Linseed Oil‐Based Thermosets by Aza‐Michael Polymerization

Exploring strategies for valorizing wood processing waste: advancing sustainable, fully lignocellulosic biocomposites

This study presents the design and synthesis of bio-composites exhibiting high properties, wherein both the matrix and filler originate from wood biomass. Notably, no additional hardener compounds or treatments/modifications of the lignocellulosic filler were employed. Thermosetting materials were developed by homopolymerizing a bio-based aromatic epoxy monomer, the resorcinol diglycidyl ether (RDGE), with different percentages, from 1 wt% to 30 wt% of natural wood processing side-product, such as spruce bark powder (SB), which was used as such without additional treatments and modifications. The DSC analyses revealed enhanced reactivities with the bio-filler content, resulting in a reduced reaction temperature range and maximum reaction temperature. These findings provide evidence of the chemical interaction between the functional groups from spruce bark and the epoxides groups. The obtained fully based lignocellulosic materials show high E' values from 2.4 GPa to 2.5-3.5 GPa (glassy state) and from 64 MPa to 99-156 MPa in the rubbery region. The damping factor of the bio-composites with 1-10 wt% SB have shown an increase of the α transition temperature from 92 °C to 94-97 °C. The excellent filler/matrix interface and optimal adhesion between them were confirmed by SEM analysis.

Polymers without Petrochemicals: Sustainable Routes to Conventional Monomers

Access to a wide range of plastic materials has been rationalized by the increased demand from growing populations and the development of high-throughput production systems. Plastic materials at low costs with reliable properties have been utilized in many everyday products. Multibillion-dollar companies are established around these plastic materials, and each polymer takes years to optimize, secure intellectual property, comply with the regulatory bodies such as the Registration, Evaluation, Authorisation and Restriction of Chemicals and the Environmental Protection Agency and develop consumer confidence. Therefore, developing a fully sustainable new plastic material with even a slightly different chemical structure is a costly and long process. Hence, the production of the common plastic materials with exactly the same chemical structures that does not require any new registration processes better reflects the reality of how to address the critical future of sustainable plastics. In this review, we have highlighted the very recent examples on the synthesis of common monomers using chemicals from sustainable feedstocks that can be used as a like-for-like substitute to prepare conventional petrochemical-free thermoplastics.

Thia-Michael Reaction: The Route to Promising Covalent Adaptable Networks

While the Michael addition has been employed for more than 130 years for the synthesis of a vast diversity of compounds, the reversibility of this reaction when heteronucleophiles are involved has been generally less considered. First applied to medicinal chemistry, the reversible character of the hetero-Michael reactions has recently been explored for the synthesis of Covalent Adaptable Networks (CANs), in particular the thia-Michael reaction and more recently the aza-Michael reaction. In these cross-linked networks, exchange reactions take place between two Michael adducts by successive dissociation and association steps. In order to understand and precisely control the exchange in these CANs, it is necessary to get an insight into the critical parameters influencing the Michael addition and the dissociation rates of Michael adducts by reconsidering previous studies on these matters. This review presents the progress in the understanding of the thia-Michael reaction over the years as well as the latest developments and plausible future directions to prepare CANs based on this reaction. The potential of aza-Michael reaction for CANs application is highlighted in a specific section with comparison with thia-Michael-based CANs.

Styrene-Free Bio-Based Thermosetting Resins with Tunable Properties Starting from Vegetable Oils and Terpenes

The substitution of fossil-based monomers in the thermosetting formulations is a fundamental issue to face the environmental concerns related to the use of traditional resins. In this paper, styrene-free thermosetting resins were prepared to start from vegetable oils with different compositions and unsaturation degrees, namely soybean, hempseed, and linseed oils. Using terpenic comonomers such as limonene and β-myrcene allows one to prepare thermosets avoiding the traditional fossil-based diluents such as styrene, thus obtaining an outstanding gain in terms of both environmental and safety concerns. Furthermore, the materials obtained reveal tunable physical properties upon the proper choice of the monomers, with glass transition temperature ranging from 40 to 80 °C and Young's modulus ranging from 200 to 1800 MPa. The possibility of preparing composite materials starting from the resins prepared in this way and natural fibres has also been explored due to the potential applications of bio-based composites in several industrial sectors.

Exploring New Horizons for Bio-Based Poly(furfuryl alcohol) by Exploiting Functionalities Offered by Side Reactions

Poly(furfuryl alcohol) is a bio-based thermoset resin with a limited application portfolio due to its brittleness. Side ring-opening reactions that occur during polymerization lead to carbonyl moieties. Such unique self-generated functionality was exploited to generate tough and ductile materials via the creation of Schiff-based macromolecular architectures.

Vegetable Oil-Based Resins Reinforced with Spruce Bark Powder and with Its Hydrochar Lignocellulosic Biomass

A bio-based polymeric matrix was developed by the copolymerization of a vegetable oil-based epoxy, epoxidized linseed oil (ELO), with dodecenyl succinic anhydride (DDSA). To obtain eco-friendly bio-composites, this matrix was combined with a natural filler: spruce bark powder (SB) with its hydrochar (HC) in various proportions ranged from 1 to 30 wt.%. The reactivities of these formulations were studied by DSC analysis that highlighted that both fillers have a high catalytic effect on the ELO–DDSA crosslinking reaction. The complementary studies by TGA, DMA, tensile tests, water absorption and Shore tests had shown that both HC and SB bring improvements to the mechanical properties of the composites, fulfilling multiple roles: (i) Both act as co-reactants in the copolymerization mechanism; (ii) HC acts as reinforcement, consolidating the network and providing stiffness and rigidity; and (iii) SB acts as plasticizer for reducing the brittle character of the epoxy resins.

The Prospering of Macromolecular Materials Based on Plant Oils within the Blooming Field of Polymers from Renewable Resources

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 on 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. 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 (nano)composites is discussed in greater detail in terms of mechanisms, structures, properties, and possible applications.