Preparation And Properties Of Microcrystalline Cellulose/Thermoplastic Starch-Based Composites

The research of bio-based materials is one kind of hotspot researches nowadays,moreover,the production of bio-based materials is becoming one of Chinese new pattern industries.Starch is a promising biopolymer for the preparation of bio-composites as its recyclable,biodegradable,and low cost.Thermoplastic starch(TPS),in the form of thermoplastic derivatives,has been considered as one of the substitutes for synthetic polymers packaging materials.Although starch itself does not have thermoplastic properties,it can be processed by mixing it with sufficient water and/or plasticizer.As the thermoplastic starchbased composites have excellent physical and chemical properties such as biodegradability,biocompatibility and barrier properties,they are suitable for making disposable plastic products which are for short-term use.Starch-based composites have two major drawbacks: poor mechanical properties and high water-sensitive properties.Since natural cellulose-microcrystalline cellulose(MCC)has excellent characteristics such as small particle size,high crystallinity,high specific surface area,high active surface,and reproducibility,microcrystalline cellulose are used as a reinforcing phase to add to the starch matrix to enhance the composites.The interfaces between microcrystalline cellulose and starch are very large,making it easily form strong hydrogen bonding interaction forces,which promote the tight combination of starch-based composites.Therefore,the mechanical properties and barrier properties of starch-based composites were greatly improved.What's more,the multifunctional modification of the microcrystalline cellulose would not only improve the dispersibility of the microcrystalline cellulose in the matrix,but also improve the reaction bonding point with other polymers,which would generate the new application of starch-based composites in packaging materials.Thermoplastic starch films reinforced by microcrystalline cellulose,have excellent mechanical properties,biocompatibility,biodegradability,barrier properties,water resistance,transparency,and other properties,which provide a good matrix environment and active sites for photoconductor immobilization and serve as excellent carriers for constructing photovoltaic materials.Graphene quantum dots(GQDs)have the advantages of smaller particle size,stronger quantum confinement effect,boundary effect,light stability,nontoxicity,and low cost.Therefore,GQDs,prepared by citric acid pyrolysis,have potential applicability in the fields of solar photovoltaic devices,biosensors,biomarkers,and so on.In this article,the following works have been carried out:Using starch(as a substrate),microcrystalline cellulose(as a reinforcing phase),glycerol(as plasticizers)and water(as plasticizers)were mixed to prepare microcrystalline cellulose/starch films by solution casting method.The experimental results show that adding6 wt.% microcrystalline cellulose to the hydroxypropyl starch matrix improved various properties of the starch films.The addition of microcrystalline cellulose not only improves the interaction between the reinforcing phase and the matrix molecules,but also improves the thermal stability and barrier properties of starch films.At the same time,the tensile strength of the microcrystalline cellulose/starch films is increased by about 300%,and the water vapor transmission rate is decreased by 31.01%.In order to further improve the enhancement of microcrystalline cellulose in the starch matrix,the microcrystalline cellulose was alkalized using different concentrations of sodium hydroxide solution,and then 6 wt.% alkalized microcrystalline cellulose(AMC)was added to the starch solution to prepare films by solution casting method.The experimental results show that as the concentration of sodium hydroxide solution is increased,the particle size and crystallinity of alkalized MCC gradually is decreased,the crystal structure of MCC is induced to change from cellulose I to cellulose II,which improved the MCC dispersion in the starch matrix.The addition of high alkalinity MCC in starch matrix solution would not only increase the glass transition temperature of films by 13.31% and improve the tensile strength by13.72%,but also reduce the water vapor transmission rate by about 75.27 %.Oxidized alkalized microcrystalline cellulose(TOMC)was obtained by oxidizing alkalized microcrystalline cellulose through TEMPO systems to improve the water solubility of the MCC.The starch,water,glycerol,and modified microcrystalline cellulose were mixed in a certain ratio to prepare wet modified starch,and then biodegradable thermoplastic starchbased films were prepared by the hot-pressing method.The experimental results show that the molecular structure of TOMC and AMC are similar,still the structure of cellulose II,and the crystallinity of TOMC are lower than that of AMC.The addition of MCC improves the water resistance of the microcrystalline cellulose/thermoplastic starch film(approximately 75.46%).However,TOMC and AMC have a certain water solubility,which improves the watersolubility of the microcrystalline cellulose/thermoplastic starch films.The surfaces of TOMC with high oxidation degree contain more active sites,which strengthens the interaction between TOMC and starch molecules,resulting in the tensile strength of the composite films are increased by 249.42%.Since thermoplastic starch films have good mechanical properties,water resistance,and thermal stability,so they can be used as carriers for photoconductive factors.In this paper,graphene quantum dots(GQDs)were prepared by pyrolysis using citric acid as the carbon source.Using GQDs storage aqueous solution and glycerol as plasticizers,mixed with starch to prepare thermoplastic starch granules by the melt extrusion method,and then GQDs/TPS photoconductive materials were prepared by hot-pressing.The experimental results show that XRD characteristic peak of GQDs appears at 2?=26.67°,which indicates that the carbonation of citric acid can produce GQDs.The luminescence factor GQDs enhance the intensity of solid-state photoluminescence emission and the fluorescent and electrical properties of thermoplastic starch films.The addition of MCC to GQDs/TPS photoconductive composites can improve the mechanical strength and thermal stability of composites.Environmentally friendly GQDs/MCC/TPS photoconductive composites fill the gaps in the application of thermoplastic starch-based plastics in photoconductive materials.Multi-layer composites are a developmental direction of current packaging materials.According to the composite principle of paper-plastic composites and the characteristics of thermoplastic starch film and paper,paper and thermoplastic starch films were combined by hot-pressing to prepare paper-plastic composites.When the thermoplastic starch films and the paper were hot-pressed,the interface layers were tightly bonded and had a good adhesion.The addition of microcrystalline cellulose could improve the thermal stability,tensile strength,water resistance and barrier properties of the paper-plastic composites.At the same time,the paper gave a certain degree of folding resistance to the thermoplastic starch films and varied the application of the paper-plastic composites.