Microencapsulation Of Ammonium Polyphosphate With Double Shells And Its Flame Retardation In Polypropylene

Ammonium polyphosphate(APP) is an excellent representative of halogen-free flame retardants because its low toxicity, absence of dioxins, and low smoke production in fire accidents. In order to achieve excellent flame-retardant effect, APP is commonly combined with pentaerythritol as carbonization agent and melamine as blowing agent to form a typical intumescent flame retardant (IFR) systems, some shortings are associated with phosphorus-based IFR, such as moisture sensitivity and poor compatibility with polymer matrices, poor dispersibility in polymer matrices. In order to overcome these drawbacks, a trinity IFR was prepared by microencapsuating APP with double shell, in which APP is as acid source, MF resin as blowing agent and PG resin as carbonization agent. The main research contents and results of this paper are as followed:First of all, investigations on thermal activation nature of two types of APP(APP-C and APP-S) were carried on. The results demonstrated that the initial thermal activation temperature of APP-C was 50℃ higher than that of APP-S. APP-C was found to be modified by FTIR. Two kinds of MFAPP were prepared respectively by microencapsuation in wet process and in dry process, and were characterized by solubility. The result demonstrated that the hydrophobicity of the MFAPP prepared in wet process was better than that of the MFAPP prepared in dry process.Second of all, the cross-linking between polyvinyl alcohol and glutaraldehyde was characterized, by measuring the polyvinyl alcohol concentration in the reaction spectrophotometrically, determining the stoichiometric ratio between polyvinyl alcohol and glutaraldehyde. The experimental results have demonstrated that the cross-linking reaction is irreversible and the stoichiometry of polyvinyl alcoholg and lutaraldehyde is about 1:525. The kinetic equation has also been established for said cross-linking reaction, with the polyvinyl alcohol and glutaraldehyde exhibiting a kinetic order of zero and 0.7 respectively, and the obtained kinetics equation is r=1.67×108exp(-77.50×103/RT)×CB07. where Cb is the concentration of glutaraldehyde, mol-LThird of all, MFAPP and PG-MFAPP microcapsules were prepared by in situ method and the properties of APP, MAPP and PG-MFAPP were investigated by water solubility, FTIR, TGA and SEM. The water solubility of APP declined by 80% after microencapsulated by MF when the mass ratio of shell and nucleus of MFAPP was 30%, while the water solubility of MFAPP increased after microencapsulated by PG. The characteristic absorption peaks of PG resin and MF resin showed in FTIR of PG-MFAPP demonstrated APP was coated by these two kinds of resin shells. The mass of MF and PG in the shell of PG-MFAPP was respectively 30% and 6% of mass of the core of APP. However, the thermostability of PG-MFAPP was slightly worse than that of MFAPP.Last of all, The combustion, thermal degradation behaviors and tensile properties of PP blended with APP, MCAPP or PG-MFAPP were investigated by TGA, UL-94 test and tensile test. The results demonstrated that among the PP compounds with the same loading levels of APP, MCAPP or PG-MFAPP respectively, the LOI value of 70PP/30PG-MFAPP composite was higher, but all three PP compounds can not reach any UL-94 rating like others. However, APP has much less negative influence on the mechanical properties than MFAPP or PG-MFAPP. The stability of APP and incarbonization of flame retardant were improved when APP was modified with PG and MF resin.A new kind of IFR was prepared in this paper by microencapsuating APP with double shell composed of PG and MF by in situ polymerization method, and the research achievements laid the foundations for future production application.