Study On Toughening Modification And Shrinkage Property Of UV-curing 3DP Materials

In the 3DP field, the products manufactured by UV-curing 3DP technology process the most high efficiency and accuracy in modeling and forming. At present, the main problems in the UV-curing 3DP materials are the low toughness and the high curing volume shrinkage.In this paper, based on the free radicals/ cationic hybrid system, through researching the content of photoinitiator, the mass ratio of prepolymer, the content of reactive diluents, the content of co-initiator and the content of polyol on the properties of 3DP materials, a kind of hybrid curing 3DP materials with low-viscosity, fast-curing and without volatile organic solvent were prepared.Hydroxyl-terminated polybutadiene(HTPB) and epoxidized hydroxyl-terminated polybutadiene(EHTPB) were used to toughen for the hybrid curing 3DP materials respectively. The results showed that with the increasing content of HTPB and EHTPB, the impact strength of the cured 3DP materials went up at the beginning and dropped after. When 4wt% HTPB was added, the impact strength of the curd 3DP materials reached the maximum value of 13.98KJ/m2, which was improved by 36.26% compared with the untoughened materials. When 6wt% EHTPB was added, the curd 3DP materials impact strength reached the maximum value of 16.91KJ/m2, which was improved by 64.81% compared with the untoughened materials. After toughening modification of the two kinds of liquid rubber, the hardness and tensile strength of the cured 3DP materials decreased slightly. The addition of EHTPB lowered the volume shrinkage of the hybrid curing 3DP materials, but the viscosity of the uncured 3DP materials rised. The surface morphology of the impact fracture showed that the ductile fracture characteristic appeared at the surface of the cured 3DP materials after modification of HTPB and EHTPB. The fluctuation on the surface of the cured 3DP materials modified by EHTPB was more obvious than that of the cured 3DP materials modified by HTPB. Thus, EHTPB was more suitable as a toughening agent for the hybrid curing 3DP materials than HTPB.In order to reduce the volume shrinkage of the hybrid curing 3DP materials, the spiro orthocarbonate expanding monomer, 3, 9- diethyl-3', 9'- dihydroxymethyl- 1, 5, 7, 11-tetraoxaspiro [5, 5] undecane(DHOM) was synthesized successfully by two steps. With the increasing content of DHOM, the results indicated that, the volume shrinkage of the 3DP materials decreased significantly. When 16 % DHOM was added, the rate of volumetric shrinkage of the uncured 3DP materials reduced from 5.46 % to 3.52 % and the impact strength and curing degree of the cured materials reached the reached the maximum value of 18.63KJ/m2 and 98.82%, which were improved by 10.17% and 0.77% respectively, compared with the untoughened materials. At the same time, the curing rate of the 3DP materials increased, but the hardness and tensile strength of the cured 3DP materials decreased slightly. The surface morphology of the impact fracture showed that the scaly structure and obvious dimples appeared at the surface of the cured 3DP materials after modification of DHOM, which indicated that the fracture mode of the cured 3DP materials was the typical ductile fracture. During the UV curing process, the volume expansion of DHOM inhibited the volume shrinkage of the hybrid curing 3DP materials.