The Flame Retardant Effects Of Chitosan Derivaives On Polyurethane Composites

Natural polysaccharides,which has multi hydroxyl groups,can be used as a potential alternative for petroleum-based charring agents in traditional intumescent flame retardant formulations.Therefore,more and more attention has been paid to the preparation of bio-based flame retardants in the past two decades,whilst the traditional flame retardants have been faced increasing environmental pressure.Chitosan is the only alkaline polysaccharose in the nature,and its char formation ability has been proved in flame retardant flexible polyurethane foam and cotton fabric.It has been rarely reported that chitosan derivatives could be introduced as flame retardant derivatives for polymeric composite by melt blending owing to its inherent relative low degradation temperature.In this work,several chitosan derivatives were prepared and applied to prepare multifunctional flame resistance of polyurethane materials.A variety of chitosan devivatives were designed and prepared according to the chemical structure of chitosan,and then were used in intumescent flame retardant formulation,organic modification of nanoparticles,microencapsulation of flame retardants and layer by layer nanocoating.All of these chitosan deviratives containing compounds have been incorporated into polyurethane materials.The effects and mechanism of chitosan derivatives on flame retardancy,thermal stability and mechanical properties of polyurethane materials have been investigated.The main work/outcome has been summarized as follows:1.Three chitosan(CS)derivatives with high thermal stability and charring ability were prepared by reacting CS with benzaldehyde,salicylaldehyde and hydroxybenzaldehyde,respectively.CS derivatives in association with ammonium polyphosphate(APP)were then introduced into thermoplastic polyurethane(TPU)to prepare flame retardant TPU composites.The sample containing 18.75%APP and 6.25%salicylaldehyde modified CS(SCS)achieved the maximal limiting oxygen index(LOI)of 29.5%,passed the UL-94 V-0 rating and significantly decreased the peak heat release rate(pHRR)from 840.8 kW/m2 of TPU to 206.2 kW/m2.Thermogravimetric analysis(TGA)and char morphology observation demonstrated that SCS/APP could promote the char formation to form more intact intumescent char structure.It is proposed that the synergism between CS derivatives and APP might be responsible for the improvement of flame retardancy.2.A novel flame retardant(ACS)was prepared by crosslinking chitosan with bis-(4-formylphenyl)-phenyl-phosphonate(ABPO).ACS in association with APP and organic modified montmorillonite(OMMT)were used to prepare flame retardant TPU composite through melt blending.For the TPU sample containing 10%flame retardants,the LOI value was increased from 20.8 to 29.0%,the UL-94 rating was upgraded from no rating to V-0,and the pHRR was decreased 73.9%.The thermal analysis indicated that ACS exhibited excellent char formation ability and greatly enhance the thermal stability of TPU.The tensile strength and elongation at break for flame retardant sample reached 16.5 MPa and 1443%,respectively.3.Phosphorylated chitosan(PCS)was synthesized and applied to decorate montmorillonite(MMT)under ultrasonic catalysis to prepare organically modified exfoliated montmorillonite(PMT).It was demonstrated that PMT had better synergism with aluminum hypophosphite(AHP)than MMT in improving the fire resistance of TPU composites.By the presence of 9%AHP and 1%PMT,the LOI of TPU composites was increased to 28.4%,the UL-94 rating was achieved to V-0,furthermore,the TSR and pHRR value were significantly reduced to 11.9%and 17.9%of its corresponding value for control samples,respectively.4.Melamine polyphosphate(MPP)was microencapsulated by toluene diisocyanate cross-linked carboxymethyl chitosan(CMCS),and then was applied to prepare flame retardant(MCMPP)and water resistant TPU composite.The water contact angle was significantly increased by microencapsulation,which was due to the reduction of hydrophilic groups in CMCS.The LOI value was increased to 28.6%,and UL-94 test rating was reached up to V-O for the TPU composite sample containing 15 wt%MCMPP.Moreover,the incorporation of MCMPP remarkably reduced the pHRR,THR,the total smoke release and carbon monoxide production by 65.9,24.1,87.3 and 60.6%,respectively.The TPU/MCMPP composite sample still achieved V-0 rating in UL-94 test after immersing in water for 72 h at 70?,which was due to the increased compatibility of MCMPP with the matrix provided by the hydrophobic structure of microencapsulated cross-linked CMCS.It is proposed that microencapsulated MPP simultaneously play roles of acid source,carbonization agent and blowing agent in the formation of intumescent char layers during combustion.5.CS,APP,CS and poly(acrylic acid)-stabilized kaolin(PAA-KAO)clay were deposited as quadlayers onto the surface of flexible polyurethane foam(PUF)via layer-by-layer assembly in order to improve the fire resistance of the foam.The effectiveness of this nanocoating on flame suppression was compared to control films without KAO and bilayer coatings.PUF coated with only five CS/APP/CS/PAA-KAO quadlayers(around 184 nm thick)maintained its open porous structure and self-extinguishes upon exposure to a butane torch flame for 10 s.Cone calorimetry test revealed the peak heat release rate and total smoke release of coated sample was reduced by 66.8%and 59.3%,respectively,compared with that of uncoated foam.Thermal behavior analysis indicated the combination of intumescent components and clay promoted char formation and improved the thermal stability of the polyurethane substrate.This multilayer coating has the potential to improve the fre safety of PUF,which could be used in home furnishings,and a variety of other polymeric substrates.In summary,chitosan derivatives can be used in flame retardant thermoplastic materials after appropriate modification.The influence of molecular structure on the thermal stability of chitosan derivatives are fully discussed.The study also provides useful experimental data and strong theoretical support for further application of chitosan derivatives in flame retardant materials industry.