| The fire safety accidents caused by textiles has become one of the worldwide problems.Fire accidents are mainly caused by the flammability of the textiles,and the lack of effective fire warning system is the direct reason for fire accidents.The traditional fire alarm device usually takes a long time to trigger warning（>100 s）,thus the sensitivity is relatively low and application scenarios are limited.With the development of nanotechnology and information technology,the intelligent fire warning coatings based on carbon-based materials such as graphene oxide have attracted widespread attention due to the advantages of intelligent responsiveness,high sensitivity,and application flexibility.However,there are the following problems in practical application for above early fire warning coatings:（1）The warning response mode is single,which can only trigger the warning under direct flame burning or high temperature（>200℃）,and non-contact fire warning cannot be realized;（2）The response process is irreversible,and the fire warning characteristics cannot be maintained after a single use;（3）The flame retardant efficiency is low and the function is single,which cannot meet the requirements of fire safety and multi-functional textiles.Therefore,it is of great scientific significance and social value to develop multi-functional fire-retardant coatings integrated with high-sensitivity,dual-mode response,reusable fire warning function to reduce the flammability of fabric and endow with intelligent fire warning ability.In this research,the cotton fabric was used as the research object.The MXene nanosheets that possessing excellent electrical conductivity,thermal conductivity,and flame-retardant properties were selected and used as novel sensing materials and nano-flame retardants to design and prepare multifunctional nano-composite flame-retardant coatings on cotton fabric.Firstly,combined with the catalytic carbon formation and gas dilution of phosphorus/nitrogen compounds,the thermostability and flame retardancy of cotton fabric were significantly improved.Meanwhile,the cotton fabric was endowed with hydrophobic,self-healing,and electromagnetic shielding properties.Then,to improve the fire contact/non-contact early warning sensitivity of the MXene-based coatings,the carrier density was regulated by nitrogen doping and heterojunction construction.Besides,to widen the monitoring distance and shorten the response time of non-contact early warning,a hierarchical interconnecting carrier transmission network and a three-dimensional high thermal conductivity path were constructed to improve the carrier migration rate and temperature response characteristics,thus realizing controllable monitoring for the flame position and distance.Finally,assisted by the Internet of Things technology,the multifunctional flame-retardant coatings provided an excellent real-time wireless fire warning function that integrated the advantages of high sensitivity and dual-mode response,realizing its application in the field of smart home fire warning.The main research works were as follows:（1）The flame-retardant CTM nanocomposite coatings were constructed on cotton fabric by using casein as dopant,tannic acid as crosslinking agent and free radical scavenger,and MXene as conductive skeleton.The repeatable flame contact/non-contact warning performance of CTM@Cotton was investigated.The relationship between the carrier characteristics and early warning performance under different warning modes was established,and the mechanisms of contact/non-contact early warning and flame retardant were analyzed.The results showed that casein containing nitrogen can catalyze the oxidation of MXene to generate nitrogen-doped titanium dioxide（N-Ti O2）under direct flame attack.Due to the effect of thermally activation of N-Ti O2,the carrier density of MXene-based coatings was increased,which led to a decrease in electrical resistance,triggering a contact fire warning within 3 s.Meanwhile,CTM@Cotton exhibited good temperature response and early warning characteristics for the non-contact flame,and its resistance temperature response coefficient（TCR）was-1.53%/℃.When the flame distance was 1 cm,early warning information can be sent to the terminal within 4 s,realizing controllable monitoring of the flame distance.In addition,the nano-barrier effect of MXene nanosheets and the free radical trapping effect of tannic acid played a synergistic flame-retardant role in the condensed phase and the gas phase.As a result,the CTM@Cotton presented high smoke inhibition and flame retardancy.Compared with pure cotton fabric,the peak CO release rate,total smoke release rate and smoke release rate of CTM@Cotton were reduced by 71.7%,90.0%and 80.8%,respectively,which reduced the smoke hazard.The peak heat release rate and total heat release were decreased by 77.1%and 62.1%,respectively,which inhibited heat release.The LOI value increased to 30.5%.