Nanopaper Properties and Adhesive Performance of Microfibrillated Cellulose from Different (Ligno-)Cellulosic Raw Materials

Biochemical characterisation of cellulose and cell-wall-matrix polysaccharides in variously oxidised sugar-beet pulp preparations differing in viscosity

Sugar-beet pulp (SBP) is an abundant, cellulose-rich, non-food by-product of agriculture. Oxidised SBP (oP) has valuable viscosity attributes, and different oxidation protocols yield higher- or lower-viscosity oP. We investigated how SBP polysaccharides change during oxidation, since these changes must define oP quality. Oxidation solubilised much pectin and hemicellulose; however, most cellulose stayed insoluble. Fresh SBP contains negligible 'hemicellulose a' (=alkali-extractable polysaccharides that precipitate upon acidification), but oxidation created abundant glucose-rich 'hemicellulose a' from SBP cellulose. We propose that the cellulose acquired COOH groups, conferring alkali-extractability and admitting more water, thereby augmenting viscosity. The pectin and hemicellulose molecules that were retained during oxidation had been partially depolymerised, and their median Mr correlated negatively with oP viscosity. We developed a novel procedure to explore cellulose's permeability by measuring the ingress of tritium from [3H]water into microfibrils and its retention during desiccation. In high-crystallinity Avicel, 75 % of the cellulose's OH groups were inaccessible to [3H]water, whereas filter-paper cellulose acquired the theoretical maximum 3H, indicating an open structure. Retention of 3H by oP preparations correlated positively with viscosity, indicating that increased cellulose accessibility generates a viscous oP. In conclusion, depolymerisation and solubilisation of matrix polysaccharides, accompanied by increasing water-accessibility of cellulose, enhanced SBP's viscosity.

Soybean-based polymers and composites

Development and evaluation of new bio-based sustainable plastics to replace the petroleum-based materials in different industrial applications has both environmental and economic benefits. Bio-based polymers can be widely used in biomedical and agriculture applications due to their excellent biodegradability and biocompatibility. Soy protein is a natural material that can be isolated from soybean, which is a major agricultural crop in the U.S. The viability of soybean-based polymers and composites is questioned due to their high-water absorption and poor mechanical properties. There have been many environmentally friendly attempts to improve the properties of soybean polymers as soybeans and their extracts are widely available worldwide. Soy protein, hulls, and oils all find use in the development of different biodegradable polymers. While the development looks promising, there is still more work to do to make the soybean polymers useful and economically viable. Blending soy protein with other biodegradable polymers, such as polylactide (PLA) and polyurethane dispersion is a valid approach to improve the mechanical properties of soy protein and reduce its water sensitivity.

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.

Reducing the Amount of Catalyst in TEMPO-Oxidized Cellulose Nanofibers: Effect on Properties and Cost

Cellulose nanofibers (CNF) are interesting biopolymers that find numerous applications in different scientific and technological fields. However, manufacturing costs are still one of the main drawbacks for the industrial production of highly fibrillated, transparent CNF suspensions. In the present study, cellulose nanofibers were produced from bleached eucalyptus pulp via TEMPO-mediated oxidation with varying amounts of NaClO and passed through a high-pressure homogenizer. The CNFs were chemically and physically characterized; cellulose nanopapers were also produced to study tensile properties. Production costs were also calculated. Results indicated that CNF properties are strongly dependent on the carboxyl content. Manufacturing costs showed that chemicals, in particular TEMPO catalyst, represent a large part of the final cost of CNFs. In order to solve this problem, a set of samples were prepared where the amount of TEMPO was gradually reduced. Characterization of samples prepared in this way showed that not only were the costs reduced, but also that the final properties of the CNFs were not significantly affected when the amount of TEMPO was reduced to half.

Preparation and Evaluation of Green Composites from Microcrystalline Cellulose and a Soybean-Oil Derivative

The present work aimed at developing fully green composites from renewable materials, i.e., acrylated epoxidized soybean oil (AESO) and microcrystalline cellulose (MCC) by a solution casting method. The reinforcing effect of MCC on AESO resins was optimized by adjusting MCC loading from 20 to 40 wt % in terms of physical, mechanical, and thermal properties as well as water absorption of the resulting MCC/AESO composites. The interaction between MCC and AESO was characterized by Fourier transform infrared (FTIR) analysis, which revealed possible hydrogen bonds between the ⁻OH groups of MCC along with the polar components of AESO including C=O, ⁻OH, and epoxy groups. This was further evidenced by a benign interfacial adhesion between MCC and AESO resins as revealed by scanning electron microscope (SEM) analysis. The incorporation of MCC into AESO resins significantly increased the density, hardness, flexural strength, and flexural modulus of the MCC/AESO composites, indicative of a significant reinforcing effect of MCC on AESO resins. The composite with 30 wt % MCC obtained the highest physical and mechanical properties due to the good dispersion and interfacial interaction between MCC and AESO matrix; the density, hardness, flexural strength, and flexural modulus of the composite were 15.7%, 25.0%, 57.2%, and 129.7% higher than those of pure AESO resin, respectively. However, the water resistance at room temperature and 100 °C of the composites were dramatically decreased due to the inherent hydrophilicity of MCC.