Microcellular Foaming And Mechanical Properties Of IPP Fiber Reinforced PPR And IPP Composites

Polypropylene(PP)has been widely used in automotive,packaging,construction and other fields because of its advantages such as low cost,good chemical resistance,excellent mechanical properties and easily recyclable.PP foam is light in weight and has a good impact resistance,which can help to achieve weight-reduction and reduce energy consumption.Therefore,it attracts much attention in industrial production.Unfortunately,some problems such as low melt strength and few nucleation sites during foaming process make PP difficult to be foamed,and its mechanical properties decline after foaming.Usually,the foaming properties of polypropylene are improved by the method of adding fillers,but there is still a problem of poor compatibility.In this work,isotactic polypropylene fiber( iPPF)was chosen as a reinforced additive phase to polypropylene random copolymer(PPR),and isotactic polypropylene(i PP)matrices,respectively.We adopted a lower temperature mixing method to prepare the PPR-iPPF and iPP-iPPF materials.Due to iPPF and the matrix materials are homogeneous,they have good compatibility.PPR-iPPF and iPP-iPPF foams were prepared by batch foaming method,and the effects of iPPF and foaming conditions on the cellular morphology were studied.Finally,the mechanical properties of the foaming samples were tested.(1)PPR-iPPF and iPP-iPPF composites were prepared by two-stage temperatures-controlled melting method(high temperature melting matrix and low temperature blending fiber).In the PPR matrix, iPPF with relatively unmelted structure was obtained.The impact strength of PPR-10 iPPF was 6.78 k J/m²,which was 76.6%higher than that of pure PPR,and the tensile strength was 27.66 MPa,38.6%higher than PPR.The partial melting of iPPF in iPP matrix does not significantly improve the mechanical properties of iPP-iPPF material.(2)Because of high aspect ratio of the fiber,the elastic modulus,viscous modulus and complex viscosity of PPR-iPPF were all improved with the increase of iPPF content.Due to the increase of composite viscosity,the morphology of PPR-iPPF foamed sample was comparatively uniform.Compared with pure PPR,the cell density of PPR-30 iPPF foamed sample increased by two orders of magnitude,and the cell size decreased to 1.5?m,because of the enhancements of melt strength and fiber's heterogeneous nucleation effect.Compared with unfoamed PPR,the impact strength of foamed PPR-10 iPPF is increased by 169.8%.The tensile strength of both unfoamed and foamed PPR-iPPF samples increases with the addition of iPPFs.However,the tensile strength of the foamed samples was lower than that of the unfoamed ones.(3)Through the study on the morphologies of the foamed samples of iPP-iPPF under different process conditions,they are sensitive to the foaming temperature and foaming pressure.When the foaming temperature or pressure was too high,the cell size became larger.Due to the heterogeneous nucleation of the semi-molten fiber,the cell morphology of the sample after the addition of the fiber was small but uniform.With the increase of the iPPF content,the cell size decreased and the cell density increased.Compared with pure iPP,when the fiber content was 30 wt.%,the cell density was 1.1×10¹⁰cells/cm³,which was increased by two orders of magnitude.The results of thermal analysis show that the melting point of the foamed sample was about 8?higher than its unfoamed counterpart.Compared with unfoamed iPP,the impact strength of PPR-30 iPPF foamed material was increased by 136.3%,due to the small and uniform cell structure,while the tensile strength of foamed sample was still lower than that of unfoamed sample,although it was improved with the increase of fiber content.