Insights into the effect of carboxylated cellulose nanocrystals on mechanical and barrier properties of gelatin films for flexible packaging applications.

In this study, gelatin/carboxylated cellulose nanocrystal (cCNC) bionanocomposite films were developed as an eco-friendly alternative to non-biodegradable flexible plastic packaging. Cellulose nanocrystals were modified by 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation (cCNC) to strategically interact with amino groups present in the gelatin macromolecular backbone. Gelatin/cCNC bionanocomposite films (0.5-6.0 wt% cCNC) obtained by solution casting were transparent to visible light while displayed high UV-blocking properties. The chemical compatibility between gelatin and cCNC was deepened by electrostatic COO-/NH3+ interactions, as detected by FTIR spectroscopy and morphologically indicated by scanning electron microscopy (SEM). Accordingly, Young's modulus and tensile strength of films were largely increased by 80 and 64 %, respectively, specifically near the cCNC percolation threshold (4 wt%), whereas the water vapor permeability (WVP) was reduced by 52 % at the optimum 6.0 wt% cCNC content in relation to the non-reinforced gelatin matrix (0.10 vs. 0.18 g H2O mm m-2 h-1 kPa-1). The oxygen transmission rates (OTR) of the gelatin/cCNC bionanocomposites were < 0.01 cm3 m-2 day-1, making them technically competitive to most promising biopolymers like polycaprolactone (PCL) and poly(lactic acid) (PLA). This study reveals how TEMPO-oxidized cellulose nanocrystals can broaden the performance of biodegradable gelatin films for use in packaging. The gelatin/cCNC bionanocomposites also represent an effective approach for designing newly sustainability-inspired flexible materials from the surface modification of nanocelluloses targeting specific interactions with protein structures.

Eco-friendly gelatin films with rosin-grafted cellulose nanocrystals for antimicrobial packaging.

We report on gelatin films incorporating rosin-grafted cellulose nanocrystals (r-CNCs), which fulfill the most relevant requirements for antimicrobial packaging applications. Transparent gelatin/r-CNCs bionanocomposite films (0.5-6 wt% r-CNCs) were obtained by solution casting and displayed high UV-barrier properties, which were superior to the most used plastic packaging films. The gelatin/r-CNCs films exhibited a moderate water vapor permeability (0.09 g mm/m2 h kPa), and high tensile strength (40 MPa) and Young's modulus (1.9 GPa). The r-CNCs were more efficient in improving the optical, water vapor barrier and tensile properties of gelatin films than conventional CNCs. Grafting of rosin on CNCs resulted in an antimicrobial nanocellulose that inhibited the growth of Staphylococcus aureus and Escherichia coli. The antibacterial properties of r-CNCs were sustained in the gelatin films, as demonstrated by agar diffusion tests and proof-of-principle experiments involving cheese storage. Overall, the incorporation of r-CNCs as active fillers in gelatin films is a suitable approach for producing novel eco-friendly, antimicrobial packaging materials.

Scaled-up production of gelatin-cellulose nanocrystal bionanocomposite films by continuous casting.

In this study, continuous casting is proposed as a suitable approach to scale up the production of gelatin-cellulose nanocrystals (CNCs) bionanocomposites. The processing conditions and bionanocomposite properties were established based on the ζ-potential and gelatin content, and CNCs concentration, respectively. Gelatin film-forming solution at 20 wt% was required for proper continuous casting processing, leading to a productivity of 0.20 m2 film/min, which was at least 1000-fold higher than that of the classical bench casting. The gelatin-CNCs bionanocomposites displayed transparency, flexibility, and improved UV-barrier and thermal properties. Adding only 0.5 wt% of CNCs resulted in an increase of 77 % and 48 % in the tensile strength and Young's modulus of gelatin, respectively. Comparison with previous nanocellulose-based nanocomposites pointed out the relatively superior performance of the gelatin-CNCs bionanocomposites obtained by continuous casting for various applications, including flexible food packaging.

Alginate films functionalized with silver sulfadiazine-loaded [Mg-Al] layered double hydroxide as antimicrobial wound dressing.

Alginate (ALG) is an abundant, biocompatible, regenerative, and nontoxic polysaccharide that has potential applications in tissue engineering. Silver sulfadiazine (SDZ) is a topical antibiotic used to control bacterial infection in burns. Aiming to combine the intrinsic alginate characteristics and silver sulfadiazine antimicrobial properties, hydrotalcite ([Mg-Al]-LDH) was used as a host matrix to obtain a system efficient in delivering SDZ from alginate films. SDZ was successfully intercalated in [Mg-Al]-LDH through structural reconstruction. Different solutions were prepared using sodium alginate at 10 wt%, glycerol at 10 wt% as a plasticizer and [Mg-Al]-LDH and [Mg-Al]-LDH/SDZ as fillers at 1 wt% and 5 wt%. Films were obtained by continuous casting and further characterized for their microstructural, mechanical, water barrier and antimicrobial properties. Cytotoxicity tests were also performed on fibroblasts cells. The incorporation of [Mg-Al]-LDH and [Mg-Al]-LDH/SDZ presented neither negative nor positive effects on the mechanical properties and morphology of the alginate films. Moreover, samples containing SDZ exhibited inhibitory activity against S. aureus, E. coli, and S. enterica. The addition of [Mg-Al]-LDH/SDZ even at the highest concentration did not afford a very significant cytotoxicity to the alginate-[Mg-Al]-LDH/SDZ films. These results describe a suitable approach for preparing innovative active wound dressings integrated to efficient drug delivery.

