| Retanning is the most important process known as the "golden"inleather process. The retanning agent can give leather the excellentperformance, such as improving softness and fullness, narrowingdifference of part, strengthenning water and light resistance, changingof surface charge, promoting the dyeing uniformity. With thedevelopment of the the industry of leather, people put forward highrequirements on the fuctional and retanned material of leather.Therefore it is one of the hot spot at home and abroad developpingmulti-function retanning agent. In this reseach, firstly graftedcopolymer of oxidized starch and vinyl monomer was prepared usingcorn starch as raw material. Secondly, multi-function retanning agentwas prepared blending by grafted copolymer of starch andmontmorillonite. It was applied in the retanning of sheepskin leatherchrome-tanned, expected to improve capturing properties offormaldehyde and flame retardancy.Grafted copolymer of oxidized starch and vinyl monomers wasprepared. The effects of the dosage of oxidant, the temperature ofdegradation and degradation time on appearance, carboxyl and carbonylgroup content of oxidized starch, emulsion stability, centrifugalstability, percentage of graft, graft efficiency and monomer conversionof the grafted copolymer of starch were investigated. The effects of thetime of reaction, the dosage of initiator, the temperature of reaction andthe dosage of acrylamide on properties of grafted copolymer of starchwere also investigated. Degraded starch and grafted copolymer of starchwere charactered by fourier transform infrared spectroscopy(FT-IR),thermogravimetric analysis(TGA), X-ray diffracttion(XRD) and scanning electron microscopy(SEM). Sodium-montmorillonite(MMT)was respectively modified with1631, urea, L-tyrosine and diphenylcarbazide. The effects of types of modifier and pH on modifiedmontmorillonite were investigated. Modified MMT were charactered byXRD and TGA. Finally, the grafted copolymer of starch/MMTnano-composites were prepared by blending with the grafted copolymerof starch and modified MMT. The effects of types of modified MMT onphysical and chemical properties and application properties ofnano-composites were investigated. Nano-composites were characteredby XRD, TGA and SEM.In this reseach, the best reaction conditions preparing graftedcopolymer were as follows: the dosage of oxidant was7.5%, thetemperature of degradation was95℃, the time of degradation was30min, the time of reaction was3h, the dosage of initiator was8%, thetemperature of reaction was55℃and the dosage of acrylamide was20%. FT-IR and TGA showed that vinyl monomer had been successfullygrafted on degradated starch. XRD showed that during the oxidateddegradation and grafting polymerization, the structure of starch grainand crystallization in the spherulite were destroyed, the crystal structureof starch had been irreversibly changed. SEM showed that oxidation andgrafting polymerization had destroyed neat and crystal structure ofstarch. Grafted copolymer of starch was applied in the retanning ofchrome-tanned sheepskin leather. The results showed that the thicknessof crust and the capturing efficiency of formaldehyde were23.53%and36.95%. Comparison of the crust of the blank and the contrast, thetensile strengh almost had not changed, the tear strength had increased.Sodium-MMT was respectively modified with1631, urea,L-tyrosine and diphenyl carbazide. XRD results showed that theinterlayer space of modified MMT had increased, in comparison tosodium-MMT. TGA showed that MMT was successfully modified by1631, urea and L-tyrosine, but the degree of diphenyl carbazide-MMTwas the poorest.Finally, the grafted copolymer of starch/MMT nano-composites were prepared by blending with the grafted copolymer of starch andmodified MMT. XRD showed that the grafted copolymer ofstarch/sodium-MMT and the grafted copolymer of starch/1631-MMTnano-composites were intercalated nanocomposites, the graftedcopolymer of starch/urea-MMT, the grafted copolymer ofstarch/L-tyrosine-MMT and the grafted copolymer of starch/diphenylcarbazide-MMT nano-composites were exfoliated nano-composites. Thegrafted copolymer of starch/MMT nano-composites showed a largercrystallinity, in comparison to the grafted copolymer of starch, and thecrystallinity of grafted copolymer of starch/L-tyrosine-MMTnano-composites was25.42%. The presence of modified MMT into themodified starch matrix probably induced a re-organized starch structureand improved the neat degree. TGA results showed that the modifiedMMT improved the thermal stability of composites. SEM resultsshowed that the introduction of MMT probably affected crystalstructure of modified strch.Grafted copolymer of starch/MMT nano-composites were appliedin the retanning of sheepskin leather chrome-tanned. The results ofapplication showed that comparison of the crust retanned by modifiedstarch, the thickness and the capturing efficiency of formaldehyde ofcrust retanned by grafted copolymer of starch/L-tyrosine-MMT nano-composites increased, the flame retardant performance of increased, thetensile strength and tear strength of crust increased. SEM resultsshowed that the distance between the fiber bundles retanned by themodified starch/L-tyrosine-MMT nano-composites increased. |
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