Polymeric nanoparticles with tunable surface functionalities were synthesized via polymerization-induced self-assembly (PISA) to study their interactions with TEMPO-oxidized cellulose nanofibrils (TO-CNFs) in wet and dry states. The nanoparticles possessed a rigid core and shells featuring anionic, polyethylene glycol (PEG)-like, and hydroxyl-rich functionalities, with different hydrogen bonding propensities, water binding, and glass transition temperatures. Hydroxyl-functional nanoparticles exhibited enhanced and irreversible adsorption onto CNFs compared to anionic and PEG-like functions, showing that shell functionality impacts the adsorption behavior in the wet state. In the dry state, shell functionality plays a minor role in the bulk mechanical properties, which depend instead on the nanoparticle amount. This work shows that additive interactions between colloidal components in water do not translate to interactions in the dry state.

Biobased cellulose nanofibrils (CNFs) constitute important building blocks for biomimetic, nanostructured materials, and considerable potential exists in their hybridization with tailorable polymeric nanoparticles. CNFs naturally assemble into oriented, fibrillar structures in their cross-section. This work shows that polymeric nanoparticle additives have the potential to increase or decrease orientation of these cellulose structures, which allows the control of bulk mechanical properties. Small amounts of these additives (<1 wt%) are shown to promote the alignment of CNFs, and the particle size is found to determine a tailorable maximum feature size which can be modified. Herein, X-ray scattering allows for the quantification of orientation at different length scales. This newly developed method of measuring cross-sectional orientation allows for understanding the influence of nanoparticle characteristics on the CNF network structure at different length scales in hybrid cellulose-nanoparticle materials, where previously quantitative description has been lacking. It thus constitutes an important foundation for further development and understanding of nanocellulose materials on the level of their nanoscale building blocks and their interactions, which in turn are decisive for their macroscopic properties.

This study investigates the thermal curing behavior and thermo-mechanical properties of bio-based thermosets generated from epoxy monomers derived from furfuryl amine and ferulic acid, in conjunction with the bio-based carboxylic acid, PRIPOL 1017. The synthesis involves use of furfuryl amine and ferulic acid to develop epoxy monomers, enhancing the potential use of these bio-based platform molecules. The thermal curing process was thoroughly examined to understand the kinetics and mechanisms involved. Differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR) and rheology were employed to monitor the progress of the curing reaction and to characterize the chemical changes occurring during the process. The influence of curing parameters such as temperature and time on the curing kinetics of the cured networks was systematically investigated. Furthermore, the thermo-mechanical properties of the cured epoxy networks were comprehensively evaluated. Dynamic mechanical analysis (DMA) and DSC were conducted to assess the relationship between the chemical structure of the monomers and the resulting thermo-mechanical properties of the cured networks. This provided a valuable insight into structure-property relationships of the bio-based thermosetting materials. Overall, this study highlights the potential of ferulic acid diepoxy and diglycidyl furfurylamine for the development of sustainable thermosetting materials.

Fiber-based materials are difficult to process at elevated temperatures as they do not flow as easily as polymers do. The aim of the present work is to obtain a lignocellulose-based thermoformable material with as high fiber content as possible, preferably above 60 wt%. Starch has been demonstrated to bring thermoprocessability when added in large amounts to cellulose fibers. However, the aim of the present work is to obtain a fibre-starch composite with a high fibre content, 60-70 wt%, by mixing bleached Kraft pulp, starch, and plasticizers (glycerol or sorbitol) in a two-step mixing process. First, the pulp was pre-mixed with water, starch, and plasticizer at 90 °C and stirred until reaching a dry content of ca. 90 wt%, where after the pre-mix was further processed using high-shear mixing. Scanning electron microscopy analyses confirmed the successful gelatinization of starch and efficient fiber dispersion after mixing. Differential scanning calorimetry revealed thermal transitions in the samples with the highest sorbitol content, 20 wt%. Sheets were successfully produced from two formulations via compression molding of the high-shear mixed materials: pulp fibers (60 wt%), starch (20 wt%), and glycerol or sorbitol (20 wt%), respectively. Sheets were pressed at 150 or 200°C. Tensile test revealed that the sorbitol-containing samples had higher strength but lower ductility compared to the glycerol-containing samples. The glycerol-containing samples processed at 200°C exhibited significantly lower strength and stiffness than samples prepared at 150°C, likely due to evaporation of glycerol and phase separation. The most favorable results showed a more than sixfold increase in stiffness and strength compared to pure Kraft pulp. Structural weaknesses in the composites were primarily observed at interfaces where starch agglomerates lacked fiber reinforcement. Nevertheless, the method shows strong promise for producing thermoformable lignocellulose-based composites with up to 60 wt% fiber through the incorporation of starch and plasticizer—without compromising mechanical performance. Further optimization of the thermoprocessing conditions is necessary to enhance material strength and uniformity.

