Water Absorption Of Short Chain Hydrophobically Modified Nylon 6

MC nylon 6 is one of the nylon varieties.It has many excellent properties,such as high rigidity,high hardness,high mechanical strength,good chemical stability and toughness,etc.,in the automotive,transportation,construction,machinery and medicine industries.Widely used.Because its structure contains amide group-(NH-CO)-,resulting in its strong water absorption,when MC nylon 6 absorbs water,its mechanical properties in the index are reduced,and the dimensional stability will also be poor,limiting its use in a certain area.In order to broaden its scope of application,we need to modify it to reduce water absorption.In this paper,three different short-chain hydrophobic groups were introduced into MC nylon 6 segments by in-situ anionic polymerization,so that the hydrogen bonds in the structure were not destroyed,and its good mechanical properties could be maintained.The short-chain hydrophobic groups thereof are a monohydroxy-terminated perfluoropolyether,a monohydroxy-terminated dimethylsiloxane,and a monohydroxy-terminated fluorinated polysiloxane.First,these short-chain hydrophobic groups with different molecular weights are reacted with TDI to obtain the modified activators,and then caprolactam polymerization is initiated using these activators to obtain modified MC nylon 6 with different mass fractions.A series of characterization and performance studies of modified MC nylon6 were performed,for instance Fourier transform infrared spectroscopy(FTIR),differential scanning calorimetry(DSC),thermogravimetric analysis(TG),and X-ray diffraction.(XRD),mechanical properties,water absorption,contact angle,and tensile fracture surface morphology.The results show that the introduction of three different short-chain hydrophobic groups has little effect on the crystal melting temperature and the thermal decomposition temperature,and the crystal form does not change.From the mechanical data,it can be concluded that the introduction of three different short-chain hydrophobic groups has little effect on the tensile strength,but thebending strength and bending modulus are improved compared with pure MC nylon 6.When MC nylon 6 was modified with mono-hydroxyl-terminated dimethylsiloxane,the mechanical properties were kept the best,and its tensile strength,elastic modulus,bending strength and bending modulus were improved compared to pure MC nylon 6respectively.0.5 MPa,141.1 MPa,25.0 MPa,and 827.3 MPa.From the analysis of water absorption and contact angle data,the introduction of three different short-chain hydrophobic groups can reduce the water absorption and increase the contact angle.When MC nylon 6 modified by monohydroxy-terminated fluoropolysiloxane containing two hydrophobic groups was used,the modification effect was the best.The molecular weight of hydroxyl-terminated fluoropolysiloxane was 500 and the mass fraction was 2%.At the same time,the water absorption at 24 h was lower by about 72.3% than that of pure MC nylon 6,and the contact angle was increased by23.4° compared with pure MC nylon 6.