Use of PLA (Biopolymer) for Short-Shelf-Life Fresh Food Packaging

INTRODUCTION
“Every Coin has two faces”, this is a perfect phrase to demonstrate role of plastics in today’s era. Decades back when plastics entered the world, it was like a boon for commercial industries because of the impressive characteristics it showcased. However contemporary world is facing second side of plastics. Nowadays plastic is a ubiquitous part our society and ecosystem. It is part of society in the form of different goods and part of ecosystem in the form of “Plastic Waste” accumulated in landfills and oceans. Protecting and preserving ecosystem for future generations is everyone’s responsibility. Changing climate & deteriorating ecological balance is a bitter truth today and packaging is contributing significantly towards it. In form of plastic packaging waste, packaging industry is paying negatively towards incredible ecosystem. Post-consumer packaging waste represents one of the major fractions of plastic packaging waste present on this planet. It represents 3% of total waste sent to landfill every year. Current packaging trends of disposable packaging and single use packaging are one of the major originators of post-consumer packaging waste. Everything we buy comes in packaging: food, household goods, personal care, electronics, medicine etc. A friendly way out to cut down the accumulation of plastic waste and its negative impacts on ecosystem is “green packaging”. What can we do is to ensure that our packaging is eco-friendly. However modern business world wants to achieve sustainability with cost effectiveness, fortunately it is possible with Biopolymer. Biopolymer-based materials have garnered increasing attention from packaging markets due to concerns in recent years from both environmental and economic perspectives of traditional petroleum-based polymers. The extensive use of these traditional synthetic polymers has already resulted in serious ecological problems. Because of the ever-increasing amount of plastic wastes worldwide, biopolymers can be a great solution for packaging to achieve ‘environmentally friendly’ status. Biopolymers have numerous advantages over conventional Petroleum derived polymers as they are biodegradable, compostable, lower Carbon footprint and best of all, not petroleum derived- so there’s no leaching of harmful chemicals into the food and body.It performs same way as traditional plastics do, but also they come with an added advantage of being 100% compostable – which could help us to divert packaging waste from ending up into ecosystem to valuable humus to further improve soil fertility so that plants can grow again.
WHY SHOULD USE “PLA” (BIOPOLYMER) IN FRESH FRUIT/SALAD/VEGETABLE PACKAGING
As society is becoming more aware of endangered ecosystem due to growing plastic waste problems, they demand the use of eco-friendly packaging materials. Now the selection of packaging polymers depends not only on polymer standard properties, but also on the sustainability aspects of polymers. Packaging companies are continuously working to develop bio-based substitutes that can decompose in a landfill same way as an ordinary paper do. PLA is great answer to all these concerns. Using PLA over conventional petroleum based polymers offer numerous advantages. In contrast to petroleum-based plastics , it is obtained from renewable resources, its production causes 60% less CO2 emission, wastes 50% less non-renewable energies, it can be recyclable, biodegradable ( It is often used in medical implants that biodegrade within the body over time) and compostable ( in commercial facility). Also PLA does not produce any toxic substance like chlorine-hydrocarbon compounds or any other inorganic substances at the time of decomposition. Thus a PLA container dripped mistakenly into ecosystem (landfill or ocean), would typically degrade in six to 24 months. However decomposition of petroleum-based plastics may release toxic substances and deteriorate fertility of the soil.
PLA is also advantageous in terms of the greenhouse effect and conservation of resources. Overall PLA is very expedient in preserving environmental balance. Apart from all these benefits, prime Unique Selling Point of PLAis its low cost, which makes PLA a win-win alternative for sustainable packaging. As fresh food packaging is a type of single use packaging which significantly add to plastic waste. Consequently substituting conventional petroleum-based plastics with sustainable PLA in fresh food packaging is highly advisable.
POLY LACTIC ACID (“PLA”) – BIO PLASTIC: AN OVERVIEWPLA is a bioplastics which means bio and plastics. A bioplastic is a material that is either derived from biological raw materials or biodegradable, or both. PLA stands for Polylactic acid or Polylactide. It belongs to the family of aliphatic bio polyesters made from –hydroxyl acids, including polyglycolic acid or polymandelic acid.
