Biobased and biodegradable barrier coatings on paper with slot die technology

The lack of biodegradability of existing barrier packaging materials has attracted attention for renewable and environmentally friendlier materials, such as nanocellulose. The barrier properties of nanocellulose against grease, oxygen and mineral oils are excellent but poor against water vapor. Polylactic acid (PLA) and Polyhydroxyalkanoate (PHA), in turn, have a very good water vapor barrier but a poor barrier against oxygen. Extensive work has been done on a small scale, but very few works have been done in the continuous processing of nanocellulose coatings. The current work aimed at producing a biobased and biodegradable barrier packaging paper in a roll-to-roll (R2R) process using three different types of microfibrillated celluloses (MFCs) and two biobased latexes. The impact of rheology on coatability is also discussed. MFC and MFC-latex blends were coated onto pigment-coated baseboard and glassine paper using a slot-die. Furthermore, PHA and PLA-based biolatexes were coated on top of MFC-coated paperboard (multilayer coating) using the reverse gravure application. Numerous methods were used for the evaluation of barrier properties and coating quality of coated substrates, such as air permeability, water vapor transmission rate (WVTR), oxygen permeability, heptane vapor transmission rate (HVTR) and scanning electron microscopy (SEM). Air permeance and HVTR for all the MFC coatings were below 0.003 μm/Pa.s and 20 g/(m2.day) respectively, whereas WVTR was poor. High oxygen permeance for MFC coating was observed due to tiny cracks and low coat weight. The MFC-latex blends did not improve the barrier properties compared to the MFC coatings. The oxygen permeance for the multilayer coating was lower than 5 cc/(m2.day.bar) at 23 °C, 50% and WVTR was reduced up to 85% on both 23 °C, 50% RH and 38 °C, 90% RH compared to the baseboard. It was evident that in a multilayer structure nanocellulose provides a barrier against oxygen and heptane, in case of defect-free coating, and biolatex protects against water vapor. The multilayer structure of nanocellulose and biobased latex on paper/paperboard has great potential for producing biobased and biodegradable barrier packaging