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With the growing requirement for lightweight structural materials in automotive, aerospace, and infrastructure applications, multi‐material joints made with adhesive have attracted intense research interest. Commercial thermoset adhesives are one‐time cures, and difficult to disassemble the bonded components for repair and recycling. Our prior work with a thermoplastic acrylonitrile‐butadiene‐lignin rubber (ABL) addresses this sustainability/recycling challenge, but the adhesive exhibits deficient joining strength compared to standard thermosets. Here, we modify the ABL matrix by loading particulate fillers to enhance its modulus and toughness. The goal is to manufacture a cure‐free thermoplastic adhesive system with a simple dispensing protocol and characteristic ductility combined with a high yield stress for improved shear strength of a bonded joint. Fumed silica (FS) and epoxidized glass spheres (EGS) were used as fillers in the ABL to promote the dispersion of lignin particles that tailored the functionalities and free energy components of the adhesive surface. With optimal loading of FS (5 wt%) and EGS (30 wt%) in the ABL adhesive matrix, the lap‐shear strength of the bonded aluminum joint was elevated by 128%, compared to the neat ABL, reaching 21 MPa, which is 90% of the performance of a commercial epoxy‐based adhesive. Highlights: A partly renewable filler‐toughened thermoplastic adhesive has been developed.This thermoplastic gives nearly equivalent performance of adhesively bonded aluminum joint compared to standard thermosets.Experimental and simulation data help understand the adhesive reinforcing mechanism by the fillers. [ABSTRACT FROM AUTHOR]

Thermoplastic polymer fiber–thermoplastic polymer matrix composites (PPCs or PRFPs), often recognized as self‐reinforced or single polymer composites, are potential candidates for future advanced polymer composites because of various advantages (e.g., recyclability, formability, low‐cost, ultra‐lightweight, environmental friendliness, etc.). The manufacturability and mechanical behavior of these composites compared to conventional carbon‐/glass‐/aramid‐fiber‐reinforced polymers is of great interest to the composites community, but there are a limited number of studies in this area. To this end, this paper reviewed fabrication methods with different processing parameters and mechanical behavior of uni‐/multi‐directional thermoplastic PPCs featuring continuous thermoplastic polymer fibers from limited data in the literature. It was shown that most specific behaviors (normalized by density) of these materials in various loading conditions (e.g., quasi‐static tension/shear/flexure, tension‐tension fatigue, and out‐of‐plane impacting, etc.) are comparable to or better than glass‐/aramid‐fiber‐reinforced polymers. Particularly, the specific ductility in the foregoing conditions outperforms all the carbon‐/glass‐/aramid‐fiber‐reinforced polymers. Thermoplastic PPCs with remarkable performance can be achieved through several uncomplicated methods (e.g., film stacking, hot compaction, powder and solution impregnations, matrix infusion and injection molding, additive manufacturing, etc.), which have some similarities to the methods used for carbon‐/glass‐/aramid‐fiber‐reinforced polymers. Moreover, several opportunities and challenging problems of thermoplastic PPCs were summarized at the end of this review paper. Efficient solutions may require countless efforts in the composites community to further strengthen the performance and understanding of thermoplastic PPCs for wide applications in various engineering fields in the future. [ABSTRACT FROM AUTHOR]

In recent years researchers have introduced different malleable and/or degradable thermosetting polymers to address the recyclability of traditional thermoset materials. Nonetheless, the mechanical properties and glass transition temperature (Tg) of these polymers are often compromised to achieve the desired depolymerization rate. In this work, a hydrothermally recyclable epoxy/anhydride thermosetting system with superior mechanical performance and high Tg (>200 °C) was developed for carbon fiber reinforced plastic (CFRP) applications, using triethanolamine as the co-curing agent and tetraglycidyl methylenedianiline (TGDDM) as the epoxy matrix. The hydrothermal recycling of such cured systems is achieved at relatively low temperature (200 °C) without the addition of a catalyst. This mild recycling process decomposes the recyclable polymer matrix into an oligomer and imparts little damage to the valuable carbon fiber. The recycled carbon fiber and the decomposed polymer resin are reused to prepare a new CFRP. Therefore, this study has introduced a simple and practical approach for the preparation of recyclable CFRPs with high Tg and a pathway for highly efficient closed-loop recycling, which sets up a framework for the future design of sustainable polymer composites. [ABSTRACT FROM AUTHOR]

The cover image is based on the Research Article Acrylonitrile‐butadiene‐lignin thermoplastic rubber adhesive for enhanced metal‐to‐metal joining by Zeyang Yu et al., https://doi.org/10.1002/pc.28258. [ABSTRACT FROM AUTHOR]

