ENHANCED FRACTURE TOUGHNESS OF ADHESIVE JOINTS WITH DOPING EPOXY BY GRAPHENE NANOPLATELETS

It is necessary to enhance the mechanical properties of adhesives to replace conventional joint methods with adhesive bonding. Epoxy in its pure state often suffers catastrophic damage due to its obvious brittleness and low fracture toughness. In this study, the double cantilever beam (DCB - Mode I) was used to characterize the fracture toughness of graphene/DGEBA-epoxy nanocomposite adhesive in bonded aluminium alloy joints and bonded composite joints. Adhesives based on an epoxy adhesive DGEBA (Bisphenol A diglycidyl ether) reinforced with two percentages (1wt.% and 2wt.%) of graphene nanoplatelets (GNP) were prepared. In this study, one shows that the fracture toughness of adhesive nanocomposites was significantly better than neat epoxy-bonded adhesives. Both types of joints contain graphene resulting in increased fracture toughness. Therefore, the maximum fracture toughness was observed until the GNP reached 1wt.%, and then it began to decrease, but it is still higher than that of the pure adhesive joint. On the other hand, this work aims to determine the influence of interfacial interactions on the behavior of enhanced bonded joints and how graphene nanoplatelets can enhance the rigidity of the interface between the substrate and the adhesive. In addition, a numerical study using ABAQUS was performed and compared with the experiments performed on DCB. For the modeling of the damage in an assembly joint, the Cohesive Zone Model (CZM) was used for the fracture behavior of the adhesive.

Modification of cellulose nanocrystals with 2-carboxyethyl acrylate in the presence of epoxy resin to enhance its adhesive property

We synthesized the cellulose nanocrystals (CNCs) by using cotton as a raw material, then it was modified with 2-carboxyethyl acrylate to improve its adhesion and thermal properties. CNCs was chosen as a modifier to improve the interfacial adhesion between the reinforced nanocrystals and E-51 epoxy resin system. This gives a better modulus of elasticity, a lower coefficient of energy, and thermal expansion. Significant improvements in modulus properties, strength, transparency and thermal stability were observed with modified cellulose nanocrystals (MCNCs) compared with the standard sample. SEM, and transmission electron microscope (TEM), powder diffraction (XRD), (TGA and DTG) and Fourier transform infrared spectroscopy (FTIR) were used for the isolation of synthetic (native and modified) cellulose nanocrystals. In addition, the MCNCs adhesion properties with E-51 (Bisphenol A diglycidyl ether) epoxy resins were also investigated using the Zwick/Roell Z020 model.

Ethoxylated Butoxyethanol-BADGE Adducts—New Potential Migrants from Epoxy Resin Can Coating Material

The acetonitrile extracts of can-coating materials have been analyzed by using high-pressure liquid chromatography/electrospray ionization-mass spectrometry (HPLC/ESI-MS). On the basis of detected ions [M + H]+, [M + NH4]+, [M + Na]+ and product ions, the ethoxylated butoxyethanol-bisphenol A diglycidyl ether adducts were identified in two of the analyzed extracts. Although the oxyethylene unit-containing compounds are widely used for the production of different kinds of materials, the ethoxylated species have not been earlier detected in epoxy resin can-coatings.

Self-Sensing Nanocomposites for Structural Applications: Choice Criteria

Epoxy resins containing multi-wall carbon nanotubes (MWCNTs) have proven to be suitable for manufacturing promising self-sensing materials to be applied in the automotive and aeronautic sectors. Different parameters concerning morphological and mechanical properties of the hosting matrices have been analyzed to choose the most suitable system for targeted applications. Two different epoxy precursors, the tetrafunctional tetraglycidyl methylene dianiline (TGMDA) and the bifunctional bisphenol A diglycidyl ether (DGEBA) have been considered. Both precursors have been hardened using the same hardener in stoichiometric conditions. The different functionality of the precursor strongly affects the crosslinking density and, as a direct consequence, the electrical and mechanical behavior. The properties exhibited by the two different formulations can be taken into account in order to make the most appropriate choice with respect to the sensing performance. For practical applications, the choice of one formulation rather than another can be performed on the basis of costs, sensitivity, processing conditions, and most of all, mechanical requirements and in-service conditions of the final product. The performed characterization shows that the nanocomposite based on the TGMDA precursor manifests better performance in applications where high values in the glass transition temperature and storage modulus are required.

Vegetable Oil-Based Thiol-Ene/Thiol-Epoxy Resins for Laser Direct Writing 3D Micro-/Nano-Lithography

The use of renewable sources for optical 3D printing instead of petroleum-based materials is increasingly growing. Combinations of photo- and thermal polymerization in dual curing processes can enhance the thermal and mechanical properties of the synthesized thermosets. Consequently, thiol-ene/thiol-epoxy polymers were obtained by combining UV and thermal curing of acrylated epoxidized soybean oil and epoxidized linseed oil with thiols, benzene-1,3-dithiol and pentaerythritol tetra(3-mercaptopropionate). Thiol-epoxy reaction was studied by calorimetry. The changes of rheological properties were examined during UV, thermal and dual curing to select the most suitable formulations for laser direct writing (LDW). The obtained polymers were characterized by dynamic-mechanical thermal analysis, thermogravimetry, and mechanical testing. The selected dual curable mixture was tested in LDW 3D lithography for validating its potential in optical micro- and nano-additive manufacturing. The obtained results demonstrated the suitability of epoxidized linseed oil as a biobased alternative to bisphenol A diglycidyl ether in thiol-epoxy thermal curing reactions. Dual cured thermosets showed higher rigidity, tensile strength, and Young’s modulus values compared with UV-cured thiol-ene polymers and the highest thermal stability from all prepared polymers. LDW results proved their suitability for high resolution 3D printing—individual features reaching an unprecedented 100 nm for plant-based materials. Finally, the biobased resin was tested for thermal post-treatment and 50% feature downscaling was achieved.

Spatial inhomogeneity, interfaces and complex vitrification kinetics in a network forming nanocomposite

A detailed calorimetric study on an epoxy-based nanocomposite system was performed employing bisphenol A diglycidyl ether cured with diethylenetriamine as the polymer matrix and a taurine-modified MgAL layered double hydroxide as the nanofiller.