A biomimetic, facile approach to cellulose modification is the utilisation of self-adsorbing, naturally occurring biopolymers, such as the hemicellulose xyloglucan (XG). Herein, XG-block-poly(sulfobetaine methacrylate) (XG-b-PSBMA) zwitterionic block copolymers have been prepared and assessed for their ability to adsorb to cellulose, specifically cellulose nanofibrils (CNF). The polymers were synthesised using reversible addition-fragmentation chain-transfer (RAFT) polymerisation, employing an XG macromolecular RAFT agent (XG-RAFT), polymerising a sulfobetaine methacrylate (SBMA) under aqueous conditions. The incorporation of the XG block shifted the upper critical solution temperature (UCST) values to higher temperatures (20 and 30 °C) compared with the PSBMA homopolymers (17 and 22 °C) and the transition was also broadened. The adsorption of the polymers to a CNF surface was monitored using quartz crystal microbalance with dissipation monitoring (QCM-D), showing that the XG block enhanced the adsorption of the zwitterionic polymer. The formation of CNF-composite films was achieved utilising a facile vacuum filtration methodology, and the targeted compositions were confirmed by FT-IR and TGA analyses. The films exhibited high degrees of swelling in water, which were investigated at two different temperatures, 5 and 60 °C (below and above the polymer USCT values). These results highlight the advantage of using an XG block for the biomimetic modification of cellulose to form new cellulose-composite materials such as super-absorbing films.

In this work we describe the grafting of cellulose nanocrystals (CNCs) by surface-initiated photoinduced Cu-mediated reversible-deactivation radical polymerization (RDRP). Initially, CNCs obtained through sulfuric acid hydrolysis were functionalized with a tertiary bromo-ester moiety as an initiating group for the subsequent RDRP of methyl acrylate, targeting three different degrees of polymerization for the polymer grafts: 50, 300 and 600. The polymerizations proceeded in DMSO in the presence of CuBr2 and Me6TREN as the catalytic system utilizing a UV source (λmax ≈ 360 nm). The technique proved highly versatile for the modification of CNCs with poly(methyl acrylate), where considerably high grafting was achieved in short reaction times (90 min), with simple purification steps. CNC morphology was maintained and polymer grafts were evident through FT-IR spectroscopy, thermal analysis, contact angle measurements, X-ray photoelectron microscopy and x-ray diffraction.

Latex nanoparticles comprising cationically charged coronas and hydrophobic cores with different glass transition temperatures (Tg) have been prepared by surfactant-free, RAFT-mediated emulsion polymerization, where the particles form through a polymerization-induced self-assembly (PISA) type mechanism. Poly(2-dimethylaminoethyl methacrylate-co-methacrylic acid) (P(DMAEMA-co-MAA)) was utilized as a hydrophilic macroRAFT agent for the polymerization of methyl methacrylate (MMA) or n-butyl methacrylate (nBMA), respectively, resulting in two different latexes, with either a core of high (PMMA) or low (PnBMA) Tg polymer. By varying the molar mass of the hydrophobic block, latexes of different sizes were obtained (DHca. 40-120 nm). The adsorption of the latexes to cellulose model surfaces and cellulose nanofibrils (CNF) was studied using quartz crystal microbalance with dissipation monitoring (QCM-D). The surfaces with adsorbed PnBMA latexes yielded hydrophobic surfaces both before and after annealing, whereas surfaces with adsorbed PMMA latex became hydrophobic only after annealing, clearly showing the influence of the Tg of the core. The latexes were also used to modify macroscopic cellulose in the form of filter papers. Similar to the CNF surfaces, no annealing was required to achieve hydrophobic surfaces with PnBMA latexes. Finally, nanocomposites of CNF and the polymer nanoparticles were prepared through a one-pot mixing procedure. It was found that the largest synthesized PMMA latex (120 nm) facilitated a more strainable CNF network at 50% relative humidity, with a nearly 200% increase in strain at break compared to the neat CNF reference film as well as to the composite films with PnBMA latexes or to the smaller sized PMMA latexes. This difference was attributed to the spherical shape and rigidity of the large PMMA latex nanoparticles during composite formation. This highly interesting result should indeed be considered in the future design of novel biocomposites.

Herein, we report a novel class of latex particles composed of a hemicellulose, xyloglucan (XG), and poly(methyl methacrylate) (PMMA), specially designed to enable a biomimetic modification of cellulose. The formation of the latex particles was achieved utilizing reversible addition-fragmentation chain transfer (RAFT) mediated surfactant-free emulsion polymerization employing XG as a hydrophilic macromolecular RAFT agent (macroRAFT). In an initial step, XG was functionalized at the reducing chain end to bear a dithioester. This XG macroRAFT was subsequently utilized in water and chain extended with methyl methacrylate (MMA) as hydrophobic monomer, inspired by a polymerization-induced self-assembly (PISA) process. This yielded latex nanoparticles with a hydrophobic PMMA core stabilized by the hydrophilic XG chains at the corona. The molar mass of PMMA targeted was varied, resulting in a series of stable latex particles with hydrophobic PMMA content between 22 and 68 wt % of the total solids content (5-10%). The XG-PMMA nanoparticles were subsequently adsorbed to a neutral cellulose substrate (filter paper), and the modified surfaces were analyzed by FT-IR and SEM analyses. The adsorption of the latex particles was also investigated by quartz crystal microbalance with dissipation monitoring (QCM-D), where the nanoparticles were adsorbed to negatively charged model cellulose surfaces. The surfaces were analyzed by atomic force microscopy (AFM) and contact angle (CA) measurements. QCM-D experiments showed that more mass was adsorbed to the surfaces with increasing molar mass of the PMMA present. AFM of the surfaces after adsorption showed discrete particles, which were no longer present after annealing (160 °C, 1 h) and the roughness (Rq) of the surfaces had also decreased by at least half. Interestingly, after annealing, the surfaces did not all become more hydrophobic, as monitored by CA measurements, indicating that the surface roughness was an important factor to consider when evaluating the surface properties following particle adsorption. This novel class of latex nanoparticles provides an excellent platform for cellulose modification via physical adsorption. The utilization of XG as the anchoring molecule to cellulose provides a versatile methodology, as it does not rely on electrostatic interactions for the physical adsorption, enabling a wide range of cellulose substrates to be modified, including neutral sources such as cotton and bacterial nanocellulose, leading to new and advanced materials.

The utilization and modification of cellulose, in particular nanocelluloses, for applications in bioplastics and biocomposites has been well studied in recent years. There is an increasing need for materials with good mechanical properties from renewable resources to replace current polymeric materials derived from fossil fuels. The modification of cellulose is essential to improve compatibility with hydrophobic matrices. For this purpose, various modification techniques have been employed such as physical adsorption of polymers to cellulosic substrates. This review aims to summarize the existing literature describing the physical adsorption of tailor-made copolymers to cellulosic surfaces. This area of cellulose modification incorporates a broad range of polymeric materials, and the expansion of this method of cellulose modification is promising for future sustainable, renewable and 'green' material development.