In this work, biocomposites made of polyhydroxyalkanoates (PHA) with natural fibers were produced via compression molding. In particular, polyhydroxybutyrate (PHB) and ...polyhydroxybutyrate‐co‐hydroxyvalerate (PHBV) were reinforced with 20 wt% of agave fibers. Different compatibilization strategies were investigated to improve the fiber‐matrix interaction: fiber surface treatment in PHA solution, fiber surface treatment in maleated PHA solution, fiber propionylation, and extrusion with maleated PHA. The biocomposites were characterized in terms of morphology, mechanical properties, water absorption, and biodegradability by CO2 production tracking. In general, fiber propionylation was the best strategy for mechanical properties enhancement and water uptake decreasing. Biocomposites with propionylated fibers showed improved flexural strength (170% for PHB and 84% for PHBV). The flexural modulus was also enhanced with propionylated fibers up to 19% and 18% compared to uncompatibilized biocomposites (PHB and PHBV, respectively). Tensile strength increased by 16% (PHB) and 14% (PHBV), and the water absorption was reduced using propionylated fibers going from 6.6% to 4.4% compared with biocomposites with untreated fibers. Most importantly, the impact strength was also improved for all biocomposites by up to 96% compared with the neat PHA matrices. Finally, it was found that the compatibilization did not negatively modify the PHA biodegradability.
A simplified procedure to synthesize zwitterionic cellulose by means of N-protected aspartic anhydride under mild conditions was developed. The preparation of modified cellulose samples was carried ...out under heterogeneous, aqueous conditions by reacting NH
OH-activated cellulose with aspartic anhydrides N-protected with trifluoroacetyl (TFAc) and carbobenzyloxy (Cbz). Modified cellulose samples Cel-Asp-N-TFAc and Cel-Asp-N-Cbz were characterized by Fourier Transform Infrared (FTIR) and
C solid state Nuclear Magnetic Resonance (NMR) spectroscopy. The functionalization degree of each cellulose sample was determined by the
C NMR signal integration values corresponding to the cellulose C1 vs. the Cα of the aspartate residue and corroborated by elemental analysis. In agreement, both analytical methods averaged a grafting degree of 20% for Cel-Asp-N-TFAc and 16% for Cel-Asp-N-Cbz. Conveniently, Cel-Asp-N-TFAc was concomitantly partially N-deprotected (65%) as determined by the ninhydrin method. The zwitterion character of this sample was confirmed by a potentiometric titration curve and the availability of these amino acid residues on the cellulose was inspected by adsorption kinetics method with a 100 mg L
cotton blue dye solution. In addition, the synthesis reported in the present work involves environmentally related advantages over previous methodologies developed in our group concerning to zwitterionic cellulose preparation.
A hybrid silica mesoporous material with l-glutathione (LG) (SG-LGPS) was synthesized by a modified sol–gel process. The chemical and structural characterization of the SG-LGPS material was achieved ...by Fourier transform infrared, solid-state 13C and 19Si NMR, and X-ray diffraction. Surface analysis showed a specific surface area of 466.8 m2 g–1. X-ray photoelectron spectroscopy and energy dispersive X-ray spectrometry measurements demonstrated the chemical composition of the hybrid material and the presence of As(V) after the uptake process. The adsorption performance for SG-LGPS reached a maximum arsenic uptake of 45.22 mg g–1 at pH = 4; kinetics and equilibrium results were better described by the pseudo-second-order and Temkin models, respectively. Competitive ion adsorption studies were also performed. The uptake mechanism proposed for this material is a bidentate arsenic–glutathione complex. The present material proposed is as follows: (1) a new scope for environmentally friendly materials with amino acids and (2) a versatile adsorption application extended to other heavy metal ions due to the LG functional group composition.
