Preparation Of Graphene Oxide Grafted Polymer And Its Effect On The Crystallization Properties Of PLAs

Bio-based polymer materials have attracted more and more attention due to their excellent properties,and the widespread use of bio-based polymer materials not only reduces human dependence on fossil resources,but also has no pollution to the environment.Polylactic acid(PLA)is a thermoplastic bio-based polymer resin.Due to its high mechanical strength,biodegradability and good biocompatibility,it has been widely used in recent years.However,the disadvantages of PLA,such as poor crystalline properties,brittleness,and poor heat resistance restrict its further development.Based on this,in this work,the investigation on synergistic effect of nucleating agent and plasticizer on the self-nucleation behavior of(PLLA),PLLA/PDLA and PLLA by grafting different polymers on graphene oxide(GO)was carried out.First of all.the influence of graphene oxide(GO)as a nucleating agent on the crystallization behavior of PLLA was studied.It is found that after the addtion of GO,the nucleation density of the PLLA matrix is increased and the spherulite size is reduced.At the same time,the crystallization enthalpy(Tc)and melting enthalpy(?Hm)of the PLLA matrix increase,and its cold crystallization temperature(Tcc)decreases about 20?.But when the content of GO is too high,GO will be unevenly dispersed in the PLLA matrix,leading to hindering movement of the PLLA molecular chains,reducing the crystallization ability of PLLA.Secondly,GO grafted dextrorotatory polylactic acid(GO-g-PDLA),GO grafted polyethylene glycol(GO-g-PEG)and GO grafted polycaprolactone(GO-g-PCL)were further prepared.The effect of nucleating agent grafted PDLA or nucleating agent grafted plasticizer(PEG,PCL)on the crystallization behavior of PLLA was studied.Differential scanning calorimetry(DSC)shows that with the content of GO-g-PEG increasing,the Tcc of the blends disappears;when the GO-g-PEG content is 1.5wt%,the ?Hm of the blend achieves the maximum value.Through the isothermal crystallization test,it shows that the crystallization rate of the blends is accelerated,and the Avrami index is about 3 which indicating the crystallization method of PLLA is not change,but the crystallization behavior of PLLA is improved.Through the POM observation,it is found that the nucleation density of the blend increases and the growth rate of spherulites increases.Comparing with GO-g-PDLA and GO-g-PCL,it can be seen from above results that GO-g-PEG has the best enhancing effect on the crystallization ability of PLLA.Again,PLLA/PDLA blends with different ratios were prapared,and the effects of GO-g-PEG and TMC-300 additives on the crystallization behavior of PLLA/PDLA with equal mass ratio and non-equal mass ratio were investigated.The POM results shows that when the mass contents of PDLA and PLLA are quite different,the spherulite morphology of the PLLA/PDLA blend is blurred and the brightness is poor.When the mass contents of PLLA and PDLAis close,the spherulite is regular,the brightness is large and the Maltese cross extinction phenomenon is obvious.It indicates that the crystallization behavior is the best when the mass ratio is close to 1:1.The DSC results show that when the contents of PLLA to PDLA are comparative,the crystallinity of SC in the blend increases and the melting peak area of homopolymer crystal(HC)decreases.For the ternary blends,adding of TMC-300 into the blends can effectively inhibit the formation of HC crystals and promote the formation of SC crystals.It shows that TMC-300 is more effective for the formation of SC crystals and inhibits the formation of HC crystals.After GO-g-PEG was added to TMC-300/PLLA/PDLA,the formation of SC crystals is inhibited.It shows that the addition of GO-g-PEG did not promote the crystallization performance of TMC-300/PLLA/PDLA.Nevertheless,the XRD test shows a different result,i.e.For PLLA/PDLA(different L/D ratio),after adding TMC-300 and GO-g-PEG/TMC-300 to PLLA/PDLA blends that the two additives do not enhance the intensity of the SC crystal diffraction peak.For PLLA/PDLA(L/D equal mass ratio),with the increasing of TMC-300 content,the diffraction peak intensity of HC crystal and SC crystal of the blend increases.After GO-g-PEG is added to TMC-300/PLLA/PDLA,when the content of GO-g-PEG and TMC-300 is 1.5wt%,the SC crystal diffraction peak of 1.5wt%GO-g-PEG/1.5wt%TMC blends is the highest and the HC crystal diffraction peak disappears.Finally,the self-nucleation behavior of homopolymer PLLA and the influence of adding different nanoparticles as nucleating agents on the self-nucleation behavior of PLLA were studied.DSC shows that the self-nucleation effect increases the crystallization temperature and its melting temperature of PLLA.Comparing the crystallization behavior of the three blends with different nanoparticles additives(GO-g-PEG,CNTs-g-PEG,POSS-g-PEG),it is found that GO-g-PEG also has a significant enhancing effect on the nucleation ability of PLLA during the self-nucleation procedure,and the crystallization temperature of the blend increases.The POM shows that the self-nucleation behavior of PLLA can increase its nucleation density,decrease the nucleation time,and the spherulitic morphology of PLLA is more regular.And the nucleation ability can furtherly be enhanced by adding of nucleation agents.Via the same melting temperature and isothermal growth procedures by the POM observation,the number of remaining nuclei in GO-g-PEG/PLLA is greater than that of CNTs-g-PEG and POSS-g-PEG blends.