Abstract
To investigate the impact of process design factors such as number of passes, screw design and screw type, a poly(ethylene‐co‐acrylic acid) and a masterbatch containing 40 vol% nanocellulose were compounded using a twin‐screw extruder with two different screw configurations. The 20 vol% composite pellets obtained, containing nanocellulose of different morphologies, cellulose nanofibrils and cellulose nanocrystals, were re‐extruded several times to study the effect of re‐extrusion. The compounded pellets were extruded into films using a single‐screw extruder. These films contained aggregates of the nanocellulose material, which was reduced in size upon re‐extrusion leading to an improvement in properties of the composites. With the best combination of process factors, the Young's modulus and stress at break of the composites increased by factors of 10 and 1.6, respectively. The presence of a strong network of the cellulosic entities was observed qualitatively using melt rheology upon re‐extrusion. Re‐extrusion had a negligible effect on the crystallinity of the composites. POLYM. ENG. SCI., 60:956–967, 2020. © 2020 The Authors. Polymer Engineering & Science published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers.
Highlights
Cellulose has been used as a reinforcement/filler in the plastics industry for decades and with the development and commercial availability of nanocellulose the possibilities of utilizing this material as a reinforcement in polymers have been rekindled [1]
The masterbatch containing 40 vol% nanocellulose and 60 vol% EAA15 was compounded with EAA7 using the twin-screw extruder (TSE) at the temperatures given in the experimental section
The material was re-extruded three times through the TSE resulting in a discoloration which became more pronounced as the number of passes through the extruder increased, see Fig. 4
Summary
Cellulose has been used as a reinforcement/filler in the plastics industry for decades and with the development and commercial availability of nanocellulose the possibilities of utilizing this material as a reinforcement in polymers have been rekindled [1]. To realize the potential of nanocellulose as a reinforcement in thermoplastics, it is necessary to solve the problems involved in the melt processing of these composites. Nanocellulose, due to its hydrophilic nature, tends to give problems during melt processing with a hydrophobic thermoplastic matrix. This incompatibility can lead to the formation of cellulose aggregates, which lead to poorly dispersed, nonuniform thermoplastic composites. Interest leans toward the use of compatibilizers due to the ease of scalability. This approach makes it necessary to explore the processability of these nanocomposites using industrial melt processing technologies such as compression molding, extrusion, and injection molding instead of laboratory-scale processing. There is, to our knowledge, no work which explores the effect of processing parameters, the effect of screw selection during extrusion and the effect of number of passes (re-extrusion) on the morphology, appearance, melt rheology and mechanical properties of these composites
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