Chitosan-based films reinforced with cellulose nanofibrils isolated from Euterpe oleraceae MART

Abstract

The use of local raw materials for the production of biodegradable films can simultaneously contribute to the development of the Amazon and global sustainability. This work aimed to evaluate the physical and mechanical performance of chitosan-based bionanocomposite films reinforced with different loads of cellulose nanofibrils obtained from açaí (Euterpe oleraceae Mart.) under two nanofibrillation degrees. Nanofibrils were obtained by 3 and 21 passages in a grinder defibrillator. The films were produced by casting with nanofibril reinforcement at 5 wt.%, 10 wt.%, 15 wt.%, and 20 wt.%. The increase in the nanofibril level and nanofibrillation degree reduced water vapor absorption (75.20% to 51.93%), water solubility (28.33% to 17.91%), and density (0.87 g.cm⁻³ to 0.61 g.cm⁻³). The water vapor permeability decreased with higher nanofibril loads for both 3-pass (47.30% to 43.61%) and 21-pass (49.82% to 44.48%) reinforced films, but not with nanofibrillation degree. The increase in 3-pass nanofibril level decreased tensile strength (8.18 MPa to 7.88 MPa), modulus of elasticity (867.62 MPa to 670.02 MPa) and elongation at break (0.02 mm.mm⁻¹ to 0.01 mm.mm⁻¹). However, the opposite effect happened to 21-pass nanofibrils, with increases from 9.16 MPa to 9.73 MPa and from 502.00 MPa to 1119.62 MPa for tensile strength and modulus of elasticity, respectively. Meanwhile, the maximum elongation at rupture did not vary. It was concluded that chitosan-based bionanocomposite films reinforced with 20 wt.% of 21-pass nanofibril were more resistant, except for water vapor permeability. Adding coarser nanofibrils enhanced this property. The 3-pass nanofibrils reinforcement enables water solubility, which benefits other packaging applications.

Keywords

Açaí lignocellulosic fibers bionanocomposites biodegradable polymer thermoplastic polymer

Introduction

Oil-derived polymers have been widely used for many decades as a result of the low production cost, excellent thermal and mechanical properties, and easiness to make products of varied shapes, colors, and sizes.^1
-3 On the other hand, the incorrect disposal of these materials has severe impacts on ecosystems, since most of them are not biodegradable, remaining for a long time in the environment. Besides, the impending scarcity of oil resources has stimulated the development of polymers from other sources.⁴

In this context, biodegradable polymers have gained considerable attention in the academy and industry in recent decades.¹ These, however, are not necessarily from renewable sources; hence, studies have been focused on biopolymers that have, among other characteristics, biodegradability and are primarily from natural renewable sources.⁴ Biopolymers are materials that undergo biological degradation under specific conditions.⁵ They can derive from many natural sources, for example, lipids, proteins, and polysaccharides, among which chitosan and cellulose are promising options.

Chitosan is a linear polysaccharide that contains copolymers of D-glucosamine (deacetylated units) and N-acetyl-D-glucosamine (acetylated units) linked by β (1→4) glycosidic bonds. It is obtained from the partial deacetylation of chitin. The physicochemical properties depend on the proportion of these two units in the polymer chain.^6,7 This polysaccharide finds many applications in agriculture, medicine, and wastewater treatment. Its useful properties include biocompatibility, non-toxicity, biodegradability, and antimicrobial and antioxidant activities. Besides, chitosan can form gels, films, nanofibers, nanofibrils, microparticles, and nanoparticles.⁸ On the other hand, chitosan-based materials are challenging to process and show overall poor physical and mechanical properties, such as fragility, low permeability, and thermal deformation, factors that limit their application. Improvements in their functional properties can be achieved through the formulation of bionanocomposites, with cellulose nanofibers as reinforcements.^5,9

Cellulose nanofibers have been researched for decades due to their unique optical, rheological, and mechanical properties.⁹ They can be obtained by chemical and mechanical procedures. In the chemical method, acid hydrolysis under controlled conditions leads to highly crystalline structures, called cellulose nanocrystals or nanowhiskers. The mechanical techniques form nanofibrils through the mechanical disintegration of cellulose pulps using homogenization at high pressure, intense refining, rectification, ultrasound, among others.^10,11

Nanofibrils, therefore, are fibrillar units resulting from the linear combination of cellulose macromolecules containing both amorphous and crystalline regions of cellulose, with the ability to form tangled networks interconnected by hydrogen bonds.^9,12 The large surface areas of nanometric reinforcements applied in polymeric matrixes provide nanocomposites with improved performance compared to conventional composites.^13
-15 Better dispersion in the matrix is another advantage of nano-sized reinforcements.⁹ The addition of cellulose nanofibers to chitosan-based biocomposites provided improvements in the mechanical, physical, and thermal properties. Also, these films are promising as antimicrobial agents.^16

