Two-stage thiol-acrylate Michael addition reactions have proven useful in programming main-chain liquid crystal elastomers (LCEs). However, the influence of excess acrylate concentration, which is critical to monodomain programming, has not previously been examined with respect to thermomechanical properties in these two-stage LCEs. Previous studies of thiol-acrylate LCEs have focused on polydomain LCEs and/or variation of thiol crosslinking monomers or linear thiol monomers. This study guides the design of monodomain LCE actuators using the two-stage methodology by varying the concentration of mesogenic acrylate monomers from 2 mol% to 45 mol% in stoichiometric excess of thiol. The findings demonstrate a technique to tailor the isotropic transition temperature by 44 °C using identical starting monomers. In contrast to expectations, low amounts of excess acrylate showed excellent fixity (90.4 ± 2.9%), while high amounts of excess acrylate did not hinder actuation strain (87.3 ± 2.3%). Tensile stress-strain properties were influenced by excess acrylate. Linear elastic behavior was observed parallel to the director with modulus increasing from 1.4 to 6.1 MPa. The soft elastic plateau was observed perpendicular to the director with initial modulus and threshold stresses increasing from 0.6 MPa to 2.6 MPa and 14 kPa to 208 kPa, respectively. Overall, this study examines the influence of excess acrylate on mechanical properties of LCE actuators.

No abstract

No abstract

No abstract

No abstract

In this study, we report, for the first time, the basic depolymerization of mixed waste polyethylene terephthalate (PET) by hydrolysis and subsequent terephthalic acid monomer recovery with high purity using benign reaction conditions. Several conditions were tested for depolymerization such as PET chip size, concentration of aqueous sodium hydroxide (20 or 30%), organic co-solvent (ethylene glycol or ethanol), temperature at which the reaction was run, and duration of the heating. More importantly, several purity grades of PET were utilized as starting materials including commercial PET, chopped PET obtained from clean bottles whose caps and labels were removed, and chopped PET containing caps, rings, and labels. The purity of the product from each condition was evaluated via nuclear magnetic resonance (1H NMR and 13C NMR), differential scanning calorimetry (DSC), and powder X-ray diffraction. Unsurprisingly, the conversion of PET is dependent on the particle size, varying from 100% conversion for fine powder to 73% conversion (for 300 μm, mesh 6–20, or mesh 14–20). Ethanol appears to be more efficient as a co-solvent than ethylene glycol, with higher PET depolymerization conversions (94% vs 75–80%), shorter reaction times (2 h vs 6 h), and lower temperatures (80 °C vs 110 °C). The terephthalic acid (TPA) recovered appeared to have only subtle differences among the batches, most notably a pink color when the reaction was run in ethanol/aqueous base. The DSC curve of the compounds produced in ethylene glycol–water appears to display a melting point (280–288 °C), while the samples prepared in ethanol and a commercial sample did not. Overall, the purity of the various TPA batches is comparable and similar to that of commercial TPA, demonstrating the utility of the method to depolymerize realistic waste streams. The method is simple, demonstrated on a multigram scale (15–30 g), and allows for the complete removal of waste other than PET while being unaffected by alkaline conditions. Eliminating the need to remove caps, labels, and rings and the copious amounts of water required for cleaning makes this process green and environmentally friendly.

A chemical recycling approach of mixed PET was demonstrated here that provides a mechanism by which PET waste can be efficiently recovered and repurposed to value-added products. The approach utilizes aminolysis of PET with a variety of amine nucleophiles, generating a small library of terephthalic amides with distinct structures, such as polar, nonpolar, and lipophilic. In order to probe the value of these products, the terephthalic amides were added to road-grade asphalt binder at 5 wt %, and the fresh resulting composite was evaluated. Specifically, rutting and fatigue characteristics as well as thermomechanical and creep performance were characterized and found to be improved by the inclusion of these additives by as much as 18%. In this work, additives made from deconstructed PET wastes were shown to improve the performance properties of asphalt at a variety of environmental conditions. It is important to note that the asphalt binder utilized in this work was a commercial product already optimized for road conditions, not the raw bitumen; perhaps higher performance metrics could be obtained with virgin bitumen.

This study explores the functionalization of main-chain nematic elastomers with a conductive metallic surface layer using a polydopamine binder. Using a two-stage thiol-acrylate reaction, a programmed monodomain was achieved for thermo-reversible actuation. A copper layer (∼155 nm) was deposited onto polymer samples using electroless deposition while the samples were in their elongated nematic state. Samples underwent 42% contraction when heated above the isotropic transition temperature. During the thermal cycle, buckling of the copper layer was seen in the direction perpendicular to contraction; however, transverse cracking occurred due to the large Poisson effect experienced during actuation. As a result, the electrical conductivity of the layer reduced quickly as a function of thermal cycling. However, samples did not show signs of delamination after 25 thermal cycles. These results demonstrate the ability to explore multi-functional liquid-crystalline composites using relatively facile synthesis, adhesion, and deposition techniques.