Recycling of waste tires is a significant issue considering both environmental and economic aspects. One of the leading recycling routes is the shredding of tires resulting in the generation of ground tire rubber. This material can be easily introduced into various polymer matrices as a filler, reducing the use of conventionally applied petroleum-based materials. In such cases, it is essential to ensure sufficient interfacial compatibility, which could be achieved by the proper modification of the rubber surface. Different methods of treatment of ground tire rubber aim to activate its surface and introduce functional groups, which could provide the possibility for interfacial interactions and incorporation of the significant amounts of recycled material. Therefore, in the presented paper, we examined the impact of thermo-mechanical treatment in twin-screw extruder on the appearance and chemical structure of ground tire rubber. Moreover, for each set of process parameters, the specific mechanical energy required for the processing was calculated, which could provide essential insights for the potential industrial application of the analyzed process. The energy demand should be considered as a very important issue during development of “greener” processes and materials.

This work is focused on the design and development of biocompatible self-assembling hydrogels which behave as soft gels at room temperature and as strong ones at the physiological temperature, suitable for potential bio-applications. A graft copolymer of sodium-alginate bearing 8 side chains of poly(N-isopropylacrylamide), enriched with the hydrophobic comonomer N-tertiary-butyl-acrylamide (NtBAM), [ALG-g-P(NIPAM-co-NtBAM)] were used as gelator. 5 wt % aqueous polymer solutions in the presence of various concentrations of Ca²⁺ cations were prepared and evaluated as thermoresponsive hydrogels. Rheological experiments revealed a twostep reversible gelation either upon heating or upon cooling .

The divalent cations operate as cross-linking agent through ionic interactions inducing the formation of a network at low temperatures. Upon heating, an additional crosslinking develops through thermo-generated hydrophobic association of the thermo-responsive P(NIPAM-co-NtBAM) side chains above a critical temperature.

The storage modulus, G’, increases with the cation concentration below and above the critical temperature. More importantly, the difference of G’ between 20 ^oC and 50 ^oC (ΔG’) increases linearly with the cation concentration, revealing a cooperative effect between the two-association mechanism, i.e. ionic and hydrophobic. In other words, the thermo-induced hydrogel elasticity is enhanced in the presence of the ionic bonds.

Furthermore, the combination of thermo- and shear-responsiveness provides shelf-assembling systems as potential candidates for injectable strategies. Especially, the systems with lower cation concentration could be used for drug delivery, while the gelators with higher cation concentration could be used for cell transplantation, which require a weak gel to protect the cells during injection and an instantaneous gelation at physiological temperature after the injection to immobilize the created scaffold in the targeting position of the host tissue.

Microbial contamination represents an undesirable event in various domains, such as in biomedical, food preservation and cosmetics. Microbial adhesion and growth on medical devices and implants can cause serious complications to human health, being source of severe nosocomial infections. Over recent decades, consistent research on the development of innovative food packaging materials has been carried out aiming to combat pathogens, to reduce spoilage and waste. Despite efforts and improvements in the food production industry, foodborne pathogens still cause a number of illness outbreaks yearly all over the world. Therefore, this communication will present some results regarding advancements in development of antimicrobial polymeric materials using surface-modification and emulsion-stabilization approaches. Two polymeric substrates, one biodegradable (polylactic acid, PLA) and one non-biodegradable (polyethylene, PE), surface functionalized by cold plasma and γ-iradiation have been modified with different bioactive compounds (antimicrobial/antioxidant) in order to obtain bioactive food packaging materials. Surface immobilization of the bioactive layers was achieved by a wet-treatment involving carbodiimide chemistry. As bioactive agents various essential and vegetal oils were incorporated into a biopolymer matrix (chitosan). The resulted materials were physico-chemical characterized in order to evaluate the molecular interactions between natural bioactive compounds and polymeric matrix, the stability of the immobilized surface layer, their morphology and barrier properties. Antimicrobial and antioxidant activities were also evaluated. Moreover, the surface functionalized polymeric substrates were tested as potential packaging materials for meat and cheese preservation. The obtained materials have demonstrated improved barrier properties, good antioxidant and antimicrobial properties, and they prolong shelf-life of the tested food.

Acknowledgments: The financial support of this work was supported by a grant of the Romanian Ministry of Education and Research, CNCS - UEFISCDI, project number PN-III-P1-1.1-PD-2019-1101, number PD 31/2020, within PNCDI III, and European Social Fund for Regional Development, Competitiveness Operational Programme Axis 1 – Project “Petru Poni Institute of Macromolecular Chemistry - Interdisciplinary Pol for Smart Specialization through Research and Innovation and Technology Transfer in Bio(nano)polymeric Materials and (Eco)Technology", InoMatPol (ID P_36_570, Contract 142/10.10.2016, cod MySMIS: 107464).

