STUDY ON STRESS INDUCED CORROSION AND LIFETIME OF DENTAL RESIN

从环境应力开裂(ESC)的角度，通过断裂韧性(K&lt；IC&gt；)、非线性断裂能分析、裂纹扩展速度(V)和应力强度因子(KI)的测定以及断口的观察，研究了热固化义齿基托树脂的开裂机理。尽管K&lt；IC&gt；取决于水和应变率，但吸水试件的最适值估计为1.0 Mpa左右。M^lt；1/2；从未发生慢裂纹扩展(SCG)。应用无因次载荷-载荷点位移曲线发现，塑性能量耗散率大于形成裂纹面所需的净能量。在乙醇和冰醋酸溶液中，无吸水和有吸水义齿基托树脂的V均随K_I的增加而增大，当K_I接近K_i时，V值集中在约1μm/S附近。在浓度较高的情况下，即使在较小的K_i时，V也收敛到相同的值。吸水后的工业树脂表现出与义齿基托树脂相似的特性，但在干燥后的试件中，V值增大而不收敛。这归因于水阻止了环境溶液的扩散。此外，任何树脂吸水后的断口均为条纹状，而未吸水的树脂在高浓度下出现光滑的断口。这些结果表明，义齿基托树脂中会发生ESC，并被认为是其发生机制之一。(1)裂解是由于高分子链在应力和环境溶液的共同作用下发生溶解，和(2)主链断裂是由于链与环境溶液的直接反应造成的。

The mechanism of cracking in heat-cured denture base resin was investigated with a view of environmental stress cracking (ESC), by the measurement of fracture toughness (K_<IC>), the analysis of non-linear fracture energy, the measurement of crack growth velocity (V) and the stress intensity factor (K_I), and the observation of fracture surface. Although the K_<IC> depends on the water and the strain rate, the most appropriate value of the specimen with absorbed water was estimated to be about 1.0 MPa. m^<1/2> when the slow crack growth (SCG) never occurred. From the application of the dimensionless load-load point displacement curve, it was found that the plastic energy dissipation rate was greater than the net energy required for the formation of the crack surface. The V of both specimens without and with absorbed water in denture base resins increased with increasing K_I in both ethanol and acetic acid solution, and converged on about 1 μm/s when K_I approached K_<IC>. In case of higher concentration, V converged on the same value even when K_I was small. The V of industrial resin with absorbed water behaved much like denture base resins, but increased without convergence in dried specimen. This was attributed that the water prevented the environmental solutions from diffusing. Furthermore, the fracture surface of any resins with absorbed water showed the striped pattern, but without water the smooth surface appeared at heigh concentration. From these results, it is suggested that the ESC in denture base resin would occur and is considered the follwing mechanisms. (1)The cracking is caused by the dissolution of polymer chain under the presence of both stress and environmental solution, and/or (2)by the rupture of primary polymer chain dur to the direct reaction between chain and environmental solution.