| Polypropylene (PP), as an thermoplastic commodity plastic, has been widely used in many fields because of its outstanding mechanical performances, low cost, and ease of processing, such as cars, electronic shells, architectural materials, furniture, interior decorations. However, the inherent flammability and dripping tendency of PP limits its wide applications in many fields where good fire retardancy is required. Among various ways to increase of flame retardancy of PP, intumescent flame retardant (IFR) has been considered to be a promising method, because it is low toxicity, low smoke and halogen free.IFR formulations consist of three parts:an acid source, a char source, and a gas source. These additives act as flame retardants by forming a carbonaceous char, and a kind of physical barrier to inhibit the transfer of heat and diffusion of inflammable gases, subsequently leading to a quick self-extinguishment of the burning materials. Ammonium polyphosphate (APP), as the most common of acid source in IFR, and a blowing agent (NH3 evolved from APP during its degradation can play this role) has been extensively investigated. Unfortunately, APP is easy to migrate and bloom, due to poor compatibility with the polymer matrix result in decrease of the mechanical properties. When used as a single flame retardant, the flame retardant efficiency is poor relatively.In this paper, different methods modified to APP and study the effects of APP’s structure and properties. The modification of APP added in PP matrix, study the burning behavior, thermal properties and mechanical properties of the composite materials. Aims to obtain excellent flame retardancy and mechanical properties of environmentally friendly halogen-free flame retardant composite materials, to provide basic data and theoretical guidance for the realization of halogen-free flame retardant used in the industry. The main results of this paper are as follows:1. APP was microencapsulated with TPU, by using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Learn the structure and properties of modified-APP are different with APP, and proved the success of the preparation modified-APP. Added modified-APP in the PP material prepared different contents of PP/modified-APP flame retardant composites, its combustion behavior, thermal stability and mechanical properties were studied. The results show the modified-APP has better flame retardancy and thermal stability compared with APP in the flame-retardant PP composites. In addition, The heat release rate (HRR), total heat release (THR), CO emmision, and CO2 emmision values of PP/modified-APP composites obtained from Cone calorimeter test (CCT) significantly decrease compared with those of pure PP and PP/APP composites. The mechanical properties of the flame retardant PP composites are worse than those of pure PP.2. PA6 as macromolecular charring agent, the combustion behavior, thermal stability and mechanical properties of the PP/modified-APP/PA6 flame retardant composites were investigated. The results show that the combination of modified-APP with PA6 to flame retarded PP composites has a high LOI value than only modified-APP to the PP matrix and reaches UL-94 V-2 rating. In addition, PP/modified-APP/PA6 flame retardant composites have better the intumescent char layer quality and thermal stability than PP/modified-APP composites.3. APP was microencapsulated with alumina-silica hydrogel, and the PP/MDAPP/PA6 flame retardant composites were prepared by melting blends. The combustion behavior, thermal stability and mechanical properties of the above composites were studied. The results show that two samples reache UL-94’V-0 rating, and the other two samples reach UL-94 V-1 rating. Compared with PP/APP/PA6 systems, PP/MDAPP/PA6 systems have higher LOI value and better flame retardancy and thermal stability. |
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