Preparation Of Modified Micro/Nanocellulose And Its Effects On The Properties Of Starch Films

Cellulose is the largest natural polymer in nature.Because of the special crystal structure,low cost,great mechanical properties as well as biocompatibility,cellulose is widely used as a reinforcing material of polymer materials.In this paper,microcrystalline cellulose was prepared by cationic modification after alkali pretreatment.On this basis,modified microcrystalline cellulose with different particle size was prepared,and nanocellulose was prepared by different methods.Finally,the effects of microcrystalline cellulose before and after modification,microcrystalline cellulose with different particle size and nanocellulose prepared by different methods on the properties of starch film were studied.The main research contents and results are as follows:(1)Alkali pretreatment made microcrystalline cellulose particles swell,destroyed the internal hydrogen bond and made its structure loose,which provided favorable conditions for the modification of microcrystalline cellulose and the preparation of nanocellulose.After modification,microcrystalline cellulose still belonged to I crystal type,with the crystallinity reduced to 68.2%;the initial thermal degradation temperature decreased,and the carbon residue increased at 500 ° C.(2)Adding microcrystalline cellulose and modified microcrystalline cellulose could improve the tensile strength,reduce the elongation at break and reduce the water vapor transmission of starch composite films.Compared with ST/MCC,the comprehensive performance of ST/MD-MCC was better.The cationic modification effectively improved the dispersion of microcrystalline cellulose in starch film matrix and enhanced the performance of starch film.The starch film with 5% modified microcrystalline cellulose had the best comprehensive properties.(3)The modified microcrystalline cellulose with different particle size had different effects on the properties of starch film.The smaller the particle size,the more uniform distribution in the starch film.The starch film had the greater tensile strength,smaller water vapor transmission coefficient,stronger light transmittance and the better comprehensive performance of the starch film.(4)Six kinds of nanocellulose were prepared by acid hydrolysis,high-pressure homogenization and ultrasound methods.The colloidal stability and yield of the nanocellulose prepared by modified microcrystalline cellulose were improved.The yield of the nanocellulose prepared by high pressure homogenization method increased by 16.2 times.The obtained nanocellulose had a fine fiber structure with a diameter of 2-15 nm.Compared with microcrystalline cellulose,the three kinds of modified nanocellulose were still cellulose I crystal,with lower crystallinity and initial degradation temperature.(5)Modified nanocellulose prepared by different methods could improve the mechanical properties and water resistance of starch films.The nanocellulose starch composite film prepared by adding high-pressure homogenization had the maximum tensile strength(28.74 MPa),and the water vapor permeability was reduced by 22%.