Preparation And Properties Of Chitosan Composite Films Reinforced By Double Nanoparticles

The non-biodegradable materils and energy crisis lead to more and more serious of environmental problems in current.It is desirable to develop a kind of renewable and natural polymers in the field of packaging film.Chitosan(CS)has attracted wide interest in science and industry for its unique properties,such as good film-forming,biodegradable,antibacterial properties and nontoxic.However,the application is limited due to the sensitivity to water and poor mechanical properties of this kind of natural polymer material.In this paper,CS was used as matrix,natural degradable material wheat gliadin(WG),zein and natural one-dimensional nano-clays(attapulgite(APT)and halloysite(HNTs))served as reinforcement,preparing the composite packaging films by solution casting method.Firstly,chitosan composite films were studied by introducing APT and HNTs as the reinforcement according to the unique nano-characteristics of one-dimensional clay,at the same time,plasticizers were added to increase the flexibility of the films during the preparation process.Then,the chitosan composite films were also prepared by introducing hydrophobic protein nanoparticles by in situ method.Finally,chitosan films were enhanced by the double nanoparticles(protein nanoparticles,one-dimensional nanoclay)synergistic effect.The structure was characterized of the composites by scanning electron microscope(SEM),ultraviolet-visible spectroscopy(UV-vis),Fourier transform infrared spectroscopy(FT-IR),X-ray diffraction(XRD).Mechanical properties,water resistance and optical properties were tested.The experimental results are as follows:(1)Glycerol(GE)and sorbitol(Sr)were used as plasticizers increasing the flexibility of the composite film.The maximum elongation at break was 71.71% when 35% GE was added,which is 7.4 times larger than pure CS films;however,the elongation at break was 47.1% when 35% Sr was added,which is only 2.3 times.Therefore,plasticizing effect of GE was the best than Sr.These two kind of one-dimensional nano-clays had a similarly enhancement effect to some extent,increasing the tensile strength of the film and improving the mechanical properties.When adding 4% of APT,the maximum tensile strength reached 37.70 MPa,which was nearly 32% higher than that pure CS film.When 3% of HNTs was added,the largest tensile strength reached 39.13 MPa,which was nearly 27% higher than that pure CS films.What's more,the addition of clays reduced moisture uptake of composite films,indicating that the introduction of inorganic nanoparticles improved the water resistance of the composites.Both kinds of nano-clays had little effect on the transmission of the composite film.However,one-dimensional nano-clays tend to agglomerate at high concentrations and are difficult to disperse,which had a negative impact on the mechanical properties and water resistance of composites.(2)Protein nanoparticles were successfully added to the CS film by in situ method.These protein nanoparticles had enhanced effect on CS.Both zein and WG increased the tensile strength of the film and improved the mechanical properties and reduced the light transmittance of the films.However,there is little difference between the two proteins in the mechanical properties of the film.Protein,a hydrophobic material,reduced the water uptake of films and improved the water resistance of the membrane.The tensile strength of the membrane was increased due to that Tan reduced the particle size of protein nanoparticles and changed morphology and Tan can form a network structure through hydrogen bond with proteins and CS molecules,leading to increase densification,improving the mechanical properties of the film.In the meanwhile,the introduction of Tan reduced the water uptake of composites,because the CS matrix,protein and Tan three macromolecules form a network structure through the physical cross-linking,thus preventing the entry of water molecules,improving water resistance of composites.Therefore,Tan,similar to other modifiers,improved various properties of CS membranes,preliminarily demonstrating that Tan can be applied to CS films as a natural,non-toxic modifier.(3)The zein and WG performed spherical and ellipsoidal structure in CS,respectively.However,the particle sizes of WG and zein became smaller after the addition of Tan,due to that Tan crosslinks of the two-phase interface between protein and CS,acting as a bridge which reduced the protein particle size.However,the introduction of Tan made films tend to brown.The films were almost opaque in the ultraviolet region because that Tan molecule contains many aromatic groups and absorbs ultraviolet rays.The results showed that the addition of Tan increased the UV resistance of the composite film.(4)The synergistic effect of protein nanoparticles and one-dimensional nano-clays synergistically enhanced the tensile strength and elongation at break of the composite films compared to single nanoparticle,improving the mechanical properties of the composites.At the same time,the introduction of two kinds of nano-particles reduced moisture uptake of the composite film,improving the water resistance of composites.However,the agglomeration of the one-dimensional nano-clays and protein nanoparticles at high concentrations led to the decrease of overall performance of the composites.In the meantime,the addition of hydrophilic clay nanoparticles and hydrophobic protein nanoparticles increased the filler content of composite films and didn't agglomerate at respective appropriate concentrations,which served as a composite enhancing effect.(5)In practical applications,light transmission is a major factor affecting consumer acceptance.Adding one-dimensional nano-clays had little effect on the optical properties of the composite films,because inorganic clays were dispersed in the CS matrix at the nanometer level.But the light transmittance of the composite films was decreased after the introduction of protein nanoparticles,according to that protein nanoparticles changed the microstructure of composite films,causing to reflect and scatter of light at the phase interface,thereby affecting light transmission.In a word,light transmittance had a slight decrease after the introduction of two kinds of nanoparticles,still had excellent optical properties.