Concurrent curing kinetics of an anhydride-cured epoxy resin and polydicyclopentadiene

Additive Manufacturing of Degradable Materials via Ring-Opening Metathesis Polymerization (ROMP)

Thermoset materials comprise a significant proportion of high-performance plastics due to their shape permanence and excellent thermal and mechanical properties. However, these properties come at the expense of degradability. Here, we show for the first time that the industrial thermoset polydicyclopentadiene (PDCPD) can be additively manufactured (AM) with degradable 2,3-dihydrofuran (DHF) linkages using a photochemical approach. Treatment of the manufactured objects with acid results in rapid degradation to soluble byproducts. This work highlights the potential of ring-opening metathesis polymerization (ROMP) chemistry to create degradable materials amenable to advanced manufacturing processes.

Unmodified Silica Nanoparticles Enhance Mechanical Properties and Welding Ability of Epoxy Thermosets with Tunable Vitrimer Matrix

Epoxy/silica thermosets with tunable matrix (vitrimers) were prepared by thermal curing of diglycidyl ether of bisphenol A (DGEBA) in the presence of a hardener-4-methylhexahydrophthalic anhydride (MHHPA), a transesterification catalyst-zinc acetylacetonate (ZAA), and 10-15 nm spherical silica nanoparticles. The properties of the resulting material were studied by tensile testing, thermomechanical and dynamic mechanical analysis. It is shown that at room temperature the introduction of 5-10 wt% of silica nanoparticles in the vitrimer matrix strengthens the material leading to the increase of the elastic modulus by 44% and the tensile stress by 25%. Simultaneously, nanoparticles enhance the dimensional stability of the material since they reduce the coefficient of thermal expansion. At the same time, the transesterification catalyst provides the thermoset with the welding ability at heating, when the chain exchange reactions are accelerated. For the first time, it was shown that the silica nanoparticles strengthen welding joints in vitrimers, which is extremely important, since it allows to repeatedly use products made of thermosets and heal defects in them. Such materials hold great promise for use in durable protective coatings, adhesives, sealants and many other applications.

Impact and shear properties of carbon fabric/ poly-dicyclopentadiene composites manufactured by vacuum‐assisted resin transfer molding

Dicyclopentadiene (DCPD) resin has gained popularity owing to its fast curing time and ease of processing with a low viscosity in the monomer state. In the present study, the impact and shear properties of a carbon fiber (CF)/p-DCPD composite were investigated. The CF/p-DCPD composite was manufactured by vacuum-assisted resin transfer molding with CF as the reinforcement and p-DCPD as the resin with a maximum fiber volume fraction of 55 weight percent. Impact and shear properties of the CF/p-DCPD composite were evaluated and compared with those of a CF/Epoxy composite. The maximum shear stress and modulus of the CF/p-DCPD composite were lower than that of the CF/Epoxy composite. However, the CF/p-DCPD composite had higher toughness than that of the CF/Epoxy composite; this indicates that it is tougher and exhibits a more ductile load-displacement response with a lower modulus and larger failure deformation. The impact strength of the CF/p-DCPD composite was about three time that of the CF/Epoxy composite. The higher impact strength of the CF/p-DCPD composite is attributed to the resin characteristics: epoxy resin has a more brittle behavior, and hence, higher energy is required for crack propagation due to fracture.

Preparation and curing behavior of high-stress solid propellant binder based on polydicyclopentadiene

The ring-opening metathesis polymerization reaction of dicyclopentadiene (DCPD) was carried out using Grubbs first generation catalyst. Fourier transform infrared (FTIR), dynamic-thermo mechanical analysis (DMA), and Raman spectroscopy were used to investigate the curing behavior of this polymer. The FTIR results showed that DCPD had not cured completely and the polymers were composed of linear and cross-linked polydicyclopentadiene (PDCPD). The DMA test showed that the polymer possesses the glass transition temperature of linear PDCPD and cross-linked PDCPD, which had also proved the FTIR result. Furthermore, in order to explain the strange phenomenon that the band at 3004 cm−1 should have been detected in infrared spectrum, the Raman spectrum of PDCPD was applied to analyze the bonding mechanism of =C–H bond in the process of polymerization. Moreover, the real-time FTIR result cure formula showed that the cure degree increases first then constants trend with cure time of increasing, the cure degree reached the maximum value (96.76%) at 60°C for 192 h.

Synthesis, Characterization, and Cross-Linking Strategy of a Quercetin-Based Epoxidized Monomer as a Naturally-Derived Replacement for BPA in Epoxy Resins

The natural polyphenolic compound quercetin was functionalized and cross-linked to afford a robust epoxy network. Quercetin was selectively methylated and functionalized with glycidyl ether moieties using a microwave-assisted reaction on a gram scale to afford the desired monomer (Q). This quercetin-derived monomer was treated with nadic methyl anhydride (NMA) to obtain a cross-linked network (Q-NMA). The thermal and mechanical properties of this naturally derived network were compared to those of a conventional diglycidyl ether bisphenol A-derived counterpart (DGEBA-NMA). Q-NMA had similar thermal properties [i.e., glass transition (Tg ) and decomposition (Td ) temperatures] and comparable mechanical properties (i.e., Young's Modulus, storage modulus) to that of DGEBA-NMA. However, it had a lower tensile strength and higher flexural modulus at elevated temperatures. The application of naturally derived, sustainable compounds for the replacement of commercially available petrochemical-based epoxies is of great interest to reduce the environmental impact of these materials. Q-NMA is an attractive candidate for the replacement of bisphenol A-based epoxies in various specialty engineering applications.