| Corn starch was modified by torque rheometer with hydroxyl terminated hyperbranched polyester(HBP)and trifluoroacetic anhydride(TFAH)respectively in this paper.Thermoplastic starch(TPS)and trifluoroacetic acid esterified starch(TACS),were prepared respectively,and then the composites were prepared by melt blending the modified starch with PBAT.The hydrogen bonding force,crystallinity,thermal properties,hydrophilicity and microstructure of the modified starch were studied.The crystallinity,rheological properties,mechanical properties,thermal properties,hydrophilicity and microstructure of the composites were studied.The effect of HBP content on TPS was studied.The results showed that HBP could form hydrogen bond with starch,mainly formed by HBP terminal hydroxyl group and starch molecular hydroxyl group.The crystallinity of TPS modified by 15% HBP decreased from 20.1% to 10.7%.And the glass transition temperature appears at 47 °C.When the contact angle increased from 13 °to 60 °,the hydrophobicity increased obviously.The effect of HBP on PBAT/TPS composites was studied.The results showed that hydrogen bond could be formed between HBP,starch and PBAT.HBP could plasticize PBAT,the melting temperature of PBAT decreased from 118.80 °C to 114.73 °C,the crystallinity decreased from 11.43% to 5.81%,and the thermal decomposition temperature decreased from 363 °C to 360 °C.HBP can improve the dispersion and compatibility of TPS in PBAT.The tensile strength,elongation at break and tensile modulus of PBAT/TPS composites are 13.2 MPA,56.8% and 133 MPa,respectively.The effects of different experimental conditions on the degree of substitution and reaction efficiency of TACS were studied.The results showed that TACS was successfully prepared.When the mixing temperature was 140 ?,the mixing time was 9 minutes,the mixing speed was 110 rpm,the content of esterification agent was 15%,the degree of substitution of TACS reach the maximum 0.254,and the reaction efficiency was 93%.At this time,the A-type crystallization of TACS disappeared and the V-type crystal was formed.The modified TACS is hydrophobic.Esterification modification destroyed the original structure of starch,made the smooth starch particles become rough,and the thermal stability decreased.The effect of different content of TACS on PBAT/TACS composites was studied.The results show that compared with PBAT/Starch composites,the compatibility of PBAT/TACS composites is obviously improved.The elongation at break and tensile modulus of the composites decreased with the increase of TACS content,while the tensile strength increased at first and then decreased.The optimum content of TACS was 10%,and the compatibility of TACS and PBAT was good.The tensile strength of the composites increased from 15.5MPa to 17.8 MPA,the tensile modulus increased from 52 MPa to 68 MPA,and the elongation at break decreased from 850% to 72.5%.The content of TACS has little effect on the hydrophilicity of the composites. |
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