Innovation in Biodegradable Composites: Wheat Flour and Hermetia illucens Larvae Flour Biocomposites Enhanced with Cellulose Nanocrystals

Abstract

The development of biocomposites derived from wheat flour and Hermetia illucens (black soldier fly) larvae flour presents a viable and sustainable alternative to conventional petroleum-based plastics, which contribute significantly to environmental degradation. The incorporation of cellulose nanocrystals (CNCs) is anticipated to enhance the functional properties of these materials, particularly for food packaging applications. The objective of this study was to develop and characterise biodegradable composites formulated from wheat and larvae flours, and to evaluate the effect of CNC addition on their physicochemical, mechanical, and structural properties. The biocomposites were produced using compression moulding and subsequently subjected to comprehensive characterisation. The results indicated that the addition of CNCs markedly improved the optical, barrier, and mechanical properties of the composites. These improvements render the materials suitable for packaging systems requiring moisture retention and reduced permeability to water vapour. From a mechanical perspective, composites incorporating CNCs exhibited increased tensile strength and stiffness, although a reduction in elongation at break was observed when compared to those prepared solely with larvae flour (LF). Scanning electron microscopy (SEM) analyses revealed that higher concentrations of larvae flour yielded composites with fewer surface fractures and reduced porosity. In conclusion, the utilisation of wheat and insect larvae flours, in combination with cellulose nanocrystals, represents an innovative and environmentally responsible approach for the development of biodegradable composites suitable for eco-friendly food packaging applications.

1. Introduction

Petroleum-derived plastics have caused numerous environmental issues due to their high resistance to degradation. These plastics contaminate both terrestrial and aquatic ecosystems by introducing microplastics into the food chain, thereby posing potential risks to human health [1].

Biodegradable packaging is expected to have a direct impact on food quality, as well as on the development of the food industry and market, in the coming years. The most commonly used biopolymers for producing biodegradable films in food packaging include polysaccharides and proteins, which are derived from natural and renewable sources, such as plants, animals, or microorganisms [2]. Starch blends and cellulose films are projected to lead the production capacity of the sector. Additionally, the agricultural sector is expected to remain unaffected by this growth. It is estimated that the volume dedicated to the production of these renewable biopolymers represents only 0.06% of the global total, indicating that their production will not significantly compete with food production or essential raw materials [3]. This reinforces the feasibility of these materials as sustainable alternatives for industrial applications, including the production of biodegradable films.

The development of biocomposites based on wheat flour and insect larvae flour offers a potential alternative to conventional plastics, which have a considerable environmental impact. Wheat flour is primarily composed of starch and gluten, which facilitate the formation of flexible biopolymer composites [4]. On the other hand, Hermetia illucens larvae have attracted considerable interest for various applications due to their high nutritional content, particularly their elevated levels of proteins and lipids, which contribute to the formation of a dense matrix [5]. In 2023, global insect production for food reached a market value of USD 587 million, with a projected annual growth rate of 7.3% through to 2032 [6]. This growing demand has led to a rapid increase in the global production of Hermetia illucens larvae. Although consolidated global figures are not yet available, it is estimated that various companies produce thousands of tonnes of these larvae annually. In this context, the incorporation of larvae flour into biomaterials could enhance barrier and mechanical properties due to its high protein content [7]. Owing to its composition, which includes chitin, essential amino acids, and fatty acids [8], larvae flour represents a promising option for the development of biopolymer composites intended for biodegradable packaging applications. Additionally, the implementation of these larvae for the development of biodegradable materials exhibits characteristics that support their sustainability from environmental, ethical, and technical perspectives. Hermetia illucens larvae meal represents a low environmental impact protein source, as these insects can be reared on organic waste, require minimal water and space, and demonstrate high biomass conversion efficiency [9].

Cellulose nanocrystals (CNCs) possess outstanding mechanical strength and excellent barrier properties, making them highly suitable for reinforcing biopolymeric matrices in food packaging applications [10]. These nanoscale materials have demonstrated considerable potential in the formulation of nanocomposites, functional coatings, and biodegradable composites, thereby contributing to the advancement of sustainable packaging technologies [11]. In this study, the structural and barrier properties of cellulose nanocrystals (CNCs) were exploited to reinforce the polymer matrix of the films, enhancing their mechanical integrity and reducing water vapour permeability.

In this context, the aim of this study was to develop and characterise biocomposites based on wheat flour and black soldier fly (Hermetia illucens) larvae flour, evaluating the effect of cellulose nanocrystal incorporation for application in food packaging. This research aims to drive innovation in the field of biomaterials and to support the implementation of high-value-added, sustainable packaging alternatives.

2. Materials and Methods

2.1. Materials

Soft wheat flour (Cartagena variety) with the following composition was purchased from local retail outlets in Cartagena, Colombia: moisture 11.9%, total carbohydrates 73%, protein 12%, fat 1.4%, and ash 1.7%. The larvae were sourced from Hartompet (New York, NY, USA). Cellulose nanocrystals were supplied by CelluForce (Montreal, QC, Canada). Finally, glycerol was provided by PANREAC in Bogotá, Colombia.