Rheological and thermo-mechanical evaluation of bio-based chitosan/pectin blends with tunable ionic cross-linking.

Bio-based chitosan/pectin blend films were prepared by solution casting and fully characterized in terms of their viscoelastic, thermo-mechanical and water affinity properties. Dynamic light scattering and rheological analyses served as a probe that polyelectrolyte complexes were formed through COO-/NH3+ ionic cross-linking, changing the chitosan/pectin solutions from Newtonian to pseudoplastic gel-like systems. The highest degree of ionic cross-linking has been found at a specific mass ratio (chitosan/pectin 25/75) and solid-state data were obtained in detail using dynamic mechanical thermal analysis. Ionic cross-linking was determining on the physical properties of chitosan/pectin blends, which was demonstrated by the thermo-mechanical spectra, high water contact angle and tensile strength of films. The specific thermo-mechanical properties of the chitosan/pectin films can be specifically modulated according to the chitosan/pectin mass ratio to ensure successfully applications in medicine, drug delivery, agricultural and food coatings.

Bionanocomposites produced from cassava starch and oil palm mesocarp cellulose nanowhiskers.

Cassava starch films reinforced with cellulose nanowhiskers from oil palm mesocarp fibers were produced by casting. Nanowhiskers were obtained by sulphuric acid hydrolysis followed by microfluidization and incorporated in starch films at various loadings (1-10wt%). Morphological and mechanical characterizations showed that the reinforcing effect of oil palm cellulose nanowhiskers was significant at loadings of up to 6wt%, which was determined to be the nanowhiskers percolation threshold. Above this content, formation of agglomerates became more significant, causing a decrease in mechanical properties of starch bionanocomposites. Below percolation threshold, such as 2wt%, elongation at break increased by 70%, showing an effective reinforcing effect. Dynamic mechanical analyses revealed filler/matrix interactions through hydrogen bonding in bionanocomposites.

Hydrophobic edible films made up of tomato cutin and pectin.

Cutin is the biopolyester that protects the extracellular layer of terrestrial plants against dehydration and environmental stresses. In this work, cutin was extracted from tomato processing waste and cast into edible films having pectin as a binding agent. The influences of cutin/pectin ratio (50/50 and 25/75), film-forming suspension pH, and casting method on phase dispersion, water resistance and affinity, and thermal and mechanical properties of films were investigated. Dynamic light scattering and scanning electron microscopy revealed that cutin phase aggregation was reduced by simply increasing pH. The 50/50 films obtained by casting neutral-pH suspensions presented uniform cutin dispersion within the pectin matrix. Consequently, these films exhibited lower water uptake and solubility than their acidic counterparts. The cutin/pectin films developed here were shown to mimic tomato peel itself with respect to mechanical strength and thermal stability. Such behavior was found to be virtually independent of pH and casting method.

Nutraceutically inspired pectin-Mg(OH)2 nanocomposites for bioactive packaging applications.

This paper reports on the development of bioactive edible films based on pectin as a dietary matrix and magnesium hydroxide (Mg(OH)2) nanoplates as a reinforcing filler. Nanocomposites of high-methoxyl (HM) and low-methoxyl (LM) pectins were prepared using the casting method at concentrations of Mg(OH)2 ranging from 0.5 to 5 wt %. Atomic force microscopy and FTIR spectroscopy were employed to characterize the nanocomposite structure. The tensile properties and thermal stability of the nanocomposites were also examined to ascertain the effect of Mg(OH)2 inclusion and degree of methoxylation. The results provided evidence that the Mg(OH)2 nanoplates were uniformly dispersed and interacted strongly with the film matrix. The mechanical and thermal properties were significantly improved in the nanocomposite films compared to the control. Mg(OH)2 nanoplates were more effective in improving properties of LM pectin. Preliminary migration studies using arugula leaves confirmed that pectin-Mg(OH)2 nanocomposites can release magnesium hydroxide by contact, demonstrating their potential for magnesium supplementation in bioactive packaging.

Brucite nanoplates reinforced starch bionanocomposites.

In this paper the mechanical reinforcement of nano-sized brucite, Mg(OH)(2) in a series of bionanocomposite films based on starch was investigated. Brucite nanoplates with an aspect ratio of 9.25 were synthesized by wet precipitation and incorporated into starch matrices at different concentrations (0-7.5 wt.%). Scanning electron microscopy revealed a high degree of nanoplate dispersion within the starch bionanocomposites and good interfacial adhesion between the filler and matrix. The brucite nanoplates formed agglomerates at high concentrations. The reinforcement factor values of the bionanocomposites were higher than the values predicted from the Halphin-Tsai model, which was attributed mainly to the high surface area of the nanoplates. Brucite (1 wt.%) nearly doubled the elastic modulus of starch films. Thermogravimetric analyses indicated some interaction between starch and the brucite that modified their decomposition profiles. Mechanical tests of glycerol plasticized bionanocomposites showed that the reinforcing efficiency of brucite remained high even at 10 wt.% and 20 wt.% of plasticizer.