Study On Crystallization Of Isotactic Polybutene-1 And Its Composites

Isotactic polybutene-1(iPB-1)is a typical polymorphous polyolefin with excellent comprehensive mechanical properties and best creep resistance at low and high temperature.When it is directly cooled from the melt,metastable crystalline form ? is obtained.Crystalline form ? transforms into form I slowly and spontaneously which is excellent in mechanical properties and thermal stability at room temperature.The transformation process takes more than one week accompanied with the change of volume which is greatly limits its commercial development.Therefore,it is of great scientific significance and practical value to study the in ternal mechanism and factors of iPB-1 crystal transformation.In this thesis,a series of iPB-1 and its compounds were prepared by solution blending method.By means of a combination of small angle X-ray scattering(SAXS),wide-angle X-ray diffraction(WAXD),fast scanning chip calorimetry(FSCC),differential scanning calorimetry(DSC)and other instruments,we investigated the effects of crystallinity and lamella thickness of crystalline form II,crystal structure of nano-particles and the blend on iPB-1 crystal transformation.The competitive growth mechanism of crystalline form ? and ? was obtained.We also get the selection rules of blending components and their promotion mechanism on iPB-1 crystal transformation.The main results are summarized as follows:1.Competitive growth mechanism of crystalline form ? and form ? in iPB-1.The process of crystal transformation from form ? to form ? in iPB-1 is divided into the nucleation and growth steps of form I.Firstly,the isothermal crystallization time and temperature were changed by FSCC to obtain a pre-crystallized crystal form ? with different crystallinity.The pre-crystallized sample immediately annealing at-15 ? to induce nucleation of form I,and then annealing at 40 ? to induce the growth of form 1.We investigate the effect of crystallinity of form II on the transformation kinetics from form II to form I.When the initial crystallinity of form ? is less than?4%,the stress in the boundary of amorphous region and the crystal region is too low to induce the nucleation of the crystalline form I at-15 ?,and then form I cannot grow rapidly during the annealing process at 40 ?.With the increase of crystallinity of form II,the low temperature treatment induces the nucleation of crystal form I,and it grows rapidly during the annealing process at 40 ?.At the same time,the newly formed crystalline form ? during the annealing process at 40? can only undergo a slow crystal transformation for that it has not been subjected to low temperature treatment.When the crystallinity of form ? is further increased,the form ? maintains rapid growth after undergoing nucleated at low temperature.This indicates that the nucleation of crystal form ? at low temperature can be only induced when the crystallinity of form ? reaches a certain value,thereby promoting the rapid transformation from form ? to form ?.In the late stage of crystallization of form ?,the polymer chain rearranges,resulting in an increase in the regularity of the crystal region.The polymer chain needs more energy to achieve the conformational transformation.The growth of form I is adversely affected by the difficulty in conformational transformation of the molecular chain.The rate of crystal is slightly reduced,but it is still much faster than the slow transformation.As the isothermal crystallization temperature increases,the thickness of the form ?lamella increases,and the rate of crystal transformation increases.This part of the work clarified the effect of crystallinity and lamella thickness of crystal form ? on the crystal transformation,and provided guidance for shortening the processing of iPB-1 products.2.The acceleration mechanism of nanoparticle on iPB-1 crystal transformation.The effects of halloysite(HNT)and palygorskite(PGS)with the same morphology but different crystal structures on the crystallization and crystal transformation of iPB-1 were investigated by means of DSC,WAXD and SAXS techniques.The results of crystal transformation kinetics showed that PGS promoted the crystal transformation from form ? to form ? more effectively than HNT under the same crystallization condition.The results of WAXD and SAXS indicate that there is a partial lattice matching between the crystal structure of PGS and iPB-1 crystal form I.This indicates that lattice matching is one of the important factors to accelerate the crystal transformation of iPB-1 from form ? to form ?.In addition,the two nanoparticles were hydrophobically modified to improve the compatibility between the nanoparticles and iPB-1.The results of crystal transition kinetics showed that the increase of compatibility between MHNT and iPB-1 enhanced the acceleration of MHNT on iPB-1 crystal transformation.However,the increase of compatibility between MPGS and iPB-1 weakened the acceleration of MPGS on iPB-1 crystal transformation.The results of WAXD and SAXS indicated that the hydrophobic modification partly shielded the lattice matching between palygorskite and iPB-1 crystal form ?,thus attenuated the acceleration effect caused by lattice matching.The selection rule of nanoparticles and its accelerating mechanism provide a simple and effective method for accelerating the crystal transformation of iPB-1.3.The effect of isotactic polypropylene mesophase on the crystal transformation of iPB?1.Polymer blending is an effective way to obtain polymer materials with excellent comprehensive properties.The molecular structure of iPP and iPB-1 is similar,and the iPP a crystal has the same polymer chain conformation as iPB-1 crystal form I.The addition of iPP ca crystal can accelerate the crystal transformation of iPB-1.iPP is also a polymorphous polyolefin.The molecular chain conformation of iPP mesophase is same as that of iPP a crystal.However,the chiral helical regularity of iPP mesophase molecular chain is slightly less ordered than iPP a crystal.Different crystal structures were obtained by varing cooling treatment of the iPP/iPB-1 melt.FSCC measured the iPP mesophase formed in the iPP/iPB-1 blend during quenching.The effect of different crystal structures of iPP on the crystal transformation of iPP/iPB-1 blend was investigated by DSC.The crystal transformation kinetics results indicate that the promotion of iPP on iPB-1 crystal transformation is enhanced when the iPP mesophase occurs in the iPP/iPB-1 blend.