دانلود رایگان مقاله پروتئین باکتریایی سلولز - سویا بر اساس نانوکامپوزیت "سبز"

Abstract

Bacterial cellulose (BC) nanofibrils are considered as promising biodegradable fiber-reinforcement for polymeric composites because of their excellent tensile properties. However, commonly obtained randomly-oriented web-like form of BC nanofibrils impedes achieving their full potential as reinforcement. In the present study, a facile and scalable method has been developed to orient the nanofibrils through a controlled stretching of BC hydrogel. An optimum hydrogel-stretching at the cross-head speed of 0.05 mm/min and strain ratio of 1.2 showed substantial improvements in the orientation and mechanical properties of BC. Degree of orientation, apparent Young's modulus and fracture stress of the dried BC were increased by 117, 103 and 85%, respectively. Consequently, a BC-reinforced soy protein isolate based fully ‘green’ composites (BC-SPI composites) were prepared by using vacuum-assisted SPI resin impregnation into BC hydrogel and then stretching the resin impregnated BC hydrogel. The stretched BC-SPI green composites, after drying and curing, showed significant improvement in their tensile properties due to higher BC nanofibrillar orientation. This study opens up new possibilities for direct fabrication of lightweight and mechanically robust ‘green’ composites that can replace traditional non-degradable composites and reduce carbon footprint significantly.

4. Conclusions

In this study, a straightforward process for the fabrication of oriented BC and BC-reinforced ‘green’ composites by simple hydrogel-stretching, drying and curing has been developed. Although the mechanical (tensile) properties of BC depend on several intrinsic, extrinsic and processing parameters, the effect of orientation has been considered in this study, keeping the other factors constant. An optimum and controlled stretching of BC hydrogel at a cross-head speed of 0.05 mm/min and a strain ratio of 1.2 demonstrated significant improvements in the orientation of randomly-oriented nanofibrils and resulted in significantly higher tensile properties. Similarly, significant improvement in the tensile properties of BC-SPI composite was obtained after similar stretching of SPI-impregnated BC hydrogel, due to nanofibrillar orientation. High density of entanglements in BC networks was seen to impede obtaining perfect alignment through stretching. The entanglements, in the future, may be reduced through the control of microbial movement during the fermentation process. Hence, considering the simplicity of the route and sustainable characteristics of the materials, the process could open up opportunities for the development of mechanically robust and lightweight advanced ‘green’ composites that can replace traditional non-degradable plastics and composites.