| Polyvinyl alcohol?PVA?has good spinability and excellent overall performance.It is one of the polymeric materials that can be produced on a large scale by non-oil routes.However,PVA fiber is highly flammable,and its limiting oxygen index?LOI?is 19%.Therefore,its application in some areas is severely limited.In this article,PVA fiber,PVA fiber modified with Melamine formaldehyde resin?MF?,PVA/sodium alginate fiber?PVA/SA fiber?,PVA/SA fiber modified with Pyrovatex CP and PVA/SA fiber modified with MF were prepared through wet spinning process.And the micro-morphology,flame retardancy,and mechanical properties of the fibers mentioned above were investigated.?1?MF was prepared and was used to improve the flame retardancy of PVA fiber.PVA fiber modified with MF was prepared through wet spinning process.The micro-morphology,flame retardancy,and mechanical properties of the modified fibers were characterized.The results showed that the MF reacted with PVA.The modified fibers have kidney section,and there are holes in the fibers.The flame retardancy of modified fibers has been greatly improved with the addition of MF.When the mass ratio of PVA to MF resin is 10:6,LOI value of the modified fibers reached 33.6%from 19.2%,and the amount of residual char was improved from 18%to 36%at 600?.With the addition of MF,the breaking strength of PVA fiber modified with MF increased first and then decreased,and the elongation at break decreased.The LOI value of the modified fiber is 26.1%after 50 times of washing,shows that the modified fibers have durability of fire-retardant.However,the formaldehyde content in the modified fibers increased with the addition of MF.The formaldehyde content of PVA fiber modified with MF reaches 740 mg/kg when the mass ratio of PVA to MF is 10:6,which was much higher than the national standard GB18401-2001 for non-direct contact skin products??300mg/kg?.?2?In order to avoid the higher content of formaldehyde in PVA fiber modified with MF,PVA/SA composite fiber was prepared by wet spinning process.The structure of the composite fiber was characterized by Fourier transform infrared spectroscopy?FTIR?.It was found that SA and PVA were blended with intermolecular hydrogen bond.Scanning electron microscopy?SEM?showed that the core layer structure of composite fibers was not obvious.The flame retardancy and mechanical properties of PVA/SA composite fiber were investigated.It was noted that the addition of SA increased the amount of residual char of composite fibers.The LOI value of the composite fiber increased as the addition of SA,while the breaking strength and elongation at break of the composite fiber decreased.When the LOI of the composite fiber increased to 27.6%,the breaking strength of the fiber decreased from 2.41 cN·dtex-1 to 1.01 cN·dtex-1,and the elongation at break decreased from 34.26%to 8.58%.These results indicated that the addition of SA can improve the flame retardancy of PVA fiber and achieve the purpose of formaldehyde free,but it reduces the mechanical properties of composite fibers.?3?In order to improve the mechanical properties of the flame retardant PVA/SA composite fiber,Pyrovatex CP was used as flame retardant and the Pyrovatex CP modified PVA/SA composite fiber was prepared.PVA/SA fiber modified with Pyrovatex CP was prepared by wet spinning process.FTIR results showed that Pyrovatex CP reacted with hydroxyl of PVA and SA.SEM results showed that the surface of the fiber was smooth,and there were few internal defects.The breaking strength of the modified fibers is slightly improved,the elongation at break increases obviously,and the maximum elongation at break is 66.29%.The LOI of the modified fiber reached 30.4%and the amount of residual char at 600?was 27%.When the additive amount of Pyrovatex CP was 25%,the LOI of modified fiber reached 28.8%,and the formaldehyde content of modified fiber was 352 mg/kg,which did not meet the requirements of environmental protection.When the mass ratio of Pyrovatex CP continued to increase,the LOI of modified fiber increased as well as the formaldehyde content in modified fiber.Pyrovatex CP can release formaldehyde during its use,so the content of Pyrovatex CP in flame retardant materials should not be too high.?4?In order to reduce the content of free formaldehyde in PVA fiber modified with MF,PVA and SA were mixed with MF to prepare PVA/SA fiber modified with MF by wet spinning process.The experimental results showed that the covalent bond was formed between MF and PVA and SA.SA and PVA were blended with intermolecular hydrogen bond.From the photos of SEM,it can be observed that the PVA/SA fiber modified with MF presented an interactive network structure.The addition of MF gave the fibers better flame retardancy.When the additive amount of MF resin was 33%,the LOI of modified fibers was 32%.The breaking strength of PVA/SA fiber modified with MF increased first and then reduced with the addition of MF,the highest breaking strength was 3.19 cN·dtex-1,but the elongation at break of modified fiber decreased.After 30 times of washing,the LOI value of modified fiber was 27.1%and after 50 times of washing,the LOI value of modified fiber was 25.9%.Because of the existence of SA and the decrease of the amount of MF resin,the content of formaldehyde in the modified fiber decreased obviously.When the content of MF resin was 33%,the formaldehyde content in the modified fiber was 506 mg/kg.Compared with the requirements of national standard GB18401-2001 for non-direct contact skin products,the formaldehyde content in the modified fiber were higher;however,the addition of SA reduced the formaldehyde content of PVA/SA fiber modified with MF. |
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