Sustainable Shielding: Comparative Analysis of Edible Thin Films from Natural Mucilage’s and HPMC

Biopolymer-based thin films have become a viable substitute for traditional synthetic plastics in the search for environmentally friendly and sustainable materials, particularly in sectors like biomedical engineering, food packaging, medicines and agriculture. Numerous benefits, including environmental compatibility, non-toxicity, renewability, and variety in functional qualities, are provided by biodegradable films. Guar gum, Sago starch (tapioca starch), Tragacanth and Hydroxypropyl methylcellulose (HPMC) and are among the many natural and semi-synthetic polymers that have attracted a lot of attention because of their distinct physicochemical properties and capacity to create films. ^[1]

The endosperm of Cyamopsis tetragonoloba seeds contains guar gum, a galactomannan polysaccharide that is prized for its high molecular weight, superior water retention, thickening capabilities, and capacity to produce cohesive films. It is a desirable option for making edible and packaging films due to its natural availability, affordability, and biodegradability. Guar gum films are frequently hydrophilic, though, which could affect their mechanical strength and barrier qualities in moist environments. ^[1,2]

Amylose and amylopectin are the primary components of sabudana, a starch derived from the roots of the tapioca or cassava plant Manihot esculenta. The moderate strength, transparency, flexibility, and remarkable film-forming ability of tapioca starch are widely known. Despite the flexibility, biodegradability, and affordability of sago starch-based films, it could be necessary to modify or combine them with other materials to improve their moisture-blocking capabilities. ^[3] Tragacanth gum, obtained from the dried exudates of Astragalus species, is a complex mixture of polysaccharides with notable emulsifying and water-retention properties. Although less commonly used in film production, its potential merits further exploration. ^[4]

Conversely, semi-synthetic cellulose derivatives Hydroxypropyl Methylcellulose (HPMC) is made to get around some of the drawbacks of natural polysaccharides. HPMC is created by chemically altering cellulose by methylating and hydroxypropylating it, which gives it better water solubility, thermal stability and superior film-forming qualities. Because HPMC films are usually robust, pliable, transparent and oil and grease resistant, they can be used in food packaging and pharmaceuticals, particularly for compositions with control release.^[4]

The objective of this comparative study is to methodically examine and evaluate the mechanical, physical, and barrier qualities of thin films derived from Guar gum, Sabudana starch, Tragacanth and HPMC. These characteristics include tensile strength, elasticity, and elongation at break. Additional physical characteristics include thickness, transparency, and surface                                                                             morphology. ^[5] The study aims to give a thorough grasp of each material's advantages and disadvantages by assessing these factors. The knowledge acquired will direct future advancements in the design of environmentally friendly, functional thin films for a range of industrial applications and assist in determining if these biopolymers are appropriate for certain applications. ^[3]

Furthermore, knowing how natural polymers like Guar gum, Sabudana and Tragacanth behave in contrast to semi-synthetic materials like HPMC might help achieve the larger objective of developing high-performance biodegradable materials that lessen their negative effects on the environment and encourage sustainability. ^[4,5]

MATERIALS AND METHODS:

Materials

1. Guar Gum­- [Laboratory grade].
2. Sago starch (Tapioca pearls) - [Laboratory grade].
3. Tragacanth- [Laboratory grade]
4. Hydroxypropyl Methylcellulose (HPMC) - [ Laboratory grade]
5. Glycerol (plasticizer) - [Laboratory grade]
6. Distilled water was used throughout the study. [Laboratory grade] ^[3]

Preparation of Film-Forming Solutions

1. Guar Gum: Distilled water was mixed with guar gum (2% w/v) and stirred constantly until the gum was fully hydrated. As a plasticizer, glycerol (30% w/w of polymer weight) was used. Bubbles were eliminated by homogenizing and degassing the solution. ^[3]

2. Sago Starch: The distilled water (1:5 w/v) was used to soak the sabudana pearls for five to six hours. The soaked pearls were stirred and heated at 85 to 90°C until they formed a transparent gel. The glycerol (30% w/w of dry weight) was combined with the sabudana gel. The fluid used for film formation was homogenized. ^[6]

3. Tragacanth: Distilled water (1:5 w/v) was used to soak tragacanth powder and left to hydrate for 5–6 hours to form mucilage. The hydrated mucilage was stirred continuously and heated at 85–90°C until a uniform viscous gel was obtained. Glycerol (30% w/w of the dry weight) was added to the gel as a plasticizer and mixed thoroughly. The resulting fluid used for film formation was homogenized to ensure uniform consistency before casting. ^[5]

4. HPMC Film: With constant stirring, distilled water (2% w/v) was gradually mixed with HPMC powder. Complete dispersion was followed by the incorporation of glycerol (30% w/w of HPMC). Until the mixture was uniform and lump-free, it was agitated. ^[7]

Film Casting and Drying: Each film-forming solution was poured onto leveled Petri dishes. Films were dried at room temperature (25–30°C) for 24–48 hours. After drying, the films were peeled carefully and conditioned in a desiccator (50% RH) for 48 hours before testing. ^[8]

Characterization of Films

1. Thickness: Thickness uniformity demonstrates a pleasing physical look. It displays a consistent distribution of the contents. How thick of thin films was measured with a vernier caliper (N-12, Mitutoyo, Japan) at three separate locations, and the average values were computed. ^[12-14]

