Study On Ammonium Dihydrogen Phosphate As Coagulation Bath To Reinforcing Polyurethane/ Silk Fibroin Composites

Polyurethane?short for PU? has a high resilience and its maximum elongation at break is800%, so the PU material has been widely used in leather, footwear, clothing, decoration,track and other fields. Silk fibroin?short for SF? is a natural protein polymer which has non-toxic, non-irritating and good bio compatibility. The PU/SF composites not only own the bio compatibility by the SF, but also own a good toughness by the PU, and therefore it have a good prospects in the bio medical field. In recent years, more and more researchers composited PU with SF, but the composites have not used in the bio medic field widely for the mechanical properties of the composites is reduced sharply. Therefore, how to reinforce the PU/SF composites is becoming more and more important. In this paper, ammonium dihydrogen phosphate?the chemical formula is NH₄H₂PO₄? was used as the coagulation bath to prepared the PU/SF composites, the composites, mechanical properties has significantly improved with this method.Firstly, PU films were prepared by the wet film forming method which used NH₄H₂PO₄ as the coagulation bath. According to the characterizations, many needles NH₄H₂PO₄ nanocrystals were found in the PU films which used NH₄H₂PO₄ as the coagulation bath and the nanocrystals have good binding interface with PU. It's also found that the hydrogen bonding force of the PU film was enhanced, crystallinity was increased. The aspect ratio of the needles NH₄H₂PO₄ nanocrystal is 6000-17000 which can play a good reinforcing effect in the PU film. On the other hand, the N-H bonds in the NH₄H₂PO₄ is easy to form hydrogen bonds with the C=O bonds in the PU molecules, so the mechanical properties of the PU film was enhanced further. When the molar concentration of NH₄H₂PO₄ was 2 mol/L, the maximum tensile strength, the elongation at break and the fracture work could respectively reached 7.64 MPa, 2245.78% and 3.81 J, which increased by 295.85%, 72.03% and 237.17%compared with those of PU films without using NH₄H₂PO₄ as the coagulation bath.Secondly, the PU/SF composite films were prepared by the same method which used NH₄H₂PO₄ as the coagulation bath. According to the SEM, many needles NH₄H₂PO₄ nanocrystals was also found in these PU/SF composite films with NH₄H₂PO₄ as the coagulation bath and the nanocrystals have good binding interface with PU. When the molar concentration of NH₄H₂PO₄ was 4 mol/L?PU:SF=9:1?, the maximum tensile strength, the elongation at break, the fracture work and Young's modulus could respectively reached 7.65 MPa, 1856.72%, 3.90 J and 3.59 N/mm, which increased by 483.97%, 98.71%, 202.33% and255.45% compared with those PU/SF composite films without using NH₄H₂PO₄ as the coagulation bath.Finally, the PU fibers and the PU/SF composite fibers were prepared by the wet spinning which used NH₄H₂PO₄ as the coagulation bath. According to the SEM result, many needles NH₄H₂PO₄ nanocrystals were also found in the PU fibers and PU/SF composite fibers which used NH₄H₂PO₄ as the coagulation bath. And the mechanical properties of the PU fibers and the PU/SF composite fibers were enhanced greatly. When the molar concentration of NH₄H₂PO₄ was 2 mol/L, compared with those PU fibers without using NH₄H₂PO₄ as the coagulation bath, the maximum tensile strength, the elongation at break, the fracture work and Young's modulus of this PU fibers could respectively increased by 57.14%, 215.86%,302.18% and 57.14%; compared with those of the the PU/SF composite fibers without using NH₄H₂PO₄ as the coagulation bath, the maximum tensile strength, the elongation at break, the fracture work and Young's modulus of this PU/SF composite fibers could respectively increased by 128.57%, 109.46%, 214.46% and 100.00%.