Castor oil derived poly(urethane urea) networks with reprocessibility and enhanced mechanical properties

Eco-Friendly Castor Oil-Based Composite with High Clam Shell Powder Content

Eco-friendly castor oil-based composites with a high content of clam shell powder were prepared in this study. Biomass composites were prepared by blending castor-oil-based polyurethane prepolymer (COPU) with a filler consisting of high-content clam shell powder (CSP), named CSP-COPU. The structure, microstructure, mechanical properties, and thermal stability of the composites were investigated. The results showed that even at a loading as high as 75 wt.% of the CSP filler, the composite still exhibited good tensile strength and elongation at break. Furthermore, compared with the CSP-COPU composites, TCOS-50 synthesized through blending OH-terminated castor oil-based polyurethane prepolymer (TCOPU) and CSP filler proved that the chemical bond between COPU containing terminal -NCO groups and CSP containing active -OH groups was the key reason to obtaining the composite material with desirable properties. These findings provide prospects for applying biomass-loaded CSP-COPU composites in the packaging industry while contributing to carbon peak achievement and carbon neutrality.

Intrinsic Permanent Shape Reconfigurable Semicrystalline Biopolyester Thermoset

Catalyst-free, volatile organic solvent (VOC)-free synthesis of biobased cross-linked polymers is an important sustainable feature in polyesterification. To date, these polyesters have been extensively studied for their fundamental sustainability across various uses. The ultimate potential sustainability for these materials, however, is constrained to static structural parts due to their intractable rigid three-dimensional (3D) network. Here, we reveal intrinsic dynamic exchangeable bonds within this type of cross-linked semicrystalline network, poly(1,8-octanediol-co-1,12-docanedioate-co-citrate) (PODDC), enabling permanent shape reconfigurability. Annealing at slightly above melting-transition temperature (Tm) allows for shape reconfigurability up to nine times, comparable in performance to the existing bond-exchange systems. No reagents are involved from synthesis to shape reconfiguration, suggesting an exciting feature exhibited by this sustainable cross-linked material without the need for further chemical modification. We further extend this benefit of reconfigurability to enable flexible shape design in a smart shape-memory polymer (SMP), showing it as one of its potential applications. After its applications, it can undergo hydrolytic degradation. We envision that such multifaceted sustainability for the material will attract interest in environmentally friendly applications such as fabricating external part of soft robots and shape-morphing devices with reduced environmental impact.

Supramolecular Polyurethane "Ligaments" Enabling Room-Temperature Self-Healing Flexible Perovskite Solar Cells and Mini-Modules

Flexible perovskite solar cells (F-PSCs) have emerged as promising alternatives to conventional silicon solar cells for applications in portable and wearable electronics. However, the mechanical stability of inherently brittle perovskite, due to residual lattice stress and ductile fracture formation, poses significant challenges to the long-term photovoltaic performance and device lifetime. In this paper, to address this issue, a dynamic "ligament" composed of supramolecular poly(dimethylsiloxane) polyurethane (DSSP-PPU) is introduced into the grain boundaries of the PSCs, facilitating the release of residual stress and softening of the grain boundaries. Remarkably, this dynamic "ligament" exhibits excellent self-healing properties and enables the healing of cracks in perovskite films at room temperature. The obtained PSCs have achieved power conversion efficiencies of 23.73% and 22.24% for rigid substrates and flexible substrates, respectively, also 17.32% for flexible mini-modules. Notably, the F-PSCs retain nearly 80% of their initial efficiency even after subjecting the F-PSCs to 8000 bending cycles (r = 2 mm), which can further recover to almost 90% of the initial efficiency through the self-healing process. This remarkable improvement in device stability and longevity holds great promise for extending the overall lifetime of F-PSCs.

Scalable Production of Self-Toughening Plant Oil-Based Polyurethane Elastomers with Multistimuli-Responsive Functionalities

Plant oils are becoming of high industrial importance due to the persisting challenges befalling with the utilization of fossil fuels. Thus, developing methodologies to produce multifunctional materials by taking advantage of the unique structure of plant oil is highly desired. In this study, castor oil served as a cross-linker and soft segments, by incorporating scalable rhodamine 6G derivatives, to systematically synthesize a series of smart polymers that possess self-toughening and multistimuli-responsive capabilities. The polyurethane elastomers showed 10 times and 60 times increases in tensile strength and toughness, respectively, in comparison with the unmodified polyurethane due to the existence of large amounts of hydrogen bonding, dynamic C-N spiro bonds, rigid benzene ring, and high cross-link densities. The novel polyurethane elastomers exhibited excellent reversible multichromic behaviors in response to light, pH, and mechanics. Notably, the resulting polyurethane elastomers exhibited ultrasensitive sustained photochromism with tunable white emission and rapid reversibility. This study provides a simple and effective strategy to utilize plant oil for multifunctional material preparation and paves the way to open access for application of plant oil-based products in a variety of industry applications, such as sensors, self-fitting tissue scaffolds, and switchable devices.

