Commercial Marine-Degradable Polymers for Flexible Packaging (1)
It is cost-prohibitive to purchase large plastic bottles or metal cans of products, like shampoo or coffee. Consumer packaged goods (CPGs) companies supply single dosages of these products in flexible plastic pouches called sachets. Sachets can be in the form of monolayer films, like low-density polyethylene (LDPE), or multilayer laminates, including materials like LDPE, polyethylene terephthalate, and/or polypropylene. Although these materials are inexpensive, lightweight, and compatible with existing packaging converters, they are not recyclable or biodegradable.
A prevalent technique is to blend molecules that are susceptible to oxidative degradation, such as rutile nano-titania, with polyolefins to form oxo-degradable polymers. After they are exposed to UV light, oxo-degradable plastics fragment more readily than unmodified polyolefins. Polyolefins have also been copolymerized or blended with known biodegradable materials, like starch, in hopes of developing biodegradable blends. a comprehensive review of marine-degradable polymers and their properties is needed. The aim of the present work is to investigate polymers that (1) biodegrade in marine environments, (2) are compatible with industrial thermoforming techniques, (3) will be stable in the presence of product formulations, and (4) possess a moisture barrier or retain biodegradation characteristics when combined with a barrier layer.
Degradation is an imperative step in the biodegradation process, but only refers to polymer deterioration from abiotic reactions, like hydrolysis, oxidation, and photo-oxidation. On the other hand, biodegradation occurs when the polymer fragments are in the presence of appropriate enzymes that can convert the residuals into benign by-products, like carbon dioxide, methane, nitrogen, and water. First, microorganisms form biofilms on the substrate’s surface, leading to the biodeterioration of the polymer. To consume the polymer, microorganisms then release extracellular enzymes to depolymerize the substrate, forming small molecules, like dimers and oligomers. These smaller molecules can then be bioassimilated by microorganisms and converted into carbon dioxide, nitrogen, methane, and water.
Most often, polymers that are certified to be biodegradable and/or compostable are tested at elevated temperatures (greater than 30°C), in aerobic conditions, and in the presence of diverse microorganisms. These conditions are not representative of the ocean, where temperatures, oxygen levels, and microorganisms are a function of depth, season, and location. Unlike bench-top studies, marine field tests incorporate biotic and abiotic factors, like microorganisms, light, the mechanical action of waves, and seasonal temperature fluctuations. Currently, ASTM and TUV Austria define samples surpassing 90% biodegradation within 6 months to be biologically assimilated in marine environments.
The marine degradation studies of PHA-based products to estimate the relative time frame in which these polymers could be expected to mineralize. PHA films ≤0.2 mm thick would biodegrade within several months in marine environments. Thin films have the advantage over bulk plastics in that their diffusion lengths are much smaller, facilitating water and microorganism penetration.
The water vapor transmission rate (WVTR) are the desiccant and water methods. The flexible packaging substrate separates the desiccant or water from the controlled atmosphere for 24-h. Throughout the test, water vapor passes from areas of high to low moisture concentrations through the permeable sample.
Metallization imparts a portion of aluminum’s absolute barrier properties and produces plastic films that are generally lightweight and inexpensive. Vacuum metallization is commonly found in multilayered structures, such as snack chip bags, granola bars, and condiments sachets.TPS and PHAs have the potential to replace conventional polyolefins in single-use flexible packaging. These materials meet established biodegradation requirements and have degraded in marine field tests.