Synthesis and characterization of chitosan/montmorillonite nanocomposites for application as edible coating.

Edible coating can improve fruits shelf life and, consequently, reduce their waste. Chitosan, which presents a potential for chemical modifications and capacity to form films, can be an alternative for coating due to its biocompatibility, biodegradability, and antimicrobial properties. Chitosan film can be obtained through casting method presenting suitable mechanical properties, such as resistance to traction and elongation, ability to adhere to surfaces and selective permeability to gases, such as O2 and CO2. However, it is highly permeable to water vapor, which can limit its potential coating use. The properties of chitosan films can be improved through the formation of composites by inserting nanoclays as montmorillonite in the polymeric matrix. The objective of this study was to develop and characterize chitosan/montmorillonite nanocomposites for fruit coating aiming for future applications in the field of smart packaging. Nanocomposites were characterized by its microstructure, thermal, mechanical, and physicochemical properties. X-ray diffraction analysis indicated changes in crystallinity with the insertion of montmorillonite. Nanocomposites became more transparent and significantly reduced its water permeability rate with 0.5% w/w montmorillonite addition. Elastic rigidity and tensile strength of the films were improved. Chitosan/montmorillonite nanocomposites demonstrated the potential to improve the storage time of Williams pears.

Biodegradability and nutrients release of thermoplastic starch and poly (ε-caprolactone) blends for agricultural uses.

Driven by the environmental stress caused by plastics, the interest on eco-friendly polymers has attracted the attention of researchers and industry. Thermoplastic starch (TPS) and poly (ε-caprolactone) (PCL) blends are good examples of sustainable material, exhibiting synergism between economic viability and properties. However, its biodegradability aligned to nutrients release has been less explored in agricultural applications. Herein, it is proposed the investigation of biodegradability of urea plasticized TPS and PCL blends, compatibilized with PCL grafted with maleic anhydride (PCL-g-MA), aiming fertilizers and sustainable agricultural products. The blends were prepared in a twin-screw extruder using a flat film die. The mechanical, thermal, morphological, and physical properties of TPS-PCL films were characterized, including biodegradation analysis via Bartha respirometer and nitrogen release in the soil. The films presented biodegradability and nitrogen release as a function of TPS content on blends formulation, presenting flexibility and robust mechanical properties. These findings may open a way of multifunctional agricultural products applied as fertilizer materials through economical and sustainable mulching films.

Effect of carboxymethyl cellulose concentration on mechanical and water vapor barrier properties of corn starch films.

The main objective of this study was to evaluate the effect of the addition of different concentrations of CMC (0, 20, 40, 60, 80 and 100 %) on the mechanical and water vapor barrier properties in corn starch films produced by casting. The addition of CMC 40 % was sufficient to significantly increase its mechanical properties (tensile strength, elongation at break and elastic modulus), and water vapor barrier of the starch films, thus improving its functionality as a packaging material for food. CMC incorporation led to a small reduction in the thermal stability of the films. CMC in low content dispersed well in the starch matrix, ensuring interaction between its constituents that formed a network structure, thus improving mechanical properties and making diffusion of water difficult.

Cellulose Nanocrystals from Fibers of Macauba (Acrocomia Aculeata) and Gravata (Bromelia Balansae) from Brazilian Pantanal.

Cellulose nanocrystals (CNC) were obtained from macauba and gravata fibers. Macauba (or Bocaiuva) is a palm tree found throughout most of Brazil and Gravata is an abundant kind of bromelia with 1-2m long leaves, found in Brazilian Pantanal and Cerrado. The raw fibers of both fibers were mercerized with NaOH solutions and bleached; they were then submitted to acid hydrolysis using H2SO4 at 45 °C, varying the hydrolysis time from 15 up to 75 min. The fibers were analyzed by X-ray diffraction (XRD), FTIR Spectroscopy, scanning electron microscopy (SEM) and thermal stability by thermogravimetric analysis (TG). XRD patterns did not present changes in the crystal structure of cellulose after mercerization, but it was observed a decrease of hemicellulose and lignin contents, and consequently an increase of cellulose content with the increase of NaOH solution concentration in the mercerization. After acid hydrolysis, the cellulose nanocrystals (CNC) were also analyzed by transmission electron microscopy (TEM) which showed an acicular or rod-like aspect and nanometric dimensions of CNC from both fibers, but the higher values of aspect ratio (L/D) were found on CNC obtained from gravata after 45 min of acid hydrolysis. The mercerization and subsequent bleaching of fibers influenced the crystallinity index and thermal stability of the resulting CNC, but their properties are mainly influenced by the hydrolysis time, i. e., there is an increase in crystallinity and thermal stability up to 45 min of hydrolysis, after this time, both properties decrease, probably due to the cellulose degradation by the sulfuric acid.

