Cellulose nanofibrils and silver nanowires active coatings for the development of antibacterial packaging surfaces

An active ink composed of cellulose nanofibrils and silver nanowires was deposited on flexible and transparent polymer films using the bar coating process, achieving controlled thicknesses ranging from 200 nm up to 2 µm. For 350 nm thick coating on polyethylene terephthalate films, high transparency (75.6% transmittance) and strong reduction of bacterial growth equal to 89.3% and 100% was noted respectively against Gram-negative Escherichia Coli and Gram-positive Staphylococcus Aureus bacteria using AATCC contact active standard test. Retained antibacterial activity was found with films produced by reverse gravure roll-to-roll process, showing the promising capability of this antibacterial solution to be deployed industrially. Finally, the same ink was also deposited on polylactic acid substrate to investigate barrier properties: for 350 nm thick coating, a reduction of 49% of oxygen transmission rate (dry conditions) and 47% reduction of water vapor transmission rate was noted, proving the enhanced barrier properties of the coatings

High-throughput Processing of Nanocelluloses into Barrier Coatings : A Focus on Nanocellulose Rheology and Multilayer Barrier Properties

Packaging is an integral part of our modern lives, especially in our interconnected world where nearly all products require some form of packaging. The global packaging market is currently valued at 1 trillion USD, with a substantial portion dedicated to barrier food packaging. This type of packaging is a complex structure, composed of multiple functional layers made from non-biodegradable plastics or metallic layers that pose challenges during recycling. Therefore, it is imperative to find sustainable alternatives to these materials. Nanocellulose is a nano-scale cellulose based natural polymer derived from plants, fungi, and bacteria. In addition to being bio-based and biodegradable, nanocellulose-based coatings and films have excellent barrier against oxygen, grease, and oils. Therefore, they are being investigated as potential alternatives to some of the non-biodegradable plastics and metallic layers in barrier food packaging. There are several challenges that need to be addressed to enable high-throughput processing of nanocellulose into barrier coatings and films. Nanocellulose suspensions exhibit high viscosity and yield stress even at a low solid content, making it difficult to achieve thin uniform coatings, especially in high speed industrial roll-to-roll processes. In addition, nanocellulose is highly moisture sensitive, with most of its barrier properties deteriorating at high humidites. The current work aims to understand and address these challenges, and to develop high-throughput continuous process concepts required to convert a wide variety of nanocellulose suspensions into barrier coatings. Flow properties of different types of nanocelluloses were examined across a wide range of shear rates, with special attention on the influence of dispersants such as carboxymethyl cellulose (CMC) and sodium polyacrylate (NaPA) on suspension processing and coating quality. A slot-die applicator was used to successfully apply different grades of nanocellulose suspensions onto paper substrates in a roll-to-roll process at speeds up to 6 m.min−1. In addition, the impact of substrate properties, including contact angle, surface roughness, porosity, and surface charge groups, on the nanocellulose adhesion and coating quality was investigated. For moisture protection, biodegradable polymers and dispersions were applied onto the nanocellulose-coated samples via extrusion or dispersion coating. The resulting multilayer structures were evaluated for barrier properties such as, water vapor, oxygen, grease, and mineral oils at different test conditions. CMC addition reduced yield stress, increased water retention, and slowed down structure recovery (post high-shear) for nanocellulose suspensions and therefore had positive influence on coating quality and barrier properties. A new Casson-Power-Cross model was introduced to explain the flow behavior of cellulose nanofibrils (CNFs) across a wide shear-rate range, and Herschel-Bulkley model explained the flow behavior for cellulose nanocrystals (CNCs). Water vapor permeance of the multilayer coatings remained below the control single-layer moisture barrier materials, and oxygen permeance was similar or lower than that of pure nanocellulose films. Glycerol and sorbitol plasticizers further improved oxygen barrier and kaolin pigment addition enhanced the adhesion at nanocellulose/thermoplastic interface. The results provide insights into the factors influencing the continuous processing of diverse nanocellulose suspensions into barrier coatings. Moreover, the approach of processing nanocellulose and moisture barrier materials together into multilayer structures complements the shortcomings of each layer and produces a paperboard with superior barrier properties that is both bio-based and biodegradable. In order to improve the commercial viability of nanocelluloses in barrier coatings, future research should prioritize achieving the required barrier