Abstract
ABSTRACTBarrier, mechanical and thermal properties of porous paper substrates dip-coated with nanocellulose (NC) were studied. Sorbitol plasticizer was used to improve the toughness, and citric acid cross-linker to improve the moisture stability of the coatings. In general, the addition of sorbitol increased the barrier properties, maximum strength and toughness as well as the thermal stability of the samples when compared to the non-modified NC coatings. The barrier properties significantly improved, especially for plasticized NC coating’s, where the oxygen permeability value was as low as 0.7 mL μm day−1 m−2 kPa−1 at 49% RH and the water vapor permeability was reduced by 60%. Furthermore, we found that the cross-linked plasticized NC coating had a smoother surface (50% lower roughness) compared to non-modified ones. This study shows that the environmentally friendly additives sorbitol and citric acid had positive effects on NC coating properties, increasing its potential use in paper-based packaging applications.
Highlights
Porous cellulose-based materials, such as paperboard, have a great impact in the packaging industry due to their eco-friendly nature and biodegradability
Knowing that the molecular weight (MW) of the citric acid (CA) is 207 g/mol, it is calculated that the amount of CA per m2 of coating is 0.1 mol/m2
When the same calculation is performed for X-NC6, it can be found that 69% of the glucose units can take part in the crosslinking
Summary
Porous cellulose-based materials, such as paperboard, have a great impact in the packaging industry due to their eco-friendly nature and biodegradability. Hydrophilic behavior and a porous structure prevent the use of paper in a wide range of applications. To overcome this issue, paper is usually coated in combination with other materials, such as plastic or aluminum, that provide improvements in barrier properties at the expense of its eco-friendly and biodegradable nature. One way to increase the flexibility of the NC coating is to reduce the amount of hydrogen bonds using plasticizers, such as sorbitol (Mathew et al 2008) or glycerol (Xiao et al 2003; Hansen et al 2012; Liu et al 2013; Wang et al 2015). These plasticizers have been shown to increase the tensile strength (Xiao et al 2003; Liu et al 2013; Mathew et al 2008; Wang et al 2015) and the oxygen barrier (Hansen et al 2012) of films
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