-19

Among the available lignocellulosic fibers for nanofibril production in the Amazonia, residues from the açaí (Euterpe oleracea Mart.) production chain raise particular interest. Açaí is a resource of immeasurable cultural, social, and economic importance for the local population.²⁰ Natural rubber composites reinforced with açaí mesocarp fibers showed mechanical properties similar to those produced with other natural fibers.²¹ The açaí fibers ensured in starch-based composites, an increase in thermal stability²² since they were resistant up to 230°C with a three-stage degradation process. This behavior is similar to the commonly observed for natural fibers already used in the industry, for example, sisal and coconut fibers.^23
-25 Short açaí fibers at 7 wt.% reinforcing the matrix of PLA (polylactic acid) and pine resin improved the mechanical properties of biocomposites.²⁶

To date, there are no studies on the application of açaí nanofibrils in chitosan-based composites. The fiber of the fruit’s mesocarp has excellent properties, mainly regarding their large pits and highly porous structure after extraction of the silicon-containing structures.²⁷ Still, improvements are expectable with their reduction to the nanoscale. A practical application of chitosan-cellulose composites is the processing of highly resistant films with excellent biocompatibility, biodegradability, and hydrophilicity.¹⁰ Thus, this work aimed to evaluate the physical and mechanical performance of chitosan-based bionanocomposite films reinforced with different loads of cellulose nanofibrils obtained from açaí (Euterpe oleraceae Mart.) under two nanofibrillation degrees.

Material and methods

Materials

The reagents used in the bioassays were sodium hydroxide PA (98%, Dinâmica, Brazil), hydrogen peroxide PA (35%, Dinâmica, Brazil), and acetic acid USP (100%, Synth, Brazil).

Bunches containing the fruits were collected from Euterpe oleracea Mart. palms. A local producer of São Miguel do Guamá (Latitude: 1° 37′ 40″ South; Longitude: 47° 28′ 55″ West), located in the Amazon state Pará, Brazil, processed the Açaí fruits using an electric beater to obtain the pulp and provided de-pulping wastes. The Açaí waste was continuously washed to remove pulp traces and dried at room conditions (∼27°C and 83% RH). The mesocarp fibers were handily separated from the seeds.

Production of cellulose nanofibrils

The fibers were immersed in distilled water for 24 h. The alkali pre-treatments were carried out with a fiber to solution proportion of 1/100 (w: v) to remove non-cellulosic components and promote fiber individualization from the bundles. The fibers were immersed in an aqueous solution of sodium hydroxide at 5% (w: w) under mechanical stirring (∼500 rpm) after the reaction temperature of 80°C was reached and kept for 2 h. The alkalized fibers were then washed with distilled water until neutral pH. Alkali pre-treated fibers were kept in water until saturation and then vigorously stirred at 18,000 rpm to increase chemical attack efficiency. An aqueous solution of NaOH at 4% and H₂O₂ at 24% mixed at 1:1 (v:v) proportion was prepared to bleach the alkali pre-treated fibers, which were added at a ratio of 1 g to 80 mL of solution.

Two bleaching steps were carried out to remove residual lignin from the surface of the isolated fibers. They were performed at 60°C for 2 h for the first time (Bc_1×2 h) and 3 h for the second time (Bc_2×3 h) under mechanical stirring at 4,000 rpm. The solution was then continuously removed with distilled water until reaching a neutral pH. Bleached fibers were dried at 50°C for 48 h.

For nanofibril production, the starting bleached fibers were immersed in 1,557 mL of distilled water (including the fiber moisture content) at a 1.5% (w:v) consistency. The fibers were immersed for 72 h for swelling of the cell walls.²⁸ Every 24 h, the fiber suspension was submitted to mechanical stirring at 700 rpm for 30 min. An additional stirring was performed immediately before nanofibrillation. Cellulose nanofibrils were obtained by mechanical nanofibrillation using a Supermasscolloider model MKCA6-2 J (Masuko Sangyo Co. Ltd.®, Japan) grinder at 1,500 rpm^28
-30 with an energy efficiency of 10,914 kWh ton⁻ ¹. The gap between the aluminum oxide stones in the grinder was adjusted to ±50 µm. The suspension was passed through the grinder 21 times, and the electric current consumed was kept at 6 A. The minimum number of cycles to form films was three (3), indicating some nanofibrillation occurred. In contrast, the highest number of cycles (21) was the maximum number, after which the suspension presented too high viscosity to allow more cycles.³¹ The 3-pass and 21-pass samples were collected to produce the chitosan-based composites reinforced with cellulose nanofibrils.

Scanning electron microscopy (SEM) of all-cellulose films

Detailed characterization of 3-pass and 21-pass all-cellulose films are reported elsewhere.³² In this work, they were used only for morphological analyses to attest different nanofibrillation degrees. The SEM micrographs of the surface and sides of 3-pass and 21-pass all-cellulose films were obtained in a scanning electron microscope TM3030PLUS model (HITACHI®) with a voltage of 15 kV. The samples were placed on double-sided carbon adhesive tapes previously fixed on aluminum sample holders (stubs).

