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The hydrogenolysis of polymers is emerging as a promising approach to deconstruct plastic waste into valuable chemicals. Yet, the complexity of plastic waste, including multilayer packaging, is a significant barrier to handling realistic waste streams. Herein, we reveal fundamental insights into a new chemical route for transforming a previously unaddressed fraction of plastic waste – poly(ethylene‐co‐vinyl alcohol) (EVOH) and related polymer blends – into alkane products. We report that Ru/ZrO2 is active for the concurrent hydrogenolysis, hydrogenation, and hydrodeoxygenation of EVOH and its thermal degradation products into alkanes (C1−C35) and water. Detailed reaction data, product analysis, and catalyst characterization reveal that the in‐situ thermal degradation of EVOH forms aromatic intermediates that are detrimental to catalytic activity. Increased hydrogen pressure promotes hydrogenation of these aromatics, preventing catalyst deactivation and improving alkane product yields. Calculated apparent rates of C−C scission reveal that the hydrogenolysis of EVOH is slower than low‐density polyethylene. We apply these findings to achieve hydrogenolysis of EVOH/polyethylene blends and elucidate the sensitivity of hydrogenolysis catalysts to such blends. Overall, we demonstrate progress towards efficient catalytic processes for the hydroconversion of waste multilayer film plastic packaging into valuable products. [ABSTRACT FROM AUTHOR]

Cadmium oleate is widely used as a cation precursor in the synthesis of cadmium chalcogenide nanocrystal quantum dots (QDs) for a broad range of photonic and optoelectronic applications. Cd oleate can noncovalently assemble to form a supramolecular coordination gel, or metallogel, in solvents commonly used to disperse oleate-capped QDs. The gelation severely impedes the purification of oleate-capped QDs from excess Cd oleate, resulting in a gelled product that cannot be reliably characterized or used in further synthesis reactions. Here, we investigate the Cd oleate gel to gain insights into its viscoelastic properties and behavior under conditions relevant to QD synthesis, purification, and storage. We then examine how to effectively mitigate gelation by adding oleylamine as an additional ligand to disrupt noncovalent assembly. We synthesize PbS/CdS core/shell QDs via cation exchange as a case study to illustrate gelation of the reaction product and further demonstrate how this issue can be resolved through a better understanding of the supramolecular gel. [ABSTRACT FROM AUTHOR]

The reinforcement of mechanically‐weak hydrogels to yield composites with increased stiffness, strength, or toughness is a well‐established approach. In particular, introducing electrospun nanofibers into hydrogels is a common strategy for biomedical applications, as the resulting hierarchical structure mimics biology and allows for control over fiber diameter and alignment and tuning of mechanical properties. However, further study of the link between the constituent materials and the mechanical properties of the composite is uncommon. One potential model to understand the mechanical properties of fiber‐reinforced hydrogels involves the Halpin–Tsai equations, which relate the modulus values of the fibers and hydrogel matrix and the fiber volume fraction, to the modulus of the composite. To assess the application of this model to fiber‐reinforced hydrogels, predicted values were compared with experimental values from mechanical testing of a poly(ethylene glycol) (PEG) matrix reinforced with an electrospun polycaprolactone (PCL) fiber mat. Although the equations described these systems well in tension, providing a facile approach to identify a fiber volume fraction that will achieve a desired modulus, the Halpin–Tsai approach was less successful under compression. This study motivates additional investigation of the role of structural features of hydrogel composites in determining mechanical properties to enable design of materials for specific applications. [ABSTRACT FROM AUTHOR]

Mechanical stretching of a partially cross-linked gel or elastomer followed by additional cross-linking to fix the alignment is the most widely employed method to synthesize aligned LCEs.[[14]] This technique can be applied to a large range of synthetic approaches. Liquid crystal elastomers (LCEs) are a class of materials where liquid crystalline order and rubber elasticity combine to yield interesting properties.[1] These elastomers can exhibit a variety of liquid crystalline phases, which results in materials with distinct functional properties. Wei, P. Shiller, J. V. Selinger, R. L. B. Selinger, and O. D. Lavrentovich, "Dynamically morphing microchannels in liquid crystal elastomer coatings containing disclinations", J. Appl. Phys. 10.1063/5.0039965 43 A. Sharma, A. M. Stoffel, and J. P. F. Lagerwall, "Liquid crystal elastomer shells with topological defect-defined actuation: Complex shape morphing, opening/closing, and unidirectional rotation", J. Appl. Phys. [Extracted from the article]

