Study On Surface Structure Control Of Polypropylene Fiber And Properties Of Its Reinforced Composites

Polypropylene(PP)fiber is one of the five synthetic fibers,because of its light weight,high strength and corrosion resistance,widely used in construction,engineering and other fields.However,PP fiber has poor hydrophilicity,no polar groups on the surface,low surface energy,poor compatibility with hydrophilic matrix materials and poor dispersity in them,which seriously limits the application of PP fiber in reinforced composites.Therefore,PP fiber surface hydrophilic,increase the surface roughness,improve its adhesion to the matrix,improve its dispersion in the matrix material,is the technical trend to improve the machinability and usability of composites.In this paper,hydroxylated polypropylene(PPOH)and maleic anhydride grafted polypropylene(PP-g-MAH)were used as modification materials,and four PPOH and PP-g-MAH with different molecular weight and functional group contents of 10wt%were added to prepare modified PP fibers by melting blending spinning method,and the fiber reinforced composites were prepared by adding cement.The specific research contents and conclusions are as follows:(1)Preparation and properties of modified PP blends:the blends with PP-g-MAH and hydroxyl insertion rate lower than 2mol%PPOH have lower zero shear viscosity(?₀)than pure PP,and are easy to spin.However,the zero-shear viscosity of PPOH-2 blend with 10wt%insertion rate of 3.5mol%was 18.1 times higher than that of PP.The strong interaction between hydroxyl groups reduced the fluidity of the blend system and made spinning more difficult.The results of thermogravimetric analyzer(TG)and differential scanning calorimetry(DSC)showed that the initial decomposition temperature and melting point of the blends did not change much,but the crystallinity of the blends decreased compared with that of PP.Scanning electron microscopy(SEM)images of PP-g-MAH and PPOH blended monofilaments showed that the surface area of PPOH-2 10%and PPOH-3 10%increased.Combined with the surface morphology of the blend fiber and DSC analysis of the blend material,the compatibility of the blend material showed that PPOH-1,PPOH-4,PP-g-MAH had good compatibility with PP,PPOH-2 had poor compatibility with PP,and PPOH-3 was partially compatible with PP.DSC test of PP-g-MAH and PPOH blend full stretch(FDY)complex fibers showed that the crystallinity of PPOH-1 10%FDY and PP-g-MAH 10%FDY decreased by 19.8%and 23.5%,respectively.The direction of 10%FDY of PPOH-1 and PP-g-MAH decreased with orientation factors of 0.76 and 0.72,respectively.SEM images of the complex fibers show that the surface of the two hydrophilic blends is smooth and there is no phase separation during the tensile process.(2)Preparation and properties of modified PP fiber reinforced composites:the fracture strength of PPOH-1 10%and PP-g-MAH 10%composites is 4.35c N/dtex and 4.05c N/dtex,respectively,which is 7.05%and 13.5%lower than that of commercial construction polypropylene fibers.Contact angle(CA)test results show that the contact angle of PPOH-1 10%FDY is 86°,26.5%lower than that of PP fiber,and it has good dispersion in water.The results show that the bond strength between modified PP fiber and cement matrix is better than that between modified PP fiber and water matrix,and the bond strength of 10%monofilm of PPOH-3 is 44.1%higher than that of pure PP.The flexural mechanical properties of the composite showed that the addition of polar polymer could improve the flexural properties of the composite.The flexural strength of PPOH-1 10%composite was 3.53MPa,which was 62.7%higher than that of pure PP fiber.