| Flexible polyurethane foams (FPUF) are primarily used for cushioning material with application in furniture, automobiles because of its better mechanical performance. As a porous polymer, FPUF readily ignites and burns rapidly with dripping and evolution of smoke and toxic gases. It is very necessary to develop such kind of FPUF with high flame retardant properties, low evolution of toxic gases, and good mechanical performance in order to avoid loss of life and property causing from fire disaster. As a type of halogen-free physical intumescence flame retardant, expandable graphite (EG) is very suitable for polyurethane foams.The innovation points of this subject are as follows:1) EG was filled in FPUF to get flame-retardant FPUF composites, and the cooperation effects of DMMP, MEL, or ZB with EG were also studied;2) the damping properties of FPUF composites were examined by dynamic mechanical analysis, and the decomposition products of FPUF composites were examined and characterized by Pyrolysis-gas chromatography/mass spectrometry and thermal thermogravimetric analyzer-Fourier transform infrared spectroscopy;3) EG was successfully encapsulated with melamine formaldehyde (MF) resin/zinc borate(ZB) or polyurethane (PU) resin, and then they were added in FPUF separately. The main contents and conclusions are as follows:(1) The FPUF formulation was optimized by selecting of different types of raw materials and adjusting their amount. Then FPUF was synthesized by one-stage process. The processing technic was found to be a good solution to the bubble problem of shrinkage, collapse, gel seriousness, size unevenness and so on during the foam forming process.(2) The EG with particle size of180μm or40μm was added to the FPUF formulation and it was investigated that their effects on bubble morphology, mechanical property, thermal stability, release of toxic gas property and flame-retardant property of FPUF composites. Small size of EG40was more likely to destroy FPUF bubble morphology and lead its mechanical performance decline than that of EG180at the same amount. The LOI value of9.3%EG180/FPUF could reach to23%which was higher than that of9.3%EG40/FPUF. Expanded graphite was so large that could effectively inhibit dripping. EG expansion reduced the rate of the second step thermal degradation of FPUF. But EG did not promote to transform burning FPUF into char, so there were no significant changes on the thermal degradation process of FPUF.(3) When FPUF was filled with too much EG, the mechanical properties of EG/FPUF would decline apparently. So it is meaningful for EG to compound with other kind of flame retardants. DMMP or/and EG were added to the FPUF formulation and it was investigated that their effects on bubble morphology, mechanical property, thermal stability, release of toxic gas property and flame-retardant property of FPUF composites. The storage modulus, loss modulus, and damping performance of FPUF composites were improved after adding EG or/and DMMP during glass transition process of PU hard segment. More decomposition product types and quantity of FPUF were evolved at750℃than at400℃. EG did not change product types obviously, but DMMP made the concentration of the decomposition products increase and types become more complicated. Adding EG decreased the yield of CO and increased the yield of CO2at the time of maximum decompose velocity, but DMMP showed opposite results, although DMMP improved the stability of FPUF. The horizontal burning test results indicated that adding3.3%DMMP could make FPUF achieve SE rating. According to the LOI test, the LOI value of9.3%DMMP/FPUF was24.5%and there is synergistic effect between EG and DMMP. The products of DMMP were so viscous that they increased bond force between expanded graphite layers.(4) MEL or/and EG were added to the FPUF formulation and it was investigated that their effects on bubble morphology, mechanical property, thermal stability, release of toxic gas property and flame-retardant property of FPUF composites. The damping performance of FPUF was improved after adding EG or/and MEL. There was synergetic effect between EG and MEL as for thermal stability when adding the two together in FPUF. The yield of CO of9.3%MEL/FPUF and (6.4%MEL+9.3%EG)/FPUF was less than that of FPUF during decompose process when MEL react with isocyanate at first. The LOI value of9.3%MEL/FPUF was22.5%and there is synergistic effect between EG and MEL.(5) ZB or/and EG were added to the FPUF formulation and it was investigated that their effects on bubble morphology, mechanical property, thermal stability, release of toxic gas property, and flame-retardant property of FPUF composites. The bubble morphology of12.8%ZB/FPUF was still good, and its aperture was even. The cell wall of (9.3%EG+12.8%ZB)/FPUF was slightly folded but integrated. There were many ZB particles buried in cell wall, leading to mechanical properties worsen because it is difficult to transfer stress effectively for the reason of poor interfacial compatibility. ZB reduced the rate of the second step thermal degradation of FPUF. The yield of ethers, aldehydes with small molecule and CO of12.8%ZB/FPUF and (12.8%ZB+9.3%EG)/FPUF was less than that of FPUF during decompose process, so it can be concluded that ZB reduced the production of toxic gas during thermal decomposition of FPUF. There is synergistic effect between EG and ZB and when the ratio of EG to ZB was9.3:12.8, the value of LOI reached28%which is the maximum value. The carbon layer structure of ZB/FPUF was so compact with no holes that it could inhibit to transfer heat, combustible gas and oxygen, which was beneficial to the flame retardant property.(6) In order to improve the expansion volume and compatibility, EG was encapsulated with melamine formaldehyde (MF) resin by the in situ polymerization, and then ZB was deposited on the surface of MF-EG to get MF/ZB-EG. MF/ZB-EG was filled in FPUF. As for MF-EG and MF/ZB-EG, there were melamine ring breathing vibration peaks at975cm-1. There was a certain amount of nitrogen, boron and zinc element in MF/ZB-EG. The mass loss rate of MF/ZB-EG was higher than EG and the residual mass MF/ZB-EG was less than that of EG. The expanding endothermic peak of MF/ZB-EG was lower than that of EG. SEM observation showed that there was a layer of pellet which should be MF/ZB on the surface of EG. The expanding volume of MF/ZB-EG was greater than that of EG significantly. These above results indicate that MF/ZB was successfully coated on EG. However, the bubble holes of (MF/ZB-EG)/FPUF were extremely bulky and its aperture was uneven. The mechanical properties of (MF/ZB-EG)/FPUF were declined obviously. The flame retardant grade of (MF/ZB-EG)/FPUF did not improve, comparing with that of FPUF.(7) PU-EG was got by encapsulating with polyurethane (PU) resin by the in situ polymerization, and then PU-EG was filled in FPUF. SEM observation showed that there was a layer of pellet which should be PU resin on the surface of EG which was integrated coated. Elemental analysis results showed that the nitrogen element of PU-EG was0.291wt%. The weight loss rate of PU-EG tested by TGA was higher than that of EG, which indicated that there were more gases released during expansion of PU-EG. The bubble morphology of9.3%(PU-EG)/FPUF was better than that of9.3%EG/FPUF, and its aperture was even. A side of PU-EG particle was embedded in FPUF matrix instead of locating, so they integrated closely, implying their very good compatibility. The mechanical properties of9.3%(PU-EG)/FPUF were improved because PU layer could take effect of transferring stress between the inorganic and the organic interface. The DMA test also showed that the PU-EG particles could improve the damping performance of9.3%(PU-EG)/FPUF and the storage modulus because the PU-EG embedded in FPUF matrix could limit restrain the movement of the molecular chain. The expanded volume of PU-EG (70mL/g) was also larger than that of EG (50mL/g). The greater the expansion volume the better effects of adiabatic anaerobic effect. Then the LOI value of9.3%(PU-EG)/FPUF was reached to 24.5%from23%of EG. |
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