2.2. Proximate Analysis of Black Soldier Fly (Hermetia illucens) Larvae

The proximate analysis included the determination of the protein, moisture, and crude fat content. The procedures were carried out according to standard methods established by the Association of Analytical Chemists [12]. The moisture content was determined by the weight difference following 24 h of drying at 105 °C. The protein content was assessed using the Kjeldahl method (N × 4.79 for insects and N × 6.25 for fishmeal), while the fat content was determined using the Soxhlet extraction system (Lenz Laborglas GmbH & CO.KG., Wertheim, Germany) All the analyses were conducted in triplicate.

2.3. Fabrication of the Composites

The methodology proposed by [2] was implemented with certain modifications. Initially, a milling process was carried out on the dried larvae, which were ground in a 1:1 ratio with wheat flour until a homogeneous mixture was achieved. Subsequently, this mixture was combined with wheat flour (see

Table 1. Mass fractions of the composites studied.

Formulations	Soft Wheat Flour	Larvae Flour	CNCs
FL	0	1	0
FW-L0.5	0.5	0.5	0
FW-L0.75	0.25	0.75	0
FW-L0.5-CNC1	0.495	0.495	0.01
FW-L0.75-CNC1	0.2475	0.7425	0.01
FW-L0.5-CNC5	0.4975	0.4975	0.005
FW-L0.75-CNC5	0.2487	0.7462	0.005

) and water in a ratio of 4:1; additionally, glycerol was added at 20% relative to the flour quantity as a plasticiser. Subsequently, the components were homogenised to achieve a uniform consistency, using a food mixer, model SL-B10 (500 W, 110 V, 50–60 Hz) (Jiangmen Shengli Food Machinery Co., Ltd., Jiangmen, China), operated at speed level 2 (medium), corresponding to the second setting on the equipment’s speed selector. After a period of 48 h, small 5 g portions were extracted to form the composites, which were subsequently introduced into a hydraulic press at a temperature of 120 °C. These portions were subjected to various pressures ranging from 0 to 100 bar. Firstly, a preheating step at 0 bar was carried out for 30 s, followed by the application of pressures of 50 and 100 bar for approximately 2 min at each pressure level.

2.4. Characterisation of the Biocomposites

2.4.1. Gloss

Gloss was measured at a 60° angle following the procedure described in reference [13], using a flat-surfaced glossmeter (multi-angle glossmeter 3NH YG268, Minolta, Langenhagen, Germany). A total of seven composites were evaluated, with three measurements taken for each individual sample. The results were expressed in gloss units (GU).

2.4.2. Colour

The colour of the composites was measured using a portable colorimeter (CHNSpec CS-10, CHN Spec Technology Co., Ltd., Hangzhou, China). The CIE Lab* coordinates, hue angle (h), and chroma (c) were recorded. Lightness (L*) is represented along the vertical axis, while the horizontal axes correspond to colour directions such as red/green (a*) and yellow/blue (b*) [14]. Colour variation relative to a reference sample was subsequently assessed by calculating the individual colour differences (ΔL, Δa, and Δb). The total colour difference (ΔE*) was then determined using the standard Equation (1).

$$∆E=\sqrt{{∆L}^2+{∆b}^2+{∆a}^2}$$

(1)

2.4.3. Transmittance and Opacity

The methodology reported by [15] was applied with slight modifications. The transmittance of the composite samples was measured in the UV–visible range using a spectrophotometer (BIOBASE BK-UV1900, Biobase Biodustry (Shandong) Co., Ltd., Jinan, China). The composites were cut into strips (1 × 3 cm) and placed against the inner wall of a quartz cuvette for analysis. Opacity was subsequently calculated using Equation (2):

$$Opacity={\displaystyle \frac{\mathrm{A}\mathrm{b}\mathrm{s}\mathrm{o}\mathrm{r}\mathrm{b}\mathrm{a}\mathrm{n}\mathrm{c}\mathrm{e} (600 \mathrm{n}\mathrm{m})}{\mathrm{T}\mathrm{h}\mathrm{i}\mathrm{c}\mathrm{k}\mathrm{n}\mathrm{e}\mathrm{s}\mathrm{s} \left(\mathrm{m}\mathrm{m}\right)}}$$

(2)

2.4.4. Thickness

The thickness of the composites was determined using a digital micrometer (TL268 TOP EU, HongKong Proster Trading Limited, Hong Kong, China). Seven random measurements were taken from each composite in order to report the mean value and standard deviation.

2.4.5. Water Vapour Permeability (WVP)

Water vapour permeability was determined gravimetrically, following the procedure described by [3] with several modifications. Environmental parameters were adjusted to establish a humidity gradient ranging from 52.8% relative humidity (RH) to 100% RH at a temperature of 25 °C. Defect-free composite samples were selected for the WVP evaluation. Payne-type permeability cups filled with distilled water were used, allowing one side of the composite to be exposed to 100% RH. These cups, along with the composites, were placed in controlled chambers maintained at 25 °C and 52.8% RH, using oversaturated magnesium nitrate solutions to regulate the humidity. Additionally, to enhance the applicability of the composites for products with high water activity, the free surface of the composites during their formation was exposed to a lower-humidity environment. The containers holding the composites were subjected to systematic weighing using a high-precision analytical balance with a sensitivity of 0.0001 g. Once a stable measurement condition was reached, the water vapour transmission rate (WVTR) was calculated from the slope of the regression line representing the weight loss over time. This value was then divided by the exposed surface area of the composite. The procedure was repeated three times, and the results were expressed as the mean value along with the corresponding standard deviation.

