Study On The Toughening Effect And Mechanism Of Nylon 12 And Montmorillonite In Benzoxazine Resin

Polybenzoxazine(PBa)resins have been developed as novel types of phenolic resins.They have been developed to overcome the shortcomings of traditional phenolic resins while keeping their original advantages.PBa resins exhibit excellent characteristics such as heat resistance,flame retardancy,good mechanical properties,high glass transition temperatures,near-zero shrinkage,low water absorption,and low dielectric constants.Therefore,they are widely used in various fields such as structural materials,adhesives,paints,electronics,and aerospace applications.Hewever,the inherit brittleness and the high curing temperature restrict their application in industrial production.Based on the brittleness of PBa resins,flexible Nylon 12 and layered montmorillonite were introduced to increase the toughness of PBa resins,and to improve the thermal stability of PBa resins without decreasing their mechanical properties.Moreover,expand the application of PBa resins.In this study,the mechanical properties and thermal properties of PBa resins were improved by adding Nylon12 and modified montmorillonite(OMMT)as the additives.The toughening mechanism of Nylon12 and OMMT was also investigated.This paper might offer theoretical basis and reference for further study and industrial production in preparing high performance PBa resins.A series of PBa/Nylonl2 composites were prepared by solution blending method.The mechanical properties and thermal stability of PBa and resulting PBa composites were investigated using an Instron universal material testing instrument and dynamic mechanical analysis.The results showed that the KIC and GIC values of PBa/Nylonl2 composites were gradually increased with the addition of Nylon12.The KIC values of PBa/Nylonl21?m-15%,PBa/Nylon1210-15%and PBa/Nylon1220?m-15%composites improved by 23.5%,54.3%and 44.4%,respectively.The GIC values increased by approximately 119.6%,167.9%,and 151.2%for PBa/Nylon12?m-15%,PBa/Nylon1210-15%,and PBa/Nylon1220?m-15%composites,respectively.The To of PBa/Nylonl2 composites gradually increases with the addition of Nylon12 compared to that of the pristine PBa with a Tg of 222 ?.The Tg of PBa/Nylonl2-15%composites is 226 0C and increased by 4 ?,compared to that of the pristine PBa.The analysis revealed that the PBa/Nylonl2 composites containing 10 wt%Nylon1210?m showed the best comprehensive mechanical properties.In order to toughen the PBa resins effectively,the nature MMT was modified by cetyltrimethylammonium bromide(CTAB).Several new characteristic peaks appeared in the Fourier-transform infrared spectroscopy(FTIR)spectra of OMMT.The X-ray diffraction(XRD)showed that the 2?° shifted from 6.26° for MMT to a lower angle(3.93°)for OMMT,and the corresponding gallery spacing enlarged from 1.41 to 2.25 nm.The MMT particles were modified successfully according to the analysis results of FTIR and XRD.The mechanical properties of PBa/Ny12/OMMT composites were prepared by adding Nylonl210?m,-10%and OMMT as the synergistic additives by Instron.The PBa/Ny12/OMMT composites with higher OMMT loading exhibited higher KIc and GIc than those with higher OMMT loading.The KIC and GIc values of the PBa/Nyl2/OMMT composites showed a maximum at l wt%OMMT loading.The KIC and GIC values of PBa/Nyl2/OMMT-lcomposites were?1.36 MPa·m1/2 and 315.76 J·m-2,respectively,and increased by 67.9%and 181.4%,respectively,compared to that of the pristine PBa.The thermal properties were investigated by thermogravimetric(TGA),DMA and the non-isothermal DSC.The results revealed that the thermal stability of PBa/Nyl2/OMMT composites was gradually increased with the addition OMMT.T5%(temperature corresponding to 5 wt%loss),T10%(temperature corresponding to 10 wt%loss)and Tmax(temperature corresponding to the maximum weight loss)of PBaNy12/OMMT-1 composites were improved by 9,16,and 15 ?,respectively.And the Tg of PBa/Ny12/OMMT composites were gradually increased.Nylonl2 reduced the curing temperature of the PBa resins,but OMMT did not substantially change the curing behavior of the benzoxazine resin from the analysis of non-isothermal DSC.The toughening mechanism of Nylon 12 and OMMT were characterized by scanning electron microscopy(SEM).The SEM results indicated that the fracture surfaces of PBa/Ny12 and PBa/Ny12/OMMT composites are much rougher than that of the pristine PBa.Cracks,crack deflection,and voids are observed in the fracture surfaces of PBa composites.More cracks,crack deflection,and microvoids were observed on the fracture surface of PBa/Ny12/OMMT-1 composites.Therefore,the PBa resins were toughened effectively.