Lactic acid and lactide (cyclic di-ester) are the two main fundamental building block of Polylactic Acid. 2-Hydroxypropanoic acid is the IUPAC name of lactic acid. Lactic acid is a hydroxyl acid with an asymmetric carbon atom and it exists in two optically active configurations, the L (+) and D (-) isomers as shown in figure. It is hygroscopic in nature,
thus have excellent water solubility. Lactic acid can be manufactured either by using carbohydrate fermentation or chemical synthesis. Carbohydrates used to make it are derived from renewable biomass, usually from plant starch such as from cassava, corn, sugarcane or sugar.
PRODUCTION OF “Polylactic Acid” BIOPLASTIC
Polylactic Acid is mainly produced using two different processes: 1) Condensation and 2) Polymerization. In condensation process, PLA is produced by direct condensation of Lactic acid. In this process water is the byproduct. The second way of producing usable PLA is Polymerization. Polymerization process further consists of two steps: – a) Fermentation and b) polymerization. In the first step, starch obtained from plant sources is fermented with the help of bacteria like lactobacilli to generate lactic acid. This Lactic acid produced act as in-feed for second step of the process, which is polymerization. During polymerization chain reaction occurs which convert lactic acid into long-chain carbon polymer i.e. polylactic acid. Polymerization used to produce polylactic acid can be of two types: Solid state polymerization and Ring opening polymerization. However the most common type of polymerization is ring-opening polymerization which utilizes metal catalysts in combination with lactide to generate larger PLA molecules. In this way usable PLA is produced using Lactic acid or lactide. At the end production process Polylactic acid is molded into small plastic pellets so that they can be easily transported. These PLA pellets are used to produce different PLA products with the aid of different machines, forms, die cutters, and impact of heat. Although there are many sources for plant starch used to produce lactic acid for PLA, but corn is the main source among all of them. However this corn is not a food grade corn, hence not suitable for human consumption. It is specially cultivated for industrial use. Only 0.05% of the global starch production is used for the manufacturing of PLA polymer. Therefore, production of PLA has no impact on the food supply of humans and animals.
FRESH FRUIT/SALAD/VEGETABLE PACKAGING (RIGID CLAMSHELLS): AN OVERVIEW
Packaging technology is a method to reduce post-harvest deteriorative processes of fresh produce items like fruits, salad and vegetables. Fresh fruit/salad/vegetablelike small fruit, berries, mushrooms, precut produce, prepared salads etc., are high value produce items or items that are easily damaged by crushing. The most important packaging requirement for Fresh fruit/salad/vegetable consumer packs is mechanical protection. Thus Clamshells are most often used packaging format for fragile Fresh fruit/salad/vegetable as they are excellent in providing mechanical protection.

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A clamshell is a single piece transparent rigid container consisting of two half portions joined together by a hinge area that allows opening and closing of clamshells. Clamshells can use a variety of means of closing or sealing like self-locking tabs, snaps, friction fit, pressure-sensitive tape, labels or are heat sealed. Heat sealing is most convenient way of making clamshell containers tamper resistant and prevent package pilferage. Clamshells are clear, product can be seen through the package and vibrant colors of fruits or vegetable can attract consumers towards package, thus clamshells also present a very pleasing consumer package. Clamshell containers for fresh produce items can be made of a variety of plastics, two of the commonly used materials are PET and polystyrene (OPS). Clamshells can either be made by thermoforming or injection molding. Clamshells are also widespread for their low cost, versatility, easier to clean; not decaying when wet, longer service life, do not harbor disease, and can be nested and made collapsible.
