Perspective on the Development of Monomer Recovery Technologies from Plastics Designed to Last.

Thermoset polymers are commonly used as the matrix material in fiber-reinforced polymer composites (FRPCs) due to their good mechanical properties, chemical stabilities, and ease of manufacturing. Conventional curing of thermosets and their composites requires heating the matrix monomers at elevated temperatures during long cure cycles for producing fully crosslinked polymers, resulting in high manufacturing cost in terms of time, energy, and capital investment. Frontal polymerization (FP) is a promising approach for rapid, energy-efficient fabrication of high-performance thermosets and FRPCs. In FP, a thermal stimulus (trigger) causes a self-propagating exothermic reaction wave that transforms liquid monomers to fully cured polymers, eliminating the need for external energy input by large ovens or autoclaves. We have used the FP of dicyclopentadiene (DCPD) to successfully fabricate thermoset polymers and composite parts. In this novel curing strategy, the final degree-of-cure of the polymer, and thereby its mechanical performance, is governed by the heat transfer phenomenon that occur at the polymerization front. During the fabrication of FRPCs some fraction of the generated heat is absorbed by continuous fibers or lost through the tooling. In this work, we will discuss the characterization of the thermo-mechanical properties of DCPD polymer manufactured by FP curing.

Unique Ligand Exchange Dynamics of Metal–Organic Polyhedra for Vitrimer-like Gas Separation Membranes

With the development of human society, technology and medicine have been widely discovered. Bisphenol A (BPA) is a kind of substance widely used in industrial production, mainly used in the production of polycarbonate, epoxy resin and other polymer materials. Many analogues of BPA like BPS, BPF and BPAF have been used as substitutes for BPA. However, BPA and its analogues exposure in daily life has been found to be harmful to people's health. In this paper, the toxicity of BPA and its analogues in the environment exposed with different concentrations, exposure time, ages, genders has been discussed. In addition, the effects of BPA and its analogues on biological endocrine system, immune system, reproductive system and nervous system have been introduced by studying the endocrine organs of animal models. Results reveal that DNA can be severely damaged at certain BPA concentration, and that BPA may act directly on the ovary due to its similar structure to secreted estrogen Besides, BPA exerts a bi-directional regulatory effect on the mouse immune system, and when exposed to BPA for a long time, activity of immune system can be suppressed. Researches on BPA and its analogues’ effects on organs and systems can give some suggestion on the use as materials for the production.

Theory of phantom networks - topology, structure, elasticity: New and open problems.- Structural properties of randomly crosslinked polymer networks.- The dynamics of tire tread compounds and their relationship to wek skid behavior.- Relaxation in permanent networks.- Do local motions influence rheological properties near the gelation threshold?.- On the dynamics of moderately and lightly crosslinked polymer networks.- A new approach to polymer networks including finite chain extensibility, topological constraints, and constraints of overall orientation.- Formation of networks - a lattice model for kinetic growth processes.- Gelation and 1,1-transition in three-dimensional condensation and chain polymerization.- Effect of thermal history on amylose gelation.- Rheological, potentiometric and 23Na NMR studies on pectin-calcium systems.- The formation of semiinterpenetrating polymer networks by photoinduced polymerization.- Observation of the curing process of epoxy resins by inverse gas chromatography.- Fluorescence probe studies during the curing of epoxy systems.- Conditions of formation and equilibrium swelling of polymer networks formed by protein macromolecules.- Cross-link fluctuations: NMR properties and rubber elasticity.- Segmental orientation in filled networks.- Field-cycling NMR relation spectroscopy of molten linear and cross-linked polymers Observation of a T 1 ? ?0.25 law for semi-global chain fluctuations.- Segmental orientation of long and short chains in strained bimodal PDMS networks: A 2H-NMR study.- Small chains in a deformed network. A probe of heterogeneous deformation?.- Aggregation of free chains within a deformed network: A SANS study.- Trapped entanglements in polymer networks and their influence on the stress-strain behavior up to large extensions.- Physical and chemical network effects in polyurethane elastomers.- Influence of the thermodynamical quality of the solvent on the properties of polydimethylsiloxane networks in swollen and dry states.- Triblock copolymers, mesogels and deformation behavior in poor solvents.- Microemulsion mediated polymer networks.- Theory of the mechanical and swelling properties of elastomers with chemical and physical networks.- The effect of free branches on the collapse of olyelectrolyte networks.- Local order and statistics of a polymer chain in an external electric field.- Charge photogeneration in carbazole-containing compounds and valency bands of oligomers.- The peculiarities and nature of large-scale motion of highly crosslinked polymers.- FTIR spectroscopy studies on epoxy networks.- Influence of imidazole on the structure of epoxy amine networks.- Epoxy polymer networks: Relaxation processes and crack resistance.- Fluorescence study of interpenetrating network morphology of polymer films.- Kinetic regularities of polymer network thermal degradation.- Interpenetrating polymer networks based on EVA copolymer and PMMA.- Fast segmental dynamics in poly(methyl metharcrylate)-polyurethane interpenetrating networks.- Thermally and mechanically activated degradation of polyesterurethane networks. Analysis of molecular weight distribution functions.- The solidification of bulk and solution cast segmented polyurethanes.

