On-going funded research projects

The PolymeReEng group coordinates or participates in the following funded research projects:

• HYSELFDROPS: Hybrid thermal spray coatings with self-lubricant properties for wear protection of Internal Combustion Engine piston rings
• FUVPP: Flame-retarded and UV-Protected Polypropylene HFLS Pipes
• SucciVitr: Comprehending and controlling the dynamics of the adaptable network in biobased vitrimers
• Encapsulation of active compounds in polymeric microcapsules: Modifying properties via solid state polymerization
• BioICEP: Bio innovation of a circular economy for plastics

HYSELFDROPS: Hybrid thermal spray coatings with self-lubricant properties for wear protection of Internal Combustion Engine piston rings, (T2EDK-01883) EPAnEK 2014-2020, 2020-2023. Visit the Project Site (in greek).

The self-lubricating coatings, used lately in diesel engines, deposited on complex shaped parts such as piston rings have significant contribution in the reduction of the total engine energy losses due to wear and abrasion. This reduction even in small percentages of the order of 1% is of high importance since it contributes to the reduction of fuel consumption and consequently in the operating and maintenance costs. These coatings present the additional advantage of avoiding toxic chemical substances release to the environment unlike liquid lubricants. This research proposal aims at the development of innovative techniques towards the deposition of hybrid self-lubricating coatings using thermal spray techniques. This way, the diesel engine piston rings will be significantly protected against wear and thus offer reduced energy losses during operation. The idea is the liquid lubricant microencapsulation in polymer capsules using in situ polymerization and their homogeneous distribution in an anti-wear thermally sprayed coating. This unique procedure will be performed using combined thermal spray techniques, Liquid Plasma Spray for the capsules deposition and simultaneously Atmospheric Plasma Spray for the ceramic/metallic anti-wear matrix material deposition. Furthermore, the development of powder mixtures, ceramic/metallic matrix with carbon nano-tubes (CNT's) to be used as Atmospheric Plasma Spray feedstock material will be investigated. The proposed innovation in HYSELFDROPS lies in the combined self lubricating and anti-wear thermally sprayed coatings that will be developed which will contribute to the significant energy loss reduction of diesel engines for marine applications. The expected mechanism is the release of the liquid lubricant through capsules break up during operation while the anti-wear coating degrades. This will significantly increase the piston ring service life. Furthermore, scale up activities in terms of feedstock materials production as well as thermally sprayed real parts (piston rings) for field testing will be performed. The coated piston rings will be implemented in a three cylinder Yanmar 3YM30 diesel engine producing 21.3 kW maximum power at 3200 rpm for marine applications.

FUVPP: Flame-retarded and UV-Protected Polypropylene HFLS Pipes, (T2EDK-01466) EPAnEK 2014-2020, 2020-2023 (Project Coordination: PolymeReEng Group). Visit the Project Site (in greek).

The project aims to develop flame retarded polypropylene (PP) of low environmental impact and high resistance to ageing and use it for the production of novel piping systems for cables protection in superfluous installations.

The majority of fatalities in fire incidents is caused from poisoning and entrapment of victims, while most of the fire incidents are due to electricity. The use of halogen free and low smoke (HFLS) plastic pipes for cables systems contributes to the protection of human lives, the environment and equipment in the case of fire, as HFLS plastics do not produce toxic or corrosive gases nor dense smoke as halogenated materials do. For this reason, the new regulation for fire protection of buildings (Presidential Decree 41/2018) imposes the use of HFLS cables in various cases of buildings, and therefore indirectly imposes also the use of plastic pipes of the same type.

Double layer corrugated plastic pipes exhibit a two-fold advantage since the smoot inner layer allows installation of the cables with low friction, while the corrugated outer layer contributes to flexibility and materials savings compared to conventional pipes with solid layers. The production process of double layer corrugated HFLS pipes requires the use of polyolefins (PP) as raw materials, since it is most compatible with the specific processing technique. However, for polyolefins to be used in this application, it is necessary to modify them with flame retardants (FRs), as pristine polyolefins are highly flammable. Accordingly, the first objective of FUV-PP is to develop optimized FR formulations for the pertinent processing and application, so as to obtain HFLS material without adversely affecting its processability and final properties.

Particularly for outdoors applications, such as superfluous electrical installations, a further need is to develop polymeric products resistant to ageing. The use of stabilized polymers containing FRs is limited in this case, firstly because the FR additives may reduce the photooxidative stability of the polymer matrix and secondly because FRs and UV/heat stabilizers have shown to exhibit antagonistic action. As a consequence, polymeric materials containing additives of both categories often present lower stability during prolonged exposure to UV irradiation compared to their photo-stabilized counterparts with no FR. Therefore, it becomes evident that a need exists to develop environment and human-friendly as well as resistant to ageing FR formulations for polyolefins, in particular for PP, used in cables protective pipes where both flame retardancy and resistance to ageing are required. In order to respond to the above challenges, FUV-PP proposes the use of environment friendly additives for the production of flame retarded PP with resistance to ageing. First, combinations of halogen free FRs and/or halogenated FRs in appropriately low concentrations will be designed and developed, allowing the production of HFLS PP-based double layer corrugated pipes. Further, combined systems of FRs and UV/heat stabilizers will be developed to simultaneously achieve flame retardancy and resistance to ageing (no reduction of initial properties after 2000 h artificial weathering). It is highlighted that research on the simultaneous use of FRs and UV/heat stabilizers is limited. The proposed approach will cover the existent gap for applications necessitating both flame retardance and resistance to ageing. In the frame of the project, the new materials will be used in a totally new and patented production process that allows producing double layer corrugated PP pipes of very low external diameters (16-32 mm). All materials and products developed in FUV-PP will be characterized in terms of FR properties, UV resistance and physicomechanical performance using standard test methods.