Vitrimeric Polylactide by Two-step Alcoholysis and Transesterification during Reactive Processing for Enhanced Melt Strength

Because of its rather low melt strength, polylactide (PLA) has yet to fulfill its promise as advanced biobased and biodegradable foams to replace fossil-based polymer foams. In this work, PLA vitrimers were prepared by two-step reactive processing from commercial PLA thermoplastics, glycerol, and diphenylmethane diisocyanate (MDI) using Zn(II)-catalyzed addition and transesterification chemistry. The transesterification reaction of PLA and glycerol occurs with zinc acetate as the catalyst, and chain scission will take place due to the alcoholysis of the PLA chains by the free hydroxyl groups from the glycerol. Long-chain PLA with hydroxyl groups can be obtained and then cross-linked with MDI. Rheological analysis shows that the formed cross-linked network can significantly improve melt strength and promote strain hardening under extensional flow. PLA vitrimers still maintain the ability of thermoplastic processing via extrusion and compression. The enhanced melt strength and the rearrangement of network topology facilitate the foaming processing. An expansion ratio as large as 49.2-fold and microcellular foam with a uniform cell morphology can be obtained for PLA vitrimers with a gel fraction of 51.8% through a supercritical carbon dioxide foaming technique. This work provides a new way with the scale-up possibility to enhance the melt strength of PLA, and the broadened range of PLA applicability brought by PLA vitrimers is truly valuable in terms of the realization of a sustainable society.

Kinetical Study, Thermo-Mechanical Characteristics and Recyclability of Epoxidized Camelina Oil Cured with Antagonist Structure (Aliphatic/Aromatic) or Functionality (Acid/Amine) Hardeners

In an attempt to prepare sustainable epoxy thermosets, this study introduces for the first time the idea to use antagonist structures (aromatic/aliphatic) or functionalities (acid/amine) as hardeners to produce reprocessable resins based on epoxidized camelina oil (ECMO). Two kinds of mixtures were tested: one combines aromatic/aliphatic dicarboxylic acids: 2,2'-dithiodibenzoic acid (DTBA) and 3,3'-dithiodipropionic acid (DTDA); another is the combination of two aromatic structures with acid/amine functionality: DTBA and 4-aminophenyl disulfide (4-AFD). DSC and FT-IR analyses were used as methods to analyze the curing reaction of ECMO with the hardeners. It was found that the thermosets obtained with the dual crosslinked mechanism needed reduced curing temperatures and reprocessing protocols compared to the individual crosslinked thermosets. Thanks to the contribution of disulfide bonds in the network topology, the obtained thermosets showed recycling ability. The final thermomechanical properties of the virgin and mechanical reprocessed materials were analyzed by DMA and TGA. The obtained thermosets range from elastomeric to rigid materials. As an example, the ECMO/DTBA704-AFD30 virgin or reprocessed thermosets have tan δ values reaching 82-83 °C. The study also investigates the chemical recycling and the solvent resistance of these vitrimer-like materials.

High concentration acid-induced discoloration polymeric dyes fabricated with UV-curable azobenzene-lignin-based waterborne polyurethane

A durable and reversible acid-induced discoloration azobenzene UV-curable lignin-based waterborne polyurethane polymeric dye (EDA-ULPD) is prepared from lignin, azobenzene and pentaerythritol triacrylate(PETA) by chemical modification of waterborne polyurethane. Lignin and PETA are chemically bonded to the polyurethane chain to improve thermal stability, UV resistance and color fastness, while also endow the polymeric dye with UV curing performance, which is a green and environmentally friendly fixing way. The acid-induced discoloration property of EDA-ULPD with azobenzene chromophore side chain is comparable to those of 4-ethyl-4-2,2'-dihydroxy diethylamine azobenzene (EDA). As the pH value decreases from 7 to 1, the maximum absorption peak of EDA-ULPD from 420 nm to 530 nm, and the color change from yellow to pink due to the transformation of EDA molecular structure from diazo to hydrazone. Interestingly, when EDA-ULPD is fixed to the fabric in the way of UV curing, its printed fabric exhibits the performance of high concentration acid-induced discoloration (1 mol·L^-1 HCl) due to the cross-linked structure formed by EDA-ULPD. The acid-induced discoloration property of EDA-ULPD printed fabrics also presents outstanding repetitious stability. The stimulus response printed fabric with reversible high concentration acid discoloration possesses a broad application prospect in smart textiles.

