Research On Plasticizing-Rolling Forming Method,Mechanism And Performance Of Cellulose

Cellulose,the most abundant natural polymers on Earth,possesses fantastic properties,e.g.,high mechanical properties and thermal stability,indicating wide applications.However,cellulosic molecular chains are difficult to move due to high molecular weight,high crystallinity,strong hydrogen bond network and amphiphilicity structure,making dissolution or melt processing extremely hard,which severely limits its application range.In this dissertation,1-butyl-3-methylimidazole chloride(Bmim Cl)and lithium chloride are introduced into cellulose serveing as plasticizers,meanwhile repeated rolling destroys the crystalline structure of cellulose to improve the mobility of molecular chain,thus plasticized cellulose compounds(PCC)films are prepared,and finally Bmim Cl and lithium chloride are removed by the regeneration to obtain high-performance regenerated cellulose films.This dissertation systematically studies the forming process of plasticizing-rolling forming,the microstructure evolution mechanism of the forming process,and performance of regenerated cellulose films.The main work is as follows:A plasticizing-rolling forming cellulose process is proposed.The formability of cellulose powders under different factors is studied,and compared with results of pure rolling and wet processing based on dissolution.The results reveal that the proposed process solves the problem that cellulose molecular chains could not freely move during the rolling process and increases cellulose contents from ～5 wt.% in wet processing to 70 wt.%,demonstrating the proposed process is high-efficiency.Furthermore,the morphology and crystalline states changes of cellulose under different rolling time,reveal plasticizing effect from Bmim Cl and rolling have coupling effects in destroying crystal areas and improving the formability.Moreover,based on the principle of solvation plasticization,a plasticizingrolling model is established,and distributions of the concentration of plasticizers in the cellulose area under different factors such as rolling time,plasticizer content,solubility,etc.,are analyzed,and flow characteristics of PCC are predicted.The rheological properties of PCC are analyzed,and the process window for forming PCC films is established.The rheological properties of PCC are characterized by a capillary rheometer,and compared with that of cellulose solutions and common plastic Low density polyethene(LDPE),indicating that compared with cellulose solutions,the viscosity of PCC increased by 4 orders of magnitude,and PCC has a more obvious non-Newtonian characteristic,closer to that of LDPE melt.Secondly,results of different factors on rheological properties of PCC reveal that optimizing material compositions(increasing the content of Bmim Cl and lithium chloride,reducing the water content),appropriately increasing temperature and shortening rolling time,can reduce the viscosity of PCC by one order of magnitude.Finally,the process window for forming PCC films is determined through all-factor experiments,and PCC films with uniform thickness are fabricated.The material composition and microstructure evolution law of cellulose powders,PCC films and regenerated cellulose films during the forming process are studied.Results of infrared absorption spectroscopy and X-ray photoelectron spectroscopy show that cellulose and plasticizers do not have chemical reactions during rolling,and Bmim Cl is completely removed in regenerated cellulose films.Scanning electron microscopy results show that the addition of Bmim Cl and lithium chloride could reduce the size of cellulose particles and realize spheroidizing.For example,the particle size of regenerated cellulose films prepared from 5 g cellulose powders,5 g Bmim Cl and 2 g lithium chloride,decreases from 25 μm of powders to 100 nm,and the shape changes from a rod with an aspect ratio of >10 to a round ball.X-ray diffractometer test results show that adding Bmim Cl and lithium chloride greatly reduces the crystallinity in PCC first and then slightly increases in regenerated cellulose films,and the cellulose crystal form changes from type I in cellulose powders to coexisting states of type I and type II in regenerated cellulose films.That is,the microstructure of cellulose powders processed from micron rod-shape to sub-micron sphere and regenerated from type I to type I and type II cellulose coexisting.The performance of regenerated cellulose films is characterized by uniaxial tensile,thermal stability and optical transmission tests,and the relationship between microstructure and performance is established.The uniaxial stretching results show that compared with PCC films,tensile performance of regenerated cellulose films is greatly improved.The tensile strength reaches 94 ± 3 MPa,the elastic modulus reaches 10.5 ± 1.2 GPa,and the elongation at break reaches 2.2 ± 0.8%.Secondly,the more Bmim Cl added in the plasticizing-rolling process,the higher tensile properties of regenerated cellulose films,due to improved interface quality.The thermogravimetric analysis results reveal that thermal decomposition temperature of regenerated cellulose films is 50 ℃ higher than that of PCC films,and 64 ℃ higher than that of films prepared by other methods,demonstrating that films prepared by this process have high thermal stability.The effect of the Bmim Cl content and lithium chloride content on the thermal decomposition temperature is less than 10 °C.The transmittance results show that adding Bmim Cl and lithium chloride increases the transmittance of regenerated cellulose films.The proposed model demonstrates that the high transmittance results from the reduction of interface scattering.That is,reducing the particle size and crystallinity would slightly reduce the tensile strength and thermal stability of regenerated cellulose films,but greatly increase its light transmittance.In this dissertation,a plasticizing-rolling forming cellulose process is proposed,rheological properties of PCC and the mechanism of microstructure evolution during the forming process are explored.It is of great significance for efficiently manufacutring highperformance cellulose materials and extending the application range of cellulose.