SUITABILITY & IMPLICATIONS OF USING “PLA” FOR SHORT-SHELF-LIFE FRESH FOOD PACKAGING (FRUITS /SALAD/ VEGETABLES) CLAMSHELLS
Polylactic Acid is “thermoplastic” polyester on the basis of its behavior towards heat. It can be easily heated to melting point (150-160 degrees Celsius in the case of PLA), cooled and reheated again without significant degradation of properties. Thermo-plastic nature also enables PLA to be easily Injection molded, blow molded, thermoformed, film formed and then subsequently recycled. PLA is a high strength and modulus polymer. Mechanical properties of PLA film are better than that of PS, but comparable to those of PET. Although melting point and glass transition temperatures of PLA is comparatively lower than that of PET and PS, but low melting temperature helps PLA clamshells to heat seal at low temperatures and make them temper evident. Because of low glass transition temperature (111°F – 145 °F) PLA can only be used for low temperature applications. Glass transition temperature of PLA is time dependent and changes with time. PLA films displays appreciable shrinking near melting temperature, thus PLA clamshells can be wrapped using PLA shrink labels to make temper proof. The surface energy of PLA is higher than that of PS which makes it better for printing and converting operations. PLA labels can be used for Marketing/Brand/ Graphics on PLA clamshells. By choosing same polymer (PLA) for label and clamshell, Fresh fruit/vegetable clamshells could be made more user-friendly as labels are not required to be detached before discarding the clamshells. Moreover PLA labels will also add to the material yield during recycling of clamshells. UV-C is not transmitted through PLA but nearly all the UV-B and UV-A light passes through it. Therefore, the application of transparent PLA films for long shelf life food products may require additives to block UV light transmission. Solubility parameters shows that PLA does not interact with ketones, esters, aromatic hydrocarbons, sulfur compounds or water which makes PLA better than PET in terms of flavor and aroma retention. PLA has higher carbon dioxide, oxygen and water permeability coefficient than that of PET but lower than that of PS. PLA is breathable, which helps to reduce fogging and keeps fruit or vegetables fresh inside the clamshells. PLA barrier to ethyl acetate and D-limonene is also comparable to that of PET, which again aid PLA clamshells to keep aroma & flavors of food intact. PLA clamshells are not risky in terms of lactic acid & its derivative’s migration to food content as the amount migrated is very much lower than permitted dietary lactic acid intake values. Therefore, PLA is a completely safe polymer to use as a packaging material for food packaging. As far as Optical Properties are concerned, PLA is superior to PET and PS in terms of appearance, clarity & gloss. Equally important is PLA’s high stiffness which makes it better in terms of down gauging potential versus Polystyrene & PET, along with its ability to run on existing extrusion lines and tools. Because of high stiffness PLA can runs at line speeds 20% faster than PET, which makes PLA better in terms of machinability in comparison to PET & Polystyrene. Physical and mechanical properties of PLA can be tailored through polymer architecture. Polylactic Acid has similar characteristics to conventional petroleum derived polymers like polypropylene (PP), polyethylene (PE), or polystyrene (PS). So existing equipment designed for petroleum derived plastics can be used to manufacture PLA commercially. This makes PLA a cost effective and efficient polymer to produce. PLA clamshells can be transported same way as PET / PS clamshells are being transported. By using PLA clamshells for fresh food packaging also enables consumers to claim extra benefits in few countries like avoiding paying a ‘‘green tax’’ in Germany and meeting environmental guidelines in Japan. PLA is an economically feasible material since it costs $0.85 per lb. or lower as compared to PET which cost about $ 0.65 per lb.Top of that PLA Cost is insulated from volatile and rising petroleum prices as it is made from biobased materials instead of petrochemicals.
CONCLUSION
PLA is a promising polymer to create “plastic waste” free world. It is an ecofriendly and cost-effective alternative to commodity of petrochemical-based materials. The introduction of PLA will shift the reliance from non-renewable petroleum to renewable biobased materials. PLA will encourage the use and expansion of agricultural based materials. As the PLA price drops and new facilities produce higher volumes of PLA, new applications will be pursued. Although PLA is a relatively new polymer, it is possible to manipulate its physical, mechanical and barrier properties by changing its chemical composition, and varying its molecular characteristics. It is also possible to blend PLA with other polymers to enhance its properties & increase its environmental benefits, thus making it a suitable alternative for use in packaging.
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