Mechanism And Functionality Study On Tunable Cellulose Nanocrystal Pickering Emulsions Using Cellulose Ethers

Cellulose nanocrystal(CNC)are entering the marketplace as new ingredients for formulated chemical products.As "green" and potentially food-grade additives,there is widespread interest in CNC particularly as rheological modifiers,emulsifiers,and reinforcing agents.To extend the food and pharmaceutical applications of Dow's cellulose ether polymers using nanocellulose,the research project quantified the improvement in material properties upon addition of nanocellulose,mainly focusing on emulsion,gel and encapsulation technologies.The goal to understand how Pickering emulsions performance changes as a function of polymer addition in the presence of nanocellulose led our research to be carried out as follows:Firstly,the work presents the role of the CNC counterions in stabilizing oil-in-water Pickering emulsions.Since CNC have been proven to be good Pickering emulsifiers,however,most research uses sodium-form CNC with added salt to screen surface charges,due to their easy storage and transport.Herein,the stability of oil-in-water Pickering emulsions,prepared from CNC with three different counterions(H+,Na+and K+),to coalescence and resistance to creaming was tested using two oil types(high-polarity corn oil and superlow polarity hexadecane).Without salt,only acid-form H+-CNC could stabilize corn oil/water emulsions and none of the CNC could stabilize hexadecane/water emulsions.However,adding salt masked the differences between the CNC types,and all CNC could stabilize both oil/water emulsions.This chapter highlights the complex nature of CNC interactions with salts,oils,acids/bases,and other additives,which is relevant for envisioned formulated products for food,cosmetic,and pharmaceutical applications and reveals that the choice of CNC counterion does influence emulsion performance.To control emulsion properties and stability the work explored combinations of CNC and nonionic cellulose ethers(methyl cellulose and hydroxypropyl methylcellulose)as Pickering emulsifiers.Such emulsions were resistant to coalescence and had smaller droplets size because the CNC surface charge was screened and the amphiphilicity was increased as a result of cellulose ether adsorption.The adsorption of cellulose ethers was investigated on model CNC films as well as in suspension via two-dimensional techniques(quartz crystal microbalance with dissipation monitoring(QCM-D)and surface plasmon resonance(SPR))and three-dimensional techniques(dynamic light scattering(DLS)and electrophoretic mobility).The result indicated that the driving force for adsorption was entropic,the adsorption was irreversible,and molecular weight and degree of substitution were the key factors which controlled adsorption.Strong adsorption was directly linked to more robust emulsions and the need for less stabilizer to be used.Based on the explored fundamental information of cellulose ether adsorbing onto CNC,the physical heat-cooling,freeze-thawing,redispersing behaviors and biological in vitro gastrointestinal digestion of cellulose ether/CNC Pickering emulsions were studied further.Compared to cellulose ether or CNC-only stabilized emulsions,the synergistic effect between cellulose ether polymers and CNC particles strengthened the emulsion physical storage stability and prevented its "breakdown" during both heat-cooling and freeze-thawing.A follow-up work of dried and redispersible emulsions was updated that both freeze-dried and oven-dried emulsion powders could be successfully redispersed in water owing to the composites synergistic cooperation.Moreover,by exposed to the simulated oral,gastric and small intestinal phases during in vitro gastrointestinal digestion,the cellulose ether/CNC Pickering emulsions could impede the enzymes lipolysis of fatty oil,therefore,it designs a strategy for reducing fatty in-taking in food diet and health care.Inspired by the above discussion on nonionic cellulose ethers,the interest was extended to anionic cellulose ethers-carboxymethyl cellulose(CMC)adsorbing onto CNC.While extensive characterization and investigation of fundamentals were proposed,the work were anticipated to lead to the development of new formulated products of relevance for nutrition and health applications.The goal is to identify the main "handles" that can be manipulated to enhance CMC(and other food-grade polymer)binding to cellulose nanomaterials.Experimentally,anionic CMC polymers adsorbing onto negative-charged CNC could be influenced by pH,salt concentration,ionic strength,salt type and other food additives.Lowering pH,adding electrolytes or even multivalent ionic electrolytes resulted in more adsorption,and likewise,the driving force of CMC adsorbing onto CNC was proven to be favorably entropic contributionEmulsions from the two components via two different routes was investigated including stability to conventional physical storage and biological in vitro gastrointestinal digestion.The CMC localization could considerably affect the modified CNC Pickering emulsions performance,i.e.,emulsions post-functionalized with CMC exhibited much more physical stability over storage,while that from pre-functionalization method showed higher tolerance to simulated gastrointestinal fluids in mimicking biological metabolism environment.Taking the CMC nature of thickening but no surface activity,the large fraction of CMC polymer distributing in water phase could only slow down the enzymes lipolysis by rising the emulsion viscosity.However,the robust CMC/CNC composites shell at the O/W interface contributed the most in preventing the CMC pre-functionalized CNC Pickering emulsion from enzymes lipolysis.The research project highlights the complex nature of CNC interactions with polymeric additives,which is relevant for envisioned formulated products for food,cosmetic and pharmaceutical applications.