| Epoxy resin（EP）is widely used in coatings,adhesives,electronics and composites due to its excellent properties;however,EP is extremely flammable and releases a lot of smoke/toxic gases during the combustion process.Environmental pollution and fossil energy depletion are important issues facing the society today,so the development of efficient green flame retardant technology has become the development trend of flame retardant science.How to obtain environmentally friendly flame retardants,which can improve the flame retardancy and restrain the smoke/toxic gases release,is a great challenge.In this paper,the different alginates were obtained by simple ion replacement,and alginates were used to improve the fire safety of EP.The effect of alginate on flame retardancy,thermal stability,combustion behavior and mechanical properties of EP and the corresponding flame-retardant and smoke suppression mechanisms were studied in detail.Besides,alginate was used as synergist and mixed with other highly efficient flame retardants to further improve the flame retardant efficiency and reduce the amount of flame retardants to achieve the effect of"1+1>2".The main results obtained are as follows:（1）Alginates（nickel alginate,cobalt alginate and iron alginate）were prepared by simple ion exchange.The results of infrared spectrum（FT-IR）,Inductively coupled plasma spectrometer（ICP）and scanning electron microscopy（SEM）-energy dispersive X-ray spectrometer（EDX）showed that alginates were successfully prepared.Thermogravimetric analyzer（TGA）was used to analyse the thermal stability and thermal oxidation degradation stability of alginates.（2）The EP/Alginate composites were prepared by mixing the alginates into EP and using m-phenyldimethylamine as curing agent.The flame retardancy,thermal stability,combustion behavior,smoke suppression and mechanical properties of EP/Nickel Alginate,EP/Cobalt Alginate and EP/Cobalt Alginate composites were studied by limiting oxygen index（LOI）,TGA,cone calorimetry test（CCT）,smoke density test（SDT）,universal material testing machine,impact test and thermal-dynamic mechanical analysis（DMA）,respectively.The flame-retardant mechanism was investigated by SEM,Raman spectroscopy and TG-FTIR.The results showed that nickel alginate,cobalt alginate and iron alginate can improve the flame retardancy of EP.Compared with pure EP,the char residues of EP/Nickel Alginate,EP/Cobalt Alginate and EP/Iron Alginate composites are more compact,complete and graphitized.The initial decomposition temperature(T5%)and the maximum thermal decomposition temperature(Tmax)of EP/Nickel Alginate,EP/Cobalt Alginate and EP/Iron Alginate composites were decreased with the increase of alginates content,while the char residues at 700℃were increased obviously.During the thermal degradation process,alginates were degraded at the lower temperature range,and produced the protective layers to improve the denser and completer char residues for EP at the higher temperature range.Besides,EP/Nickel Alginate,EP/Cobalt Alginate and EP/Iron Alginate composites displayed the higher storage modulus（E’）,crosslinking density（Ve）,glass transition temperature（Tg）and impact strength,and the molecular chains networks were much tighter.However,the EP/Nickel Alginate,EP/Cobalt Alginate and EP/Iron Alginate composites can not pass UL-94 V-0 rating,and it still needs further exploration and research.（3）Alginate and ammonium polyphosphate（APP）were mixed into EP to form a synergistic flame retardant system.The flame retardant properties,thermal stability and mechanical properties of EP/APP-Iron Alginate composites were studied repectively.The flame-retardant mechanism of EP/APP-Iron Alginate composites was researched by SEM,Raman and TG-FTIR.The results showed that EP/APP9.0-Iron Alginate1.0composite had the highest LOI（28.4%）when the content of flame retardant was 10%and the weight ratio of APP and iron Alginate was 9:1.And EP/APP9.0-Iron Alginate1.0passed the UL-94 V-0 rating.Although the total smoke release（TSP）of EP/APP9.0-Iron Alginate1.0composite was increased compared with EP;the TSP of EP/APP9.0-Iron Alginate1.0composite was decreased by 23.4%,compared with EP/APP composite.Besides,EP/APP9.0-Iron Alginate1.0composite exhibited the highest graphitization degree of char residues and the densest completeintumescent char residues.The T5%of EP/APP-Iron Alginate composites was decreased and the char residues of EP/APP-Iron Alginate composites were obviously increased at high temperature range.More importantly,the flexural strength,impact strength,E’,Ve and Tgof EP/APP-Iron Alginate composites were significantly improved,compared with EP.（4）Alginate was used as a synergistic agent with aluminum diethylphosphite（Al Pi）for improving the flame retardancy of EP.The flame retardancy,combustion behavior,thermal stability and mechanical properties of EP/Al Pi-Nickel Alginate composites were studied by UL-94,LOI,TGA,CCT,SDT,universal material testing machine,impact test and DMA,respectively.The flame retardant mechanism of EP/Al Pi-Nickel Alginate composites were studied by SEM,Raman and TG-FTIR.The results indicated that nickel alginate and Al Pi had synergistic flame retardant effect for EP,and the EP/Al Pi9.5-Nickel Alginate0.5composite can pass the UL-94 V-0rating when the addition of additives was only 4%.The LOI value of EP/Al Pi9.5-Nickel Alginate0.5composite reached 28.9%and PHRR decreased by58.3%.EP/Al Pi-Nickel Alginate compoaites generated more char residues at 700°C in N2/air atmospheres;and produced the higher graphitization degree,the char residues were more complete and dense.CO and other combustible gases were reduced during the thermal decomposition process.And the denser char layer can act as a barrier to prevent heat/oxygen transfer during the combustion.In conclusion,Al Pi and nickel alginate have synergistic flame retardant effect on the flame retardancy of EP,and have little destructive effect on the mechanical properties of EP. |
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