Preparation of bionanocomposites films

The chitosan-based films reinforced with cellulose nanofibrils were formed by the solvent evaporation method (casting). The film solution was prepared according to Zhong et al.³³ with some adaptations: 2.0 g of chitosan were dissolved in a solution of acetic acid at 0.5% (v/v). The polysaccharide remained immersed for 2 hours. Afterward, the solution went under mechanical stirring for 2 h at room temperature. The 3-pass and 21-pass cellulose nanofibrils were added at 5 wt.%, 10 wt.%, 15 wt.%, and 20 wt.%, based on chitosan dry mass (Table 1). The mixtures were stirred for 30 min using a mechanical stirrer, and every 30 mL solution filled 8 cm diameter Petri dishes to form the films. Drying lasted approximately 7 days at room temperature of 26°C and relative air humidity of 85%, Belém (Pará, Brazil) conditions.³⁴

Table 1.

Concentration of cellulose nanofibrils (CN) produced by different passages in grinder in the matrix of chitosan.

Number of passage in grinder	CN (%)	Identification
3	5 wt.%	3P_5%
	10 wt.%	3P_10%
	15 wt.%	3P_15%
	20 wt.%	3P_20%
21	5 wt.%	21P_5%
	10 wt.%	21P_10%
	15 wt.%	21P_15%
	20 wt.%	21P_20%

Physical properties of films

Three specimens of each film kind were cut with a 3 cm-diameter, previously dried at 70°C for 24 h, and subsequently weighed. The water vapor absorption (WVA) test was performed in a controlled environment at 19°C and 100% RH, in a desiccator, according to ASTM E104-02.³⁵ Samples were weighed after 1, 2, 3, 4, 5, 48, 72, and 96 h. WVA was estimated according to the next equation:

W V A = (\frac{M c - M i}{M i}) 100

where WVA is the water vapor absorption (%), Mc is the current mass (g), and Mi is the dry mass (g).

The water solubility (WS) of the films was determined following Gontard et al.³⁶ in 2 cm-diameter circular specimens. Triplicates were evaluated for each film type. The initial dry mass was obtained after drying at 55 ± 2°C for 24 h. The samples were immersed in 40 mL of distilled water for 24 h at room temperature. The resulting suspensions were filtered, dried at 105°C for 24 h, and weighed. The solubility of films was calculated as follows:

W S = (\frac{M d - M s}{M d}) 100

where WS is the water solubility (%), Ms is the non-solubilized mass (g), and Md is the initial dry mass (g).

The water vapor permeability rate and water vapor permeability of the films were determined in duplicates by gravimetric parameters according to ASTM E96-00³⁷ and literature.^38,39 Circular specimens of 1.05 cm of diameter were cut with steel molds and placed in amber glass with 3/4 of its volume containing silica gel (desiccant), with particle size ranging from 1 to 4 mm, previously dried in an oven at 150°C for 24 h. The recipient’s dimensions were 1.5 cm of top diameter, 5.8 cm of length, and 2.6 cm of base diameter. The covers had a height and diameter of 1.8 cm and 20 cm, respectively. They were perforated at the top with the same dimensions of the glass permeation area. The specimens were placed between the glass and cover.

The specimens were kept in an environment with zero water activity. The recipients were placed in sealed desiccators at environment temperature (30 ± 2°C) filled with 800 mL of water, giving 0.1 atmospheric water activity in contact with the upper surface of the specimens. Weighing the specimen at a precision of 0.0001 g every 24 h for 7 days gave the mass gain.

The water vapor permeability rate (WVPR) of the films was estimated using linear regression between mass gain and time (24 h) per area, as showed below. The slope of the linear part of the curve represented the amount of water vapor diffusion through the specimen per unit time. After determining the saturated vapor pressure of water (sp), water vapor permeability (WVP) was calculated by the following equations:

W V P R = (\frac{g}{T x A}) 100

s p = 0.6108 e^{\frac{17.27 T}{T + 237.3}}

W V P = \frac{W V P R t}{(\frac{s p R H}{100} - \frac{s p R H i}{100})}

where WVPR is the water vapor permeability rate (g.h⁻ ¹.m⁻ ²), g/T is the slope of the line obtained by linear regression of mass gain (g) to conditioning time (h), A is the permeation area of each specimen (m²), sp is the saturated vapor pressure of water at the test temperature of 30°C (KPa), T is the conditioning temperature (20°C) of the desiccator containing cells with films and distilled water, WVP is the water vapor permeability (g.mm.KPa⁻ ¹.day⁻ ¹.m⁻ ²), t is the thickness of the specimen (mm), RH is the relative humidity inside the desiccator containing distilled water (100%), and RHi is the relative humidity (%) inside the glass containing white silica equals to 0%.

The density of the films was determined by the ratio between their mass (weighted with a precision of 0.0001 g) and volume in the dry condition (at 100°C until constant mass). The thickness of the films was measured by a digital pachymeter of 150 mm, while the diameters were obtained with a ruler (0.1 cm-precise). Diameter and thickness provided the sample’s volume. The density was calculated as follows:

D = \frac{m}{v}

where D is the density (g.cm⁻ ³), m is the mass (g), and v is the volume (cm³).

