Study On The Crystallization Behavior Of Natural Rubber

As a green polymer material,natural rubber has the advantage that synthetic rubber cannot match.Natural rubber has strain-induced crystallization and low-temperature crystallization characteristics.Strain-induced crystallization can make natural rubber self-reinforcing,making natural rubber have higher strength and crack propagation resistance,but crystallization under low shear strain has an adverse effect on natural rubber processing.Natural rubber will harden and increase in strength at low temperatures,which is related to the low temperature crystallization of natural rubber.The study of the crystallization behavior of natural rubber helps to provide theoretical guidance for the production of natural rubber processing and related products.As a kind of polymer elastomer,natural rubber,its research on the crystallization behavior,helps to construct and understand the molecular chain structure of natural rubber,and provides ideas for the related research of other crystallizable elastomers.In this paper,the low temperature crystallinity and grain size of natural rubber were studied by differential scanning calorimetry(DSC)and wide-angle X-ray diffraction(WAXD).The strain-induced crystallization of natural rubber was studied by WAXD.DSC results show that there are two types of crystallization of unvulcanized natural rubber at low temperature,and their crystallinity increases with the crystallization time of low temperature,and the melting peak of the crystal structure becomes larger as the crystallization temperature increases.The unvulcanized natural rubber crystallizes completely at about 5 h,and the crystallinity is 19.8%;the natural rubber vulcanizate does not easily crystallize at low temperatures.The results of low temperature WAXD study show that the grain size of natural rubber has no relationship with crystallization time,about 40.5 nm;a new crystal structure is formed at temperatures of-80? and-30?,indicating that DSC measures the low temperature crystallization of natural rubber at constant temperature.The increase in crystallinity is due to the increase in grain size rather than the increase in the number of grains.The difference in crystallinity at different temperatures is due to the growth of crystal grains and the formation of new crystal forms.The low temperature crystallization of deproteinized natural rubber was studied by DSC.It was found that natural rubber was more easily crystallized than unvulcanized natural rubber under the same conditions after protein removal,indicating that natural rubber tends to be homogeneously nucleated.WAXD found that there may be traces of crystallization of unvulcanized natural rubber at room temperature,and natural rubber vulcanizates cannot crystallize.The effect of strain on the crystallization behavior of natural rubber was investigated by fixing the natural rubber to different stretch lengths.The results of strain-induced crystallization studies show that the crystallinity of natural rubber increases with increasing elongation.When reaching a certain length,the crystallinity of the unvulcanized natural rubber will decrease with stretching;when the natural rubber reaches a certain elongation,a new crystal structure will appear.