Study And Characterization Of The Mesocrystalline Structure Of EU Gum/natural Rubber And Their Compounds

Traditionally,crystalline polymer materials can be explained by the twophase theory of crystalline and amorphous phases,but nowadays,the threephase theory of crystalline,mesocrystalline and amorphous phases has been gradually proposed to explain the phase structure of crystalline polymers.However,at present,people can only qualitatively study the three-phase structure of crystalline polymers,and are not able to quantitatively measure the three-phase composition of crystalline polymers.Natural rubber(NR)and Eucommia gum(EU gum),as intermediate transition materials between plastic and rubber materials,can be a good platform for the study of three-phase crystalline polymers.NR and EU gum,as green and sustainable rubber materials,both have great research value and strategic significance.NR has excellent elasticity and mechanical properties,and EU gum has special rubber-plastic duality.One of the reasons why both rubbers can have excellent properties is that they all can crystallize.NR can achieve stretching and low-temperature induced crystallization(SIC and TIC),meanwhile EU gum can crystallize at room temperature,and the crystallization disappears at high temperature to reflect the elasticity of rubber.Therefore,it is necessary to study the crystallization properties of both rubbers in order to make better use of them.In this thesis,the crystalline phase distribution of NR and EU gum and their blends were studied based on the theory of multi-step growth of intermediate phases.Wide angle X-ray diffraction(WAXD)and small angle X-ray scattering(SAXS)were used to test the crystalline phase changes in the stretching process of NR,the stretching and melting process of EU gum,and the stretching process of the blends,and to corroborate the existence of intermediate crystals and calculate their contents by using Porod’s law and correlation function methods to develop new ideas and directions in rubber crystallization research.The SIC processes of raw and vulcanized NR were investigated by WAXD and SAXS methods.The stretching process of NR was explored by SAXS and it was found that the two-dimensional image changes of the whole process only reflected the changes of molecular chain orientation,and no special image of crystallization appeared,meanwhile the one-dimensional curves did not show the corresponding peak positions,and the curves under different strains almost overlapped.The presence of mesocrystalline phases could not be discerned from the images when verified using Porod’s law.The vulcanized NR present the same situation,where the SIC process of NR is not characterized by SAXS due to the occurrence of orientation,which allows the rise and fall of the overall electron density.The crystallization changed during the melt of raw EU gum were investigated by WAXD and SAXS.During the melting process,the SAXS curves showed a peak at 30 and 40,the peak disappearance curves at 70 and80 overlapped,and the scattering intensity was higher at 50 although the peak disappeared.The curve showed a negative deviation below 50 by Porod’s law,which indicated that there was a transition mesocrystalline state of EU gum at this time,and the thicknesses of transition layer were 1.25,1.21 and1.28 nm by fitting the curves,and then the correlation function curve of melting EU gum was obtained by using the correlation function to find the thicknesses of mesocrystalline layer and crystalline layer.The mesocrystallinity increased from 9.93% to 11.46% and the crystallinity decreased from 19.93% to 16.75%with increasing temperature.For the tensile process of EU gum,the results of WAXD revealed that the peak intensity of crystallization of EU gum gradually decreased with increasing strain.The two-dimensional diagram of EU gum with molecular chain orientation and crystalline orientation was studied by SAXS,and the onedimensional curves showed obvious scattering peaks,meanwhile the peaks increased with increasing strain while the long period decreased.The correlation function curves showed that the mesocrystallinity decreased from10.42% to 6.42% and the crystallinity decreased from 23.23% to 17.39%.In order to investigate the phase distribution of EU gum/NR blends,blends of different ratios were prepared.The SAXS of these copolymers showed different two-dimensional images,but the scattering peaks were present in all the one-dimensional curves.By Porod’s law and correlation function,it was found that the SAXS of different EU gum contents had transitional mesocrystalline layers,with mesocrystallinity and crystallinity of 20 phr EU gum being 2.75% and 8.18%,respectively,and mesocrystallinity and crystallinity of 80 phr EU gum increasing to 4.43% and 15.3%,respectively.For the study of the tensile process of the co-blends,it was found that the orientation degree of different EU gum contents at 300% strain was different,and although the SAXS curves showed obvious scattering peaks,the curves processed by Porod’s law found that all co-blends at 300% strain showed positive deviation and no obvious transition layer could be distinguished.