Many commodity plastics, such as thermoplastic polyurethanes (PUs), require reinforcement for use as commercial products. Cellulose nanocrystals (CNCs) offer a "green" and scalable approach to polymer reinforcement as they are exceptionally stiff, recyclable, and abundant. Unfortunately, achieving efficient CNC reinforcement of PUs with industrial melt processing techniques is difficult, mostly due to the incompatibility of the hydrophobic PU with hydrophilic CNCs, limiting their dispersion. Here, a hydrophilic PU is synthesized to achieve strong reinforcement in melt‐processed nanocomposite fibers using filter paper‐sourced CNCs. The melt‐spun fibers, exhibiting smooth surfaces even at high CNC loading (up to 25 wt%) indicating good CNC dispersion, are bench‐marked against solvent‐cast films—solvent processing is not scalable but disperses CNCs well and produces strong CNC reinforcement. Mechanical analysis shows the CNC addition stiffens both nanocomposite films and fibers. The stress and strain at break, however, are not significantly affected in films, whereas adding CNCs to fibers increases the stress‐at‐break while reducing the strain‐at‐break. Compared to earlier studies employing a hydrophobic (and stiffer) PU, CNC addition to a hydrophilic PU substantially increases the fiber stiffness and strength. This work therefore suggests that rendering thermoplastics more hydrophilic might pave the way for "greener" polymer composite products using CNCs. [ABSTRACT FROM AUTHOR]

Amphiphilic polymer conetworks (APCNs) are polymer networks composed of hydrophilic and hydrophobic chain segments. Their applications range from soft contact lenses to membranes and biomaterials. APCNs based on polydimethylsiloxane (PDMS) and poly(2‐hydroxyethyl acrylate) are flexible and elastic in the dry and swollen state. However, they are not good at resisting deformation under load, i.e., their toughness is low. A bio‐inspired approach to reinforce APCNs is presented based on the incorporation of poly(β‐benzyl‐L‐aspartate) (PBLA) blocks between cross‐linking points and PDMS chain segments. The mechanical properties of the resulting peptide‐reinforced APCNs can be tailored by the secondary structure of the peptide chains (β‐sheets or a mixture of α‐helices and β‐sheets). Compared to non‐reinforced APCNs, the peptide‐reinforced networks have higher extensibility (53 vs. up to 341%), strength (0.71 ± 0.16 vs. 22.28 ± 2.81 MPa), and toughness (0.10 ± 0.04 vs. up to 4.85 ± 1.32 MJ m−3), as measured in their dry state. The PBLA peptides reversibly toughen and reinforce the APCNs, while other key material properties of APCNs are retained, such as optical transparency and swellability in water and organic solvents. This paves the way for applications of APCNs that benefit from significantly increased mechanical properties. [ABSTRACT FROM AUTHOR]

Polymer nanocomposites are an important class of materials.[[1], [3], [5]] They combine the many desirable physical properties of polymers, such as their mechanical properties and ease of processing, with functionalities provided by a nanoparticle component. A common example is using thiol-terminated polymers to graft to the surface of Au nanoparticles.[[10]] The "grafting-to" approach may be easier to accomplish experimentally but typically results in lower grafting densities, especially for high molecular weight polymers. The particles are not unlike those formed by surfactants in solution; in fact, polymer chains can self-assemble in solution to form micellar structures that behave like PGNPs in many ways.[13] Recently, virus-like particles have been synthesized and functionalized with a polymer brush.[14] Finally, nanoparticles can be synthesized by crosslinking single chains into small, dense nanoparticles. [Extracted from the article]

