Molecular Design, Synthesis And Application Of Bio-based Plasticizers In Polylactic Aci

Plasticizers are the most widely used plastic additives to improve the properties of polymer products.Conventionally used petroleum-based phthalate plasticizers faced increasing concerns for their unsustainability and environmental threat.The development of non-toxic,efficient and migration-resistant bio-based plasticizers emerges the trend of industry development.Biobased plasticizers produced from renewable biomass are important for the achievement of“carbon peaking and carbon neutrality”goals.For this purpose,the high value-added ultilization of nonfood related biomass,such as glycerol,epoxidized soybean oil,microbial lipids,cellulose,levulinic acid,succinic anhydride,and angelica lactone has great importance.We noticed the abuadant of hydroxyl,carboxyl and epoxy groups in these chemicals,a series of novel green bio-based plasticizers have been successfully prepared by methods such as esterification reaction,transesterification reaction and graft polymerization.As a proof of concept,based on a model polymer poly（lactic acid）（PLA）,the feasibility of these as-prepared plasticizers to replace traditional phthalate petroleum-based plasticizers was systematically evaluated.The plasticization behavior and its mechanism,and the correlation relationship between chemical structures and plasticizing properties were studied.This study provides insights for the molecular structural design of new green bio-based plasticizers.The main content was shown below:1.Herein,we chose a biodiesel by-product glycerol derived from renewable resources as the raw material and branched levulinic acid or angelica lactone on the glycerol through the glycerin and acetyl esterification reaction of propionic acid,glycerol and angelica lactone turn esterification reaction to obtain a containing ketone carbonyl structure of glycerin ketone of aliphatic acid esters plasticizer（GLE）small molecule.The chemical structure was characterized by Fourier transform infrared spectroscopy（FTIR）,hydrogen nuclear magnetic resonance（¹H NMR）,carbon nuclear magnetic resonance(¹³C NMR)and mass spectrometry（MS）.The molecular weight of GLE was 386 g?mol^-1,which was similar to the traditional commercial plasticizer dioctyl terephthalate（DOTP）（390）.The plasticizing behavior of GLE to PLA was investigated,and the plasticizing effectiveness of GLE in the model polymer PLA was evaluated and compared with the plasticizer DOTP.The results showed that GLE can significantly reduce the glass transition temperature（T_g）of PLA blends,improve the flexibility,heat resistance and processing properties of the blends,and has good solvent extraction resistance due to the hydrogen bond interaction between the enol-ketone tautology of ketone carbonyl group and the PLA molecular ester bond.When the content of GLE was increased to 20wt%,the T_g of the plasticized blends decreased from 63.6℃to 50.1℃,elongation at break increased from 6.3%to 223.2%,and impact strength increased from 3.79k J/m²to 8.70 k J/m²,all of those performance were better than DOTP plasticized blends.In addition,the solubility parameter difference（DS）betweenthepolymerandplasticizerswas DS_PLA-GLE=1.1（J/cm³）^1/2<DS_PLA-DOTP=2.6（J/cm³）^1/2,which is important for predicting compatibility.The SEM analysis showed that GLE with more appropriate compatibility than DOTP in PLA matrix.When the addition content of GLE is 20wt%,the phases of GLE and PLA can still be uniformly mixed,while the phase separation of DOTP and PLA occurs obviously.2.The plasticizing behavior of nonfood related microbial grease（ML） and fungus residue on PLA was systematically studied,and the potential substitution effect was evaluated and compared with the DOTP.The results show that the ML and PLA is with fine compatibility which was close to the compatibility between DOTP and PLA,both of them show similar plasticizing effectiveness to PLA.The DSC and mechanical properties test showed that with the increase of ML content to 20wt%,the T_g of the plasticized samples decreased to 53.71℃.The melting temperature decreased to 164.95℃.The surface hardness of the blends decreased to 79.6D.At the same time,when the content of ML was10wt%,the tensile strength and modulus of the blends decreased,while the elongation at break（58.2%）and notch impact strength（4.88 k J/m²）of the blends were similar to those of DOTP plasticized PLA system.3.A series of crosslinked large molecular weight bio-based plasticizers （BGE-R）containing flexible long carbon chains were prepared by adjusting carboxyl/epoxy equivalent ratio（R value）,which contains a multi-step reaction with the organic basic catalyst1,8-diazabicyclo[5.4.0]undec-7-ene（DBU）,succinic anhydride and glycerin,and the epoxidized soybean oil（ESO）.The results show that the plasticizing effect of BGE is closely related to R value.The R value determines the chemical structure and morphology of PLA/BGE-R blends,and plays a key role in the compatibility,morphology and toughness of PLA/BGE plasticized samples.When R=0.4,the glassy transition temperature（T_g）,elongation at break and impact strength of BGE blends are 56.2℃,64.6%and 5.6 k J/m²,respectively,while those of pure PLA blends are 63.6℃,6.3%and 3.89 k J/m²,respectively.The results of volatilization resistance,extraction resistance and migration resistance showed that the BGE plasticizer with large molecular weight has better extraction resistance.4.Under the DBU/DMSO/CO₂ system to dissolve cellulose and then a ring-opening polymerization of?-caprolactone initiated by cellulose with the DBU in-suit organic functional catalysis was wisely realized.The rheological results showed that MCC-g-PCL as plasticizer,the introduction of PCL flexible chain increases the mobility of PLA molecular chain,and the complex viscosity,storage modulus and loss modulus of the blends decrease.MCC-g-PCL with flexible side chain structure has plasticizing effect on PLA,and the flexibility and impact strength of the blends were improved.When the addition of MCC-g-PCL is 15%,the elongation at break of PLA blends increased from 6%to22.6%,the T_g of the blend was 58.4℃.When the added mass fraction is20wt%,the hardness of PLA blends decreases from 85 D to 79 D.Compared with GLE and ML,MCC-g-PCL polyester plasticizer has better thermal stability,T_5%（℃）can still keep above 300℃.MCC-g-PCL polyester plasticizer is better than DOTP in extraction resistance and volatilization under temperature and light condition.It is a kind of bio-based polyester plasticizer with excellent performance.