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Cellulose nanopaper (CNP) has been considered as a promising material with great application potential in diverse fields. However, the hydrophilic nature of CNP significantly limits its practical application. In order to improve its water resistance, we demonstrate a facile approach to functionalize CNP by impregnating it with chitosan (CS), followed by in situ polymerization of polypyrrole (PPy). The results indicate that the obtained CNP/CS/PPy shows excellent water resistance with the wet tensile strength of up to 80 MPa, which is more than 10 times higher than that of the pure CNP. Intriguingly, new features (e.g., electrical conductivity, antibacterial activity, and so forth) are achieved at the same time. The functionalized CNP/CS/PPy shows a high conductivity of 6.5 S cm-1, which can be used for electromagnetic interference shielding applications with a high shielding performance of around 18 dB. In addition, the CNP/CS/PPy exhibits good antibacterial activity toward Staphylococcus aureus and Escherichia coli, with the bacterial reductions of 99.28 and 95.59%, respectively. Thus, this work provides a simple and versatile approach to functionalize CNP for achieving multifunctional properties.

In this work, tension and fracture behaviors of cellulose nanopaper (CNP) made from two different preparation approaches are comparatively studied. The CNP are prepared by casting (or C-CNP) and filtration (or F-CNP) of CNF suspension. The resulting CNP are mechanically characterized using the vision-based full-field optical method of Digital Image Correlation. Tension tests show that F-CNP has a higher strength and greater nonlinearity than the C-CNP. The crack initiation and growth characteristics of the two types of CNP are investigated using optical measurements. The data are analyzed under small-scale-yielding conditions to quantify the fracture parameters such as stress intensity factors and energy release rates at crack initiation as well as during crack growth. The results indicate that both C-CNP and F-CNP show significant crack growth resistance in the post-crack initiation regime. The F-CNP particularly offers substantial resistance to crack growth relative to the C-CNP demonstrating that filtration is the preferred method to make CNP with higher tensile strength and better fracture properties.

We report that a simple, low-cost type of spray-freeze drying (SFD) significantly improves the dispersion of single-walled carbon nanotubes (SWNTs) in thermoplastic polymers. Conventional SFD requires costly specialized equipment and large amounts of material, both of which are impediments to laboratory research on nanomaterial composites. Our method uses more readily available equipment and can be adapted to use milligrams to grams of material. A household spray bottle containing an aqueous nanomaterial dispersion is used to spray the dispersion into a dish of liquid nitrogen. The resulting material is then lyophilized in a standard laboratory freeze dryer. The usefulness of this simplified method was explored by comparing the properties of polypropylene (PP) composites produced by this method to those produced by a previously reported rotary evaporation method in which the dispersion is vacuum-dried onto the polymer. The role of the initial dispersion state was explored by using pristine SWNTs as well as SWNTs stabilized by two common SWNT stabilizers: polyvinylpyrrolidone (PVP) and sodium dodecyl sulfate. Based on rheological, thermal, and morphological characterization, the porous friable structures produced by SFD resulted in better SWNT dispersion compared to composites produced by a previously reported rotary evaporation method. However, the PP/PVP-SWNT nanocomposites produced by both methods contained large aggregates. To verify that this aggregation behavior was the result of thermodynamic incompatibility between PP and PVP, ethylene vinyl alcohol (EVOH) nanocomposites containing PVP-SWNT were also produced using the SFD method. The results of this research show how a low-cost alternative to SFD along with careful consideration of compatibility is a promising approach to produce nanocomposites.

PEDOT:PSS has been widely used as the electrode materials for supercapacitors. However, processing PEDOT:PSS bulk films with good flexibility and mechanical stability is still challenging. The present study is aimed at providing a facile and low-cost strategy for the preparation of mechanically strong and conductive PEDOT:PSS based bulk films by using Cellulose nanofibrils (CNF) as building blocks. PEDOT:PSS/CNF suspension was firstly prepared via a simple in situ polymerization process. Afterwards, flexible and conductive PEDOT:PSS/CNF nanopaper (PEDOT:PSS/CNP) were prepared from the PEDOT:PSS/CNF suspension by vacuum filtration and Dimethyl sulfoxide (DMSO) post-treatment. Results showed that the optimized PEDOT:PSS/CNP exhibited excellent flexibility, high tensile strength (72 MPa), and high electrical conductivity (66.67 S/cm). Finally, a symmetric supercapacitor was assembled using the PEDOT:PSS/CNP as electrodes. The assembled supercapacitor could deliver the maximum areal specific capacitance of 854.4 mF cm−2 (corresponding to 122.1F cm−3) at 5 mV/s and offer the highest areal energy density of 30.86 μWh cm−2 (corresponding to 4.41 mWh cm−3), which are among the highest values reported for PEDOT:PSS based supercapacitors. More importantly, the assembled supercapacitor showed remarkable cycling stability with the capacitance retention of 95.8% after 10,000 charge/discharge cycles. Considering the good mechanical properties and excellent electrochemical performance, the PEDOT:PSS/CNP could be a promising electrode material for flexible supercapacitors.