Conventional carbon fiber reinforced thermosetting polymers (CFRPs) are neither recyclable nor repairable due to their crosslinked network. The rapid growing CFRP market raises a serious concern of the waste management. In this work, a viable method to develop a readily recyclable CFRP based on epoxy vitrimer is introduced. First, a self‐catalytic epoxy prepolymer with built‐in hydroxy and tertiary amine groups is designed, which upon reaction with an anhydride formed a catalyst‐free epoxy vitrimer. The epoxy prepolymer is synthesized from a diamine and an excess of bisphenol A epoxy resin. The hydroxyls and tertiary amines of the epoxy prepolymer efficiently catalyze both curing and the dynamic transesterification of the crosslinked polymer without the need of a catalyst. Then, the epoxy vitrimer is used as the matrix resin to prepare CFRP. The resulting CFRP exhibited a tensile strength as high as 356 MPa. More interestingly, the matrix of the CFRP is efficiently degraded in pure water at above 160 °C. This is because the built‐in tertiary amines catalyze the hydrolysis of the ester bonds of the crosslinked network. The simple method developed in this work provides a framework for the development of recyclable CFRP. [ABSTRACT FROM AUTHOR]

A multiscale modeling approach to analyze filament-wound composite pressure vessels is developed in this article. The approach, which extends the Nguyen et al. [Prediction of the elastic-plastic stress/strain response for injection-molded long-fiber thermoplastics. J Compos Mater 2009; 43: 217–246.] model developed for discontinuous fiber composites to continuous fiber ones, spans three modeling scales. The microscale considers the unidirectional elastic fibers embedded in an elastic–plastic matrix obeying the Ramberg–Osgood relation and J2 deformation theory of plasticity. The mesoscale behavior representing the composite lamina is obtained through an incremental Mori–Tanaka [Average stress in matrix and average elastic energy of materials with misfitting inclusions. Acta Metall 1973; 21: 571–574.] type model and the Eshelby [The determination of the elastic field of an ellipsoidal inclusion and related problems. Proc R Soc Lond, Ser A 1957; 241: 376–396.] equivalent inclusion method. The implementation of the micro–meso constitutive relations in the ABAQUS® finite element package (via user subroutines) allows the analysis of a filament-wound composite pressure vessel (macroscale) to be performed. Failure of the composite lamina is predicted by a criterion that accounts for the strengths of the fibers and of the matrix as well as of their interface. The developed approach is validated in the analysis of an aluminum liner – T300 carbon/epoxy pressure vessel to predict the burst pressure. The predictions compare favorably with the numerical and experimental results by Lifshitz and Dayan [Filament-wound pressure vessel with thick metal liner. Compos Struct 1995; 32: 313–323]. The approach will be further demonstrated in the study of the effects of the lamina thickness, helical angle, and fiber–matrix material combination on the burst pressure. [ABSTRACT FROM AUTHOR]

Microsized pore parameters, such as pore size and distance between pores in a series of model EPDM rubbers, were determined in situ under the pressure of 500 psi using 129 Xe nuclear magnetic resonance (NMR) techniques: spin-lattice ( T 1 ) and spin-spin ( T 2 ) relaxation measurements, pulsed-field gradient (PFG) NMR, and two-dimensional exchange spectroscopy (2D EXSY). The T 1 / T 2 (≫1) ratio for the xenon confined in the pores is larger than that for nonconfined free xenon. This suggests that almost the entire pore surface interacts with xenon atoms like a closed pore. While these pores still connect each other through very narrow diffusion/exchange channels, it is possible to observe the echo decay in PFG-NMR and cross-peaks in 2D EXSY. The results show that both diffusion ( D pore ≈ 2.1 × 10 -10 m 2 /s) and exchange (exchange rate, τ exch = a few tens of milliseconds) of xenon between a pore within the material and outer surface are prolonged. The exchange distances ( l ), which correspond to the xenon gas penetration depth, were estimated to be 70-100 μm based on the measured diffusion coefficients and exchange rate (1/τ exch ). NMR diffraction analysis reveals that pore size ( a ) and pore distance ( b ) are on the order of magnitude of micrometers and tens of micrometers, while the diffusion coefficients of xenon gas in the diffusion channels ( D eff ) are about 10 -8 m 2 /s. Overall, this study suggests that the pores with a few micrometers connected through very narrow flowing channels with the length of several tens of micrometers are developed 70 to 100 μm below the rubber surface. Furthermore, the overall steady-state diffusion of xenon is slower, approximately 2 orders of magnitudes, than the diffusion in the channel between the pores. The pore and exchange distances correlated with the composition of rubbers showed that the properties of EPDM rubber as a high-pressure gas barrier could be improved by reducing the size of cracks and the depth of gas penetration by the addition of both carbon black and silica fillers.

Aqueous solutions of poly(DL-lactic acid-co-glycolic acid)-g-poly(ethylene glycol) copolymers exhibited sol-to-gel transition with increasing temperature. Further increase in temperature makes the system flow and form a sol phase again. Subcutaneous injection of a copolymer aqueous solution (0.5 mL) resulted in a formation of a hydrogel depot by temperature-sensitive sol-to-gel transition in a rat model. The reliable determination and control of sol-to-gel transition temperatures are the most important issues for this kind of sol-gel reversible hydrogel. The sol-to-gel transition temperature determined by the test tube inverting method, falling ball method, and dynamic mechanical analysis coincided within 1-2 degrees C. Fine tuning of the sol-to-gel transition temperature was achieved by varying the ionic strength of the polymer solutions and by mixing two polymer aqueous solutions with different sol-to-gel transition temperatures. The sol-to-gel transition temperature of polymer mixture aqueous solutions was well described by an empirical equation of miscible blends, indicating miscibility of the two polymer systems in water on the molecular level.