| Polymer foaming technology is an important pattern to reduce the weight of polymers.With the rapid development of emerging industries,aerospace,transportation,wind power,military and civil fields,the demand for foaming materials has increased significantly.The basic theories and applications have been paid more and more attention by researchers.Polypropylene(PP)is a general-purpose plastic with a wide-source and high cost-performance.As a crystalline polymer,the foaming process of PP and cell structure are greatly affected by crystallization and orientation,especially in solid-state foaming conditions,controlling the crystallization and orientation are the key factors to optimize the performance of foam materials.In this paper,the effects of isothermal and non-isothermal crystallization methods on the morphology of PPB crystal were analyzed,and the microporous structure of foam materials controlled by this method.The rare earth ?-nucleating agent was used for PPB modified,and the mechanism and laws of the effect on different ?-nucleating agent content and ?-crystal relative content on crystal morphology and foaming were revealed.The orientation trend of LCB-PP under shear flow conditions was studied,and the degree of orientation in the flow direction influence on the cell structure and expansion ratio of foamed materials at different cross-section positions were analyzed.The impact of solid-state foaming and the process conditions of PP foam materials under the conditions of solid-state foaming were analyzed by using the foam compression molding method.The specific research content as follows.(1)The influenced law of isothermal and non-isothermal crystallization conditions on the average diameter,grain density and crystallinity of PPB grains were studied.The influence mechanism of crystal morphology on PPB foaming was analyzed,and the quantitative law between crystal morphology and cell parameters was established.(2)The influence of rare earth ?-nucleating agent on the crystallization characteristics and crystal morphology of PPB were analyzed,and the effect of?-nucleating agent content on ?-crystal relative content was obtained.We analyzed the non-isothermal crystallization conditions on the formation tendency of ?-PPB crystallization behavior,and the effects of different process conditions and ?-nucleating agent on the foaming properties of PPB were obtained.It provides a basis for the application of rare earth ?-nucleating agent in the foaming field.(3)The influence of shear flow on the orientation degree of LCB-PP under different process conditions were studied,and the degree of orientation was characterized by infrared dichroism.The influence of orientation degree on the foam structure along the longitudinal and transverse sections is systematically analyzed.Especially in the surface and sub-surface layers of samples,the influence of shish-kebab structure on cells structure and size distribution of the sub-micron and nano scale foams produced by foaming was analyzed,and the quantitative relationship between the degree of orientation and the expansion ratio was obtained.(4)The device of compression molding foam was designed and developed,and the influence of foaming process conditions on the cell parameters was studied by compression molding foam method.We used the response surface method to establish the quantitative relationship between the mechanical properties of foamed products and the process conditions Under the conditions of free foaming and compression molding foam,the influence mechanism and law of the expansion ratio and apparent density on the axial and radial thermal conductivity were compared and analyzed,which provides a theoretical and application guidance for the industrial application of compression molding foam. |
PDF Full Text Request