Background

Biodegradable packaging is defined as packaging that will naturally disintegrate ordecompose, usually in a certain period of time. Most plastic containers currently used for food packaging are made up of petroleum-based polymeric materials. Their use is widespread in this and many other applications, due to their numerous advantages, including large scale availability, relatively low production cost, lightweight, versatile and good mechanical and barrier properties. However, these materials have certain disadvantages since, in addition to being synthesized from a non-renewable source, they are not biodegradable, proving a major source of generation and accumulation of residues. At present, the bio-polymer concept is emerging. Biodegradable materials are associated with the use of renewable raw materials such as proteins and polysaccharides extracted from agricultural, marine, animal or microbial sources. These materials can be degraded by the environment (exposed to soil optimum moisture, microorganisms and oxygen) into simple substances (water and carbon dioxide) and biomass. However, materials from natural polymers are associated with poor mechanical and “barrier” properties and also low thermal stability. For this reason, researchers need to develop synthetic modification strategies to improve their poor properties.

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Types of Biodegradable Packaging

Biodegradable packaging comes in many shapes and sizes, as well as materials and uses. Among those uses are as water bottles, yogurt cups, injection-molded cups, spoons and forks, thermoformed cups and trays, packaging for short shelf-life supermarket products such as fruits and vegetables. These packaging systems, known as “active packaging systems”, involve the use of material that can change their packaging conditions to extend its shelf life by interacting with the food. On the side of the materials, many of them that are used are made from proteins and polysaccharides extracted from agricultural, marine, animal, or microbial sources. These materials can degrade easily when exposed to the environment (soil optimum moisture, microorganisms, and oxygen). One of those materials involves the use of soy protein-Poly(lactic) Acid, aside from being cheap due to extensive production of soybeans in some countries or due to extraction from industrial waste, it has excellent film-forming properties and provides good barriers towards oxygen, aromas and lipids that are below low to intermediate moisture conditions.

Polylactic Acid

Polylactic acid, also known as poly(lactic acid) or polylactide (PLA), is a thermoplastic polyester with backbone formula (C3H4O2)n. PLA is derived from renewable resources, such as cornstarch or sugarcanes. PLA polymers are considered biodegradable and compostable. PLA is a thermoplastic, high-strength, high-modulus polymer that can be made from annually renewable sources to yield articles for use in either the industrial packaging field or the biocompatible/bioabsorbable medical device market. Bacterial fermentation is used to make lactic acid, which is then converted to the lactide dimer to remove the water molecule that would otherwise limit the ability to make high molecular weight polymers. The lactide dimer, after the water is removed, can be polymerized without the production of the water. (See the figure below)

Why is Poly-Lactic Acid (PLA) the best?

Poly-Lactic Acid (PLA) is currently one of the most promising biodegradable polymers (biopolymer), it is considered so because PLA can undergo abiotic degradation (can degrade without the need for an enzyme), this is true as long as the PLA is produced from renewable sources (carbohydrates) by fermentation, and because PLA can form composites with other materials such as soy, starch, fibrous cellulose, etc. As an advantage, PLA when compared to other biopolymers such as Polystyrene, prove to have better mechanical properties. Also, PLA, when mixed with Nisin, shows limited bacterial activities, which could be beneficial when coated onto food containers or water bottles. On the other hand, market studies show that PLA, when made into composites with other materials, is economically feasible for packaging. PLA when plasticized with other materials often show a faster degradation rate, with some plasticizers performing better than others. 

Characteristics of PLA Materials

PLA may be specifically designed for a variety of fabrication techniques, including injection molding, sheet extrusion, blow molding, thermoforming, film forming, and fiber spinning, because of its excellent thermal processability. However, some factors need to be adjusted based on the procedure (D-isomer content, molecular weight distribution). Different PLA materials may be created for various uses by adding L-, D-, or meso lactide stereoisomers to the polymer backbone. Despite the fact that PLA is hydrophobic, the pellets must typically be dried from 60 to 100 C for a number of hours before processing in order to prevent excessive hydrolysis and changes to the polymer’s physical characteristics. Since PLA-based materials are rigid and brittle, plasticizers have been added to enhance the mechanical performance of the PLA films.

Environmental Benefit

There are a great number of benefits that can be attained simply by switching to biodegradable packaging in our daily life. First, it can reduce piles of unrecycled, non-biodegradable packaging that are thrown away into the environment, possibly to landfills or as land and water pollution, as biodegradable packaging can be degraded in a shorter period of time compared to non-biodegradable items. Next, if the packaging is thrown in soil, it can lead to better composting of soils, which can make soil more suitable for planting (fertile). The following benefit is that it can lead to lower carbon footprints, as fossil fuels are not involved in the production of biodegradable materials. Finally, for manufacturing at a larger scale, biodegradable products often need less energy to produce it. 

Disadvantage of Biodegradable Packaging

Biodegradable materials, even though they have a lot of benefits, there are a few drawbacks associated with them. First, since the materials are produced from crops such as soybeans and corn, there is a risk of contamination due to the use of pesticides. Next, when biodegradable materials decompose, some of them release gasses such as Methane and Carbon Dioxide that are harmful to the environment, some of them don’t even decompose in places such as seas, lakes, etc. This shows that a particular environment and conditions are required for certain biodegradable materials. Finally, even though a lot of people are using biodegradable materials, most of them do not know how to differentiate between biodegradable and non-biodegradable materials, which can lead to more waste in the end. 

References

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