Biodegradable Polyurethanes Based on Castor Oil and Poly (3-hydroxybutyrate)

Biodegradable polyurethanes (PUs) were produced from castor oil (CO) and poly (3-hydroxybutyrate) diol (PHBD) using hexamethylene diisocyanate as a crosslinking agent. PHBDs of different molecular weights were synthesized through transesterification of bacterial PHB and ethylene glycol by changing the reaction time. The synthesized PHBDs were characterized in terms of Fourier transform infrared and proton nuclear magnetic resonance spectroscopy. A series of PUs at different NCO/OH and CO/PHBD ratios were prepared. The resulting CO/PHBD-based PUs were then characterized in terms of mechanical and thermal properties. Increasing PHBD content significantly increased the tensile strength of CO/PHBD-based PUs by 300% compared to neat CO-based PU. CO/PHBD-based PUs synthetized from short chain PHBD exhibited higher tensile strength compared to those produced from long chain PHBD. As revealed by scanning electron microscopy analysis, such improvement in stiffness of the resulting PUs is due to the good compatibility between CO and PHBD. Increasing PHBD content also increased the crystallinity of the resulting PUs. In addition, higher degradation rates were obtained for CO/PHBD-based PUs synthetized from long chain PHBD compared to neat CO PU and PUs produced from short chain PHBD.

Long-chain polyamide covalent adaptable networks based on renewable ethylene brassylate and disulfide exchange

Long-chain polyamide covalent adaptable networks with high strength and short relaxation times were prepared based on a renewable ethylene brassylate and disulfide exchange.

Polymers and Composites Derived from Castor Oil as Sustainable Materials and Degradable Biomaterials: Current Status and Emerging Trends

Recent years have seen rapid growth in utilizing vegetable oils to derive a wide variety of polymers to replace petroleum-based polymers for minimizing environmental impact. Nonedible castor oil (CO) can be extracted from castor plants that grow easily, even in an arid land. CO is a promising source for developing several polymers such as polyurethanes, polyesters, polyamides, and epoxy-polymers. Several synthesis routes have been developed, and distinct properties of polymers have been studied for industrial applications. Furthermore, fillers and fibers, including nanomaterials, have been incorporated in these polymers for enhancing their physical, thermal, and mechanical properties. This review highlights the development of CO-based polymers and their composites with attractive properties for industrial and biomedical applications. Recent advancements in CO-based polymers and their composites are presented along with a discussion on future opportunities for further developments in diverse applications.

Recyclable, Repairable, and Reshapable (3R) Thermoset Materials with Shape Memory Properties from Bio-Based Epoxidized Vegetable Oils

The preparation of thermosets based on epoxidized vegetable oils (EVOs) involved a peculiar attention in recent years; however, most of them cannot be recycled once cross-linked. In the present work, epoxy thermosetting resins like-vitrimers with dynamic disulfide covalent bonds were prepared by copolymerizing twelve EVOs with 2,2'-dithiodibenzoic acid, as hardener. Here, we show for the first time the reprocessability, repairability, and recyclability properties of EVOs thermosets. The 3R abilities were evaluated in correlation with the EVO epoxy contents, which influence the final thermo-mechanical properties of the recycled material. The virgin versus recycled materials' comparison was studied by FT-IR, DSC, TGA, and DMA, also comparing their swelling ability and high gel content. The study investigates, in addition, the excellent shape memory properties of the reprocessed EVOs/disulfide materials.