（2）To improve the the sensitivity of non-contact early warning,transition metal oxide Ti O2-MXene heterojunction（Ti O2@MX）was designed and constructed to increase the carrier density of MXene.Then Ti O2@MX was used as a photothermal conversion and conductive filler.A photothermal self-healing flame-retardant coating（TMPNP）based on dynamic imine bond was constructed on cotton fabric by Schiff base reaction between aldehyde hexachlorotripolyphosphonitrile and branching polyvinylimide.The effect of Ti O2@MX heterojunction on carrier density in flame contact/non-contact mode was studied,and the mechanism of dual-mode fire warning was analyzed.The effect of TMPNP coating on the heat release and smoke release behavior of cotton fabric was analyzed,and the synergic flame-retardant mechanisms on the gas phase and condensed phase were revealed.The self-healing properties and mechanisms of TMPNP composite films were investigated.The results showed that the potential barrier of electron transition from valence band to valence band was effectively reduced by Ti O2@MX heterojunction during flame non-contact warning.The heterojunction was excited by thermal energy to releases abundant free electrons as charge carriers,which led to a high TCR（-1.87%/℃）and a timely monitoring of the flame distance（distance is 3 cm,the response time is 3 s）.Upon direct flame attack,TMPNP@Cotton quickly triggered early warning within 1.5 s.Compared with pure cotton,the flame retardancy of TMPNP@Cotton was improved,reflected by a high LOI（34.5%）and the remarkable reduction in peak heat release rate（82.3%）and smoke release rate（96.4%）.Besides,the dynamic exchange of imine bonds was accelerated by the photothermal effect of Ti O2@MX,endowing TMPNP with a high self-healing efficiency（89.3%）,which allowed the healed TMPNP coating to maintain good fire warning performance.（3）While effectively increasing the carrier density,in order to further improve the carrier migration rate to broaden the flame monitoring distance of non-contact early warning,Sn O2@MX heterojunction and phytic acid（PA）-doped polypyrrole（p-PPy）nanotubes were designed and synthesized.Then,a leaf like interweaving interconnect coating was constructed on the surface of cotton via layer by layer self-assembly method to provide a continuous carrier transport network.Finally,polydimethylsiloxane（PDMS）was in-situ polymerized.The prepared cotton fabric（Sn O2@MX/p-PPy/PDMS@Cotton）possessed integrated functions of flame retardant,fire warning,hydrophobic,and electromagnetic shielding.The effect of the hierarchical interconnecting carrier transport network on the carrier migration rate was investigated,and the structure-activity relationship between the carrier transport channel and the fire contact/non-contact early warning response performance was clarified.The results showed that when the flame approached,Sn O2@MX released free carriers,and the leaf shape hierarchical interconnecting coating reduced the carrier transport barrier,which improved the migration rate,realizing the rapid response to the flame at 5 cm within 3 s and high TCR value（1.94%/℃）.After the flame is removed,the coating resistance returned to its initial value,endowing repeatable responsiveness.Under direct flame attack,the carrier density of the coating was increased by Sn O2@MX and N-Ti O2,triggering fire warning within 1 s.Compared with pure cotton fabric,Sn O2@MX/p-PPy/PDMS@Cotton possessed high flame-retardant and smoke suppression properties,reflected by the decrease in peak heat release rate（86.1%）and total smoke release（96.0%）.The LOI value reached up to 35.0%,and the LOI was 33.6%after20 washing cycles.The ohmic loss and polarization loss of electromagnetic waves were enhanced because of the high conductive MXene nanosheets and the hierarchical interconnecting transmission network,resulting in a high electromagnetic shielding efficiency（30 d B）.（4）To further improve the sensitivity of flame contact/non-contact early warning and the detectable distance of flame,the Fe3O4@MX heterojunction and functionalized carbon nanotubes were designed and prepared.A three-dimensional flame retardant nanoparticle coating（Fe3O4@MX/DPP-CNT）with high thermal conductivity was constructed on the surface of cotton fabric by electrostatic interaction,which would promote transport of carriers and phonons.The effect of Fe3O4@MX/DPP-CNT coating on flame contact/non-contact warning performance was systematically investigated,and the influence of thermal conductivity on resistance response rate was analyzed.The results showed that the carrier density of the coating was increased by synergistic effect of Fe3O4@MX heterojunction and N-Ti O2 under flame contact,which shorten the response time（0.84 s）of fire contact warning.Three-dimensional continuous coating effectively reduced the transport barrier of carrier interlayer,which led to remarkable increases in carrier mobility and TCR value（-2.00%/℃）.Meanwhile,it promoted the transmission of phonons and increased the thermal conductivity of Fe3O4@MX/DPP-CNT@Cotton to 0.244 W/m·K.As a result,the heating rate was improved by the high thermal conductivity,reducing the response time to 1 s（the flame distance is 5 cm）and realizing timely monitoring and early warning of the flame at a longer distance（8 cm）.Besides,the flame retardancy of Fe3O4@MX/DPP-CNT@Cotton was enhanced,reflected by the decreases in peak heat release rate（88.9%）and smoke release rate（97.1%）,as well as a high LOI value（35.4%）. |
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