Preparation and characterization of TiO 2 -coated hollow glass microsphere and its ﬂame-retardant property in thermoplastic polyurethane Hongzhi Wang 1 • Chuanmei Jiao 1 • Li Zhao 1 • Xilei Chen 1 Received: 19 June 2017 / Accepted: 15 September 2017 / Published online: 25 September 2017 Ó Akade ´miai Kiado ´, Budapest, Hungary 2017 Abstract In this paper, a novel and efﬁcient halogen-free ﬂame retardant, HGM@TiO 2 , was synthesized by coating hollow glass microspheres (HGM) with TiO 2 . The ﬂame- retardant and smoke suppression properties of HGM@TiO 2 in thermoplastic polyurethane (TPU) have been investi- gated using several techniques including cone calorimeter test (CCT), smoke density test (SDT), thermogravimetric analysis (TGA) and fourier infrared, respectively. The CCT results showed that HGM@TiO 2 could greatly improve the ﬂame-retardant properties of TPU composites. The peak heat release rate of the sample with 0.5 wt% HGM@TiO 2 (405 kW m -2 ) was reduced by 64% compared with the sample with the same loading HGM (1117 kW m -2 ), and the structure of char residue layer of TPU composites was obviously changed. The SDT results showed that HGM@TiO 2 could effectively decrease the amount of smoke production in the test. Furthermore, the TGA results indicated that HGM@TiO 2 could decrease the initial decomposition temperature and improve the thermal sta- bility of TPU. And the FTIR results revealed that HGM@TiO 2 could promote the composites to release inﬂammable gas such as CO 2 earlier to suppress the combustion. According to this study, there may be some new methods to obtain ﬂame-retardant polymer with low loading level. Keywords Hollow glass microspheres Á Coating Á TiO 2 Á Thermoplastic polyurethane Á Flame retardant Introduction In recent years, thermoplastic polyurethane (TPU) has been widely used in coatings, ﬁlms, automotive and infrastruc- ture cables, etc. [1–4]. However, high ﬁre risks associated with TPU, including dense smoke generation, high heat and toxic gases release, have greatly limited its broad applications. As a consequence, the study on how to improve the ﬂame-retardant properties of TPU has attrac- ted more and more attentions. Traditionally, ﬂame retar- dants containing the halogen [5] will be harmful to people in the process of application, and the demands for halogen- free ﬂame retardants have become more and more impor- tant due to the healthy and environmental concerns [6–8]. Intumescent ﬂame retardant, as an environmental friendly ﬂame retardant, has been widely used in the TPU composites [9]. The effect is good, but there are still some disadvantages. Such as the amount of intumescent ﬂame retardant is usually relatively large, which will have a great inﬂuence on mechanical properties [10]. Inorganic nano- materials and nano-composite (montmorillonite, clay and nano-ZnO) are also used as ﬂame retardants being added into polymer materials [11–13] and have a good ﬂame- retardant effect [14–17]. But the nano-materials are easy to agglomerate, leading to the particle size too large to dis- perse uniformly, and the effective controlling of nanopar- ticle agglomerates is not easy. Hollow glass microspheres (HGM) have attracted con- siderable interest in the past few decades because of its excellent physical, such as well-deﬁned morphology, uni- form size, strong ﬁlling ability, low density, and large surface area, small and well-distributed internal stress in products [18, 19]. HGM were often used to reinforce polymer for its high compression strength and good ﬂuidity [20]. In our previous work, it has been found HGM could & Xilei Chen xilei_chen@foxmail.com 1 College of Environment and Safety Engineering, Qingdao University of Science and Technology, Qingdao 266042, Shandong, People’s Republic of China 123 J Therm Anal Calorim (2018) 131:2729–2740 https://doi.org/10.1007/s10973-017-6719-0