properties with low coat weights and high suspension solid content. This entails exploring various avenues, such as investigating the use of different rheology modifiers, employing CFD modeling to create custom coating applicators tailored specifically for nanocelluloses, blending diverse grades of nanocelluloses to enhance barrier performance, and employing cross-linkers to mitigate swelling in high humidity conditions. Lastly, it is crucial to assess the barrier performance following various converting operations to provide comprehensive perspective on the final barrier properties.Förpackningar är en väsentlig del av vårt moderna liv, där nästan alla produkter behöver skyddas eller förvaras på något sätt. Den globala förpackningsmarknaden omsätter för tillfället ungefär en triljon USD, och en betydlig del av detta utgör barriärförpackningar för livsmedel. Förpackningar av denna typ har en komplex struktur och består av flera funktionella skikt som är tillverkade av icke-bionedbrytbara plast- eller metallager som leder till utmaningar under återvinning. Det är därför viktigt att hitta hållbara alternativ till dessa material. Nanocellulosa, som består av cellulosafibriller i nanostorlek, baserar sig på naturpolymerer utvunna från växter, svampar och bakterier. Förutom att de är biobaserade och bionedbrytbara har nanocellulosabaserade bestrykningar och filmer utmärkt impermeabilitet mot syre, fett och oljor. Därför undersöks nanocellulosa som potentiell ersättare för icke-bionedbrytbara plaster och metallskikt i barriärförpackningar för livsmedel. Det finns många utmaningar i att möjliggöra höghastighetsprocessering av nanocellulosa till barriärbestrykningar och filmer. Nanocellulosasuspensioner har hög viskositet och flytspänning redan vid låg torrhalt, vilket gör det svårt att uppnå tunna och enhetliga bestrykningsskikt, speciellt i industriella kontinuerliga processer. Dessutom är nanocellulosa extremt fuktkänslig och vid hög fukthalt försämras dess barriäregenskaper. Målet med detta arbete var att förstå och ta itu med dessa utmaningar, och att utveckla ett kontinuerligt processkoncept som behövs för konvertering av olika nanocellulosasuspensioner till barriärbestrykningar. Flödesegenskaper av olika typer av nanocellulosa undersöktes vid olika skjuvhastigheter, och speciellt undersöktes inverkan av dispergeringsmedel som karboximetylcellulosa (CMC) och natriumpolyakrylat (NaPa) på processeringen av suspensionen och bestrykningskvaliteten. En slot die-applikator användes för applicering av nanocellulosasuspensioner på papper i en rulle-till-rulle process vid hastigheter upp till 6 m/min. Därtill undersöktes effekten av substratens ytegenskaper, såsom kontaktvinkel, ytråhet, porositet och ytladdning, på nanocellulosans adhesion och bestrykningskvalitet. Som fuktskydd applicerades bionedbrytbara polymerer och dispersioner på de nanocellulosabestrykta proven med dispersions- eller extrusionsbestrykning. Den resulterade flerskiktsstrukturens barriäregenskaper mot vattenånga, syre och mineraloljor utvärderades. Addition av CMC minskade flytspänningen, ökade vattenretentionen och saktade ner strukturåterhämtningen (efter hög skjuvning) av nanocellulosasuspensioner och hade på grund av det en positiv inverkan på bestrykningskvaliteten och barriäregenskaperna. En ny Casson-Power-Cross-modell användes för att förklara flödesbeteendet av cellulosananofibrillsuspensioner (CNF) över ett brett skjuvhastighetsintervall, och en Hershley-Bulkley-modell förklarade flödesbeteendet för cellulosa nanokristallsupensioner (CNC). Vattenångspermeabilitet av flerskiktsbestrykningar var lägre jämfört med referensmaterialen med fuktbarriär, och syrepermeabiliteten var på samma nivå eller lägre jämfört med rena nanocellulosafilmer. Glycerol- och sorbitolmjukgörare förbättrade syrebarriären ytterligare, och tillsats av kaolinpigment förbättrade adhesionen vid gränsytan nanocellulosa/termoplast. Resultaten indikerar vilka faktorer som påverkar den kontinuerliga processeringen av olika nanocellulosasuspensioner för barriärbestrykningar. Därtill visades att processering av nanocellulosa och fuktbarriärmaterial tillsammans till flerskiktsstrukturer kompletterar bristerna i de enskilda lagren och resulterar i en biobaserad och bionedbrytbar kartong med utmärkta barriäregenskaper. För att förbättra förutsättningarna för kommersialisering av nanocellulosa i barriärbestrykningar borde framtida forskning prioritera barriärbestrykningar med låga bestrykningsmängder och höga torrhalter av suspensioner som skulle resultera i de eftersträvade barriäregenskaperna. Detta kräver forskning på bred front, såsom undersökning av användning av olika reologimodifierare, användning av CFD-modellering för specifika bestrykningsapplikationer specifikt för nanocellulosa, blandning av olika nanocellulosor för förbättring av barriärprestandan, och användning av tvärbindare för att minska svällningen vid höga fukthalter. Slutligen är det viktigt att evaluera inverkan av olika konverteringsoperationer på barriäregenskaperna för att få en omfattande förståelse av användningen av nanocellulosamaterial i förpackningar

High-Throughput Processing of Nanographite-Nanocellulose-Based Electrodes for Flexible Energy Devices

