Green Packaging Alternatives- Facts and challenges
Sustainability is going to play a major role in the future of packaging as the consumer expects businesses to be accountable for their environmental impact. Over the last decade, green practices have gained ever-increasing importance in global conscience.
According to NielsenIQ, 81% of people believe that companies should help in the fight against climate change. Businesses across the globe are looking for packaging that serves the same function as prior forms and is ecologically responsible. This has led to a lot of development activities for alternatives to plastics or for making plastics degradable.
As a result, various terminologies like bioplastics, oxo-degradable, compostable, biodegradable, and recyclable, have come into the picture, which creates a lot of confusion among users. This article will have a dig into this terminology and will differentiate them according to their application.
Bio-based Plastics
Bio-based plastics or bioplastics are being confused as plastics that are Biodegradable, but these are plastics manufactured using bio-resources. Bio-based plastics can be defined as “ man-made or man–processed organic macromolecules derived from biological resources and for plastics and fiber applications”. Bio-based plastics can be
– Biodegradable
– Compostable; or
– Synthesized from plant and/or animal resources
They can be biodegradable or not. The biodegradability depends upon the chemical structure of the polymer not on the sources used for the monomer.
Bio-based plastics can be categorized into three groups:
1. Bioplastics that are based on renewable resources and are biodegradable, like starch, cellulose, proteins, lignin, Polylactic acid (PLA), Polyhydroxyalkanoates ( PHAs), poly hydroxybutyrate ( PHB),
2. Bio-plastics that are petroleum-based but are 100% biodegradable, for example, polycaprolactone ( PCL), polybutylene succinate (PBS ), Polybutylene adipate (PBA), and Polyvinyl alcohol ( PVOH)
3. Bio-plastics are obtained by using monomers coming from mixed biological and petroleum resources like polyester obtained from petroleum-based terephthalic acid and plant-based ethanol. This class includes bio-PE, bio-PVC, bio-PET, bio-Polyamide
Biopolymers are derived from different natural resources mainly polysaccharides, proteins, and fibers. The two main groups of biodegradable plastics entering the market are polylactic acid (PLA) and starch-based polymers. These polymers have significant potential as their properties can easily be altered in order to impart desirable properties.
Polylactic acid is compostable and has characteristics similar to polypropylene, polyethylene, and polystyrene. It has the second largest production volume among bioplastic. There are a vast array of applications for PLA, which includes plastic films, bottles, biodegradable medical devices. PLA can be processed using conventional processing techniques, which makes it a cost-effective alternative.
Bioplastics developed from starch have advantages like higher biodegradability, renewability, and good oxygen barrier properties, which makes it the most suitable alternative for some commercial packaging applications. Keeping these features in mind, several attempts have been made to incorporate starch in conventional
polymers to impart biodegradability.
However, the hydrophilic nature of starch molecules and the hydrophobic nature of the plastics results in poor starch polymer interfacial interaction leading to loss of mechanical properties. However, a stronger interaction between the starch granules and the plastic matrix has been achieved
with gelatinized or destructured starches.
The surge in the bioplastic market is mainly because of two reasons; petroleum-based plastics are normally non-biodegradable, and bioplastics are considered sustainable solutions owing to limited petroleum resources. Bioplastic alternatives to conventional plastics materials with nearly the same properties and performance but with the great advantage of reducing the carbon footprint are now available commercially.
However, the main concern in the case of bioplastics is land used for renewable feedstock for the production of bioplastics. At present, the land used for renewable feedstock is 0.016%, which comes out to be 0.79 million hectares out of 4.8 billion hectares. Though production of bioplastics is growing it is estimated that in 2024 the land dedicated to them will reduce to 0.021% owing to growing competition between renewable feedstock used for the production of plastics and that used for food and feed.
Biodegradable and Compostable Plastics
Biodegradable plastics are materials that can be completely converted into water, CO2, and biomass through the action of microorganisms such as fungi and bacteria. These plastics have the ability to be degraded by microorganisms present in the environment by entering the microbial food chain. Biodegradability is not dependent on the raw material origin, but on the chemical composition of the polymers. Biodegradability is not a uniform process due to varying climatic conditions.
