Study On Modified Copolyesters PETG Used For The Invisalign System

Hot-pressing membrane material is a kind of transparent thermoplastic polymer material used in orthodontics rectification. Its main characteristic is excellent mechanical properties, transparency and chemical stability. In terms of thermal membrane materials research in our country is not a lot, and the material almost relying on imports. In this paper, thermoplastic polymer PETG is used as matrix material, which was modified by adding nano-SiO2, PC and TPU respectively. We selected the appropriate injection molding process to make hot-pressing membrane material for orthodontic treatment. According to the molecular structure of modified materials used, the material group, fineness, hardness, thermal, optical properties, microstructure and rheological properties, studying the effect of all aspects of performance of PETG. Through the experiment discovered:(1) The mechanical properties and transparency properties were better than that unmodified and modified nano-SiO2by precipitation method, and the absorbed dose is less than the latter two SiO2.Which was the optimal performance in the three kinds of SiO2, when the gas phase SiO2content at0.5%～1.0%. The elongation at break is162.0%, the saliva uptake is0.0100 mg/g in the two weeks, but the tensile strength is44.0MPa, which can not provide better treatments.(2) The impact strength, elongation at break, and less saliva uptake transparency of PETG/PC2858were better than PETG/APeC under the same quality, and softening point of the former is lower than the latter, which was more easily in the hot-pressing membrane forming processing. Although the tensile strength of the former is lower than the latter, the tensile strength of the latter is57.3MPa, the elongation at break is160.0%, the absorption rate of saliva in not more than0.0120mg/g within two weeks when the proportioning is70/30. Under the ratio, the performance is close to hot-pressing membrane material.(3) The comprehensive performance is better than the other two TPU when Polyester NX-95A blend with PETG/PC. After joining the NX-95A in the matrix, the tenacity and the elongation at break increased dramatically, and the uptake of saliva also significantly reduced, but the tensile strength is reduced, and the transparency becomes worse.So its mechanics and transparency is not in conformity with the hot-pressing membrane materials.(4) When making hot-pressing membrane material, in addition to select suitable raw materials and comprehensive performance better formula, it is also so important to optimize the processing and molding process. We select the larger influence factor of material by one-variable method, and then select the optimal forming factors by orthogonal test. After analysis and testing, we choose high mold temperature and injection molding temperature, the appropriate injection pressure and quick injection speed, and then we got the excellent hot-pressing membrane material which the tensile strength is58.2MPa, the elongation at break is163.2%,and the light transmittance is90.6%.