The polymer network structure of epoxy thermosets plays a significant role in its final material properties. However, the effects of mild thermal exposure on these network structures are poorly studied. In this work, wide-angle X-ray scattering was used to investigate the polymer network structure of two epoxy thermosets: homopolymerized bisphenol A (BPA) epoxy resin and BPA epoxy resin cured with a polyether amine hardener (BPA/T-403). Using density functional theory and wide-angle X-ray scattering, insights into the polymer network structure were obtained. Diffraction features were determined to originate from hardener-to-hardener molecular distance, perpendicular π–π stacking of aromatic p-phenylene rings, and the average carbon–carbon distance in the polymer. Thermal exposure was found to permanently alter these structural features for both thermosets, with an increase in the π–π stacking distance. Homopolymerized BPA had an additional decrease in the hardener-to-hardener distance. These structural alterations were found to be detectable using Fourier transform infrared spectroscopy and Raman spectroscopy, with changes in the hardener-to-hardener distance having the largest variations in the resulting spectra specifically at the aromatic and ether frequencies.

In fiber-reinforced composites, the interphase nanostructure (i.e., the extended region between two phases in contact) has a pronounced influence on their interfacial adhesion. This work aims at establishing a link between the interphase design of PS-based polymeric fiber coatings and their influence on the micromechanical performance of epoxy-based composite materials. Thiol-ene photochemistry was utilized to introduce a polymeric gradient on silica-like surfaces following a two-step approach without additional photoinitiator. Two complementary grafting-techniques were adapted to modify glass fibers: "Grafting-onto" deposition of PB-b-PS diblock copolymers for thin-film coatings (thickness<20 nm) at low grafting density (<0.1 chains/nm2)--and "grafting-from" polymerization for brush-like PS homopolymer coatings of higher thickness (up to 225 nm) and higher density. Polymer-coated glass fibers were characterized for polymer content using thermogravimetric analysis (TGA) and their nanostructural morphologies by scanning electron microscopy (SEM). Model substrates of flat glass and silicon were studied by atomic force microscopy (AFM) and spectroscopic ellipsometry (SE). The change in interfacial shear strength (IFSS) due to fiber modification was determined by a single fiber pull-out experiment. Thick coatings (>40 nm) resulted in a 50% decrease in IFSS. Higher shear strength occurred for thinner coatings of homopolymer and for lower grafting densities of copolymer. Increased IFSS (10%) was found upon dilution of the surface chain density by mixing copolymers. We show that the interfacial shear strength can be increased by tailoring of the interphase design, even for systems with inherently poor adhesion. Perspectives of polymeric fiber coatings for tailored matrix-fiber compatibility and interfacial adhesion are discussed.

