Tallinn University of Technology School of Engineering, Department of Materials and Environmental Technology offers a 4-year PhD position in chemical, materials and energy technology.

The proposed PhD thesis topic: "Reactive extrusion based synthesis of thermoplastic cellulose derivatives"

Supervisors: Tenured Associate Professor Andres Krumme and Senior Researcher Illia Krasnou (TalTech)

Summary

The overall goal of the project is elaborating sustainable and up-scalable method for synthesis of thermoplastic cellulose derivatives using fully biobased reagents and mechanochemical action of reactive extrusion. The project addresses critical issue of providing bio-based alternatives for fossil-based plastics. Cellulose is the most relevant but strongly underutilized raw material for this. The project should provide solution for conducting synthesis of thermoplastic cellulose derivatives on sustainable and energy efficient way. The work is conducted in international team in collaboration with relevant academic and industrial research partners. 

Description

Cellulose, as the most common biopolymer in the world, is an important resource for replacing fossil-based plastics as it has good mechanical properties, chemical durability and is not competing food resources. However, only minor amount of global plastic production is covered by cellulose derivatives or regenerates. This is pointing strong need to increase utilization of this sustainable, carbon neutral raw material for plastics. Unlike most of the commodity plastics, cellulose is not intrinsically thermoplastic and must be chemically modified to achieve melting behavior, expected by plastics processing industry. The cellulose modification methods known so far are resource- and energy-intensive. This stimulates development of more sustainable routes. There are two main aspects of sustainability of synthesis of thermoplastic cellulose derivatives: biobased, sustainable reactants and fast and energy efficient process. However, several perspective bio-based reactant candidates have intrinsically low reactivity with cellulose functional groups. Therefore, the synthesis process should provide strong support to the reactions. Increasing reactivity of the reactants by mechanochemical action is a perspective research area, where nearly no relevant publications exist. The most promising mechanochemical method, where both high shearing and elongational forces are present is reactive extrusion (REX) in co-rotating twin-screw extruder. REX is known in general as a method in polymer synthesis and modification, providing highest yield with the shortest time, minimum usage of energy, solvents, and reactants. The extrusion process is continuous, having therefore good perspectives for industrial up-scaling. REX can process highly viscous substances and therefore, much higher cellulose concentrations can be expected than in a batch-wise stirred reactor, significantly reducing the need of solvents.

Therefore, the main objective of the PhD project is to elaborate sustainable and up-scalable method for the synthesis of thermoplastic cellulose derivatives using fully biobased reagents and mechanochemical action of REX.

Responsibilities and specific tasks 

• Modelling and simulation of the REX process by the screw design, input material characteristics and process conditions for understanding thermo-mechanical conditions, energy balance and materials behavior/reaction evolution along the process. 
• Optimizing the reaction conditions, screw profile, screw rotation speed, temperature profile, feed rates etc. for obtaining maximum reactivity in shortest time with minimum usage of energy and solvents. 
• Studying effect of preparative procedures of cellulose (as swelling, partial dissolution, application of ultrasound or microwave radiation etc.) for maximizing the reaction efficiency. 
• Improving the REX based laboratory pilot technology by specific components.
• Conducting LCA of the REX process addressing critical aspects of sustainability and environmental impact. Improving the process accordingly.
• Contributing to analyzing, publishing and dissemination of the results of the study as a member of the research team.