Preparation And Performance Study Of Adhesive For Boron Phenolic Resin-based Composite Material

Reinforced by inorganic fiber boron phenolic resin composite materials have outstanding advantages such as high tensile strength,good ablation resistance,and insulation.They have broad application prospects in various fields such as shipbuilding,but their disadvantages are obvious.Boron phenolic resin composite materials cannot be connected by hot melt welding or other methods,and the difficulty in connecting components has become a key factor restricting their use.At present,the bonding strength and high-temperature resistance of adhesives in the market cannot meet practical needs.It is urgent to develop adhesives with high bonding strength,good toughness,and low ablation rate for boron phenolic resin composite materials.In order to solve the problem of bonding and molding of boron phenolic resin composite materials,this thesis uses boron phenolic resin as the main raw material,characterizes the structure of the main functional groups of the resin through infrared spectrum analysis,determines the thermal stability of the resin and adhesive by thermogravimetric analysis（TG）,detects the shear strength and bending strength of the resin and adhesive through a mechanical universal testing machine,and uses a scanning electron microscope to observe the appearance of the bonding surface after fracture,The effects of3-aminopropyltriethoxysilane（APTES）,nitrile rubber,and their synergistic effects on the structure and properties of boron phenolic resin were studied,and their mechanism of action was discussed.The effects of boron powder,silicon powder,and B₄C inorganic fillers on the mechanical properties and heat resistance of modified boron phenolic resin were investigated.A modified boron phenolic resin adhesive reinforced with inorganic fillers was prepared,and the curing temperature,coating amount,and External pressure and other bonding conditions.（1）Using APTES polymer to modify boron phenolic resin,the effect of addition amount on the mechanical properties of boron phenolic resin was studied.The structure of boron phenolic resin before and after modification was characterized by infrared spectroscopy analysis,and the mechanism of APTES polymer modification of boron phenolic resin was speculated.Thermogravimetric analysis（TG）was used to determine the change in heat resistance of the resin.The results show that when the concentration of DMF is 42.8%,the maximum shear strength is 40 MPa,and the bending strength is only 1.58 MPa when the boron phenolic resin is dissolved with N,N-dimethylformamide（DMF）;When the amount of APTES polymer is 1.5%,the bending strength of the modified boron phenolic resin reaches3.15MPa,increasing by 49.96%,and the shear strength is 43MPa.The shear strength and thermal decomposition temperature are slightly increased,which solves the problem of low toughness and poor impact resistance of boron phenolic resin.The effect of APTES polymer on the properties of boron phenolic resin is mainly through hydrolysis of APTES-the hydroxyl group and amino group in the polymer are crosslinked with the hydroxyl group condensation on the boron phenolic resin,graft modification,and the introduction of polysiloxane long chain with good toughness and low surface energy into the boron phenolic resin,thus greatly improving the bending strength of boron phenolic resin,a small amount of amino group improves the crosslinking density during curing,and shear strength and heat resistance are slightly improved.Too much addition will hinder the crosslinking curing due to the low miscibility with boron phenolic resin,and on the contrary,the bending strength and shear strength will decrease significantly.（2）Based on the high toughness and good impact resistance of nitrile rubber,boron phenolic resin was modified with nitrile rubber.The results showed that when the content of NBR was less than 10%,it could be well dispersed in boron phenolic resin.The bending strength reached 3.68 MPa,with an increase of 57.17%,and the shear strength was 45 MPa,slightly increased,but the thermal stability decreased and the curing time prolonged.The boron phenolic resin was modified by 1.5%APTES and 10%nitrile rubber,and the bending strength was 3.97MPa,and the shear strength was 45MPa,which was higher than the mechanical properties of APTES and nitrile rubber modified alone.The results of infrared analysis showed that NBR and boron phenolic resin were modified by blending,and excessive content affected the crosslinking density of boron phenolic resin,resulting in a rapid decline in bending strength and shear strength.The introduction of a small amount of polysiloxane increases the dispersion performance of nitrile rubber in boron phenolic resin,thereby improving the bending strength.Excessive use of polysiloxane results in a significant increase in adhesive viscosity,making it difficult for nitrile rubber to be uniformly dispersed and resulting in a decrease in strength.（3）Inorganic fillers such as boron powder,silicon powder,and B₄C have excellent high-temperature resistance.By detecting the influence of the dosage of three fillers in boron phenolic resin on the adhesive strength and residual carbon rate,the type and optimal dosage of inorganic fillers were selected to speculate on the influencing mechanism.The research results show that when the boron powder content is 1%,the shear strength increases by 20%,but the toughness decreases,and the bending strength decreases by 18.4%.When 10%silicon powder is added,the shear strength increases by 2.2%,and the bending strength increases by17.6%.After the addition of 1%-10%B₄C,the mechanical properties are significantly reduced,and the thermal stability has no obvious change.When the three are mixed,the shear strength and bending strength are significantly reduced,and there is no synergistic effect.The influence of boron powder on the modified boron phenolic resin is mainly due to the fact that the boron atom is electron deficient and can form a ring structure with the hydroxyl and amino groups in the modified boron phenolic resin through coordination bonds.A small amount of boron powder is added to significantly increase the cross-linking density,thus significantly improving the shear strength and reducing the bending strength.Silicon powder mainly improves the bending strength by reducing the curing stress of the adhesive.（4）The bonding process is an important factor affecting the bonding strength.By measuring the shear strength of the cured sample and observing the section morphology,the best conditions such as external pressure,glue amount,curing conditions,etc.were determined.The experimental results show that the optimum curing temperature of the modified boron phenolic resin adhesive prepared by adding 1%boron powder is 120°C-140°C.When the adhesive content is 1-2 parts（0.25g/m²）and the external pressure is 1-2 parts,the maximum shear strength reaches 55MPa.The failure mode is interface fracture.When the external pressure increases to 5 parts,the shear strength decreases by 50%,and the failure mode is self fracture.