Plastics are ideal for numerous applications, as driven by the development of complex formulations containing various additives to improve performance and processability. Unfortunately, chemical valorization strategies (e.g., catalytic deconstruction) often can be challenged by the presence of small-molecule additives, and quantification of the impact of these molecular constituents on upcycling processes remains elusive. This dearth of information restricts catalyst design efforts to combine the robustness and performance necessary to improve plastics circularity. In this communication, we describe a systematic study of common plastics additives—phenolic antioxidants, and we quantify the relationship between additive content and deconstruction yields of high-density polyethylene (HDPE) over a platinum on tungstated zirconium (Pt/WO3/ZrO2) hydrocracking catalyst. In the simplest case of a base (antioxidant- and slip agent-containing) HDPE resin versus a pure (additive-stripped) HDPE polymer, a two-fold decrease in the yield of gas and liquid products is noted for base HDPE resin. Furthermore, both antioxidant chemistry and concentration strongly impact conversion and individual product selectivities. Using infrared spectroscopy, we determine that antioxidants change the effective ratio of metal to acid sites (i.e., metal-acid balance) through reactions of phenols and/or other functional groups (e.g., acids, esters) with catalyst active sites. Overall, this work demonstrates the impact of one common set of additives on plastics deconstruction, and the analysis herein provides a blueprint for quantitatively assessing the effects of additives on plastics deconstruction processes and for evaluating the development of more robust catalytic strategies or more tolerable additive formulations. [ABSTRACT FROM AUTHOR]

Plastics have revolutionized modern life, but have created a global waste crisis driven by our reliance and demand for low-cost, disposable materials. New approaches are vital to address challenges related to plastics waste heterogeneity, along with the property reductions induced by mechanical recycling. Chemical recycling and upcycling of polymers may enable circularity through separation strategies, chemistries that promote closed-loop recycling inherent to macromolecular design, and transformative processes that shift the life-cycle landscape. Polymer upcycling schemes may enable lower-energy pathways and minimal environmental impacts compared with traditional mechanical and chemical recycling. The emergence of industrial adoption of recycling and upcycling approaches is encouraging, solidifying the critical role for these strategies in addressing the fate of plastics and driving advances in next-generation materials design. [ABSTRACT FROM AUTHOR]

Intelligence of living and nonliving systems is often characterized by the ability to communicate through signal and response. In the polymer science community, this intelligence is realized through the reaction of a material construct to environmental triggers. These smart materials are modeled after natural materials, which utilize matrix-fiber architectures to detect stimuli, release small molecules, or alter their macroscopic morphology in response to stimuli. As such, researchers have designed matrix-fiber composites, which function as release vehicles, sensors or switches, and actuators. Through the examination of the architecture and environmental triggering of these natural muses, the fundamental design parameters necessary for functional response in matrix-fiber composites and the ability to utilize these composites in targeted applications are highlighted. Opportunities for innovation in composite design are also discussed. [ABSTRACT FROM AUTHOR]

Uniaxial drawing of melt-coextruded poly(ε-caprolactone) (PCL) microfibers was investigated to understand impact on topological, mechanical, and chemical properties of the fibrous scaffolds. Fibers were uniaxially elongated up to 7-fold to observe polymer chain orientation and crystal structure. Crystallinity and orientation of crystal domains were investigated by DSC and X-ray scattering. Polymer physical properties were directly correlated to bulk fiber properties. Furthermore, the drawn fibers were modified photochemically with functionalized benzophenones. The results of these studies allowed for comparison between fiber dimension/surface area, mechanical properties, and photochemical reaction yield for surface modification. As drawing increased, the modulus and tensile strength of the fibers increased as did the surface area of the scaffolds. By contrast, increased drawing led to a decrease in the ability to undergo photochemical reaction at the polymer surface. This fundamental investigation provides a predictive framework to understand how post-processing impacts three critical parameters for coextruded fibrous biomaterial scaffolds. [ABSTRACT FROM AUTHOR]

