Preparation Of Cardanol Modified Phenalkamine Epoxy Curing Agent And Study Of Its Adhesive Properties

Phenalkamine has excellent adhesion properties and thermal resistance.However,it has some deficiencies,such as high brittleness,poor toughness and short pot life.The impact toughness has been improved significantly in cardanol modified phenalkamine.However,the poor thermal resistance has limited applications of this curing agent.In this paper,the polyamine was modified via the Mannich reaction by modifier synthesized through introducing the cardanol side chain into the benzene ring via the Friedel-Crafts alkylation.The main objective of the present work was to improve the impact toughness and thermal resistance of the curing agent with proper pot life.Ethylenediamine curing agents modified respectively by cardanol,bisphenol combined cardanol with phenol,cardanol-phenol mixed phenol were prepared.The synthesis process parameters,such as reaction time,the amount of catalyst and the proportions of cardanol,formaldehyde and ethylenediamine,for preparing the curing agents were optimized,and the structure of the curing agents were characterized by GPC and IR,etc.The adhesion properties and heat resistance of the cured product of the modified curing agents and epoxy resin were studied.The experimental results showed that epoxy resin(E51)cured by the cardanol modified curing agent had good peel strength and low thermal resistance.The thermal resistance was improved by the bisphenol modified curing agent,but the peel strength and toughness were reduced.Both the thermal resistance and toughness were improved simultaneously,when the ethylenediamine curing agent was modified by the cardanol-phenol mixed phenol.The optimum comprehensive performance occurred at cardanol/phenol ratio:1/2 and(cardanol+phenol)/formaldehyde/ethylenediamine ratio:1/1.2/1.5.Three epoxy curing agents had been synthesized by reacting Triethylenetetramine(TETA)with cardanol-phenol mixed phenol,cardanol and phenol respectively.The curing degree of epoxy resin cured by three curing agents was determined by means with the infrared spectrometer(IR)and the differential scanning calorimetry(DSC).Shear strengths,impact strengths,tensile and compression performance of the products cured at room temperature and by heating respectively were obtained.The shore D hardness,dynamic thermo-mechanical properties and thermal stabilities of the products cured at room temperature were investigated in detail.The experimental results showed that the cardanol-phenol mixed phenol modified TETA/E51 system had very good properties after room temperature curing.Its pot life was 70 min,and room temperature shear strengths reached 17.92 MPa and 18.61 MPa after curing for 5 h and 24 h at room temperature respectively,and shear strengths at 80℃reached 18.19 MPa and 20.58MPa respectively.The impact strength reached 28.58kJ/m~2 after curing for 7 days at room temperature.The results indicated that the cardanol-phenol mixed phenol modified TETA not only retained the excellent impact toughness of cardanol modified TETA,but also possessed outstanding thermal resistance and adhesion of phenol modified TETA.In addition,it had higher activity and longer pot life.It was an epoxy resin curing agent with excellent comprehensive performance.According to the analysis of the above results,the phenalkamine from reaction of the cardanol-phenol mixed phenol(a mixture of bisphenol,cardanol and phenol)with TEDA had more excellent comprehensive performance than amine curing agents modified singly by cardanol or bisphenol.