2.4.6. Moisture Content and Water Solubility

The methodology proposed by [16] was followed. Composite samples (2 × 2 cm) were initially weighed (W₀) and then dried in an oven at 60 °C until a constant weight was reached (W₁) to determine the moisture content. Subsequently, the samples were immersed in distilled water at a ratio of 1:10 (composite: water) for 24 h. After immersion, the undissolved material was collected and dried again to a constant weight (W₂).

$$Moisture content (\%)={\displaystyle \frac{W_0-W_1}{W_1}}\times 100\%$$

(3)

$$Solubility (\%)={\displaystyle \frac{W_1-W_2}{W_2}}\times 100\%$$

(4)

2.4.7. Water Absorption Capacity

The measurement of the water absorption capacity allows for the determination of the amount of water a sample can retain under controlled conditions [17]. In this procedure, the composite sample was first placed in a desiccator containing calcium chloride, maintaining 0% relative humidity. The sample weights were recorded at 24 h intervals until a constant mass was achieved, corresponding to the dry mass of the composite (W_s). Subsequently, the samples were transferred to another desiccator containing a saturated solution of potassium sulphate. As in the previous stage, the samples were weighed every 24 h until equilibrium was reached, with the final weight representing the fully hydrated mass of the composite (W_h). The water absorption capacity was then calculated using the following Equation (5).

$$Absorption capacity (\%)={\displaystyle \frac{W_h-W_s}{W_s}}\times 100\%$$

(5)

2.4.8. Water and Oil Contact Angle

A composite sample was placed on a horizontal surface with a white background. A drop of water (containing dye) or oil was then deposited onto the surface of the composite. After 30 s, an image was captured using a digital camera positioned at a constant distance of 20 cm from the droplet. The captured image was subsequently analysed using Goniotrans software (version 1.0.3). This procedure was performed in triplicate for each formulation, and the results were reported as mean values with their corresponding standard deviations [18].

2.4.9. Cumulative Weight Loss

To evaluate moisture loss, the films were cut into 2 × 2 cm specimens and placed in a desiccator containing anhydrous calcium chloride, which maintains an environment of 0% relative humidity at room temperature. The weight of each sample was recorded every 24 h over a period of 72 h. The final weight, corresponding to the dry or equilibrium weight, was defined as the point at which no significant variation was observed between consecutive measurements. Based on the data obtained, graphs were constructed to represent the cumulative weight loss of each formulation over time, calculated at 24 h intervals as described in Equation (6). This procedure was carried out in triplicate for each formulation tested [19].

$$Cumulative loss=P_0-P_t$$

(6)

2.4.10. Mechanical Properties

The methodology proposed by [14] was employed. The elastic modulus (EM), tensile strength (TS), and elongation at break (E) of the composites were determined using a texture analyser (TX-700, Lamy Rheology, Champagne, France) equipped with a 500 N load cell, operating at a crosshead speed of 50 mm/min. Composite samples measured 1 cm × 100 cm, with a gauge length of 5 cm.

2.4.11. Microstructure

To analyse the structural properties of the composites, 1 cm × 1 cm samples were taken to observe the surface area using an optical microscope (ZEISS model 415500-1800-000, Primostar, Oberkochen, Germany) at 10× magnification. Prior to observation, the composites were conditioned at 52.8% relative humidity and 25 °C for one week [20]. Regarding the analysis of the cross-sectional microstructure, this was carried out using a scanning electron microscope (JSM-5910, JEOL Ltd., Tokyo, Japan). For sample preparation, the composites were stored in desiccators containing P₂O₅ for two weeks to ensure the absence of moisture. Fragments measuring 0.5 cm were cut, mounted on copper stubs, coated with gold, and examined under an accelerating voltage of 10 kV [2].

2.5. Statistical Analysis

For the statistical evaluation, an analysis of variance (ANOVA) was employed. Significant differences (p < 0.05) were assessed using Fisher’s Least Significant Difference (LSD) test among the various analyses conducted on the different samples. Statistical evaluations were performed using Statgraphics Plus for Windows 5.1 software (Manugistics Corp., Rockville, MD, USA).

3. Results and Discussion

3.1. Proximate Analysis of Black Soldier Fly Larvae

The proximate composition of black soldier fly (Hermetia illucens) larvae is summarised in

Table 2. Proximate analysis of black soldier fly (Hermetia illucens) larvae.

Parameter	Weighted (%)
Moisture	6.140 ± 0.20
Protein	38.59 ± 2.35
Fat	35.84 ± 0.48

Data are presented as mean ± standard deviation.

. The protein content obtained was 38.59 ± 2.35%, which is consistent with the values reported by [21], where a value of 32.3% was recorded. This similarity may be attributed to the larvae being reared on the same feeding substrate and collected at the same developmental stage (larval phase). Regarding the moisture and fat contents, the values obtained were 6.14% and 35.84%, respectively. These findings align with the study conducted by [8], where the moisture content ranged from 4.14% to 6.46%. In terms of the fat content, values were reported between 25.78% and 38.6%. The chemical composition of the larvae depends on various factors, among which the type of feeding substrate plays a crucial role, highlighting the importance of selecting appropriate feed ingredients to optimise their nutritional value [22].

3.2. Optical and Colour Properties

The optical and colour properties of the composites produced from larval flour and wheat flour with added CNCs are presented in

Table 3. Mean values and standard deviation of the gloss (GU) and the colour parameters (lightness (L), red/green (a*), yellow/blue (b*), chroma (C), and hue angle (h, °) of the composites studied.

