| Sheet extrusion of four grades of cellulose acetate butyrate i.e. CAB with 5%, 8%, 10% and 12% plasticizer content showed that an increase in plasticizer content led to a decrease in melt shear viscosity, resulting in a higher extruder output. The length (m/min) of the sheet extruded increased with an increase in take-off speed and was independent of screw speed. The characteristics of the sheet i.e. degree of neck-in, bead thickness ratio and draw down ratio of the extruded sheet increased with an increase in take-off speed, but decreased with an increase in plasticizer content. Some mechanical properties of the extruded CAB sheets decreased with an increase in plasticizer content i.e. CAB 5% had the highest values for stiffness, hardness and tensile strength. However, other properties such as impact resistance and linear shrinkage increased with increase in plasticizer content in the CAB formulation, with CAB 12% exhibiting the highest values. The optical quality of the extruded CAB sheets varied with the level of plasticizer content, i.e. regular light transmittance increased with an increase in plasticizer content, while uv absorbance decreased with an increase in plasticizer content. The defect analysis revealed that the number of defects in the CAB sheets was independent of the plasticizer content, but a function of foreign contaminants and/or machine malfunctioning. To improve the optical quality of the CAB formulations, small quantities of dyes, uv absorbers and antioxidant were used to enhance the properties of CAB.;CAB 8% showed balanced properties that are desirable for optical applications. |
