Graphene oxide crosslinker for the enhancement of mechanical properties of polylactic acid

Enhancing Structural and Thermal Properties of Poly(lactic acid) Using Graphene Oxide Filler and Anionic Surfactant Treatment

Graphene has attracted extensive attention in various fields due to its intriguing properties. In this work, nanocomposite films based on poly(lactic acid) (PLA and PLLA) polymers filled with graphene oxide (GO) were developed. The impact of treating GO with the anionic surfactant dioctyl sulfosuccinate sodium salt (AOT) on the properties of the resulting nanocomposites was investigated. To determine the morphological, optical, and structural properties of the obtained materials, physicochemical analyses were performed, including scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) analysis. Additionally, the thermal properties and wettability of neat polymers and nanocomposites were thoroughly investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and contact angle analysis. It was observed that GO was well dispersed throughout the PLA and PLLA matrix, leading to stronger interface bonding. The results demonstrate that the untreated and treated GO improved the crystallinity and thermal stability properties of the PLA and PLLA. However, the AOT-treated GO has significantly higher performance compared to the untreated GO in terms of crystallinity, melting temperature (increased by ~15 °C), and wettability (the contact angle decreased by ~30°). These findings reveal the high performance of the developed novel composite, which could be applied in tissue engineering as a scaffold.

Probing interaction forces associated with calcite scaling in aqueous solutions by atomic force microscopy

The prevention of calcite aggregation and scaling remains a challenging problem in aqueous based systems and environmental science. Decades of research studies have proposed microscopic mechanisms of aggregation control, but experiments at the nanoscale and molecular level are rarely conducted. Here we show that the nanoscale topographic features of calcite during its aggregation depend significantly on the intermolecular and surface forces involved in this process. By measuring the forces between a calcite or silica particle and a calcite surface in aqueous solutions using atomic force microscopy, we found that higher solution pH and inhibitor concentration and lower salinity resulted in a system of stronger repulsion and weaker adhesion, which is favorable for reducing the possibility of calcite aggregation and surface deposition. Conflicting roles of Mg²⁺ in calcite aggregation prevention, being positive in acidic pH and negative in alkaline pH, were also observed. The nanoscale structural changes of calcite, visualized by atomic force microscopy or scanning electron microscopy, indicated a size dependence of aggregated and deposited calcite crystals on the calcite-calcite and calcite-silica interactions, respectively. The generalized framework of the calcite aggregation mechanism achieved in this work can be extended to other types of systems and provides a basis for investigating the anti-aggregation strategy of calcite from industrial and environmental perspectives.

Effects of chemical inhibitors on the scaling behaviors of calcite and the associated surface interaction mechanisms

HYPOTHESIS

It is hypothesized that the performance of a chemical inhibitor to interfere with the precipitation and scaling of calcite (calcium carbonate, CaCO₃) is achieved through its chelating interaction with calcium ions. The effectiveness of a chemical inhibitor in removing existing scales from the mineral surfaces is proposed to rely on its ability to modify the calcite crystal structures.

EXPERIMENTS

Bulk scaling tests and dynamic adsorption experiments using a quartz crystal microbalance with dissipation monitoring were conducted to systematically investigate the scaling behaviours (i.e., buildup and breakup processes) of calcite crystals, in the absence and presence of chemical inhibitors, that include polyacrylic acid, sodium hexametaphosphate, 2-phosphonobutane-1,2,4-tricarboxylic acid, and diethylenetriamine penta(methylene phosphonic acid). Scanning electron microscope imaging and thermodynamic characterization using isothermal titration calorimetry were further applied to reveal the surface interactions that contributed to the differences among the effects of the four additives.

FINDINGS

The results indicate that sodium hexametaphosphate is most efficient in alleviating the amount of CaCO₃ deposited by reducing the concentration of free Ca²⁺, and diethylenetriamine penta(methylene phosphonic acid) shows an outstanding ability to clean the mineral surface by destroying the ordered crystal layers of the scales so that they can be washed away with water. This work provides useful insights into the fundamental interactions of chemical inhibitors and calcite, with implications for the development of effective chemical solutions for anti-scaling and descaling applications.