Technically, every organic material biodegrades with time, but the rate of biodegradation of different materials can vary on an exponential scale, as the length of the degradation process is highly dependent on parameters such as humidity and temperature. That means all the plastics break into small fragments when left in the environment due to weathering and photodegradation. However, after degradation, they yield so-called micro-plastics which further pollute soil and water bodies. Hence, the term biodegradable is meaningless unless a timeframe or environmental conditions are specified.
Compostable plastics are a subset of biodegradable plastics, defined by the standard conditions and timeframe under which they will biodegrade. All compostable plastics are biodegradable but not all biodegradable plastics can be considered compostable. In other words, compostable plastics are a more specific form of biodegradable plastics.
According to ASTM D6400 or EN13432, materials that weeks and biodegrade at least 90% within 180 days in a municipal or industrial composting facility can be categorized as compostable. The left 10 %mass at the end of six months is valuable compost, or biomass and water. The standard also ensures that the leftover compost is free of toxins and can be used for agricultural applications.
By definition, “Plastics that undergo degradation by biological processes during composting to yield CO2, water, inorganic compounds, and biomass at a rate consistent with other compostable materials, leaving no distinguishable, visible or toxic materials are called compostable plastics”.
Compostable plastics can be produced with either bio-based or fossil raw materials. There is a misconception that bioplastics are compostable, but this is not always true as some of the conventional plastics are manufactured using biomass, but they do not biodegrade. Compostable plastics degrade in industrial composting facilities. There are a number of ASTM and European standards to check the compostability
and biodegradability of plastics in different environments
Internationally, there is no standard for home composting of plastics and almost all compostable plastics must be disposed of in a designated municipal composting facility. Many certified compostable materials require the higher temperatures of industrial settings to biodegrade or to enhance the rate of biodegradation. The
mechanism of degradation is that the bacteria or microorganisms consume the compostable plastics and breathe out CO 2 .
The first phase of degradation is “abiotic degradation”, which basically is chain scission and reduces the molecular weight of the polymer to enable it to be digested by the microorganism. Microorganism does
not play part in this first phase and that’s the reason it is called abiotic. Normally, presence of water/moisture causes this phase and is a hydrolytic degradation of esters. High temperature further accelerates the reaction which is the reason it is to be done in industrial composts.
In the second phase bacteria starts eating the fragmented plastics, water and CO2 are released in the process. Eventually, the bacteria die and the resulting biomass is the dead bodies of the microorganism, the biomass compost.
Theoretically compostable plastics appear to be the solution for overflowing landfills and oceans, but that seems impossible if there are no commercially available composting facilities. Moreover, for a consumer it is difficult to discern, whether the packaging is compostable, biodegradable, or recyclable, making all end up in similar waste streams though they may have different futures at the end. Compostable packaging can be a good choice for ready-to-eat food items, since, it can be disposed of in the same bin along with remaining food from where it can go for composting.
Oxo-degradable plastics
On one hand, there are plastics that are derived from natural resources and are biodegradable, but on the other hand, pro-degradant additives are incorporated into conventional plastics to make them degradable under certain conditions. Oxo-degradable is such material, which is made degradable by adding additives,
which facilitates the degradation of materials.
The additives are incorporated into polyethylene, polypropylene, polystyrene, polyethylene terephthalate, at the time of processing and conversion to the final product. These additives are normally based on the chemical catalysts, containing transition metals such as cobalt, manganese, and iron which cause chain scission as a result of chemical oxidation of the plastics polymer chains triggered by UV radiation or heat exposure.
In the second, phase, the resulting fragments are claimed to eventually undergo biodegradation. In addition to
additives that trigger oxidative fragmentation, stabilizers are also incorporated into plastics to inhibit the unwanted fragmentation of the polymer chain while plastic is still in use.
The world is divided if oxo-biodegradable are detrimental or beneficial for the environment. Producers of pro-oxidant additives claim their masterbatch degrades products made using conventional plastics, while there are certain groups that say that these additives only facilitate fragmentation of the materials.