Cellulose nanopapers, 2D flat and foldable film made of network-forming cellulose nanofibers, are strong, tough and biodegradable materials of great interest as they have potential to replace the conventional fossil based polymers in various applications. Although there are several cellulose nanopaper preparation methods described in the literature, no standard method is available for the preparation of uniform and smooth nanopapers within a practical time frame. In present study, TAPPI standard method of preparation of pulp handsheets was systemically modified/optimized to prepare flat and wrinkle free cellulose nanopapers in few hours of preparation time. Physical properties of these cellulose nanopapers such as tensile strength and water vapor transmission rate were comparable to the reported values in the literature. The proposed standard preparation method will enable the comparison of the physical properties of cellulose nanopapers prepared in different studies.

As a kind of agro-industrial wastes, paper mill sludge (PMS) has posed serious environmental and economic challenges for disposal due to the more stringent regulations and diminishing land availability in recent years. The present study is aimed at providing a sustainable approach to efficiently convert PMS to cellulose nanofibrils (CNFs) and cellulose nanopaper (CNP) by formic acid (FA) hydrolysis pretreatment and the followed microfluidization. It is found that FA hydrolysis (4–6 h) could swell and shorten PMS fibers, and only two-pass microfluidization is sufficient to get uniform CNFs from the collected cellulose residual. Results indicate that the obtained CNFs show high thermal stability and crystallinity index, surface functionality (ester groups), as well as a high yield of over 75 wt.%. Notably, more than 90 % FA can be recovered and the hydrolyzed sugars could be potentially used to produce platform chemicals (e.g. lactic acid, furfural). Finally, transparent CNP is prepared from the CNFs suspension via a simple vacuum filtration technique. The resultant CNP shows good mechanical properties with the maximum tensile strength and toughness of 106.4 MPa and 6.62 MJ/m3, respectively. Therefore, the current work provides a green and sustainable method to valorize PMS for the production of valuable CNFs and CNP.

Polypyrrole (PPy) and cellulose nanofiber (CNF) based conducting composite films were synthesized using two new approaches, in-situ polymerization of pyrrole onto cellulose nanopaper (PPy/CNP) and polyvinyl alcohol coated cellulose nanopaper (PPy/PVA-CNP). Significant improvement in the conductivity, tensile strength, water resistance, and electromagnetic shielding effectiveness (SE) was observed for these composite films compared to commonly used in-situ nanofiber (ISF) approach, where PPy is coated on nanofibers prior to film preparation. Maximum improvement in conductivity, SE and tensile strength of PPy/PVA-CNP compared to ISF films was attributed to highly uniform and compact PPy coating and reduced porosity. SE of -23 dB (thickness upto 138.4 μm) and tensile strength of 103.8 MPa for PPy/PVA-CNP films are the highest values found in the literature for PPy and CNF based composite films at a comparable thickness. These new approaches could enable a scalable preparation of flexible conducting composite films with superior physical and electrical properties for EMI shielding applications.

Three types of buckypapers (BPs), two of them fabricated with arc discharge (AD) single-walled carbon nanotubes (SWNTs) (acetone-cleaned AD BP and methanol-cleaned AD BP) and one with high-pressure carbon monoxide (HiPco) SWNTs (HiPco BP), were heat-treated at different conditions to find the specific conditions for each type that improve the adsorption properties. Based on thermogravimetric analysis (TGA) data, three heat treatment conditions were designed for the AD BPs and another three conditions for the HiPco BPs. Also, changes in weight and physical integrity before and after the heat treatment were considered. Heating at 300°C for 90 minutes was selected for acetone-cleaned AD BP, in which the BP kept its physical integrity and yielded a relatively high Brunauer, Emmett, and Teller (BET) surface area (970 ± 18 m2/g), while methanol-cleaned AD BP was excluded because of its physical change. For HiPco BP, a condition of 300°C heating for 30 minutes was chosen as a relatively higher surface area (933 ± 54 m2/g) and less weight loss (5%) were observed.