.4% compared with PVA/MMT/APP because of the increase in interfacial adhesion between matrix and PA-APP fillers. The densities of the PVA/MMT/PA-APP samples were slightly lower than those of the unmodified aerogels because of reduced shrinkage in the presence of PA-APP. All the tests results indicated that the incorporation of PA-APP not only improved the thermal stability and flame retardancy of aerogels but also maintained their mechanical properties.
authors.affiliation: Center for Degradable and Flame-Retardant Polymeric Materials, College of Chemistry, State Key Laboratory of Polymer Materials Engineering, National Engineering Laboratory of Eco-Friendly Polymeric Materials (Sichuan), Sichuan University , Chengdu 610064, China.
authors.forename: Yu-Tao
authors.initials: YT
authors.lastname: Wang
authors.forename: Shi-Fu
authors.initials: SF
authors.lastname: Liao
authors.forename: Ke
authors.initials: K
authors.lastname: Shang
authors.forename: Ming-Jun
authors.initials: MJ
authors.lastname: Chen
authors.forename: Jian-Qian
authors.initials: JQ
authors.lastname: Huang
authors.forename: Yu-Zhong
authors.initials: YZ
authors.lastname: Wang
authors.forename: David A
authors.initials: DA
authors.lastname: Schiraldi
keywords: aerogel; ammonium polyphosphate; flame retardant; mechanical behavior; piperazine; poly(vinyl alcohol)