Study On Morphology Of Isotactic Polypropylene/Cellulose Acetate Butyrate System

The properties of multicomponent polymers not only depend on the chemical structure but also the morphology of system. While, the morphology of multicomponent system can be affected by the blend ratio, interface tension, viscoelasticity ratio, processing parameters and so on. So it is valuable both in theory and practical to study the phase evolution mechanisation of the multicomponent polymers.In this paper, the process of phase evolution of isotactic polypropylene/cellulose acetate butyrate (iPP/CAB) system was analyzed by scanning electron microscopy (SEM) and small angle X-ray scattering(SAXS), then the theory model of which was simulated. What is more, the influence of the material viscoelasticity, the temperature field, blending machine and the blend ratio on the phase development was also discussed.To study the process of phase evolution of iPP/CAB system, the samples were taken out at different positions of the twin-screw extruder. Two kinds of morphology evolution mechanization were found. (1) The separated phase droplet is drawn into cylinder at the initial stage of compounding, then the cylinder breaks into small particles, at last the small particles change into long fibers. (2) The separated phase is stretched into a sheet at the initial stage of compounding, then the sheet would break up into small particles, at last the small particles change into long fibers. According to the theory of droplet deformation and breakup, the process of phase development was analyzed. The time of the separated phase evolution was calculated, and the process of ellipsoid separated phase changes into sphere was also simulated. It was found that the separated phase's morphology and size changes greatly at the initial stage of compounding. At last, the sketch map of the separated phase morphology evolution was given.The influence of the viscoelasticity ratio, temperature field, blending machine and blend ratio on the phase development was also studied. It was found that the process of phase development was not the same for systems different in viscoelasticity ratio:for the systems with larger viscoelasticity ratio, the separated phase droplets would change into long strips at the initial stage, and the final size of separated phase is large; for the systems with small viscoelasticity ratio, the separated phase droplets would change into thin sheets at the initial stage, and the final size of separated phase is small. The blending machines have significant effects on the separated phase size:the size of separated phase made by twin screw extruder is smaller than that made by a single screw extruder and a mini extruder. The separated phase would form different morphology and have different size distribution at different temperature field:when the blends specimen was placed in a silicone oil both at 150℃, the size of separated phase would increase greatly and the distance between two phases become larger; when the blends specimen was placed in the air oven at 140℃, the size of separated phase would increase slowly and the distance between two phases would not change. At last, the influence of blend ratio on the phase morphology and size was studied by SAXS. It was found that the correlation distance and average chord lengths of separated phase would increase with the increasing of blend ratio, which means the size of separated phase would increase with the increasing of blend ratio.