Preparation Of Cellulose Nanowhiskers From Mulberry Barks And Their Application To Reinforce Regenerated Bombyx Moir Fibroin Fibers

Bombyx mori silk is one of the most valuable materials for clothing industry due to its outstanding glossiness property, wearing comfort, and physiological properties (compatibility, biodegradability, thermo-insulating, etc). In order to produce specialty materials, silk processing techniques have been investigated for artificial silk, including spin dopes, concentration, coagulation bath, post-drawn, etc. But the mechanical properties of artificial silk fibre do not compete with native silk yet.Cellulose is one of the most ubiquitous and abundant bioresourse polymers on the planet, giving the renewability and biocompatibility. Cellulose nanowhisker (CNW), a nanocrystal prepared by acid hydrolysis of native cellulose, usually has good mechanical properties, high aspect ratio, and strong interfacial adhesion between the CNW and the matrix. Thus, it can be used as the reinforcing agent in environmental-friendly composite materials due to its special physical properties.In an effect to improve the mechanical properties of artificial silk fiber and utilize waste materials, CNW suspension was prepared by acid hydrolysis of cellulose from mulberry branch-barks (Morus alba L.), and subsequently mixed with regenerated silk fibroin (SF) solution to obtain concentrated SF/CNW aqueous solutions as spinning dopes. Then reinforced artificial silk fibers by cellulose nanowhisker (SF/CNW) were produced by wet spinning through methanol coagulant to investigate the relationship between SF matrix and CNW reinforcing agent. To realize the environmental-friendly production of mulberry cellulose and maximum utilization of sericultural resources, mulberry pectin and cellulose were extracted via two-step method, i.e. acid extraction-alkali treatment, respectively, and the degumming waste liquid was further treated to recycle pectin, hemicellulose, lignin.The extracted pectins from mulberry barks had different degrees of esterification. And the cellulose nanowhiskers presented rod-like with a length of 300-400 nm, and a diameter of 20 nm, and had a crystallinity of 86.4%. The thermal analysis showed a two-stage thermal decomposition behavior of cellulose nanowhisker with a maximum weight loss attained at 567℃. The obtained cellulose nanowhiskers may have the potential application as a reinforcing agent in the field of composite materials.From the research about the spinnability of regenerated SF solution, it was found that the concentration of spinning dope play an important role on the morphologies and mechanical properties of artificial neat SF fibers, when the dope concentration is about 27%, the artificial fibers presented a good surface and cross-section morphology, excellent mechanical properties. There was a rapid initial shear thinning at low shear rate for SF/CNW solution with different CNW content, so it was necessary to control the shear rate according to initial stage of stabile apparent viscosity. Moreover, the characteristic indexes decreased, while the degree of entanglement of SF molecular enhanced with the increase of CNW content from 1% to 7%. And the studies on stability of solution to temperature and storage time indicated that apparent viscosity remained almost unchanged below 25℃, and the SF/CNW dope is rheologically stable for at least 5 days.The SF/CNW fibers with super mechanical strength were successfully fabricated under an optimized technologic processing. The Young’s modulus and tensile strength of SF/CNW fibers with CNW content of 5% reached 28.84 GPa and 728.51 MPa, respectively, which was 1.8 and 1.5 times compared with that of raw silk, respectively, moreover, breaking elongation was 20.3%, near that of raw silk. The spun fiber had well crystallinity and was well-oriented along the long axis after postspinning treatment at 60℃. In other hand, CNW were uniformly dispersed in the SF matrix. Dynamic mechnical analysis revealed that the elastic modulus of SF/CNW fibers increased significantly as a consequence of the reinforcing effect of CNW via the procolation network held by hydrogen bonds, finally leading to increase of glass transition temperature.In conclusion, it was an effective approach to improve the mechanical properties of artificial silk fiber via introduction of CNW with high aspect ratio, well crystallinity, and good mechanical strength. It would be significant for exploiting novel functional materials through investigating formation of aggregation structure, relationship between structure and properties, and interaction of matrix and dispersed phase. Furthermore, this research which was a recycling of sericulture waste resource might possess the potential economic and social benefits.