Research On Modification Of Silk And Preparation Of Functional Silk Fabric Based On Nano-SiO₂

Silkworm silk has excellent mechanical property,good environmentally stability and biocompatibility.It is widely used in the traditional textile and modern material and medical area.But silk also has some disadvantages,easy to yellow and wrinkle is the main disadvantage of silk fabric,which greatly affect the noble appearance and use of it.In order to improve the defects and the properties,even endue the new special performance,and expand the application area of silk,many studies had focused on the research of silk modification and fabric functional finishing.At present,the commonly used methods of modifying silk are physical,chemical,molecular biology and feeding method.Among them,the feeding method is simple and relatively eco-friendly,which is the most direct and effective method for large-scale production of modified silk.However,there are still some problems in the previous studies on feeding method,such as toxicity,high cost and low conversion rate of additives.And most of previous studies focused on the improvement of silk’s mechanical performance,and pay little attention to improve ultraviolet resistant performance.In addition,chemical method is the most commonly used method of silk modification and silk fabric finishing.Although some improvements have been achieved in these studies,there still have several problems,such as poor finishing effect,complex process,environmental pollution and influence on the comfort of silk fabric.Therefore,it is necessary to explore better silk modification and functional finishing methods.Nano-silica（nano-SiO₂）is a kind of white inorganic nanoparticle with non-toxicity,good mechanical property,thermal stability and high UV shielding ability.And its surface has various forms of hydroxyl groups,which are easy to interact with other materials with chemical groups.Thus,it is an excellent nanometer material.In this study,nano-SiO₂ was used to modify and finish silk fiber and fabric as a functional material.On the one hand,the incorporated diet with of nano-SiO₂ was used to feed silkworm for preparing modified silk.The effects of different concentrations of nano-SiO₂ on the growth of silkworm larvae,the structure and performance of silk were investigated,the modifying mechanism of the nano-SiO₂ on silk was analyzed.On the other hand,nano-SiO₂ was used to prepare finishing agent and finish silk fabric by KH570crosslinking.The finishing condition was optimized,and the performance of finished silk fabric was evaluated.The major achievements were summarized as follows:1.Fabrication of modified silk with excellent performance by directly feeding nano-SiO₂The mulberry leaves sprayed with different concentrations（0.1%,0.5%,1%,2%,3%,4%）of nano-SiO₂ were fed to silkworms from the second day of fifth instars to cocooning.The average weight and average growth rate of these silkworm were not affected after feeding silkworm with nano-SiO₂.The morphologies of modified silk fibers were the same as that of ordinary silk,showing a smooth surface for all silk fiber.However,nano-SiO₂ had some effect on the cocoon weight and the diameter of silk fiber,both showing a tendency of increasing first and then decreasing as its concentration increased.The result of measuring the content of silicon in silk fibers showed that SiO₂ nanoparticles were absorbed by silkworm larvae and eventually spun into silk fibers,and the content of silicon in silk fiber increased gradually with the increased concentration of nano-SiO₂.The maximum content of silicon reached 869.70 mg/kg,which is the maximum concentration tested at present in silk fiber by using feeding method for silk modification.The structure of silk fiber was further characterized by Fourier transform infrared spectroscopy（FTIR）and X-Ray diffraction（XRD）,indicating the nano-SiO₂ may slightly hindered the conformation transition of the silk protein from random coil/α-helix toβ-sheet,and decreased crystallinity of silk,which did not affect the excellent mechanical properties of silk.The mechanical properties of silk fiber were enhanced after feeding nano-SiO₂,while the increase of breaking stress had no relation with the increase of silicon content.2%nano-SiO₂ modified silk had higher stress value compared with control and other concentration group,it’s stress was increased by 17.22%and reached up to 468.38 MPa.Most importantly,the modified silk fibers exhibited the excellent ultraviolet（UV）resistant property that their stress could remain after exposing to 300 MJ/m² UV energy.The improved mechanical and ultraviolet resistance properties are help to improve the embrittlement and yellowing defects of silk caused by ultraviolet irradiation.Therefore,this modified silk likely has a higher value and wider application in the future.Moreover,thermal stability and cytotoxicity test showed the nano-SiO₂ modified silk also had improved thermostability and good biocompatibility.2.Improving the function of silk fabric by coating with nano-SiO₂The nano-SiO₂ particles and 3-（Trimethoxysilyl）propyl methacrylate（KH570）were mixed in deionized water to obtain finishing solution（SiO₂@KH570 solution）,which was used to finish silk fabric by the method of the cycle of dipping and oscillating.Using orthogonal experimental design to achieve the high ultraviolet protection factor（UPF）of the fabric,experimental trials were optimized for the three testing parameters of nano-SiO₂,KH570concentration and water bath temperature.According to the results,the optimum conditions for finishing silk fabric were 10 g/L SiO₂ and 20 g/L KH570 and 80℃in water bath.The surface morphology of the functional silk fabric was characterized by scanning electron microscope（SEM）and energy dispersive spectrometer（EDS）.The result showed that the modified silk fabric had the rough surface and the higher silicon content,indicating nano-SiO₂ particles had been grafted onto surface of it.Further,the crosslink action of the functional silk fabric was characterized by Fourier transform infrared spectroscopy（FTIR）,which illustrated that the strong chemical bonds between silk fiber and nano-SiO₂ were formed and the“bridging”effect of KH570 was helpful for grafting SiO₂ nanoparticles on the surface of silk fiber.The whiteness test of silk fabric showed that color difference between original and functional silk fabrics was unapparent.After finishing,the UPF value of silk fabric reached to 84.52,improving 240%compared with untreated silk fabric,indicating its application potential for UV resistant products（UPF>40）.And also,the UPF value could maintain 77.31 after washing for 20 times,which demonstrated the prepared silk fabric had laundry resistance.Moreover,the WRA of modified silk fabric was 270.6°,which increase by 16.5%in comparison with that of the water treated sample.Its contact angle reached to 132.7°.Both results indicated this modified silk fabric has good anti-wrinkle property and hydrophobicity.Thermal stability and cytotoxicity test showed the modified silk fabric had good thermostability and cytocompatibility.In conclusion,through this method,the silk fabric with excellent UV and wrinkle resistance could be fabricated without effecting the original property and structure of silk,indicating their good application prospect in self-cleaning,water repellent,protection and non-ironing clothes.