Preparation And Properties Of Natural Melanin Nanoparticles Modified Self-Healing Polyurethane

A novel hydroxy terminated acylhydrazone compound,which worked as the chain extender to crosslinked the self-healing polyurethane based on reversible acylhydrazone bond was synthesized in this paper.Melanin Nanoparticles（MN）extracted from cuttlefish worked as an active filler to modify the self-healing polyurethane and further to improve their mechanical properties.Aromatic Acylhydrazone compounds（named AAD）were prepared from terephthalic acid dihydrazide and diacetone alcohol.The soft segment of polyurethane prepolymer is polycaprolactone diol（PCL-210）and polyether polyol（TEP-240）,the hard segment is diphenylmethane diisocyanate（MDI-50）.AAD reacted with the pre-polyurethane to obtain a self-healing polyurethane（PU-0）.PU-0 was characterized by FTIR,1HNMR,DSC,swelling test,tensile test and polarized light microscope（POM）observation.The target structure was consistent with the designed molecular structure confirmed by IR.The DSC results showed that the glass transition temperature（Tg）was-39.56℃,which shown at high elastic state at room temperature.At the same time,the gentle heat flux curve of DSC indicated a moderate degree of microphase separation of the soft segments and the hard segments.PU-0 sample was placed in N,N-dimethylformamide solvent at room temperature.After 190 min,their equilibrium swelling rate was 220%and the gel content was 81%,indicating a crosslinked structure.From the tensile test,theirσandεwere 0.81 MPa and 405%respectively.After 24 hours of repairing,bothσandεcan be recovered to almost 90%.The natural melanin nanoparticles from the cuttlefish pouch were washed by deionized water with a high speed（1500r/min）to remove impurities such as organic matter and soluble inorganic salts.The main reactive groups of MNs were-NH₂ and-OH,which could react with-NCO group in pre-polyurethane to form chemical cross-linkings.The residue of the-NCO group indicated the reaction situation of per gram of MNs with different mass of MDI-50,so the optimum reaction volume of MDI-50 to 1g of MNs was 0.75g.The content of active groups on MNs surface was about 6.0mmol/g.Their particle size distribution was 100-600nm,the peak was at about 350 nm.And the MNs was sphere in shape shown from SEM.AAD and MNs were adjusted to make the ratio of-OH and-NCO was equimolar.The modified self-healing PU with different content（MNswt%≤2.5wt%,named as PU-1/2/3/4/5）of MNs were synthesized.And their performances were characterized.The results show that 1.5wt%of MNs modified polyurethane owned better mechanical properties,and itsσandεincrease to 2.75MPa and 483%respectively.With the addition of MNs,the hydrophilicity of the self-healing polyurethane have increased.The hydrophilic angle of PU-0 was 78°,while the hydrophilic angle of PU-5 modified with 2.5wt%of MNs was decreased to 56°.Therefore,the addition of MNs not only improves the mechanical properties of the self-healing polyurethanes synthesized in this paper,but also improves their biocompatibility.