Coaxing Native Starch Granules Into Supramolecular Biocolloids For Use As Papermaking Additives

Starch is widely used in the paper industry.To facilitate efficient uses,native starch is oftentimes engineered by controlled hydrolysis,oxidation,or derivatization.Unavoidably,such treatments can generate undesirable byproducts owing to the "harsh" conditions for chemical reactions.In terms of industrial sustainability,starch-based additives prepared via green routes are promising.The concept of forming starch inclusion complexes would provide an environmentally benign strategy for the use of starch toward diverse capabilities.In light of supramolecular science and starch science,the concept of forming starch-based supramolecular biocolloids was demonstrated.Ionic amphiphilic molecules were used to"engineer" partially disassembled starch to generate biocolloids with miscellaneous characteristics.Specifically,starch-based supramolecular biocolloids were fabricated by downsizing of starch granule in combination with host-guest interactions.The pathways associated with the concept and the wet-end performances of biocolloids were explored.Key hypotheses of forming biocolloids are heating-induced downsizing and noncovalent functionalization.Downsizing involves partial disassembly of semicrystalline granules in an aqueous medium.Multi-components such as free macromolecules,clusters,and blocky swollen pieces are readily available in biocolloidal systems.Hydrophobic alkyl chain of amphiphilic molecules can recognize the helical cavities of starch molecules,thus inducing the formation of inclusion complexes.On the basis of sequential processes of downsizing and noncovalent functionalization,starch-based aqueous dispersions show supramolecular biocolloidal features,and multi-components are dispersible in such miscellaneous systems.On the basis of key variables including ligand type,ligand dosage,turbidity,swelling power,and solubility,the behaviors pertaining to host-guest inclusion complexes were examined.Starch-based supramolecular biocolloids can be described as dispersed systems containing multiple components,e.g.,microsized particles or nanosized molecular assemblies.Cationic amphiphilic molecules(dodecyltrimethylammonium chloride,tetradecyltrimethylammonium chloride,cetyltrimethylammonium chloride,and octadecyltrimethylammonium chloride,)can induce the formation of host-guest inclusion complexes,leading to an increase in transparency of starch dispersion,swelling power,and solubility.Oily moieties of guest molecules are dynamically attractable into inner cavities of helical structures of biomacromolecules.It is demonstrated that host-guest ratio plays an important role in governing the characteristics of supramolecular biocolloids.At a ligand dosage of below 1.5%,the trapping of ligand molecules in helical structures can enhance the optical transparency of supramolecular biocolloids films,and supramolecular biocolloids show pronounced features of host molecules.At a ligand dosage of above 6%,ligand molecules can efficiently interact with starch,and a complexing index of about 80%is achievable.The quaternary ammonium-based groups are in two forms:out of the helical cavities and within interstitial space of helices.These different forms endow supramolecular biocolloids possbility with antimicrobial activity.Freeze-dried biocolloidal samples can be readily redispersed in water at room temperature,and in this case,supramolecular biocolloids show pronounced features of guest molecules.In aqueous systems,hydrophilic moieties of guest molecules facilitate the charge-related interactions between supramolecular biocolloids and other dispersed components.As wet-end additives,supramolecular biocolloids interact with anionic substances,resulting in enhancement of filler retention and starch retention.The combination of supramolecular biocolloids with microparticle retention system consisting of cationic polyacrylamide and bentonite can significantly improve filler retention,starch retention,filler bondability,and paper strength.