Biopolymers are biodegradable and renewable and can significantly reduce environmental impacts. For this reason, biocomposites based on a plasticized starch and cross-linker matrix and with a ...microfibrillated OCC cardboard cellulose reinforcement were developed. Biocomposites were prepared by suspension casting with varied amounts of microfibrillated cellulose: 0, 4, 8, and 12 wt%. Polyethylene glycol diglycidyl ether (PEGDE) was used as a cross-linking, water-soluble, and non-toxic agent. Microfibrillated cellulose (MFC) from OCC cardboard showed appropriate properties and potential for good performance as a reinforcement. In general, microfiber incorporation and matrix cross-linking increased crystallization, reduced water adsorption, and improved the physical and tensile properties of the plasticized starch. Biocomposites cross-linked with PEGDE and reinforced with 12 wt% MFC showed the best properties. The chemical and structural changes induced by the cross-linking of starch chains and MFC reinforcement were confirmed by FTIR, NMR, and XRD. Biodegradation higher than 80% was achieved for most biocomposites in 15 days of laboratory compost.
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•Zwitterionic cellulose was prepared by grafting anionic and cationic groups.•The functionalized polysaccharide exhibited removal versatility to different ionic dyes.•Zwitterionic ...moieties increases the dye removal capacity up to 14-fold.•The novel sorbent demonstrated promising features for dye adsorption in mixtures.
This work aimed to develop zwitterionic cellulose with a versatile potential for removing anionic and cationic dyes. A grafting degree of 22% in a 3:2 ratio of the anionic and cationic groups was determined by elemental analysis. Spectroscopic characterization by carbon 13 Nuclear Magnetic Resonance (13C NMR) confirmed the zwitterionic functionalization of cellulose. Removal tests showed that zwitterionic cellulose could interact with different dyes (Congo red, Crystal violet, Mordant blue 9, Malachite green, Xylidine ponceau, and Reactive black 5), achieving from 2 to 14-fold of removal at tested conditions.
Bacterial cellulose (BC) samples were obtained in a static culture of K. xylinus under the effect of a low-intensity magnetic field, UV light, NaCl, and chloramphenicol. The effect of such stimuli on ...the amount of BC produced and its production rate, specific area, pore volume, and pore diameter were evaluated. The polysaccharide production was enhanced 2.28-fold by exposing K. xylinus culture to UV light (366 nm) and 1.7-fold by adding chloramphenicol (0.25 mM) to the medium in comparison to BC control. All the stimuli triggered a decrease in the rate of BC biosynthesis. BC membranes were found to be mesoporous materials with an average pore diameter from 21.37 to 25.73 nm. BC produced under a magnetic field showed the lowest values of specific area and pore volume (2.55 m2 g−1 and 0.024 cm3 g−1), while the BC synthesized in the presence of NaCl showed the highest (15.72 m2 g−1 and 0.11 cm3 g−1). FTIR spectra of the BC samples also demonstrated changes related to structural order. The rehydration property in these BC samples is not mainly mediated by the crystallinity level or porosity. In summary, these results support that BC production, surface, and structural properties could be modified by manipulating the physical and chemical stimuli investigated.
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•Novel L-cysteine hybrid adsorbent prepared by sol–gel route used in As(V) removal.•High As(V) uptakes by adsorbent and fast adsorption kinetics obtained.•Low loss of As(V) removal ...capacity demonstrated after reuse cycles.•A bidentate complex of AsO2(OH)2- and L-cysteine helped explain As(V) uptake data.•As(V) adsorption results suggest potential industrial use.
An L-cysteine functionalized environmentally friendly adsorbent was synthesized via sol–gel processing and applied in the removal of As(V) from aqueous media. The adsorbent demonstrated enhanced As(V) uptake capacities with maximum uptake of 147.5 mg g−1 at pH 3. Equilibrium was reached at 120 min. Kinetic data were explained by a pseudo-second order model; isotherm data were fitted by a Freundlich model. Reuse of adsorbent after 5 adsorption/desorption cycles indicated ∼23% removal capacity loss. Elemental analysis results indicated high ligand densities of SG-3PS-Cys. The L-cysteine moieties were thermally stable up to ∼170 °C. Solid state NMR and XPS techniques confirmed the presence of cysteine on the surface of SG-3PS-Cys. Efficient adsorption of As(V) was ensured by the formation of a bidentate complex between the AsO2(OH)2- anion, the NH3+ and carboxyl groups of L-cysteine. The results of this work demonstrated that SG-3PS-Cys possesses potential in the removal of As(V) from industrial wastewater discharges.
