Research has been undergoing for years on the development of renewable and green polymers to replace petroleum-based plastics. Herein, inexpensive and sustainable films were made by applying some mild etherification reactions on kraft and dissolving pulps to obtain carboxymethylated fibers (CMFs). CMFs were subsequently dissolved in alkaline solutions then cast, immersed in an acid bath, washed, and dried to form regenerated cellulose-based films, which do not dissolve in water. Pulps were chemically analyzed and films were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), field emission scanning electron microscopy (FE-SEM), and UV–vis, and their physical and strength properties were measured. It was found that kraft pulp films were denser, stronger, more transparent and crystalline, had a smoother surface, and were more water absorbent than the dissolving pulp films due to their higher hemicellulose content. Overall, low cellulose carboxymethylation as a scalable method is promising for making biodegradable, recyclable, insoluble, transparent, and strong films that can compete with cellophane and various plastic products used in packaging.

Transversal variations of some ultrasound wave parameters (phase velocity, group velocity, attenuation coefficient and acoustic radiation) were measured from the pith to the bark of poplar tension wood discs in different orthotropic directions. Over 80 cubic specimens of 2 × 2 × 10 cm 3 (radial, tangential and longitudinal, respectively) were prepared and tested acoustically. Samples containing tension woods were separated from normal ones using anatomical experiments. Results showed acoustical behaviour of normal and tension wood improved in longitudinal direction while the distance between pith and bark increased; also, wave parameter variations were less important in radial and tangential directions. In addition, phase velocity and acoustic radiation -which significantly varied -were the best parameters for quality assessment of poplar wood compared with group velocity and attenuation coefficients. Since samples near the bark were acoustically better than counterparts near the pith, they could be used in products requiring more strength, like lumber. Finally, acoustic radiation and phase velocity were correlated more strongly with density than group velocity and attenuation.

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Modified pure cellulose-based films were prepared via a scalable process by cellulose carboxymethylation, producing an alkaline dope and flow casting through a slit in an acid bath, followed by washing and drying. The effect of different carboxyl charge densities (0.9, 1.5, and 2.5 mmol/g) on several properties of the films was investigated. Fourier transform infrared and nuclear magnetic resonance spectroscopy showed the formation of carboxyl bonds on cellulose. However, more carboxyl charge caused more fiber dissolution, which greatly affected physical and mechanical properties of the films. It was found that the most transparent, stretchable, moisture absorbent, and densest films were produced with a 2.5 mmol/g charge density, while the highest tenacity and lowest water vapor permeation was measured for 1.5 mmol/g films. Overall, this straightforward procedure can be applied for the fabrication of biodegradable, recyclable, water insoluble, and strong films, a great promising alternative to plastics for packaging.

A mild etherification of spruce kraft pulp was performed to introduce 1.3 and 2.5 mmol/g carboxyl groups on cellulose chains. 1.3 mmol/g carboxymethyl fibers (CMF) were dissolved partially in alkaline water to form balloons and collars on the tracheid and their ultra-structure was investigated. Primary wall, expanded S1, swollen S2, wrinkled S3, spiral bands of S1, parallel microfibrils of S2 and their transverse splitting were observed on swollen fibers. It is indicated that balloons, collars and wrinkled S3 were formed due to different cellulose microfibril features in different layers of tracheid cell wall. Microspheres with a size up to about 0.6 µm were observed by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). It is shown that they originated from transverse splitting of S2 microfibrils and contain bundles of well-known cellulose nanocrystals (CNC). After homogenization and sonication of an aqueous dispersion of 2.5 mmol/g CMF, electroacoustic spectroscopy showed the presence of nanorods with a size distribution of 18-208 nm. Similar sizes were observed by TEM.