Mechanical tensile strength of bionanocomposites

The mechanical strength tests were carried out using a universal testing machine model WDW 100E (AROTEC®, China). Analyses were performed according to ASTM D882-12.⁴⁰ The samples’ nominal dimensions were 10 ± 2 mm in width, 100 ± 10 mm in length, and 0.10 ± 0.08 mm in thickness. Six replicates of films were tested for each biocomposite type. The distance between the jaws, the test velocity, and the maximum load of the equipment was 80 mm, 0.5 mm.s⁻ ¹, and 196,133 N, respectively. The modulus of elasticity (MOE) was determined from the coefficient of the linear slope of the stress-strain curves. The maximum tensile strength (σ_max) and elongation at break (∊brk) were calculated according to the following equations:

σ_{max} = \frac{F}{A}

ε b r k = \frac{Lbrk}{d}

where σmax is the maximum tensile strength (MPa), F is the maximum force applied to the specimen (N), A is the first area of the specimen (mm²), ∊brk is the elongation at break (mm.mm⁻1), Lbrk is sample length at break (mm), and d is the distance between the jaws (80 mm).

Results and discussion

SEM micrographs show an inferior nanofibrillation degree, rougher surface, and entire fibers of the 3-pass all-cellulose films (Figure 1(a)). On the other hand, 21 passages favored the mechanical disintegration of the fibers resulting in smooth and uniform films (Figure 1(b)).

Figure 1.

SEM micrographs of (a) 3-pass and (b) 21-pass all-cellulose films.

Long and poorly nanofibrillated fragments are not uncommon in nanofibril suspensions.⁴¹ However, more passages in the grinder lead to all-cellulose films with increased density and a more compact structure due to size reduction of the nanofibril fragments, higher specific area, and more inter-cellulose hydrogen bonds.⁴² Such differences are likely to influence the performance of the reinforced composites.⁴³

The bionanocomposite films reinforced with 3-pass cellulose nanofibrils showed an increasing WVA until 96 h, with remarkable raise intensity after 5 h. The increase in the proportion of cellulose nanofibrils provided a reduction in WVA (Figure 2).

Figure 2.

Water vapor absorption of chitosan-based bionanocomposites reinforced with 3-pass nanofibrils during 96 h.

WVA of the films reinforced with 21-pass nanofibrils followed the same behavior observed for films reinforced with 3-pass nanofibrils. However, a subtle drop from 72 to 96 h occurred for all treatments. Besides, the values of films with 10 wt.% and 15 wt.% nanofibril levels approximated after 72 h. The 21-pass nanofibrils provided composites with slightly less absorption capacity than 3-pass nanofibrils (Figure 3).

Figure 3.

Water vapor absorption of chitosan-based bionanocomposites reinforced with 21-pass nanofibrils during 96 h.

Regardless of the nanofibrillation degree, the increase in the cellulose nanofibril level provided a reduction in WVA. Thus, the chitosan matrix is supposedly more hydrophilic than the açaí nanofibrils. WVA in bionanocomposites can result from the hydrophilicity of the components of the films (matrix and reinforcement). However, despite the water affinity of OH groups, cellulose nanofibrils can be useful in promoting water barrier resistance in hydrophilic matrices, such as alginate and starch. The explanation is the strong hydrogen bonds between the nanofibrils and the matrix, which improves the material cohesion.⁴⁴ Lopes et al.⁴⁵ produced carrageenan and starch-based nanocomposites reinforced with 10 wt.%, 20 wt.%, and 30 wt.% of eucalyptus cellulose nanofibrils. The authors noted that nanofibril addition at 30% to carrageenan-starch blend decreased WVA and improved the physical strength of films for packaging purposes.

The increases in the nanofibril level and degree of defibrillation consistently reduced the WS of the films. Bionanocomposites produced with 3-pass and 21-pass nanofibrils showed similar behaviors concerning WVP. The variations in 21-pass nanofibril content above 10 wt.% did not change the WVP. Raising the cellulose nanofibril level decreased the thickness and raised the density of bionanocomposites reinforced with 3-pass and 21-pass nanofibrils up to 15 wt.%. This property decreased when the nanofibril level raised from 15 wt.% to 15 wt.% (Table 2).

Table 2.

Water solubility (WS), water vapor permeability (WVP), and density of chitosan-based bionanocomposites reinforced with açaí nanofibrils.

Bionanocomposites	WS (%)	WVP (%)	Thickness (cm)	Density (g.cm⁻³)
3P_5%	28.33 ± 0.40	47.30 ± 0.87	0.025 ± 0.004	0.86 ± 0.03
3P_10%	28.01 ± 4.40	45.81 ± 2.40	0.016 ± 0.001	0.87 ± 0.02
3P_15%	27.14 ± 0.52	41.87 ± 1.32	0.014 ± 0.001	0.94 ± 0.03
3P_20%	20.06 ± 0.52	43.61 ± 1.77	0.017 ± 0.001	0.83 ± 0.01
21P_5%	21.07 ± 4.25	49.82 ± 0.28	0.023 ± 0.001	0.47 ± 0.02
21P_10%	20.43 ± 10.61	45.88 ± 1.80	0.017 ± 0.002	0.46 ± 0.05
21P_15%	19.44 ± 0.30	45.67 ± 0.26	0.016 ± 0.001	0.63 ± 0.09
21P_20%	17.91 ± 0.25	44.48 ± 0.14	0.017 ± 0.001	0.55 ± 0.01

The overall increase of film density by raising nanofibril loads is likely explained by the higher density of cellulose nanofibrils than the chitosan matrix’s density combined with the substantial reduction in the film thickness. Carrageenan and starch composites reinforced with cellulose nanofibrils exhibited a similar trend.⁴⁵ The slight decrease of film density found for 20%-reinforced composites is unlikely explained by a void occurrence since their WVA and WVP reduced compared to 5%-reinforced biocomposites. The aggregation of excessive nanofibrils when the load was raised from 15 wt.% to 20 wt.% possibly slightly raised film thickness and decreased density.

