Microencapsulation of ammonium polyphosphate with PVA–melamine–formaldehyde resin and its flame retardance in polypropylene Kun Wu 1 , Lei Song 1 , Zhengzhou Wang 1,2 * and Yuan Hu 1 * 1 State Key Laboratory of Fire Science, University of Science and Technology of China, Anhui 230026, P.R. China 2 School of Materials Science and Engineering, Tongji University, Shanghai 200092, P.R. China Received 30 April 2008; Accepted 17 June 2008 With a shell of PVA–melamine–formaldehyde resin, microencapsulated ammonium polyphosphate (VMFAPP) is prepared by in situ polymerization and characterized by FTIR and XPS. Microencap- sulation gives VMFAPP better water resistance and flame retardance compared with APP in PP. Thermal stability and fire resistance behavior have been analyzed and compared. The LOI value of the PP/VMFAPP composite is higher than that of the PP/APP composite. The UL 94 ratings of most of the PP/VMFAPP composites are V-0, whereas PP/APP gives no rating at the 30% additive level. The water resistant properties of the PP composites are studied. Results of the cone calorimeter experiment show that VMFAPP is an effective flame retardant in PP compared with APP. The thermal degradation behaviors of APP and VMFAPP have been studied using TG and dynamic FTIR. Copyright # 2008 John Wiley & Sons, Ltd. KEYWORDS: microencapsulation; ammonium polyphosphate; intumescent flame retardation; thermal degradation; PVA; melamine– formaldehyde; PP INTRODUCTION There has been enormous loss of materials and high rates of human mortality due to the weak flame resistance properties of polymers. Intumescent flame retardants (IFRs) have attracted considerable attention in recent years because they are more environmentally friendly than the traditional halogen-containing flame retardants. IFR systems contain three active ingredients: an acid source (e.g. ammonium polyphosphate (APP), etc.), a carbonization agent (e.g. pentaerythritol, polyurethane, etc.), and a blowing agent (e.g. melamine). Bourbigot and co-workers have carried out extensive studies on the APP IFR system in polyolefins 1–3 and have reviewed recent developments of IFR systems in great detail. 4 But these systems are not durable due to the weak water resistance and low compatibility with organic materials of APP. In order to overcome this problem, microencapsulation is a good choice. Melamine–formaldehyde (MF) resin is commonly used in microencapsulation of red phosphorus, 5 n-octadecane, 6 etc. Poly(vinyl alcohol) (PVA) is used for the microencapsulation of di-ammonium hydrogen phosphate (DAHP) using coacervation and the interfacial polymerization technique, and the shell can be used as a charring agent in the flame retardance of polymers. 7,8 PVA, with many O–H groups, readily reacts with low molecular weight compounds and various functional polymers can be obtained with relative ease. 9 Our group has recently microencapsulated APP with a MF and urea–melamine–formaldehyde (UMF) resin shell. 10,11 Compared with APP, the microencapsulated APP (MCAPP) coated with MF or UMF resin can be dispersed well in the PP matrix and has lower water solubility. Because of the scarcity of the carbonization agent in MCAPP, there are no ratings in the UL 94 test for the PP composites containing MCAPP although the LOI values of the PP composites containing MCAPP are higher than those of the PP composites containing APP at the same content. To solve the problem, we developed a different approach to microencapsulate APP with a PVA modified MF resin shell. Our aim is to synthesize microcapsules which contain the three ingredients of a typical IFR system: acid source (APP), carbonization agent and blowing agent (PVA–melamine–formaldehyde (VMF)). The advantage of this is that it is possible to synthesize an intrinsic flame retardant which may have better flame retardance and higher water resistance in the polymer, compared with APP. In this paper, microencapsulated APP (VMFAPP) with a VMF resin shell was prepared by in situ polymerization and characterized by water solubility, Fourier transform infrared (FTIR), thermogravimetry (TG), and X-ray photoelectron spectroscopy (XPS). The use of VMFAPP as a flame retardant in PP is evaluated by limiting oxygen index (LOI), UL-94, TG, cone calorimetry, and scanning electron microscopy (SEM), POLYMERS FOR ADVANCED TECHNOLOGIES Polym. Adv. Technol. 2008; 19: 1914–1921 Published online 2 September 2008 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/pat.1231 *Correspondence to: Z. Wang and Y. Hu, State Key Laboratory of Fire Science, University of Science and Technology of China, Anhui 230026, P.R. China. E-mail: wwang@uste.edu.cn and yuanhu@ustc.edu.cn Copyright # 2008 John Wiley & Sons, Ltd.