Pseudoplastic behavior of melaleuca oil Pickering Emulsions stabilized with nanocellulose

Pseudoplastic behavior of melaleuca oil Pickering Emulsions stabilized with nanocellulose

• Autor
• Greiciele Da Silva Ferreira
• Co-autores
• Daniel José da Silva , Derval dos Santos Rosa
• Resumo

• In recent years, surfactants have generated severe environmental problems, such as enzyme inhibition, water pollution, and difficulty in degradation, among others. Nanocellulose fibers (CNF) are biopolymers with reactive hydroxyl groups in their structures and bending characteristics due to their length/width ratio (L/W). CNF, when placed in an emulsion system, acts as an emulsifier, giving stability to the system by steric hindrance, making it difficult for droplets to coalesce (CNF reference). Cellulose nanofibrils (CNF) are natural polymers with a high potential to replace synthetic stabilizers.

  Rheological evaluations of Pickering emulsions help assess the final characteristics of products because most procedures in cosmetics production depend on the flow of this material to define formulations, material packaging, storage, and process parameters (pumping, mixing time, rotation). This study investigates the rheological behavior of Pickering emulsions of Melaleuca alternifolia oil (MaEO) stabilized with CNF. The internal structure, diameter variations, and distributions over 30 days under static conditions were analyzed using small amplitude oscillatory shear. A CNF dispersion was prepared using high-intensity ultrasound (Sonics Vibra Cell, 400W power, 24 KHz) for 2 minutes. Then, the MaEO oil was added to the CNF solution and homogenized with a Turrax, model IKA T25 (IKA Werke, Staufen, Germany). The Pickering emulsion was made with the following parameters: CNF content (1% w/v) or (0.5% w/v), O/W ratio (30%v/v) and (20% v/v), homogenization speed (15,000 rpm and 12,000 rpm) and mixing time (5 or 7 min). The emulsion was designated XEO/YT/ZCNF/WRPM, where X corresponds to the MaEO content (% v/v), Y is the mixing time (min), Z is the CNF concentration (% wt/v), and W is the mixing speed (rpm).

  The O/W emulsions were submitted to rheological measurements using an MCR-501 rheometer (Anton Paar, Austria), using a concentric cylinder geometry (specifications: body diameter=24.001 mm; body length=25.005 mm; inner cup diameter=40mm; active length=103.5 mm; positioning length=72.5 mm).

  Emulsion systems are complex because they depend on numerous process variables. Two emulsions with process parameters with slight differences have been analyzed: (1) 30OE/5T/0.5CNF/15RPM and (2) 20EO / 5T / 0.5CNF / 12RPM. The steady-state shear viscosity (?) showed a shear-thinning fluid behavior. In this sense, the (?) decreases as the shear rate (? ?) increases because of the internal structure-breaking processes of the Pickering emulsion of MaEO/CNF. This behavior is based on the literature due to intermolecular interactions with low levels of energetic resistance. 

   The fragmentation of the internal structure of the emulsion includes the collapse of oil droplets, desorption of CNF, and phase aggregation accompanied by the orientation movement of oil droplets and CNF in the direction of the flow line . The steady-state shear viscosity with a shear thinning behavior has a favorable point on the cosmetic base in the sense of functional performance, such as creams, gels, lotions, and foams.

  The linear viscoelastic domain of the oscillatory strain scanning tests exhibits the cohesive force of an internal multiphase structure. Multiphase systems show a nonlinear viscoelastic response when their three-dimensional structure (network entanglement formed by the CNF) breaks down. The cohesive energy density (E_c) was determined to investigate the energy resistance of the emulsions to rupture against mechanical shear stress. The critical storage modulus (G_c^') and the critical oscillation strain (?_c) were extracted from the storage modulus versus strain curves as indicated in the inset. Observing a difference in the internal structure according to the CNF content is possible. In this sense, the network entanglements are undone, leading to the desorption of CNF at the droplet interface. However, a difference in the behavior of the two emulsions is noted when comparing the amount of CNF present in the systems.

   

   CNF was used to stabilize the Pickering emulsions with MaEO. It was observed that the amount of CNF used in the production of Pickering affects the internal structure of the emulsions. In this system, the smaller the amount of CNF used, the better it is for the system's stability. The rheologic tests indicate that the emulsions show a shear thickening behavior under oscillatory shear stress. However, the flow profiles of the emulsions do not obey the Cox-Merz rule since the emulsion shows a different flow behavior under steady state shear. Under mechanical shear stress, the relaxation processes are faster, and the elastic responses are slower in the emulsion due to the network entanglement.

• Palavras-chave
• Melaleuca oil, nanocellulose, Pickering Emulsion, Pseudoplastic behavior
• Modalidade
• Pôster
• Área Temática
• Nanociência e Nanotecnologia