Cortez-Vega et al.⁴⁶ analyzed corvine protein-based biofilms and found a similar WS range of 18.10% to 27.60%. This property establishes the application of biofilm as packaging for food products. In some cases, its total solubilization in water can be beneficial, for example, for semi-finished products for preparation by cooking without package removal. However, when the food is liquid or exudes an aqueous solution, biofilms with this characteristic are not acceptable.⁴⁷

Deng et al.⁴⁸ observed that the incorporation of chitosan by immersion significantly reduced WVA in all-nanofibril films explained by the interaction between chitosan and cellulose nanofibrils, which reduced the number of hydroxyl groups available. Films made by adding 20 g and 10 g of chitosan for each 100 g of cellulose nanofibrils showed both lower WVA and WS. In another study, to verify the effect of the addition of cellulose nanofibrils from the pineapple leaf on the properties of bionanocomposite films of jícama starch (Pachyrhizus erosus) using ultrasound methodology, Mahardika et al.⁴⁹ observed that the addition of different concentrations (0.5; 1.0; 1.5 and 2.0%) resulted in lowest WVA and WVP.

Dutta et al.⁵⁰ observed lower WVP in bionanocomposites based on poly (N-isopropyl acrylamide) -g-guar gum and reinforced with cellulose nanofibrils compared to the neat polymer. Ahmadi et al.⁵¹ added cellulose nanofibrils in the carboxymethyl cellulose matrix and observed a decrease of the WVP of the bionanocomposites. In this case, the formation of new inter-nanofibrils and nanofibrils-matrix hydrogen bonds hindered the adsorption and diffusion of water vapor.

The WVP directly relates to the film’s thickness,⁵² which is difficult to control using the casting method.⁵³ Denser bionanocomposites (3P_5% and 21P_5%) were also thinner films, which can be explained by the higher chitosan proportion based on the total mass. Regarding the degree of defibrillation, bionanocomposites reinforced with 3-pass nanofibrils are denser. The progressive decrease in the size of the 21-pass nanofibrils caused an increase in their specific area and volume,^54,55 and consequently, in the film thickness. WVP is an important quality parameter for materials destined for food packaging since the susceptibility to chemical action or bacterial decomposition causes insecurity, especially for edible products.⁵⁶

The tensile strength and the MOE varied among the formulations of bionanocomposites. Films reinforced with 21-pass nanofibrils at 20 wt.% load showed the maximum values (21P_20%). However, the increase in cellulose nanofibrillation provided bionanocomposites with less elongation (Table 3).

Table 3.

Mechanical properties of chitosan-based bionanocomposites reinforced with açaí nanofibrils.

Bionanocomposites	Tensile strength (MPa)	∊brk (mm.mm⁻¹)	MOE (MPa)
3P_5%	8.18 ± 1.77	0.02 ± 0.00	867.62 ± 230.30
3P_10%	8.04 ± 0.69	0.02 ± 0.00	681.98 ± 192.50
3P_15%	9.64 ± 1.23	0.02 ± 0.00	681.33 ± 131.20
3P_20%	7.88 ± 0.86	0.01 ± 0.00	670.02 ± 275.85
21P_5%	9.16 ± 0.95	0.01 ± 0.00	502.27 ± 254.35
21P_10%	8.17 ± 1.76	0.01 ± 0.00	458.60 ± 140.33
21P_15%	6.49 ± 0.08	0.01 ± 0.00	687.20 ± 416.15
21P_20%	9.73 ± 1.14	0.01 ± 0.00	1119.92 ± 782.25

Eventually, irregular distribution and dispersion of nano-reinforcements in the matrix impair the nanocomposite properties.^57,58 Medeiros et al.⁵⁹ stated that property variations are related to surface defects of the biocomposites that occur during processing, leading to premature flaws or cracks in their morphology.

Despite nanofibrillation degree, increases in nanofibril levels led to variations in tensile strength. The literature reports that the addition of nanofibrils should be up to 5 wt.% to improve tensile strength and MOE.^51,60 The interaction between the cellulose reinforcement and the chitosan matrix, both polysaccharides, guarantees strong surface adhesion and inter-chain hydrogen interactions.⁶¹ Besides, the high aspect ratio of nanofibrils improves tension strength since adequate tension transference from the matrix to the reinforcement occurs.^62,63

For 3-pass nanofibrils, the maximum recommended level to ensure the highest MOE is 5 wt.%. From this concentration on, this property decreased. Stable and strong interfacial adhesion requires nanofibrils homogeneously dispersed and correctly arranged in the matrix,⁶⁴ which is achieved by lower concentrations. Agglomeration is likely to occur at higher levels, decreasing the reinforcement effectiveness and reducing mechanical properties.

