In a bid to improve the gas barrier properties of recyclable, compostable and sustainably sourced packaging material, researchers from Mae Fah Luang University, Thailand, and Queen Mary University of London, U.K., have developed a shellac-based coating for instant, dehydrated, frozen and chilled foods.

According to the researchers, molded pulp, composed of renewable materials such as eucalyptus wood or sugarcane bagasse, and used in the making of sustainable packaging materials to protect products in shipping, for food serving trays, containers and beverage carriers, demonstrates poor gas barrier properties and limited resistance to water and oil, thus making molded pulps unsuitable for maintaining the shelf-life and the quality of many products.

Source: Prof Nattakan SoykeabkaewSource: Prof Nattakan Soykeabkaew

As such, the material is typically laminated or coated with petroleum-based polymers including polyethylene and a thin layer of metals like aluminum. However, this tends to make recycling or composting challenging.

To remedy this, the team sought to improve molded pulp’s barrier properties and surface resistance while simultaneously maintaining the material’s green profile and environmental sustainability by creating a new coating derived from environmentally friendly, renewable and biodegradable materials.

In doing so, the team turned to the material shellac, which is derived from a resin produced by the Indian “lac” bug. The lac bug is an insect that attaches to a tree, consuming its sap and converting it to the material often used in the making of glossy protective coatings.

Due to its non-toxic nature, thermoplastic behavior, moisture barrier properties and oil resistance, shellac is used in a wide range of industries including pharmaceuticals and food. Further, shellac also demonstrates good adhesion finish and dissolves in low-toxicity solvents. Yet, what tends to prevent the use of pure shellac coating is the material’s reportedly brittle nature and high oxygen permeability.

To overcome these barriers, the researchers coated molded pulp with a nanocomposite layer of nanofibrillated cellulose (NFC) and shellac, thereby improving its barrier and surface resistance performance. The team then increased the water resistance of NFC by preparing modified nanofibrillated cellulose (mNFC) via an esterification reaction, which is a reaction of an alcohol with an acid to produce an ester and water.

When compared in the lab with other samples, including those coated in pure shellac as well as uncoated samples, the nanocellulose content and modification coating demonstrated water vapor and oxygen transmission rates in the range of conventional food packaging materials. Meanwhile, the nanocomposite coating layer also reportedly demonstrated superior water resistance, greaseproof properties when applied to the surface of molded pulp sheet, enhanced tensile properties and good thermal stability.

An article detailing the shellac-based coating titled, Sustainable nanocomposite coating for moulded pulp with enhanced barrier properties for food packaging applications, appears in the journal Polymer International.

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