A critical aspect in materials design of polymer nanocomposites is the nature of the nanoparticle/polymer interface. The present study investigates the effect of manipulation of the interface between cellulose nanofibrils (CNF) and poly(methyl methacrylate) (PMMA) on the optical, thermal, and mechanical properties of the corresponding nanocomposites. The CNF/PMMA interface is altered with a minimum of changes in material composition so that interface effects can be analyzed. The hydroxyl-rich surface of CNF fibrils is exploited to modify the CNF surface via an epoxide-hydroxyl reaction. CNF/PMMA nanocomposites are then prepared with high CNF content (similar to 38 wt %) using an approach where a porous CNF mat is impregnated with monomer or polymer. The nanocomposite interface is controlled by either providing PMMA grafts from the modified CNF surface or by solvent-assisted diffusion of PMMA into a CNF network (native and modified). The high content of CNF fibrils of similar to 6 nm diameter leads to a strong interface and polymer matrix distribution effects. Moisture uptake and mechanical properties are measured at different relative humidity conditions. The nanocomposites with PMMA molecules grafted to cellulose exhibited much higher optical transparency, thermal stability, and hygro-mechanical properties than the control samples. The present modification and preparation strategies are versatile and may be used for cellulose nanocomposites of other compositions, architectures, properties, and functionalities.

Alfa fibers (Stipa Tenacissima) were effectively utilized in this study as a promising cellulose source for isolation of carboxy-functionalized cellulose nanofibrils (CNFs) using multiple treatments. Pure cellulose microfibers (CMFs) were firstly extracted by alkali and bleaching treatments. CNFs with an average nanofibrils diameter ranging from 1.4 to 4.6 nm and a crystallinity of 89% were isolated from CMFs by a combination of TEMPO-oxidation and mechanical disintegration processes. The morphology and physico-chemical properties of cellulosic materials were evaluated at different stages of treatments using several characterization techniques. Various CNF loadings (5-15 wt%) were incorporated into PVA polymer to evaluate the nanoreinforcement ability of CNFs and to produce CNF-filled PVA nanocomposite materials. The tensile and optical transmittance properties, as well as the morphological and thermal properties of the as-produced CNF-filled PVA nanocomposite films were investigated. It was found that the tensile modulus and strength of nanocomposites were gradually increased with increasing of CNF loadings, with a maximum increase of 90% and 74% was observed for a PVA nanocomposite containing 15 wt% CNFs, respectively. The optical transmittance was reduced from 91% (at 650 nm) for neat PVA polymer to 88%, 82% and 76% for PVA nanocomposites containing 5, 10 and 15 wt% CNFs, respectively. It was also found that the glass transition temperature was gradually increased from 76 degrees C for neat PVA to 89 degrees C for PVA nanocomposite containing 15 wt%. This study demonstrates the importance of Alfa fibers as annual renewable lignocellulosic material to produce CNFs with good morphology and excellent properties. These newly developed carboxy-functionalized CNFs could be considered as a potential nanofiller candidate for the preparation of nanocomposite materials of high transparency and good mechanical properties.Graphic abstract

Herein, we present a route to obtain bi-functional cellulose nanofibrils (CNF) by a one-pot approach using an already established functionalisation route, carboxymethylation, to which a subsequent functionalisation step, allylation or alkynation, has been added in the same reaction pot, eliminating the need of solvent exchange procedures. The total charge of the fibres and the total surface charge of the nanofibrils were determined by conductometric and polyelectrolyte titration, respectively. Furthermore, the allyl and alkyne functionalised cellulose were reacted with methyl 3-mercaptopropionate and azide-functionalised disperse red, respectively, to estimate the degree of functionalisation. The samples were further assessed by XPS and FT-IR. Physical characteristics were evaluated by CP/MAS C-13-NMR, XRD, AFM and DLS. This new approach of obtaining bi-functionalised CNF allows for a facile and rapid functionalisation of CNF where chemical handles can easily be attached and used for further modification of the fibrils.