On the other hand, MOE of films reinforced with 21-pass nanofibrils beyond 10 wt.% increased. This result is possibly related to a higher crystalline index of the better-disintegrated nanofibrils after 21 passages.³² Regarding elongation at rupture, a decrease is observed for loads above 15 wt.% when 3-pass nanofibrils were applied. According to Khan et al.,⁶¹ matrix-nanofibrils interaction decreases matrix fluidity, making films rupture earlier. All bionanocomposites reinforced with 21-pass nanofibrils showed the same elongation at break.

The low flexibility affects the range of packaging applications of chitosan-based films reinforced with cellulose nanofibrils. The shape of rigid (e.g., glass and metal) and semi-rigid (e.g., paper and board) packages are not readily changed for wrapping objects. However, they can be precisely pre-molded into a wide range of shapes, such as boxes and bags. Besides suitable barrier properties, rigid packages are useful to protect the contents from physical damage during transport and distribution.⁶⁵

Conclusion

Chitosan-based bionanocomposite films reinforced with açaí mesocarp nanofibrils were successfully produced. The increase in the nanofibrillation degree mostly improved density and water uptake properties, but fewer passages in the grinder provided a better barrier to water vapor. Progressive increases in nanofibril loads consistently improve water resistance performance of the materials but decreased density.

The highest nanofibrillation degree and reinforcement load also optimize mechanical strength; hence, chitosan-based bionanocomposites produced with 21-pass nanofibrils at 20 wt.% are suitable as semi-rigid packaging for the protection of meat, fruits, vegetables, and other products from moisture and physical damage. However, future studies to improve water vapor permeability are recommended. If the primary requirement for packaging applications is lower water vapor permeability, 3-pass nanofibrils should be preferred. In this case, 15 wt.% and 5 wt.% loads prioritize tensile strength and MOE, respectively.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research and publication of this article: This work was supported by the National Council for Scientific and Technological Development/CNPq (research project’s process number 431553/2016-5, public call CNPq Universal 2016), and Coordination for the Improvement of Higher Level Personnel (CAPES) with scholarships and partnership project sponsor (project’s process number 88881.199859/2018-01, public call PROCAD/Amazônia 2018).

ORCID iD

L Bufalino

References

Motloung

Ojijo

Bandyopadhyay

, et al. Cellulose nanostructure-based biodegradable nanocomposite foams: a brief overview on the recent advancements and perspectives. Polymers 2019; 11: 1270.

Andrady

Neal

. Applications and societal benefits of plastics. Philos Trans R Soc Lond B Biolog Sci 2009; 364: 1977–1948.

Reddy

CSK

Ghai

Kalia

. Polyhydroxyalkanoates: an overview. Bioresource Technol 2007; 87: 137–186.

Corsello

Bolla

Anbinder

, et al. Morphology and properties of neutralized chitosan-cellulose nanocrystals biocomposite films. Carbohyd Polym 2017; 156: 452–459.

Rong

Mubarak

Tanjung

. Structure-property relationship of cellulose nanowhiskers reinforced chitosan biocomposite films. J Environ Chem Eng 2017; 5: 6132–6136.

Alvarenga

. Characterization and Properties of Chitosan. In: Elnashar

(ed) Biotechnology of biopolymers, 1st ed. Viçosa: InTech, 2011, pp. 91–108.

Hamed

Özogul

Regenstein

. Industrial applications of crustacean by-products (chitin, chitosan, and chitooligosaccharides): a review. Trends Food Sci Technol 2016; 48: 40–50.

Knidri

Belaabed

Addaou

, et al. Extraction, chemical modification and characterization of chitin and chitosan. Int J Biol Macromol 2018; 120: 1181–1189.

Abdul Khalil

HPS

Chaturbhuj

Adnan

, et al. A review on chitosan-cellulose blends and nanocellulose reinforced chitosan biocomposites: properties and their applications. Carbohyd Polym 2016; 150: 216–226.

10.

Nechyporchuk

Belgacem

Bras

. Production of cellulose nanofibrils: a review of recent advances. Indust Crops Products 2016; 93: 2–25.

11.

Potulski

Viana

Muniz

GIB

, et al. Characterization of fibrillated cellulose nanofilms obtained at different consistencies. Sci Forestalis 2016; 44: 361–372.

12.

Eichhorn

Dufresne

Aranguren

, et al. Review: current international research into cellulose nanofibers and nanocomposites. J Mater Sci 2010; 45: 1–33.

13.

Seydibeyoglu

Oksman

. Novel nanocomposites based on polyurethane and micro fibrillated cellulose. Compos Sci Technol 2008; 68: 908–914.

14.

Suh

Lim

Park

OOK

. The property and formation mechanism of unsaturated polyester-layered silicate nanocomposite depending on the fabrication methods. Polymer 2000; 41: 8557–8563.

15.

Lebaron

Wang

Pinnavaia

. Polymer-layered silicate nanocomposites: an overview. Appl Clay Sci 1999; 15: 1–2.

16.

