Properties And Structures Of Biaxial Cellulose Films From NMMO Solution

The process using NMMO as the direct solvent of cellulose can be used to prepared Lyocell fibers. Lyocell fibers have excellent mechanical properties and biodegradable merit. Similarly, cellulose films prepared from NMMO process have also many good advantages and can be applied in many fields. In this paper, the cellulose tubal film is also prepared successfully by blown-extrusion technique. The biaxial elongational films from blown-extrusion technique have better properties than the uniaxial elongational flat films. At present, only several overseas companies are engaged in industrial study of this kind of films. Till now, few fundamental studies about this film have been done in the world.In this dissertation, the effects of process parameters on the mechanical properties, orientation and performance water vapor transmission of cellulose films are also studied. On the other hand, morphologies of film section have been studied through scan electronic microscopy (SEM). Elongational flow behavior ofcellulose solution in the blown-extrusion process is investigated for the first time. The main conclusions are as follows:In this paper, strength, modulus and elongation at break of the films in the longitudinal are discussed under the different process parameters. The chain orientations of cellulose increase with take up speed, blown-up ratio or air gap length, while decrease with the temperature of the coagulation bath. The performance of water vapor transmission has close relationship with the chain orientation of cellulose. It decreases with the length of air gap, take up speed and blown-up ratio, while increases with the temperature of the coagulation bath.At the same time, scan electronic microscopy (SEM) investigation has also done on the film section. An asymmetric structure can be obtained in the case of different inner and outer coagulation bath. Dry has also important effect on structure and morphologies of film section. The effects of different process parameters on film structure are also discussed.The rheology model of cellulose solution in the blowing process is deducted according to C.D.Han's model. In this paper, elongational viscosities have been determined during the process of blown film. The results show that the elongational viscosity is affected by elongational rate, temperature and other processparameters. It shows that the elongational viscosities decrease first, then increase gradually along the extrusion direction. As the take up speed and the pressure difference inside and outside the tube increase, consequently the wall of the tube becomes thinner, elongation rate increases and the elongational viscosity deceases.