Designing Innovative Flame Retardant Treatments Of Polyamide 66 Fabrics Using Sustainable Approaches

Among the synthetic polymeric textiles,Polyamide 66(PA66)is one of the most widely used materials,especially as apparel and industrial uses for its excellent properties likely higher strength and good wear resistance.Unfortunately,due to its organic structure,it shows relative ease of burning which poses a great risk to fire.Moreover,due to semi-crystalline polymeric structure,it shows inferior hydrophilic property compared with some natural fibers and thus restricts its application in civil life as well.For the flame retardant treatment of textiles,several strategies have been developed throughout the years and the earlier studies show the enormous uses of petroleum-based compounds with N and S moieties via different grafting methods in the flame retardant treatment of PA66.However,with rapid improvement in living standards,the recent request for a reduction of environmental impact and of formaldehyde release during manufacturing and utilization have pushed researchers to come up with environmentally benign chemistries and processes.Therefore,the challenges in search of the most sustainable,efficient and durable flame retardant treatments for polyamide 66 textiles still remain which inspired me to come up with this project.This PhD work aims at investigating the effectiveness and the possibilities of the use of some novel compounds and approaches,including the use of nanoparticles,synthesizing and application of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO)-based different P,and N containing flame retardants via UV-induced grafting polymerization,and none the less,various kinds of bio-based polyelectrolytes via layer by layer assembly and hybrid manner to improve the flame retardant and hydrophilic properties of PA66.The research work of this dissertation can be discussed as follows:1.The flame retardant and hydrophilic treatment of Polyamide 66(PA66)fabrics was carried out using metal oxide nanoparticles likely TiO2 and Ti2/SiO2 nanocomposites along with Chitosan(CS),Citric acid(CA),and Sodium hypophosphite(SHP)through a simple dip-coating technique.The obtained results indicated that the application of TiO2 NPs with CS could improve the LOI values,char yield%in TGA test and hydrophilic behavior of treated fabric moderately;moreover the incorporation of SiO2 NPs could further enhance the above mentioned properties due to the synergism of applied nanoparticles.However,the introduction of phosphorus compound likely SHP as a catalyst into this system left no significant improvement except in attaining UL-94-V1 rating in UL-94 test and a handful reduction of pHRR by 11%in cone test;even though hydrophilic behavior was disturbed with the presence of this compound which may be due to their subsequent involvement in crosslinking reaction with CA,CS and PA66.Later,a novel approach,including the application of metal oxide nanoparticles likely Ti02 and Si02 along with naturally occurring phytic acid(PA),and Chitosan(CS)was followed to improve the flame retardant and hydrophilic properties of Polyamide 66(PA66)fabrics via a pad-dry-cure technique.A polycarboxylic acid[1,2,3,4-butanetetracarboxylic acid(BTCA)]was used as a cross-linking agent to stabilize and improve the adhesion of nanoparticles onto fabric surfaces.The obtained results indicated that the application of TiO2 NPs with PA could improve the LOI values(i.e.,LOI-24.5%for the PA66-PA-T fabric sample),char yield%in TGA test and hydrophilic behavior of treated fabric significantly,which may be due to a joint flame retardant effect from PA and TiO2;whereas the incorporation of Si02 NPs instead of Ti02 altered the properties slightly.Conversely,the introduction of CS into the PA-Ti02 formulation brought a significant reduction in pHRR(i.e.,about 25%)which indicated the char forming ability of CS while the hydrophilic behavior of this system was drastically reduced due to the esterification reaction between CS and PA66.Finally,when we introduced CS with PA-SiO2 formulation,a composed improvement was noticed both in flame retardant and hydrophilic properties except any rating in UL-94 test.2.A novel DOPO-based phosphorus and nitrogen containing monomer named DOPO-DAAM was synthesized and grafted onto the surface of polyamide 66(PA66)fabrics via UV grafting in order to improve the flame retardancy.To facilitate the grafting efficiency,the PA66 fabric surface was first modified through the HCl treatment.In the UL-94 vertical burning test,all the PA66 fabrics treated with DOPO-DAAM could stop the melt-dripping and fabric treated with 30 wt.%DOPO-DAAM could able to attain VO rating.A considerable increase up to a maxm LOI of 23.5%and a maxm of 22%reduction in peak heat release rate was achieved for PA66 fabrics grafted with 20 wt.%DOPO-DAAM.Thermogravimetric analysis revealed that a very small residue was observed at 800 ℃ for all the formulations,indicating the limited condensed phase interaction.Later,a novel DOPO-based phosphorus monomer(DOPA)was synthesized and applied onto the pure and chitosan modified polyamide 66(PA66)fabric surfaces via a simple cross-linking reaction in order to improve the flame retardant properties and compared here with.The pure PA66 fabric crosslinked with 20 wt.