The cellulosic polysaccharide shows many potential applications due to its abundance, renewability, biodegradability and biocompatibility. Nowadays, the dissolution of this biopolymer via the alkaline based green solvent system has gained much attention in developing cellulose based composites for pharmaceuticals, waste water treatment or packaging applications. In this work, we aim at dissolving different grades of sustainable pulps in an aqueous NaOH/urea/thiourea system, involving the freeze thawing process, followed by re-precipitation with distilled water. This particular dissolving medium is chosen as it is economic and environment-friendly. Optical microscopy is used to study the extent of cellulose solubility in this system. Dissolving grade pulp (D.G.P.), with a degree of polymerization DP = 678.27, exhibits higher solubility after 3 freeze thawing cycles, compared to bleached hardwood pulp (B.G.P., DP = 990.67) and tissue grade pulp (T.G.P., DP = 1356.54). DP is further correlated with the average fibre length of the three samples obtained from a Morfi fibre analyser. Additionally, fibre identification through the microscopic slide staining procedure reveals that the long flexible softwood fibres present in the T.G.P. sample are responsible for its high DP. The solubility percentage calculated for D.G.P., B.G.P. and T.G.P. is 72.90%, 57.2% and 57%, respectively. The flow behaviour of each dissolved cellulosic sample is of Newtonian type at high shear rates, considering the same cellulose concentration at ambient temperature. X-ray diffraction patterns (XRD) and ATR-FTIR spectra indicate that the ordered crystalline structure of the samples is successfully destroyed and converted to cellulose II during the dissolution and regeneration process. Field emission scanning electron microscopy (FE-SEM) reveals porous structures for all samples, created due to phase separation of the cellulose solutions during regeneration with distilled water. Thus, the key finding of the study establishes that the regeneration via the green solvent can produce more amorphous cellulosic materials, which may be a suitable additive for papermaking, due to their enhanced bonding ability with wood fibres.
Industries from different business sectors are facing challenges against global competitions for the development of sustainable and renewable products in the twenty-first century. Likewise, constant effort from pulp and paper manufacturers in minimizing paper cost with better quality in the active field of filler modification technology is much appreciated. In the present study, chitosan has been explored as a surface modifier alternative to conventional starch for precipitated calcium carbonate (PCC) to design chitosan/PCC composite filler. Two different dissolution mediums, hydrochloric and acetic acid, for chitosan have been seen to affect PCC crystals. Commercial PCC comprises mostly aragonite polymorphs along with some calcite crystals as implied by FTIR, XRD and FE-SEM images. It is interesting to note that surface treatment of PCC with 4.5% chitosan can successfully induce crystal transformation of PCC from aragonite to calcite polymorphs. Further, the deposition of chitosan was estimated from TOC measurements and the presence of deposited amount was validated from TGA analysis. Moreover, the introduction of chitosan (dissolved in HCl) to PCC dispersion was found to raise the zeta potential from − 14.43 to − 11.3 mv. Finally, the tensile strength of handsheets increased by 8.2% with 20% enhancement in ash with chitosan/PCC composite filler compared to the unmodified PCC. Therefore, bio-based PCC composites which proved to be promising for the development of high ash paper without compromising essential properties may result in saving wood pulp and production cost. Thus, implementing such seafood waste as a value-added additive is beneficial both to the industries and the environment because of its biodegradability and eco-friendliness.
In this work, gums from guar seeds were evaluated as a potential precipitated calcium carbonate (PCC) filler pre-flocculant to induce functional filler in papermaking applications. In recent years, guar has been conidered one of the promising wet-end additives due to its abundance, rich source of hemicellulose content, and bio-degradability. However, application of guar gum in filler pretreatment methods for producing high ash paper has scarcely been reported. In this paper, the flocculating ability of three types of guar gum was established with charge analysis and turbidity (NTU) of the system at 1% and 5% for each gum: native gum (NG) having a degree of substitution (DS) of 0, and cationic gums having a DS value of 0.07 (CL) and 0.15 (CH). It was interesting to observe that even at a 5% dose of G, the charge density of PCC did not deviate much from the initial values. The system carried a weak negativeharge, resulting in an unstable colloidal suspension that led to PCC-PCC particle bridging. On the other hand, the operative mechanism of CL and CH during adsorption and PCC flocculation was predicted to be charge neutralization and electrostatic-patch formation, accompanied by particle bridging. Note that CL, with a maximum 47.5% eduction in residual turbidity of PCC at a 1% dose, was much more efficient in doing so than the other two gums; NG had a 40% maximum reduction in residual turbidity at a 5% dose and CH had a maximum 30% reduction at a 1% ose. Later on, floc formation and structure were correlated with optical and field emission scanning electron microscopy (FE-SEM) images. In the next set of trials, paper properties were determined by varying the different gum dosages from 0.2% to 5% at a constant dose of 20% filler. It is also noteworthy to mention that with 1% CL (low DS) dose, PCC retention increased by 39%, which also enhanced the tensile, tear, burst, and opacity properties by 11%, 19%, 5%, and 4.4%, respectively, without significantly affecting the bulk properties. Further, wide-angle X-ray diffraction (XRD) analysis and Fourier transform infrared (FTIR) analysis revealed that pre-flocculating PCC with a 1% gum dose did not induce any change in crystalline transformation. Based on observation, it was found that cationic gums with low DS values re a better choice for maximizing the strength of paper while maintaining bulk and high opacity when pre-flocculaion is adopted to increase the filler retention in paper.
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