Influence Of Inorganic Nano-fillers On Properties Of PLLA/PDLA

Poly(lactide acid)(PLA)was a new type of biodegradable material that was made from crop materials extracted from renewable plant resources(corn,sugar cane or beets,etc.),and eventually produce carbon dioxide and water,can be recognized as environmentally friendly materials.PLA has good thermal stability,can be processed in a variety of ways,such as extrusion,spinning,injection,blow molding.Due to the high temperature and high shear,PLA was easily degradable which reduced the molecular weight,fracture the polymer chain,and the performance.The equal proportions of PLLA/PDLA blended products have stereocomplex polylactic acid(sc-PLA)complexes and homopolymers(hc-PLA)coexisted,but the former is higher than the melting point of about 50? than the latter.Therefore,in order to obtain the more sc-PLA composites crystallization forms.The article had added inorganic nano-fillers to enhance its contents,to improve their nano-composites properties and to broaden its applications.Mainly from the following three aspects:(1)In this paper,the equal proportions of PLLA/PDLA was blended with the mixer at240?,which was added the modified sepiolite(SEP-KH550)to increase the content of sc-PLA crystal,and to raise the heat resistance of the composites.The results showed the thermal stability of PLLA/PDLA/SEP-KH550 nano-composites was improved with the addition of modified sepiolite.Meanwhile,it is able to promote the formation of the sc-PLA crystal,such as the sc-PLA crystallinity degree Xsc was improved.When the content of SEP-KH550 was 1.0%,the tensile strength increased from 53.94 MPa to 60.26 MPa,and when the modified sepiolite content was 3.0%,the Young's modulus reached the maximum value,compared with the pure PLLA/PDLA increased by 23.1%.(2)Due to the unique properties of grapheme,the grapheme nano-sheets were added to the PLLA/PDLA matrix with the melt blending method,which were used to raise the content of sc-PLA crystals,to improve the heat resistance and mechanical properties of the composites.Firstly,the grapheme oxide and grapheme were prepared by Hummers method.The results of AFM test showed that the thickness of the layer was 1.0 nm grapheme oxide,and the FTIR and XRD analysis were also proved to be grapheme.The results of TEM test conformed grapheme which presented a pleat-like structure.The effects obtained from TGA data displayed that the initial decomposition temperature and final decomposition temperature increased to about 15?,10?.Therefore,the thermal properties of composites had been greatly improved.Data analysised by DSC,grapheme can be uniformly dispersed in the matrix,so that with a strong interaction between the filler and the matrix,and thus to limit the mobility of the molecular chains of PLA,which increased the PLLA/PDLA/Grapheme nanocomposites Tg.When the content of grapheme was added 0.1%,the XSC increased to37.55%,which was improved 84.07% higher than that of pure PLLA/PDLA(20.40%),vastly heightened the sc-PLA crystallinity.The improvement of crystallinity and melting parameters indicated that the two-dimensional grapheme filler played the role of heterogeneous nucleating agent in PLA matrix.The results showed that when the content of two-dimensional grapheme was from 0 to 0.1wt%,the tensile strength tended to increase linearly,and reached76.32MPa(PLLA/PDLA/Grapheme(0.1wt %))increased by 41.49% compared to 53.94MPa(PLLA/PDLA).The best addition was in PLLA/PDLA/Grapheme(0.2wt %),the Young's modulus increased by 11%.(3)The rheological properties of the PLLA/PDLA/Grapheme composites were studied through the rheological curve test analysis:PLA blends are typical shear thinning non-Newtonian fluids.The apparent viscosity(?a)decreased with the increased temperature.The non-Newtonian index increased with the raised temperature,which the pseudoplasticity of the composites melt became smaller and the system gradually changed to Newtonian fluid.After the addition of grapheme,the non-Newtonian index of the composites was declined,and tended to increase and then drop with the improved addition content.When the grapheme content was 0.1%,the non-Newtonian index was 0.7437 to the maximum,and the melt spinning became easier.With the promotion of the shear rates,the apparent activation energy(?E?)of the composites material decreased gradually.At the same temperature,the ?E? of PLLA/PDLA/Grapheme composites showed a tendency to fall and then promote with the raise of the amount ofgrapheme.Comparing with the ?E? of other polymers,the ?E? of the PLA blends was larger,so the ?a of the blended melt was more sensitive to temperature.Therefore,to avoid changing in viscosity on the impact of products quality who we must strictly control the temperature in the subsequent spinning process.In the range of temperature and shear rates,with temperature increasing the viscosity index structure(??)of composites decreased,indicating that blends spinnability and stability getting better and better.Added ?? grapheme composites were larger.It was demonstrating that grapheme was added in the melt spinning process so the degree of structure became larger that spinning and stability will be reduced.What`s more,when grapheme content of 0.1%,?? was a minimum of 4.28,signifying that the structure of the melt at the smallest degree,so the spinnability and stability was relatively good.