%DOPA showed considerable flame retardant behavior in the limiting oxygen index(LOI),UL-94(UL-94-V0 rating),and cone calorimetry tests(reduction in pHRR by 36%).However,the chitosan modified PA66 fabric crosslinked with only 10 wt.%DOPA showed superior flame retardant performance than the earlier one,especially in terms of the higher LOI(LOI value of 23.5%),great reduction in pHRR by 40%,and improved charring in N2 atmosphere(about 7.5%of char yield%).So,the improved flame retardant properties of CS modified PA66 fabrics with low loading of FR monomer were due to the P-N synergism between CS and DOPA where DOPA might decompose at the early stage to generate free radicals with quenching effect,facilitating the predominant gas-phase mechanism and a slightly condensed-phase activity(increased char yield%);contributed to form intumescent char layers with CS modified fabric samples which was revealed from the Py-GC-MS and char FTIR analysis tests.3.Green polyelectrolytes including chitosan(CS),phytic acid(PA)and oxidized sodium alginate(OSA)were also deposited on polyamide 66(PA66)fabrics in a quadralayer(QL)fashion like(CS-PA-CS-OSA)n(where "n" denotes the number of quadralayers)via layer-by-layer(LbL)assembly to improve the flame retardant property.In the vertical burning test,the PA66 fabric with 10 and 15 QL depositions could stop the melt dripping.Cone calorimetry results showed that a maximum reduction(24%)in the peak heat release rate was achieved for the PA66 fabric with 5 QL depositions.Thermogravimetric analysis indicated that the presence of the polyelectrolytes catalyzed the degradation pathway of virgin PA66 fabric where the initial decomposition temperature was reduced and the char yield was enhanced for all the coated fabrics significantly.Moreover,UV-vis spectroscopy demonstrated that the use of OSA could improve the durability of such a multilayered nanocoating.Later,borate cross-linked thin coatings made from green polyelectrolytes,chitosan(CS)and phytic acid(PA),were deposited on polyamide 66(PA66)fabrics via layer-by-layer(LbL)assembly to develop a durable flame retardant method.The surface and morphological characterization showed that CS and PA were successfully deposited onto the PA66 fabrics and cross-linked by borate.The presence of the coating slightly changed the Limiting Oxygen Index(LOI)values,but suppressed the flame spread and completely stopped melt-dripping of PA66 in UL 94 vertical burning test.The CS-PA coating also decreased the peak heat release rate of PA66 observed in cone calorimeter tests,and a maximum reduction of 31%was observed for PA66-10 BL fabric sample.The addition of CS,PA and borate moieties lowered the initial decomposition temperature of PA66,but the char yield and char quality were improved.Especially,the char of the PA66 fabrics treated by borate exhibited better thermal resistance in Thermogravimetric analysis(TGA)tests.More importantly,it was noticed that the stability of deposited CA-PA coating in sodium dodecyl sulfate(SDS)solution was enhanced significantly after cross-linking by borate,which would be favourable to durable flame-retardant treatment.4.Phosphorylated chitosan(PCS)was synthesized and also grafted onto the surface of polyamide 66(PA66)fabrics via UV-induced grafting polymerization in order to improve the flame retardant properties.Subsequently,PCS grafted PA66 fabrics were modified by(3-aminopropyl)triethoxysilane(APTES)through sol-gel process in order to form a cross-linking coating.The results obtained from the vertical burning test indicated that only the PCS grafted and simultaneously sol-gel treated fabrics could stop the melt dripping.A maximum reduction(30%)in the peak heat release rate was achieved for the PA66-PCS-4W-SG fabric sample.The optimal flame retardant effect was achieved for the PA66 fabrics treated by PCS and APTES simultaneously,which was attributed to the joint effect of thermal shielding exerted by the silica and char-forming effect derived from PCS.Finally,a hybrid approach,including layer-by layer deposition and sol-gel process was followed in constructing a flame retardant coating on polyamide 66(PA66)fabrics from organic and inorganic materials.Firstly,a few layers of green polyelectrolytes likely chitosan(CS)and phytic acid(PA)were deposited via layer-by-layer(LbL)assembly to improve the flame retardant properties of PA66.Later on,these LbL treated PA66 fabrics were impregnated in APTES and boron doped APTES sol solutions to enhance the thermal stability and durability of the hybrid coatings further.PA66 fabric samples with hybrid deposition(i.e.,PA66-5BL-APTES and PA66-5BL-B-d-APTES)could able to stop the melt-dripping in UL-94 test.The cone calorimetry and the thermogravimetric analysis tests also indicated improved flame retardancy for the PA66-5BL-B-d-APTES fabric sample.More interestingly,the boron doped silica sol could boost up the hydrophilicity of the treated fabrics and also able to retain the flame retardant properties after laundering.