Enzymatically Pretreated High-Solid-Content Nanocellulose for a High-Throughput Coating Process

Abstract

There is an ever-increasing interest toward utilizing nanocellulose as barrier coatings and films, and recent studies have underlined the efficiency of using innovative fibrillation processes such as twin-screw extrusion with an enzymatic pretreatment for producing nanocellulose suspensions with solid contents as high as 20 wt %, which can lead to faster coating speeds and reduced drying energy costs. The current work aims at understanding the factors that influence high-throughput processability of high-solid-content nanocellulose during roll-to-roll coating. The rheological properties of 12.5, 10, and 7.5 wt % suspensions were evaluated across a wide range of shear rates and geometries (rotational, pipe, and slot). The influence of dispersants [carboxymethyl cellulose (CMC) and sodium polyacrylate (NaPA)] on the rheology and coating quality was assessed. A Casson-power-cross model is proposed to explain the rheological behavior across a wide shear rate range and is used to predict useful parameters, viz., yield stress, transition shear rate, and power-law index at high shear rates. Finally, a 12.5 wt % nanocellulose suspension with CMC or NaPA dispersant was roll-to-roll-coated on paperboard using a slot-die applicator. CMC addition had a positive influence on the yield stress, thixotropy, and water release and, therefore, resulted in a better mineral oil and grease barrier of the coated samples compared to the rest.

Electrostatically Complexed Natural Polysaccharides as Aqueous Barrier Coatings for Sustainable and Recyclable Fiber-Based Packaging

“…that cause adverse environmental impacts and increase the energy cost and carbon footprint. Some emerging bio-based building blocks such as CNFs and CNCs still face challenging commercial-scale processability for coating application and drying processes due to their low solid content and high viscosity profiles; more efforts on the high solid content grade of nanocellulosic materials and their continuous coating application are being implemented to further explore their commercialization potential. , In comparison, our natural, sustainable, waterborne complex dispersion barrier coating exhibits a combination of the highest grease resistance and reduced moisture sensitivity, as well as has the promise of scale-up for industrial production (see description of scalable manufacturing of complex dispersions in the Supporting Information). Moreover, our material selection and one-pot processing pathway align well with green chemistry principles such as use of renewable feedstocks, benign solvents, design for energy efficiency, and design for degradation …”

Tailoring the Performance of Nanocellulose-based Multilayer-Barrier Paperboard using Biodegradable-Thermoplastics, Pigments, and Plasticizers

“…The description of rheology measurements and influence of CMC addition on MFC and CNF suspensions' yield stress are given in the supporting information. A more detailed discussion on the role of rheology during continuous coating of nanocellulose can be found in Koppolu et al (2022).…”

“…MFC and CNF suspensions were then coated on top of the starch-coated baseboard using the same R2R coater fitted with a slot-die applicator. A detailed description of the working principles of slot-die coating of nanocellulose suspensions is provided in our previous work (Koppolu et al, 2018(Koppolu et al, , 2019(Koppolu et al, , 2022, and is briefly discussed in the supporting information of the current work. Table 1 lists the different nanocellulose coatings done in this work along with their respective wet thicknesses (set value), line speeds, and dry-coating thicknesses (measured value).…”

“…Nanocellulose is both bio-based and biodegradable, and therefore, nanocellulose-based coatings and films are being considered as a potential replacement to non-biodegradable plastics and metallic aluminum layers in food packaging applications (Tyagi et al, 2021;Cherian et al, 2022). Several companies have already started producing nanocellulose at pilot or commercial-scale to be used primarily for barrier applications (FutureMarkets, 2021), with many research groups including the authors of this work demonstrating roll-to-roll (R2R) coating of nanocellulose on paper/paperboard using slot-die (Kumar et al, 2016;Koppolu et al, 2018Koppolu et al, , 2019Koppolu et al, , 2022Jung et al, 2022), gravure (Chowdhury et al, 2018), spray coating (Shanmugam, 2022;Satam et al, 2018;Beneventi et al, 2014Beneventi et al, , 2015, and wet lamination (Guerin et al, 2020) methods.…”