Tailor-made starch-based adhesives chemically modified with NaOH:urea and their applications on a cellulosic substrate

Adhesives formulated with native starches have high viscosity, low solids content, poor bond strength and stability due to the starch retrogradation. To overcome this problem, a strategy is the starch treatment with NaOH solution combined with urea, capable of intercalating in the polymeric chains of starch. The aims of this work were to develop adhesives based on chemically modified cassava starch with different NaOH:urea ratios and to study in depth the effect induced by the addition of different concentrations of alkali and urea in the adhesive capacity of formulations that determine their subsequent application in paper-based packaging. Firmness and consistency of the adhesive increased for the 1:1 ratio while it decreased for the NaOH:urea 2:1 ratio, suggesting that the hydrolysis of polymer chains occurred. Additionally, adhesives prepared with 15 % starch maintaining NaOH:urea ratios of 0.5:1: and 1:1 exhibited the highest stress values. ATR-FTIR studies supported the results obtained. It was possible to obtain formulations with different adhesive properties with applications in paper-based packaging. From the analysis of the studied parameters, the combination of 15 % w/w cassava starch with a ratio of NaOH:urea 1:1 allows obtaining adhesives with adequate consistency and adhesive capacity which remain stable during the adhesive storage.

APTES-Modified Nanocellulose as the Formaldehyde Scavenger for UF Adhesive-Bonded Particleboard and Strawboard

This work examines the possibility of applying non-modified nanocellulose and nanocellulose functionalized with 3-aminopropyltriethoxysilane (APTES) as a formaldehyde scavenger for commonly used urea-formaldehyde (UF) adhesive. The effect of silanization was determined with the use of Fourier transform infrared spectroscopy (FTIR), flame atomic absorption spectrometry (FAAS), and elemental analysis. Moreover, the ability of cellulosic nanoparticles to absorb the formaldehyde from an aqueous solution was investigated. After homogenization, cured UF adhesives were examined with the use of FTIR, energy-dispersive spectroscopy (SEM-EDS), and the perforator method to determine the content of formaldehyde. Manufactured boards made of rape straw particles and wood particles were tested in terms of their physico-mechanical properties and formaldehyde emission. Studies have shown that the applied method of silanization was effective. Furthermore, in the case of non-modified nanocellulose, no sign of formaldehyde scavenging ability was found. However, the functionalization of cellulosic nanoparticles with APTES containing an amino group led to the significant reduction of formaldehyde content in both the aqueous solution and the UF adhesive. The mechanical properties of both strawboards and particleboards were improved due to the nanocellulose reinforcement; however, no effect of silanization was found. Nevertheless, functionalization with APTES contributed to a decrease in formaldehyde emission from boards, which was not found in the case of the introduction of non-modified cellulosic nanoparticles.

Nanocellulose in Heterogeneous Water-Based Polymerization for Wood Adhesives

The interest in the development of biobased adhesives has increased due to environmental concerns. Moreover, as the production of engineered wood products (EWPs) is expected to grow, the wood adhesives market needs to transit toward formaldehyde-free products. Cellulose nanoparticles (CNPs) are a material with unique properties and advantages for producing hybrid materials as biobased wood adhesives. Besides their traditional use as reinforcing additives, CNPs can be incorporated at the beginning of the polymerization reaction to form in situ polymerized hybrid adhesives with better mechanical and physicochemical properties than the neat adhesive. Despite their outstanding characteristics, CNPs are still an emerging nanomaterial in the wood adhesive field, and the studies are incipient. This review explores the utilization of CNPs in heterogeneous polymerization for the production of polyvinyl acetate, polymeric isocyanates, waterborne polyurethane systems, and other waterborne polymer latexes. The main challenges are discussed, and some recommendations are set down for the manufacture of these novel hybrid nanocomposites.

Nanocellulose from Agricultural Wastes: Products and Applications—A Review

The isolation of nanocellulose from different agricultural residues is becoming an important research field due to its versatile applications. This work collects different production processes, including conditioning steps, pretreatments, bleaching processes and finally purification for the production of nanocellulose in its main types of morphologies: cellulose nanofiber (CNF) and cellulose nanocrystal (CNC). This review highlights the importance of agricultural wastes in the production of nanocellulose in order to reduce environmental impact, use of fossil resources, guarantee sustainable economic growth and close the circle of resource use. Finally, the possible applications of the nanocellulose obtained as a new source of raw material in various industrial fields are discussed.

