Preparation of multi-component organic polysiloxane for flame retardancy of polyamide 6 fabrics with anti-dripping behavior
Objective Polyamide 6 fabrics are widely used in the fields of textiles and garment,aerospace,construction,and other industries by virtue of its lightweight,softness,high-strength,and abrasion resistance.However,polyamide 6 fabric is a combustible material,which is easy to ignite with fast burning speed,high heat release,and serious melt-dripping behavior,which greatly limits the application of polyamide 6 fabrics in some special regions.Thus,developing the flame-retardant polyamide 6 fabrics with good anti-dripping behavior becomes an important and meaningful task.Method A multi-component synergistic flame retardant of organic polysiloxane containing phosphorus and Schiff base units was designed by hydrolysis-condensation reaction.Subsequently,flame-retardant polyamide 6 fabric was prepared by dipping method,and its chemical structure,thermal stability,combustion behavior,char residues,and pyrolysis volatiles were systematically investigated by fourier transform infrared spectro scop(FT-IR),thermo-gravimetric analysis(TGA),microscale combustion calorimetry(MCC),and Py-GC/MS test methods,respectively.Results FT-IR and XPS results showed that polyamide 6 fabric was finished by the synergistic flame retardant successfully.According to TGA results,the degradation behavior of the finished polyamide 6 fabric changed to a two-stage degradation mode under the assistance of flame retardant.The initial degradation temperature(T5%)and the temperature at maximum weight loss rate(Tmax)of the finished polyamide 6 fabric decreased distinctly.On the contrary,the carbon yield(Yc)of the finished fabric approached 33.9%,which was largely higher than that of polyamide 6 fabric(3.6%).The increased carbon residue as a physical barrier was conducive to protecting the underlying fabric from heat and combustible gases.Significant differences were also observed between polyamide 6 fabric and the finished fabric from real-time combustion images.The polyamide 6 fabric was ignited quickly with fast fire spreading speed and serious melt-dripping behavior after being heated,and the fabric kept burning until the whole fabric was burnt up.In contrast,the finished fabric was self-extinguished rapidly after the fire was removed,and no melt droplet was produced during combustion.Meanwhile,the peak of heat release rate(PHRR)and the total heat release rate(THR)values of the finished fabric decreased by 23.8%and 20.4%,respectively,compared with the polyamide 6 fabric.Moreover,the PHRR and THR values of the finished fabric after washing were still lower than that of polyamide 6 fabric.During combustion of flame-retardant polyamide 6 fabric,a compact and dense carbon layer containing large quantities of small-sized SiO2 particles was generated.This generated char layer with lower intensity D-peak/intensity G-peak(ID/IG)value exhibited higher graphitization degree than the char residues of polyamide 6 fabric.The higher graphitization degree represents higher thermal stability of char layer,which is more beneficial to improve the flame retardancy of fabric.Main pyrolysis volatiles of the finished fabric were common with polyamide 6 fabric,including carbon dioxide(CO2),caprolactam,nitriles,and carbonyl fragments.Besides,some phosphorus-containing volatiles were also produced,and the proportion of caprolactam,the major combustible pyrolysis volatiles,was reduced in the pyrolysis process of the finishing fabric,reflecting flame retardant helped to retard the chain degradation reaction of polyamide 6 backbone.Conclusion A multi-component organic polysiloxane flame retardant is synthesized and adopted to finish a polyamide 6 fabric.With the assistance of flame retardant,the carbonization capacity and fire safety,especially the anti-dripping behavior,of polyamide 6 fabric are improved significantly.In detail,a satisfactory reduction of 23.8%in PHRR value is achieved for the finished polyamide 6 fabric,and the melt-dripping behavior of the finished polyamide 6 fabric is suppressed effectively.This significantly improved flame retardancy of polyamide 6 fabric can be attributed to synergistic effects of the formation of stable carbon layer and the release of incombustible pyrolysis volatiles,which are originated from the cooperation of polysiloxane,phosphorus group,and Schiff base structure.Moreover,the finished fabric after washing still remains good carbonization capacity and fire safety,which is crucial to post-processing and application of fabric.The reported multi-component organic polysiloxane for preparing flame-retardant polyamide 6 fabric results in good anti-dripping behavior,which will help the formation of a versatile strategy for further developing functional polyamide 6 fabric and organic polysiloxane-based flame retardants for various applications.
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