Formulations	Gloss 60°	Colour Parameters
		L*	a*	b*	C	h	ΔE
FL	12.5 ± 0.8 b	62.3 ± 0.7 c	3.7 ± 0.1 b	25.6 ± 0.2 b	25.9 ± 0.2 b	81.7 ± 0.1 cd	-
FW-L0.5	13.3 ± 0.5 a	66.0 ± 0.7 a	2.8 ± 0.1 c	22.4 ± 0.2 d	24.1 ± 0.01 c	78.7 ± 1.3 bc	-
FW-L0.75	12.9 ± 0.4 ab	67.4 ± 0.5 a	2.4 ± 0.5 c	21.8 ± 0.5 d	22.3 ± 0.4 c	83.1 ± 0.7 b	-
FW-L0.5-CNC1	7.30 ± 0.5 c	60.1 ± 0.2 d	4.5 ± 0.2 b	27.4 ± 0.9 a	27.4 ± 0.9 a	80.6 ± 0.4 d	6.9 ± 0.5 a
FW-L0.75-CNC1	13.4 ± 0.5 a	67.5 ± 0.3 a	2.9 ± 0.1 c	23.7 ± 0.3 c	23.5 ± 0.8 c	83.7 ± 0.7 b	2.3 ± 0.6 c
FW-L0.5-CNC5	7.28 ± 0.9 c	62.9 ± 0.6 c	4.0 ± 0.2 ab	26.0 ± 0.7 ab	26.3 ± 0.1 ab	94.7 ± 0.1 a	5.3 ± 0.2 b
FW-L0.75-CNC5	13.1 ± 0.4 ab	63.4 ± 0.7 c	3.7 ± 0.5 b	25.2 ± 0.4 b	25.4 ± 0.3 b	81.6 ± 1.0 d	7.5 ± 0.1 a

Different superscript letters indicate statistically significant differences (p < 0.05) between formulations. These values are used as blanks to calculate the colour change of the respective samples containing the same amount of larvae flour.

. Gloss at 60°, CIE Lab*parameters, hue angle, chroma, and colour difference were determined, providing a detailed visual characterisation of the obtained materials.

The optical properties of the studied formulations vary according to the addition of CNCs. These nanocrystals influence light scattering, thereby altering the perception of the gloss, lightness, and colour of the material. Figure 1 shows photographs of the films obtained. The presence of CNCs may promote the formation of a more organised and crystalline surface, which can enhance controlled light reflection and increase lightness [23]. In this context, the formulation F_W-L0.75-CNC1 exhibited the highest gloss (13.4 ± 0.5) and the highest lightness (67.5 ± 0.3), which may be related to reduced light scattering. Conversely, the formulation F_W-L0.5-CNC5 showed the highest hue angle (94.7 ± 0.1), suggesting an opaquer surface. The a* and b* values increased in the formulations containing CNCs, indicating reddish and yellowish tones, respectively. Regarding chroma (saturation), the formulation F_W-L0.5-CNC1 exhibited the highest value for this parameter (27.4 ± 0.9), suggesting that the distribution of CNCs influences the interaction of light with the material, thus altering its optical appearance. With respect to colour difference (ΔE), an increase was observed in the formulations with CNC incorporation (F_{W-L0.5-CNC5, FW-L0.75-CNC5}, and F_W-L0.5-CNC1). A similar significant increase in ΔE was reported by [24] in chitosan-based composites incorporating CNCs.

3.3. Transmittance and Opacity

Figure 2 shows the direct transmittance spectrum in the UV–Vis range (200–900 nm) of the composites developed from larval flour and wheat flour with the addition of CNCs. Transmittance is a parameter that measures the passage of light through a material [25] and thus allows us to determine the transparency of the studied composites.

The formulation F_W-075-CNC1 exhibited the highest transmittance, with a value of approximately 50%, reaching its peak in the visible and near-infrared region (600–800 nm). This suggests that at this concentration, the CNCs are homogeneously dispersed, allowing greater light transmission. However, in the formulations where transmittance decreased in the presence of CNCs (F_W-L0.5-CNC5, F_W-L0.5-CNC1, and F_W-L0.75-CNC5), the reduction of this parameter may indicate increased light scattering due to particle aggregation. This aggregation could be influenced by the interaction among the CNCs, larval flour, and wheat flour, resulting in a decrease in the amount of light passing through the composite [26]. These findings indicate that the interaction between larval flour, wheat flour, and CNCs is essential to maintaining good transparency in the composite. In other words, the uniform distribution of CNCs and their compatibility with the matrix reduce light scattering and enhance the transmittance of the composites. Additionally, the difference in transmittance between F_W-075-CNC1 and F_W-L0.5-CNC1 can be explained by the proportion of ingredients in each formulation. F_W-075-CNC1, which contains 75% larval flour and 25% wheat flour, promotes better CNC dispersion due to the adhesive and bioactive properties of larval flour, which interact favourably with CNCs and enable a more homogeneous distribution. This reduces particle agglomeration and enhances light transmission. In contrast, F_W-L0.5-CNC1, with a 1:1 ratio of larval flour to wheat flour, exhibits a greater tendency toward CNC agglomeration due to the less homogeneous interaction between the two types of flour, which increases light scattering and decreases transmittance [21,27].

