Study Of Preparation And Properties Of Cellulose-based Biodegradable Plastics

The non-degradability of traditional plastics leads to“white pollution”problems,and because they are prepared from petroleum-based raw materials,sustainable development of resource utilization cannot be achieved.Therefore,it is necessary to develop degradable plastics to replace traditional plastics.Herein,cellulose-based biodegradable plastics are considered to be one of plastics with commercializing potential.Natural plant fibers,such as Reed Fiber（RF）,have the advantages of high cellulose content,large reserves in nature,and low cost,but the mechanical properties are lower when used alone.Compared with plant fibers,synthetic degradable resins,such as polylactic acid（PLA）,polybutylene succinate（PBS）and polycaprolactone（PCL）have higher mechanical properties.However,high cost makes it difficult to be applied on a large scale.Thus,the composites can be prepared by blending the above two types of materials.The addition of cellulose can reduce the cost while degradable resins are able to improve the mechanical properties of the blends and achieve an optimal balance of mechanical properties and cost.As cellulose is hydrophilic,and degradable resins are hydrophobic,the interface properties of cellulose and degradable resins are different.Therefore,cellulose modification is required to reduce the hydrophilicity and improve the compatibility with degradable resins before blending.In this paper,Reed Cellulose（RC）was extracted from RF,and RC was modified by esterification with Glutaric Anhydride（GA）.Then The composites were prepared by blending modified cellulose with degradable resins and their properties were characterized.Firstly,RF was pretreated with alkaline H₂O₂ solution,and the extraction conditions were optimized to improve the purity of RC.The optimal conditions were as follows:NaOH solution concentration was 4%,reaction temperature was 50℃,reaction time was 100 min and H2O2 solution concentration was 2%.Under the optimal conditions,the purity of RC was 85.5%.Fourier Transform Infrared Spectrometer（FTIR）and Thermogravimetric Analysis（TGA）showed that impurities such as hemicellulose and lignin in the RF raw material were removed after the extraction process.X-ray diffraction analysis showed that structure of RC was still the type I of cellulose crystalline form.Then,the RC was modified by esterification with GA as a modifier to prepare Esterified Cellulose（EC）.And the esterification reaction conditions were optimized to increase the degree of substitution of EC.The optimum conditions were as follows:the reaction temperature was 160℃,the mass ratio of EC and GA was 1:9,the concentration of the catalyst,concentrated sulfuric acid,was 10μL,and the reaction time of vacuum stage was 5 h.Under this condition,the degree of substitution of EC was 1.8.FTIR tests indicated that the GA group was successfully grafted onto the structure of RC.Compared with RC,the contact angle of EC with distilled water increased,and the hydrophilicity was remarkably lowered.Finally,cellulose-based degradable plastics were prepared from RC,EC,PLA,PBS and PCL.RC or EC was blended with PLA,PBS and PCL respectively,and the composites were prepared through a twin-screw extruder and an injection molding machine.The effects of RC and EC content on the mechanical properties of composites were studied,and the processing parameters of twin-screw extruder were optimized.The main results are as follows:For EC/PLA composites,it reached the best mechanical properties when the EC content was 40%,the cycle time was 7 min,the processing temperature was 185℃,and the screw speed was 40 r·min^-1.Under this condition,the tensile strength was59.2±0.4 MPa,elongation at break was 22.8±0.6%,elastic modulus was 289.1±2.5MPa,and impact strength was 6.2±0.2 kJ·m^-2.Compared with RC/PLA blend which was prepared under the same conditions,Thermal decomposition temperature（T_d）of EC/PLA increased by 30℃,and Melt Flow Rate（MFR）was higher.Scanning Electron Microscope（SEM）analysis showed that the interface binding of PLA/EC was better than PLA/RC;For EC/PBS composites,it reached the best mechanical properties when the EC content was 30%,the cycle time was 10 min,the processing temperature was 165℃,and the screw speed was 40 r·min^-1.The tensile strength was 13.6±0.2 MPa,the elongation at break was 44.2±1.0%,the elastic modulus was 49.3±0.4 MPa,and the impact strength was 57.9±0.6 kJ·m^-2.Compared with the RC/PBS which was prepared under the same conditions,T_d of EC/PBS increased by 20℃,and MFR was lower.SEM analysis showed that EC was better dispersed than RC in PBS;For EC/PCL composites,it reached the best mechanical properties when the EC content was 10%,the cycle time was 3 min,the processing temperature was 140℃,and the screw speed was 30 r·min^-1.The tensile strength was 17.0±0.2 MPa,the elongation at break was 798.0±16.1%,the elastic modulus was 51.6±3.0 MPa,and the impact strength was 6.0±0.2 kJ·m^-2.Compared with RC/PCL which was prepared under the same conditions,MFR of EC/PCL was lower,and T_d had small difference.SEM analysis showed that compared with RC/PCL,EC and PCL were more tightly combined in EC/PCL and the interfacial compatibility was significantly improved.