Dispersion Of MWNTs Assisted By Polyhedral Oligomeric Silsesquioxane As Dispersant And Preparation Of Their Composite Films With Cellulose

The environmental problems caused by the low biodegradability of plastic packaging and the evergrowing shortage of their raw materials-petro-chemical resources have received increasing attentions.Thus the development and utilization of bio-based polymers with good biodegradablity and excellent performance is imminent.Cellulose and its derivatives have great potential in the applications of food packaging owing to their excellent film-forming property and low cost.However,the poor mechanical property and weak moisture resistance of cellulose films largely limited their practical application.Incorporation of nano-fillers into polymers has been widely studied in recent years,which can effectively improve the performance of polymer films.However,the improvements are closely related to the dispersion state of nanoparticles in polymer films.Under this background,multi-walled carbon nanotubes(MWNTs)were chosen as the nano-fillers to improve the properties of carboxymethyl cellulose(CMC)films in this research,with the application of a physical dispersant and wet ball-milling to improve the dispersion of MWNTs in the films.Firstly,using polyhedral oligomeric silsesquioxanes(POSS)as the physical dispersant of MWNTs,the effects of POSS structure,MWNTs structure and weight ratio of POSS and MWNTs on the dispersity of MWNTs in aqueous solution were investigated taking UV absorbency as the indicator;Secondly,wet ball-milling of MWNTs/POSS mixture was applied to further enhance the dispersion of MWNTs in MWNTs/POSS,in which the wight ratio between MWNTs and POSS,ball-milling time and speed were optimized;Thirdly,the mechanism of enhanced dispersion of MWNTs by POSS was explored by Transmission Electron Microscopy,Raman spectra,fluorescent spectra,and Utroviolent Near Infrared Spectra of MWNTs/POSS;Finally,the composite films of CMC with the incorporation of MWNTs/POSS dispersions were fabricated and characterized on the micro-structure,crystal morphology,tensile properties and water vapor permeability,in order to explore the effects of nanoparticles on the structure and properties of the composite films and the synergistic effects of MWNTs and POSS.Based on these studies,the main results obtained are as follows:1.The dispersion effects of POSS on MWNTs was dependentto the structure of POSS,the concentration of MWNTs and the weight ratio between POSS and MWNTs.Among the five POSS with different structures,POSSC with a comparable non-polarity presented a good performance in improving both the concentration and stability of dispersed MWNTs.Under the conditions of this study,the best dispersity and stability of MWNTs in aqueous solution was obtained when the initial MWNTs concentration was 30 mg/L and the weight ratio between POSSC and MWNTs was 1.2.The MWNTs/POSSC mixture were wet ball-milled and dispersed to obtained the optimum conditions of wet ball-milling as following: the weight ratio between POSSC and MWNTs was 1,the ball-milling speed and ball-milling time were 200 rpm and 60 min,respectively.Under this condition,the initial dispersed concentration was 15.45 mg/L,which remained at 96.79% after standing for 180 min.3.As observed by the Transmission Electron Microscopy,POSSC were absorbed onto the surface of MWNTs with the aid of ball-milling.The results from Raman spectra,fluorescent spectra,and Utroviolent Near Infrared Spectra furtther indicated the physical interactions between MWNTs and POSSC and the effective charge transfer between them.Therefore,the dispersion effects of POSSC on MWNTs were basically resulted from the steric hindrance caused by the absorption of POSSC on MWNTs.The shear effects provided by wet ball-milling enhanced the adsorption of POSSC on MWNTs surface,thusing improving the dispersity of MWNTs in aqueous solution.4.When different amount of MWNTs/POSSC mixture were incorporated into CMC films,good dispersion were obtained when the addition amount was less than 1 wt.%;When the addition amount was 0.75 wt.%,the tensile strength,Young's modulus and elongation at break increased by 30%,11% and 41%,respectively,compared to the neat CMC films,while the water vapor permeability decreased by 10%.The properties of composite film containing MWNTs/POSSC were better than those containing only MWNTs or POSSC with the equivalent amount,which indicated the combined application of MWNTs and POSS was superior to those of single nanoparticle to improve the comprehensive performance of CMC films.