Phan Van Hoang- 09/05/2020
- 6221
Biodegradable packaging is a product made from natural materials. Packaging made from bio-based materials must meet standards such as: moisture and water resistance, optical properties, flexibility, easy sealing and printing, heat and chemical resistance, stability, environmental friendliness, and competitive pricing.
In addition, packaging must comply with food packaging regulations, and the interaction between the packaging and food must ensure product quality and food safety.
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The materials used to produce biodegradable packaging include:
1. PLA - (Polylactic Acid)
PLA is produced through starch fermentation. This type of polymer consumes less energy than conventional plastic. Although it is environmentally friendly, it is not widely used due to its high production cost.
PLA is produced using corn starch as the raw material. The corn is ground and rolled. It is then converted into dextrins through saccharification. These dextrins are converted into lactic acid through fermentation.
The concentration process causes two plastic molecules to combine into a ring structure called lactide. This compound is purified through distillation and then polymerized to form long polymer chains.
The material is then sold to companies for further processing into final products. After a period of use, PLA can be degraded or recycled.
Producing PLA (Polylactic Acid) packaging from watermelon rinds
Currently, watermelon rinds are available in large quantities and have relatively low economic value, making them suitable as a raw material for packaging production.
After being crushed, watermelon rinds are fermented to produce a lactic acid solution. The lactic acid is then crystallized for purification, followed by polymerization to obtain polylactic acid. The material is then formed into the required shape.
2. Poly(hydroxyalkanoates) materials
Poly(hydroxyalkanoates), or PHA, is another promising polymer material. This polymer is being studied as a potential replacement for plastic packaging. Biologists first discovered the existence of PHA in bacterial cells in 1925. Many types of PHA have been synthesized from different carbon sources and microorganisms and then processed into usable materials.
There are two main methods for synthesizing PHA:
- Fermentation method: Crops such as corn are cultivated and harvested, after which glucose is extracted from the plants. The sugar is then fermented in cells containing PHA. The cells are washed and centrifuged to release PHA, which is then concentrated and dried in molds.
- PHA production within plant cells: This is a technique currently being studied. The process is similar to the method described above but skips the fermentation stage. A large amount of solvent is used to extract the polymer from the plants, after which the solvent must be removed. Therefore, this method requires a significant amount of energy.
- Advantages of PHA compared with PLA: PHA has a high biodegradability and is relatively easy to synthesize. When placed in a natural biological environment, it can decompose into CO₂ and water. This gives PHA a wide range of potential applications.
3. Thermoplastic starch - TPS
TPS is a polymer made from 100% starch and has already established a position in the market. Its advantages include low energy consumption and a lower cost compared with conventional plastics.
To obtain properties similar to those of plastic, TPS is blended with other materials. Starch can be combined with other polymers, and when the starch content is greater than 50%, different types of plastic materials can be produced.
a. Starch/Vinyl alcohol copolymers
There are many types of plastic with different shapes and properties. Starch-containing plastics with an AM/AP ratio greater than 20/80 will not dissolve immediately, even in boiling water, while those with a lower ratio will partially dissolve.
A limitation of this material is that it is brittle and sensitive to moisture.
Degradation mechanism:
The natural components, although protected by the polymer network structure, can still be degraded by extracellular enzymes produced by microorganisms. The synthetic components are degraded through surface adsorption by microorganisms.
b. Aliphatic polyesters
When starch is blended with aliphatic polyesters, the resulting material becomes thermoplastic and can be easily processed by blow molding.
Some suitable aliphatic polyesters include:
- Poly-3-caprolactone.
- Polymers formed from reactions involving glycols.
This combination improves mechanical properties, reduces sensitivity to water, and increases biodegradability.
Many studies have explored replacing petroleum-based plastic packaging with plastic packaging made from corn-based materials. Materials produced from these renewable sources can help reduce environmental pollution because their decomposition does not generate toxic substances.
4. Cellulose-based materials
Properties of cellulose-based materials
Cellophane is transparent and has a highly glossy surface.
Its mechanical strength is relatively low, including tear and tensile strength. It can be easily torn once a cut has been made.
It has low rigidity.
It cannot be heat-sealed directly. Cellophane can be coated with nitrocellulose to enable heat sealing during lamination and improve gas barrier properties.
Cellophane film is relatively stiff and brittle. It can be stretched and wound easily on film-forming equipment and has fairly good mechanical strength, but if it is cut or punctured, it can tear very easily.
It can be easily folded and creased.
Its cost is relatively high.
Cellophane production
- Cellulose is extracted from wood.
- The cellulose is placed in a solvent and chemically treated.
- It is extruded to form a film.
- Impurities are removed to produce a transparent film.
5. Chitosan film
Properties of chitosan
Chitosan is a polysaccharide containing non-toxic nitrogen and has a high molecular weight.
It is a solid, porous, lightweight material with a flake-like structure that can be ground into different particle sizes.
Chitosan is white or pale yellow and has no odor or taste.
It is insoluble in water, alkaline solutions, and concentrated acids, but dissolves in dilute acid (pH 6), forming a clear colloidal solution with good film-forming properties. Its melting point is approximately 309–311°C.
How to produce chitosan packaging film
Chitosan is finely ground using a machine to increase its contact surface area.
A 3% chitosan solution is prepared in a 1.5% acetic acid solution.
PEG-EG 10% additive (1:1 ratio) is then added and thoroughly mixed. The mixture is left to stand for a while to remove air bubbles.
The resulting mixture is then evenly coated onto a stainless-steel tube heated to 64–65°C. The stainless-steel tube is heated using steam.
The film is dried for approximately 35 minutes and then removed from the tube.
The resulting film is a glossy, ivory-yellow, odorless and tasteless layer with improved functional properties. This is chitosan film.
Applications of chitosan
In practice, chitosan film has been used to package and preserve various fruits and vegetables, such as peaches, cucumbers, beans, kiwifruit, and others.
Advantages of chitosan film
- Easily biodegradable.
- Waste shrimp shells are an abundant, low-cost natural raw material available year-round, making them a convenient source of chitin and chitosan.
- Utilizes waste from seafood processing to support food preservation applications
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