SucciVitr: Comprehending and controlling the dynamics of the adaptable network in biobased vitrimers (PEVE0050). Basic Research Programme NTUA. PEVE 2020 NTUA, 2020-2023.

Polymers are classically divided into thermoplastics and thermosets, while the invention of smart, recyclable and healable thermoset polymers is in high demand. Vitrimers emerge as a viable solution bridging the gap between thermosets and thermoplastics; they possess a dynamic crosslinked structure which upon heating allows rapid chemical exchange reactions and network rearrangement, enabling deformation, healing and reprocessing. For most applications, vitrimers behave as classical thermosets, taking advantage of chemical crosslinks benefits eg insolubility, high melt strength, good barrier properties. Only under heating does the rearrangement of the dynamic network become significant, leading to controlled macroscopic flow like viscoelastic fluids, without losing network integrity.

The mechanism and kinetics of these associative exchange reactions are responsible for the dynamic nature of the crosslinked macromolecular structures and until now are considerably neglected, as scientific literature focuses mainly on fine-tuning vitrimers properties and optimization of their scaled-up production. On the other hand, compared to their fossil counterparts, biobased polymers offer significant benefits with regard to environmental performance, especially with regard to global warming potential.

SucciVitr research activities include a vigorous kinetics study of the transesterification reactions in a model biobased polymer, i.e. polybutylene succinate, which will attempt to integrate the effect of varying parameters (reaction temperature and time, reacting species concentrations) in kinetics constants, such as the apparent reaction rate constant and activation energy. The derived kinetics parameters will be correlated to the mechanisms of the associative exchange reactions that endow vitrimers their dynamic rheological behavior determining also the rate-controlling steps and variables.

Encapsulation of active compounds in polymeric microcapsules: Modifying properties via solid state polymerization (MIS 5049531). ESPA 2014-2020, Human Resources Development, Education and Lifelong Learning 2014-2020, 2020-2021.

Progress in the controlled release of active substances is related to the development of polymeric microencapsulation systems with the aim of maximizing the effectiveness of the active substance. The release rate / mechanism in these systems is linked to the properties of the polymeric carrier, such as purity, molecular weight, thermal properties and crystallinity, which in turn are affected by the monomers or polymers and the parameters of encapsulation process. The research in this area is oriented towards the development of new systems of polymeric carriers with properties adapted to the desired application.

In this project, the aim is to examine solid state polymerization (SSP) technique as a "tool" for upgrading already formed polymeric microcapsules for adapted physicochemical properties. Solid State Polymerization is an established industrial process in which the initial prepolymer is heated, in inert conditions, to a temperature range between the glass transition point and the melting point so that polymerization reactions take place in the amorphous regions of the prepolymer.

Specifically in the present project SSP will be applied to two types of polymeric systems with microcapsule morphology:

• Polyamide microcapsules prepared via interfacial polymerization
• Polyester microcapsules prepared via emulsficiation-solvent evaporation

The aim of the post-encapsulation SSP is to increase the molecular weight and thermal properties (crystallinity) while in the case of polyamide microcapsules the action of SSP will be considered in terms of residual monomers removal.

BioICEP: Bio innovation of a circular economy for plastics (GA 870292), Horizon 2020, 2020-2024. Visit the Project Site.

The BioICEP consortium is a pan European-Chinese collaboration formed to reduce the burden of plastic waste in the environment. The countries have been selected to represent different mixed plastic pollution environments, with specific partners chosen which have the expertise and facilities to carry out the necessary technical innovations. A number of innovative booster technologies are at the core of this solution accentuating, expediting, and augmenting mixed plastics degradation to levels far in excess of those current achievable.

Our approach is a triple-action depolymerisation system where mixed plastic waste will be broken down in three consecutive processes: 1) mechano-biochemical disintegration processes, including a new proprietary sonic-green-chemical technology to reduce the molecular weight (MW) of the base polymer making it amenable to biodegradation; 2) biocatalytic digestion, with enzymes enhanced through a range of innovative techniques including accelerated screening utilising novel fluorescent sensors coupled with directed evolution; and 3) microbial consortia developed from best in class single microbial strains, which when combined lead to highly efficient degradation of mixed plastic waste streams. The outputs from this degradation process will be used as building blocks for new polymers or other bioproducts to enable a new plastic waste-based circular economy.