Co-authors​ :

 Haruya BABA (JAPAN), Tatsuya TANAKA , Masahiro SASADA , Hiroshi OHSAKI , Kana MIYAMOTO  

In recent years, the development of polymer composite materials has been progressing to improve the functionality and performance of materials, and composites, in which fillers are mixed with polymers, are used as a method. The equipment used for this method is a co-rotating twin-screw extruder, which is capable of continuous production and has good productivity. A co-rotating twin-screw kneading extruder is a device widely used in the field of extrusion processing of polymeric materials. Generally, the flow in a kneading extruder is dominated by shear flow, which causes rotational motion of the filler, and the loss ratio to the given energy is large, making it difficult to knead materials with small filler particle sizes. Therefore, we focused on extensional flow.
Extensional flow is a flow that is stretched in the direction of principal stress. There is less loss of energy acting on the particles, the extensional viscosity is three times the shear viscosity, and the force acting on the fibers is greater. Therefore, it is thought that it can be dispersed more efficiently. However, particle dispersion using a co-rotating twin-screw extruder is not suitable for materials such as polyvinyl chloride (PVC), which are greatly affected by shear heat generation. Therefore, we attempted to apply the method of this twin-screw kneading extruder to a single-screw extruder. Therefore, the purpose of this study is to disperse fillers using extensional flow in a single-screw extruder.
The experimental materials used were a base material made of polyvinyl chloride (PVC), calcium carbonate, plasticizer, etc. used in flooring materials, and cellulose nanofibers (CNF) as a reinforcement. The experimental equipment used was a single screw extruder. On the way of the flow, a blister disk (BD) was used to partially block the resin, and the resin was pushed out under pressure to generate extensional flow. The pressure was measured before and after BD, and the pressure drop was calculated. The extruded sample was pressed into a sheet, and an SEM image was taken. By quantifying the CNF agglomeration area, we calculated the area frequency distribution. The dispersibility was compared between a sample kneaded with a full flight screw and a sample passed through a BD.
As a result, when kneading in full flight and kneading in extensional flow were compared, the proportion of small particles remained unchanged, but in kneading in extensional flow, large particle agglomerates decreased, and medium particles increased. It was found that dispersion was progressing. Furthermore, although the rotation speed and pressure drop were proportional, no significant correlation could be found between pressure drop and particle dispersibility as in a twin-screw kneading extruder.