The current work aims at understanding factors that influence the processability of nanographite-nanocellulose suspensions onto flexible substrates for production of conductive electrodes. A custom-built slot-die was used in a continuous rollto-roll process to coat the nanomaterial suspension onto substrates with varying surface smoothness, thickness, pore structure, and wet strength. The influence of a carboxymethyl cellulose (CMC) additive on suspension rheology, water release properties, and coating quality was probed. CMC addition reduced the suspension yield stress by 2 orders of magnitude and the average pore diameter of the coated electrodes by 70%. Sheet resistances of 5-9 Omega sq(-1) were obtained for the conductive coatings with a coat weight of 12-24 g m(-2). Calendering reduced the sheet resistance to 1-3 Omega sq(-1) and resistivity to as low as 12 mu Omega m. The coated electrodes were used to demonstrate a metal-free aqueous-electrolyte supercapacitor with a specific capacitance of 63 F g(-1). The results increase our understanding of continuous processing of nanographite-nanocellulose suspensions into electrodes, with potential uses in flexible, lightweight, and environmentally friendly energy devices

Stencil Printing—A Novel Manufacturing Platform for Orodispersible Discs

Stencil printing is a commonly used printing method, but it has not previously been used for production of pharmaceuticals. The aim of this study was to explore whether stencil printing of drug containing polymer inks could be used to manufacture flexible dosage forms with acceptable mass and content uniformity. Formulation development was supported by physicochemical characterization of the inks and final dosage forms. The printing of haloperidol (HAL) discs was performed using a prototype stencil printer. Ink development comprised of investigations of ink rheology in combination with printability assessment. The results show that stencil printing can be used to manufacture HAL doses in the therapeutic treatment range for 6–17 year-old children. The therapeutic HAL dose was achieved for the discs consisting of 16% of hydroxypropyl methylcellulose (HPMC) and 1% of lactic acid (LA). The formulation pH remained above pH 4 and the results imply that the drug was amorphous. Linear dose escalation was achieved by an increase in aperture area of the print pattern, while keeping the stencil thickness fixed. Disintegration times of the orodispersible discs printed with 250 and 500 µm thick stencils were below 30 s. In conclusion, stencil printing shows potential as a manufacturing method of pharmaceuticals

Influence of Substrate in Roll-to-roll Coated Nanographite Electrodes for Metal-free Supercapacitors

Due to the high electric conductivity and large surface area of nanographites, such as graphene and graphite nanoplatlets, these materials have gained a large interest for use in energy storage devices. However, due to the thin flake geometry, the viscosity of aqueous suspensions containing these materials is high even at low solids contents. This together with the use of high viscosity bio-based binders makes it challenging to coat in a roll-to-roll process with sufficient coating thickness. Electrode materials for commercial energy storage devices are often suspended by organic solvents at high solids contents and coated onto metal foils used as current-collectors. Another interesting approach is to coat the electrode onto the separator, to enable large-scale production of flat cell stacks. Here, we demonstrate an alternative, water-based approach that utilize slot-die coating to coat aqueous nanographite suspension with nanocellulose binder onto the paper separator, and onto the current collector as reference, in aqueous metal-free supercapacitors. The results show that the difference in device equivalent series resistance (ESR) due to interfacial resistance between electrode and current collector was much lower than expected and thus similar or lower compared to other studies with a aqueous supercapacitors. This indicates that electrode coated paper separator substrates could be a promising approach and a possible route for manufacturing of low-cost, environmentally friendly and metal-free energy storage devices.

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

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

Continuous Processing of Nanocellulose and Polylactic Acid into Multilayer Barrier Coatings

Recent years have seen an increased interest towards utilizing bio-based and biodegradable materials for barrier packaging applications. Most of the above said materials usually have certain shortcomings that discourage their adoption as a preferred material of choice. Nanocellulose falls into such category. It has excellent barrier against grease, mineral oils and oxygen, but poor tolerance against water vapor, which makes it unsuitable to be used at high humidity. In addition, nanocellulose suspensions' high viscosity and yield stress already at low solids content, and poor adhesion to substrates create additional challenges for high-speed processing. Polylactic acid (PLA) is another potential candidate that has a reasonably high tolerance against water vapor, but rather poor barrier against oxygen. The current work explores the possibility to combine both these materials into thin multilayer coatings onto paperboard. A custom-built slot-die was used to coat either microfibrillated cellulose (MFC) or cellulose nanocrystals (CNCs) onto pigment-coated baseboard in a continuous process. These were subsequently coated with PLA using a pilot scale extrusion coater. Low-density polyethylene (LDPE) was used as a reference extrusion coating. Cationic starch pre-coating and corona treatment improved the adhesion at nanocellulose/baseboard and nanocellulose/PLA interfaces, respectively. Water vapor transmission rate for nanocellulose + PLA coatings remained lower than the control PLA coating, even at a high relative humidity of 90% (38 oC). The multilayer coating had 98% lower oxygen transmission rate compared to just PLA coated baseboard and heptane vapor transmission rate reduced by 99% in comparison to baseboard. Grease barrier for nanocellulose + PLA coatings increased 5-fold compared to nanocellulose alone and 2-fold compared to PLA alone. This approach of processing nanocellulose and PLA into multiple layers utilizing slot-die and extrusion coating in tandem has the potential to produce a barrier packaging paper that is both 100% bio-based and biodegradable.publishedVersionPeer reviewe