Poly(epsilon-caprolactone) (PCL) is a ductile thermoplastic, which is biodegradable in the marine environment. Limitations include low strength, petroleum-based origin, and comparably high cost. Cellulose fiber reinforcement is therefore of interest although uniform fiber dispersion is a challenge. In this study, a one-step wet compounding is proposed to validate a sustainable and feasible method to improve the dispersion of the cellulose fibers in hydrophobic polymer matrix as PCL, which showed to be insensitive to the presence of the water during the processing. A comparison between unmodified and acetylated cellulosic wood fibers is made to further assess the net effect of the wet feeding and chemical modification on the biocomposites properties, and the influence of acetylation on fiber structure is reported (ATR-FTIR, XRD). Effects of processing on nano fibrillation, shortening, and dispersion of the cellulose fibers are assessed as well as on PCL molar mass. Mechanical testing, dynamic mechanical thermal analysis, FE-SEM, and X-ray tomography is used to characterize composites. With the addition of 20 wt % cellulosic fibers, the Young's modulus increased from 240 MPa (neat PCL) to 1850 MPa for the biocomposites produced by using the wet feeding strategy, compared to 690 MPa showed for the biocomposites produced using dry feeling. A wet feeding of acetylated cellulosic fibers allowed even a greater increase, with an additional 46% and 248% increase of the ultimate strength and Young's modulus, when compared to wet feeding of the unmodified pulp, respectively.

In the present work, cellulose nanocrystals (CNCs) have been surface-modified either via covalent grafting or through physisorption of poly(n-butyl methacrylate) (PBMA) and employed as reinforcement in PCL. Covalent grafting was achieved by surface-initiated atom transfer radical polymerization (SI-ATRP). Two approaches were utilized for the physisorption: using either micelles of poly(dimethyl aminoethyl methacrylate)-block-poly(n-butyl methacrylate) (PDMAEMA-b-PBMA) or latex nanoparticles of poly(dimethyl aminoethyl methacrylate-co-methacrylic acid)-block-poly(n-butyl methacrylate) (P(DMAEMA-co-MAA)-b-PBMA). Block copolymers (PDMAEMA-b-PBMA)s were obtained by ATRP and subsequently micellized. Latex nanoparticles were produced via reversible addition-fragmentation chain-transfer (RAFT) mediated surfactant-free emulsion polymerization, employing polymer-induced self-assembly (PISA) for the particle formation. For a reliable comparison, the amounts of micelles/latex particles adsorbed and the amount of polymer grafted onto the CNCs were kept similar. Two different chain lengths of PBMA were targeted, below and above the critical molecular weight for chain entanglement of PBMA (M-n,M-c similar to 56 000 g mo1(-1)). Poly(epsilon-caprolactone) (PCL) nanocomposites reinforced with unmodified and modified CNCs in different weight percentages (0.5, 1, and 3 wt %) were prepared via melt extrusion. The resulting composites were evaluated by UV-vis, scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), and tensile testing. All materials resulted in higher transparency, greater thermal stability, and stronger mechanical properties than unfilled PCL and nanocomposites containing unmodified CNCs. The degradation temperature of PCL reinforced with grafted CNCs was higher than that of micelle-modified CNCs, and the latter was higher than that of latex-adsorbed CNCs with a long PBMA chain length. The results clearly indicate that covalent grafting is superior to physisorption with regard to thermal and mechanical properties of the final nanocomposite. This unique study is of great value for the future design of CNC-based nanocomposites with tailored properties.

The study presented describes the preparation of solvent-free nano composite gel electrolytes in combination with copper(I)-based dye-sensitized solar cells (DSSCs). The electrolytes comprise poly(ethylene oxide) (PEO) and cellulose nano crystals (CNCs) and an I-3(-)/I- redox shuttle. The quasi-solid-state DSSCs show increased photoconversion performance with increased amount of CNC in the electrolyte. DSSC performances measured on the day that the devices are fabricated show that when the electrolyte is composed of 80% CNC, a cell efficiency of 1.09% is reached compared to 1.16% using a standard liquid I-3(-)/I- electrolyte. DSSCs containing the nano composites and the copper(I)-based dye show robust stability over time, and after 60 days, DSSCs with the PEO/CNC/I-3(-)/I- electrolyte outperform those containing the liquid electrolyte.

In the present work, poly(vinyl acetate) grafted cellulose nanocrystals (CNC-g-PVAc) were prepared via surface initiated reversible addition-fragmentation chain transfer and macromolecular design via the interchange of xanthates (SI-RAFT/MADIX) polymerization. Successful grafting of PVAc from CNC was confirmed by FT-IR and TGA analysis. PVAc nanocomposites reinforced with CNC-g-PVAc, as well as pristine CNC for comparison, of different weight percentages (0.5, 1, 3 and 5 wt%) of CNC were prepared via solvent casting. The PVAc reinforced with CNC-g-PVAc resulted in higher transparency and improved mechanical properties compared with unmodified CNC nanocomposites. The addition of 5 wt% CNC-g-PVAc increased the modulus of neat PVAc with as much as 154%. The proposed SI-RAFT/MADIX on CNC could be applied to wide range of monomers, and it is believed to be an efficient and robust method for CNC functionalization, thus expanding the potential applicability of CNC.

