The Study On Curing Of Vinyl Ester Resin And Its Flame Retardant Modification

Vinyl ester resin（VER）owns the superiorities of epoxy resin and unsaturated polyester resin,with excellent chemical corrosion resistance,heat resistance and mechanical properties,fast curing speed,room temperature curing,good molding and processing properties,so it is widely used in solvent storage tanks,sewage pipes,architecture,coatings,automotive structures and marine composite materials and other fields.As the curing process of VER directly affects the comprehensive properties of VER and its composites,the study of the curing kinetic characteristics of VER can guide the application of VER more scientifically and reasonably.At the same time,the flammability of VER resin is its main disadvantage,which greatly limits its application in the field of some flame retardant materials.Therefore,the research on flame retardant modification of VER has important theoretical and practical engineering significance.In this paper,the curing reaction of VER was investigated by differential scanning calorimetry（DSC）,and the optimal curing process of VER was explored.In order to prepare flame retardant modified VER,E-51 epoxy resin（EP）,9,10-dihydro-9-oxa-10-phosphafi-10-oxide（DOPO）,and maleic anhydride（MA）were used to synthesize a phosphoric anhydride containing phosphoric anhydride groups.In addition,DOEPMA was compounded with melamine cyanurate（MCA）to further improve the flame retardant properties of VER.The details of the study and the results are as follows:（1）The curing properties of VER were analyzed and calculated by DSC.The activation energy of the VER solidification reaction was calculated to be 48.3 k J/mol,with a reaction level of 0.89 and a frequency factor of 7.09×10⁶ s^-1 According to the extrapolation method,the gel temperature,curing temperature and post-treatment temperature of VER resin curing system were 34.23℃,55.32℃and 115.62℃respectively.The mechanical properties of the resin cured at 40°C,60°C and 120°C for 2 hours were superior to other processes.,with bending strength and modulus of 70.38 MPa and 3460.17 MPa respectively,tensile strength and modulus of 122.83 MPa and 3723.47 MPa respectively,Babbitt hardness of 45 and impact strength of 12.08 k J/m².（2）DOEPMA was introduced into VER for its flame retardant modification,and the flame retardant capabilities and mechanical capabilities of the flame retardant modified VER cured products were tested and characterized.It was shown that when DOEPMA was added to 20%and 50%of VER by mass,the ultimate LOI values of flame retardant VER reached 27.6%and29.6%,respectively,and the vertical combustion classes（UL-94）reached V-1 and V-0,respectively.The bending strength and bending modulus were enhanced by 10.85%and14.32%,and the tensile strength and tensile modulus were enhanced by 11.24%and 8.98%,respectively,compared with VER;when DOEPMA was added at 50%by mass,the bending strength and tensile strength were cut down by 20.99%and 26.12%,and the bending modulus and tensile modulus enhanced by 6.74%and 16.43%,respectively,compared with VER.The heat deflection temperature and glass transition temperature of the resin reached the maximum value of 85.9℃and 95.7℃,respectively,when DOEPMA was added at 20%by mass,which were 17.57%and 2.14%lower than those of VER.（3）DOEPMA was compounded with MCA and introduced into VER for flame retardant modification,and the flame capabilities and mechanical capabilities of flame retardant modified VER were tested and characterized.The study showed that the flame retardancy of the material was dramatically upgraded due to the synergistic flame retardant effect of nitrogen and phosphorus flame retardants by introducing DOEPMA and MCA.When the mass additions of DOEPMA and MCA were 20%and 20%of VER respectively,the LOI of flame retardant VER achieved 32.2%and the UL-94 grade also achieved V-0.Due to the addition of MCA filler,the modulus,bending modulus and tensile modulus of VER enhanced by 28.84%and 20.73%,respectively,but the bending strength and tensile strength of the material were cut down by28.71%and 25.98%,respectively.