Polylactic acid (PLA) belongs to the few thermoplastic polymers that are derived from renewable resources such as corn starch or sugar cane. PLA is often used in 3D printing by fused deposition modelling (FDM) since it is relatively easy to print, does not show warping and can be printed without a closed building chamber. On the other hand, PLA has interesting mechanical properties which are influenced by the printing parameters and geometries. Here we present shape-memory properties of PLA cubes with different infill patterns and percentages. We investigate the material response under defined quasi-static load and varying temperature as well as the possibility to restore the original 3D printed shape. The quasi-static flexural properties are linked to the porosity and the infill structure of the samples under investigation, examined optically and by simulations. Our results underline the importance of designing the infill patterns carefully to develop samples with desired mechanical properties.

Membranes were used in many aqueous applications, including in food processing, e.g. clarification of fruit juices. Typical drawbacks of membrane processes are membrane fouling which promotes deterioration of process products. During application of membranes for fruit juice clarification, biofouling occured as the process deals with food subtances. Biofouling is commonly dominated by bacterial attachment and growth on membrane surface, following the deposition of organic molecules from food substances. Natural antibiotics such as Olea europaea leaves extract might be used to improve the antibiofouling properties of membranes due to its phenolic contents. In this work, Olea europaea substances were obtained by extraction to get the green active solid nanoparticles. Phenolic green nanoparticles then impregnated into cellulose acetate polymer to form mixed matrix membranes with higher and safe (foodgrade) antibiofouling properties. The anti-bioulant effect has been proven by decreasing bacterial attachment down to 23% from initial condition, especially for Gram-negative bacteria such as Eschericia coli.

The recently approved restriction on diisocyanates highlights the health and safety issues concerning polyurethane manufacturing and the relevance of developing sustainable insulating polymeric foams. This is particularly challenging for applications where the foam is subjected to high temperatures (>80°C) and bear loads, such as insulating and bonding material for district heating pipes.

As part of a PhD project concerning pre-insulated district heating pipes for the circular economy, polybutylene (PB-1) has been identified as a promising candidate for the application, due to its low thermal conductivity, high temperature mechanical properties retention, excellent environmental stress cracking resistance (ESCR) and outstanding creep resistance. It is a recyclable thermoplastic and of non-toxic nature, pre-requisites for circular product development. On the contrary to other polyolefins, PB-1 is reported to strain-harden and has high melt strength, required properties for foaming. The purpose of the study is to assess the foamability of PB-1 through extrusion foaming experiments.

A twin-screw extruder was used with varying concentrations of a chemical blowing agent. The obtained samples have been characterised for density, expansion ratio and microstructure. Foams with a volume expansion ratio of 1,8 were achieved. The results confirm the foamability of this polymer. The increase of the die pressure and its contribution to strain hardening were identified as key parameters for successful foaming. Further research will include improving the expansion ratio with a physical blowing agent and mechanical characterization of the foam.

The determination of mechanical properties of materials provides the basis for the fundamental understanding of the behaviour of components that can experience degradation in operation and/or even during storage. A very representative example of this is the thermal aging mechanism that severely affects materials that are ultimately intended to operate in a harsh operating environment as that of a nuclear reactor.

Polymers, and especially elastomers, play a key role as part of the many mechanical, electrical and electronic components found in nuclear power generation plants. The degradation of polymeric materials is a frequent phenomenon that is accelerated, in many cases, by arduous operating conditions. Elastomers, especially rubbers - such as acrylonitrile butadiene, NBR - experience degradation that is favoured by contact with oxygen [1]. This type of reaction -which triggers the irreversible damage of the component- is favoured by an increase in the operating temperature. Therefore, it is of interest to analyse how their intrinsic properties influence their thermal aging.

One of most usual parts with relevant safety-related function in nuclear equipment is the NBR O-rings or gaskets that are used as mechanical sealing elements, since their safety function is being capable of preventing any leakage (whether internal or external) throughout the useful life of the equipment [2].

The objective of this work is the development of a methodology to determine the useful life -based on the storage temperature- of NBR O-rings using a reliability-based approach that allows to obtain the health condition at different supposed storage scenarios, considering the required in-service performance.

For the study, NBR has been selected as a gasket material, since a previous work has shown that acrylonitrile is the best option [3] to withstand moderate levels of radiation thresholds extracted from databases [4-5] as well as its recyclability providing a sustainable life cycle. The evaluated parameter has been the Shore A hardness in accordance with ISO 868 [6] during a period of five years (between 2014 and 2019). Thus, the thermal embrittlement is quantified based on an adaptation of Arrhenius model-based correlation between hardness and temperature and storage time. The study incorporates a comparison between the results obtained for newly manufactured and existing O-rings in the warehouse, considering several statistical scenarios.