Szyman´ska-Chargot

Chylin´ska

Pertile

, et al. Influence of chitosan addition on the mechanical and antibacterial properties of carrot cellulose nanofibre film. Cellulose 2019; 26: 9613–9629.

17.

Fernandes

SCM

Freire

CSR

Silvestre

AJD

, et al. Transparent chitosan films reinforced with a high content of nanofibrillated cellulose. Carbohyd Polym 2010; 81: 394–401.

18.

Dehnad

Mirzaei

Emam-Djomeh

, et al. Thermal and microbial properties of chitosan-nanocellulose films for extending shelf life of ground meat. Carbohyd Polym 2014; 109: 148–154.

19.

Falamarzpour

Behzad

Zamani

. Preparation of nanocellulose reinforced chitosan films, cross-linked by adipic acid. Int J Mol Sci 2017; 18: 396.

20.

Almeida

Melo

Pinheiro

, et al. Appreciation of acai core of a pulp producer from Ananindeua/PA: proposal of reverse channel structure oriented by NPSW and reverse logistics. Revista Gestão da Produção Operações e Sistemas 2017; 12: 59–83.

21.

Pessoa

JDC

Teixeira

GHDA

. Tecnologias para inovação nas cadeias euterpe, 1st ed. Brasília: EMBRAPA, Brasília, 2012. 343p.

22.

Kennedy

. Studies on the properties of natural fibers-reinforced thermoplastic starch composites. Carbohyd Polym 2005; 62: 19–24.

23.

Martins

Mattoso

LHC

Pessoa

JDC

. Thermogravimetric evaluation of açaí fruit (Euterpe oleracea Mart.) agro industry waste. Rev Brasil Frutic 2009; 31: 1150–1157.

24.

Chand

Sood

Singh

, et al. Structural and thermal studies on sisal fiber. J Ther Analy 1987; 32: 595–599.

25.

Varma

. Thermal-behavior of coir fibers. Thermochim Acta 1986; 108: 199–210.

26.

Santos

Silva

Alves

. Reinforcement of a biopolymer matrix by lignocellulosic agro-waste. Proced Eng 2017; 200: 422–427.

27.

Oliveira

DNPS

Claro

PIC

Freitas

, et al. Enhancement of the Amazonian açaí waste fibers through variations of alkali pretreatment parameters. Chem Biod 2019; 16: 1–12.

28.

Dias

Mendonça

Damásio

RAP

, et al. Influence of hemicellulose content of Eucalyptus and Pinus fibers on the griding process for obtain cellulose micro/nanofibrils. Holzforschung 2019; 73: 1035–1046.

29.

Tonoli

GHD

Holtman

Glenn

, et al. Properties of cellulose micro/nanofibers obtained from eucalyptus pulp fiber treated with anaerobic digestate and high shear mixing. Cellulose 2016; 23: 1239–1256.

30.

Scatolino

Silva

Bufalino

, et al. Influence of cellulose viscosity and residual lignin on water absorption of nanofibril films. Proced Eng 2017; 200: 155–161.

31.

Iwamoto

Nakagaito

Yano

. Nano-fibrillation of pulp fibers for the processing of transparent nanocomposites. Appl Phys A 2007; 89: 461–466.

32.

Braga

DG.

Tratamento químicos das fibras do mesocarpo de açaí para a produção de filmes de nanocelulose e nanocompósito de quitosana. Master Dissertation, Universidade Federal Rural da Amazônia, Brazil, 2019.

33.

Zhong

Song

. Antimicrobial, physical and mechanical properties of kudzu starchchitosan composite films as a function of acid solvent types. Carbohyd Polym 2011; 84: 335–342.

34.

Alves

OS.

Zoneamento bioclimático da mesorregião metropolitana de Belém e influência do clima na modernização da avicultura no Estado do Pará. PhD Thesis, Universidade Federal Rural da Amazônia, Brazil, 2006.

35.

ASTM E104:2002. Standard practice for maintaining constant relative humidity by means of aqueous solutions. West Conshohocken, PE: ASTM.

36.

Gontard

Duchez

Cuq

, et al. Edible composite films of wheat gluten and lipids: water vapour permeability and other physical properties. Inter J Food Sci Technol 1994; 29: 39–50.

37.

ASTM E96-00:2000. Standard test methods for water vapor transmission of materials. West Conshohocken, PE: ASTM.

38.

Bourtoon

Chinnan

. Preparation and properties of rice starch/chitosan blend biodegradable film. LWT Food Scie Technol 2008; 41: 1633–1641.

39.

Guimarães Junior

Development of bionanocomposites using bamboo cellulosic nanofibers as reinforcing agent in starch matrix and polyvinyl alcohol. PhD Thesis, Universidade Federal de Ouro Preto, Brazil, 2015.

40.

ASTM D882-12:2012. Standard test method for tensile properties of thin plastic sheeting. West Conshohocken, PE: ASTM.

41.

Siró

Plackett

. Microfibrillated celulose and new composite materials: a review. Cellulose 2010; 17: 459–464.

42.

Zimmermann

Bordeanu

Strub

. Properties of nanofibrillated cellulose from different raw materials and its reinforcement potential. Carbohydr Polym 2010; 79: 1086–1093.

43.

Damasio

RA.

