## 2 Nature and Characteristics of _A. altissima_
### Utilization in Paper, Pulp- and Nanocellulose-Based Products  
_A. altissima_ wood, bark, and leaves have been used for papermaking in different parts of the world, especially in China. The bark of the tree contains long and strong fibers that are suitable for producing strong paper, while the leaves contain short fibers that can be used to produce softer and smoother paper [94]. The bark fibers can be obtained by scraping the external bark of the tree, boiling it, and then introducing it into the pulp, mixed with water, and formed into sheets, which are dried and finished into paper. _A. altissima_ paper has a distinctive light brown color and a slightly rough texture. The paper is also known for its strength and durability, making it suitable for various applications, such as bookbinding and printing [94].  
There is limited literature concerning the utilization of this species in paper and pulp production, although there are some studies conducted evaluating the potential of this species for use in the paper industry. Nevertheless, _A. altissima_ has been found to have a high cellulose content, which is a key component in the production of paper and pulp [31]. [PERSON] et al. [95] investigated the suitability of _A. altissima_ as a raw material for kraft pulp production and found that this species presented a similar pulp yield and kappa number (a measure of pulp quality), as other hardwood species commonly used in the paper industry. [PERSON] et al. [87] examined the potential of using this species as an alternative fiber source for papermaking in terms of the physical and mechanical properties of the produced paper, as well as the chemical composition of the fibers. The paper made of this species' fibers demonstrated satisfying mechanical properties, including high tensile strength and burst resistance, attributed mainly to the high cellulose content and low lignin content, which are desirable properties for papermaking. It was noticed that _A. altissima_ had a lower lignin content than other hardwood species, which could potentially make it easier to bleach the pulp to achieve the desired whiteness [95]. [PERSON] and [PERSON] [32], who examined the impact of tree age on the wood and bark properties, reported that as the tree age increases, the wood and bark present lower lignin content, though a linear increase in holocellulose and extractives. It was found that the optimum harvesting time for the highest possible utilization of holocellulose (as well as extractives) is after the 21 st year when the cellulose, hemicelluloses, and extractives content increase. Further research is undoubtedly necessary to explore the environmental implications of using this tree species as a fiber source, as well as to develop more sustainable methods of fiber harvesting. Overall, although there is some evidence to suggest that _A. altissima_ could be used as a raw material in the paper and pulp industry, further research is needed to fully understand the potential of the species for this application.  
[PERSON] et al. [96] produced nanocellulose using invasive tree species of _A. altissima_ and _Acacia dealbeta_, in order to create high-value-added materials. The process involved producing bleached pulps from the wood of these trees using kraft cooking, followed by pre-treatment through either TEMPO-mediated oxidation (_A. dealbeta_) or enzymatic hydrolysis (_A. altissima_) and high-pressure homogenization. The resulting hydrogels were characterized in terms of physical and chemical properties, including rheology and surface energy. The study found that nano/microfibrils could be obtained from the wood of these invasive species and that TEMPO cellulose nanofibrils formed strong gels with high-yield stress points and viscosities (tensile strength of 79 MPa, Young's modulus of 7.9 GPa, and transparency of 88%, although the water vapor barrier was modest). Films produced from cellulose hydrogels were found to be characterized by good mechanical and optical properties.