Study On Toughening Polylactide With Epoxidized Elastomer/Thermoplastic Resin

Polylactic(PLA)is a kind of thermoplastic aliphatic polyester prepared by chemical synthesis from renewable botanical resources(lactic acid).Because of its biodegradability and excellent physical and mechanical properties,PLA is considered as the most potential alternatives for petroleum-based polymer.PLA has high strength and rigidity,but poor toughness with low elongation at break and impact strength,which restricting the wide application of PLA significantly.Currently,blending with elastomers is the main method of PLA toughening.In order to make the material to achieve brittle-ductile transition,a lot of elastomers need to be added in general.However,the addition of a large number of elastomers will have significant impact on other characteristics(such as degradation,modulus etc.)of PLA.Therefore,the development of more efficient elastomer toughened PLA system is very important.In addition,PLA has good contact safety with food,which is the first choice of food packaging materials.There is a very significant practical value to improve the toughness and flow performance of PLA,which will expand its application in food packaging fields.Polybutadiene rubber(PB),poly(styrene-butadiene-styrene)thermoplastic elastomer(SBS)and styrene-butadiene impact resin(SBC)were selected as toughening agents in this thesis.In order to improve the compatibility of the toughening agent with PLA matrix,epoxidation on toughening agents was employed.A serial of super-toughened PLA-based blends with super high impact strength and excellent tensile toughness were prepared by melt blending.The effects of epoxidation degree and content of toughening agent on the mechanical properties,thermal properties,rheological properties and morphologies of the blends were investigated.And the toughening mechanism was also discussed.The main research contents and results are as below:Epoxidized polybutadiene(EPB)with different epoxidation degree were prepared by epoxidation using in situ peroxoformic acid method.A series of PLA/EPB blends were prepared by reactive melt blending.When the EPB content was 10 wt%,the impact strength of EPB blends increased firstly then decreased with the increasing of epoxidation degree.The impact strength of PLA/EPB20.9%(90/10)was the highest,384.4 J/m,which was around 13 times of pure PLA(29.9 J/m).The impact strength of PLA/EPB increased significantly with increasing the amount of EPB.The impact strength of PLA/EPB29.2%(85/15)was 733.1 J/m.When EPB29.2%(10 wt%)was added,the elongation at break of the blends increased from 3.5%of pure PLA to 189.1%.Meanwhile,the tensile strength and tensile modulus maintained at 80%of pure PLA.The particle size of EPB dispersed phase decreased with increasing the epoxidation degree of EPB,and the particle size distribution was more uniform.The compatibility of the rubber phase and PLA matrix was improved remarkably.Epoxidized poly(styrene-b-butadiene-b-styrene)(ESBS)with different epoxidation degree were prepared by epoxidation using in situ peroxoformic acid method.A series of PLA/ESBS blends were prepared by reactive melt blending.When the amount of ESBS was 10 wt%,the impact strength of PLA/ESBS blends increased firstly and then decreased with epoxidation degree increasing.The impact strength of PLA/ESBS35.8%(90/10)was highest,198.9 J/m,and the elongation at break increased from 3.5%of pure PLA to 218.8%.The tensile strength and tensile modulus slightly decreased to 54.9 MPa and 1.38 GPa,which were 79%and 86%of pure PLA respectively.The impact strength of PLA/ESBS blend was significantly increased with increasing the amount of ESBS35.8%.The impact strength of PLA/ESBS35.8%(70/30)was 891.0 J/m.When ESBS was 10 wt%in the blends,the particle size of ESBS dispersed phase gradually decreased with increasing the epoxidation degree of ESBS and the particle size distribution was more uniform.The compatibility between ESBS phase and PLA matrix was improved significantly.Epoxidized styrene-butadiene impact resin(ESBC)with different epoxidation degree were prepared by epoxidation using in situ peroxoformic acid method.A series of PLA/ESBC blends were prepared by melt blending.The addition of ESBC at 30 wt%could improve the tensile toughness and ductility of the blends.The elongation at break of the blends was 305.0%when using ESBC28.8%(30 wt%)toughened PLA.Comparing with ESBS as the toughening agent for PLA,the tensile strength and tensile modulus of the blends were maintained at higher extend.The tensile strength and tensile modulus of PLA/ESBC28.8%(70/30)were 55.5 MPa and 1.25 GPa,80%and 78%of pure PLA respectively.With increasing the epoxidation degree of ESBC,the particle size of ESBC dispersed phase decreased and the distribution became more uniform.Two-phase compatibility had been significantly improved.The results showed that PLA/ESBC(70/30)blends belonged to pseudoplastic fluid.With the increasing of shear rate,the shear thinning index of blends decreased obviously and the correlation between apparent viscosity and shear rate increased.The apparent viscosity of blends was lower than that of pure PLA when the shear rate was higher than 0.3 s-1.The addition of ESBC significantly improved the flow performance.