Caracterização e aplicações de celuloses nanofibrilada (CNF) e nanocristalina (CNC). Master Dissertation, Universidade Federal de Viçosa, Brazil, 2015.

44.

Slavutsky

Bertuzzi

. Water barrier properties of starch films reinforced with cellulose nanocrystals obtained from sugarcane bagasse. Carbohydr Polym 2014; 110: 53–61.

45.

Lopes

Bufalino

Júnior

, et al. Eucalyptus wood nanofibrils as reinforcement of carrageenan and starch biopolymers for improvement of physical properties. J Tropical Forest Sci 2018; 30: 292–303.

46.

Cortez-Vega

Bagatini

Souza

JTA

, et al. Nanocomposite biofilms obtained from Whitemouth croaker (Micropogonias furnieri) protein isolate and monmorilonite: evaluation of the physical, mechanical and barrier properties. Braz J Food Technol 2013; 16: 90–98.

47.

Fakhouri

Fontes

LCB

Gonçalves

PVDM

, et al. Films and edible coatings based on native starches and gelatin in the conservation and sensory acceptance of Crimson gra. Food Sci Technol 2007; 27: 369–375.

48.

Deng

Jung

Zhao

. Development, characterization, and validation of chitosan adsorbed cellulose nanofiber (CNF) films as water resistant and antibacterial food contact packaging. LWT Food Sci Technol 2017; 83: 132–140.

49.

Mahardika

Abral

Kaim

, et al. Properties of cellulose nanofiber/bengkoang starch bionanocomposites: effect of fiber loading. LWT Food Sci Technol 2019; 116: 108554.

50.

Dutta

Das

Orasugh

, et al. Bio-derived cellulose nanofibril reinforced poly(N-isopropylacrylamide)-g-guar gum nanocomposite: an avant-garde biomaterial as a transdermal membrane. Polymer 2018; 135: 85–102.

51.

Ahmadi

Ghanbarzadeh

Ayaseh

, et al. The antimicrobial bio-nanocomposite containing non-hydrolyzed cellulose nanofiber (CNF) and Miswak (Salvadora persica L.) extract. Carbohydr Polym 2019; 214: 15–25.

52.

Pereda

Ponce

Marcovich

, et al. Chitosan-gelatin composites and bi-layer films with potential antimicrobial activity. Food Hydrocolloids 2011; 25: 1372–1381.

53.

Sobral

PJA

. Thickness effects of myofibrillar protein based edible films on their functional properties. Pesq Agropec Brasil 2000; 35: 1251–1259.

54.

Jonoobi

Harun

Shakeri

, et al. Chemical composition, crystallinity, and thermal degradation of bleached and unbleached kenaf bast (Hibiscus cannabinus) pulp and nanofibers. Bioresource 2009; 4: 626–639.

55.

Viana

. Desenvolvimento de filmes celulósicos nanoestruturados a partir da polpa kraft de Pinus sp. PhD Thesis, Universidade Federal do Paraná, Brazil, 2013.

56.

Fonseca

Silva

TFD

Silva

, et al. Eucalyptus cellulose micro/nanofibrils in extruded fiber-cement composites. Cerne 2016; 22: 59–68.

57.

Celebi

Kurt

. Effects of processing on the properties of chitosan/cellulose nanocrystal films. Carbohyd Polym 2015; 133: 284–93.

58.

Husseinsyah

Amri

Husin

, et al. Mechanical and thermal properties of chitosan-filled polypropylene composites: the effect of acrylic acid. J Vinyl Addit Technol 2011; 17:125–131.

59.

Medeiros

Santos

ASF

Dufresne

, et al. Bionanocomposites. In: Thomas

Joseph

Malhotra

, et al. (eds) Polymer composites, 1st ed. New York, NY: Wiley-VCH Verlag GmbH & Co. KGaA, 2013, pp. 361–430.

60.

Gopi

Amalraj

Jude

, et al. Bioanocomposite films based on potato, tapioca starch and chitosan reinforced with cellulose nanofiber isolated from turmeric spent. J Taiwan Instit Chem Eng 2019; 96: 664–671.

61.

Khan

Salmieri

, et al. Mechanical and barrier properties of nanocrystalline cellulose reinforced chitosan based nanocomposite films. Carbohyd Polym 2012; 90:1601–1608.

62.

Rubentheren

Ward

Chee

, et al. Effects of heat treatment of chitosan nanocomposite film reinforced with nanocrystalline cellulose and tannic acid. Carbohyd Polym 2016; 140: 202–208.

63.

Tang

Zhang

Zhao

, et al. Preparation and properties of chitosan/guar gum/ nanocrystalline cellulose nanocomposite films. Carbohyd Polym 2018; 197: 128–136.

64.

Salehudin

Salleh

Mamat

SNH

, et al. Starch based active packaging film reinforced with empty fruit bunch (EFB) cellulose nanofiber. Proced Chem 2014; 9: 23–33.

65.

Kumar

Morya

. Packaging of fruits and vegetables. In: Singh

Kaur

(eds) Advances in horticultural crop management and value addition, 1st ed. New Delhi: Laxmi Publications Pvt Ltd., 2018, pp. 363–374.