Structural performance of alkali/acid‐ultrasound modified Agave fibers during the melt mixing process with polyvinyl alcohol

Abstract

This study aims to investigate changes in the structural properties of alkali/acid‐ultrasound modified Agave fibers and their performance immersed on a polyvinyl alcohol (PVA) matrix with plasticizer during melt mixing processing. Structural analysis revealed that ultrasound enhances the effectiveness of the conventional alkaline/acid treatments to modify fibers since the simultaneous treatment increased the partial removal of lignocellulosic components, water molecules, and amorphous regions which improved their processability on a PVA matrix. Specific energy consumption values indicated that during melt mixing the modified fibers required more energy to expose the chains of cellulose fraction to function as an interaction site for PVA chains. Once the mixture was homogenized, the fiber‐matrix interactions promoted high viscosity, friction, and mechanical stress in the chamber. Therefore, the modified fibers restricted the interaction between plasticizer and PVA in the obtained films, resulting in a highly structured, and reinforced network, increasing the storage modulus as dynamic mechanical analysis indicated. These findings highlight a feasible way to valorize Agave fibers and allow the understanding of the matrix‐fiber interactions during melt mixing processing, useful to predict the structural and mechanical properties of the films.

Effect of treatment type of natural fibers on the rheological and micromechanical behavior of polyvinyl alcohol composites

“…According to Figure 3a, the unmodified Agave fibers increase the shear stress necessary for the material to flow, corroborating that the fiber hinders the mobility of the polymer chain segments. However, the shear stress decreases by incorporating AFSA and AFPH as an effect of better compatibility between the fiber and the polymer since the fiber treatment promotes their engagement with the matrix, holding the adjacent chains more separated from the plasticizer 15 . This effect is more noticeable in those composites containing modified fibers by ultrasound or dual treatment (Figure 3b), verifying high fiber‐polymer interactions; thus, lower shear stress is required for the materials to flow.…”

“…Acid and alkali treatments were performed following the methodology reported by Sifuentes‐Nieves et al 15 Briefly, Agave fibers (AF) were immersed in a stearic acid (AFSA) or potassium hydroxide (AFPH) for 12 h. Next, AF, AFSA, and AFPH fibers were sonicated (AFU, AFSAU, and AFPHU) using an Ultrasonic Processor (Cole‐Parmer, CPX750) at 20 kHz and 40%amplitude for 30 min, rinsed with water, and dried at 90°C for 12 h.…”

“…The composite blends were prepared by melt mixing PVA (20 g) and glycerol (10 g) for 3 min in a 75 cm 3 plasticorder mixing chamber (Brabender) with CAM rotors at 200°C and 60 rpm. Subsequently, 20 g of Agave fiber was added to the chamber and mixed with the polymer‐plasticizer blend 15 . Then, the compression molding method was used to prepare square sheets of 150 × 150 × 1 mm 3 in a PHI press operated at 210°C and 25 t of pressure.…”

Effect of interface on elastic and toughening behavior in poly lactic acid/thermoplastic starch blends: Micromechanical finite element analysis

“…A key to success of FEA micromechanics models is the accuracy to predict the real physical behavior of materials, making use of the correct boundary conditions that mimic the deformation of the material at the microscale 21 . In this regard, micromechanics‐based FEA makes it easier to study systematically the influence of the microstructure on the mechanical behavior of heterogeneous materials and describes the degree of interfacial adhesion realistically, whereas it circumvents some limitations of the analytical formulations 22–28 . By using micromechanics‐based FEA, the different phases (matrix and foreign inclusion), morphology, and interface strength of heterogeneous materials, such as polymer blends, can be modeled, approximating the microstructure as a unit cell (UC).…”

“…In the UC approach, one inclusion is embedded into the matrix to represent a periodic array of the microstructure 29 . To model the interface, the bonding between the inclusion and the matrix can be assumed to be either perfect or imperfect, according to the constitutive law of a spring element introduced to define the interphase 28 . The UC is subject to boundary conditions that mimic uniform tensile deformation, and then the macroscopic response of the material (i.e., elastic modulus) is predicted based on Hooke's law after averaging the stress and strain over the UC 29 .…”