Influence of Metal Powder Partiucle Geometry on Ultrasonically Embedded Nanocellulose Composites

Abstract

This study investigates the embedding of copper, iron, zinc, and bronze metal powders with varying particle morphologies into bacterial nanocellulose sheets using ultrasonic techniques. Bacterial nanocellulose, known for its eco-friendly nature, high mechanical strength, and biocompatibility, serves as an excellent substrate for enhancing material properties through metal incorporation. The research focuses on the influence of ultrasonification timing on the embedding process and the resulting composite properties.

The methodology employs ultrasonic energy to embed particles non-invasively, preserving the structural integrity of the nanocellulose sheets. By varying the duration of ultrasonication, the study explores its impact on particle distribution. Results indicate that shorter ultrasonication times lead to greater metal embedding, while longer durations result in less embedding with potentially different distribution patterns.

The findings underscore the significance of process parameters in tailoring nanocomposite properties for specific applications, such as sensors or medical devices, where precise control over material characteristics is crucial. This research highlights the versatility of ultrasonic techniques in developing high-performance nanocellulose composites, offering valuable insights for advancements in materials science.

1. Introduction

Bacterial nanocellulose (BNC) has emerged as a promising material due to its unique properties, including eco-friendly biodegradability, high mechanical strength, and excellent biocompatibility. These attributes make it an ideal candidate for use in advanced composite materials tailored for specific applications in fields such as electronics, medicine, and environmental science. The integration of functional materials, such as metal powders, into bacterial nanocellulose sheets can significantly enhance their properties, including thermal conductivity, electrical conductivity, and mechanical performance.

In this study, we focus on the embedding of copper, iron, zinc, and bronze metal powders with varying particle morphologies into bacterial nanocellulose sheets using ultrasonic techniques. The choice of metals is driven by their distinct physical and chemical properties, which can impart specific functionalities to the resulting composites. Copper, for instance, offers excellent electrical conductivity and antimicrobial properties, while iron’s magnetic properties, makes it suitable for electronics applications.

The embedding process is a critical step in determining the final properties of the composite material. Ultrasound-assisted techniques have gained attention due to their ability to disperse, extract, or self-assembly of cellulose nanocrystals. However, the influence of ultrasonication on particle embedding remains understudied. This study investigates how varying durations of ultrasonication and particle morphologies affect the embedding efficiency, and resultant distribution patterns.

The findings of this research will contribute to the development of tailored nanocomposite materials with desired functionalities for diverse applications, such as sensors, medical devices, and energy storage systems. Furthermore, this work highlights the potential of ultrasound-based techniques in achieving precise control over composite properties, offering new insights into the field of materials science.

2. Materials and Methods

2.1 Materials

Metal powders:

• Unrefined cane sugar
• Distilled water
• Previous culture medium (kombucha) Processing:
• NaOH
• Sodium Lauryl Sulfate (SLS)

2.2 Processing

BNC preparation:

1. Medium Preparation The growth medium was prepared using 50 g of unrefined cane sugar, 750 mL of distilled water, and 250 mL of the previous culture medium. Unrefined cane sugar served as the primary carbon source, providing glucose essential for bacterial growth and nanocellulose synthesis. Distilled water acted as the solvent to dissolve these components effectively. The inclusion of the previous culture medium aimed to inoculate the fresh medium with Gluconacetobacter xylinus bacteria, leveraging their proven ability to produce substantial amounts of bacterial nanocellulose.
2. Incubation The prepared medium was incubated at room temperature (approximately 25°C) for a period of 10 days. This duration was selected to allow sufficient time for bacterial growth and nanocellulose production, balancing between maximizing yield and avoiding over-growth that could lead to contamination or degradation.
3. Cleaning Process After the incubation period, the bacterial nanocellulose sheets were harvested and washed under distilled water to remove residual impurities and unbound components. This washing step ensured the purity of the nanocellulose. The sheets were then treated in a stirred solution of 1 M NaOH for 15 minutes, which facilitated the removal of any remaining organic residues. Following this treatment, the sheets were rinsed three times with distilled water to eliminate traces of sodium hydroxide and other chemicals, ensuring the final product was clean and ready for further use.
4. Storage The cleaned bacterial nanocellulose sheets were stored in distilled water to maintain their structural integrity and prevent dehydration. This storage method also minimized contamination risks, preserving the material’s mechanical and chemical properties until it was used in subsequent experiments or applications.