Table 4. Mean values and standard deviations of the opacity of the studied composites.

Formulations	Opacity
FL	1.50 ± 0.03 d
FW-L0.5	1.48 ± 0.02 d
FW-L0.75	2.21 ± 0.02 a
FW-L0.5-CNC1	1.74 ± 0.04 d
FW-L0.75-CNC1	1.44 ± 0.03 c
FW-L0.5-CNC5	1.71 ± 0.06 c
FW-L0.75-CNC5	1.93 ± 0.01 b

Different superscript letters indicate statistically significant differences (p < 0.05) between formulations.

presents the opacity values of the composites produced from larval flour and wheat flour with the addition of CNCs. Opacity is associated with the fraction of light that is blocked or absorbed by the composite, and this parameter is inversely related to transmittance [27]. In this context, the opacity data reveal significant differences among the formulations. The formulation F_W-L0.75 exhibited the highest opacity value (2.21 ± 0.02), suggesting lower transmittance. Conversely, the least opaque formulation was F_W-L0.75-CNC1, and is therefore more transparent (see Figure 2). This may be related to the light-scattering capacity of the larval and wheat flours, potentially due to their protein structure or interactions with other matrix components, which could have contributed to the formation of aggregates or networks that alter the interaction of light with the surface of the material, thereby increasing the opacity. However, the formulation composed solely of larval flour (F_L) showed a lower opacity value (1.50 ± 0.03) compared to F_W-L0.75. This could be attributed to a higher content of proteins and lipids, which may have contributed to the formation of a more homogeneous and compact structure, reducing light scattering and thus lowering the opacity [28].

3.4. Physical and Water Absorption Properties

Table 5. Mean values and standard deviations of the thickness (μm), water vapour permeability (WVP, g·mm/kPa·h·m²), water absorption capacity (WAC, g of dry composite/g of wet composite), moisture content (Xw, g of water/g of dry composite), and solubility (Sw, g of solubilised composite/g of initial composite) of the studied composites.

Formulations	Thickness	WVP	WAC	Xw	Sw
FL	228.14 ± 0.035 ab	1.79 ± 0.08 b	0.60 ± 0.03 a	0.180 ± 0.07 a	0.38 ± 0.06 ab
FW-L0.5	235.14 ± 0.057 ab	1.80 ± 0.035 b	0.40 ± 0.03 c	0.183 ± 0.01 a	0.36 ± 0.07 ab
FW-L0.75	209.14 ± 0.042 b	1.20 ± 0.09 c	0.55 ± 0.05 ab	0.184 ± 0.07 a	0.45 ± 0.08 a
FW-L0.5-CNC1	237.28 ± 0.015 ab	2.10 ± 0.08 a	0.60 ± 0.06 a	0.146 ± 0.08 c	0.29 ± 0.03 b
FW-L0.75-CNC1	238.00 ± 0.019 ab	2.16 ± 0.08 a	0.46 ± 0.07 bc	0.167 ± 0.04 b	0.26 ± 0.08 b
FW-L0.5-CNC05	250.28 ± 0.030 a	1.16 ± 0.02 c	0.62 ± 0.09 a	0.146 ± 0.03 c	0.30 ± 0.03 b
FW-L0.75-CNC05	210.85 ± 0.022 b	1.19 ± 0.01 c	0.61 ± 0.10 a	0.164 ± 0.04 b	0.27 ± 0.01 b

Different superscript letters indicate statistically significant differences (p < 0.05) between formulations.

presents the mean values and standard deviations of the physical and water absorption properties of the composites developed from larval flour and wheat flour with the addition of CNCs. The evaluated parameters include the thickness (μm), water vapour permeability (WVP), solubility (Sw), moisture content (Xw), and water absorption capacity (WAC) of the studied composites.

The thickness of the studied composites ranged from 209.14 to 250.28 µm. It was observed that the incorporation of CNCs influences this parameter [29]. Composites containing CNCs tended to be thicker than those without CNCs, with the formulation F_W-L0.5-CNC5 exhibiting the greatest thickness (250.28 µm) and F_W-L0.75 the lowest (209.14 µm). These results are consistent with those reported by [30], who observed an increase in composite thickness with a higher CNC content. The increase in thickness can be attributed to the role of CNCs as fillers and reinforcements within the polymer matrix, preventing its compaction and consequently expanding the polymer network [31].

Regarding water vapour permeability (WVP), the results show significant differences (p < 0.05) among the formulations, confirming that the concentration of CNCs influences water vapour permeability. In this regard, the formulations with the highest WVP values were F_W-L0.5-CNC1 and F_W-L0.75-CNC1 (2.10 ± 0.08 g·mm/kPa·h·m² and 2.16 ± 0.08 g·mm/kPa·h·m², respectively), suggesting that at this CNC concentration, the structure of the matrix facilitates water vapour diffusion.

Conversely, the formulations with lower CNC concentrations (F_W-L0.5-CNC05 and F_{W-L0.75-CNC05)} exhibited the lowest WVP values (1.16 ± 0.02 g·mm/kPa·h·m² and 1.19 ± 0.01 g·mm/kPa·h·m²), indicating that this concentration promotes a more compact structure, hindering water vapour transmission by reducing the availability of hydrophilic groups capable of interacting with water molecules [32]. It is noteworthy that the formulations without CNCs presented intermediate values, suggesting that CNCs indeed influence the microstructure and barrier capacity of the resulting composites. This contrasts with the findings reported by [33], in which water vapour permeability did not show significant variation following the incorporation of CNCs into their composites.

