Periodic Reporting for period 1 - REDONDO (REVERSIBLY DESIGNED CROSS LINKED POLYMERS)
Période du rapport: 2022-09-01 au 2024-02-29
REDONDO (Reversibly Designed Cross linked Polymers) is a Horizon Europe project that aims to produce recyclable cross-linked polyethylene. Cross-linked polyethylene (PEX) is a difficult to recycle material due to the presence of very stable cross-links between the PE chains. REDONDO aims at developing a fully reversible cross-linking process to produce reversibly cross-linked polyethylene (rPEX), therefore enabling its recycling on demand.
PEX exhibits improved thermal stability, chemical resistance and structural integrity and is thus used in a number of applications for which polyethylene (PE) lacks temperature-related, strength-related, and other required properties. PEX has a wide variety of applications, notably as an insulation material for electric wires and cables and for hot and cold-water pipes and heating systems. Cross-linking modifies the nature of PE from thermoplastic to thermoset. As a result, PEX cannot be melted, as thermoplastics do, and recycled appropriately per application. It seems today that the only recycling technology for waste PEX scrap is grinding it to powder and directly moulding it with other thermoplastic blends as a filler, loosing most of its value.
REDONDO aims to achieve a fully reversible cross-linking process, that will enable the synthesis of reversibly cross-linked polyethylene (rPEX), that will be inherently recyclable and thus sustainable-by-design. Additionally, innovative biobased/green additives will be used to confer to rPEX novel/improved properties. Overall, rPEX will obtain significant added value due to its recyclability and its lower toxicity, compared to the use of traditional PVC-based polymeric materials or expensive and non-recyclable PEX. rPEX will be tested in two test-cases: pipes and photovoltaic cables. Complementarily, safety- and sustainability-by-design (SSbD) aspects will be incorporated to the design of the REDONDO products, while EoL scenarios will be investigated. Finally, two digital tools aiming at assisting stakeholders with SSbD concepts will be created: the additive inventory tool and the PLACE-me tool.
PEX exhibits improved thermal stability, chemical resistance and structural integrity and is thus used in a number of applications for which polyethylene (PE) lacks temperature-related, strength-related, and other required properties. PEX has a wide variety of applications, notably as an insulation material for electric wires and cables and for hot and cold-water pipes and heating systems. Cross-linking modifies the nature of PE from thermoplastic to thermoset. As a result, PEX cannot be melted, as thermoplastics do, and recycled appropriately per application. It seems today that the only recycling technology for waste PEX scrap is grinding it to powder and directly moulding it with other thermoplastic blends as a filler, loosing most of its value.
REDONDO aims to achieve a fully reversible cross-linking process, that will enable the synthesis of reversibly cross-linked polyethylene (rPEX), that will be inherently recyclable and thus sustainable-by-design. Additionally, innovative biobased/green additives will be used to confer to rPEX novel/improved properties. Overall, rPEX will obtain significant added value due to its recyclability and its lower toxicity, compared to the use of traditional PVC-based polymeric materials or expensive and non-recyclable PEX. rPEX will be tested in two test-cases: pipes and photovoltaic cables. Complementarily, safety- and sustainability-by-design (SSbD) aspects will be incorporated to the design of the REDONDO products, while EoL scenarios will be investigated. Finally, two digital tools aiming at assisting stakeholders with SSbD concepts will be created: the additive inventory tool and the PLACE-me tool.
During the first reporting period, transversal work was carried out in WP2 to establish an initial set of requirements regarding the new rPEX materials that will be developed as well as required properties that the pipes and cables demonstrator should exhibit. Most partners participated to this task and a smooth and fruitful collaboration was built from the first months of the project.
In WP3, despite various difficulties, some encouraging results have emerged regarding PE cross-linking.
In the context of WP4 the synthesis of several modified lignins was optimised, while preparation and modification of microfibrillated cellulose and cellulose nanocrystals were also achieved. HDPE composites with these additives were prepared and promising properties were observed. Additionally, HDPE composites with calcium pimelate were prepared and studied. The presence of the inorganic filler seems to confer an improved thermal stability at higher temperatures. Finally, tannic acid was investigated as a bio-based filler for HDPE.
Regarding the processability of the composite materials (WP5), trials have been performed with commercial HDPE and LDPE, as a benchmark materials, and modified lignins; this work will be extended firstly to investigate the effect of nanocellulose-based additives and then to rPEX composites.
Safety and sustainability criteria were defined (WP6 & WP7), while literature review for the additives inventory is in progress (WP7).
In WP3, despite various difficulties, some encouraging results have emerged regarding PE cross-linking.