Corn and cassava starch with carboxymethyl cellulose films and its mechanical and hydrophobic properties.

The amylose and amylopectin content of starch influences its functional characteristics and its interaction with other materials. Thus, it is important to study the mechanical strength and hydrophilicity of starch films of different botanical origins to elucidate the influence of their constituents in the interaction with carboxymethyl cellulose (CMC). The objective of this work was to evaluate the mechanical and physico-chemical properties of corn and cassava starch films and their blends with CMC by casting. The addition of CMC improved the tensile, increasing the strength at 206% for its blends with corn starch and 51% for its blends with cassava starch, the rupture stress at 89% and 74%, respectively, and the rupture strain at 381% and 57%, respectively. The elastic modulus presented increase of 20% for corn starch/CMC and 18% for cassava starch/CMC and the water vapor permeability at 48 and 40%, respectively. The corn starch film was more hydrophobic due to its higher amylose content, which contributed to the interaction between starch and glycerol OH groups and CMC COOH groups. This interaction was evidenced by FTIR and contact angle analysis, turning corn starch/CMC films into less hydrophilic material and reducing its water vapor permeability rate, which made this material promising for several applications, including food packaging.

In vitro growth of Physalis peruviana L. affected by silver nanoparticles.

The effect of silver nanoparticles (AgNPs) on plant cells, since their phytotoxicity potential is not yet fully understood. In this context, the aim of the present study was to elucidate the effects of AgNPs in the in vitro culture of Physalis peruviana. For this purpose, P. peruviana seeds were grown in MS medium supplemented with different concentrations of AgNPs. Growth and development of seedlings were evaluated through germination, seedling size and biomass and biochemical and anatomical analyses. At the end of 60 days of cultivation, it was observed that the in vitro germination of this species is not affected by the presence of AgNPs and that at low concentrations (0.385 mg L-1) it can promote an increase in seedlings biomass. However, higher concentration (15.4 mg L-1) leads to a reduction in seedling size and root system, but no changes were observed in the seedlings antioxidant metabolism and anatomy. These results demonstrate that the phytotoxicity of AgNPs in P. peruviana is related to the concentration of nanoparticles to which the specie is exposed.

Curaua and eucalyptus nanofibers films by continuous casting: Mechanical and thermal properties.

A wide variety of new green materials such as curaua leaf fibers (CLFs) has potential applications in nanotechnology. This study aims to investigate the thermomechanical properties and morphological structure of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) films obtained by continuous casting. The CNCs were obtained by acid hydrolysis and CNFs by mechanical shearing from bleached CLFs and eucalyptus pulp. The morphology after continuous casting resulted in oriented nanofibers, and as a consequence there was mechanical anisotropy. CNCs films showed the greatest values of tensile strength (36±4MPa) and the more effective fibrillation provided better mechanical strength of eucalyptus CNFs films than curaua CNFs films. Sulfur groups and mechanical shear degradation affected the stability of CNCs and CNFs films, respectively. Thus, the type of nanostructure, the way they interact to each other, the cellulose source and the process interfere significantly on the properties of the films.

Solution blow spun nanocomposites of poly(lactic acid)/cellulose nanocrystals from Eucalyptus kraft pulp.

Cellulose nanocrystals (CNCs) were extracted from Eucalyptus kraft pulp by sulfuric acid hydrolysis, and esterified with maleic anhydride (CNCMA). The incorporation of sulfate ester groups on the cellulose surface resulted in higher stability of the nanoparticles in aqueous suspensions and lower thermal stability. Then, PLA/CNC and PLA/CNCMA nanocomposites were successfully obtained by solution blow spinning (SBS) using dimethyl carbonate (DMC) as solvent. CNC and CNCMA indicated to be acting both as nucleating agents or growth inhibitors of PLA crystal and tends to favor the formation of PLA crystals of higher stability. A fraction of the nanocrystals indicate to be exposed on the surface of the PLA fibers, since the hydrophilicity of the composite films increased significantly. Such composites may have potential application as filtering membranes or adsorbents.

