Modification And Application Of Cellulose Nanocrystals

Cellulose nanocrystals(CNCs)are the crystalline parts obtained by the removal of the amorphous part of cellulose.CNCs exhibit many advantages,such as excellent mechanical properties,large specific surface area,and good biocompatibility as well as good water-dispersity,etc,which endow CNCs with various applications in diverse fields,such as solar cell,emulsion,cosmetic,and so on.However,CNCs are highly hydrophilic owing to the existence of a lot of hydroxyl groups on the surface,which make them incompatible with hydrophobic polymeric matrixes.Therefore,functional modification of CNCs is very necessary,which can widen the application of CNCs in much more fields.In this work,the functional modification of CNCs derived from sulfuric acid hydrolysis and their application in emulsion and hydrogel were conducted,and the detail contents were as follows:(1)Preparation of heterogeneously modified CNCs and their application as responsive Pickering emulsifiers.First,18-carbon alkyl long chains were selectively introduced at the reducing ends of CNCs through a two-step chemical process including the hydrazone reaction and the amidation reaction.The as-obtained heterogeneously modified CNCs(CNC-C18)were then used as emulsifiers for the formation of oil in water Pickering emulsions.Compared with the pristine CNCs used in this study,CNC-C18 exhibited a high emulsifying performance.Highly stable oil in water Pickering emulsions could be formed at a low content of CNC-C18 nanoparticles.Because of the pH-responsive stability of the C=N bond linkages between 18-carbon alkyl chains and CNCs,the introduced 18-carbon alkyl chains could be cleaved completely at a suitable acid condition,and this endowed the formed Pickering emulsions with a pH-triggered de-emulsification character.Upon the replacement of n-hexane with a styrene/divinyl benezene mixed oil,cross-linked PS microspheres with amino-rich surfaces were created by the Pickering emulsion directed-radical copolymerization reaction,followed by acid treatment.(2)Surface grafting polymer modified CNCs and their hydrogel application.Hydrophilic poly(glycerol-monomethacrylate)chains(PGMA)with 1,2-cis-diol group were firstly grafted onto the surface of CNCs via traditional free radical polymerization reaction using(NH4)2S2O8 as initiator,resulting in the formation CNC-g-PGMA copolymers,and poly(N/N-dimethylacrylmide)-stat-(3-acrylamidophenylboronic acid)](PDMA-stat/-PAPBA)copolymers were synthesized by copolymerization of DMA with APBA.Under the alkaline surrounding,hydrogel nanocomposites could be rapidly formed by means of the complexion between phenylboronic acid groups of PDMA-stat-PAPBA and the diols of CNC-g-PGMA.The storage modulus(G')of hydrogels have been increased by the increase of crosslinking density.In comparison with pure PGMA/PDMA-stat-PAPBA hydrogel without CNCs,the storage modulus(G')of CNC-g-PGMA/PDMA-scat-PAPBA hydrogel nanocomposites was largely enhanced.Due to the presence of the reversible boronate ester,the hydrogels were exhibited good self-healable,and pH and glucose responsiveness.The formed hydrogel composites showed good injectable properties.Additionally,the hydrogel exhibited good biocompatibility.