Research On Surface Modification Of Cotton Fabric By Flame Retardants And Its Performance

Cotton fabric has been widely used in clothing,aviation,building decoration and other fields due to its low cost and easily available and some other superior merits,such as excellent gas permeability and biodegradability.However,cotton fabric was flammable with the low limiting oxygen index(LOI)of 18%,which seriously limited its widely application in some areas.Thus,it has very critical scientific significance and application prospects for endowing the cotton fabric effectively flame retardant propertites.Up to now,the methods such as paddry cure and coating were used to flame retardant cotton fabric due to their simple operation properties,but the prepared products in these ways presented poor washing durability and difficult to achieve long-term flame retardant for cotton fabric.In this paper,cotton fabric was firstly selectively oxidized with sodium periodate and the aldehyde groups produced on cotton fabric surface.Based on the reactivity of aldehyde groups,a series of flame retardant cotton fabric with the P or P-N elements grafted on the surface were prepared through phosphine hydride addition reaction between P-H bonds and aldehyde groups,or the ammonia derivative reacted with aldehyde groups by the nucleophilic addition reaction and formed C=N bond,and then P-H bond reacted with C=N bond by addition reaction.The flame retardant cotton fabric defined as FR-cot-1 were prepared by the P-H bonds of Dimethyl phosphite(DMP)reacted with aldehyde groups by phosphine hydride addition reaction.The flame retardancy of FR-cot-1 was evaluated by LOI and vertical burning(UL-94)tests.The results revealed that the LOI was 24.8% and reduced to 23.4% after 10 times washing treated,and the damaging char length of FR-cot-1 were both 30 cm before and after washing tests.The results of thermogravimetric analysis(TGA)and cone calorimeter(CONE)tests demonstrated that the introduction of DMP changed the thermal degradation behavior of cotton fabric,and the combustion paremeters such as the heat release rate(HRR)and total heat release(THR)reduced to a certain extent.Scanning electron microscope(SEM)test revealed that the char of FR-cot-1 retained the fabric mesh structure.Methylamine(MY)and ethylenediamine(EDA)were respectively reacted with aldehyde group on the oxidized cotton fabric surface and formed two kinds of Schiff base.Then the C=N bonds in Schiff base reacted with DMP by the phosphine hydride addition reaction.In this way,organic amine and DMP were grafted on the surface of cotton fabrics and obtained MY/DMP modified cotton fabric(FR-cot-2)and EDA/DMP modified cotton fabric(FR-cot-3).The results revealed the LOI values of FR-cot-2 and FR-cot-3 were 26.9% and 27.8%,respectively.After washing tests,the LOI values were reduced to 25.1% and 26.6%,respectively.Compared with that of FR-cot-1,the char residue of FR-cot-2 and FR-cot-3 became more thick and the damaging char length were both 30 cm,which indicated that P-N grafted cotton fabric presented more excellent flame retardancy and washing durability.TGA tests results revealed that the char residue for FR-cot-2 and FR-cot-3 increased from 18.4% for FR-cot-1 to 33.3% and 36.6% at 600 °C,respectively,which indicated the P-N grafted modification enhanced the charring abilitiy for cotton fabric.Cone tests result revealed that the HRR and THR of FR-cot-2 and FR-cot-3 were further decreased compared with FR-cot-1,and the decline for FR-cot-3 more obvious.SEM results demonstrated that the introduction of EDA makes the char of FRcot-3 more swell and compact.The mechanical tests result revealed that the tensile strength of FR-cot-3 was higher than that of FR-cot-2.In summary,EDA/DMP modified flame retardant cotton fabric process excellent flame retardancy,washing durability,thermal stability and mechanical properties.On the basis of the obtained FR-cot-3,trimethylol melamine(TMM)was used to graft on FR-cot-3 surface by the reaction with the hydroxyl groups on cotton fabric surface and the TMM modified cotton fabric(TMM-cot)were prepraed.When TMM with the concentration of 4% was grafted on FR-cot-3,the LOI value of TMM-cot was significantly increased to 37.2% and the damage char length was reduced to 6.5 cm.After washing treated,LOI value and the char length of TMM-cot respectively increased to 36.5% and 7.3 cm,and maintaining excellent flame retardant properties.TGA test results revealed that the char residue of TMM-cot was increased to 39.0% at 600 oC and the maximum thermal decomposition rate was decreased obviously.Cone test result revealed that compared with FR-cot-3,HRR and THR of TMM-cot further reduced.SEM test revealed that the char morphology of TMM was more dense and smooth.