Present Status and Future Prospects of Jute in Nanotechnology: A Review

Nanotechnology has transformed the world with its diverse applications, ranging from industrial developments to impacting our daily lives. It has multiple applications throughout financial sectors and enables the development of facilitating scientific endeavors with extensive commercial potentials. Nanomaterials, especially the ones which have shown biomedical and other health-related properties, have added new dimensions to the field of nanotechnology. Recently, the use of bioresources in nanotechnology has gained significant attention from the scientific community due to its 100 % eco-friendly features, availability, and low costs. In this context, jute offers a considerable potential. Globally, its plant produces the second most common natural cellulose fibers and a large amount of jute sticks as a byproduct. The main chemical compositions of jute fibers and sticks, which have a trace amount of ash content, are cellulose, hemicellulose, and lignin. This makes jute as an ideal source of pure nanocellulose, nano-lignin, and nanocarbon preparation. It has also been used as a source in the evolution of nanomaterials used in various applications. In addition, hemicellulose and lignin, which are extractable from jute fibers and sticks, could be utilized as a reductant/stabilizer for preparing other nanomaterials. This review highlights the status and prospects of jute in nanotechnology. Different research areas in which jute can be applied, such as in nanocellulose preparation, as scaffolds for other nanomaterials, catalysis, carbon preparation, life sciences, coatings, polymers, energy storage, drug delivery, fertilizer delivery, electrochemistry, reductant, and stabilizer for synthesizing other nanomaterials, petroleum industry, paper industry, polymeric nanocomposites, sensors, coatings, and electronics, have been summarized in detail. We hope that these prospects will serve as a precursor of jute-based nanotechnology research in the future.

Nanocellulose: Recent Fundamental Advances and Emerging Biological and Biomimicking Applications

In the effort toward sustainable advanced functional materials, nanocelluloses have attracted extensive recent attention. Nanocelluloses range from rod-like highly crystalline cellulose nanocrystals to longer and more entangled cellulose nanofibers, earlier denoted also as microfibrillated celluloses and bacterial cellulose. In recent years, they have spurred research toward a wide range of applications, ranging from nanocomposites, viscosity modifiers, films, barrier layers, fibers, structural color, gels, aerogels and foams, and energy applications, until filtering membranes, to name a few. Still, nanocelluloses continue to show surprisingly high challenges to master their interactions and tailorability to allow well-controlled assemblies for functional materials. Rather than trying to review the already extensive nanocellulose literature at large, here selected aspects of the recent progress are the focus. Water interactions, which are central for processing for the functional properties, are discussed first. Then advanced hybrid gels toward (multi)stimuli responses, shape-memory materials, self-healing, adhesion and gluing, biological scaffolding, and forensic applications are discussed. Finally, composite fibers are discussed, as well as nanocellulose as a strategy for improvement of photosynthesis-based chemicals production. In summary, selected perspectives toward new directions for sustainable high-tech functional materials science based on nanocelluloses are described.

Effect of boric acid on poly vinyl alcohol- tannin blend and its application as water-based wood adhesive

The work presented here focusses on developing adhesive by blending tannin and polyvinyl alcohol (PVA) in water. To furthermore enhance the properties crosslinking is carried by using boric acid at varying concentrations. Presence of free hydroxyl groups in PVA and tannin acts as a site for crosslinking reaction. The empty p orbital of trivalent boron atom attracts nucleophilic hydroxyl groups of PVA and tannin, hence are expected to form crosslinks. The interaction of boric acid with the blend was confirmed by FTIR spectra studies. The acidic pH favoured the reaction and its effects were observed by increase in viscosity and glass transition temperature (Tg). Films cased with the crosslinked blend demonstrated less hydrophilic behaviour from water contact angle test also increment in pencil hardness value and stress-bearing capacity. Adhesive performance properties like wet tack and time-dependent tensile lap shear strength on softwood and hardwood specimens were evaluated. The crosslinking-enhanced cohesion by reducing the free volumes between the chains and due to this, enhancement in tensile strength on bonded wood substrates was observed. Overall, it was found that the adhesive prepared by crosslinking PVA/tannin blend with boric acid is suitable for wood adhesive application.

Impact of Bio-Based (Tannins) and Nano-Scale (CNC) Additives on Bonding Properties of Synthetic Adhesives (PVAc and MUF) Using Chestnut Wood from Young Coppice Stands

Sustainability and ecotoxicity issues call for innovations regarding eco-friendly adhesives in the production of biocomposite wood materials, and solutions involving nano-scale and bio-based compounds represent a valid and promising target. One possible approach is to increase the performance of adhesives such as polyvinyl acetate (PVAc) or melamine-urea-formaldehyde (MUF) by means of nanoparticles in order to obtain a material with better mechanical and environmental resistance. When applying cellulose-based nanoparticles or tannin, the concept of a circular economy is successfully implemented into the forest/wood value chain, and chances are created to develop new value chains using byproducts of forestry operations. In this study, assortments coming from young sweet chestnut (Castanea sativa Mill.) coppice stands were utilized for the preparation of single lap joint assemblies using different commercial adhesives (PVAc, MUF) and cellulose nanocrystals (CNC) and tannin as additives. The results showed that addition of CNC and tannin to PVAc glue increased tensile shear strength in lap joint tests presenting a promising base for future tests regarding the addition of CNC and tannin in MUF or PVAc adhesive formulations. Unfortunately, the tested bio-based additives did not reveal the same encouraging results when tested in the wet state.