Poly(vinyl acetate), PVAc, adhesives are commonly used for wood bonding; however, they are fossil-based and the final products usually do not have a sufficient water resistance for more durable applications. In this study we prepared an adhesive formulation by grafting VAc from chitosan using emulsion polymerization, chitosan-graft-PVAc. Thereby, we could decrease the fossil-based content of the adhesive and at the same time significantly improve the water resistance. Chitosan by itself has very good bonding properties as a wood adhesive, especially regarding water resistance; however, very low solid contents of the adhesive formulation can be achieved due to a very high viscosity of chitosan adhesives. In our chitosan-graft-PVAc adhesives, we explored two chitosan samples with different molecular weights, by using as-received chitosan and hydrolyzing it to a lower molecular weight. The chitosan fractions in the adhesives prepared with a higher molecular weight chitosan were 15, 20 and 25 wt%. However, due to the high viscosity, a solid content higher than 17 wt% could not be achieved for these adhesives. Sufficient bond strengths were achieved when the adhesive was applied in 122 g/m2 solid spread rate. In order to decrease the viscosity, we used hydrolyzed chitosan, with a lower molecular weight, to allow for a higher adhesive solid content, 34 wt%, and for a higher chitosan fraction, 40 wt%. In the adhesive with 40 wt% chitosan and 17 wt% solid content, all VAc was grafted from chitosan. This decreased the molecular mobility of the chains, leading to a lower susceptibility to plastic creep in the adhesive which contributes to the final bond strength. The dry and wet strengths of the specimens bonded with adhesives containing chitosan were higher than the strength of the specimens bonded with the reference PVAc adhesive.

Locust bean gum, derived from the carob tree, was evaluated as a biobased adhesive in particleboard manufacturing, investigating the effect of adhesive amount, mat moisture content, and process parameters such as temperature and time. Single-layer particleboards prepared with locust bean gum showed that effective hydration of the polymer chains is necessary to achieve satisfactory interactions with wood and thus yield a sufficient particleboard strength. A mat moisture content below 30 % resulted in weak particleboards, which easily broke immediately after pressing. With increasing mat moisture content, while keeping the adhesive amount constant, the internal bond strength was increased. Moreover, with constant mat moisture contents (40 %), the internal bond strength increased when the adhesive amount was increased, even though not proportionally. With an increase from 9 % to 18 % adhesive, the internal bond strength was increased by more than 100 %. However, with a further increase in adhesive content from 18 % to 36 %, the increase in internal bond strength was statistically insignificant. Even with high mat moisture contents (35–45 %), larger lab-scale particleboards had internal bond strength that fulfilled standard requirements for P2 boards, commonly used for furniture in dry conditions (SS EN 312), when the pressing time was long enough (75 s/mm) to allow for water and vapors to be removed before releasing the pressure. Using biopolymers as adhesives, without extensive chemical modification and hazardous crosslinkers, could lead to a more benign and sustainable particleboard production. Since the chemistry and setting/curing processes of biopolymer-based adhesives differ from those of the fossil-based adhesives used today, increased understanding of how production parameters affect the properties of the particleboards prepared with biopolymers may pave the way for their better utilization in this field.

