Study On Activation Modification Of Polypropylene Fiber And Its Application In Cement Concrete

Polypropylene fiber(PP)is an organic crystalline polymer fiber which possess regular structure and gains good antiseptic,mechanical properties.It is an ideal cement concrete additive whose elastic modulus is lower than cement base.The fiber is expected to be used in cement concrete to improve the overall strength and crack resistance of concrete.However,there is no active group in the entire molecule of polypropylene fibers.It is a kind of hydrophobic material with smooth surface and low surface energy.It is seriously restricting the application of this fiber in cement concrete due to the low viscosity between polypropylene fiber and cement matrix.And the reason that lead to the bad effects are the poor compatibility and dispersity of this material.Therefore,it is of great significance to improve the brittleness of cement concrete pavement if the dispersion of polypropylene fiber in cement concrete is enhanced.In this study,the polypropylene fiber was modified by UV grafting method.And the primary modified fiber(MPP)was introduced into the surface of the fiber.The best experimental condition under the response surface method as followed: The concentration of maleic anhydride was 1.2mol/L,the mass ratio of Benzophenone accounted for maleic anhydride was 0.8% and the UV light time can be reached to 2.25 h.The status which indicated the before and after reaction of the fibers were characterized by means of analytical balance,fourier transform infrared spectroscopy,microscopy,atomic force microscope,friction coefficient tester,contact angle meter,electronic pH instrument and fiber strength tester.It can be seen from these tests that PP fiber successfully grafted with carboxyl group which could affect PP fibers under the optimum conditions,the grafting ratio was 2.13,a clear carboxyl characteristic peak appears in the infrared spectrum,the surface has obvious etching or bifurcation,the coefficient of static friction increases and pH is significantly reduced.Nevertheless,the fiber strength and elongation decreased little.In order to further improve the performance of the cement-based admixture of the fiber,the MPP fiber was subjected to secondary acylation with diethylenetriamine to obtain the final fiber modified product(D-MPP).The optimum reaction condition were also investigated using the response surface method: The concentration of diethylenetriamine was 1.8 mol/L,Carbodiimide The weight fraction of diethylene triamine was 1.2% and the reaction time was 6.75 h.The conditions of the final modified products were characterized by the analytical balance,fourier transform infrared spectroscopy,microscopy,atomic force microscopefiber,friction coefficient tester,contact angle meter,electronic pH instrument and fiber strength tester.It can be seen that the acylation reaction is positive and the acylation rate under the optimum conditions was 0.47.There is a significant amide base characteristic peak in the infrared spectrum and the surface etching or bifurcation is more obvious.Meanwhile,the degree of surface roughness,static friction coefficientis,contact angle and pH value all increased.while the tensile strength and elongation of the fiber changed a little.Finally,the performance of PP fiber,MPP fiber and D-MPP fiber under the same conditions were quantitatively analyzed and evaluated by concrete laboratory simulation.The workability,flexural strength,compressive strength,splitting tensile strength,impermeability,fatigue resistance and impact resistance of fiber reinforced concrete were measured.The results showed that the hydrophilicity,dispersibility and the construction workability of fiber concrete are all improved with the continuous modification of the fiber.Also the same as the flexural strength,compressive strength,splitting tensile strength,impermeability,fatigue resistance and impact resistance of fiber reinforced concrete.