Designed and tailor-made double hydrophilic block copolymer-graphene nanoplatelet hybrids for reinforcing epoxy thermosets

Because of their propensity to build micellar nanostructures, amphiphilic block copolymers (ABCs) are an appropriate and unique toughening agent for epoxy systems individually on their own and in grafted form. The presence of epoxiphilic and phobic ends in ABCs is responsible for the self-assembly and the micellar structure. Nanofiller-grafted ABCs can effectively enhance the toughness of epoxy via the synergistic interaction of nanofillers and the ABCs. Even though there is sound literature supporting the effect of ABCs in epoxy, the action of double hydrophilic block copolymers (DHBC) in the epoxy matrix is less handled. Hence, the grafting of nanofillers in DHBCs and their subsequent role in tuning the properties of epoxy is a new concept. Hence this paper tries to bridge the gap via studying the effect of grafted fillers based on DHBCs in epoxy matrix. As a result, the current study focuses on the synthesis of double hydrophilic graphene nanoplatelets (rGO-g-DHBC) via nitrogen oxide-mediated polymerization for epoxy toughening application. The prepared rGO-g-DHBC was effectively utilized for epoxy toughening applications, resulting in a 457% improvement in toughness without compromising its inherent tensile strength. The mechanism behind the improved toughness was elucidated with the help of a scanning electron microscope, and the thermal, and rheological characteristics were studied.

Incorporation of cinnamaldehyde, carvacrol, and eugenol into zein films for active food packaging: enhanced mechanical properties, antimicrobial activity, and controlled release

Active packaging with antimicrobial functions to improve the quality and extend the shelf life of food products has gained great interest. Because commercial plastic packaging materials are not biodegradable and cause great environmental problems, plant-derived natural materials have been widely studied for the application of biodegradable packaging materials. Herein, we reported a study of essential oils (EOs)-loaded zein film. Cinnamaldehyde (CIN), carvacrol, and eugenol were added to equip the films with antimicrobial effects, while polyethylene glycol (PEG) and oleic acid (OA) were selected for the improvements of mechanical properties. The results showed that PEG efficiently improves the tensile strength and elongation (%E) of zein films compared to OA, although PEG induced weaker water barrier properties of the films than OA. FTIR spectra confirmed the formation of the hydrogen bonds between zein and PEG/OA. The EO-embedded zein film showed better antimicrobial effects than EO themselves. CIN-embedded films showed the highest antimicrobial effect among the three EOs. The sizes of the inhibition zones against Staphylococcus aureus of PEG-added zein films with 1%, 3%, and 5% CIN were 5.67, 12.67, and 16.67 mm, which were larger than that of pure CIN, with the sizes of 0.00, 3.00, and 4.67 mm, respectively. The developed films demonstrate a gradual release of EOs and show antimicrobial effects up to 96 h, indicating their high potential for the applications as active food packaging.

Sound Insulation Properties of Hollow Polystyrene Spheres/Polyethylene Glycol/Epoxy Composites

The generation of noise requires a noise source, transmission path, and passive acceptance target of noise, all of which are indispensable. Blocking the propagation path of noise is one of the available means when the existence of the noise source and passive receiving target cannot be addressed. This is an effective way to prevent noise pollution, often using sound insulation materials to block the path of noise transmission. In this work, composites with excellent sound insulation properties were designed and prepared. These composites, using epoxy resin (EP) as the matrix, polyethylene glycol (PEG), and hollow polystyrene spheres (HPS), were added to epoxy resin as a toughening agent and functional filler to prepare the ternary HPS/PEG/EP composites. The soundproofing results showed that when the thickness of the sample was 3 mm, the average sound transmission loss (STL) value of the neat EP and the HPS/PEG/EP composites with an HPS 32 vol% was up to 19.0 dB and 42.1 dB, and the STL values of the composites were increased by approximately 120% compared to the pure epoxy. When the sample was 10 mm thick, the average STL value of the HPS/PEG/EP composites with HPS 32 vol% contents was enhanced to 55.7 dB.

Analysis of the effect and mechanism of microwave curing on the chemical shrinkage of epoxy resins

The microwave cure–induced chemical shrinkage of epoxy resins in composite materials was researched in this article. Four kinds of epoxy resins were cured using the microwave and thermal heating process. An improved device containing fiber Bragg grating sensors was applied to accurately measure the chemical shrinkage–induced linear strains in those samples. Experimental results indicated that the chemical shrinkage of diglycidyl ether of bisphenol A (DGEBA)/polyetheramine (PEA) and tetraglycidyl diaminodiphenylmethane/4,4′-diaminodiphenyl sulfone epoxy resins was significantly reduced by microwave curing, and the reductions about 37.1 and 38.4% were achieved compared with the thermal-cured counterparts. However, the chemical shrinkage of the thermal- and microwave-cured samples was almost the same for DGEBA/methyl tetrahydrophthalic anhydride and DGEBA/dicyandiamide epoxies. In order to analyze the influencing mechanism of microwaves on the chemical shrinkage, the chemical structure of various samples was characterized by using Fourier-transform infrared spectroscopy, and the free volume was measured by positron annihilation lifetime spectrometer. It was found that microwaves can greatly decrease the contents of hydroxyl groups in epoxy resins, leading to the reduction of the chemical shrinkage. Furthermore, the mechanical properties of both microwave- and thermal-cured DGEBA/PEA epoxies were studied, and the results showed that the microwave-cured specimens have a higher impact strength but a lower tensile strength.

Synthesis, characterization, and shape-memory performances of monoamine-toughened epoxy resin

Epoxy resins were toughened by octylamine, dodecylamine, and hexadecylamine, respectively. The curing temperature and the curing kinetics were studied by non-isothermal differential scanning calorimetry (DSC) to optimize the cure conditions. The mass ratios of the monoamine to the total mass of triethylenetetramine and monoamine were varied to obtain polymers with different compositions. The cured polymers were analyzed by DSC, scanning electron microscopy (SEM), and mechanical analyses. Shape-memory performance was evaluated by fold-deploy tests. The glass transition temperature ( Tg) decreased with increasing carbon numbers of monoamine, and the decrease in Tg scaled with the content of monoamines added in the system. The elongation increased with an increase in monoamine content and alkyl chain length. The better toughness of the monoamine-rich system was further confirmed by the results of SEM. The strain fixity ratio increased with a decrease in monoamine content. The strain recovery ratios of all systems were greater than 98%.

Nano-engineered design and manufacturing of high-performance epoxy matrix composites with carbon fiber/selectively integrated graphene as multi-scale reinforcements

Three different architectural designs are developed for manufacturing advanced multi-scale reinforced epoxy based composites in which graphene sheets and carbon fibers are utilized as nano- and micro-scale reinforcements, respectively.