| Polyacrylonitrile(PAN)fiber,i.e.acrylic fiber,is one of the synthetic fibers with good elasticity,comfortable handle and good warmth retention.It is widely used in decoration,clothing,industry and other fields,and occupies an important position in the textile industry.However,PAN fiber is flammable fiber and the limited oxygen index(LOI)value of it is about 17%,which greatly limits its application.Therefore,the development of flame retardant PAN fiber is of great significance.In the first part of this paper,PAN and polyvinyl alcohol(PVA)were blended to prepare composite fibers(PVA/PAN)via wet-spun technique,afterthat,it was treated by boric acid solution to obtain the cross-linked PVA/PAN fiber(B-PVA/PAN),then flame retardant PAN composite fibers(FR-PVA/PAN)was obtained through the flame retardant modification of B-PVA/PAN.The compatibility of PAN and PVA in the same solvent dimethyl sulfoxide(DMSO),the relationship between PVA and PAN blending ratio and the spinning solution viscosity were investigated.The results showed that there was no phase separation between PAN and PVA in DMSO,indicating excellent compatibility.With the increase of PVA content,the viscosity of the blend solution increased,and the measured values were closer to the fitting curve.The structure and thermal properties of the composite fiber were characterized by X-ray photoelectron spectroscopy(XPS),Fourier transform infrared spectroscopy(FTIR),Thermogravimetric(TG),Differential scanning calorimetry(DSC),Cone calorimetry(CC)and TGA coupled with Fourier transform infrared spectrometry(TG-FTIR).The results showed that the char residue of FR-PVA/PAN was up to 42.3 wt%after thermal decomposition.After CC testing,a carbon foam layer with the thickness of 1.89 cm was formed on the surface of the sample,which played an important role in separating oxygen and heat from samples.At the same time,some non-combustible gases decomposed from the flame retardant PAN composite fiber were released.Both the char residue and the inflammable gases exert a good flame retardant effect in gas phase and condensed phase.As the mentioned above,the thermal stability and flame retardance of FR-PVA/PAN were significantly improved.Within the main mass loss range of FR-PVA/PAN(640-800?),the degraded gaseous compounds are mainly H2O,CO2 and POˇfree radical,and no harmful gases are generated.In the second part of this paper,LIG/PAN composite fiber was prepared by blending lignin(LIG)biomass macromolecular with PAN.Subsequently,the LIG/PAN composite fibers were modified by phosphoric acid and urea to impart LIG/PAN composite fibers flame retardant performance.The structure of the samples was characterized by XPS and FTIR.The thermal stability and combustion behavior of the samples were studied by TG,CC and TG-FTIR.The results showed that the char residue of FR-LIG/PAN increased by 12.3 wt%and 15 wt%respectively compared with that of LIG/PAN and PAN at 800?.Furthermore,HRR,THR,SPR and TSP of FR-LIG/PAN were significantly lower than those of LIG/PAN and PAN.This indicates that the flame retardancy and thermal stability of FR-LIG/PAN were greatly improved.The char layer of FR-LIG/PAN after CC testing was up to 1.3 cm thickness,which can play an excellent role in condensed phase flame retardant mechanism.The main gaseous products derived from the decomposition are non-toxic small molecular substances,such as H2O,CO2 and POˇfree radical,which meet the requirements of environmentally friendly protection. |
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