Study On Properties Of PLA/PCL Blends Prepared By Tri-screw Extruder

With the increase of consumers’ environmental awareness and the tightening of national environmental policies,biodegradable materials have attracted more and more attention.Polylactic acid(PLA)is considered to be the most promising "green material" due to its high mechanical strength and biodegradability.However,the industrial applications of PLA have been restricted because of its inherent brittleness,poor ductility,and low melt strength.Melt blending with elastomers is an effective method to improve toughness of PLA.Based on the excellent plasticizing and mixing characteristics of the parallel arranged tri-screw extruder(pa TSE)and the outstanding low-temperature toughness of Polycaprolactone(PCL),modified PLA materials toughened by PCL were prepared by melt blending using a pa TSE under the guidance of simulation results.The effect of the process parameter(speed),the modification method(physical blending and reactive blending),the matrix ratio(PCL content)and the compatibilizer content on the properties of the blend were explored.The main content and results are as follows:The particle tracing method was used to simulate the mixing process of materials in a pa TSE,and the mixing characteristics of PLA-based materials in the pa TSE were explored and verified by experiments.The simulation results demonstrate that the particles have experienced a complicated flow in the pa TSE.As the rotational speed increases,the maximum shear rate experienced by the particles and the distance between neighbouring particles increase.Scanning electron micrographs(SEM)results of experiments show that increase in rotation speed leads to particle size reduction.It is also observed that the compatibilizer particles wrapped in PCL gradually transfer to the phase interface during the reaction blending.These results prove that high speed is beneficial to the dispersion and distribution mixing of materials.But the dynamic rheological results show that too high rotation speed and strong shear will cause PLA degradation,and the low residence time is not conducive to in-situ reaction.Mechanical results show that 80 rpm is the optimal speed.80 rpm was selected as the processing speed,physical and reactive PLA/PCL blends with different matrix ratio have been prepared and characterized.The results of dynamic rheology and SEM reveal that increase in the PCL content cause more poorer the compatibility.After adding 8phr compatibilizer ethylene-butyl acrylate-glycidyl methacrylate(PTW),the compatibility of blends was improved to different degrees,and the compatibility of blends with low PCL content was more obvious: when the PCL content is less than 20wt%,the impact strength of the reactive blends is greatly improved compared to the physical blends,and the growth rate is significantly reduced after exceeding 20wt%;Differential scanning calorimetric(DSC)results show that reactive blends with low PCL content have opposite change of crystallization behaviour compared to physical blending.This phenomenon can be attributed to the compatibilization of PLA/PCL caused by the in-situ reaction.These results indicate that the compatibility of PLA/PCL is determined by both the PCL content and the in-situ compatibilization reaction.Fixing the PLA/PCL component ratio to 90/10(w/w),the effect of compatibilizer content on PLA/PCL performance was further explored.The interfacial tension results indicate that PTW is selectively located at the interface between PLA and PCL.Dynamic rheology,dynamic mechanical analysis(DMA)and DSC results all show that increase in PTW content improve the compatibility of PLA/PCL blends significantly.When the addition amount of PTW is 10 phr,the super-tough modification of PLA is achieved,and the impact strength and elongation at break reach 68.3k J/m2 and 430%,respectively.The “multiple stacked structure” was observed in the cryo-fractured section and the etching SEM images,which confirmed that PTW was distributed at the interface,and revealed the mechanism of PTW’s compatibilization by “bridging” the two phases.Based on the above analysis,the toughening mechanism of PTW to PLA/PCL blends was proposed.This article explores the influence of different factors on the performance of PLA/PCL blends,especially the role of PTW in reactive blending.The research results are of important significance in the preparation of PLA-based modified materials by continuous processing equipment.