Synthesis And Biodegradation Of Biobased Copolvesters PBAF And PBSF Derived From 2,5-furandi-Carboxylic Acid

Poly(butylene adipate-co-butylene furandicarboxylate)(PBAF)and poly(butylene succinate-co-butylene furandicarboxylate)(PBSF)derived from furandicarboxylicacid are novel biobased(bio)degradable polyesters with composition-dependent crystallization and thermo-mechanical properties and potential biodegradability,and therefore may find application as biobased biodegrable materials in many fields.For biodegradable application,it is indispensable to undertand the degradation behavior and mechanism under different simulated conditions.In this study,high molecular random copolyester PBAFs and PBSFs with virious butylene furandicarboxylate(BF)unit molar fractions(?BF)were synthesized.The composition dependence of thermal-mechanical properities,compost degradation and hydrolytic degradation behavior crystallization kinetics and melting behavior of them were investigated in this work.PBAFs(?BF 40-60%)and PBSFs(?BF 0-10%,40-60%)were prepared by a two-step esterification-polycondensation method with tetrabutyl titanate(TBT)as catalysts and 1,4-butanediol(BDO),succinic acid(SA),adipic acid(AA)and 2,5-furandicarboxylicacid(FDCA)as raw materials and characterized with 1H NMR,GPC,intrinsic viscosity([?]),DSC and tensile test.The copolyesters are random copolymers,with high molecular weight over 95,000 g/mol and a high intrinsic viscosity over 1.0.The copolymer composition,namely,?BF is close to FDCA molar fraction in diacid feed.The thermal transition properties and the tensile properties is composition dependent(?BF40-60%:Tmh:54-112?;?Hm:13-34 J/g;E:34-300 Mpa;?b:28-56 Mpa;?b:430-940%).The controlled compost degradation test of PBAFs40-60 and PBSFs40-60 copolyesters was conducted at a 58 ? and simulated compost environment according to the standards ISO 14855.2-2007 and GB/T 19277.2-2013.It is found that all these copolyesters mineralized over the demanded biodegradability 90%within 180 days.The biodegradation rate decreased with ?BF.At the same,PBAF degraded more rapidly in the compost than PBSF did,possibly due to lower crystallinity.PBAFs and PBSFs were hydrolyzed in PBS buffer solutions with different pH(4.0,7.0 and 12.0)at 25 ? for 22 weeks to study the change of composition,[?],thermal transition and tensile properties with degraded time.In the mild hydrolysis process at pH 7.0,the mass loss(1%-2%)was not obvious but the[?]decreased a lot from 35%to 44%,suggesting the hydrolysis happened.The apparent hydrolyzed rate constant K decreased with increasing ?BF and initial crystallinity,and PBAF seemed to be hydrolyzed faster than PBSF with same ?BF.A slight increase of ?BF and crystallinity during hydrolysis indicating the aliphatic moiety and the amorphous region are more vulnerable or susceptible to hydrolysis.The tensile properties decreased in such an order:strength>elongation>modulus,and high enough tensile properties were retained after 22 week of hydrolysis degradation.The results indicate that PBAF and PBSF copolyesters are hydrolytically degradable,with tunable hydrolytic degradation rate and good balance between hydrolytic degradability and durability.Moreover,the hydrolytic degraded behavior is pH dependent.As the pH increased,the mass lost more rapidly but[?]decreased more slowly,and no obvious change of ?BF was observed at pH 4.0 and 12.0.Besides,the thermal transition properties did not show no siginifcant change at pH 4.0 or 10.The pH dependent changes might result from pH-dependentdiffustion and solubility of oligomers generated from hydrolysis and pH-dependent chain scission,preferential chain scission at aliphatic unit in acid and neutral solutionbut random chain scission in alkaline solution.The crystalline structure and isothermal melt crystallization kinetics of PBSF 10 was inverstigated with WAXD,SXAD and DSC.In comparison with PBS,PBSF 10 has the same crystalline structure but 3 A more in length of amorphous region and therefore lower crystallinity.The BF chain segments are located in amorphous region and the crystalline obeys the so-called exclusion model.The isothermal melt crystallization abided by Avrami equation with an Avrami exponent about 2.5.The total crystalliatoin rate decreased with Tc in the range 57-82 ? with a minimum crystallization half time of 0.87 min appeared at 57 ?..The equilibrium melting temperature was estimated to be 119 ?.