Document Type : Composite Wood Products
Authors
1 gorgan university of agricultural science and natrual resorces
2 Minnesota university
3 Minnesota University
Abstract
One of the main causes of environmental damage and pollution is petroleum-based plastics and packaging materials. Despite the numerous advantages of petroleum-based plastics in the packaging industry, such as affordable cost, high mechanical strength, and moisture resistance, their non-biodegradability leads to persistent accumulation in the environment and poses serious risks to ecosystems and human health. In this regard, nanobiopolymers such as nanocellulose and bio-nanocomposites derived from it, due to their biocompatibility, renewability, and reasonable production costs, are promising alternatives for various applications including packaging. Despite the numerous technical and environmental advantages of nanocellulose, energy consumption and relatively high production costs remain global challenges to the commercial development of this nanobiopolymer. To address this, Kaffash-Saie et al. (2021) successfully produced cellulose nanofibers directly from sawdust through a simultaneous oxidation/purification process. The present study aims to directly produce cellulose nanocrystals from wood sawdust, which differ from cellulose nanofibers both in production stages and in morphological and technical characteristics. Direct production of cellulose nanocrystals from sawdust implies reduced energy consumption, chemical usage, water consumption, wastewater generation, and ultimately lower production costs compared to samples produced by conventional methods. The prepared cellulose nanocrystals were then used to reinforce carboxymethyl cellulose (CMC)-based films.
Materials and Methods: The wooden raw material used in this study was Fir wood sawdust (Abies alba), obtained from the furniture industry workshop of the university. Chemical materials included sodium hydroxide, sodium hypochlorite, and hydrogen peroxide (purchased from Mojallali Co.), as well as sodium sulfite, sodium bromide, and TEMPO (purchased from Sigma-Aldrich). For the direct production of cellulose nanocrystals from sawdust, the purification and oxidation steps were performed simultaneously. At the end of this stage, an oxidized bleached cellulose pulp was obtained, in which the hydroxyl group at the C6 position of the pyranose ring was replaced by a carboxyl group. For comparison, cellulose nanocrystals were also produced indirectly (conventional method) from Fir sawdust. After producing both types of nanocrystals, they were added to carboxymethyl cellulose polymer at weight ratios of 0.5%, 1%, 3%, 5%, and 10% to produce nanocomposites via solution casting. Finally, the characteristics of the nanocrystals and the prepared nanocomposites were investigated and compared. Analytical methods used included Fourier-transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and static tensile testing.
Results: TEM images showed that the average diameter of nanocrystals produced by direct and indirect methods was 8±4 nm and 7±4 nm, respectively, with no significant dimensional or morphological differences observed between them. FE-SEM images showed uniform dispersion of nanocrystals within the CMC matrix. XRD patterns confirmed an increase in the crystallinity of nanocomposites with increasing cellulose nanocrystal content, while FTIR spectra revealed no significant structural differences between the samples. The results of static tensile testing showed that the neat CMC film had a tensile strength of 34 MPa. Upon the addition of 1% and 10% cellulose nanocrystals by both methods, tensile strength increased, with the increase being more pronounced at 10% nanocrystal content. At 10% mixing ratio, the tensile strength for direct and indirect method nanocrystals reached 58 MPa and 62 MPa, respectively.
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