Effect Of Nano Titanium Dioxide On Mechanical Properties Of Regenerated Silk

Due to the unique molecular structure,silk fibers have good mechanical properties,excellent cell compatibility,biodegradability,and have been widely used in biomedical,tissue engineering and other fields.Modification of silkworm by adding food method,the use of high dose of nanomaterials will cause the death of silkworm,and the output and performance of the silk cannot be guaranteed.In order to avoid this drawback and realize the mass production of functional materials,it is crucial to improve the performance of recycled fibers through a simple and effective spinning process.Compared with other spinning methods,wet spinning has the characteristics of simple process and low energy consumption,which meets environmental protection concept of green low-carbon and sustainable development.Feeding Ti O₂ NPs to silkworms can improve the mechanical properties of silk,but the preparation of regenerated silk fibroin protein?RSF?fibers by combining wet spinning with Ti O₂ NPs has been rarely reported.In this paper,Ti O₂ NPs with different particle sizes were blended with fibroin protein solution.The influence of the size of nanomaterials on the morphology,structure and mechanical properties of RSF fibers was investigated by wet spinning.The main research results of this paper are as follows:1.The optimal spinning conditions were found out based on the effects of different silk fibroin?SF?solution concentration,different spinneret diameter and injection rate on the mechanical properties of regenerated silk:spinning solution concentration is 15%,spinneret size is 27G?inner diameter is 0.21mm?,injection rate was 2 m L/h.The fracture strength reached 146.61±13.65 MPa,and the elongation at break reached 18.41±6.79%.It provides a foundation for the follow-up study on the influence of nanoparticles on the mechanical properties and structure of regenerated silk.2.By mixing Ti O₂ NPs with different contents and sizes to prepare RSF fibers,the effects of different sizes and blending ratio on the mechanical properties of RSF fibers were investigated.The mechanical test results showed that when the mixing ratio reached 4 mg/g Ti O₂ NP/SF,the prepared RSF fiber had the best mechanical properties.Five different particle sizes of Ti O₂ NPs were investigated,which were 5-10 nm?breaking strength:312.44±20.31MPa,breaking strain:46.55±2.76%?,25 nm?breaking strength:280.63±15.69 MPa,breaking strain:42.16±5.52%?,35 nm?breaking strength:259.77±14.35 MPa,breaking strain:40.60±2.62%?,45 nm?breaking strength:266.38±16.59 MPa,breaking strain:38.48±2.85%?,55 nm?breaking strength:228.76±16.59 MPa,breaking strain:32.27±3.62%?.The best mechanical properties of RSF fibers were obtained by mixing 5-10 nm Ti O₂ NPs.The breaking strength and breaking strain of RSF fibers added with 5-10 nm Ti O₂ NPs were113.11%and 152.85%higher than the control group.Meanwhile,it was found that in a certain blend ratio,Ti O₂ NPs with a smaller size would lead to better mechanical properties of RSF fiber.The improvement effect of different particle sizes was:5-10 nm>25 nm>35 nm>45nm>55 nm.3.The influence of Ti O₂ NPs with different particle sizes on the morphology,secondary structure and crystal structure of RSF fibers under different blending ratios was investigated by SEM,synchrotron infrared spectroscopy and X-ray diffractometer.The SEM showed that the mixing of Ti O₂ NPs had no significant effect on the morphology of RSF fiber,The results of synchrotron infrared spectroscopy showed that the secondary structure of the RSF fiber prepared by blending Ti O₂ NPs did not change significantly compared to the blank control group,but the secondary structure of the RSF fiber amide III region was found by split peak fitting of the conformational content has changed,showing the increased?-sheet content and the decreased random coil content and the helix content.When the mixing ratio of Ti O₂NPs/SF was 4 mg/g,the RSF fiber prepared by Ti O₂ NPs with different sizes had the highest?-sheet content.Five different size were 5-10 nm?47.27±0.25%?,25 nm?46.00±0.01%?,35 nm?45.46±0.42%?,45 nm?44.51±0.42%?,55 nm?41.34±0.55%?.Among them,the RSF fiber with 5-10 nm Ti O₂ NPs has the highest?-sheet content,which increased by 27.53%compared with 37.05±0.85%in the blank group.It was found that with the increase of Ti O₂NPs particle size,the?-sheet content of RSF fiber decreased,and the random crimp and r-helix content increased.XRD results showed that compared with the blank group,the crystallinity of the RSF fiber with Ti O₂ NPs was higher and its crystalline size was smaller.With the increase of Ti O₂ NPs particle size,the crystallinity of RSF fiber decreased and the crystalline size increased.In summary,the influences of Ti O₂ NPs with different particle size and blending ratio on the mechanical properties of RSF fibers were investigated.It was found that when the particle size was 5-10 nm and the mixing ratio of Ti O₂ NPs/SF was 4 mg/g,the mechanical properties of RSF fibers were the best,which provided a basis for further development of novel RSF fiber materials.