In this work, hexavalent chromium adsorption onto LDPE and agave fiber composites coated with chitosan or cellulose was studied in batch experiments. Chemical modifications consisting in cross-linked ...chitosan, cross-linked chitosan xanthate, and cellulose xanthate were applied to the polysaccharide-coated sorbents in order to increase their stability and adsorption capacity. The sorbents were characterized in terms of morphology by scanning electron microscopy and their chemical composition was evaluated by infrared and nuclear magnetic resonance spectroscopies. The results showed that the adsorption kinetics followed the pseudo-second-order model in all cases (i.e., chemisorption as the rate-limiting step of the adsorption reaction). Moreover, the isotherms evidenced a monolayer adsorption on homogeneous sites described by the Langmuir model. The maximum adsorption capacity of 284.7 mg Cr(VI)/g was obtained for the cross-linked chitosan xanthate sorbent at pH 4 which represents an increase of 43% against the chitosan-coated sorbent (199.1 mg Cr(VI)/g). Besides, functionalized cellulose sorbent also increased its capacity from 84.5 to 106.0 mg Cr(VI)/g cellulose due to the xanthate group. Up to six adsorption-desorption cycles were completed for the case of functionalized chitosan sorbent, confirming that the stability was increased with the cross-linking and the material could be reused several times without losing its adsorption capacity. In the case of cellulose xanthate, only three adsorption cycles were completed. However, improvements were observed in the desorption capacity considering that it decreased below 20% after two cycles in the cellulose-coated sorbent.
The present work inspects the preparation of bio-composites of cassava starch with particles of eucalyptus wood through the application of a novel method of thermal compression. Bio-composites with ...different amounts of wood particles (5 to 30%), with particle sizes of 4 and 8 mm, were obtained. Chemical and mechanical evaluation of these samples was carried out using optical microscopy, infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and the moisture absorption effect. The effect of the amount and size of the wood particles was tested by comparison with a thermoplastic matrix sample. Results from these evaluations demonstrated that the thermo-compression method produced bio-composites with a distribution of particles in the matrix that contributed to an increase in their tensile strength. This mechanical property is also enhanced by interfacial adhesion between the matrix and particles, as confirmed by SEM. Furthermore, the maximum amount of particles in the bio-composites (30%) showed the maximum resistance to moisture absorption. Temperature and time parameters contributed to the formation of diffraction patterns VH and EH as a consequence of the structural disruption of native starch. Finally, FTIR showed the chemical compatibility between the starch, glycerol, and wood particles.
In this work, agave fibers were surface treated using maleated PLA (MAPLA) in order to increase the fiber content (from 10 up to 40% wt.) in polylactic acid (PLA) biocomposites produced by rotational ...molding and to study the effect of the agave fiber and its treatment on the physical, mechanical and thermal properties of the biocomposites. This chemical modification between agave fibers and MAPLA was evaluated by FTIR spectroscopy. In general the results indicate that MAPLA surface treatment produces a more homogeneous morphology with lower interfacial gaps and overall porosity, especially at higher agave contents. This improved compatibility promoted better stress transfer leading to increased mechanical properties. For example, the tensile strength and modulus of treated fiber composites increased by up to 68% (from 25 to 41 MPa) and 32% (from 1.30 to 1.74 GPa) respectively, in comparison with untreated fiber composites. Fiber surface treatment also decreases hydrophilicity, lowering water absorption and diffusion coefficient. From thermo–mechanical analyses, the damping behavior of the biocomposites decreased with MAPLA treatment since a stronger interface is able to sustain higher stresses and dissipates less energy. Finally, the thermal stability was also improved as a result of better interfacial chemical bonding leading to a 12 °C increase in thermal stability (from 254 to 266 °C).
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