Epoxy-gold nanoparticle nanocomposites with enhanced thermo-mechanical properties: An integrated modelling and experimental study

Highly efficient recycling of carbon fiber reinforced polymer composites into monomers and fibers is a formidable challenge. Herein, we present a closed-loop recycling approach for carbon fiber reinforced polymer composites using reversible amidation chemistry, which enables the complete recovery of intact carbon fibers and pure monomers. The polymer network, synthesized by amidation between a macromonomer linear polyethyleneimine and a bifunctional maleic anhydride cross-linker, serves as a matrix for the construction of composites with exceptional mechanical properties, thermal stability and solvent resistance. The matrices can be fully depolymerized under the acidic condition at ambient temperature, allowing the effective separation and recovery of both carbon fibers and the two monomers. The reclaimed carbon fibers retain nearly identical mechanical properties to pristine ones, while pure monomers are recycled with high separation yields (>93 %). They can be reused in for multiple cycles for the manufacture of new composites, whose mechanical properties recover over 95 % of their original properties. This line of research presents a promising approach for the design of high-performance and sustainable thermoset composites, offering significant environmental and economic benefits.

Over the past couple of decades, polymers that depolymerize end-to-end upon cleavage of their backbone or activation of a terminal functional group, sometimes referred to as "self-immolative" polymers, have been attracting increasing attention. They are of growing interest in the context of enhancing polymer degradability but also in polymer recycling as they allow monomers to be regenerated in a controlled manner under mild conditions. Furthermore, they are highly promising for applications as smart materials due to their ability to provide an amplified response to a specific signal, as a single sensing event is translated into the generation of many small molecules through a cascade of reactions. From a chemistry perspective, end-to-end depolymerization relies on the principles of self-immolative linkers and polymer ceiling temperature (Tc). In this article, we will introduce the key chemical concepts and foundations of the field and then provide our perspective on recent exciting developments. For example, over the past few years, new depolymerizable backbones, including polyacetals, polydisulfides, polyesters, polythioesters, and polyalkenamers, have been developed, while modern approaches to depolymerize conventional backbones such as polymethacrylates have also been introduced. Progress has also been made on the topological evolution of depolymerizable systems, including the introduction of fully depolymerizable block copolymers, hyperbranched polymers, and polymer networks. Furthermore, precision sequence-defined oligomers have been synthesized and studied for data storage and encryption. Finally, our perspectives on future opportunities and challenges in the field will be discussed.

This paper deals with the effect of clay addition on improving the mechanical properties of epoxy polymer and glass fiber-reinforced epoxy-clay hybrid composites. The clays used in the present system were alkyl ammonium treated montmorillonite (MMT) based organoclay (OC) and unmodified MMT clay (UC). The OC and UC were added individually to epoxy polymer and glass fiber-reinforced epoxy composites. Structure and morphology of epoxy filled with OC and UC were examined by X-ray diffraction (XRD) and transmission electron microscope (TEM) techniques. It is observed that the clay nanolayer dispersion takes place in a polymer matrix filled with OC particles. However, the UC filled composites show the formation of micro-composites. The effects of clay addition (1—3%, 5% and 10% by weight) in epoxy polymer shows that OC filled composites possess enhanced tensile strength over UC filled composites. A similar result is observed in the OC filled glass fiber-reinforced epoxy composites. Dynamic mechanical analysis (DMA) and thermogravimetry analysis (TGA) of hybrids show that the addition of OC increases the thermal properties of epoxy-glass fiber more than that of UC filled hybrids.

To meet the growing demand for bio-based chemicals and improve the profitability and efficiency of the emerging biorefinery industry, lignin is an abundant and attractive feedstock. Spero Renewables has developed a proprietary and patent-pending technology, the Selective Process for Efficient Removal of Lignin and Upgrading (SPERLU). The technology is a catalytic deconstruction and upgrading of lignin in lignocellulosic biomass or commercially available technical lignin to produce multi-functional phenol (MFP) products. The SPERLU process has been demonstrated and vetted on a lab scale to convert commercially available technical lignin to MFPs in yields of 60-90% (based on lignin). The MFP products can be separated and further upgraded through catalytic or biological means. Spero performed a detailed kinetic study of the SPERLU process and used the resulting kinetic data to design and construct a mini-pilot-scale reactor for routine production of hundreds of grams of MFP products. Spero’s lignin-based MFPs have been demonstrated for use as a drop-in replacement for bisphenol A (BPA) in the synthesis of thermoset polymers. Spero’s lignin-based thermoset polymers exhibit excellent mechanical properties and can be used in many applications. Additionally, a collaboration with the National Renewable Energy Lab (NREL) was used to evaluate the feasibility of upgrading SPERLU products through biological means into valuable chemicals. A comprehensive technoeconomic analysis (TEA) and Life-cycle analysis (LCA) have been completed and support the case for commercialization of the SPERLU technology. Through this project Spero has significantly de-risked the SPERLU technology and is actively planning larger scale pilot projects.

