| Poly?ethylene terephthalate??PET?as one of five major general-purpose plastics,with excellent mechanical,fiber forming and abrasion resistance properties,has been applied widely in various fields,such as engineering plastics,fibers,and films.PET fiber ranks the first in the synthetic fiber.However,PET,with the limit oxygen index?LOI?value of 21%,belongs to flammable materials,and produces a large amount of black smoke during combustion process,resulting in its limited application.Therefore,it is of equal significance to endow flame retardancy and smoke suppression to PET.The requirements for current flame retardants are halogen free,low toxicity and little smoke.On this basis,the purpose of this dissertation is to reduce flame-retardant amount,enhance the interfacial compatibility between flame retardant and PET substrate,and minimize the deteriorating impact on the mechanical property of PET.Carbon materials with low dosage can reduce the thermal hazards produced by polymer combustion.In view of the flame retardancy,structural characteristics,process cost of carbon materials,and the fibrous requirement of PET fiber,this dissertation put emphasis on multi-walled carbon nanotubes?MWCNTs?with large aspect ratio and carbon microspheres?CMSs?with rich functional groups for the flame retardant modification of PET.Then,to achieve simultaneously the flame retardancy and smoke suppression of PET,the MWCNTs-based and CMSs-based acid,gas source composites were separately constructed by integration technology.Meanwhile,the CMSs-based smoke suppressant composites can also achieve the flame retardancy and smoke suppression of PET.Finally,the three kinds of carbon-based composite flame retardants were applied in PET fiber.The main research contents and conclusions are as follows:1.The effects of MWCNTs or CMSs on the flame retardancy of PET were investigated:through the melt blending method,the MWCNTs/PET and CMSs/PET composites were prepared.The flame retardancy,flame-retardant mode and mechanism were discussed.The results showed that,MWCNTs and CMSs improved the flame retardancy of PET by changing the carbon layer structure,molten viscosity and thermal oxygen stability,and the amount of carbon materials affected the flame retardancy.When the MWCNTs dosage was only 0.5%,MWCNTs/PET formed the network carbon layer and increased the melt viscosity,increasing the LOI value from 21%to only 22.1%.But the peak heat release rate?pk-HRR?and total heat release?THR?decreased from 513.22 kW/m2,71.9 MJ/m2to 397.73 kW/m2,69.3 MJ/m2,respectively,and the combustion time was shortened.MWCNTs reduced the heat damage and terminated the combustion in advance.The flame-retardant mode was mainly physical barrier and flame inhibition.When the CMSs dosage was only 1%,CMSs/PET composites formed the turbulent carbon layer and decreased the melt viscosity,increasing the LOI value from 21%to 26.1%.Thermal parameters pk-HRR and THR value respectively decreased to 349.47kW/m2 and 69.7 MJ/m2,indicating that CMSs increased the oxygen content required for PET combustion and decreased the heat hazard.The flame-retardant mode was mainly physical barrier and catalytic charring.However,the MWCNTs/PET and CMSs/PET composites cannot inhibit smoke and reach the V-0 level because of no self-quenching,so sole MWCNTs or CMSs cannot meet the requirements of flame retardancy and smoke suppression of PET.2.To achieve simultaneously the high efficient flame retardancy and smoke suppression of PET,the integration technology was used to construct carbon-based composite flame retardant?PCS-MWCNTs,Si MP-CMSs,PMH-CMSs?.The following three aspects were mainly carried out:With MWCNTs as carbon base,the construction of MWCNTs-based acid and gas source and the effects on the properties of PET were investigated:chitosan?CS?as gas source and phosphoric acid?H3PO4?as acid source were introduced onto the MWCNTs surface by chemical deposition cross-linking and esterification to construct the MWCNTs-based phosphorylated chitosan?PCS-MWCNTs?composites.And the PCS-MWCNTs/PET composites were prepared through melt blending.The results showed that:?1?PCS-MWCNTs had a core-shell structure with a PCS loading of about 36.1%on the surface.Compared with MWCNTs,PCS-MWCNTs exhibited stronger interfacial bonding force with PET matrix.?2?When the PCS-MWCNTs dosage was 2%,the LOI value was 26.1%and V-0 level was reached.The pk-HRR and THR values reduced respectively to 269.69 kW/m2 and 62.4 MJ/m2.And the total smoke production?TSP?and average specific extinction?av-SEA?has decreased reaspectively from 14.7 m2 and 447.82 m2/kg to11.7 m2 and 275.29 m2/kg.PCS-MWCNTs increased the oxygen content for PET combustion and self-quenching,meawhile reduced the heat damage and smoke harm.The corresponding flame-retardant mode was43.46%physical barrier+15.39%flame inhibition+4.35%catalyztic charring.?3?The flame retardant mechanism was that:PCS