Graphene Oxide and Biomolecules for the Production of Functional 3D Graphene-Based Materials

Graphene and its derivatives have been widely employed in the manufacturing of novel composite nanomaterials which find applications across the fields of physics, chemistry, engineering and medicine. There are many techniques and strategies employed for the production, functionalization, and assembly of graphene with other organic and inorganic components. These are characterized by advantages and disadvantages related to the nature of the specific components involved. Among many, biomolecules and biopolymers have been extensively studied and employed during the last decade as building blocks, leading to the realization of graphene-based biomaterials owning unique properties and functionalities. In particular, biomolecules like nucleic acids, proteins and enzymes, as well as viruses, are of particular interest due to their natural ability to self-assemble via non-covalent interactions forming extremely complex and dynamic functional structures. The capability of proteins and nucleic acids to bind specific targets with very high selectivity or the ability of enzymes to catalyse specific reactions, make these biomolecules the perfect candidates to be combined with graphenes, and in particular graphene oxide, to create novel 3D nanostructured functional biomaterials. Furthermore, besides the ease of interaction between graphene oxide and biomolecules, the latter can be produced in bulk, favouring the scalability of the resulting nanostructured composite materials. Moreover, due to the presence of biological components, graphene oxide-based biomaterials are more environmentally friendly and can be manufactured more sustainably compared to other graphene-based materials assembled with synthetic and inorganic components. This review aims to provide an overview of the state of the art of 3D graphene-based materials assembled using graphene oxide and biomolecules, for the fabrication of novel functional and scalable materials and devices.

Graphene oxide based crosslinker for simultaneous enhancement of mechanical toughness and self-healing capability of conventional hydrogels

Extraordinary self-healing efficiency is rarely observed in mechanically strong hydrogels, which often limits the applications of hydrogels in biomedical engineering. We have presented an approach to utilize a special type of graphene oxide-based crosslinker (GOBC) for the simultaneous improvement of toughness and self-healing properties of conventional hydrogels. The GOBC has been prepared from graphene oxide (GO) by surface oxidation and further introduction of vinyl groups. It has been designed in such a way that the crosslinker is able to form both covalent bonds and noncovalent interactions with the polymer chains of hydrogels. To demonstrate the efficacy of GOBC, it was incorporated in a conventional polyacrylamide (PAM) and polyacrylic acid (PAA) hydrogel matrix, and the mechanical and self-healing properties of the prepared hydrogels were investigated. In PAM-GOBC hydrogels, it has been observed that the mechanical properties such as tensile strength, Young's modulus, and toughness are significantly improved by the incorporation of GOBC without compromising the self-healing efficiency. The PAM-GOBC hydrogel with a modulus of about 0.446 MPa exhibited about 70% stress healing efficiency after 40 h. Whereas, under the same conditions a PAM hydrogel with commonly used crosslinker N,N'-methylene-bis(acrylamide) of approximately the same modulus demonstrated no self-healing at all. Similar improvement of self-healing properties and toughness in PAA-GOBC hydrogel has also been observed which demonstrated the universality of the crosslinker. This crosslinker-based approach to improve the self-healing properties is expected to offer the possibility of the application of commonly used hydrogels in many different sectors, particularly in developing artificial tissues.

Utilization of lignin upon successive fractionation and esterification in polylactic acid (PLA)/lignin biocomposite

The study presents the preparation of novel biocomposites based on different lignin fractions and polylactic acid (PLA). The lignin was extracted from pine residue using deep eutectic solvent (DES) and was subjected to fractionation with ethanol and acetone as well as esterification modification with succinic anhydride (SAn). Different lignin fractions were characterized and analyzed, while lignin-based biocomposites were prepared by melt injection. The results showed that lignin molecular weight was inversely proportional to the phenolic hydroxyl content and positively proportional to the alcohol hydroxyl group. The mechanical properties of the composites were also significantly affected by different molecular weights of lignin, indicating that the non-homogeneity of lignin affects its value-added utilization. In contrast to other performances of composites, the flexural and impact strengths of the materials prepared by acetone extracted lignin (AL) were improved by 18.2% and 28%, respectively, while the antibacterial properties against Staphylococcus aureus were up to 95%. The enhanced mechanical properties, antibacterial effect, and steady biocompatibility provide potential possibilities for lignin-based composites in biomedical applications.