Designing Bio-based Plasticizers:Effect Of Chemical Structures On Their Plasticization Properties

Phthalates play an important role and account for more than 80%of the total production among commercial plasticizers.Unfortunately,researchers have found that phthalates may have potentially toxic effects on humans and are harmful to environment.Meanwhile,with the increasing shortage of oil resources,petro-based plasticizers are under big pressure in recent years.Therefore,many efforts have been devoted to developing bio-based plasticizers with low toxicity and low migration levels.According to the chemical structures of plasticizers,we designed and synthesized a series of bio-based plasticizers based on isosorbide,p-coumaric acid and 2,5-furandicarboxylic acid,which were all derived from renewable resources,and the feasibility of these bio-based plasticizers as alternatives to petro-based plasticizers was evaluated.Besides,the effects of the chemical structures of the synthesized plasticizers on their plasticizing properties were investigated in detail,and the results provide an experimental basis for further design and development of new bio-based plasticizers with high plasticizing efficiency.The following studies were carried out in this dissertation:1.Isosorbide dioctoate(SDO)was synthesized and evaluated as bio-based plasticizer for poly(lactic acid)(PLA),and the effect of SDO content on the plasticization properties of PLA was investigated.As the content of SDO increased from 0 wt%to 20 wt%,the glass transition temperature(T_g)of PLA decreased from60.7~oC to 32.5~oC,the tensile modulus of PLA decreased from 3167 MPa to 390 MPa,while the elongation at break of PLA improved from 3.5%to 281.1%.Besides,SDO exhibited better miscibility with PLA than that of dioctyl terephthalate(DOTP).With the addition of 20 wt%plasticizers,phase separation occurred in PLA/DOTP blend while PLA/SDO blend still exhibited uniform phase.Furthermore,the plasticizing efficiency of SDO was much higher than that of DOTP in PLA,reflected in the lower T_g and lower modulus of PLA/SDO blend.2.In this part,we focused on designing,synthesizing and evaluating four isosorbide diesters with different alkyl chain length as bio-based plasticizers for PVC,namely isosorbide dibutyrate(SDB),isosorbide dihexanoate(SDH),isosorbide dioctanoate(SDO)and isosorbide didecanoate(SDD).The effect of the symmetric variation of alkyl chain length on the plasticizing properties of PVC was studied systematically.As a result,with the shortening of the alkyl chain length on both sides of the isosorbide diester,the plasticizing efficiency increased gradually(SDD<SDO<SDH<SDB),however,the thermal stability and volatility of corresponding plasticized PVC became much poorer.3.Six bio-based plasticizers with asymmetric variation of alkyl chain length were designed and synthesized using p-coumaric acid,which was derived from renewable resources.By tuning the alkyl chain length on the left side of the synthesized diesters,the influence of the unilateral asymmetric variation of alkyl chain length on the plasticizing properties of PVC was investigated.As a result,with the shortening of the alkyl chain length on the left side,the plasticizing efficiency of the synthesized diesters increased gradually,while the thermal stability and volatility of corresponding plasticized PVC became poorer simultaneously.Besides,by maintaining the molecular weight of the synthesized diesters invariant,namely increasing the alkyl chain length on the left side and decreasing the alkyl chain length on the right side,the influence of the bilateral asymmetric variation of alkyl chain length on the plasticizing properties of PVC was studied.It was found that this design improved the plasticizing efficiency of the plasticized PVC without decreasing its thermal stability and volatility.4.The bio-based dibutylfuran-2,5-dicarboxylate(DBF)and the petro-based dibutyl terephthalate(DBT)were synthesized and used as plasticizers for PVC,which had different polarities but similar chemical structures.The plasticization properties of PVC/DBF and PVC/DBT blends were investigated to evaluate the influence of polar furan ring and non-polar benzene ring on the plasticizing efficiency of plasticizers.It was found that the plasticizing efficiency of DBF was higher than DBT,reflected in the lower T_g of PVC/DBF blend.Meanwhile,the shore hardness of PVC/DBF blend was much lower than that of PVC/DBT blend.However,the elongation at break of PVC/DBF blend was much lower than that of PVC/DBT blend,because phase separation of DBF occurred in PVC matrix and the DBF phase formed defects during the tensile testing.