Plasticizing Modification Of Cassava Bagasse Enhanced By Mechanical Activation

Cassava,one of the world's three major potato crops,is widely cultivated in tropical and subtropical regions,and it is often used to produce starch alcohol and feed.Processing one ton of cassava tuber may generate approximately 900 kg residue(moisture content 85%),so a large amount of waste cassava bagasse is produced.Cassava bagasse is mainly composed of starch(40-60%),cellulose(15-50%),and a small amount of protein and lipid.Currently,except for using as feed,cassava bagasse is also used for the production of ethanol,cultivation of mushrooms,etc.,but the utilization is still limited.In order to further develop the applications of cassava bagasse,in this paper,the thermoplastic modification of cassava bagasse was carried out with glycerol as plasticizer enhanced by mechanical activation(MA),and the modified cassava bagasse was used for the preparation of biodegradable composites.The main research contents and results are as follows:(1)Cassava bagasse was mechanically activated in a customized stirring ball mill,and Fourier transform infrared spectroscopy(FT-IR),X-ray diffraction(XRD)and scanning electron microscope(SEM)were used to characterize microscopic morphology,crystal structure and molecular groups of the MA modified cassava bagasse.FT-IR analysis showed that the vibration absorption peak of hydroxyl groups at 3330 cm-1 was broadened,proving that mechanical force interrupted the intermolecular and intramolecular hydrogen bonding and produced free hydroxyl groups.XRD results showed that two spikes at 170 and 180 changed to a wide dispersion peak,indicating the decrease in ordered crystal structure and increase in the degree of amorphous.SEM analysis showed that spherical particles of cassava bagasse were destroyed by MA.(2)Thermoplastic cassava bagasse(TPCB)was prepared by MA with cassava bagasse as raw material and glycerol as plasticizer,and then the TPCB composites were produced by hot pressing.The effects of MA speed,reaction temperature,reaction time,particle size of cassava bagasse,and dosages of glycerin,citric acid and stearic acid on the mechanical properties of TPCB composites were investigated,respectively.The results showed that under the conditions of MA speed 250 r·min-1,reaction temperature 70?,reaction time 80 min,particle size of cassava bagasse 80 mesh,glycerol dosage 20%(w/w),citric acid dosage 4%(w/w),stearic acid dosage 2%(w/w),the flexural strength and tensile strength of TPCB composite were 14.33 and 4.28 MPa,respectively.FT-IR results showed that with the increase of glycerin dosage,absorption peak of hydroxyl groups gradually shifted to lower wavenumber,and the content of free hydroxyl groups decreased.XRD results showed that sharp crystallization peak became wide and the diffraction intensity decreased,attributing to the destruction of crystalline structure of cassava bagasse.SEM showed that the spherical particles of cassava starch were destroyed and stick together,indicating that MA effectively enhanced the plasticizing of cassava bagasse with glycerol.(3)The biodegradable TPCB composites were directly prepared by hot pressing with TPCB as raw material.The influence of hot pressing temperature,time and pressure on the mechanical properties of the composites were studied to determine the optimum process conditions of hot pressing,and the application performances such as thermal properties,moisture resistance and biodegradability of the TPCB composites were also preliminarily investigated.The results showed that under the optimum conditions of hot pressing temperature 155?,pressure 7 MPa,time 14 min,the TPCB composite possessed better mechanical properties,with the flexural strength of 20.01 MPa and tensile strength of 5.87 MPa.DSC and TG curves showed that the softening point of the thermal plasticizing modified cassava bagasse declined and the thermal decomposition temperature increased,indicating that its thermal stability improved and could be processing molded.The greater humidity had greater effect on the mechanical properties of the composites.After buried the composites in soil for more than 30 days,a number of colonies and deformation appeared in the composite,indicating that TPCB composites possessed excellent biodegradability.