Nanocelluloses have attracted great interest during recent decades owing to their renewability, abundancy and remarkable physical and mechanical properties. The aim of this work was to investigate new strategies for surface modification and functionalization of nanocelluloses and their subsequent incorporation in polymer-host matrices.

Nanocomposites of cellulose nanofibrils (CNF) and polycaprolactone (PCL) were produced by employing CNF nanopaper (NP) as a template and surface-initiated ring-opening polymerization (SI-ROP) of ε-caprolactone (ε-CL). SI-ROP of ε-CL from filter paper (FP) was also carried out for comparison. A larger amount of PCL was grafted from NP than from FP. The grafted NP had stronger mechanical properties than neat PCL.

Cellulose nanocrystal (CNC)-reinforced polyvinyl acetate (PVAc) nanocomposites were also investigated. CNC were modified via “SI-reversible addition-fragmentation chain transfer and macromolecular design via the interchange of xanthate” (SI-RAFT/MADIX) polymerization of vinyl acetate (VAc). The resulting nanocomposites exhibited improved mechanical performance than the unmodified CNC.

It is generally agreed that covalent grafting is superior to physical adsorption for the modification of a reinforcing agent. However, this hypothesis has never been thoroughly investigated. CNC was modified either through covalent grafting or through physical adsorption of poly(butyl methacrylate) (PBMA). Both methods resulted in improved mechanical performance than that of pure PCL or PCL containing unmodified CNC. However, covalent grafting gave the best mechanical performance even at high relative humidity.

Functionalized CNC (F-CNC) were obtained through a versatile methodology employing organic acids bearing a functional group were employed for the simultaneous acid hydrolysis and esterification of cellulose fibers. This provided a facile route for the preparation of F-CNC.

Intresset för nanocellulosa har ökat markant under de senaste decennierna eftersom de är förnyelsebara, finns att tillgå i stor mängd, och har mycket bra fysikaliska och mekaniska egenskaper. Syftet med detta arbete var att undersöka nya strategier för ytmodifiering och funktionalisering av nanocellulosa och dess inkorporering i polymera matriser.

Nanokompositer av cellulosa nanofibriller (CNF) och polykaprolakton (PCL) framställdes genom att CNF nanopapper (NP) användes som ett startmaterial från vilken ε-kaprolakton (ε‑CL) polymeriserades med ringöppningspolymerisation (SI-ROP). Som jämförelse ympades även ε-CL från filterpapper (FP) med SI-ROP. Resultatet var att större mängd av polykaprolakton (PCL) ympades från NP jämfört med FP. Det ytmodiferade NP hade bättre mekaniska egenskaper jämfört med ren PCL.

Nanokompositer av cellulosananokristaller (CNC) och polyvinylacetat (PVAc) undersöktes också. CNC modifierades via “SI-reversible addition-fragmentation chain transfer and macromolecular design via the interchange of xanthate” (SI-RAFT/MADIX) polymerisation av vinylacetat (VAc). Nanokompositerna uppvisade bättre mekaniska egenskaper jämfört med omodifierade CNC.

Man har antagit att kovalent ympning är en överlägsen metod för modifiering av ett förstärkande element jämfört med fysikalisk adsorption, men denna hypotes har aldrig undersökts ordentligt. CNC har modifierats endera genom kovalent ympning eller fysikalisk adsorption av poly(butylmetakrylat) (PBMA). Båda metoderna gav förbättrad mekanisk prestanda jämfört med ren PCL och PCL innehållande omodifierad CNC, men kovalent ympning gav bäst prestanda även vid hög relativ fuktighet.

Funktionell CNC (F-CNC) framställdes genom en användbar metod som baseras på organiska syror med en funktionell grupp. F-CNC erhålls genom att hydrolysen av cellulosafibrer utförs genom att använda en kombination av sur hydrolys och förestring. Detta är en enkel och mycket användbar metod för att framställa F-CNC.