Preparation And Computer Simulation Of Polylactide/Organomontmorillonite Nanocomposites

Polylactide(PLA) is a completely biodegradable polymer,and it is originated from renewable plant resourees.PLA has been widely used in medical field because of its good biocompatibility.Degradation can occure during the process of modern large-scale production,so PLA is rarely used as durable goods. A little amount of organomontmorillonite which is added into polylactide in a suitable way will give a remarkable enhancement to the propertities of the polymer matrix including thermal stability,mechanical property,gas barrier property,degradation rate and so on.In this paper,the Na-montmorillonite(MMT) was organically modified by hexadecyl trimethylammonium bromide (CTAB) and chitosan(CTS).We successfully prepared nanocomposites which were composed of the organically modified montmorillonites and PLA by the solution intercalated method. In order to explore the process of the organic modifier and PLA intercalating the MMT layers,we studyed the structures and properties of the PLA/organ-montmorillonite nanocomposites by the means of molecular simulation combining experimental media,the main work is as follows:1) Na-montmorillonite(MMT) was modified by CTAB and we got the OMMT,then the OMMT was twice modified by CTS to prepare the twice functional MMT (TFC).The pure MMT,OMMT,TFC were separately composited with PLA by the solution intercalated method,so three kinds of composites were prepared: PLA/MMT,PLA/OMMT,PLA/TFC.2) The microstructure of the composite was studyed though the fourier transform infrared radiation(FTIR),X-ray,transmission electron microscope(TEM),and the thermostability of the composite was tested by thermogravimetry(TG). X-ray and TEM showed that PLA/OMMT was an intercalated nanocomposite,and PLA/TFC was an exfoliated nanocomposite,PLA/MMT was just a mirocomposite.In the three kinds of composites, PLA/TFC represented the best thermostability,and the initial degradation temperature was improved by 24℃than pure PLA. 3) The models of MMT crystalloid,CTAB,CTS and PLA were structured basing the experiment materials,then the models of OMMT,TFC,PLA/OMMT,PLA/TFC was also structured on the basis of the previous models.The processes of the MMT swelling in aqueous solution,and the organic modifier intercalating the MMT layers,and the modified MMTs compositing with PLA were simulated by the methods of molecular mechanics(MM) and molecular dynamics(MD).We explored the driving power in the intercalating process by analying the simulation results and experiment datas.4) We analyzed the compatibility of the organic compositions in the nanocomposites though the dissipative particle dynamics(DPD) method,and found that CTS coupled the PLA and CTAB,so CTS can improve the compatibility of the PLA and TFC,and the MMT layers can be equably dispersed in the PLA matrix,this phenomenon confirmed the experiment results.