REFERENCES

1. Azura A., Thomas A (2006): “Effect of heat ageing on crosslinking scission and mechanical properties. elastomer and components. service life prediction–progress and challenges”. In Coveney, V. (Ed.). Elastomer and components: Service life prediction - progress and challenges, 27–38, Cambridge: Woodhead Publishing.
   Available from: https://www.researchgate.net/publication/281852920_Effect_of_Curing_Systems_on_Thermal_Degradation_Behavior_ofNatural_Rubber_SMR_CV_60 [accessed Sep 08 2020].
2. EPRI CGI-OR02 (1992): “Commercial grade item evaluation for national O-Rings”. Electrical Power Research Institute, Palo Alto-CA (USA).
3. Rodríguez-Prieto A., Camacho A.M., Sebastián M.A., Yanguas-Gil A. (2019): “Analysis of mechanical and thermal properties of elastomers for manufacturing of components in the nuclear industry”. Procedia Manufacturing 41, 177–184.
4. IAEA-TECDOC-1551 (2007): “Implementation strategies and tools for condition based on maintenance at nuclear power plants”. International Atomic Energy Agency, Vienna, Austria.
5. Van de Voorde M.H., Restat C. (1972): “Selection guide to organic materials for nuclear engineering”. European Organization for Nuclear research, CERN, Geneva, Switzerland.
6. ISO 868 (2003): “Plastics and ebonite — Determination of indentation hardness by means of a durometer (Shore hardness)”. International Standardization Organization (ISO), Geneva, Switzerland.

This paper provides an overview of the recent progress in research and development dealing with polymers derived from plant oils. It highlights the widening interest in novel approaches to the synthesis, characterization and properties of these materials from renewable resources and emphasizes their growing impact in sustainable macromolecular science and technology. The monomers used include unmodified triglycerides, their fatty acids or the corresponding esters, and chemically modified triglycerides and fatty acid esters. Comonomers include styrene, divinylbenzene, acrylics, furan derivatives, epoxides, etc. Blends and composites are also discussed. The synthetic pathways adopted for the preparation of these materials are very varied, going from traditional free radical and cationic polymerizations to polycondensation reactions, as well as metatheses and Diels-Alder syntheses.

In addition to this general appraisal, the specific topic of the use of tung oil as a source of original polymers, copolymers and nanocomposites is discussed in greater details in terms of mechanisms, structures, properties and possible applications.

This study reveals the ability of an eco-friendly luminescent xerogel prepared by chitosan crosslinking with a phenothiazine chromophore to detect and remove heavy metals. Its ability to give a different morphological and optical response towards fifteen environmental relevant metals was investigated by naked eye and UV lamp, fluorescence spectroscopy and scanning electron microscopy. A particular response was observed for mercury, consisting in the transformation of the xerogel into a rubber-like material accompanied by the red shifting of the color of emitted light from yellow-green to greenish-yellow domain. The peculiarities of the metals anchoring into the xerogel were analyzed by FTIR spectroscopy and X-ray diffraction. The morphological changes and the metal uptake were analyzed by SEM-EDAX, swelling and gravimetric methods. It was concluded that mercury has a bigger affinity towards this heteroatoms rich system, leading to a secondary crosslinking, generating a great absorption capacity of 1673 mg/g and a specific morphological response for mercury ion concentrations up to 0.001 ppm.

Nowadays, modern societies are striving to adopt a more environmental-friendly lifestyle. In this context, the conversion of biomass to value-added products has attracted a lot of interest both from academia and industry, and replacing monomers based on fossil resources by bio-based monomers is one of the key issues in polymer science. Lignin, among others, is a renewable feedstock, that can be used for the production of monomers for the preparation of bio-based polymers [1]. An interesting alternative bio-based building block which can be produced from lignin is vanillic acid or 4-hydroxy-3-methoxybenzoic acid [2]. In the present communication, our recent work on the synthesis of vanillic polyesters and their copolymers with poly(ethylene furanoate) will be presented [3]. Vanillic acid has been derivatized via a Williamson reaction to afford ω-hydroxyalkylene vanillic acids which were further polymerized. The thermal properties and crystallization behavior of the obtained polymers has been studied with differential scanning calorimetry, polarizing light microscopy and X-ray diffractometry. New insights, such as the enthalpy and entropy of fusion of 100% crystalline polyesters and the equilibrium melting temperature, will be presented. Additionally, the thermal stability of these polyesters has been measured by thermogravimetric analysis and the thermal decomposition mechanism has been studied by pyrolysis-gas chromatography/mass spectroscopy. Finally, the synthesis and characterization of novel poly(ethylene vanillate)-poly(ethylene furanoate) copolymers will be presented.

[1] Hillmyer, M.A. The promise of plastics from plants. Science 2017, 358, 868

[2] Fache, M.; Darroman, E.; Besse, V.; Auvergne, R.; Caillol, S.; Boutevin, B. Vanillin, a promising biobased building-block for monomer synthesis. Green Chem. 2014, 16, 1987

[3] Zamboulis, A.; Papadopoulos, L.; Terzopoulou, Z.; Bikiaris, D.N.; Patsiaoura, D.; Chrissafis, K.; Gazzano, M.; Lotti, N.; Papageorgiou, G.Z. Synthesis, Thermal Properties and Decomposition Mechanism of Poly(Ethylene Vanillate) Polyester, Polymers 2019, 11, 1672