Research Article
SN Applied Sciences (2020) 2:1577 | https://doi.org/10.1007/s42452-020-03313-w
including shape, particle size distribution, aspect ratio, average particle size, aggregate size and density during the manufacturing of fillers. It was found that the smallest particles are detrimental to the paper strength at constant shape. However, the size of PCC is comparatively smaller than that of cellulose fibers resulting in poorer first-pass ash retention in the wire section [1, 2]. Furthermore, the traditional route of stochastic incorporation of fillers in the cellulose network weakens the fiber–fiber bonding at high filler addition level as they may partially reside at fiber interstice which deteriorates the ultimate strength of individual fibers as well as paper. Since papermakers crave for high ash content paper, different classical routes were explored in integrating these pigment fillers with pulp fib- ers [2–6]. Pre-flocculation or surface modification of PCC through coating or encapsulation among preceding tech- niques has been an impressive approach to mitigate nega- tive effects on mechanical properties of paper at high ash level [2–4, 7]. Industrial low-cost native starch or cationic starch is a widely accepted biopolymer in filler modifica- tion among various researchers as this hydrogen bonding polymer can develop strong bonds with pulp fibers when dried after starch/mineral composite fillers are added to the furnish. Another approach to fabricate these bio-based composite fillers with paper sheet is in situ crystallization of calcium carbonate in the presence of biopolymers [8]. But there are certain limitations associated with starch such as consumption of extra chemicals during the coat- ing process, loss of cationicity at alkaline pH, sensitivity to water and its prone to microbial attack [9]. In addition to starch, several other synthetic or biodegradable poly- mers were considered for filler modification by adsorbing these polyelectrolytes onto them to confer the enhanced bonding ability between fillers and fibers. Thus, polymer- induced aggregation leads to a larger particle size of the composite fillers which can then be sufficiently retained in the sheet. In paper technology, synthetic polymeric materials are vastly applied as retention and strength aids [10, 11]. Processing with such synthetic polymers results in environmental pollution, serious health issues due to their carcinogenicity and creates problems in recycling or composting paper materials reported by consum- ers and government bodies. This might have motivated researchers to look for an alternate approach to utilizing biodegradable resources. Since the processing of crusta- ceans in the seafood industries constitutes 60% of shell waste according to Environmental Protection Agency (EPA), it should be a major concern for the industries to look for solid waste management. Hence, interest lies in the extraction of value-added products from such wastes and their potential application in diverse fields [9, 12, 13]. Chitosan is that biogenic environmental-friendly polymer having natural cationic charge density, biodegradability,
non-toxicity, antibacterial and antifungal properties. Not only in medical science and other sectors, chitosan has also emerged as a value-added potential additive among paper industries. Although expensive compared to con- ventional wet-end additives, its unique property of floc- culation ability both at acidic and alkaline pH makes it a better retention-drainage aid in stock preparation [14–16]. In contrast to conventional starch, 30% faster drainage rates, higher internal bond strength, wet/dry strength with no tendency of slime formation, and desired surface and optical properties were notable for chitosan in terms of good machine runnability and energy consumption. It was anticipated that this would minimize the overall cost of production to manufacture an economically feasible paper with high-quality specifications as per customers’ demand [17, 18]. This polymer was found to be effective both for surface coating and wet-end section in develop- ing specialty grade or packaging papers. The NH 2 group in the polymer backbone not only provides additional bond- ing ability with cellulose but also imparts water resistance to the paper when made at alkaline conditions as revealed in these studies. So there is an urge to modify filler surface with this polymer proving possibilities to widen the scope of its application [14, 15, 19]. In the year 2012, a US patent disclosed that PCC’s inherent alkalinity enables chitosan’s precipitation that can effectively functionalize the PCC surface for the development of paper-based composite materials. However, the patent did not reveal either the effect of functionalization on PCC structure or illustrate any mechanism for acidic chitosan-basic PCC reaction [20]. Synthetically produced PCC can exist in three anhy- drous polymorphs namely calcite, aragonite and vaterite. Calcite, being the most thermodynamically stable has become a choice to the papermakers. Under different pro- cess conditions, it exhibits different morphologies which can be either rhombohedral, scalenohedral or prismatic [3]. Crystallization of calcium carbonate starts with nuclea- tion and crystal growth takes place either by aggregation or by phase transformation mechanism [21]. Thus, crystal- lization of PCC particles is tailored by manipulating super- saturation, reactant feed, temperature or with some addi- tives to acquire desired properties required for paper [8]. The templating action of many polymers in controlling the calcium carbonate crystal growth and their orientation has been discussed extensively [22–24]. Stabilization of phase, growth rate and ultimate crystal morphology depends on the degree of inorganic/additive interactions. Biomimetic approaches of mineralization show the presence of dif- ferent polymorphs which can certainly be elucidated by stereochemical complementary between calcium ions and active groups in the polymer chain as well as geom- etry matching. Chitosan-mediated bio-mineralization has gained a lot of attention and has been observed that
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