Preparation Of Cellulose-based Films For Packaging Applications

Petroleum-based plastics such as polyethylene?PE?,polypropylene?PP?,polystyrene?PS?,polyethylene terephthalate?PET?,polyvinyl alcohol?PVA?are currently the most prevalent raw materials for packaging mainly due to their low cost,excellent mechanical performance,and barrier properties.On the other hand,the large consumption of petroleum-based plastics has posed serious environmental impacts due to the non-biodegradability of these plastics.Alternatives to petroleum-based plastics are of great significance not only from the point of view of their scientific and practical impact but to reduce the environmental footprint.Cellulose,especially cellulose nanofiber?CNF?possess high stiffness and low density.In addition,they are renewable and biodegradable.These features make CNF a promising candidate of reinforcement filler for polymers.However,the inherent hydrophilicity of CNF is one of the main obstacles that hinder its compatibility with hydrophobic polymers.Nevertheless,a large amount of hydroxyl groups on CNF also facilitates the surface modification of CNF.Several chemical modification strategies,such as esterification,salinization,and polymer grafting,have been developed to tune the interfacial compatibility of cellulose.This work is directly aimed to address the afore mentioned problems.Several cellulose modification strategies have been developed to introduce different functional groups to cellulose macromolecules.And a series of composite films using the resulting modified cellulose and other polymer matrix were perpared.The properties of these cellulose films with different functions are studied comprehensively.The main contentsdetails of this work are as follows:1.Cellulose nanofiber?CNF?was modified by rosin and used as a reinforcement filler within a polylactic acid?PLA?matrix.The resulting film was then coated with chitosan?CHT?to prepare a two-layer composite film for antimicrobial food packaging.The FT-IR spectra of rosin modified CNF?R-CNF?displayed a clear peak at 1730 cm^-1,which confirmed the successful esterification of CNF by rosin.The R-CNF showed a better dispersion in the PLA matrix than CNF and the loading of R-CNF had a significant effect on the mechanical properties of the resulting film.A percolation network was formed when the R-CNF loading was 8%,where the composite film displayed optimum mechanical properties.The antimicrobial test showed that the R-CNF/PLA/CHT composite film exhibited excellent antimicrobial performance against E.coli and B.subtilis,which could be attributed to the synergistic antimicrobial effect of CHT and rosin.2.Multifunctional composite films were synthesized with cellulose nanofibers?CNFs?and poly?vinyl alcohol??PVA?.First,TEMPO-oxidized CNFs were modified in heterogeneous phase with benzophenone,diisocyanate and epoxidized soybean oil via esterification reactions.A thorough characterization was carried out via elemental analysis,as well as FT-IR,X-ray photoelectron spectroscopies,and solid-state NMR.Following,the surface-modified CNFs were combined with PVA to prepare a highly transparent composite films with UV-absorbing capabilities and high thermo-mechanical strength.Compared to neat PVF films,the tensile strength,Young modulus,and elongation of the films underwent dramatic increases upon the addition of modified CNF?maximum values of⁹6 MPa,⁷14 MPa,and³50%,respectively?.A high UV blocking performance,especially in the UVB region,was observed for modified CNF/PVA films at CNF loadings even below 5 wt%.The tradeoff between modified nanofibril function as interfacial reinforcement and aggregation leads to an optimum loading.The results indicate promising applications,for example,in active packaging.3.Inspired by the plant cell wall components and structure,phenolic acids were used to modify cellulosic fibers with new functionalities.The dissolution and modification were performed in a homogeneous and recyclable ionic liquid?IL?medium(tetrabutylammonium acetate([N₄₄₄₄][OAc]):dimethyl sulfoxide).Different levels of reaction activity of the three phenolic acids studied?p-Hydroxybenzoic acid,vanillic acid,and syringic acid?with cellulose were noted.The successful autocatalytic Fischer esterification reaction was thoroughly investigated by Fourier transform infrared spectroscopy,X-ray photoelectron spectroscopy,elemental analysis and nuclear magnetic resonance spectroscopy?13C CP-MAS,diffusion-edited ¹H NMR,and multiplicity-edited HSQC?.Control of the properties of cellulose in the dispersed state,welding,and IL plasticization was achieved during casting and recrystallization to the cellulose II crystalline allomorph.The films of cellulose carrying grafted acids were characterized with respect to properties relevant to packaging materials.Most notably,despite the low degree of esterification?DS<0.25?,the films displayed a remarkable strength?3.5 GPa?,flexibility?the strain of up to 35%?,optical transparency?>90%?and water resistance?WCA⁹0°?.Moreover,the measured water vapor barrier was similar to that for composite films of PLA.Overall,the results contribute to the development of the next generation green,renewable,and biodegradable films for packaging applications.In summary,a series of cellulose-based films with different functions were fabricated.This facile and versatile strategy provided an insight to prepare high-performance cellulose based composite films with tailorated functions.In addition,these functional cellulose-based films possess comparable physical mechanical properties to that of petro-based plastics and have greate potential to be used as the alternatives to petro-based plastics for packaging materials.