The opponents of the oxo-degradable claim that plastics do not fully degrade but break down into very small fragments that remain in the environment and claims of oxo- degradability are misleading as they cannot be verified due to lack of standard specifications, which provides an explicit set of requirements to be satisfied by the product. The present standard on oxo-biodegradability merely tells the parameters for the testing degradation process, however, the criteria for passing the test degradation is not given in this method.
While on the contrary, proponents of oxo masterbatch claim that in presence of oxygen it turns ordinary plastics into a material with a different molecular structure. At the end of the biodegradation process, it is no longer plastic but turns into a material that is biodegradable in the open environment.
Photodegradable
Photodegradable plastics decompose in presence of light. When light strikes a molecule, it may initiate a number of reactions depending upon the chemistry of the molecule, light intensity, etc. In Photochemically degradable or photodegradable polymers the reaction results in the destruction of polymer chains. In the case of a photodegradable polymer, it is important to understand that the photochemical reactions that occur do not intend to completely degrade the polymer chains to low molecular weight species.
The purpose of photochemical reactivity is to fragment the polymer chains to introduce various functional groups like carboxylic acid, ketone, aldehyde, or alcohol. The formation of these functional groups in the chain facilitates biodegradation. The low molecular weight chains and these polar functional groups make plastics “wettable”
which supports the microorganism that carries out the biodegradation process. The formation of the oxygenated end groups is important for the cellular β- oxidation process, which is responsible for the stepwise dismantling of polymer chains.
The two-step process consisting of the abiotic reaction followed by biodegradation is called “oxo- biodegradation”, but when the abiotic process is facilitated by photochemical reactivity then the process is known as “photochemical oxo- biodegradation” or Photodegradation. Generally, aromatic base polymers are more susceptible to photodegradation. In addition to the type of plastics, the kind of light that falls on material
also affects the rate of photodegradation. Ultraviolet (UV) light is more effective in degrading all plastics than most other forms of light.
Photodegradability can either be induced by incorporating a photosensitive degradable chromophore into the backbone of the polymer chain or by the addition of certain additives which facilitate degradation reactions. Certain metallic ions and organic groups are known to absorb visible light strongly. If these ions or groups are included in plastic material, they are susceptible to light, heat, moisture, and mechanical stress, which in turn weaken the tensile strength of the polymer chain.
However, the rate of degradation depends upon the type of catalytic additives incorporated into the polymer chain. ASTM D5071 and ASTM D5208 are two test methods that are used to assess the biodegradability of photodegradable plastics by exposing them under standard light and heat conditions using accelerated
weathering chambers.
Recyclable
Another alternate for plastic environmental conversation is recycling. Confusion runs among consumers as to what can and cannot be recycled and in what manner. Interestingly, this confusion is not limited to consumers. Many brand owners, particularly smaller ones, don’t have the in-house knowledge to help guide them.
Recycling means the process of transforming segregated plastic waste into new products or raw materials for producing new products. It involves converting plastic waste into new products, changing them from their original form by physical and chemical processes. Although recycling uses the energy it helps to prevent new
resources from being used and old materials from entering the waste stream.
Recycling plastic materials either involves changing it into any other physical form (mechanical recycling), chemical form (pyrolysis), or energy recovery. Mechanical recycling is most common in the case of plastics and is preferred in the case of rigid packaging, but flexible packaging has certain limitations as they contain multiple
layers of different polymers having different chemical nature and processing behavior. Mono-material laminates are preferred over mixed plastics materials, as they are easier to recycle and contribute to an improved quality of recycled materials.
A mono-material laminate contains predominately one material type, such as PE, PP, PET, or Paper. According to CEFLEX guidelines, this means over 90% of one polymer type, as this is the upper threshold when adhesives, additives, and inks are excluded. BOPE and MDO PE-based mono-material laminates have been introduced in this category. Additionally, PP-based mono laminates also have replaced traditional multi-material laminates.
It is certain that in the coming years, sustainability will play a major role in designing packaging, and countless alternatives will find their way without proper consideration. However, without due consideration, it may end up in switching to materials and systems that actually have higher carbon footprints. Brand owners and packaging companies both have to work in alignment to get a solution that is sustainable and doesn’t compromise the quality of the product packed in it.
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