| Polyamide 6(usually known as nylon 6,PA6)fibers have been widely used in civilian and industrial fields because of its chemical stability and excellent mechanical properties.However,in some of these applications,it's desirable to provide this material with a high level of flame retardance in addition to its inherent properties.As we known,PA6 has low limiting oxygen index(LOI)and can easily burn.Thus,how to impart flame retarding property to PA6 fibers becomes an important research topic.In this paper,two approaches were adopted to fabricate the flame-retardant PA6(FR/PA6)resins:(1)the flame-retardant additives were incorporated into PA6 matrix during the twin-screw extrusion process;(2)the flame-retardant monomers were introduced in situ hydrolytic ring-opening polymerization of caprolactam.Then the FR/PA6 resins were melt-spun to prepare FR/PA6 fibers.Firstly,the PA6 chips,halogen-free flame retardants melamine cyanurate(MCA)and cyclic phosphate compounds(M102B)were used to prepare B-FR/PA6 resins through melt blending.The morphology and properties of blends were investigated by scanning electron microscopy(SEM),melt flow index(MFI),differential scanning calorimetry(DSC),thermogravimetric analysis(TGA),pyrolysis-gas chromatogram/mass spectrometer(Py-GC/MS)approach and combustion testing,respectively.SEM showed that MCA could be well-dispersed in PA6 matrix with-500nm particle size.The MFI of B-FR/PA6 increased greatly with the FRs concentration increasing.B-FR/PA6 samples had higher T,values,which was speculatively caused by the heterogeneous nucleating effect of MCA in the blends.TG indicated that the weight loss of pure PA6 took place in a single step,with the maximum weight-loss rate at 460?.B-FR/PA6 exhibited weight loss that began at lower temperature and had two weight-loss steps.Py-GC/MS showed the kinds of volatile products were not affected,whereas the relative concentration of volatile product was significantly changed.MCA and M102B flame retardant compound system,could show the synergistic effect and work in both condensation phase and gas phase.By adding 9%MC.A and 3%M102B,the UL-94 rating was V-0 level(3.0mm)and the LOI value was 35.9%.Secondly,the melamine/adipic acid salt and cyanuric acid/hexane diamine salt were introduced into the hydrolytic polymerization system of caprolactam to synthetic MCA-based PA6(P-MCA/PA6)resins.The structures,thermal properties and rheological behaviors were fully characterized and investigated by Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),DSC and advanced capillary rheometer.The FTIR and XRD results indicated that the self-assembly reaction of melamine(MEL)and cyanuric acid(CA)was complete and P-MCA/PA6 resins were prepared successfully.With the in situ-formed MCA particles increasing.Tm decreased from 220?(pure PA6)to 199?(P-10%MCA/PA6)and the crystallization degree decreased from 24.6%(pure PA6)to 16.2%(P-10%MCA/PA6).The rheological test indicated that both the PA6 and P-MCA/PA6 were Non-Newtonian fluids and followed the shear-thinning behavior.Moreover,the P-MCA/PA6 system was more sensitive to shear rate and temperature.It indicated that the melt spinning process had to be controlled strictly.Lastly,The FR/PA6 fibers were prepared through melt spinning process.The mechanical properties,flame resistant properties and dyeing properties were investigated.The main results obtained were as follows:The spinnabilities and mechanical properties of B-FR/PA6 fibers were affected greatly with addition of 8%to 12%FRs.However,the P-MCA/PA6 fibers with MCA content from 6%to 10%showed good spinnabilities and mechanical properties for practical applications,which was due to the uniform dispersion of situ-formed MCA particles in PA6 matrix.The LOI value of B-10%FR/PA6 textile reached 25.3%.The P-8%MCA/PA6 textile had obviously improved flame retardancy:the LOI value was 26.7%and the UL-94 test was B1 level.Moreover,dyeing properties indicated that the FR-PA6 fibers were better than pure PA6 fibers. |
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