Improvement On Water Proof Properties And Melt Processibility Of Thermoplastic Starch Based Biocomposites Modified With Citric Acid And Glutaraldehyde

Melt Processibility of thermoplastic starch(TPS)were successfully improved by addition of proper amounts of citric acid(CA)during acidolysis processes of CA acid-hydrolyzed TPS(AMTPSx/3)resins.The melt flow rate(MFR)of original TPS sample measured at 190?/2.16 kg is only 1.5 g/10 minutes,while the MFR of AMTPSx/3 samples acid-hydrolyzed by CA for 3 hours increased significantly from 2.4 to 5.9,9.2,11.6 and 14.5,when CA contents ofAMTPSx/3 increased from 1 to 2,4,8 and 16 part per hundred parts of TPS resin(PHR),respectively.Water proof properties of TPS and/or AMTPSx/3 resins were successfully improved after reacting TPS and/or AMTPSx/3 with glutaraldehyde(GA)during their gelatinization processes;however,the MFR value of GA modified TPS(TPS100GA0.5)resin is too small to measure.In contrast,MFR values of GA modified AMTPSx/3(AMTPSx/3100GA0.5)specimens increased from 0 to 1.2,3.9,7.2,9.6 and 11.2 g/10min,as the CA contents increased from 1 to 2,4,8 and 16 PHR,respectively.After blending 25wt%of poly(lactic acid)(PLA)with TPS100GA0.5 or AMTPSx/3100GA0.5(i.e.(TPS 100GA0.5)75PLA25 and(AMTPSx/3100GA0.5)75PLA25)specimens,their water proof properties were further improved.The moisture contents of all specimens increased with the increase in conditioned time and/or CA contents.After remaining at 20?/50%relative humidity(RH)for certain amounts of time,the moisture contents of TPS100GA0.5 and AMTPSx/3100GA0.5 specimens are-were significantly lower than those of corresponding conditioned TPS and AMTPSx/3 specimens without modification by GA,respectively.The rapid reduction in initial values of tensile strength(?f),impact strength(Is)but increase in initial values of elongation at break(?f)was found in TPS specimens.The conditioning time dependence of ?f,Is and ?f of AMTPSx/3 specimens became more demarcated,when AMTPSx/3 specimens were acid-hydrolyzed with higher CA contents for 3 hours.In contrast,reduction in initial ?f,Is but increase in ?f values with the increase in conditioning time was significantly improved after modification TPS and AMTPSx/3 resins with 0.5PHR GA,or melt-blending with 25wt%of PLA resin.For instance,after conditioning at 20?/50%RH for 56/168 days,the ?f,Is and ?f retention values of(AMTPS8/3100GA0.5)75PLA25 specimen remained at 16.5 MPa/12.6 MPa,0.44 KJ/m2/0.37 KJ/m2 and 12.8%/19.4%,respectively,which are equivalent to 79%/60%,37.4%/30%and 2.0/3.1 times of its initial ?f,Is and ?f values,respectively;and more than 33/63 and 8.8/18.5 times higher but 33/30%lower than those of AMTPS8/3 specimens conditioned at 20?/50%RH for 56/168 days,respectively.In order to understand the significantly improved water proof properties and melt processibility of AMTPS8/3100GA0.5 and(AMTPS8/3100GA0.5)75PLA25 resins prepared in this study,Fourier transform infrared spectroscopy,wide angle X-ray diffraction,differential scanning caloremetric and scanning electron microscopic analyses of TPS,AMTPSx/3,TPSiooGA0.5,AMTPSx/3100GA0.5,(TPS100GA0.5)75PLA25 and(AMTPSx/3100GA0.5)75PLA25 specimens were performed in this study.