Sustainable Series of New Epoxidized Vegetable Oil-Based Thermosets with Chemical Recycling Properties

This work reports for the first time the copolymerization studies of 11 newly synthesized epoxidized vegetable oils (EVOs) that reacted with a disulfide-based aromatic dicarboxylic acid (DCA) to produce thermoset materials with recyclability properties. These new EVOs' reactivity and properties were compared with those of the two commercial references: epoxidized linseed oil (ELO) and epoxidized soybean oil (ESO). The structure-reactivity correlation is proposed by differential scanning calorimetry (DSC) analysis, corroborating the epoxy content of EVO monomers, the initiator effect, the copolymerization reaction enthalpy, and the temperature range. The thermomechanical properties of the obtained thermosets were evaluated and discussed in correlation with the structure and reactivity of monomers by dynamic mechanical analysis (DMA), tensile testing, and thermogravimetric analysis (TGA). It has been found that the higher the EVO functionality, the higher is the reactivity, cross-linking density, and final performances, with tan δ values ranging from 34 to 111 °C. This study investigates the chemical recycling and the solvent resistance of these vitrimer-like materials that have a high bio-based carbon content, from 58 to 79%, with potential application in coating or composite materials in the automotive sector.

Synthesis and Properties of Novel Polyurethanes Containing Long-Segment Fluorinated Chain Extenders

In this study, novel biodegradable long-segment fluorine-containing polyurethane (PU) was synthesized using 4,4′-diphenylmethane diisocyanate (MDI) and 1H,1H,10H,10H-perfluor-1,10-decanediol (PFD) as hard segment, and polycaprolactone diol (PCL) as a biodegradable soft segment. Nuclear magnetic resonance (NMR) was used to perform ¹H NMR, ¹⁹F NMR, ¹⁹F–¹⁹F COSY, ¹H–¹⁹F COSY, and HMBC analyses on the PFD/PU structures. The results, together with those from Fourier transform infrared spectroscopy (FTIR), verified that the PFD/PUs had been successfully synthesized. Additionally, the soft segment and PFD were changed, after which FTIR and XPS peak-differentiation-imitating analyses were employed to examine the relationship of the hydrogen bonding reaction between the PFD chain extender and PU. Subsequently, atomic force microscopy was used to investigate the changes in the microphase structure between the PFD chain extender and PU, after which the effects of the thermal properties between them were investigated through thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. Finally, the effects of the PFD chain extender on the mechanical properties of the PU were investigated through a tensile strength test.

Reinforcement of Castor Oil-Based Polyurethane with Surface Modification of Attapulgite

Polyurethane/attapulgite (PU/ATT) nanocomposites derived from castor oil were prepared by incorporation of 8 wt % ATT, acid-treated ATT, and KH560-treated ATT. The effects of three ATTs (ATT, acid-ATT, and KH560-ATT) on the comprehensive properties of PU/ATT nanocomposites were systematically investigated. The results showed that the incorporation of 8 wt % of three ATTs could produce an obvious reinforcement on the castor oil-based PU and that the silane modification treatment, rather than the acid treatment, has the more effective reinforcement effect. SEM images revealed the uniform dispersion of ATT in the PU matrix. DMA confirmed that the storage modulus and glass transition temperature (Tg) of PU/ATT nanocomposites were significantly increased after blending with different ATTs. For PU/KH560-ATT8 nanocomposites, the thermal stability of the PU was obviously enhanced by the addition of KH560-ATT. In particular, 8 wt % KH560-ATT loaded castor oil-based PU nanocomposites exhibit an obvious improvement in tensile strength (255%), Young's modulus (200%), Tg (5.1 °C), the storage modulus at 25 °C (104%), and the initial decomposition temperature (7.7 °C). The prepared bio-based PU materials could be a potential candidate to replace petroleum-based PU products in practical applications.

Sorbitol as a Chain Extender of Polyurethane Prepolymers to Prepare Self-Healable and Robust Polyhydroxyurethane Elastomers

A self-healable polyhydroxyurethane (S-PU) was synthesized from sorbitol, a biomass of polyhydric alcohol, by a simple process that is suitable for practical applications. In the synthesis, only two primary hydroxyl groups of sorbitol were considered for the chain extension of the polyurethane (PU) prepolymers to introduce free hydroxyl groups in PU. As a control, conventional PU was synthesized by hexane diol mediated chain extension. Relative to the control, S-PU showed excellent intrinsic self-healing property via exchange reaction, which was facilitated by the nucleophilic addition of the secondary hydroxyl groups without any catalytic assistance and improved tensile strength due to the enhanced hydrogen bonding. We also investigated the effect of the exchange reaction on the topological, mechanical, and rheological properties of S-PU. The suggested synthetic framework for S-PU is a promising alternative to the conventional poly hydroxyurethane, in which cyclic carbonates are frequently reacted with amines. As such, it is a facile and environmentally friendly material for use in coatings, adhesives, and elastomers.