Shellac-Based Coating for Sustainable Packaging

Shellac-Based Coating for Sustainable Packaging Researchers at Mae Fah Luang University School of Science in Thailand and the School of Engineering and Materials Science at Queen Mary University of London have developed a shellac-based coating to improve gas barrier properties of packaging materials for fresh, dried, frozen and chilled foods in a recyclable, compostable and sustainable manner. Moulded paper pulp made from renewable materials such as eucalyptus wood or sugarcane bagasse is widely used as a sustainable packaging material to protect products during transport of service trays, containers and beverage carriers. Moulded pulp production volume represents more than 30% of all paper-based packaging materials and, in addition to its renewable raw materials, is also suitable for recycling and composting. However, the poor gas barrier properties of the materials as well as their limited resistance to water and oil make moulded pulp unsuitable for maintaining the shelf life and quality of many products. This problem is typically solved by laminating or coating the materials with petroleum-based polymers such as polyethylene and thin metal layers such as aluminium, which makes recycling and composting difficult. The aim of this study, published in Polymer International on 7 February, was to improve the barrier properties and surface resistance of moulded pulp by developing a new coating based on environmentally friendly, renewable and biodegradable materials while prioritising environmental sustainability. Shellac is obtained from a resin secreted by lac beetles and has been used for centuries in many products ranging from nail polish to furniture polish and various paints. Among the largest shellac-producing countries are India, Thailand and China, although shellac is also produced in Bangladesh, Myanmar, Laos, Vietnam and Mexico. Shellac is a biopolymer belonging to the polyester group and is widely used in the pharmaceutical and food industries due to its properties such as thermoplastic structure, oil resistance, good moisture barrier and non-toxicity. It also provides good adhesion and is soluble in low-toxicity solvents. However, due to its brittle nature and high oxygen permeability, coating layers made from pure shellac are not commonly used. In this study, a moulded pulp was coated with a nanocomposite layer consisting of nanofibrillated cellulose (NFC) and shellac to improve barrier and surface resistance performance. To increase compatibility with the shellac phase and increase the water resistance of NFC, modified nanofibrillated cellulose (mNFC) was prepared through an esterification reaction. Researchers also prepared uncoated samples and samples coated with pure shellac for comparison purposes. In addition to the nanocomposite coating formulation (nanocellulose content and modification) and different thicknesses of the coating layer on the moulded pulp, the effects on morphology, barrier properties (water vapour transmission rate [WVTR], OTR), water and oil resistance of the prepared samples, thermal stability and mechanical properties were systematically examined. Researchers reported that water vapour and oxygen transmission rates were in the same range as conventional food packaging materials such as low-density polyethylene, oriented polypropylene and polyethylene terephthalate. A test comprising water contact angle, oil contact angle and oil absorption rate showed that the nanocomposite coating layer provided superior water resistance to the moulded paper pulp layer and a good oil-impermeable surface. The coating layer was also found to increase tensile properties, particularly in samples coated with shellac and mNFC. Samples achieved good thermal stability (approximately 250 °C), with the shellac layer subjected to lower thermal decomposition temperatures, which confirmed its suitability for packaging applications. Nattakan Soykeabkaew, lead researcher at Mae Fah Luang University School of Science, stated, "Our next goal is to develop a more cost-effective and scalable sustainable coating through material selection and design as well as certain process modifications." The current barrier to commercialisation of the product lies in the cost, which Professor Soykeabkaew estimates to be three to ten times higher than currently used materials. However, Professor Soykeabkaew notes that the coating "could also be applied to other eco-materials to reduce water/moisture sensitivity." Supattra Klayya et al, Sustainable nanocomposite coating for moulded pulp with enhanced barrier properties for food packaging applications, Polymer International (2022). DOI: 10.1002/pi.6469 Source https://phys.org/news/2023-02-shellac-based-coating-pulp-materials-suitable.html