The statistical differences in WAC indicate significant variations among the formulations (p < 0.05). The formulations F_W-L0.5-CNC05 and F_{W-L0.75-CNC05} (0.62 ± 0.09 and 0.61 ± 0.10, respectively) exhibited the highest WAC values, which may be associated with a composite structure that allows greater water absorption, possibly due to increased porosity or enhanced interaction with water. The formulation composed solely of larval flour (F_L) showed a WAC value of 0.60 ± 0.03, which may be attributed to the presence of proteins with hydrophilic functional groups that promote water absorption. However, F_W-L0.5 (0.40 ± 0.03) exhibited the lowest WAC value, which could be related to the incorporation of wheat flour and its starch content, modifying the composites microstructure and reducing the number of sites available for water absorption [34].

The moisture content is a key factor in the stability of food packaging composites. This parameter varied among the different formulations. The composites without CNCs—F_L (0.180 ± 0.07), F_W-0.50 (0.183 ± 0.01), and F_W-L0.75 (0.184 ± 0.07)—showed the highest moisture content values. However, these differences were not statistically significant (p > 0.05). This increase may be attributed to the composition of the wheat and larval flours, which contain proteins and starches with hydrophilic functional groups capable of interacting with water [35]. In contrast, the formulations containing CNCs exhibited lower moisture values: F_W-L0.5-CNC1 = 0.146 ± 0.08, F_W-L0.75-CNC1 = 0.167 ± 0.04, F_W-L0.5-CNC05 = 0.146 ± 0.03, and F_{W-L0.75-CNC05} = 0.164 ± 0.04. Although a general reduction in the moisture content was observed with the incorporation of CNCs, increasing their concentration (from 0.5% to 1%) did not result in significant differences. This suggests that CNCs contribute to the structural stability of the composite, but their effect on moisture may could be masked due to the effect of other components of the larval meal. This finding is consistent with [24], who reported a slight decrease in moisture content in composites composed of CNCs and chitosan, likely due to the interaction between the chitosan matrix and the CNCs, which reduces the water content within the composite network.

The solubility results indicate greater resistance to dissolution in water for the composites containing CNCs (F_W-L0.5-CNC1 = 0.29 ± 0.03, F_W-L0.75-CNC1 = 0.26 ± 0.08, F_W-L0.5-CNC05 = 0.30 ± 0.03, F_{W-L0.75-CNC05} = 0.27 ± 0.01). In contrast, the composites without CNCs showed the highest solubility values (F_L = 0.38 ± 0.06, F_W-0.50 = 0.36 ± 0.07, F_W-L0.75 = 0.45 ± 0.08), indicating a more hydrophilic behaviour. Water solubility is an indicator of a composite’s resistance to water; high solubility reflects a strong affinity for water, which can be a drawback for certain biodegradable composites [36].

Therefore, these findings suggest that the incorporation of CNCs increases thickness, reduces water vapour permeability, and enhances water absorption capacity in wheat and larval flour-based composites. These modifications may influence their potential applications as coatings or bioplastics.

3.5. Contact Angle

Figure 3 compares the water contact angles (CAws) and oil contact angles (CAos) of various composite formulations developed from larval flour and wheat flour with the addition of CNCs. The contact angle serves as an indicator of the hydrophilic or hydrophobic properties of the composites.

In this context, the composites without CNCs, composed of wheat flour and larval flour (F_L = 62.6 ± 2.52, F_W-0.50 = 57.3 ± 1.53, F_W-L0.75 = 56.0 ± 2.12), exhibited the lowest CAw° values, indicating a greater affinity for water. This observation is consistent with the solubility and moisture content results. It is worth noting that the FL formulation showed a significantly high CAw° value, which may be attributed to the fat content of the larval flour, suggesting a reduced affinity for water.

Regarding the formulations containing CNCs, an increase in the CAw° was observed, suggesting a structure more resistant to moisture. CNCs possess hydroxyl groups on their surface, enabling the formation of hydrogen bonds with functional groups in the polymer matrix, such as proteins, polysaccharides, etc. [37]. This interaction enhances the material’s structure.

Similarly, the CAo values increased in the formulations with CNCs, indicating a lower affinity for oily substances. This behaviour may result from increased cohesion within the polymer matrix due to the incorporation of CNCs, which limits the availability of sites for interaction with oil [38]. Taken together, these results suggest that the composites exhibit both hydrophilic and oleophilic characteristics, although the incorporation of CNCs tends to reduce interaction with both polar and non-polar liquids, thereby enhancing the material’s structural integrity and barrier properties.

3.6. Cumulative Weight Loss of Films

Figure 4 illustrates the cumulative weight loss of the composites stored at room temperature (25 °C). It is evident that the formulations without CNCs, primarily composed of wheat flour and larval flour, exhibit higher weight loss rates in their fitting equations, indicating greater susceptibility to material degradation and a more hydrophilic structure. This facilitates increased water diffusion into the composite, leading to the leaching of water-soluble components [39]. On the other hand, the formulations containing CNCs display lower weight loss rates, with F_W-L0.5-CNC5 and F_W-L0.75-CNC5 showing the lowest values. This suggests that CNCs reinforce the polymer matrix by reducing water diffusion and the degradability of the composite [40].