Controlling the molecular structure of amorphous cross-linked polymeric materials is a longstanding challenge. Herein, we disclose a general strategy for precise tuning of loop defects in covalent polymer gel networks. This “loop control” is achieved through a simple semibatch monomer addition protocol that can be applied to a broad range of network-forming reactions. By controlling loop defects, we demonstrate that with the same set of material precursors it is possible to tune and in several cases substantially improve network connectivity and mechanical properties (e.g., ∼600% increase in shear storage modulus). We believe that the concept of loop control via continuous reagent addition could find broad application in the synthesis of academically and industrially important cross-linked polymeric materials, such as resins and gels. [ABSTRACT FROM AUTHOR]

Polymeric fibrous constructs possess high surface area-to-volume ratios when compared with solid substrates and are quite commonly used as tissue engineering and cell growth scaffolds. An overview of important design and material considerations for fibrous scaffolds as well as an outline of both established and emerging solution- and melt-based fabrication techniques is provided. Innovative post-process surface modification avenues using “click” chemistry with both single and dual active cues as well as gradient cues, which maintain the fibrous structure are described. By combining process parameters with post-process surface modification, researchers have been able to selectively tune cellular response after seeding and culturing on fibrous constructs. [ABSTRACT FROM AUTHOR]

A continuous fibrous composite tape of poly(ethylene oxide) (PEO) and poly(ε-caprolactone) (PCL) was produced using novel multilayer coextrusion fiber manufacturing. A three-step washing process was utilized to remove the PEO matrix, resulting in a PCL fiber mat (>99 wt %). Synchrotron X-ray radiation was utilized to determine the optimized postprocessing uniaxial drawing conditions to achieve efficient crystalline orientation. An examination of small-/wide-angle X-ray scattering (SAXS/WAXS) revealed two regimes in the uniaxial drawing process; at DR < 5, crystalline orientation kinetics were dominant, while at DR > 5, amorphous chain alignment kinetics were dominant. Uniaxial drawing was shown to be an effective tool for tuning individual fiber size from 2.6 ± 0.6 μm by 1.6 ± 0.4 μm in the as-extruded state to 0.31 ± 0.05 μm by 0.13 ± 0.02 μm in the oriented state, while increasing specific surface area 3.5-fold. The elastic modulus and tensile strength of the PCL fiber mat were also increased by a factor of 30 and ~10, respectively, through uniaxial drawing. Compared to electrospun PCL fiber systems produced with individual fiber dimensions similar to those of the asextruded and oriented PCL fiber mats, the melt-processed PCL fibers exhibit a 6-fold increase in specific surface area over the corresponding circular, electrospun PCL fibers while maintaining similar thermomechanical properties. The elastic modulus of the oriented, coextruded PCL fiber mat was increased by a factor of 50 compared to the corresponding electrospun PCL fiber mat, while exhibiting a 2.5-fold increase in specific surface area. The ability to melt-process and utilize uniaxial drawing to produce PCL fibers in high volume with a consistent, tunable range of properties that are similar or enhanced when compared to traditional electrospun fibers provides a unique advantage in the field of tissue engineering, surface modification, and drug delivery. [ABSTRACT FROM AUTHOR]

Bio-inspired materials design is an important strategy used in the fabrication of tunable and mechanically enhanced polymeric systems. An important aspect of bio-inspiration is to understand how components, such as hierarchy and self-assembly, affect the properties of the designed materials. In this investigation, we explore the use of polypeptide secondary structure and hydrogen bonding arrangement, in order to determine their effects on the thermal and mechanical properties of fully synthetic peptidic polyureas. Specifically, we incorporate either short β-sheet forming peptide blocks of poly(β-benzyl-L-aspartate)5 or poly(ε-carbobenzyloxy-L-lysine)5 or longer peptide blocks of poly(β-benzyl-L-aspartate)20 or poly(ε-carbobenzyloxy-L-lysine)20 as α-helix forming domains into non-chain extended polyureas based on 1,6-hexamethylene diisocyanate and poly(dimethysiloxane). Secondary structure was found to be influenced by the weight fraction of peptide, e.g. increasing peptide weight fractions increased sheet or helical ordering. Additionally, the polyurea microstructure was comprised of nanofibrils with a secondary structure dependent fiber width, attributed to the peptidic motif alignment within the nanothreads. Analysis of the thermomechanical and tensile response revealed multiple trends, such as increased toughness attributed to β-sheet ordering and increased modulus with increased peptide weight fraction. It is anticipated that this observed interplay between peptide organization and mechanics will be applicable to engineering and biomaterial development due to the simplicity of the synthetic protocol and the promising mechanical tunability guided by the peptide segment. [ABSTRACT FROM AUTHOR]