2. Moisture Content:  Determine the thin film's initial weight prior to drying. Dry the film for a predetermined amount of time at a predetermined temperature (for example,100–120°C) in an oven or vacuum chamber. To stop the film from absorbing moisture again, cool it in a desiccator. Once the film has dried, weigh it one more time (final weight). Use the following formula to determine the moisture content: ^[12,13,15]

Where,

Initial Weight= weight of the sample before drying

Final Weight= weight of the sample after drying

3. Water Solubility: 2 cm × 3 cm pieces of each film were cut and stored in a desiccator with silica gel for 7 days. Samples were weighed and placed into test beakers with 80 ml of deionized water. The samples were maintained under constant agitation at 200 rpm for 1 h at 25 °C. The remaining pieces of film were then collected by filtration and dried again in an oven (at 60 °C for 24 h) to constant weight. The percentage of total soluble matter (% solubility) was calculated as follows: ^[12,16]

Where,

Wi= Initial dry weight of the sample

Wf = Final dry weight of the sample

4. Water Vapour Permeability (WVP) Test: For water vapor transmission studies glass vials of approximately equal diameter were used as transmission cells. These transmission cells were washed thoroughly and dried to constant weight in an oven. About 1 g of fused calcium chloride as a desiccant was taken in the vials and the polymeric films were fixed over the brim with the help of an adhesive tape. These pre-weighed vials were kept in a chambers filled with saturated salt solutions to achieve the required humidity conditions for a period of 24 h. Different saturated salt solutions are used to maintain the desired humidity condition like Potassium chloride (90 % RH), Sodium chloride (75 % RH), Potassium carbonate (45 % RH). The weight gain was determined after a period of 24 h and water vapor transmission rate was calculated. Water vapor transmission (Q) usually expressed as number of grams of moisture gain per 24 h per square centimeter. It was calculated as follows: ^{[12,13,16,17]}

Where,

X = film thickness (m)

ΔP = water vapour pressure difference across the film (Pa)

5. Tensile strength: Tensile strength, which can be calculated from the highest stress applied to a point at which the specimen breaks, applied load at rupture and the film’s elongation, as indicated by the equation that follows. Tensile strength measurement provided a straightforward way to ascertain the mechanical properties of the polymeric films. A manually created tensile strength measurement tool was used to ascertain the films' tensile strength. A 25 mm wide by 50 mm long film was cut, secured between two clamps, and weighted on the other side of the pan until the film broke. Tensile strength and the weight needed to shatter the film were recorded. ^[12,13,15]

Where,

TS = Tensile strength (MPa)

F??? = Maximum force at break (N)

A = Cross-sectional area of the film (mm²)

6. Transparency: The transparency of a mucilage film, was calculated by using a UV-Vis spectrophotometer. The film is cut into a rectangular shape, placed in a cuvette, and its light transmittance at a specific wavelength (like 540 or 600 nm) is measured. The transparency value is then calculated by multiplying the transmittance percentage by the film thickness. Higher transparency values indicate more opaque films. ^[18,19]

Where,

A600: is the absorbance of the film at 600 nm

x: is the thickness of the film in millimeters

RESULT AND DISCUSSION:

Table 1: Comparative Properties of Edible Films from Guar Gum, Sago Starch, Tragacanth and HPMC

1.  Thickness:

Fig no. 1: Thickness Graph

The graph shows a decreasing trend in film thickness from Guar Gum (0.20 mm) to HPMC (0.12 mm). Guar Gum produced the thickest film due to its high viscosity and gel-forming ability. In contrast, HPMC formed the thinnest film, likely due to its better film-spreading and uniformity. Sago Starch and Tragacanth showed intermediate values. These differences are influenced by the polymers' molecular structure and film-forming behavior.

2.  Moisture Content:

Fig no. 2: Moisture Content Graph

The graph illustrates that Tragacanth films exhibit the highest moisture content (14.8%), followed by Sago Starch (13.2%) and Guar Gum (12.5%), whereas HPMC films have the lowest moisture content (6.5%). The higher moisture retention in natural polymers is attributed to their hydrophilic groups, which facilitate water binding. In contrast, HPMC's lower moisture content suggests greater water resistance. However, the higher moisture content of natural polymers may enhance film flexibility and biodegradability, supporting their greater acceptability for sustainable and eco-friendly applications.

3. Water Vapour Permeability:

Fig no. 3: Water Vapour Permeability Graph

The graph presents the water vapour permeability (WVP) of edible films made from different materials. Among the materials, natural polymers like Tragacanth and Guar Gum show moderate WVP values, indicating a good balance between barrier properties and breathability. While HPMC (a semi-synthetic polymer) shows the lowest WVP, this may limit moisture transfer too much in some applications. Sago Starch, another natural polymer, shows the highest WVP, which may be beneficial in applications requiring higher moisture transmission.

4. Tensile Strength:

Fig no. 4: Tensile Strength Graph

The graph shows that natural polymers like Guar Gum and Tragacanth can form edible films with varying tensile strengths. While HPMC, a semi-synthetic polymer, exhibits the highest strength, Guar Gum- a natural polymer- also demonstrates relatively high tensile strength (~28 MPa), outperforming Sago Starch and Tragacanth. This suggests that some natural polymers can offer strong mechanical properties, making them viable and sustainable alternatives to synthetic options. With further optimization, natural polymers can be enhanced to meet performance requirements while also being environmentally friendly and biodegradable.

5. Transparency:

Fig no. 5: Transparency Graph