Moreover, the determination coefficients (R²s) of graphs were considerably high, indicating a good fit of the data to the linear models.

3.7. Mechanical Properties

The mechanical properties provide insight into the strength and flexibility of the composites.

Table 6. Mean values and standard deviations of mechanical properties (EM: elastic modulus; TS: tensile strength; E: elongation at break) of the studied formulations.

Formulations	EM (MPa)	TS (MPa)	E (%)
FL	20.2 ± 0.5 f	6.1 ± 0.2 d	230 ± 3 a
FW-L0.5	22.1 ± 0.4 cd	6.7 ± 0.3 c	203 ± 5 bc
FW-L0.75	21.3 ± 0.2 e	6.4 ± 0.3 cd	211 ± 3 b
FW-L0.5-CNC1	22.5 ± 0.3 c	6.9 ± 0.2 c	198 ± 2 c
FW-L0.75-CNC1	21.6 ± 0.2 de	6.5 ± 0.3 cd	208 ± 5 b
FW-L0.5-CNC5	24.2 ± 0.4 a	9.3 ± 0.2 a	185 ± 3 d
FW-L0.75-CNC5	23.4 ± 0.2 b	8.3 ± 0.3 b	197 ± 5 c

Different superscript letters indicate statistically significant differences (p < 0.05) between formulations. The superscript letters (a, b, c, d, e, f) indicate statistically significant differences among the mean values of each mechanical property evaluated (EM, TS, and E), as determined by the analysis of variance (ANOVA) followed by a multiple comparison test (p < 0.05). Values bearing different letters within the same column reflect significant differences between formulations.

presents the mean values and standard deviations of the mechanical properties (EM: elastic modulus; TS: tensile strength; E: elongation at break) of the studied formulations.

The tensile strength (TS), the formulations containing CNCs also display significantly higher values compared to those without these nanomaterials, particularly F_W-L0.5-CNC5 (9.3 ± 0.2 MPa) and F_W-L0.75-CNC5 (8.3 ± 0.3 MPa), indicating greater resistance compared to composites made solely with larval flour (F_L = 6.1 ± 0.2 MPa). This improvement may be attributed to the ability of CNCs to enhance continuity within the polymer matrix, reducing polymer chain mobility and thus increasing tensile strength. Additionally, potential interactions between protein and polysaccharide components in the composite may lead to the formation of supplementary bonds that reinforce the material structure [41]. These findings are consistent with those of [42], who reported that the incorporation of cellulose nanocrystals increased the TS of corn-starch-based composites. A similar trend was observed for the Young’s modulus (EM) of the composites. The Young’s modulus is a measure of the stiffness of the material.

The formulations with CNCs have a significantly higher elastic modulus, indicating greater rigidity compared to the formulations without CNCs, with FL showing the lowest value. The highest values of this parameter were also recorded for the formulations F_W-L0.5-CNC5 (24.2 ± 0.4 MPa) and F_W-L0.75-CNC5 (23.4 ± 0.3 MPa), which included the addition of cellulose nanocrystals (CNCs), indicating greater stiffness in comparison with the composites made with larval flour (F_L = 20.2 ± 0.2 MPa). These results are consistent with those reported by [43], where an increase in the Young’s modulus was also observed in biocomposites containing CNCs. On the other hand, deformation assesses the ability of the composites to elongate before breaking, i.e., their flexibility. The composites based on larval flour (LF = 230 ± 3%) exhibited the highest elongation (E) values, thus indicating greater elasticity or flexibility. This may be attributed to the potential plasticizing effects conferred by the proteins and lipids present in the larval flour [8,44]. Elongation decreased in all the formulations containing CNCs, indicating that the composites are less flexible but more resistant.

Therefore, these findings suggest that composites incorporating cellulose nanocrystals (CNCs) are more resistant and rigid, albeit less elastic, in comparison with formulations made solely with larval flour (F_L). This indicates that both the type of flour and the inclusion of CNCs not only enhance the mechanical strength but also reduce the flexibility of the composites. These mechanical properties could render CNC-containing formulations more suitable for applications requiring higher strength and rigidity, whereas formulations without CNCs may be more appropriate for applications demanding greater flexibility.

The incorporation of cellulose nanocrystals (CNCs) led to a significant increase in the elastic modulus (EM) and tensile strength (TS), particularly in formulations FW-L0.5-CNC5 and FW-L0.75-CNC5, which bear the superscript letters “a” and “b”, corresponding to the highest rigidity and strength values. This behaviour demonstrates the reinforcing filler effect of CNCs within the matrix. Conversely, the elongation at break (E) significantly decreased with increasing CNC concentration, as indicated by the shift in superscript letters from “a” to “c” and “d”, reflecting a loss of flexibility. Collectively, these results confirm that the addition of CNCs alters the mechanical behaviour of the material, impacting both its strength and deformability.

3.8. Microstructure

Figure 5 presents surface 2.5D micrographs of the films under study, which reveal variations in surface roughness and elevation, allowing for the observation of significant differences in surface morphology. The formulations FL, FW-L0.5, and FW-L0.75 exhibit relatively homogeneous surfaces. In contrast, the FW-L0.5-CNC1 formulation displays increased roughness and heterogeneity, likely resulting from the interaction between the larval flour matrix and the cellulose nanocrystals (CNCs). The micrograph corresponding to FW-L0.5-CNC5 shows more pronounced peaks and valleys, indicating a substantial increase in surface roughness. This may be attributed to CNC oversaturation, leading to the formation of micro-aggregates or localised domains that disrupt surface continuity.

