Scientists from Mae Fah Luang University in Thailand and Queen Mary University in London have produced a shellac-based coating that can make pulp materials suitable for food without requiring laminating or coating with petroleum-based polymers or metals. The new coating enhances the gas barrier properties of recyclable, compostable and sustainably sourced packaging materials for use with instant, dehydrated, frozen and chilled foods.
With concerns about plastic pollution on the increase, moulded pulp, which is made from renewable materials such as eucalyptus wood and sugarcane bagasse, is popular as a packaging material. It protects products during transportation, as well as being used in containers, drink carriers and food serving trays, comprising nearly one-third of all paper-based packaging materials.
However, it is also has poor barrier properties and offers limited resistance to water and oil, making it unsuitable for maintaining the quality and shelf-life of many products. Although this can be aided by laminating binders, this brings issues for recycling or composting.
As reported in Polymer International [Klaya et al. Polym. Int. (2023) DOI: 10.1002/pi.6469], here the researchers used shellac, which has long been used in nail varnishes, furniture lacquer and various dyes. Due to its non-toxicity, thermoplastic behaviour, oil resistance and moisture barrier properties, it is also has applications in the medical and food industries.
One problem is that shellac coatings can be brittle and have high oxygen permeability. To resolve this, moulded pulp was coated with a nanocomposite layer of nanofibrillated cellulose (NFC) and shellac to help enhance its barrier and surface resistance performance. To improve the compatibility with the shellac phase and increase the water resistance of NFC, modified nanofibrillated cellulose (mNFC) was prepared by esterification reaction.
When a bio-nanocomposite layer combining nanocellulose and shellac of various thicknesses was coated on the surface of moulded pulp, it offered effective gas and water barrier performance similar to standard food packaging materials. As lead researcher Nattakan Soykeabkaew of Mae Fah Luang University told Materials Today, “With the right combination and approach, renewable or biobased materials can be made into sufficient sustainable options/products for our modern lifestyle consumption.”
While the cost of the process remains a constraint to commercialisation, the coating could find applications in single use packaging and even as coating for other biobased or eco-materials to improve their moisture sensitivity, mould resistance and durability. The team also hope to develop a sustainable coating that is cheaper and scalable based on material selection and design along with some useful process modifications.
“With the right combination and approach, renewable or biobased materials can be made into sufficient sustainable options/products for our modern lifestyle consumption.”Nattakan Soykeabkaew
New shellac-based coating for moulded pulp food packaging