layer first produced the CS and phosphide,covering on the carbon layer constructed by MWCNTs and enhancing the barrier effect.H3PO4 catalyzed the charring of PET,and ammonia?NH3?inhibited the flame spread.On the basis of previous research,with CMSs as carbon base,the construction of integrated CMSs-based acid and gas source and the effects on the properties of PET were investigated:H3PO4 still as acid source and melamine?MEL?as gas source were introduced on CMSs surface by the hydrothermal method,and then modified by silanization to form the CMSs-based melamine phosphate?SiMP-CMSs?.The Si MP-CMSs/PET composites were prepared by melt blending method.The results showed that:?1?SiMP-CMSs had core-shell structure with an SiMP loading of about 64.1%on the surface,and the silanized Si MP-CMSs strengthened the interface binding with the PET matrix.?2?When the SiMP-CMSs dosage was 3%,the LOI value was 27.7%and V-0 level was reached.And the pk-HRR,THR,TSP and av-SEA values reduced respectively to 221.66 kW/m2,59.3 MJ/m2,12 m2 and 369.45m2/kg.SiMP-CMSs made PET reach the refractory level with self-extinguishment,and also reduced the heat damage and smoke harm.The corresponding flame-retardant mode was 47.63%physical barrier+19.04%flame inhibition+9.04%catalytic charring.?3?The flame retardant mechanism was that,the SiMP layer decomposed MEL and H3PO4.Then MEL was gasified to release much NH3,which rapidly diluted the flammable gas and inhibited the flame spread.The char produced by H3PO4 catalyzing PET matrix and the triazine ring structure produced from MEL all covered on the carbon layer constructed by CMSs,enhancing the barrier effect and thermal stability.This terminated the flame in advance,and blocked the smoke way,consequently achieving flame retardancy and smoke suppression.To simultaneously reach the flame retardancy and smoke suppression of PET,the construction of integrated CMSs-based smoke suppressant and the effects on the properties of PET were investigated:Magnesium hydroxide?MH?was loaded on CMSs surface to obtain the CMSs-based MH?MH-CMSs?by liquid phase deposition.The MH-CMSs were further encapsulated and oligomer PET was coated on MH-CMSs surface?PMH-CMSs?.The PMH-CMSs/PET composites were obtained by melt blending method.The results showed that:?1?PMH-CMSs had a capsule structure with CMSs as core,MH and oligomer PET as inner and outer shells.And the interface bonding between the encapsulated PMH-CMSs and PET matrix was enhanced.?2?When the PMH-CMSs dosage was 2%,the LOI value was 27.6%and V-0 level was reached,implying that PMH-CMSs made PET reach the refractory level with self-extinguishment.The pk-HRR,TSR,TSP and av-SEA values reduced respectively to 279.29 kW/m2,52.8 MJ/m2,8.2m2 and 350.57 m2/kg,demonstrating the heat damage and smoke harm were reduced,especially in the smoke aspect.The corresponding flame-retardant mode was 25.89%physical barrier+12.30%flame inhibition+18.34%catalyztic charring.?3?The flame retardant mechanism was that,the PMH-CMSs decomposition turned stepwise,and oligomer PET first decomposed,causing heat accumulation around the flame-retardant particles.Then the MH layer rapidly absorbed the heat,decomposed and released much water vapor,rapidly reducing the heat and oxygen concentration.And the magnesium oxide?MgO?covered the carbon layer constructed by CMSs and increased the compactness.The smoke production was reduced,and flame retardancy and smoke suppression were achieved.3.To achieve the flame retardant modification of PET fiber,the above carbon-based composites were applied in PET fiber by melt spinning method.The morphology,aggregation structure,flame retardancy and mechanical property of the PET fiber were analyzed in detail.The results showed that,the interfacial compatibility between the three kinds of flame retardants and PET fiber was better,and the aggregation structure was also optimized.When the flame retardant dosage was 0.9%,the LOI values of PCS-MWCNTs/PET,Si MP-CMSs/PET and PMH-CMSs/PET fiber were respectively 25.1%,27.4%and 27.2%.The damaged lengths were less than 15 cm.With the continuous burning and smoldering time of less than 5 s,the vertical burning all reached B1 level.And the smoke production was all decreased.The thermal stability,crystallinity and orientation degree of PET fiber were improved,and the tensile strength met the demands for use.In conclusion,constructing the carbon-based composite flame retardant for PET can reduce the flame-retardant dosage.Compared with traditional direct compounding,the“integration”method was proposed to construct multiple components as a whole.This method can not only simplify the numerous interface problems between various flame retardants and PET matrix,but also effectively exert the comprehensive effect of various flame retardants,finally achieving the flame retardancy and smoke suppression. |
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