Cytotoxic and genotoxic effects of silver nanoparticle/carboxymethyl cellulose on Allium cepa.

Several mutagenic agents may be present in substances released in the environment, which may cause serious environmental impacts. Among these substances, there is a special concern regarding the widespread use of silver nanoparticles (AgNP) in several products due to their widely known bactericidal properties, including in the medical field and the food industry (e.g., active packaging). The assessment of the effects of AgNP released in the environment, having different concentrations, sizes, and being associated or not to other types of materials, including polymers, is therefore essential. In this research, the objective was to evaluate the genotoxic and cytotoxic effects of AgNP (size range between 2 and 8 nm) on root meristematic cells of Allium cepa (A. cepa). Tests were carried out in the presence of colloidal solution of AgNP and AgNP mixed with carboxymethylcellulose (CMC), using distinct concentrations of AgNP. As a result, when compared to control samples, AgNP induced a mitotic index decrease and an increase of chromosomal aberration number for two studied concentrations. When AgNP was in the presence of CMC, no cytotoxic potential was verified, but only the genotoxic potential for AgNP dispersion having concentration of 12.4 ppm.

Biodegradable blends of urea plasticized thermoplastic starch (UTPS) and poly(ε-caprolactone) (PCL): Morphological, rheological, thermal and mechanical properties.

Biodegradable blends of urea plasticized thermoplastic starch (UTPS) and poly(ε-caprolactone) (PCL) were prepared in a co-rotating twin screw extruder. The UTPS and PCL content varied in a range of 25wt%. The materials were characterized by capillary rheometry, scanning electron microscopy (SEM), termogravimetry (TGA), differential scanning calorimetry (DSC) and tensile tests. Capillary rheometry showed better interaction between UTPS and PCL at 110°C than at 130°C. SEM showed immiscibility of all blends and good dispersion of UTPS in PCL matrix up to 50wt%. However, a co-continuous morphology was found for UTPS/PCL 75/25. Thermal analysis showed that introducing PCL in UTPS, increased Tonset due to higher thermal stability of PCL, and blends presented an intermediate behavior of neat polymers. The presence of PCL in blends improved significantly the mechanical properties of neat UTPS. Because they are totally biodegradable, these blends can be vehicles for controlled or slow release of nutrients to the soil while degraded.

Effect of replacement of corn starch by whey protein isolate in biodegradable film blends obtained by extrusion.

The aim of this study was to evaluate the effect of replacing corn starch by whey protein isolated (WPI) in biodegradable polymer blends developed by extrusion. X-ray diffraction showed the presence of a Vh-type crystalline arrangement. The films were homogeneous, indicating strong interfacial adhesion between the protein and the thermoplastic starch matrix (TPS) as observed in scanning electron microscopy. The addition of WPI on TPS matrix promoted an increase in the thermal stability of the materials. It was observed 58.5% decrease in the water vapor permeability. The effect of corn starch substitution by WPI on mechanical properties resulted in a more resistant and less flexible film when compared the TPS film. The addition of WPI caused greenish yellow color and less transparent films. The substitution of corn starch by WPI made it possible to obtain polymer blends with improved properties and represents an innovation for application as a packaging material.

Evaluation of reaction factors for deposition of silica (SiO2) nanoparticles on cellulose fibers.

This study aimed to evaluate reaction conditions for deposition of SiO2 nanoparticles on the surface of cellulose fibers and their influence on moisture adsorption of the hybrid organic-inorganic material formed. SiO2 nanoparticle deposition was carried out with the sol-gel process testing four reaction times (2, 12, 18, and 24h) and three contents of the tetraethyl-orthosilicate (TEOS) precursor (1.9, 4.2 and 8.4g g(-1) of cellulose fiber). Modification time and TEOS content directly influence the amount of Si deposited on the fiber surface, nanoparticle diameter distribution, thermal stability, and resistance to moisture adsorption. There is a tendency of slight increase of nanoparticle size and the amount of Si deposited with increasing reaction time. SiO2 nanoparticles were bonded on the surface of the cellulose fibers and are able to improve thermal stability of the material, increasing onset degradation temperature. The moisture adsorption capacity of the modified cellulose fiber was reduced up to 50%.