Annealing And Recrystallizatin Of Oriented Ultrathin Polyolefin Films

We prepared oriented ultrathin films of high-density polyethylene(HDPE)and poly-1-butene(iPBu)by melt-drawn technique.Atomic force microscope(AFM),optical microscope(OM),and Fourier transform infrared spectroscopy(FTIR),Transmission Electron Microscope(TEM)and Differential Scanning Calorimetry(DSC)were employed to study recrystallization behavior of the ultrathin films after annealing.There are main conclusions:1.PE oriented ultrathin film was annealed at 135? and then cooled to T_c for isothermal crystallization.When T_c is 116?,asymmetric leaf-shaped crystals were obtained,and when T_c was increased,morphology of PE crystals also changed;when the T_c was high,we got small crystals in the gaps between the crystallization units during cooling.The structure of the crystals in the gaps is related to the cooling method,but no matter how we cooled the sample,small crystals extending from the highly-ordered side and the ones growing spontaneously outside the big crystalline unit still had an asymmetric structure,while small crystals that extending from the less-ordered had no asymmetric structure.2.The morphology of PE crystals in oriented ultrathin films after melting and recrystallization was related to the properties of substrates and film thicknesses.When the ultrathin film was annealed at 135? for 10 min and then recrystallized at 5?/min to room temperature,crystals with different morphologies will be obtained on a glass substrate and a mica substrate.On the mica substrate,the relaxation process was more difficult than on silicon substrates and glass substrates.The crystal morphology obtained after melting and recrystallization changed with changing film thickness.In general,leaf-like crystals tended to grow in thin films.As the film thickness increased,the relaxation of polymer molecular chains in the melt became easier.we annealed PE oriented ultrathin films of the same thickness on different substrates,and the annealing time required for the molecular chains in the PE melt to reach equilibrium on different substrates is the longest for mica substrates,followed by glass substrates,and the shortest for silicon substrates.3.After annealing iPBu oriented ultrathin film with form I crystals on silicon substrates,when T_a was less than or equal to 142 ?,form I crystals were obtained,which were still parallel to melt-drawn direction;when T_a is greater than or equal to 143?,form ? crystals were obtained.The crystal structure changed greatly and no longer had obvious orientation.Moreover,the structure of crystal in the annealed film was related to the initial orientation of the film and the interaction between molecular chains and substrates.Form I crystals were not obtained when the film was not put on a substrate or there was no orientation of chains in the initial film.