The addition of cellulose nanocrystals induces the formation of rough and relief-rich zones, suggesting greater heterogeneity, which could be associated with interactions between the larval flour matrix and CNCs. Such interactions may generate microdomains or local aggregates, compromising the structural continuity of the film. Furthermore, these alterations could directly affect functional properties such as permeability, surface adhesion, or the mechanical behaviour of the material [45].

Figure 6 presents the cross-sectional microstructure of the biodegradable composites as observed through scanning electron microscopy (SEM). The SEM images reveal differences in the microstructure of the biodegradable composites depending on their formulation. Composites based on larval flour (F_L) tend to exhibit fewer fractures and pores, which may be related to the fat and protein content of the larvae, acting as plasticising and structuring agents that confer greater stability to the composites [8,44]. In contrast, composites formulated with a mixture of wheat and larval flour (F_W-L0.5 and F_W-L0.75) display a rougher texture with more pronounced cracks. In the composites with added cellulose nanocrystals, both smooth and rough areas are observed, suggesting a possible combination of compact and porous regions. Additionally, brighter zones are visible, particularly in the F_W-L0.75-CNC1 composite. The presence of cracks and rough areas could be associated with the interaction between the larval flour matrix and the cellulose nanocrystals. CNCs reinforce the polymer matrix by reducing porosity; however, at higher concentrations, they may affect the uniformity of the structure, leading to pore formation, which in turn impacts the overall structural integrity of the material [46].

Considering the mechanical properties, the microstructure observed by SEM is consistent with the values of the tensile strength (TS), elongation at break (%E), and Young’s modulus (EM). The greater homogeneity of the F_L composites without cellulose nanocrystals is reflected in their higher elongation (230%), indicating better cohesion within the polymeric matrix. In contrast, the increased roughness and presence of cracks in the composites containing cellulose nanocrystals are associated with greater stiffness and mechanical strength, as evidenced by the higher Young’s modulus (24.2 MPa in F_W-L0.5-CNC5). The reduced deformability in these formulations suggests that the more heterogeneous and porous structure hinders polymer chain mobility, resulting in stiffer composites. With regard to barrier properties, the microstructure also accounts for the differences in water vapour permeability (WVP). The incorporation of cellulose nanocrystals enhances the water vapour barrier; however, at higher concentrations (F_W-L0.5-CNC1 and F_{W-L0.5-CNC10),} composites exhibit increased water vapour permeability. This may be attributed to the formation of aggregates that disrupt structural uniformity, thereby increasing WVP in certain formulations.

4. Conclusions

The incorporation of cellulose nanocrystals into biodegradable composites based on larvae and wheat flour improved their optical, barrier, and mechanical properties. The F_W-L0.5-CNC5 composite exhibited the highest thickness values and the lowest water vapour permeability, enhancing its moisture barrier properties. This makes it suitable for applications requiring moisture retention and reduced permeability. On the other hand, F_W-L0.75-CNC1 showed the highest gloss (13.4 ± 0.5) and luminosity, associated with reduced light scattering, whereas F_W-L0.75 presented the highest opacity value (2.21 ± 0.02), suggesting lower transmittance. Conversely, the least opaque formulation was F_W-L0.75-CNC1; therefore, it was the most transparent. Overall, the materials developed in this study are considered translucent, which may be advantageous for food products sensitive to UV radiation or excessive light exposure.

Regarding the water interaction properties, the incorporation of cellulose nanocrystals reduced water vapour permeability and improved the water absorption capacity, with the most notable effect observed in the F_W-L0.5-CNC05 composite. The F_W-L0.5-CNC1 formulation exhibited the highest CAw° value. However, it is also worth highlighting the FL formulation, which showed a significantly high CAw° value, possibly related to the fat content of the larval flour, indicating a lower affinity for water.

With respect to mechanical properties, the composites incorporating cellulose nanocrystals were stronger and stiffer, although less deformable, compared to the formulations prepared solely with larval flour (F_L). These mechanical characteristics suggest that formulations containing nanocrystals may be more suitable for applications requiring higher strength and rigidity, whereas formulations without nanocrystals could be more appropriate for applications where greater flexibility is desired. Additionally, SEM micrographs indicate that as the larval flour (F_L) content increases, the composites exhibit fewer fractures and reduced porosity. On the other hand, the addition of nanocrystals reinforces the polymer matrix by decreasing porosity; however, at high concentrations, they may affect structural uniformity, leading to the formation of pores that compromise the material’s overall structure.

In this context, the use of wheat and Hermetia illucens larvae flour combined with cellulose nanocrystals (CNCs) for film production represents a sustainable and innovative alternative for environmentally friendly packaging. The use of these flours not only utilises a non-conventional protein and lipid source, but also provides significant improvements in the mechanical, barrier, and optical properties of the material.

The developed composite exhibits characteristics that support its sustainability from environmental, ethical, and technical perspectives. Hermetia illucens larvae flour is a low-impact protein source, as these insects can be reared on organic waste, require minimal water and land, and display high biomass conversion efficiency. Moreover, its application in non-food products such as biodegradable packaging helps to avoid direct competition with human food consumption. This research contributes not only to plastic reduction but also promotes circular economy principles and the development of materials with lower environmental impacts.