Understanding block copolymer (BCP) self-assembly under confinement via conventional melt extrusion is advantageous as technology moves towards thin film applications. Previous research has revealed that confining elastomeric BCPs in thin films with polystyrene (PS) via microlayering results in an increase in ductility with decreasing layer thickness and that the interfacial region dramatically influences the elastic modulus. This contribution investigated the role of interfacial width and layer thickness on deformation mechanics by comparing poly(methyl methacrylate) (PMMA) and PS as wetting layers in confined multilayers. The interfacial region was found to be crucial to tailoring the mechanical response of composite materials. [ABSTRACT FROM AUTHOR]

New bio-derived strategies have been recently explored in the design of polymer nanocomposites, particularly in the area of responsive materials, which offer pathways toward tailored interfacial adhesion, responsive interactions and controlled dispersion. In this Feature article, we discuss: (1) precise control of dispersion via self-assembly driven approaches in responsive mechanics, (2) inherent and strong interfacial adhesion in single polymer composites, and (3) percolating, electrospun nanofiber networks as filler elements in adaptable composites. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 [ABSTRACT FROM AUTHOR]

We report the electrospinning of mechanically-tunable, cellulose nanocrystal (CNC)-reinforced polyurethanes (PUs). Using high-aspect ratio CNCs from tunicates, the stiffness and strength of electrospun PU/CNC mats are shown to generally increase. Furthermore, by tuning the electrospinning conditions, fibrous PU/CNC mats were created with either aligned or non-aligned fibers, as confirmed by scanning electron microscopy. PU/CNC mats having fibers aligned in the strain direction were stiffer and stronger compared to mats containing non-aligned fibers. Interestingly, fiber alignment was accompanied by an anisotropic orientation of the CNCs, as confirmed by wide-angle X-ray scattering, implying their alignment additionally benefits both stiffness and strength of fibrous PU/CNC nanocomposite mats. These findings suggest that CNC alignment could serve as an additional reinforcement mechanism in the design of stronger fibrous nanocomposite mats. [ABSTRACT FROM AUTHOR]

The facile synthesis of well‐aligned, main‐chain liquid crystalline elastomers that retain the cholesteric phase (CLCEs) is reported. The selective reflection inherent to this phase is thermally tuned more than 200 nm in these solid films, across the visible spectrum. The optical response is directly correlated to thermomechanical expansion of the CLCE film thickness. The bandwidth of the selective reflection of the CLCEs is increased to more than 200 nm by the incorporation of photosensitive chiral dopants that introduce heterogeneity in the pitch distribution. The mirror‐like reflection of this CLCE film is also thermochromic, shifting from the visible to infrared. Reminiscent of cephalopods, when combined with the mechanical deformation of voxelated nematic liquid crystal elastomer, the thermochromic response of the CLCE produces solid‐state elements with concurrent variation of specular and diffuse reflectance. These results demonstrate distinctive potential opportunities for liquid crystal elastomers to control light enabling new application in textiles, optics, and architecture. Nature employs concurrent shape and color change to control light and enable function. Concurrent shape and color change is realized in bilayer laminates of liquid crystal elastomers. The optical response is enabled by the facile synthesis of well‐aligned and main‐chain liquid crystalline elastomers retaining the cholesteric phase. Full‐spectrum thermochromism is observable in both narrow and broadband reflections in cholesteric liquid crystal elastomers. [ABSTRACT FROM AUTHOR]