New insights into the chemical activation of lignins and tannins using K₂CO₃—a combined thermoanalytical and structural study

Engineering of activated carbons (ACs) through chemical activation of organic precursors has been extensively studied for a wide variety of biopolymers, biomasses, wastes and other fossil-based precursors. Despite huge efforts to engineer evermore performant and sustainable ACs, “searching-for-the-best-recipe” type of studies are more the rule than the exception in the published literature. Emerging AC applications related to energy and gas storage require strict control of the AC properties and a better understanding of the fundamentals underlying their engineering. In this study, we provide new insights into the K2CO3 chemical activation of plant-based polyphenols—lignins and tannins—through careful thermoanalytical and structural analyses. We showed for the the first time that the reactivity of polyphenols during K2CO3 chemical activation depends remarkably on their purity and structural properties, such as their content of inorganics, OH functionalities and average molecular weight. We also found that the burn-off level is proportional to the K2CO3/lignin impregnation ratio (IR), but only within a certain range—high impregnation ratios are not needed, unlike often reported in the literature. Furthermore, we showed for the first time that the K2CO3 chemical activation of different carbon surfaces from lignins and tannins can be modelled using simple global solid-state decomposition kinetics. The identified activation energies lay in the range of values reported for heterogenous gas-carbon surface gasification reactions (O2-C, H2O-C, or CO2-C) in which the decomposition of C(O) surface complexes is the common rate-limiting step.</p

Flexible pigment-cellulose nanofibril composites for printed electronics applications

The aim of this work was to expand the possibilities of novel use of cellulose micro- and nanofibrils (CMNF) for bio-based composites. The new approach in this work was to combine inorganic pigments and CMNF in a relatively wide range of component combinations for the generation of pigment-cellulose micro- and nanofibril (PCMNF) composites. The amount of CMNF in these studies varied between 20 and 50 wt-% in the studied composites. The main focus of the work was on clarifying the relationship between the raw materials used and the composite structural properties of the final product, such as smoothness and porosity. The influence of manufacturing process steps on the composite properties was studied experimentally in both laboratory and semi-pilot scale. The composites were manufactured by vacuum filtration in laboratory scale and by film casting in semi-pilot scale, in both cases followed by wet pressing, drying, and calendering. Based on feasibility studies including techno-economic and life-cycle assessment, new product opportunities and markets can be captured with PCMNF composites for printed electronics applications. There is nowadays a growing need for the production of flexible, cost-effective, and environmentally friendly substrates for printed electronics applications. CMNF as a raw material has attracted significant interest in this field. In this work, different functional devices were manufactured as proof-of-concept structures to demonstrate the usability of the developed composites for printed electronics applications. The studied proof-of-concepts were: 1) ink-jet printing with a silver-nanoparticle ink, 2) double-functional separator substrate for printed supercapacitors, 3) an ion-modulated transistor deposited on the substrate, and 4) screen printed antennas using silver ink and a commercial radio frequency identification (RFID) chip attached using a silver epoxy resin as a functional near field communication RFID tag on the substrate. The developed PCMNF composites have a nanoporous pigment-CMNF network structure that allows controlled ink absorption properties. The required substrate porosity and smoothness strongly depend on the used printing method, ink, solvent, and device design. The PCMNF composites offer a sustainable substrate for printed electronics applications to be used at high temperatures that only very special plastic films can currently withstand.Arbetet strävar att utvidga användningsmöjligheterna för cellulosa mikro- och nanofibriller (CMNF) inom biobaserade kompositer. Det nya sättet att närma sig detta är att kombinera inorganiskt pigment med CMNF i relativt höga komponentproportioner för att generera pigment-cellulosa mikro- och nanofibrill (PCMNF) kompositer. Halten av CMNF i dessa studier varierade mellan 20 och 50 v- % i kompositerna. Den huvudsakliga fokusen i arbetet var att utvärdera sambandet mellan råmaterial och strukturella egenskaper, såsom släthet och porositet, i den producerade kompositen. Påverkan av produktions-processsteg på kompositernas egenskaper studerades experimentellt både i laboratorie- såsom i semi-pilot skala. Kompositerna producerades genom vakuumfiltrering i laboratorieskala och via filmgjutning i semi-pilot skala, följt av våtpressning, torkning och kalandrering. På basis av genomförbarhetsstudier, som inkluderar tekno-ekonomiska och livscykelutvärderingar, kan man nå nya produktmöjligheter och -marknader med PCMNF-kompositer inom tryckta elektronikapplikationer. I denna dag finns ett växande behov för flexibla, kostnadseffektiva samt miljövänliga substrat för tryckta elektronikapplikationer. Intresset för CMNF som råmaterial i detta område har ökat märkbart. I detta arbete har olika funktionella apparater tillverkats för att konceptvalideras och demonstrera kompositernas användbarhet inom tryckt elektronik. De rannsakade konceptvalideringarna var: 1) utskrift av silver-nanopartikel bläck med bläckstråle 2) ett dubbel-funktionellt separator-substrat för tryckta superkondesatorer 3) en jon-modulerad transistor deponerad på substratet 4) en funktionell närfältskommunikationstagg på substratet genom serigrafi-tryckta antenner med silverbläck samt ett kommersiellt radiofrekvens identifikationschipp (RFID) fäst med silver-epoxi. De utvecklade PCMNF-kompositerna har en nanoporös pigment-CMNF nätverksstruktur som tillåter kontrollerad bläckabsorption. Substratets porositets- och släthetskrav beror starkt på tillämpad tryckmetod, bläck, lösningsmedel samt apparatdesign. PCMNF-kompositerna erbjuder ett hållbart substrat för tryckta elektronikapplikationer för höga temperaturförhållanden, vilka enbart ett fåtal specialplaster klarar av i denna dag