Modeling the dissolution of thermosetting polymers and composites via solvent assisted exchange reactions

Closed‐loop recycling of polymers represents the key technology to convert plastic waste in a sustainable fashion. Efficient chemical recycling and upcycling strategies are thus highly sought‐after to establish a circular plastic economy. Here, we present the selective chemical depolymerization of polycarbonate by employing a vanillin derivative as bio‐based feedstock. The resulting di‐vanillin carbonate monomer was used in combination with various amines to construct a library of reprocessable poly(imine‐carbonate)s, which show tailor‐made thermal and mechanical properties. These novel poly(imine‐carbonate)s exhibit excellent recyclability under acidic and energy‐efficient conditions. This allows the recovery of monomers in high yields and purity for immediate reuse, even when mixed with various commodity plastics. This work provides exciting new insights in the design of bio‐based circular polymers produced by upcycling of plastic waste with minimal environmental impact.

Polymers are indispensable to humans in different applications due to their ease of manufacturing and overall performance. However, after a material lifetime, there is a large amount of polymer-based waste, which greatly contributes to the loss of valuable resources and environmental pollution. Thermoplastics may be readily recycled, but because of their flammability, large amounts of flame retardant (FR) additives are required for many applications. This results in a significant volume of FR polymeric wastes too, particularly halogenated plastics, which are subject to severe recycling regulations. In general, thermoplastics containing FRs are raising concerns, as their effective recycling is strongly influenced by the chemical composition, additive content, and physicochemical characteristics of the waste stream. The recycling of FR thermosets is even more challenging due to their crosslinked and cured nature, which makes them resistant to melting and reprocessing. In many cases, traditional mechanical recycling methods, such as grinding and melting, are not applicable to thermosetting polymers. Current recycling methods do not always consider the recovery of the thermosetting/thermoplastic matrix and the presence of toxic FRs in the polymer network. Sorting and solvent washing treatment are important steps, which are usually performed before recycling the FR polymeric waste to reduce contamination in the following steps.Considering all the technical difficulties during recycling, the high cost of sorting and solvent washing, and the increasing demand for more sustainable procedures, the scientific community is fostering the transformation toward more feasible and energy-efficient recycling strategies. Also, many directives are imposing strict disposal and sorting rules, limiting the use of FR halogen-based compounds, and promoting the commercialization of more recyclable polymers. This review aims to provide a general overview of currently applied approaches for recycling FR thermoplastics and thermosets, and possible approaches for designing the next generation of FR polymer-based materials. The existing recycling strategies for FR polymers are summarized. Developments in the manufacturing of covalent adaptable networks as an outlook towards circularity in polymers are also addressed in this review.

As environmental worries over synthetic material consumption have grown, attention has switched to sustainable materials and a circular economy model that incorporates recycling channels. The various latest recycling technologies for composite materials and plastic polymers are compiled in this review article. Due to the environmental implications of their end-of-life management, the review primarily focuses on fibre-reinforced polymer composites, with a particular emphasis on epoxy-based systems and carbon/glass fibres as reinforcement. Analyses include thermal procedures (fluidized bed, pyrolysis), chemical processes (various solvolysis types), combination processes (microwave, steam, and ultrasonic aided methods), and exceptional recycling efforts (electrochemical, biological, and with ionic liquids). In comparison to chemical recycling, thermal recycling uses a lot less energy and allows recovered materials to match raw material qualities. In contrast to alternative recycling methods, mechanical recycling uses a relatively little amount of energy to recycle composites. It was concluded that the composite materials consumption in different industries would only be justified when recycling and reusing of composites should be given equal consideration. In addition, the recycling of polymer composites will boost the circular economy.