The Siamese people utilized the bark of the Coi tree (Streblus asper Lour.) to manufacture paper approximately 330 years ago. However, there are no studies yet related to the chemical properties of Coi bark as well as the morphological properties of Coi bark fiber and Coi pulp fiber. This research paper discussed such properties of Coi bark. The results indicated that Coi bark possessed a chemical composition that could potentially be used for pulp production, although it contained a high value of ash content, due to many calcium particles in the bark. Even though Coi pulp fibers were very long and stiff, with small lumens and thick cell walls, they could be felted naturally on a washing screen to make a strong wet sheet. This was due to a high felting power of fibers derived from a high value of fiber length and slenderness ratio. Therefore, the handsheets produced from Coi pulp fiber were obtained without chemical and beating treatments. These observations mean that both the archaeological and industrial applications of Coi bark, i.e., an ancient Samud Coi preservation and a new potential source of pulp fiber, are possible.
The synthesis of TEMPO-oxidized bamboo cellulose nanofibrils (TOBCNs) was attempted using two locally available species in Thailand (Dendrocalamus asper and D. membranaceus). Bamboo powder was first delignified with NaClO2. The obtained bamboo holocelluloses (BHs) were then oxidized via a TEMPO/NaBr/NaClO system in water at pH 10 for 2 h. The effects of NaClO addition level on the weight recovery ratio, carboxylate content, and nanofibrillation yield were studied. At a higher level of NaClO addition, the weight recovery ratio of TEMPO-oxidized bamboo holocelluloses (TOBHs) decreased from 90% to 70%, while the carboxylate content of TOBHs increased up to 0.8 mmol/g to 0.9 mmol/g for both species. Fourier transform infrared spectra indicated that C6-hydroxyl groups of cellulose were converted to negatively-charged carboxylate groups. After a gentle mechanical treatment with water, transparent liquid of TOBCNs were obtained after the removal of unwanted fraction, which gave a nanofibrillation yield of more than 90% at a NaClO addition level of 7.5 mmol/g to 15.0 mmol/g-BHs. Well individualized TOBCNs were successfully prepared and had a length of several microns and an average width of 5 nm to 7 nm under transmission electron microscopy. Thus, ultra-long TOBCNs are applicable for use as nano-reinforced polymer composites in non-food industries.
There have been recent attempts to revive the traditional production of handmade paper from the bark of the Coi (Streblus asper Lour.) tree in Thailand. A sheet sample of Coi handmade paper, made from the traditional production, was collected and examined microscopically for the first time. Film-like material and cubic calcium particles were found on the sheet sample surface, which is consistent with the results of the authors’ previous research. Meanwhile, handsheets derived from Coi pulp fiber, freshly made in the laboratory, demonstrated a low air permeance and brightness with high opacity due to the film-like material and cubic calcium particles. With a high felting power of Coi pulp fiber coupled with a possible strengthening role of the film-like material, both the beaten and unbeaten fibers were used to form handsheets with high strength. Some potential aspects of Coi pulp fiber suitable for creating a unique Thai banknote paper have been demonstrated, for which further studies are suggested.
Bamboo holocellulose was oxidized by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) in water at pH 10 with an addition of 7.5 mmol g-1 of NaClO for 2 h. After oxidation, the weight recovery ratio of TEMPO-oxidized bamboo holocellulose (TOBH) was 73% with a carboxylate content of 0.65 mmol g-1. The water-insoluble TOBH was converted to an aqueous dispersion of bamboo TEMPO-oxidized cellulose nanofibrils (TOBCN) through mechanical defibrillation and centrifugation, with the nanofibrillation yield of around 90%. Transmission electron microscopy (TEM) indicated that the widths of TOBCN were estimated to be between 3 and 4 nm and lengths of several micrometers. The TOBCN dispersions had high light-transparencies of 99% at a wavelength of 600 nm. These nanofibrils were used as reinforcing nanoparticles in thermoplastic starch (TPS) films. The TOBCN dispersions were added in dosages of 0, 0.3, 0.6, 0.9, 1.2, and 1.5 wt%. Glycerol was used as a plasticizer. Nanocomposite films were prepared through a solution casting process. The TOBCN/TPS nanocomposite films exhibited high optical transparencies and their tensile strength, Young’s modulus, elongation around failure, and work to cause a fracture increased, compared to the TPS films without TOBCN. The presence of TOBCNs, at 1.5 wt%, improved moisture resistance.
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