Sample preparation:

1. Cutting:
   Nanocellulose sheets were carefully cut into squares with dimensions of 2 cm × 2 cm using a scalpel. The uniform size of the samples was ensured to guarantee consistency in subsequent steps and facilitate easy handling during testing.
2. Inserting:
   Each prepared square was transferred to individual 3D printed testing vessels.
3. Loading:
   A total of 5 mL of a 10% SLS water solution was added to each testing vessel. This concentration of SLS was selected to ensure proper wetting and dispersion of the metal powder, which is critical for achieving uniform embedding within the nanocellulose matrix. Subsequently, 0.5 mL of the respective metal powder was gently loaded into each vessel, ensuring that the powder was evenly distributed in the solution.
4. Sonication:
   Each sample was subjected to sonication at 28 kHz and 240 W for a specified duration to ensure uniform dispersion of the metal powder within the nanocellulose matrix.
5. Rinsing:
   After sonication, each sample was rinsed with distilled water multiple times to remove any unbound metal powder and excess SLS solution.
6. Drying:
   Samples were dried between two stainless steel plates. This method of drying ensured uniform removal of moisture while applying gentle pressure to flatten the nanocellulose sheets and maintain their structural integrity.

2.3 Characterization Techniques

• Macro Photography: High-resolution macrographs (108 MP) of the samples were acquired. Each image was subsequently processed using dedicated software to calculate the surface coverage.
• Scanning Electron Microscopy (SEM): The microstructure of each sample was analyzed using scanning electron microscopy.

3. Results

3.1 Macrophotography

The experimental data revealed significant variations in metal powder coverage on bacterial nanocellulose sheets depending on both the morphology of the metal particles and the duration of sonication. The coverage percentages for each metal at different sonication times are summarized in the table below:

Table 1. Percentage coverage of copper, iron, bronze, aluminium, and zinc powders on bacterial nanocellulose sheets as a function of sonication time.

The experimental results revealed significant variations in metal powder coverage on bacterial nanocellulose sheets, depending on both the type of metal and the duration of ultrasonic treatment. Copper exhibited the highest coverage among all metals, with particularly notable performance at 10 seconds (46.28%), suggesting that shorter sonication times are optimal for achieving efficient and effective embedding. In contrast, iron showed minimal coverage overall and demonstrated a tendency to agglomerate, indicating challenges in achieving uniform deposition due to potential surface interactions or particle characteristics. Zinc exhibited the most variable results, with notable oxidation during the process leading to fluctuating coverage across different durations, which underscores the importance of controlling oxidative effects to maintain consistent deposition and functional properties. These findings highlight the critical role of both powder morphology and processing parameters in determining the success of metal embedding in bacterial nanocellulose composites.

3.2 SEM

4. Discussion

The observed variations in metal powder coverage can be attributed to the interplay between particle morphology and sonication duration. Dendritic copper particles demonstrated superior adhesion due to their increased surface area and irregular shape, which facilitates better interaction with the nanocellulose matrix during ultrasonic treatment. Conversely, spherical particles, such as those of zinc, exhibited a propensity for detachment, likely due to their smooth surfaces reducing mechanical interlock.

The tendency of iron powders to agglomerate could be linked to surface interactions or impurities, highlighting the importance of particle shape and purity in achieving uniform deposition. The oxidation of zinc particles underscores the need for controlled processing environments to preserve material integrity and functional properties.

5. Conclusions

The study highlights the critical influence of both powder morphology and sonication duration on the coverage and deposition efficiency of metals onto bacterial nanocellulose sheets. Key conclusions include:

• Particle Morphology: Dendritic shapes, particularly for copper, yield higher coverage due to increased surface area and mechanical interlock.
• Sonication Duration: Optimal results are achieved within shorter sonication times (5-10 seconds), suggesting the need for precise control over processing duration to maintain efficiency.
• Oxidation Challenges: Zinc particles are prone to oxidation, which affects their deposition and functional properties.

These findings underscore the importance of selecting appropriate metal powders and optimizing process parameters to achieve desired composite properties. Future work should explore impact of different particle shapes and sizes on deposition efficiency to further enhance the functionality and reliability of bacterial nanocellulose composites in various applications.