Bio-based monomers are under investigation to replace fossil-based materials due to the concerns regarding climate change and depletion of fossil raw materials. Lignin, cellulose and hemicellulose represent the main interesting platform to use for developing new monomers due to their significant abundance. Ferulic acid is one of the moieties derived from lignin which can be suitable for many applications. In this study, the ferulic acid was epoxidated and it was investigated in cationic UV-curing. Due to the limited performance obtained during UV-curing, two alternative strategies were developed to overcome the initial problem of poor material properties. A thiol-ene epoxy system based on the ferulic epoxy derivative and a commercially available thiol as well as a thermally cured system based on pure cationic curing of ferulic acid diepoxy were chosen as alternative methods. The different curing processes were thoroughly investigated by means of FTIR (Fourier transform infrared spectroscopy) and photo-DSC (differential scanning calorimetry). The thermo-mechanical properties of the thermosets employing DMA- (dynamic mechanical analysis) and tensile analysis were deeply evaluated. Finally, the possibility to use the best cured system as an adhesive was raised investigating the shear strength of metallic and composite joined samples using the single lap offset (SLO) test under compression.

The colloidal layer formation on porous materials is a crucial step for printing and applying functional coatings, which can be used to fabricate anticounterfeiting paper. The deposition of colloidal layers and subsequent thermal treatment allows for modifying the hydrophilicity of the surface of a material. In the present work, wood-based colloidal inks are applied by spray deposition on spray-deposited porous cellulose nanofibrils (CNF) films. The surface modification by thermal annealing of the fabricated colloid-cellulose hybrid thin films is investigated in terms of layering and hydrophobicity. The polymer colloids in the inks are core-shell nanoparticles with different sizes and glass transition temperatures (T-g), thus enabling different and low thermal treatment temperatures. The ratio between the core polymers, poly(sobrerol methacrylate) (PSobMA), and poly(-butyl methacrylate) (PBMA) determines the T-g and hence allows for tailoring of the T-g. The layer formation of the colloidal inks on the porous CNF layer depends on the imbibition properties of the CNF layer which is determined by their morphology. The water adhesion of the CNF layer decreases due to the deposition of the colloids and thermal treatment except for the colloids with a size smaller than the void size of the porous CNF film. In this case, the colloids are imbibed into the CNF layer when T-g of the colloids is reached and the polymer chains transit in a mobile phase. Tailored aggregate and nanoscale-embedded hybrid structures are achieved depending on the colloid properties. The imbibition of these colloids into the porous CNF films is verified with grazing incidence small-angle X-ray scattering. This study shows a route for tuning the nanoscale structure and macroscopic physicochemical properties useful for anticounterfeiting paper.

Self-catalyzed hydrolysis upon storage of the common RAFT chain-transfer agent (CTA) 4-cyano-4-[(thiothiopropyl)sulfanyl] pentanoic acid (CTPPA) is confirmed, where the nitrile group is transformed into an amide by catalysis from the adjacent carboxylic acid moiety. The amide-CTA (APP) is found to poorly control molecular weight evolution during polymerization of two methacrylates, methyl methacrylate (MMA) and N,N-(dimethylamino)ethyl methacrylate (DMAEMA), likely due to poor reinitiation speed in the pre-equilibrium. However, when attached to a macromolecule, the impact of this amide moiety becomes insignificant and chain extension proceeds as expected with CTPPA. In light of CTPPA and similarly hydrolyzable CTAs being extensively employed for aqueous polymerizations of methacrylates, these findings highlight the importance of CTA purity when performing RAFT polymerizations.

Bio-based or partially bio-based thermally expandable microspheres were synthesized by suspension (co)polymerization of the bio-based monomer α-methylene-γ-valerolactone (MeMBL) together with acrylonitrile and/or methyl methacrylate to form expandable core/shell particles by encapsulating a hydrocarbon-based blowing agent. The core/shell polymers were characterized with respect to their chemical structure, thermal expansion and morphology. The obtained particles, thermally expandable microspheres (TEMs), showed an increasing onset expansion temperature with increasing content of MeMBL owing to the high glass transition temperature of PMeMBL. As a result, bio-based/partially bio-based TEMs are achieved with high thermal stability and expansion properties which can be tailored for various applications.