In the context of WP4 the synthesis of several modified lignins was optimised, while preparation and modification of microfibrillated cellulose and cellulose nanocrystals were also achieved. HDPE composites with these additives were prepared and promising properties were observed. Additionally, HDPE composites with calcium pimelate were prepared and studied. The presence of the inorganic filler seems to confer an improved thermal stability at higher temperatures. Finally, tannic acid was investigated as a bio-based filler for HDPE.
Regarding the processability of the composite materials (WP5), trials have been performed with commercial HDPE and LDPE, as a benchmark materials, and modified lignins; this work will be extended firstly to investigate the effect of nanocellulose-based additives and then to rPEX composites.
Safety and sustainability criteria were defined (WP6 & WP7), while literature review for the additives inventory is in progress (WP7).
Significant progress has been achieved in the context of WP4, concerning the design and production of bio-based nanoadditives and the preparation of HDPE composites with several different fillers.
Several modifications were carried out to potentially enhance the properties of the lignin- and cellulose-based nanoadditives. These additives have been fully characterised by the respective partners, while preliminary studies regarding their incorporation in HDPE with different approaches and at different scales have been conducted. The properties of these composite materials are now under study. In the upcoming months, on the one hand toxicological studies and on the other hand preliminary LCA and LCC studies will be conducted.
Furthermore, noteworthy results were obtained with calcium pimelate/HDPE composites. Calcium pimelate (CaPi) has been developed as a highly effective and thermally stable β-nucleating agent and is frequently used in isotactic polypropylene, inducing the formation of β-crystals, which are thermodynamically difficult to obtain without the presence of a nucleating agent. Compared to PP and due to the faster rate of crystallisation of HDPE, it is difficult to control nucleation in HDPE and the impact of CaPi on the properties of HDPE is considerably less documented. In the context of REDONDO, CaPi/HDPE composites were prepared to investigate the performances of CaPi as an additive for HDPE. According to the obtained results, the addition of CaPi filler led to a slight increase in crystallinity in nanocomposites, with values ranging from 77% to 79% when neat HDPE exhibited a crystallinity of 76%. Mechanical properties were retained overall. DSC analysis demonstrated that the incorporation of CaPi filler into HDPE led to increased melting temperatures. Non-isothermal crystallization of HDPE/CaPi composites revealed complex crystallisation mechanisms, with nucleation and growth processes influenced by CaPi content. Interestingly, a higher thermal stability is observed with increasing CaPi content. Isoconversional results depicted a complex degradation mechanism, with distinct processes influencing the early and late stages of degradation kinetics. Model-fitting analysis further confirmed a two-step degradation mechanism for the nanocomposites, combining nth-order and autocatalysis mechanisms. The present work is a preliminary study on HDPE/CaPi nanocomposites and will be further extended to hybrid fillers containing CaPi.
Several modifications were carried out to potentially enhance the properties of the lignin- and cellulose-based nanoadditives. These additives have been fully characterised by the respective partners, while preliminary studies regarding their incorporation in HDPE with different approaches and at different scales have been conducted. The properties of these composite materials are now under study. In the upcoming months, on the one hand toxicological studies and on the other hand preliminary LCA and LCC studies will be conducted.
Furthermore, noteworthy results were obtained with calcium pimelate/HDPE composites. Calcium pimelate (CaPi) has been developed as a highly effective and thermally stable β-nucleating agent and is frequently used in isotactic polypropylene, inducing the formation of β-crystals, which are thermodynamically difficult to obtain without the presence of a nucleating agent. Compared to PP and due to the faster rate of crystallisation of HDPE, it is difficult to control nucleation in HDPE and the impact of CaPi on the properties of HDPE is considerably less documented. In the context of REDONDO, CaPi/HDPE composites were prepared to investigate the performances of CaPi as an additive for HDPE. According to the obtained results, the addition of CaPi filler led to a slight increase in crystallinity in nanocomposites, with values ranging from 77% to 79% when neat HDPE exhibited a crystallinity of 76%. Mechanical properties were retained overall. DSC analysis demonstrated that the incorporation of CaPi filler into HDPE led to increased melting temperatures. Non-isothermal crystallization of HDPE/CaPi composites revealed complex crystallisation mechanisms, with nucleation and growth processes influenced by CaPi content. Interestingly, a higher thermal stability is observed with increasing CaPi content. Isoconversional results depicted a complex degradation mechanism, with distinct processes influencing the early and late stages of degradation kinetics. Model-fitting analysis further confirmed a two-step degradation mechanism for the nanocomposites, combining nth-order and autocatalysis mechanisms. The present work is a preliminary study on HDPE/CaPi nanocomposites and will be further extended to hybrid fillers containing CaPi.